机械专业中英文翻译文章(毕业设计)
KBE-based stamping process paths generated for automobile panels
Jinqiao Zheng . Yilin Wang . Zhigang Li
Abstract: As automobile body panels are one kind of sheet metal part with groups of free
form surfaces, the process planning is more complicated than common sheet metal stamping to implode effectively and practically. Based on KBE, new frameworks have been presented as intelligent master model at the system level and as procedure model at the activity level. In accordance with these frameworks, an intelligent CAPP system has been specifically developed. Based on feature technology, features have been extracted and represented by the object-oriented method. Stamping features and their parameters have been defined and extracted based on feature technology and stamping process rules. The whole product knowledge has been represented by frames which directly map to objects (or features) in the object-oriented sense. Relevant appropriate operations features have been assigned to stamping features of a product based on feature-operation criteria, parameters of the stamping feature and their correlativity. This assignment is a decision-making activity using a set of rules with a decision-making tree and model-based reasoning methods. With knowledge between operations, such as operations order constraint (do-after) and operations combination constraint, process paths have been improved based on relevant intelligent reasoning methods. Based on the relationships (preferred-to) between processes and machines/dies, the structure of die and machine for each process can be identified, since the process route has been determined. In this stamping process planning, the procedure and information have been controlled by a process control structure that is associative and integrated.
1 Introduction
Recently, research on the computer-aided process planning (CAPP) system for sheet metal has been widely reported. Park et al. [1] constructed an automated process planning system for ax symmetric deep drawing products. Tessa [2] and Kang and Park [3] presented a group technology and modularity to construct a CAPP system for process sequence design in an expert system for non-ax symmetric deep drawing products with elliptical shape. Gao et al. [4] developed an advanced software toolset used for the automation of sheet metal fabrication planning for aircraft components. Zussman and Horsch [5] proposed a motion planning approach for robot-assisted multiple-bent parts based on C-space and a potential field. Wang and Bourne [6] proposed an automatic process planning system with the features well investigated and the production plans researched with near-minimum manufacturing costs. De Vin et al. [7 , 8] developed a sheet-metal CAPP system called PART-S, which integrates cutting, nesting, bending and welding processes for bending sequences. Streppel et al. [9] showed the ambiguity of conventional tolerances and presented a method which replaces conventional tolerances with geometrical tolerances for process planning in small batch sheet metal part manufacturing. Amoral et al. [10] proposed a method which generated feasible bending sequences of a sheet metal part handled by a robot, and discussed the determination of the best grasping positions and repositions. Aomura and Koguchi [11] pro- posed a method to generate bending sequences of a sheet metal part handled by a robot. Liao and Wang [12] proposed an evolutionary path-planning approach for robot-assisted handling
of sheet metal parts in bending. Lutters et al. [13] developed a generic architecture for computer aided process planning based on information management for sheet metal manufacturing in a small batch part environment. Kumar and Rajotia [14] had proposed a method of scheduling and its integration with CAPP, so that on-line process plans can be generated taking into account the availability of machines and alternative routes. The contents above are mainly for process parameter calculating, path-planning and some sketch map of work-pieces for specific types of sheet metal, such as axis-metric and non-ax symmetric deep drawings, complex bandings and sheerings, and so on. The automobile body panel is one kind of sheet metal part, which is complicated in shape, with groups of free form surfaces, a large figure in size and is always manufactured by stamping processes. Automobile panels can be considered as a combination of some common stamping, such as irregular drawing, flanging/bending, trimming and piercing, etc. The process planning of these panels is more complicated than common sheet metal stamping, which is generally dependent on engineers experience to complete. It is believed that the process path plan for automobile panels is requisite and acquirable. In essence, the stamping process path for automobile panels is to determine the necessary forming processes and their sequences in order to produce a particular part economically and competitively. Process paths generation is a decision-making process. Decisions on stamping operations for a particular feature have to be formed on various independent conditions such as which operation should be performed with which die and tools and under what forming parameters. A CAPP system for these should be an integrated environment to deal with knowledge to reduce the dependence on engineers or experts, and realize the process planning with scientism. Thus, knowledge based engineering (KBE) is applied to advance the stamping CAPP system for automobile panels, and even to improve the competitiveness for the automobile industry. This paper is particularly concerned with the construction involved with developing a CAPP system based on KBE.
2 KBE in CAPP system for stamping
2.1 KBE
Knowledge based engineering (KBE) is one innovative method of artificial intelligence for engineering design developed in the 1980s. So far, there is no generally accepted and mature definition for KBE. However, it is recognized that KBE is an intelligent method to resolve engineering problems, which can realize inheritance, integration, innovation and management of domain expert knowledge through the drive, multiplication and application of knowledge. A knowledge-based system (KBS) is one that captures the expertise of individuals within a particular field (the “domain”), and incorporates it and makes it avai lable within a computerized application [15]. The level of complexity of the tasks performed by such a system can vary greatly. However, it can generally be said that while a domain expert would find them routine, they would be outside the capabilities of a person unfamiliar with the domain [16]. KBE provides an open architecture and reuse ability of experience and knowledge, which can deal with multi- domain and multi-expression of knowledge, and can form an integrated environment. A KBE application is further specialized, and typically has the following components of geometry, configuration, and engineering knowledge: – Geometry – there is very often a substantial element of computer-aided design (CAD). Most of the software used to create KBE applications either has CAD capabilities built in, or is able to integrate closely with a CAD package. – Configuration – this refers to the
matching of valid combinations of components. –Engineering knowledge –this enables manufacturing and other considerations to be built into the product design. When a candidate application area requires a high degree of integration of the above elements, KBE is likely to be the best method for its integration. KBE is sometimes termed rule-based engineering, as within the discipline, knowledge is often represented by rules. These may be mathematical formulae or conditional statements, and although simple in concept, they may then be combined to form complex and powerful expressions. KBE systems, on the other hand, are usually provided with specialized geometrical capabilities, with the ability to embed engineering knowledge within a product model. The following examples of typical KBE applications demonstrate some of the considerable benefits to be gained from its use.
1) Lotus engineering. This used the integrated car engineer (ICE) system in the design of the Lotus Elise. ICE consists of a vehicle layout system, and modules to support the design of suspension, engines, power-train, wheel envelope and wipers [ 17].
2) The Boeing Commercial Airplane Group. This uses KBE as a tool to capture airplane knowledge to reduce the resources required for producing a design [18].
3) Jaguar cars. The company’s KBE group devised a system that reduced the time taken to design an inner bonnet from 8 weeks to 20 min [19].
2.2 Problem to solve in a CAPP system based on KBE
A stamping CAPP system should deal with all knowledge including geometry, non-geometry, engineers experience, rules and criteria, results of tests and numerical simulation, or even successful cases, because of the complexity of automobile body panels. The knowledge is involved in diverse fields, such as metal forming technology, metal forming mechanics, modern design methodology, numerical simulation technology, and artificial intelligence. Accordingly, the CAPP system has to solve the problems with expression and application of all knowledge, and integration of all multidisciplinary design. A CAPP system is essentially a set of instructions and guidelines on how to perform a complex procedure. It details the individual sub-tasks, how they should be carried out, in what order, and how the work should be documented. Furthermore, as system requirements change, new solutions tend to evolve from existing ones, so computer applications and their descendants can outlive the personnel involved in their initial development. All in all, a stamping CAPP system for automobile panels based on KBE should readily solve the following problems:
(1) Representations for all knowledge.
(2) Reasoning based on all this knowledge.
(3) Appropriate operation features acquired from stamping features and process rules incorporated with form- ability analysis.
(4) Process routes based on process sequencing and process combination knowledge.
(5) The control or management of process procedures for rapid response to all changes.
3 Framework of a CAPP system
3.1 The integrated master model for a CAPP system
To solve all corresponding problems mentioned above, the integrated ma ster mode l is advanced at the system level t o control and frame t he CAPP system for automobile panels. I t is a
common concept and framework to generalize and specialize the function, course control , process planning circumstance, and act iv it ies involved in t he development o f an integrated and intelligent system into abstract groups, and to make t he m carry out all contents and processes. This mode issue table for knowledge expression and application, process controlling, information integration, change response , etc .The intelligent master model (IMM) of stamping process planning for automobile panels is composed of a knowledge base, process control structure (PCS), process planning optimization (PPO), process information model (PIM), and linkable environment (LE), which are integrated and combined based on KBE. The structure of the IMM is shown in Fig. 1. The IMM of process planning is
not only the foundation of intelligent CAPP for automobile panels, but also the integration of knowledge and methods, which combines the KBE system with the process planning. With this model, KBE acts as a knowledge source to drive PCS, PIM, and LE, which makes process planning integrated and associative. The PIM is a dynamic expanded information model, in which the information can be added and updated along with process planning. Using knowledge multi-expression format, the integrated information model of process planning is built based on a feature model. For the hierarchy and framework of the features, semantic net and object- oriented methods are adopted to express knowledge and establish an information model in which process knowledge, e.g. database, parameter, rules, and experience, act as rules and attributes of the objects, and where whole product knowledge acts as a framework for relationships of objects. With a process information model, the process planning can be completed through knowledge-reasoning and decision-making based on knowledge encapsulated in the objects. The PCS is a key point to ensure process planning is integrated and consistent; it manages the process information model, process planning to generate stamping process plans and detail design, and controls the changes of the planning. In IMM, the PCS comes into being dynamically along with the process planning. If one part of PCS is created, it will monitor and control relevant planning and information subsequently. When results of process planning are deleted, the corresponding PCS part will fade away accordingly. The LE provides several methods to deal with the links among process planning procedures, the geometry between product and detail design of work
pieces. To achieve intelligent process planning for large complicated stampings, there are problems to solve, i.e. linking of process planning procedures, the geometry link between product and detail design of work pieces. The LE provides several methods to deal with these links, e.g. parameters variable link, data structures link, and geometrical link. The PPO is a methodology of design optimum for complex engineering, which can deal with the complicated optimization problem of process planning in an economic view.
