【作者】 黄超；

【导师】 曲嘉；

【作者基本信息】 哈尔滨工程大学 ， 工程力学， 2016， 硕士

【摘要】 316L不锈钢由于其耐腐蚀、具有良好的力学和工艺性能,正在被越来越多的应用到建筑领域和航空制造业等领域中。不锈钢材料虽然初期成本投入较高,但是其维护费用低、使用寿命长、可回收再利用,综合成本较普通钢结构而言可能更低。然而不锈钢材料导热系数低,韧性较大,容易导致在机械加工过程中表面硬化严重,刀尖处切削温度较高等问题,对材料加工的完整性和表面质量会有很大的影响。材料的本构关系作为能够反映材料力学性能的一个重要特性,在力学模型的建立中有着广泛的应用。本文采用机械加工后进行冷却硬化的试件,分别进行准静态、中应变率和高应变率实验以及断裂韧性实验,研究316L不锈钢的力学性能,并对实验方法进行了改善。通过有限元软件计算同一尺寸下三点弯曲试件分别在试验中和仿真中的断裂韧性,并通过数字散斑的方法观察试件起裂现象。本文主要工作内容如下:(1)、利用万能材料试验机对冷作硬化后316L不锈钢材料取样制备试件进行准静态拉伸和压缩实验,利用扭转试验机进行扭转实验,测得该材料在准静态下的力学性能参数。(2)、利用Zwick-Roell示波冲击试验机进行中应变率下的冲击拉伸实验,得到中应变率下的工程应力-应变曲线,并基于体积不变假设进一步得到真实应力应变关系曲线。同时,完成夏比试样摆锤实验,分析材料的塑性。(3)、利用分离式霍普金森压杆进行高应变率下的冲击压缩试验,利用三波法计算应力应变曲线,并计算了材料的Johnson-Cook本构模型参数。(4)、利用电液伺服试验机对三点弯曲试件进行疲劳预制裂纹后,先用万能材料试验机对其进行准静态三点弯曲实验,测得该材料准静态断裂韧性参数;然后应用霍普金森压杆装置进行三点弯曲冲击试验,通过实验数值法计算动态断裂韧性参数。同时,利用数字图像相关方法分析试样表面喷涂的散斑,检测试样表面裂纹尖端应变场变化。更多还原

【Abstract】 A creasing number of 316L stainless steels are applied in construction and aviation fields on account of its corrosion resistance and mechanical and processing properties. Besides its high costs in initial period, 316L stainless steels’ combined costs are lower than the ordinary steel structures because of its low maintenance costs,long service life and recycle materials. In the process of machinery, while the low thermal conductivity and the great toughness of stainless steels leads to serious surface hardening and high cutting temperature at the tip of knives problems, which have a great impact on the integrity and surface quality of materials processing. As a significant characteristic in reflecting material mechanics properties,the constitutive relation of materials has extensive applications in the construction of mechanical model.This paper analyzes the mechanical properties of 316L stainless steels in quasi-static,intermediate strain rate and high strain rate experiments and fracture toughness experiment using cooled and hardened specimens after machining, and improves the experimental methods. In the meanwhile, the calculation of fracture toughness of three point bending specimens with the same size by the finite element software in both experiments and simulations,and the observation of crack phenomenon of specimens by digital speckle correlation method are also mentioned in this paper.The main contents of this paper are as follows:(1). Quasi-static stretching and compression experiment on 316L stainless steel samples after machining referring to relevant experimental standards using universal material testing machine, and torsion experiment on specimen by torsion testing machine to measure its mechanical property parameters under the quasi-static state.(2). Impact tensile experiment and Charpy pendulum impact test on 316L metal specimen under intermediate strain rate using Zwick-Roell instrumented impact testing machine to obtain its engineering stress and strain curve under the strain rate, and further get the true stress-strain curve based on volume invariable assumptions. Meanwhile, Charpy pendulum test was completed to analyze the plasticity of materials.(3). Impact compression test on specimens at high strain rate using Split Hopkinson Pressure Bar and stress and strain curve calculated by three-wave method are used to calculate its Johnson-Cook constitutive model parameters.(4). After adopting fatigue precracking on three-point bending specimens by electrohydraulic servo tester, quasi-static three-point bending test was conducted by universal material testing machine to measure its quasi-static fracture property parameters, and the impact three-point bending test was implemented to measure its dynamic fracture toughness parameters through numerical method. Also, analyzing sprayed speckles and detecting the change of strain field at the crack tip on sample surfaces using digital image correlation method are all necessary.更多还原