Surface-crack fracture toughness test of 31Si2MnCrMoVE steel on thin plate

Abstract

31Si2MnCrMoVE steel is ultra-high strength steel which is specially developed for manufacturing solid rocket motor shell.The fracture toughness increases continuously, correspondingly,the steel plate thickness can be reduced due to development of the smelting technology.However,the increas- ing of fracture toughness and reduction of plate thickness result in the difficulty of measuring its surface crack fracture tough- ness because too small ligament sizes of specimens could not satisfy the validity criterion.So the linear elastic fracture me- chanics can not be used to evaluate the fracture toughness of thin ultra-high strength steel,but the ductile fracture tough- ness(J_(IC))of thin ultra-high strength steel can be evaluated using the elasto-plastio fracture mechanics.The fracture mechanics test and finite element method had been conducted to calculate the J-integral in the vicinity of the crack tip under the condi- tional load in the condition when the conditional fracture toughness(K_(IQ))Can not satisfy the validity criterion.The com- puted J-integral can be used as the ductile fracture toughness J_(IC) of the material.Surface-crack fracture toughness K_(Ie)is com- puted on the fracture mechanics method from J_(IC).However,if J_(IC)is used as the fracture parameter,the validity of J-integral must be analyzed.So,the conservation of loop J-integration and the J-dominant characteristic of ultra-high strength steel surface crack are studied.These are important technical pa- rameters for design of aerospace solid rocket motor.