Abstract: Based on the logarithmic strain’s principle of superposition and volume compressible material’s plastic function, the analytic formulas for large forging porosity and cavity ratio, stress and deformation are established . Then the porosity collapse factor is given. Through the discussion of the relationship between porous material’s cavity ratio and stress, deformation, it can be concluded that stress state and strain state play an irreplaceable role in porosity collapse process. The existence of hydrostatic stress is the prerequisite of porosity collapse process. At the beginning of the collapse process, hydrostatic stress plays an important role, and at the end of the collapse process, deformation takes the function of reducing stress value. An experiment is also carried out using lead porous material. The result shows the porosity collapse factor given can be well used in real production for reference.

Key words: Large forging, Material processing, Plastic deformation, Plastic mechanics