3.2 The framework of CAPP system based KBE
The stamping CAPP system for automobile panels based on the intelligent master model above consists of several stages such as stamping features extraction from product data, operation features reasoning from stamping features to form a process information model, process planning to get the sequence of operations and relevant tools, detail design for work pieces, simulation for detail design, and finally the process plans and 3D die-face model generation which is shown in Fig.2. It is a tangible activity level to control and frame a CAPP system for automobile panels.
In the CAPP system, stamping process planning of automobile panels needs to first establish a process information model based on a 3D model product and feature technology. Stamping features are extracted, and operation features are attained subsequently. The features all carry knowledge about themselves, the process and constraints. Then the PIM and PCS are established. There-after, the sequence planning is setup based on PIM and knowledge such as operation sequence rules, operation combination guides and reasoning methods, and then the dies and machinery are options. Along with the process of the planning, PCS, PPO and LE of IMM are built by knowledge driving. PCS consists of an integrated collection of tasks that can initiate, control, manage, evaluate and update all the planning information and results timely. PPO optimizes process paths and enterprises resource environments, and PCS and PPO carry out the optimization and find the optimal solution. PCS and LE make process planning associated and linkable.
4 Key points of process path generation
Unigraphics has several features that provide a subset of the capabilities of a KBE language —UG/KFL, which provides a way to specify knowledge rules that can cover all Unigraphics applications. The stamping CAPP system for automobile panels has been developed based on the
frameworks advanced above, which choose C and UG/KF language as t he implementation language, a nd ACCESS as its database o n t he UG/CA D development environment. UG/Open and UG/Open++ allow custom i zation and extension of Unigraphics using a standard procedural language (C and C++). UG/KFL provides a way to specify knowledge rules that can cover all Unigraphics applications. Rules of UG/KFL are easily written by the developer, easy to read, understandable, and reusable by the user. Furthermore, UG/Open can be integrated with KBE by accessing C programs from the KBE language described under External Function. For access to named attributes from C, there will be a utility program that takes a design definition in the language and produces C bindings to access the attributes of an object instance of that design. The access consists of functions and methods for getting and setting the value of the named attributes of object instances. Additionally, there are UDF and UDO in UG/ CAD and UG/KF, which can be dealt with by UG/Open and UG/KF. What is more, Unigraphics is integrated with many other knowledge tools and sources, such as spread sheets, other ICAD KBE language systems, finite element analysis, CAM, etc.
4.1 Stamping feature
To generate appropriate process plans, the product data requires the original inputs, which includes the geometry, topology, tolerance, material and quantity of product. Based on the feature technology and stamping technology, a stamping feature is the portion of a part which can be formed by means of certain stamping operations. For ex- ample, a drawn feature or bend feature is defined as the main feature, which is to describe the near net shape of a component, while flange, hole, emboss, bead, notch and flange-hole are defined as the auxiliary ones, which are required to describe the local part of the final shape. Using feature technology and the geometry extraction method, the stamping design features, such as the main forming feature (e.g. drawing, bend), flange, hole, emboss, bead, notch, and so on, can be extracted from a 3D solid model, which are first defined as UG/UDO. For example, Fig. 3 shows the stamping features of one automobile panel. The stamping feature model should then be defined to represent product knowledge integrated and unambiguous. The stamping feature is represented as object-oriented class or object and instance using UG/KF language (UG/KFL);it
not only represents feature parameters, tolerance, material, etc. as attributes of class or
instance, but also represents geometrical objects by importing UG/UDO and UG/UDF referenced solid geometry as an instance attribute or child. And this realizes the connectivity and integration between the symbol of a feature and its geometrical object. It can also get an attribute value from a function, rule, expression and database.
4.2 Operation feature
Accordingly, stamping operation features are categorized into initial and subsequent, such as drawing, bending, flanging, trimming, hemming, re-striking, and piercing and so on. The relevant appropriate operations are assigned to form stamping features of products based on feature- operation criterion, parameters of the stamping feature and their correlativity. This assignment is a decision-making activity using a set of rules with decision-making tree and model-based reasoning methods. For example, drawing→trimming is reasoning from the main draw feature, flanging is reasoning from the flange feature, and piercing is reasoning from the hole. Fig. 5 show the typical illustration of flanging operation features reasoning from its stamping feature, and the sequence rules of these operation features are attached to the operation features. Customarily, relationships between features, especially the hierarchy, should be an important factor, while the operation feature is the reasoning. In Fig.4, the features flange3, flange1 and bead1 should be in the form of a set together to deduce relevant appropriate operations. In this way of reasoning, the operation features can get fundamental knowledge for subsequent planning. In this paper, the operations features reasoned from stamping features are represented as object-oriented entities and UG/UDO, and the relationships are expressed as network based on the stamping feature model of the product (shown in Fig. 6). The operation features not only refer themselves to stamping features, but also relate to other operations, such as relevant forming dies and machinery with the relationships among them. The relationships between operations consist of operations order constraint and operations combination constraint. Another type of relation between processes and machines/dies is preference (preferred-to). For example, flanging is always preferred to flanging die and relevant press machine, while trimming is always preferred to trimming die and press machine. ALL these constraints and relationships among them are reprsented as attributes, rules and methods in the operations. It is through the citation of stamping features that the description of the geometrical objects are realized in the operation features; while the relevant dies and machinery can be represented in operation by options and the constraints expressed as relevant rules, functions or methods.
4.3 Process information model (PIM) for path
Planning Now the PIM of process planning can be defined as the foundation to process planning. And the PCS of IMM is created to control and monitor the stamping feature and its operation features by the control variable or state variable. The process planning of large complicated stampings is a dynamic process. The PIM must involve all data, such as process planning data, analysis data, die design data, and circumstance, etc. The basic knowledge expression of the model should have adaptability to the changes of geometry, attribute, features, constraints and the way of thinking. Using the knowledge multi-expression format of KBE technology, the integrated information model of process planning for large complicated stampings is built based on the feature model. The process information model is shown in Fig. 7. The object-oriented method and feature technology are adopted mainly to form the model. There are
three basic classes of features: stamping design features, operation features, and sequence features, in which process knowledge, e.g. database, parameter, rules, and experience, acts as rules and attributes of the objects. Using feature technology and the geometry extraction method, the stamping design features, such as the main forming feature (e.g. drawing, bend), flange, hole, emboss, notch, and so on, that are defined first as UG/UDO, can be extracted from a 3D solid model. Relevant appropriate operations can then be assigned from stamping design features of a product using a set of rules with a decision-making tree and model-based reasoning methods of feature-operation criteria. Hierarchy and framework of the product model and semantic net of feature-operation-tools are used to establish the relationship information for PIM. With PIM, where the knowledge is encapsulated in objects or decision-making knowledge procedures, the process planning can be completed through corresponding sets of knowledge-reasoning. This model is a dynamic expanded information model, in which the information can be added and updated along with the process of planning. Information management and control is a part of PCS in IMM of process planning, which can monitor the change or modification of process plan- ning, and timely update the information to insure the process information model and process planning synchro-
nization. In process planning, the information management and control begins its control and judgment from the time that the stamping design features have been created until the planning ends.
4.4 Process path planning and tools option
Generally, the forming of an automobile panel includes several operations, such as drawing, trimming, flanging, piercing, re-striking, hemming, etc. Among the operations, drawing, trimming and flanging are the main operations to form the main shape of the product, and other operations are auxiliary operations, which work together with the main operations to form complex shapes of the product. To get precedence relations among operations based on the PIM, the main operations must first be determined, and then the decisions are made about how to arrange the initial main
operations, how to combine the auxiliary operations with the main operation, and how to insert auxiliary operations to the operation sequence. For the integration of planning, it should consider the stamping dies’ capability, cost and capacity of machinery or workshop as critical issues at the sequencing level. Theoretically, case-based reasoning (CBR), rule-based reasoning (RBR), and model-based reasoning (MBR) are all applied for process planning. In this paper, CBR, RBR and artificial neural network are joined up as the decision- making methods after model-based reasoning during process planning, which is shown in Fig. 8. Firstly, the model-based reasoning is used to form a code of the product and operation for CBR based on feature entities and their interrelationships, and relevant rules or knowledge for others reasoning. Then the CBR is selected to get similar plans for the case base; if CBR is not suited, the RBR and ANN are select to complete the task cooperatively. During sequencing of forming operations, the structure of the die for each operation can be performed from the operations and assigned stamping features. The system can plan the equipment and operators for each operation to meet design specifications, and to achieve minimum machining time and maximum efficiency based on the above activity and knowledge. Finally, the optimal process plans obtained can be added into the case base of plans for the planning of other similar products. Customarily and practically, the relationships between operations consist of operations order constraint (do-after), which relates to the necessary order of operations to be
used, and operations combination constraint, which relates to relevant operations that can be formed at one process and die together (mentioned in Sect. 4.1). For example, flanging is after trimming, while piercing and trimming are always formed in one process. For the aims of economic efficiency and top-quality, it is always recommended to combine the potential operations together, while making the sequence operations practical. Therefore the initial main operation sequence is Blank- ing→Drawing →Trimming →Flanging for a flange feature comprised part, and Blanking →Drawing →Trimming for no flange feature part. With operations sequencing and combination rules, auxiliary operations are added to the initial main operation sequences to form final process routing. The following is the combination rules for hole1 and hole3 shown in Fig. 3 : (Logical) combination (for hole1 and hole3): IF distance between hole1 and hole3 >DIS && the angle of the vectors of the two hole<15· THEN TRUE ELSE FALSE; Thereafter, the structure of the die for each process can be performed from operations and the assigned features, while the process route is determined. Then the equipment such as a set of machinery or the product line can be selected to insure the stamping die meets design specifications. For example, Fig. 9 shows generation routes of process planning for the automobile panel shown in Fig. 3 . During process planning, different process routes can be found by different planners; therefore, the best process route should be selected according to the batch of production, design and manufacturing of stamping dies, cost, etc. while tool options, the equipment and dies for each process should be assigned to meet design specifications, and to achieve minimum machining time and maximum efficiency. Finally, the optimization of process planning [20] is realized for multiple purposes (best- quality, maximizing efficiency, minimizing cost and time) by PPO based on KBE.
