A further discussion of virtual work principle for deformable body

In the existing structural mechanics textbook, the expression of virtual work principle in general can be divided into four categories: Virtual work principle is one type of sufficiency and necessity. It only proves necessity part. It only necessity. It has two applications - virtual displacement principle and virtual force principle. Virtual work principle only is the proposition of necessity, virtual work principle and virtual displacement principle and virtual force principle is the similarities and differences. In the recently published in the "11th Five " plan textbooks, virtual work principle still is part of sufficiency and necessity. Therefor we give the correct exposition and certification of this principle to indicate that is needs distinction for virtual work principle and virtual displacement principle, we also elaborate on the similarities and differences between them.