【作者】 朱聪聪；

【导师】 张荻； 覃继宁；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 硕士

【摘要】 小冲杆试验法是近几年发展起来的一种新型的测试方法,它利用尺寸极其微小的试样对服役材料进行失效分析和寿命评估,在测试材料基本性能(屈服极限,强度极限等)、韧脆性转变温度、断裂韧性和蠕变性能等方面得到了较广泛的认可、应用和发展。目前,小冲杆试验的一个研究热点在于找到小冲杆试验结果与传统常规试验结果之间的联系,以达到在某些领域,利用小冲杆试验最终代替传统试验的目的。在小冲杆试验研究过程中,研究者普遍采用试验与模拟相结合的方式对小冲杆试验进行全面的研究。有限单元法在模拟小冲杆试验过程中起到了非常重要的作用。为了模拟小冲杆试验中材料所表现出的力学性能、研究不同试验条件对试验结果的影响并找到小冲杆试验结果与材料断裂性能之间的关系,本文建立了一个有限元模型,用来研究小冲杆试验过程,并以Ti-6Al-4V合金和原位生成体积分数为10%的TiB与TiC颗粒混合增强Ti-6Al-4V复合材料为例,做了以下的研究:1.根据实际小冲杆试验,搭建了一个有限元模型。该模型能够成功地模拟小冲杆试验过程,并输出与实际情况相符的结果曲线,从而验证了此有限元模型的正确性和有效性。2.利用上述模型,研究了试样厚度和冲头与试样之间的摩擦系数这两个试验条件对试验结果的影响。对不同厚度试样的模拟结果表明,模拟所得到的载荷-位移曲线的走向基本一致,但是试样所承受的最大载荷对于厚度十分敏感。因此在实际试样制备过程中要特别注意试样厚度的精度。同时说明不同厚度试样的试验结果之间没有可比性。对于摩擦系数的研究表明载荷-位移曲线对于摩擦系数的变化不敏感。3.通过有限元模型中的参数,计算了Ti-6Al-4V合金、原位生成体积分数为5%及10%的TiB与TiC颗粒混合增强Ti-6Al-4V复合材料三种钛材料的断裂韧性JΙC和小冲杆试验总能量E sp,建立了等效断裂应变、断裂韧性和总能量之间的关联公式。结果表明:对于钛材料来说,断裂韧性JΙC、小冲杆试验总能量E sp与小冲杆试验中所测得的等效断裂应变εqf之间存在着线性关系,从而找到了小冲杆试验与传统常规试验之间的联系。更多还原

【Abstract】 Small punch test (SPT) is a new type of assessment method which was invented in recent years. It uses extremely small samples to perform failure analysis and life assessment for materials in service, and SPT has been widely acknowledged, used and developed in assessing materials’basic performance(yield limit, strength limit etc), ductile-brittle transition temperature, fracture toughness and creep properties. Currently, the research focus of small punch test lies on finding the relationship between SPT and conventional test methods, in order to replace them with SPT in some industry fields. Researchers commonly use the combination of test and simulation as a method for conducting a comprehensive study. Finite element method plays a very important role in simulating SPT.In order to simulate the mechanical properties of materials shown in small punch test, to analyze the effect of samples’thickness and friction coefficient on the results of SPT and to find the relationship between the results of SPT and fracture properties, an effective finite element mode was developed. Ti-6Al-4V alloy and particulate reinforced 10 vol.% (TiB+TiC)/Ti-6Al-4V metal matrix composites(MMCs)were studied by small punch test method.1. A finite element mode was developed according to the actual small punch test. This mode can successfully simulate the process of SPT and output curves which agree with experiment results,which demonstrate that the model is correct and can be used in the further study.2. With the model generated by the program, the effect of samples’thickness and friction coefficient on the results of SPT was analyzed. Simulation results show that the load-displacement curves of different samples’thickness go along the same direction; however the maximum load is quite sensitive to the changes of thickness. Therefore, the accuracy of samples’thickness should be paid attention during the process of sample preparation. It also tells us that it is not comparable between the test results of samples with different thickness. Study on the friction coefficient show that the load-displacement is not sensitive to the change of friction coefficient between sample and punch.3. Fracture toughness JΙCand small punch energy E spwere calculated with the parameters used in the finite model for Ti-6Al-4V alloy and particulate reinforced 5% and 10 vol.% (TiB+TiC)/Ti-6Al-4V metal matrix composites. Correlation formulas was built up between JΙC, E spand equivalent fracture strain. It shows that for titanium there exists a linear relationship between the three parameters.更多还原