4.5 PCS in process path generation
Since the process planning is a dynamic course with several plans and design stages, PCS is a key point to ensure process planning is integrated and consistent. PCS man- ages the process information model, assists in generating stamping process plans and detail design, and controls the changes during planning. There are several control variables for PCS including state variables for process planning, control variables for IMM, and state variables for stamping features, etc. The process control structure is shown in Fig. 10. In this CAPP system, the process planning is defined as a project. The project control can create a project, insert the part or work-pieces to suitable positions of the project, and decompose the process planning task into subtasks. In IMM and process planning, according to the knowledge expression and decision-making rules, the planning process control can set up the process information model based on features and their state variable, monitor planning process, feed the planning information and changes back to IMM, and control information transfer. The process planning is a dynamic process of information flow and transfer. The information link control ensures process planning information is associative and consistent. The added, extended, and modified information and its effects on the planning can be fed back to PIM and IMM so that the information of process planning can be updated timely and shared by different parts of the system. For the complicated and mass geometry information involved during the process planning, the links between features and product geometric information have been dealt with. The geometry link control can monitor and control the links and transfer the geometry information between different parts of the process planning. In IMM, the parts of PCS come into being dynamically along with proceeding of the process planning. If one part of PCS is created, it will monitor and control relevant planning and information subsequently. When some results of process planning are deleted, the corresponding PCS part will fade away.
5 Conclusions
As the automobile body panel is one kind of sheet metal part with groups of free form surfaces and large size, the process planning is more complicated than common sheet metal stamping. Yet the automobile panels can be considered as a combination of some common stamping, such as irregular drawing, flanging/bending, trimming, and piercing, etc. However, because of over-complexity, stamping CAPP system for automobile panels is more difficult to implode effectively and practically. It should deal with all knowledge from geometry, non-geometry, engineers’ experience, rules and criterions and successful cases of planning process-paths for automobile panels. The process plans should instruct or guide how to perform a complex procedure. Based on KBE, new frameworks have been presented as an intelligent master model in the system level and as a procedure model in the activity level. This master model brings forward a new concept and notion that knowledge, and thus KBE, is the kernel object of technology for specific domains in the manufacturing industry. In accordance with these frameworks, an intelligent CAPP system has been specifically developed. Based on feature technology, features have been extracted and represented by the object-oriented method. Stamping features and their parameters have been defined and extracted based on feature technology and stamping process rules. The whole product knowledge has been represented by frames which directly map to objects (or features) in the object-oriented sense. Relevant appropriate operations features have been assigned to stamping features of products based on feature- operation criteria, and parameters of stamping features and their correlativity. This assignment is a decision-making activity using a set of rules with a decision-making tree and model-based reasoning methods. With knowledge between operations, such as operations order constraint (do-after) and operations combination constraint, the process path has been improved based on relevant intelligent reasoning methods. Based on the relation (preferred-to) between processes and machines/dies, the structure of the die and machine for each process can be performed, while the process route has been determined. In this stamping process planning, the procedure and information have been con- trolled by the process control structure to be associative and integrated. This study can be used as the basis for future studies to enhance the complicated system. Indisputably, much effort will be required in advancing the establishment of the practicality process planning function blocks and their mutual interaction. Moreover, the conversion of these architectures into a prototype CAPP system will be a considerable endeavor.
References
1. Park SB, Choi Y, Kim BM, Choi JC (1998) A study of a computer-aided process design system for asymmetric deep- drawing products. J Mater Process Techno 75:17–26
2. Tisza M (1995) Expert system for metal forming. J Mater Process Techno 53:423 –432
3. Kang SS, Park DH (2002) Application of computer-aided process planning system for non-asymmetric deep drawing products. J Mater Process Technol 124:36–48
4. Gao JX, Tang YS, Sharma R (2000) A feature model editor and process planning system for sheet metal products. J Mater Process Technol 107:88 –95
5. Zussman E, Horsch T (1994) A planning approach for robot- assisted multiple-bent profile handling. Robot Com-Int Manuf 11(1):35– 40
6. Wang CH, Bourne DA (1997) Design and manufacturing of sheet-metal parts: using features to aid process planning and resolve manufacturability problems. Robot Com-IntManuf 13 (3):281 –294
