From the derivation, why there are two independent elasticity coefficients for isotropic elastic material and five for transverse isotropic elastic material can be seen more clearly.

• 从推导过程可以更清楚地看出为什么横观各向同性材料和各向同性材料的应力应变关系中分别有5个和2个独立的弹性常数，材料有几个独立的弹性常数是由其应变能函数的形式所决定的。