材料力学英文版ch09.1-3PPT课件.ppt

Chapter 9 Stength theories;一、Complication of failure of materials;1、 Maximum tensile stress theory（最大拉应力理论） （伽利略播下）;9.2 Strength theories for fracture;二、 Maximum tensile strain (The second strength)theory： Marerial fracture is due to maximum tensile strain. Once the maximum tensile strain reaches the ultimate tensile strain under one-direnctional tension, the fracture takes place.;一、 Maximum shearing stress(the third strength)theory：;二、 Maximum distortion energy (The fourth strength)theory;9.4 Combined deformation bending-torsion-axial load;二、 Strength calculation under combination of benging-torsion-axial load ;160Nm;The level bar is safety.;9.5 Application of strength theories;二、强度理论的选用原则：依破坏形式而定。;Solution：Stress state at critical point A;300;图a;用纵截面将容器截开，受力如图c所示;Ex. 9.3 The thin-walled circular cylinder is subjected to maximum internal pressure, ?x=1.88?10-4, ?y=7.37?10-4, Verify the strength by 3-th strength theory[E=210GPa，[?]=170MPa, ?=0.3].;例9.４ 薄壁圆筒受内压p和扭矩M作用。已知内径D,壁厚 ,长度l. 弹性模量E，[?],泊松比?，M= D3p/4。试 （1）用第三强度理论建立筒体的强度条件； （２）计算筒体的轴向变形； （３）计算筒体内径的改变量。;（３）计算筒体内径的改变量;例9.4 薄壁圆筒受最大内压时,测得?x=1.88?10-4, ?y=7.37?10-4,已知钢的E=210GPa，[?]=170MPa,泊松比?=0.3，试用第四强度理论校核其强度。;破坏判据：;解;9.8 Morh theory of strength;近似包络线;[? y];三、相当应力：（强度准则的统一形式）。