【作者】 董钢；

【导师】 杨伯源； 巫绪涛；

【作者基本信息】 合肥工业大学 ， 固体力学， 2005， 硕士

【摘要】 分离式Hopkinson压杆(简称SHPB)实验装置是测量材料动态力学特性的基本实验装置。随着SHPB实验技术应用领域的拓宽,对SHPB实验设备和实验精度的要求日益提高,分析基于传统SHPB实验假定的试验精度,改进和优化SHPB实验技术就显得尤为迫切。数值模拟在这方面发挥着越来越重要的作用。 本文应用Ansys/Ls-dyna有限元平台建立了SHPB实验装置的三维有限元模型,着重从单元选取、沙漏控制、最小时间步、网格划分、接触设置以及初始加载等几方面讨论了有限元模拟的可靠性。建立有效的数值模型后,本文对SHPB实验技术中若干关键问题进行了数值模拟分析。主要包括如下内容: 1、分析了单元的划分对碰撞模拟的影响,提出针对SHPB实验装置几何模型的特点,网格划分时必须控制单元的径向尺寸和纵向尺寸的比例关系。 2、讨论了子弹、压杆和试样之间接触设置问题,指出接触刚度是影响模拟真实性的一个重要因素,尤其在试样与压杆的接触设置中,接触刚度对接触面应力应变的计算结果比较敏感。 3、使用直接在入射杆子弹撞击端加矩形速度波形可以模拟子弹的的撞击,并应用该方法研究了不同波形在SHPB实验中的效应。 4、杆径、材料泊松比,压杆变截面对波的弥散影响问题。得到500mm子弹撞击φ14.5mm、φ37mm、φ100mm的压杆波传播到不同位置处的弥散的上升沿时,分析上述因素对波传播弥散的影响。 5、考察了试样压杆阻抗比和不同波形对试样早期应力应变均匀性的影响,完成了从给定材料性能的数值模拟到利用模拟结果重构材料的性能的一个循环过程,为建立数值模拟在SHPB实验技术中应用的标准化过程打下基础。 6、研究了波形整形器的几何尺寸和材料参数对波的整形影响,波形整形器的直径和材料的杨氏模量对波的上升沿时有显著影响,而波形整形器的厚度和强化模量对波形曲率有明显影响。 7、试样加工的质量对试样的影响。试样的不平整度对试样二维效应影响明显;试样表面初始缺损会形成应力集中造成试样过早的损伤破坏。更多还原

【Abstract】 Split Hopkinson pressure bar(SHPB) is the basic technique that has been used to measure the dynamic mechanical property of materials.With the widen of SHPB experimental technique application area and with the improve of the request for experimental equipment and experimental accuracy ,to improve and optimize SHPB experimental technique is very important. Numerical simulation plays an important role in it.With the help of the software Ansys/Ls-dyna this article presents the three dimensional numerical simulation of SHPB, discussed the dependability of numerical simulation from the element selection, the Hourglass control, the minimum interval of time, the mesh divide, the contact control, and initial loading etc. Next, this article make a numerical analysis of several key problems about the split Hopkinson pressure bar experimental technique.1. Effects of the mesh divide on collision contact simulation. When mesh dividing , it is necessary to control element proportional relations between radial sizes and vertical sizes according to SHPB geometric model characteristics.2.The contact option between bullet and bar ,bar and specimen. Contact stiffness is an important factor in the simulation fidelity. Especially contact option between bar and specimen, Contact stiffness is very sensitive to the result of stress and strain in the contact interface3. To make it easier for us to study Effects of different wave form on the SHPB , the method, loding rectangle velocity wave form directly on one end of the press bar where come into collision with bullet, is practicable4. Effects of the the diameter, material Poisson ratio and variable cross-section of the press bar on the dispersion of wave .Come to the wave dispersion risetime , which the wave result of collision between different diameter- φ 14.5mm φ37mm φ100mm bullet, which length is 500mm ,and pressure bar, in different positions of the pressure bar.5.Effects of acoustical impedance proportion and different wave form on the specimen’s stress and strain uniformity. Pull off a cycle that is from numerical simulation under a given mechanical properties of materials to properties reconfiguration of materials with the help of the numerical simulation result. Set up a standardization process about the application of numerical simulation to the split Hopkinson pressure bar experimental technique6. Effects of the diameter geometric size of pulse shaper and property parameter of material on the wave shape . The diameter of pulse shaper and Young modulus have great influence to the risetime, on the other hand, the thickness and Tang model have obvious influence to the wave curvature7.The specimen processing quality(for example The uneven degree of specimen) have great influence to the two dimensional effect of specimen. Because of defect on the specimen surface, stress concentration cause prematurely damage to the specimen更多还原