7. de Vin LJ, de Vries J, Streppel AH, Klaassen EJW, Kals HJJ (1994) The generation of bending sequences in a CAPP system for sheetmetal components. J Mater Process Technol 42:331 – 339
8. de Vin LJ, Streppel AH, Kals HJJ (1994) Tolerancing and sheet bending in small batch part manufacturing. Ann CIRP 43 (1):421 –431
9. Streppel AH, Lutters DH, Kals JJ (1997) Process planning in small batch sheet metal part manufacturing. In: Proceedings of the 2nd world congress on intelligent manufacturing processes and systems, Budapest
10. Aomura S, Koguchi A, Niwa Y (1999) Automated and optimized process planning in sheet metal bending by a robot. International conference on industria l tools ICIT ’ 99, 18 –20 April, Roga? ka Slatina, Slovenia, pp 109–11 3
11. Aomura S, Koguchi A (2002) Optimized bending sequences of sheet metal bending by robot. Robot Com-Int Manuf 18:29 –39
12. Liao X, Wang GG (2003) Evolutionary path planning for robot assisted part handling in sheet metal bending. Robot Com-Int Manuf 19:425–430
13. Lutters D, ten Brinke E, Streppel AH, Kals HJJ (2000) Computer aided process planning for sheet metal based on information management. J Mater Process Technol 103(1):120 – 127
14. Kumar M, Rajotia S (2003) Integration of scheduling with computer aided process planning. J Mater Process Technol 138:297–300
15. Bancroft C (1998) Revitalisation of expertise in foundries using information technology. In: Proceedings of the 24th European conference on investment casting, Rome, Italy, pp 701– 712
16. Lovett PJ, Ingram A, Bancrof CN (2000) Knowledge-based engineering for SMEs —a methodology. J Mater Process Technol 107(1 –3):384 –389
17. Calkins D (1996) Learning all about knowledge based engineering. Intelligent Manufacturing Report 2(3) March
18. Selbeck C (1998) Open architecture. Vertigo —The Official Newsletter of the International ICAD Users’ Group 7(1) August
19. MacLeod M (1998) See all, know all, tell all. Prof Eng 11 (12):19 –20
20. Zheng J-Q, Wang Y-L, Li Z-G (2004) Evaluating model of process plan for large complicated stampings. Forging Stamp Technol 29(5):12 –15
基于知识工程的汽车覆盖件冲压路线分析
摘要
汽车车身覆盖件是一种由各种自由曲面组成的金属薄板，其过程归化比普通薄板有效的实际的冲压到内爆更复杂。基于知识工程，新的框架已经出现，作为在系统级和程序模式的活动水平上的智能主模型。根据上述框架，一个智能CAPP系统已经被专门开发。基于特征技术，功能已被提取并代表通过面向对象的方法。基于特征的技术和冲压工业规则，冲压功能和参数已经确定和提取。整个产品的信息直接映射到物体（或功能）的面向对象的意义上。基于特征的操作标准，冲压特征的参数及相关性，这项任务是一个决策活动，使用一套与规则决策树和基于模型的推理方法。不同操作中间，如操作顺序约束和不同操作组合约束，进程路径得到改善，根据有关智能推理方法。基于关系（首选地）之间工艺和设备模具，可以确定每道工序机和模具的结构，因为工艺路线已经确定。在这种冲压工艺规划中，程序和信息的关联和集成由一个进程控制结构控制。
关键词：汽车覆盖件；知识工程；工艺规划；特征
1引言
近日，计算机辅助工艺规划（CAPP）板材设计加工的系统已被广泛报道。Park构建了一个自动化过程规划轴对称拉深产品的系统。Tisza、Kang and Park提出了成组技术和模块化建造工艺CAPP系统和非轴对称序列设计专家系统用以设计椭圆形的产品。Gao et.开发使用先进的软件工具集自动化的飞机钣金制造规划组件。Horsch提出了议案规划方法，利用机器人辅助的多弯部分研究了C-空间和潜力的领域。Bourne提出了一种功能较好的自动工艺规划系统研究生产计划如何接近最低的制造成本。VIN等人开发了一个表金属的CAPP 系统部分- S，它集成了切割，嵌套，弯曲及弯曲顺序、焊接工艺。streppel等总结了传统公差的模糊性并提出了一种方法，取代了传统的公差与几何公差工艺规划在小批量钣金零件的制造Aomura等提出了一种可行的方法用弯曲机器人处理钣金部分序列，并对比不同决策系统从而把握最佳位置和重新定位。aomura和Koguchi提出了一个方法用机器人来生成一个表序列处理金属部分。Liao and wang提出了一种进化路径规划方法辅助计算机处理钣金零件的弯曲。lutters等人开发了一个通用的架构计算机辅助工艺规划，以小批量的钣金制造管理部分环境资料为基础。Kumar和Rajotia提出了调度及其与CAPP集成的方法，所以考虑到上线的过程规划可以考虑到机器的可用性和替代路线。上述内容主要的工艺参数计算，路径规划和一些示意图为特定类型的钣金件设计，如axisym度量和非轴对称深图纸，复杂的弯曲，车身面板是钣金一种，形状复杂的自由组曲面，大量的尺寸数字，始终是由冲压工艺制造。汽覆盖件形状不规则，含有翻边/弯曲，修剪和穿孔等，这些面板的工艺规划是常见的钣金冲压，这些复杂的加工一般依赖工程师的经验来完成。因此汽车面板的路径规划是必须认识研究的。从本质上讲，冲压汽车覆盖件的工艺路径就是确定必要的成型工艺和它们的加工序列，以产生一个特定的经济效益和竞争力。由流程路径生成是一个决策过程。决定形成各种特定功能的冲压操作，如操作应该用的模具和工具，以及用选用什么成形参数。CAPP系统应该是一个集成环境与知识处理，以减少对工程师或专家的依赖，并实现科学化的进程规划。因此，研究基于知识工程（知识经济），用于推进冲压汽车面板的CAPP系统，甚至可以改善汽车行业的竞争力。
2基于知识经济的冲压CAPP系统
2.1知识工程
基于知识工程（KBE）是一种创新工程设计的人工智能方法,在20世纪80年代开发的。到目前为止，还没有一个普遍公认的成熟的定义。但是，可以认为，知识经济是一种智能的方法，用来来解决工程问题，它可以实现继承，集成，运移，创新和专家通过驱动，乘法和应用知识的管理。一个以知识为基础的系统（KBS）可以获取专家的专长并结合计算机进行交互应用。执行这样任务的系统不同，复杂程度也相差很大。但是，一般专家都可以发现他们的规律。这个领域外的专家也可以轻松掌握这个系统知识工程提供了一个开放的架构和可重用的能力经验和知识，可以处理多领域知识的表达，并能形成一个集成的环境。知识型工程的应用是进一步专业化，通常有以下几部分组成：几何尺寸，配置和工程方面的知识：-几何尺寸往往是很重要的计算机辅助设计（CAD）元素。大多数用于创建知识工程的应用软件拥有内置CAD功能，或者是能够密切结合CAD软件包。-配置- 这指的是有效的匹配组件的组合。-工程知识- 这是基于制造和其他方面的考虑，将有助于产品设计。当操作人员的应用领域难度较大以及需要上述要素的一体化，知识工程可能是其集成的最好方法。知识工程有时被称为以规则为基础的工程，知识往往是由规则表示。这些可能是数学公式或条件语句，虽然是简单的概念，他们可以被合并，形成复杂和强大的表达式。另一方面，知识型工程，通常提供专门的几何能力，嵌入在工程方面的知识与能力产品型号。下面例子是典型的知识型工程的应用，这些应用展示了它的经济效益。1）莲花工程：使用集成的汽车莲花设计工程师（ICE）系统埃莉斯。ICE包括车辆布局系统，模块支持的悬浮式设计，发动机，动力传动系统，雨刷器。2）波音民用飞机集团。这将使用知识工程作为一种工具来获取飞机的已有知识，以减少用于生产设计的所需的资源。3）捷豹汽车。该公司的知识工程组，制定了采取内在知识应用系统将设计时间从8个星期减少至20分钟。
2.2以知识工程为基础的CAPP系统的问题
冲压CAPP系统应处理的知识包括几何，非几何，工程师经验，规则和标准，测试和数值模拟的结果，甚至在成功的情况下，由于复杂车身面板。涉及不同的领域的知识，如金属成形技术，金属成形力学，现代设计方法，数字中的仿真技术，人工智能。因此，CAPP 系统是解决这些问题的所有知识表达和应用，所有的多学科设计的一体化的CAPP系统本质上是一个指令集指引，是关于如何执行一个复杂的过程。如各个子任务，每一个子任务应该如何进行，以什么样的顺序，以及如何制定工作。此外，作为系统需求的变化，新的解决方案往往从现有的方法发展而来，所以计算机应用程序和他们的衍生可以比操作人员存在更长的时间，以知识工程为基础的汽车覆盖件冲压CAPP系统应该很容易解决以下几个问题：（1）所有的知识交涉。
（2）基于某方面的知识推理。
（3）从冲压件结构特征和过程的规则形式获取的操作特征，进行功能分析。
（4）基于过程测序和与过程相结合的工艺路线。
（5）控制或管理过程中的程序实现变化的快速反应。
3 CAPP系统框架
3.1CAPP系统的集成主模型
为了解决上述所有的问题，系统集成是先进的在主模型控制和框架CAPP系统方面。它是一种常见的概念和框架，用来概括和研究特征，过程控制和工艺规划循环，将其抽象成组，使其适合于知识的表达和应用程序、过程控制、信息集成、变化的响应等。冲压工艺智能模型（IMM）汽车板的规划组成在知识库的基础上，结合控制结构过程规划优化，工艺信息模型，可连接环境的集成磨碎，并结合基于KBE和结构IMM的显示图。IMM的工艺规划不仅是汽车智能化CAPP板基础，但在相结合的过程也融合了中KBE系统规划的知识和方法。有了这个模型，知识工程作为知识源驱动器的PC，PIM和LE，这使得工艺规划具有综合性和关联性。PIM是一个动态扩展的信息模型，可以添加和更新其中的信息工艺规划。使用知识，多表达格式，过程的信息集成模型规划并基于特征模型，对于层次结构和框架语义网和对象的特点，通过导向的方法来表达知识和建立信息模型。在这过程中，知识优势例如：数据库，参数，规则和经验，作为规则和对象的属性，以及整个产品知识作为一个对象关系框架，同一个过程的信息模型，工艺规划就可以完成，通过知识推理和在决策的基础上封装知识对象。PCS是一个关键点，以确保工艺规划是综合和一致的;管理过程的信息的TION模型，工艺规划生成冲压工艺计划和详细设计和控制的变化规划。在IMM中PCS随着这一进程的规划应运而生的。如果一个PCS创建，它将监测和控制相关的规划和其后信息。当结果过程被删除，相应的电脑部分信息将淡出。LE提供了几个方法来处理链接在工艺规划过程中，几何之间工件的产品设计和详细设计。实现大型复杂的智能工艺规划，如果有问题要解决，即连接过程规划程序，产品之间的几何链接和工件的详细设计。LE提供了几个方法来处理这些链接，例如：可变参数链接，数据结构链接和几何链接。PPO是一个设计复杂的工程的最佳方法，它可以处理复杂在经济规划过程的优化问题查看。
3.2冲压CAPP系统为基础的汽车板
