弯曲弹性模量计算公式的推导

1.惯矩的定义:(图1)J_y=integral from n=F(x~2dF)简单图形的惯矩,如矩形:(图2)dF=bdzJ_y=integral from n=F(z~2dF)=integral from n=F(z~2bdz)=bintegral from n=F(z~2dz)=bintegral from n=-(h/2) to +(h/2)z~2dz=b|z~3/3|_(-(h/2))~(+(h/2))=b[(h/2)~3/3-(-h/2)~3/3]=bh~3/12