本文对最大正应力理论、能量释放率理论、应变能密度理论和等W线上的最大正应力理论等作了评论。本文提出了最大拉应变理论和最大拉应变能密度理论。认为最大拉应变和最大拉应变能密度才是材料脆性断裂的决定因素,最大剪切应变能密度是材料剪切断裂的决定因素。 This article reviews the maximum normal stress theory, the energy release rate theory, the strain energy density theory, and the maximum normal stress theory on the W line. This paper presents the theory of maximum tensile strain and the theory of maximum tensile strain energy density. It is believed that the maximum tensile strain and the maximum tensile strain energy density are the decisive factors of the brittle fracture of the material, and the maximum shear strain energy density is the decisive factor of the material shear fracture.