【作者】 史文超；

【导师】 李大永；

【作者基本信息】 上海交通大学 ， 车辆工程， 2009， 硕士

【摘要】 相变诱发塑性(TRIP,Transform Induced Plasticity)钢板是一种新型钢板,其室温下的显微组织主要由铁素体、贝氏体和残余奥氏体构成。这种残余奥氏体稳定性较差,在一定的塑性变形量下,会向较稳定的马氏体转变。生成的马氏体的硬化性能比相变前的奥氏体有较大的提高,提高了材料的均匀变形能力,从而改善了材料塑性。本文以宝钢生产的TRIP780高强钢板为研究对象,通过准静态及动态单向拉伸试验、微观金相实验和X射线衍射实验,研究了TRIP780高强钢板的动态变形力学性能,构建了其率相关材料本构模型,并应用于高强钢结构件冲击碰撞过程的数值模拟。通过准静态单向拉伸试验和拉伸条件分别为0.15 m/s,4 m/s,10 m/s,15 m/s四种速度下的动态拉伸试验,得到了不同拉伸速度条件下的材料应力-应变曲线。通过断口形貌和金相组织的观测,分析了TRIP780动态变形过程中相变的情况,并利用X射线衍射实验,对残余奥氏体相变对拉伸性能的影响进行了定量分析。根据对TRIP780的变形行为宏微观的研究,基于Johnson-Cook简化型本构模型,建立了描述其动态力学行为的率相关本构方程,并通过商用软件ABAQUS模拟单向拉伸过程验证了本构方程的正确性。基于所建立的本构方程对高强钢冲击碰撞过程进行了模拟,并和其他两种钢板进行了对比,考察高强钢在碰撞过程中的力学行为和吸能特性,评估材料的使用特性。研究结果表明:TRIP780高强钢是一种兼有高强度和高塑性的应变率强化特性的汽车用钢,具有良好的碰撞吸能潜力;所建立的率相关本构模型实现了对TRIP780钢力学行为的准确描述。更多还原

【Abstract】 TRIP steel is a new type steel, and is characterized by its Transform Induced Plasticity property. Usually, TRIP steel has a multi-phase micro structure under room temperature,which consists of ferrite(F), bainite(B) and retained austenite(Ar). The retained austenite is unstable, and will transform into martensite under certain plastic deformation conditions. The new-born martenite has a better hardening property comparing to the former austenite, which increases the deformation capability and contributes to plasticity property of the material.This thesis focused on mechanical properties of the TRIP780 steel produced by Baoshan Steel Company. Experiments were carried out based on both macroscopic and microscopic methods. The dynamic mechanical properties of TRIP780 steel were studied through the study on tensile tests, metallographic microstructure observation, and XRD measurement. A strain rate dependent material constitutive equation was developed and introduced into the numerical simulation of dynamic deformation during impact processes of high strength steel components. Firstly, the static uni-axial tensile experiment and the dynamic uni-axial tensile experiment under four different tensile speeds (0.15m/s,4m/s,10m/s and 15m/s) were carried out, then the stress-strain curves under various strain rates were obtained. Through the analysis on the microstructure near to the fracture surface, the Transform Induced Plasticity effect was investigated. Then, through the XRD experiment, the major factors which have impacts on the transformation of retained austenite were discussed. Johnson-Cook model was employed to describe the rate-dependent deformation behavior of the TRIP steel. Based on the macroscopic and microscopic research of dynamic deformation of TRIP780, a strain rate dependent material constitutive model was developed. The constitutive model was verified by simulation of the uni-axial tensile experiment. Finally, the crash process of a column and B-pillar made of high strength steel were carried out by introducing the developed constitutive model into ABAQUS. The mechanical behavior of TRIP steel during the crash processes was studied and compared with other two steels, especially the capability of crash energy absorbtion.The research results show that, TRIP steel exhibits both high strength and high plasticity deformation properties. The rate-dependent hardening property and energy absorbtion potential enable TRIP steel a good choice in vehicle manufacturing. The developed strain rate dependent constitutive model can predict the dynamic deformation of the TRIP steel well.更多还原