31Si2MnCrMoVE钢薄板试样表面裂纹断裂韧度测试

31Si2MnCrMoVE钢是为符合固体火箭发动机壳体设计需要而专门研制的超高强度钢。随着冶炼技术的进步，31Si2MnCrMoVE钢断裂韧度不断提高，构件采用的板厚也越来越薄。由于较高的断裂韧度和较小的板厚，给钢板表面裂纹断裂韧度测试带来困难，韧带尺寸偏小，难以满足有效性判据。这种情况下，不应该用线弹性断裂力学方法评价材料的断裂韧度，而应采用弹塑性断裂力学测试材料的延性断裂韧度JIC。基于以上原因，在条件断裂韧度不满足有效性判据的情况下，采用试验与有限元分析相结合的方法，通过试验测出裂纹启裂时的条件载荷，用有限元法计算出在条件载荷作用下的延性断裂韧度JIC，再用断裂力学理论转换成表面裂纹断裂韧度KIe。用JIC作为断裂参量，就必须分析J积分的有效性，因此讨论超高强度钢表面裂纹前缘的J守恒和J主导的有效性，从而为固体火箭发动机设计提供依据。

SURFACE-CRACK FRACTURE TOUGHNESS TEST OF 31Si2MnCrMoVE STEEL ON THIN PLATE

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.