Unit_3_Structure-Property_Relationships_of_Materials.doc

Unit 3 Structure-Property Relationships of Materials 材料的结构-性质相关关系 Today’s materials can be classified as metals and alloys, as polymers or plastics, as ceramics, or as composites, most of which are manmade, actually are combinations of different materials.当今的材料可以分为金属和合金，聚合物或者塑料，陶瓷或复合材料，它们大多数是人造的，实际上是不同材料组合而成。 Applications of these materials depend on their properties; therefore, we need to know what properties are required by the application and to be able to relate those specifications to the material. 这些材料的应用取决于它们的性质；因此，根据应用的场合，我们需要知道什么样的性质是必需的，我们需要能够把这些详细说明同材料联系起来。 For example, a ladder must withstand a design load, the weight of a person using the ladder. However, the material property that can be measured is strength, which is affected by the load and design dimension. Strength values must therefore be applied to determined the ladder dimensions to ensure safe use. Therefore, in general, the structures of metallic materials have effects on their properties.比如，一个梯子必须能经受住设计的载荷，也就是使用这个梯子的人的重量。然而，能够测量的材料的性质是强度，它为载荷和设计尺寸所影响。强度值因此被用来判定梯子的尺寸大小以保证安全使用。因此，通常说来，金属材料的结构对它们的性质有影响。 Stress and strain 应力与应变 In a “tensile test” a sample is gradually elongated to failure and the tensile force required to elongate the sample is measured using a load cell throughout the test. The result is a plot of tensile force versus elongation.在一个张力测试实验中，样品缓慢地拉长直到失败，并且拉长样品所必需的拉力在整个测试过程中，用测压元件测量。结果是拉力同伸长度之间的一个图。 The problem is that the load required to elongate the sample by a certain extent depends upon the dimension of the sample. This would be a big problem if, for example, mechanical property data were to be used to design a bridge, since it is clearly impossible to test an entire bridge. Thus what is clearly needed is to make the data from the tensile test independent of the size of the sample. To achieve this end, we use “stress” and “strain”.问题是，拉伸样品到一定程度所必需的载荷取决于样品的尺寸。比如，如果机械性质的数据被用于设计一座桥梁，既然测试整个桥梁是明显不可能的，这样，明显需要的就是从与样品尺寸无关的拉伸实验中获得数据。为了达到这个目标，我们使用“应力”和“应变”。 The “true” stress ( )