武汉理工大学材料力学第05章(弯曲应力复习)-06.ppt

zIyM???xyz一、弯曲正应力公式二、最大正应力zWM?max??maxM62bhWz?bhzy矩形三、抗弯截面系数323dWz??实心圆zdy)1(3243????DWz空心圆Ddzyb2h2hzy一、矩形截面梁四、弯曲切应力?yFSbISFzz*S??max??max?二、工字形截面梁B2H2H2h2hbyzmax?min?bISFzz*S???y][maxmax??zWM?五、梁的正应力强度条件?max六、切应力强度条件bISFzz*maxmaxSmax??][???maxSF?≤≤T 字形截面的铸铁梁,受力如图,铸铁的[?t]=30MPa,[?c]=60 MPa,其截面形心位于C点,y1=52mm,y2=88mm,Iz=763cm4,试校核此梁的强度。F1=9kN1m1m1mF2=4kNABCD[例1]·m4kN·mMx-+解:F1=9kN1m1m1mF2=4kNABCDy1y2C负弯矩,上边缘受拉,下边缘受压zBIyM1t??zBIyM2c??<[?t]<[?c]+-?t?·m4kN·mMx-+??????????(1)B截面的强度(2)C截面的强度F1=9kN1m1m1mF2=4kNABCDy1y2C正弯矩,下边缘受拉,上边缘受压zCIyM2t??<[?t]+-+-∴梁安全?t?????-+?[例2]已知:C为形心位置,y1=,y2=,惯性矩Iz=2×109mm4,q=407kN/m,[?]=190MPa,[?]=130 MPa,校核梁的弯曲正应力和弯曲切应力强度。qAB3700200200300×20650×16400×22y2y1Cz==+xmkN/?M847150150x/kNFS753+–753qAB3700200200FAFBx/kNFS753+–753解:zIyM1maxmax??????(1)弯曲正应力强度)MPa(162?][??300×20650×16400×22y2y1Cz==+xmkN/?M847150150