期末作业讲评.ppt

第四章作业讲评第九次作业 4-1 :铝的弹性模量为 70GPa, 泊松比为 ,在 83MPa 的静水压时,此单位晶胞的体积是多少? 解:由 E=3K(1-2 ν)得 K=E/[3(1-2 ν)] =70Gpa/[3(1-2 * )]= △ V/V= σ/K=83Mpa/= ‰ V= 3× 10 -30× (1- ‰)= ? 10 -30 (m 3) 答:此单位晶胞的体积是 ? 10 -30 (m 3) P176 表3- 9 点阵常数单位? 4-14. 有哪些途径可以提高高分子材料的刚性? 结晶交联提高分子量热处理复合材料 Cite the primary differences between elastic , anelastic , and plastic deformation behaviors. 概念、原子论角度、施加应力后的应变、材料的差别(或对应的材料) 4-12 热处理(退火)的实质是什么?它对材料的拉伸强度、硬度、尺寸稳定性、冲击强度和断裂伸长率有什么影响? 结构弛豫,非晶至结晶转变 P112-113 拉伸强度、硬度、尺寸稳定性冲击强度和断裂伸长率第十次作业 4-13 有哪些方法可以改善材料的韧性,试举例说明。晶粒细化(晶格类型); 成分,高分子共混橡胶,金属种杂质; 热处理; 高分子中的银纹。 4-24 按照粘附摩擦的机理,说明为什么极性高聚物与金属材料表面间的摩擦系数较大, 而非极性高聚物则较小。摩擦系数: ?=S/P mS为剪切强度; P m为抗压强度,极性聚合物作用力大, S大。第十一次作业 4-29 试从金属、陶瓷和高聚物材料的结构差别解释它们在热容、热膨胀系数和热导率等性能方面的差别。原子键合方式不同; 结构不同,包括结晶。热导率金属≈>无机非金属>高分子导热的微观机制不同热容高分子>无机非金属>金属热运动基团单元大小不同热膨胀系数金属≈无机非金属<高分子化学键的键能不同自由电子晶格振动分子传导 1mol 材料升高 1℃所需的能量原子在热能增加时的平均振幅 (a) Briefly explain why Cv rises with increasing temperature at temperatures near 0 K. (b) Briefly explain why Cv es virtually independent of temperature at temperatures far removed from 0 K. (a) The Cv is zero at 0 K , but it rises rapidly with temperature; this corresponds to an increased ability of the lattice waves to enhance their average energy with ascending temperature. (b) Above what is called the Debye temperature D, Cv levels off and es essentially independent of temperature at a value of approximately 3R , R being the gas constant. Thus even though the total energy of the material is increasing with temperature, the quantity of energy required to produce a one-degree temperature change is constant.