基于各向异性的超高强度管线钢延性剪切断裂机理及模型研究

The application of ultra-high strength pipeline steel is assumed to both remarkably increase the transport efficiency and reduce the cost of construction of long-distance natural gas pipeline. Since long-range propagation of ductile dynamic fracture is an important failure mode of high-pressure gas pipeline, which always leads to a catastrophic consequence, it is greatly significant for ensuring operation security of pipeline to reveal its ductile fracture mechanism and controlling factors. Till now, the influence of anisotropy of void growth in the process of damage on ductile fracture has not been reported yet, and the micro-mechanism of damage of the effect of localized shear strain on slant fracture is not explicit as well. In this project, ultra-high strength X100 pipeline steel with great potential for usage is chosen to investigate the microscopic evolution of void in the process of damage. Based on fracture mechanics and continuous damage mechanics, factors of coupling effect of the initial anisotropy of material and anisotropy of void growth and localized shear strain was sufficiently studied. Then, the mechanism of damage in ductile fracture is presented to construct an anisotropy-based ductile shear fracture prediction model by means of microstructure observation, macroscopic mechanical property testing and theoretical model derivation. Through the study in this project, the more scientific understanding of ductile fracture of pipeline steel will be presented to provide theoretical base and analyze methodology for correct prediction of ductile fracture propagation, and further to establish important theoretical foundation for the next generation large-throughput gas pipeline.

超高强度管线钢的应用可显著提升天然气长输管道的输送效率、降低建设成本。动态延性裂纹的长程扩展是高压输气管道的重要失效模式，往往带来灾难性后果，揭示延性断裂机理及控制因素是确保管道运行安全的关键。目前，损伤过程中的空洞长大各向异性对延性断裂的影响未见报道，局部剪切应变对倾斜裂纹作用的微观损伤机制尚未明确。本项目拟选具有巨大应用潜力的超高强度X100管线钢作为研究对象，以断裂力学和连续损伤力学为理论基础，以考察材料损伤过程中空洞的微观演化规律为主线，充分考虑材料初始各向异性和空洞长大各向异性耦合作用、局部剪切应变等影响因素，通过微观组织观察、宏观力学性能测试、理论模型研究等手段，揭示延性断裂的损伤机理，建立基于各向异性的延性剪切断裂预测模型。为管线钢延性断裂行为提供更加科学的认识，为正确预测管线钢延性裂纹扩展提供理论依据和分析方法，为下一代高压输气管道的建设和运行安全奠定重要的理论基础。

超高强度管线钢可显著提升天然气长输管道的输送效率、降低建设成本,是天然气管道发展的趋势。动态延性裂纹的长程扩展是管道的常见失效模式，揭示延性断裂机理及控制因素是确保管道运行安全的关键。本项目超高强度X100管线钢作为研究对象，基于损伤力学的完整Gurson模型，考虑了材料初始各向异性和空洞长大各向异性耦合作用、局部剪切应变等影响因素，通过微观组织分析、宏观力学试验、有限元分析等等手段，完成了X100管线钢各向异性对损伤的影响研究、延性裂纹扩展倾斜裂纹损伤机理研究、基于各向异性的管线钢延性剪切裂纹扩展模拟的研究工作，通过开展的X100管线钢各向异性试验（基于DIC的力学性能试验、微观组织分析试验等），将微观组织性能与管线钢宏观断裂行为建立了联系，获得了各向异性参数，在此基础上建立了各向异性耦合及局部剪切应变作用的延性裂纹扩展损伤模型（完整Gurson模型），对管道的断裂、启裂过程进行了有限元模拟，获得了X100管线的裂纹扩展阻力关系及启裂韧性。.通过该项目的完成，建立了基于各向异性行为X100管线钢的损伤模型，可用于描述X100管线钢不同阶段的力学损伤特性，可准确的表征断裂行为，为管线钢延性断裂行为提供更加科学的认识，为正确预测管线钢延性裂纹扩展提供了理论依据和分析方法，为下一代高压输气管道的建设和运行安全奠定了重要的理论基础。