对上述智能主模型由几个从产品的冲压特征提取阶段，如数据，操作功能推理冲压功能形成过程的信息模型，处理计划得到序列，详细的操作和相关的工具设计工件，详细设计模拟，终于计划的过程和3D模人脸模型生成如图。2。这是一个有形的活动水平汽车板的CAPP系统的控制和帧。CAPP系统框架基于知识经济在CAPP系统，冲压工艺规划汽车板，首先需要建立一个进程基于三维模型的产品和信息模型特征技术。冲压特征提取，随后取得操作功能。的特点所有关于自己随身携带的知识，过程和限制。然后PIM和PCS建立。有-之后，序列规划是建立在PIM如操作顺序规则，操作知识结合指南和推理方法，然后模具和机械选项。随着规划的过程中，药盒，PPO和建立由知识驱动的IMM乐。只包含综合收集任务，可以启动，控制，管理，评估和更新所有的规划信息和结果及时。PPO的优化过程中的路径，并输入一九八六年四月十二资源环境，PCS和PPO的开展优化，并找到最佳的解决方案。PCS和LE使规划相关的和可交联的过程。
4进程的路径生成的关键点
Unigraphics的有几个特点，提供的一个子集一个知识工程language-UG/KFL，能力提供一种方式来指定，可以覆盖的知识规则所有Unigraphics的应用。冲压CAPP系统汽车板已开发的基础上，上述框架先进，选择C和UG / KF语言作为实现语言，访问作为其在UG/ CAD开发环境的数据库MENT。UG / OPEN和UG/开++允许定制和使用一个标准的程序Unigraphics的延伸语言（C和C+）。UG/自由联盟提供了一个方法来指定知识规则，可以涵盖所有Unigraphics的应用tions。UG/自由联盟的规则很容易写的开发，易于阅读，理解，和用户重用。此外，UG / OPEN可以被整合与知识经济从知识经济的语言访问C程序介绍根据外部函数。有关访问命名的属性从C，会有一个实用程序设计在语言和定义产生C绑定访问的对象，设计实例的属性。访问包括职能和获取方法并设置对象的命名属性的值实例。此外，还有一些在UG/ UDF和UDOCAD和UG / KF，它可以处理UG / OPENUG / KF。更重要的是，Unigraphics是结合许多其他知识的工具和传播源，如，张，其他ICAD的知识经济的语言系统，有限元分析，CAM等。
4.1烫印功能
要产生相应的进程计划，产品数据需要原始投入，其中包括几何，拓扑，公差，材料和产品的数量。基于特征的技术和冲压技术，冲压功能的一部分，可以是部分形成一定的冲压作业的手段。为前例如，绘制功能或弯曲功能被定义为主要的功能，这是来形容近净形组成部分，而法兰孔，浮雕，珠，缺口和法兰孔被定义为辅助的，这是需要说明的最终形状的本地部分。使用功能，技术和几何提取方法，冲压的设计特点，如主形成功能（如图纸，弯曲），法兰，孔，浮雕，珠，缺口，因此，可以从三维实体中提取模型，这是第一个定义为UG/ UDO光盘。例如，fig.3showsthestampingfeaturesofoneautomobilepanel。冲压特征模型应该被定义为代表产品知识集成和毫不含糊的。冲压功能表示为面向对象的类或对象和实例，利用UG / KF语言（UG/自由联盟）不仅代表着功能参数，公差，材料，等类或实例的属性，但也代表通过导入UG/ UDO光盘和UG/ UDF的几何对象引用一个实例的属性或儿童立体几何。这实现之间的连接和集成符号的功能和它的几何对象。它可以也从一个函数，规则，表达的属性值和数据库。
4.2操作功能
因此，冲压操作功能分类为初始和后续如拉伸，弯曲，翻边，切边，卷边，再引人注目，穿孔等上。被分配到有关的适当行动形成冲压产品的特点，基于功能操作标准，冲压功能参数他们的相关性。这个任务是一个决策用树和一套规则，决策活动基于模型的推理方法。例如，绘制→修剪是从正选赛功能推理，翻边从法兰特征的推理，炯炯有神从洞的推理。图5显示了典型的例子翻边冲压运作功能推理功能，这些操作功能的序列规则附加的操作功能。习惯上，之间的关系特点，特别是层次，应该是一个重要因素，而操作功能是推理。图。4，功能flange3，flange1和bead1应该是在一组的形式共同演绎有关适当行动。在这推理的方式，操作功能可以得到丰达后续规划的心理知识。在本文中，操作功能的理由从冲压功能代表面向对象enti的关系和UG / UDO光盘，和之间的关系表示为基于网络的冲压产品特征模型（如图6）。操作功能，不仅是指自己冲压功能，而且还涉及到其他如相关的成型模具
和机械操作，它们之间的关系。的关系之间的业务包括经营秩序约束和操作相结合的约束。其他类型的工艺和设备/模具之间的关系是偏好（首选地）。例如，翻边总是首选翻边模具和有关的新闻机，而修剪总是倾向于修整模具和压力机。所有这些制约因素和它们之间的关系是只代表了为的规则操作。ITIS通过冲压功能的引用，描述几何对象实现操作功能，而相关的模具和机械能操作选项和约束代表表示有关规则，函数或方法。
4.3工艺信息模型（PIM）的路径
规划现在的工艺规划的PIM可以被定义为处理规划的基础。和入境事务处处长的电脑创建控制和监视的冲压特征和其控制变量或状态变量的操作功能。的大型复杂冲压件工艺规划一个动态的过程。在PIM必须涉及的所有数据，如工艺规划数据，分析数据，模具设计数据，情况等基本知识表达模型应该有几何变化的适应性，属性，特征，制约因素和思维方式。知识经济的知识多表达格式技术，工艺的集成信息模型规划的大型复杂冲压件的基础上建立特征模型。显示过程信息模型图。7。面向对象的方法和功能技术OGY主要是通过形成模型。有三种基本类的特点：冲压件的设计功能，操作，A TION功能，序列特征，在哪个进程知识，例如：数据库，参数，规则和经验，作为对象的属性和规则的行为。使用功能技术和几何提取方法，邮票ING的设计特点，如形成的主要功能（如绘图，弯曲），法兰，孔，浮雕，缺口，所以，被定义为UG / UDO光盘，可以提取三维实体模型。有关适当的操作可以同一个决策树和基于模型的一套规则功能操作标准的推理方法。阶层产品模型和语义网和框架功能操作工具是用来建立关系为PIM信息。与PIM，知识是封装在对象或决策知识亲cedures，流程规划，就可以完成通过相应的知识推理集。这个模型是一个动态扩展的信息模型，在其中的信息可以添加和更新，沿着规划的过程中。信息管理和控制的PCS在IMM的工艺规划的一部分，这可以监控过程中的变化或修改计划宁，并及时更新信息，以确保工艺信息模型和流程规划同步nization。在流程规划，信息化管理控制开始从时间的控制和判断。冲压件的设计特点，已创建直到规划结束。
4.4进程的路径规划和工具选项
一般来说，形成包括汽车面板一些操作，如绘画，剪裁，翻边，穿孔，重新引人注目，折边等，在操作中，画，修剪和翻边主营业务形成对产品的形状，和其他业务辅助操作，工作与主营业务，形成复杂形状的产品。至操作之间的优先关系的基础上，PIM时，主营业务必须首先确定，然后是如何安排的初步决定主营业务，如何结合辅助操作主要的运作，以及如何插入辅助操作顺序操作。为整合规划时，应考虑冲压模具的能力，机械或车间的成本和能力为关键测序水平的问题。从理论上讲，基于案例的推理（CBR），基于规则推理（RBR 的），和基于模型的推理（MBR）所有申请过程规划。在本文的CBR，RBR的人工神经网络联合起来决定后，基于模型的推理方法在工艺规划，这是图。8。首先，基于模型的推理是用来形成一个代码基于CBR的产品和经营功能实体及其相互关系，以及相关的规则或知识边缘人的推理。然后被选中的CBR得到类似的情况下，基地的计划，如果是不适合的CBR，红牛和人工神经网络是选择完成任务的合作tively。测序成形操作过程中，每个操作的模具结构可以进行从操作和分配冲压功能。“系统可规划为每个设备和运营商操作，以满足设计规范，并实现最小加工时间和最高的效率为基础上述活动和知识。最后，最佳的流程计划取得可添加到案例库其他同类产品的规划，计划。习惯和实践之间的关系业务包括操作顺序约束（做后），其中涉及到必要的经营秩序和操作相结合的约束，其中涉及可以在
oneprocess形成的有关业务和同归于尽（在第4.1节所述）。例如，翻边修整后，刺入和修剪时总是在一个过程中形成的。对于经济效率和最优质的目标，这是总是推荐相结合的潜在操作在一起，而实际操作序列。因此，最初的主要操作顺序是空白ING→绘图→切边→翻边，法兰功能组成部分，冲裁→绘图→修剪没有法兰功能的一部分。与操作测序和组合规则，辅助操作添加到最初的主要操作序列，形成最后过程的路由。以下是组合规则hole1和hole3如图。3：（逻辑）组合（为hole1和hole3）：IFdistance>在hole1和hole3之间的DIS&&向量的角度两孔<15?TRUE，否则返回FALSE; 此后，每道工序的模具结构可以进行操作和分配的功能，而工艺路线的决心。然后设备如集的机械或生产线，可选择，以确保冲压模具符合设计规范tions。例如，图。9显示代路线图的汽车覆盖件工艺规划。3。在流程规划，可以是不同的工艺路线发现不同的规划者，因此，最佳工艺应根据批次选择路线冲压模具生产，设计和制造，工具选项，设备和死亡的成本等，而每一个过程中应分配给符合设计规范tions，并达到最低的加工时间和最高的效率。最后，优化过程规划[20]实现多种用途（最佳质量，最大限度地提高效率，降低成本和时间）基于KBE PPO的基础。
4.5进程的路径生成PCS
由于theprocess规划是一个动态过程与几个计划和设计阶段，PCS是一个关键点，以确保工艺规划是综合性和一贯的。只人年龄工艺信息模型，协助生成冲压工艺规划和详细设计，和控制在规划过程中的变化。有几个控制只包括进程状态变量的变量规划，IMM的控制变量，状态变量冲压特性，过程控制结构如图。10。在此CAPP系统，这一过程被定义为一个规划项目。项目的控制，可以创建一个项目，插入部分或工件项目适合的岗位，工艺规划任务分解成子任务。在IMM和工艺规划，根据的知识边缘的表达和决策规则，规划过程控制，可以设立过程中的信息模型特点和他们的状态变量的基础上，规划监察过程中，饲料的规划信息和更改回IMM的，控制信息的传递。工艺规划是一个动态过程信息，TION流和转让。确保信息链路控制工艺规划信息关联和一致的。增值，扩展和修改的信息和其对规划的影响，可以反馈到PIM和IMM规划过程中的信息可以更新及时和共享系统的不同部分。对于复杂和大规模的几何信息参与在规划的过程之间的联系，已处理的功能和产品的几何信息使用。几何链路控制，监测和控制链接和转移之间的几何信息工艺规划的不同部位。在IMM的电脑零件来动态应运而生随着工艺规划出发。如果其中的一部分PCS的创建，它会监视和控制有关随后规划和信息。当一些成果工艺规划将被删除，相应的PCS部分会消失。
5结论
由于车身面板是一种自由曲面和大尺寸钣金部分的群体，工艺规划是比普通钣金更复杂的金属冲压。然而，汽车板可以结合了一些常见的冲压，如不规则图形、翻边/弯曲、修剪、穿孔等，然而，由于过度的复杂性，汽车覆盖件冲压CAPP系统更复杂。它应该处理所有的知识，从几何、非几何、工程师的经验、规则，在汽车板成功的过程路径规划的中。应指导如何执行复杂过程的规划。基于知识工程，新的框架已经出现，作为在系统级和程序模式的活动水平上的智能主模型。这个主模型提出了一种新的知识的概念，因此，知识工程是制造业中技术对象的特定域。在这些框架，基于特征技术，功能提取和面向对象的方法，智能CAPP系统已被专门开发。在冲压特征及其参数已被定义和提取的基础上，进行制定功能技术和冲压工艺的规则。整个产品知识直接映射到面向对象的系统（或功能）上。根据冲压产品的特征进行相关的特征操作，基于特征操作标准，冲压功能参数和他们的相关性，使用
一套规则与决策树和基于模型的推理方法。随着知识之间操作，如操作顺序约束（做后）和操作相结合的约束，进程的路径在相关的智能推理的基础上得到改善。基于特征之间的关系工艺和设备/模具，模具的结构和每道工序的机器可以被确定，从而确定工艺路线。在此冲压工艺已规划，程序和信息由过程控制结构进行联想和整合。未来研究可以在这项研究的基础上加强系统的复杂性。无可否认，在推进建立实用性工艺规划功能块和其相互交流中还需更多的努力。这些转换原型CAPP系统的体系结构将发挥很大的作用。
《机械工程专业英语教程》课文翻译
Lesson 1 力学的基本概念 1、词汇： statics [st?tiks] 静力学；dynamics动力学；constraint约束；magnetic [m?ɡ＇netik]有磁性的；external [eks＇t?:nl] 外面的, 外部的；meshing啮合；follower从动件；magnitude [＇m?ɡnitju:d] 大小；intensity强度，应力；non-coincident [k?u＇insid?nt]不重合；parallel [＇p?r?lel]平行；intuitive 直观的；substance物质；proportional [pr?＇p?:??n?l]比例的；resist抵抗，对抗；celestial [si＇lestj?l]天空的；product乘积；particle质点；elastic [i＇l?stik]弹性；deformed变形的；strain拉力；uniform全都相同的；velocity[vi＇l?siti]速度；scalar[＇skeil?]标量；vector[＇vekt?]矢量；displacement代替；momentum [m?u＇ment?m]动量； 2、词组 make up of由……组成；if not要不，不然；even through即使，纵然； Lesson 2 力和力的作用效果 1、词汇： machine 机器；mechanism机构；movable活动的；given 规定的，给定的，已知的；perform执行；application 施用；produce引起，导致；stress压力；applied施加的；individual单独的；muscular [＇m?skjul?]]力臂；gravity[ɡr?vti]重力；stretch伸展，拉紧，延伸；tensile[tensail]拉力；tension张力，拉力；squeeze挤；compressive 有压力的，压缩的；torsional扭转的；torque转矩；twist扭，转动；molecule [m likju:l]分子的；slide滑动; 滑行；slip滑，溜；one another 互相；shear剪切；independently独立地，自立地；beam梁；compress压；revolve (使)旋转；exert [iɡ＇z?:t]用力，尽力，运用，发挥，施加；principle原则, 原理，准则，规范；spin使…旋转；screw螺丝钉；thread螺纹； 2、词组 a number of 许多；deal with 涉及，处理；result from由什么引起；prevent from阻止，防止；tends to 朝某个方向；in combination结合；fly apart飞散； 3、译文： 任何机器或机构的研究表明每一种机构都是由许多可动的零件组成。这些零件从规定的运动转变到期望的运动。另一方面，这些机器完成工作。当由施力引起的运动时，机器就开始工作了。所以，力和机器的研究涉及在一个物体上的力和力的作用效果。 力是推力或者拉力。力的作用效果要么是改变物体的形状或者运动，要么阻止其他的力发生改变。每一种
