习题答案 2.doc

Chapter 2:Q uestions & Answers 1. Why do we have to know the performance posites ? The performance of an engineering material is judged by its properties and behavior , including tensile, compressive and flexural properties as well as other static and dynamic properties, and this information is essential for selecting the proper material ina given applicationas well as designing a structure with the selected material. 2. How is the load tranferred from matrix to fibers? The load applied on posite material of interest causes the deformation of matrix, which is of lower mechanical properties. The interfacial shear stress is then generated by the matrix deformation, which applies action to the fiber, leading to the corresponding response from the fiber. Hence, the load is transferred the matrix to the fiber. 3. Why is the yield strength more important than the tensile strength in most design situations? The yield strength is the stress level at which a material plastically deforms; when plastically deformed, the material is permanently stretched. T he tensile strength is the stress at which the sample pulls apart /breaks . The yield strength is the limit of elastic deformation. So it is more important than tensile strength. 4. What is creep ? Why is it an improtant factor for polymer posites? This property is used to rate the resistance ofa material to plastic deformation under su