机械工程英语第2课翻译.doc

LESSON 2 Properties of MaterialsThe properties of a material are those characteristics that help modify and distinguish one material from another. 材料的特性是变改和区分一种材料和另一种材料的特征。 All properties are observable and most can be measured quantitatively. 所有的特性都是可观察的，而且大多数是可以量化的。 Properties are classified into two main groups, physical and chemical properties. Physical properties involve no change in the composition of the material. 材料特性可分为物理特性和化学特性两大类。物理特性指的是材料成分不发生改变的特性。 Chemical properties are associated with the transformation of one material into another. 化学特性指的是能够结合一种材料变成另外一种的特性。 Physical properties are, in turn, arbitrarily subdivided into many categories. 物理特性，反而可以被任意地分为许多种类。 These subdivisions bear names such as mechanical,metallurgical,fabrication,general,magnetic,electrical,thermal,optical,thermonuclear,and electro-optical. 这些子分类的名称包括机械特性，冶金特性，装配特性，通用特性，磁性特性，电子特性。 Regardless of the name of subdivision, physical properties result from the response of the materials to some environmental variable, such as a mechanical force, a temperature change, or an electro-magnetic field. 忽略这些细分的名字，这些物理特性是由于材料在环境变化下形成的反应而产生，比如机械力，温度的改变或者电磁场。 In the following, the mechanical property of materials will be discussed.在接下来中，我们将要讨论材料的机械特性。Mechanical Property of MaterialsIn selecting a material for a product such as a piston in an internal combustion engine, a designer is interested in properties such as strength, ductility, hardness, or fatigue strength. 在为一个产品选择材料上，比如内燃机上的一个活塞，一个设计者感兴趣的特性是材料的长度，延展性，硬度或者疲劳强度等。 Mechanical properties are defined as a measure of a material’s ability to carry or resist mechanical forces or stresses. 机械特性被定义为衡量材料抵抗机械载荷或者压力性能的指标。 When any matter is at rest, the atomic or molecular structure is in equilibrium. 当任何材料在静止状态时，原子或分子结构保持着平衡。 The bonding forces in this structure resist any attempt to disrupt this equilibrium. 它们之间的结合力阻止任何破坏这种平衡的意图。 One such attempt may be an external force or load. 一个这样的意图也许是一个外力或外载荷。 Stress results from forces such as te