机械专业术语英文翻译
陶瓷 ceramics 合成纤维 synthetic fibre 电化学腐蚀 electrochemical corrosion 车架 automotive chassis 悬架 suspension 转向器 redirector 变速器 speed changer 板料冲压 sheet metal parts 孔加工 spot facing machining 车间 workshop 工程技术人员 engineer 气动夹紧 pneuma lock 数学模型 mathematical model 画法几何 descriptive geometry 机械制图 Mechanical drawing 投影 projection 视图 view 剖视图 profile chart 标准件 standard component 零件图 part drawing 装配图 assembly drawing 尺寸标注 size marking
技术要求 technical requirements 刚度 rigidity 内力 internal force 位移 displacement 截面 section 疲劳极限 fatigue limit 断裂 fracture 塑性变形 plastic distortion 脆性材料 brittleness material 刚度准则 rigidity criterion 垫圈 washer 垫片 spacer 直齿圆柱齿轮 straight toothed spur gear 斜齿圆柱齿轮 helical-spur gear 直齿锥齿轮 straight bevel gear 运动简图 kinematic sketch 齿轮齿条 pinion and rack 蜗杆蜗轮 worm and worm gear 虚约束 passive constraint 曲柄 crank 摇杆 racker 凸轮 cams
毕业设计外文翻译资料
外文出处： 《Exploiting Software How to Break Code》By Greg Hoglund, Gary McGraw Publisher : Addison Wesley Pub Date : February 17, 2004 ISBN : 0-201-78695-8 译文标题： JDBC接口技术 译文： JDBC是一种可用于执行SQL语句的JavaAPI（ApplicationProgrammingInterface应用程序设计接口）。它由一些Java语言编写的类和界面组成。JDBC为数据库应用开发人员、数据库前台工具开发人员提供了一种标准的应用程序设计接口，使开发人员可以用纯Java语言编写完整的数据库应用程序。 一、ODBC到JDBC的发展历程 说到JDBC，很容易让人联想到另一个十分熟悉的字眼“ODBC”。它们之间有没有联系呢？如果有，那么它们之间又是怎样的关系呢？ ODBC是OpenDatabaseConnectivity的英文简写。它是一种用来在相关或不相关的数据库管理系统（DBMS）中存取数据的，用C语言实现的，标准应用程序数据接口。通过ODBCAPI，应用程序可以存取保存在多种不同数据库管理系统（DBMS）中的数据，而不论每个DBMS使用了何种数据存储格式和编程接口。 1．ODBC的结构模型 ODBC的结构包括四个主要部分：应用程序接口、驱动器管理器、数据库驱动器和数据源。应用程序接口：屏蔽不同的ODBC数据库驱动器之间函数调用的差别，为用户提供统一的SQL编程接口。 驱动器管理器：为应用程序装载数据库驱动器。 数据库驱动器：实现ODBC的函数调用，提供对特定数据源的SQL请求。如果需要，数据库驱动器将修改应用程序的请求，使得请求符合相关的DBMS所支持的文法。 数据源：由用户想要存取的数据以及与它相关的操作系统、DBMS和用于访问DBMS的网络平台组成。 虽然ODBC驱动器管理器的主要目的是加载数据库驱动器，以便ODBC函数调用，但是数据库驱动器本身也执行ODBC函数调用，并与数据库相互配合。因此当应用系统发出调用与数据源进行连接时，数据库驱动器能管理通信协议。当建立起与数据源的连接时，数据库驱动器便能处理应用系统向DBMS发出的请求，对分析或发自数据源的设计进行必要的翻译，并将结果返回给应用系统。 2．JDBC的诞生 自从Java语言于1995年5月正式公布以来，Java风靡全球。出现大量的用java语言编写的程序，其中也包括数据库应用程序。由于没有一个Java语言的API，编程人员不得不在Java程序中加入C语言的ODBC函数调用。这就使很多Java的优秀特性无法充分发挥，比如平台无关性、面向对象特性等。随着越来越多的编程人员对Java语言的日益喜爱，越来越多的公司在Java程序开发上投入的精力日益增加，对java语言接口的访问数据库的API 的要求越来越强烈。也由于ODBC的有其不足之处，比如它并不容易使用，没有面向对象的特性等等，SUN公司决定开发一Java语言为接口的数据库应用程序开发接口。在JDK1．x 版本中，JDBC只是一个可选部件，到了JDK1．1公布时，SQL类包（也就是JDBCAPI）
机械专业外文翻译(中英文翻译)
外文翻译 英文原文 Belt Conveying Systems Development of driving system Among the methods of material conveying employed，belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost．Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do so．Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine)．The ability to control drive acceleration torque is critical to belt conveyors’performance．An efficient drive system should be able to provide smooth，soft starts while maintaining belt tensions within the specified safe limits．For load sharing on multiple drives．torque and speed control are also important considerations in the drive system’s design. Due to the advances in conveyor drive control technology，at present many more reliable．Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers’ choices[1]. 1 Analysis on conveyor drive technologies 1．1 Direct drives Full-voltage starters．With a full-voltage starter design，the conveyor head shaft is direct-coupled to the motor through the gear drive．Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors．With direct fu11-voltage starters．no control is provided for various conveyor loads and．depending on the ratio between fu11-and no-1oad power requirements，empty starting times can be three or four times faster than full load．The maintenance-free starting system is simple，low-cost and very reliable．However, they cannot control starting torque and maximum stall torque；therefore．they are
机械专业中英文对照(完整版)1
机械专业英语词汇 陶瓷ceramics 合成纤维synthetic fibre 电化学腐蚀electrochemical corrosion 车架automotive chassis 悬架suspension 转向器redirector 变速器speed changer 板料冲压sheet metal parts 孔加工spot facing machining 车间workshop 工程技术人员engineer 气动夹紧pneuma lock 数学模型mathematical model 画法几何descriptive geometry 机械制图Mechanical drawing 投影projection 视图view 剖视图profile chart 标准件standard component 零件图part drawing 装配图assembly drawing 尺寸标注size marking 技术要求technical requirements 刚度rigidity 内力internal force 位移displacement 截面section 疲劳极限fatigue limit 断裂fracture 塑性变形plastic distortion 脆性材料brittleness material 刚度准则rigidity criterion 垫圈washer 垫片spacer 直齿圆柱齿轮straight toothed spur gear 斜齿圆柱齿轮helical-spur gear 直齿锥齿轮straight bevel gear 运动简图kinematic sketch 齿轮齿条pinion and rack 蜗杆蜗轮worm and worm gear 虚约束passive constraint 曲柄crank 摇杆racker 凸轮cams 共轭曲线conjugate curve 范成法generation method 定义域definitional domain 值域range 导数\\微分differential coefficient 求导derivation 定积分definite integral 不定积分indefinite integral 曲率curvature 偏微分partial differential 毛坯rough 游标卡尺slide caliper 千分尺micrometer calipers 攻丝tap 二阶行列式second order determinant 逆矩阵inverse matrix 线性方程组linear equations 概率probability 随机变量random variable 排列组合permutation and combination 气体状态方程equation of state of gas 动能kinetic energy 势能potential energy 机械能守恒conservation of mechanical energy 动量momentum 桁架truss 轴线axes 余子式cofactor 逻辑电路logic circuit 触发器flip-flop 脉冲波形pulse shape 数模digital analogy 液压传动机构fluid drive mechanism 机械零件mechanical parts 淬火冷却quench 淬火hardening 回火tempering 调质hardening and tempering 磨粒abrasive grain 结合剂bonding agent 砂轮grinding wheel 后角clearance angle 龙门刨削planing 主轴spindle
(机械制造行业)机械英文翻译
英文翻译 机械设计 一台完整机器的设计是一个复杂的过程。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。 Machine Design The complete design of a machine is a complex process. The machine design is a creative work. Project engineer not only must have the creativity in the work, but also must in aspect and so on mechanical drawing, kinematics, engineerig material, materials mechanics and machine manufacture technology has the deep elementary knowledge. 任何产品在设计时第一步就是选择产品每个部分的构成材料。许多的材料被今天的设计师所使用。对产品的功能，它的外观、材料的成本、制造的成本作出必要的选择是十分重要的。对材料的特性必须事先作出仔细的评估。 One of the first steps in the design of any product is to select the material from which each part is to be made. Numerous materials are available to today's designers. The function of the product, its appearance, the cost of the material, and the cost of fabrication are important in making a selection. A careful evaluation of the properties of a. material must be made prior to any calculations. 仔细精确的计算是必要的，以确保设计的有效性。在任何失败的情况下，最好知道在最初设计中有有缺陷的部件。计算（图纸尺寸）检查是非常重要的。一个小数点的位置放错，就可以导致一个本可以完成的项目失败。设计工作的各个方面都应该检查和复查。 Careful calculations are necessary to ensure the validity of a design. In case of any part failures, it is desirable to know what was done in originally designing the defective components. The checking of calculations (and drawing dimensions) is of utmost importance. The misplacement of one decimal point can ruin an otherwise acceptable project. All aspects of design work should be checked and rechecked. 计算机是一种工具，它能够帮助机械设计师减轻繁琐的计算，并对现有数据提供进一步的分析。互动系统基于计算机的能力，已经使计算机辅助设计（CAD）和计算机辅助制造（CAM）成为了可能。心理学家经常谈论如何使人们适应他们所操作的机器。设计人员的基本职责是努力使机器来适应人们。这并不是一项容易的工作，因为实际上并不存在着一个对所有人来说都是最优的操作范围和操作
毕业设计外文翻译附原文
外文翻译 专业机械设计制造及其自动化学生姓名刘链柱 班级机制111 学号1110101102 指导教师葛友华
外文资料名称： Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处：Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件： 1.外文资料翻译译文 2.外文原文
应用旋风技术真空吸尘器的设计和性能介绍 吉尔泰金，洪城铱昌，宰瑾李， 刘链柱译 摘要：旋风型分离器技术用于真空吸尘器 - 轴向进流旋风和切向进气道流旋风有效地收集粉尘和降低压力降已被实验研究。优化设计等因素作为集尘效率，压降，并切成尺寸被粒度对应于分级收集的50％的效率进行了研究。颗粒切成大小降低入口面积，体直径，减小涡取景器直径的旋风。切向入口的双流量气旋具有良好的性能考虑的350毫米汞柱的低压降和为1.5μm的质量中位直径在1米3的流量的截止尺寸。一使用切向入口的双流量旋风吸尘器示出了势是一种有效的方法，用于收集在家庭中产生的粉尘。 摘要及关键词：吸尘器; 粉尘; 旋风分离器 引言 我们这个时代的很大一部分都花在了房子，工作场所，或其他建筑，因此，室内空间应该是既舒适情绪和卫生。但室内空气中含有超过室外空气因气密性的二次污染物，毒物，食品气味。这是通过使用产生在建筑中的新材料和设备。真空吸尘器为代表的家电去除有害物质从地板到地毯所用的商用真空吸尘器房子由纸过滤，预过滤器和排气过滤器通过洁净的空气排放到大气中。虽然真空吸尘器是方便在使用中，吸入压力下降说唱空转成比例地清洗的时间，以及纸过滤器也应定期更换，由于压力下降，气味和细菌通过纸过滤器内的残留粉尘。 图1示出了大气气溶胶的粒度分布通常是双峰形，在粗颗粒（>2.0微米）模式为主要的外部来源，如风吹尘，海盐喷雾，火山，从工厂直接排放和车辆废气排放，以及那些在细颗粒模式包括燃烧或光化学反应。表1显示模式，典型的大气航空的直径和质量浓度溶胶被许多研究者测量。精细模式在0.18?0.36 在5.7到25微米尺寸范围微米尺寸范围。质量浓度为2?205微克，可直接在大气气溶胶和 3.85至36.3μg/m3柴油气溶胶。
机械专业英文翻译
启动轴starting axle 启动齿轮starting gear 启动棘轮starting ratchet wheel 复位弹簧restoring, pull back spring 弹簧座spring seating 摩擦簧friction spring 推力垫圈thrust washer 轴挡圈axle bumper ring 下料filling 切断cut 滚齿机gear-hobbing machine 剪料机material-shearing machine 车床lathe 拉床broaching machine 垂直度verticality, vertical extent 平行度 parallelism同心度 homocentricity 位置度position 拉伤pulling damage 碰伤bumping damage 缺陷deficiency 严重缺陷severe deficiency 摩擦力friction 扭距twist 滑动glide 滚动roll 打滑skid 脱不开can’t seperate 不复位can’t restore 直径diameter M值= 跨棒距test rod span 公法线common normal line 弹性elasticity 频率特性frequency characteristic 误差error 响应response 定位allocation 机床夹具jig 动力学dynamic 运动学kinematic 静力学static 分析力学analyse mechanics 拉伸pulling 压缩hitting 机床machine tool 刀具cutter 摩擦friction 联结link 传动drive/transmission 轴shaft 剪切shear 扭转twist 弯曲应力bending stress 三相交流电three-phase AC 磁路magnetic circles 变压器transformer 异步电动机asynchronous motor 几何形状geometrical 精度precision 正弦形的sinusoid 交流电路AC circuit 机械加工余量machining allowance 变形力deforming force 变形deformation 电路circuit 半导体元件semiconductor element 拉孔broaching 装配assembling 加工machining 液压hydraulic pressure 切线tangent 机电一体化mechanotronics mechanical-electrical integration 稳定性stability 介质medium 液压驱动泵fluid clutch 液压泵hydraulic pump 阀门valve 失效invalidation 强度intensity 载荷load 应力stress 安全系数safty factor 可靠性reliability 螺纹thread 螺旋helix 键spline 销pin 滚动轴承rolling bearing 滑动轴承sliding bearing 弹簧spring 制动器arrester brake 十字结联轴节crosshead 联轴器coupling 链chain 皮带strap 精加工finish machining 粗加工rough machining 变速箱体gearbox casing 腐蚀rust 氧化oxidation 磨损wear 耐用度durability 机械制图 Mechanical drawing 投影projection 视图view 剖视图profile chart 标准件standard component 零件图part drawing 装配图assembly drawing 尺寸标注size marking 技术要求 technical requirements 刚度rigidity 内力internal force 位移displacement 截面section 疲劳极限fatigue limit 断裂fracture 塑性变形plastic distortion 脆性材料brittleness material 刚度准则rigidity criterion 垫圈washer 垫片spacer 直齿圆柱齿轮 straight toothed spur gear 斜齿圆柱齿轮 helical-spur gear 直齿锥齿轮 straight bevel gear 运动简图kinematic sketch 齿轮齿条pinion and rack 蜗杆蜗轮worm and worm gear 虚约束passive constraint 曲柄crank 摇杆racker 凸轮cams 反馈feedback 发生器generator 直流电源DC electrical source 门电路gate circuit 外圆磨削external grinding 内圆磨削internal grinding 平面磨削plane grinding 变速箱gearbox 离合器clutch 绞孔fraising 绞刀reamer
毕业设计外文翻译
毕业设计（论文） 外文翻译 题目西安市水源工程中的 水电站设计 专业水利水电工程 班级 学生 指导教师 2016年
研究钢弧形闸门的动态稳定性 牛志国 河海大学水利水电工程学院，中国南京，邮编210098 nzg_197901@https://www.sodocs.net/doc/b88426955.html,，niuzhiguo@https://www.sodocs.net/doc/b88426955.html, 李同春 河海大学水利水电工程学院，中国南京，邮编210098 ltchhu@https://www.sodocs.net/doc/b88426955.html, 摘要 由于钢弧形闸门的结构特征和弹力，调查对参数共振的弧形闸门的臂一直是研究领域的热点话题弧形弧形闸门的动力稳定性。在这个论文中，简化空间框架作为分析模型，根据弹性体薄壁结构的扰动方程和梁单元模型和薄壁结构的梁单元模型，动态不稳定区域的弧形闸门可以通过有限元的方法，应用有限元的方法计算动态不稳定性的主要区域的弧形弧形闸门工作。此外，结合物理和数值模型，对识别新方法的参数共振钢弧形闸门提出了调查，本文不仅是重要的改进弧形闸门的参数振动的计算方法，但也为进一步研究弧形弧形闸门结构的动态稳定性打下了坚实的基础。 简介 低举升力，没有门槽，好流型，和操作方便等优点，使钢弧形闸门已经广泛应用于水工建筑物。弧形闸门的结构特点是液压完全作用于弧形闸门，通过门叶和主大梁，所以弧形闸门臂是主要的组件确保弧形闸门安全操作。如果周期性轴向载荷作用于手臂，手臂的不稳定是在一定条件下可能发生。调查指出:在弧形闸门的20次事故中，除了极特殊的破坏情况下，弧形闸门的破坏的原因是弧形闸门臂的不稳定;此外，明显的动态作用下发生破坏。例如:张山闸，位于中国的江苏省，包括36个弧形闸门。当一个弧形闸门打开放水时，门被破坏了，而其他弧形闸门则关闭，受到静态静水压力仍然是一样的，很明显，一个动态的加载是造成的弧形闸门破坏一个主要因素。因此弧形闸门臂的动态不稳定是造成弧形闸门(特别是低水头的弧形闸门)破坏的主要原是毫无疑问。
机械类英语论文及翻译翻译
High-speed milling High-speed machining is an advanced manufacturing technology, different from the traditional processing methods. The spindle speed, cutting feed rate, cutting a small amount of units within the time of removal of material has increased three to six times. With high efficiency, high precision and high quality surface as the basic characteristics of the automobile industry, aerospace, mold manufacturing and instrumentation industry, such as access to a wide range of applications, has made significant economic benefits, is the contemporary importance of advanced manufacturing technology. For a long time, people die on the processing has been using a grinding or milling EDM (EDM) processing, grinding, polishing methods. Although the high hardness of the EDM machine parts, but the lower the productivity of its application is limited. With the development of high-speed processing technology, used to replace high-speed cutting, grinding and polishing process to die processing has become possible. To shorten the processing cycle, processing and reliable quality assurance, lower processing costs. 1 One of the advantages of high-speed machining High-speed machining as a die-efficient manufacturing, high-quality, low power consumption in an advanced manufacturing technology. In conventional machining in a series of problems has plagued by high-speed machining of the application have been resolved. 1.1 Increase productivity High-speed cutting of the spindle speed, feed rate compared withtraditional machining, in the nature of the leap, the metal removal rate increased 30 percent to 40 percent, cutting force reduced by 30 percent, the cutting tool life increased by 70% . Hardened parts can be processed, a fixture in many parts to be completed rough, semi-finishing and fine, and all other processes, the complex can reach parts of the surface quality requirements, thus increasing the processing productivity and competitiveness of products in the market. 1.2 Improve processing accuracy and surface quality High-speed machines generally have high rigidity and precision, and other characteristics, processing, cutting the depth of small, fast and feed, cutting force low, the workpiece to reduce heat distortion, and high precision machining, surface roughness small. Milling will be no high-speed processing and milling marks the surface so that the parts greatly enhance the quality of the surface. Processing Aluminum when up Ra0.40.6um, pieces of steel processing at up to Ra0.2 ~ 0.4um.
机械专业相关词汇中英文翻译大全
机械专业相关词汇中英文翻译大全 单价unit price 工日合计Man-day total/work-day total 人工费cost of labor 材料费materials expenses 机械的mechanical 检查接线connection test 发电机generator 调相机phase regulator 周波cycle 减负荷装置 load-shedding equipment 断路器柜circuit breaker cabinet 单母线single busbar 互感器transformer 每相电流Current by Phase 封闭式插接close type socket joint 发电机控制面板generator control panel 分级卸载sorted unloading 同步控制synchronization control 调速器 speed governor 信号屏signal screen 继电器relay 高压柜high pressure cabinet 油浸电力变压器oil-immersed power transformer 空气断路器air circuit breaker 控制屏control panel 直流馈电屏direct current feed control panel 电容器electric condenser 计量盘metering panel 成套配电箱whole set of distribution box 落地式floor model 控制开关Control switches 铜芯电力电缆Copper core power cable 控制电缆actuating cable 热缩式电力电缆终端头pyrocondensation power cable terminal 钢结构支架配管steel structure bracket tubing 万用槽钢versatile U-steel 电缆托架 cable bracket 钢制托盘式桥架steel Tray-type cable support system waterproof socket 防水插座 防爆插座Explosion-proof socket 接地绞线earthing twisted pair 接地母线 earthing bus
毕业设计外文翻译
毕业设计（论文） 外文文献翻译 题目：A new constructing auxiliary function method for global optimization 学院： 专业名称： 学号： 学生姓名： 指导教师： 2014年2月14日
一个新的辅助函数的构造方法的全局优化 Jiang-She Zhang，Yong-Jun Wang https://www.sodocs.net/doc/b88426955.html,/10.1016/j.mcm.2007.08.007 非线性函数优化问题中具有许多局部极小，在他们的搜索空间中的应用，如工程设计，分子生物学是广泛的，和神经网络训练．虽然现有的传统的方法，如最速下降方法，牛顿法，拟牛顿方法，信赖域方法，共轭梯度法，收敛迅速，可以找到解决方案，为高精度的连续可微函数，这在很大程度上依赖于初始点和最终的全局解的质量很难保证．在全局优化中存在的困难阻碍了许多学科的进一步发展．因此，全局优化通常成为一个具有挑战性的计算任务的研究． 一般来说，设计一个全局优化算法是由两个原因造成的困难：一是如何确定所得到的最小是全球性的（当时全球最小的是事先不知道），和其他的是，如何从中获得一个更好的最小跳．对第一个问题，一个停止规则称为贝叶斯终止条件已被报道．许多最近提出的算法的目标是在处理第二个问题．一般来说，这些方法可以被类?主要分两大类，即：（一）确定的方法，及（ii）的随机方法．随机的方法是基于生物或统计物理学，它跳到当地的最低使用基于概率的方法．这些方法包括遗传算法（GA），模拟退火法（SA）和粒子群优化算法（PSO）．虽然这些方法有其用途，它们往往收敛速度慢和寻找更高精度的解决方案是耗费时间．他们更容易实现和解决组合优化问题．然而，确定性方法如填充函数法，盾构法，等，收敛迅速，具有较高的精度，通常可以找到一个解决方案．这些方法往往依赖于修改目标函数的函数“少”或“低”局部极小，比原来的目标函数，并设计算法来减少该?ED功能逃离局部极小更好的发现． 引用确定性算法中，扩散方程法，有效能量的方法，和积分变换方法近似的原始目标函数的粗结构由一组平滑函数的极小的“少”．这些方法通过修改目标函数的原始目标函数的积分．这样的集成是实现太贵，和辅助功能的最终解决必须追溯到
机械工程专业英语 翻译
2、应力和应变 在任何工程结构中独立的部件或构件将承受来自于部件的使用状况或工作的外部环境的外力作用。如果组件就处于平衡状态,由此而来的各种外力将会为零,但尽管如此,它们共同作用部件的载荷易于使部件变形同时在材料里面产生相应的内力。 有很多不同负载可以应用于构件的方式。负荷根据相应时间的不同可分为: (a)静态负荷是一种在相对较短的时间内逐步达到平衡的应用载荷。 (b)持续负载是一种在很长一段时间为一个常数的载荷, 例如结构的重量。这种类型的载荷以相同的方式作为一个静态负荷; 然而,对一些材料与温度和压力的条件下,短时间的载荷和长时间的载荷抵抗失效的能力可能是不同的。 (c)冲击载荷是一种快速载荷(一种能量载荷)。振动通常导致一个冲击载荷, 一般平衡是不能建立的直到通过自然的阻尼力的作用使振动停止的时候。 (d)重复载荷是一种被应用和去除千万次的载荷。 (e)疲劳载荷或交变载荷是一种大小和设计随时间不断变化的载荷。 上面已经提到，作用于物体的外力与在材料里面产生的相应内力平衡。因此,如果一个杆受到一个均匀的拉伸和压缩，也就是说, 一个力,均匀分布于一截面,那么产生的内力也均匀分布并且可以说杆是受到一个均匀的正常应力,应力被定义为 应力==负载 P /压力 A, 因此根据载荷的性质应力是可以压缩或拉伸的,并被度量为牛顿每平方米或它的倍数。 如果一个杆受到轴向载荷，即是应力，那么杆的长度会改变。如果杆的初始长度L和改变量△L已知，产生的应力定义如下: 应力==改变长△L /初始长 L 因此应力是一个测量材料变形和无量纲的物理量 ,即它没有单位;它只是两个相同单位的物理量的比值。 一般来说,在实践中,在荷载作用下材料的延伸是非常小的, 测量的应力以*10-6的形式是方便的, 即微应变, 使用的符号也相应成为ue。 从某种意义上说，拉伸应力与应变被认为是正的。压缩应力与应变被认为是负的。因此负应力使长度减小。 当负载移除时，如果材料回复到初始的，无负载时的尺寸时，我们就说它是具有弹性的。一特定形式的适用于大范围的工程材料至少工程材料受载荷的大部分的弹性, 产生正比于负载的变形。由于载荷正比于载荷所产生的压力并且变形正比于应变, 这也说明,当材料是弹性的时候, 应力与应变成正比。因此胡克定律陈述, 应力正比于应变。 这定律服从于大部分铁合金在特定的范围内, 甚至以其合理的准确性可以假定适用于其他工程材料比如混凝土，木材，非铁合金。 当一个材料是弹性的时候，当载荷消除之后，任何负载所产生的变形可以完全恢复,没有永久的变形。