【作者】 陶俊林；

【导师】 陈裕泽；

【作者基本信息】 中国工程物理研究院 ， 工程力学， 2005， 博士

【摘要】 SHPB实验系统是广泛应用的测试材料动念力学性能的装置,在文献调研的基础上指出,为了提高SHPB实验结果的精度和可比性,应对SHPB实验技术做进一步的研究。围绕上述目的,以金属材料为研究对象,本文对SHPB实验技术做了以下几个方面的研究:试件惯性效应与界面摩擦效应的综合分析;波导杆与试件阻抗匹配关系的研究;SHPB系统端面平行度加工要求分析;试件与波导杆应力应变均匀性分析;恒应变率实验技术研究以及其他实验方法探索。 ① 试件惯性效应与界面摩擦效应的综合分析。通过综合分析在SHPB系统圆柱形试件的惯性效应、试件与波导杆端面摩擦效应对实验结果的影响,给出一个新的理论分析模型,用以修正Gorham(1989)所得的惯性效应分析公式。在此基础上,归纳出为提高SHPB实验结果精度,SHPB实验应遵循的几个要求。并对SHPB试件设计中(特别是大应变情况)试件尺寸比例的设计作了进一步的分析,获得了试件设计时应满足的尺寸比要求。 ② 波导杆与试件阻抗匹配关系研究。通过将试件看作为一个刚度系数变化的弹簧,建立了一个理论模型,并进行了相应的分析工作。为SHPB系统波导杆和试件的材料和尺寸应当如何选择才满足阻抗匹配适度的要求提供依掘。提出了可反映波导杆与试件阻抗匹配关系的无量纲参数α和β,并给出了波导杆与试件阻抗适度匹配所要求的α和β的取值范围。 ③ SHPB系统端面平行度加工要求分析。通过数值计算,分析了SHPB系统的端面平行度对测试结果的影响,进而获得了实际加工过程中对系统端面平行度的量化要求。另外,根据计算结果,还可对实验中的测试方法的选择,以及实验中异常波形的分析提供有益的指导。 ④ 试件与波导杆应力应变均匀性分析。通过三维数值模拟,在理想接触状态下,分别对SHPB系统中试件为弹性和弹塑性材料情况时,试件与波导杆的应力应变均匀性问题进行了分析,重点分析了试件为弹塑性材料时的情况。通过改变试件直径与波导杆直径之比、试件材料的弹性模量、屈服强度和硬化模量,研究了试件与波导杆横截面积及材料性能不一致对试件与波导杆的应力应变均匀性的影响,获得了满足试件应力和应变均匀性要求的试件直径与波导杆直径的比值,并简单分析了SHPB实验数据处理方法计算所得的结果与试件单元输出结果之间的关系。 ⑤ 恒应变率实验技术研究。提出了两套可实现试件恒应变率加载的实验方法,并通过实验和数值模拟手段进行了相应的验证和分析工作,揭示了应变率时间历程对材料应力应变曲线的影响,指出了只使用平均应变率来表征材料动念应力应变曲线的不足,更多还原

【Abstract】 SHPB is a widely used apparatus for testing dynamic materials properties. In this dissertation, based on review of literatures, it is suggested that some investigations into SHPB technique should be conducted in order to improve the precision and comparability of SHPB testing results. For this purpose, some studies on the SHPB technique for metals are carried out in this dissertation: the comprehensive analysis of inertial effect of cylinder specimen and interfacial friction effect between bars and specimen, studies on the impedance matching between bars and specimen, analysis of machining requirement for tolerance of parallelism of the bar ends, analysis of stress and strain uniformities in specimen and bars, investigations into constant rate experimental technique and other methods.① The comprehensive analysis of inertial effect of cylinder specimen and interfacial friction effect. By comprehensive analyzing the inertia effect and friction effect on the experimental results, a new theoretical model is presented to modify Gorham’s formula (1989) for analysis of inertia effect. On the base of these analysis results, some requirements for SHPB testing are summarized for improving SHPB experimental precision. The specimen size ratio is studied in detail, and the design requirement for specimen size ratio is clearly pointed out.② Studies on the impedance matching between bars and specimen. A theoretical model is established by taking the specimen as a spring with varying stiffness in SHPB experiments. The corresponding analysis gives a foundation for choice of material and size for bars and specimen according to the impedance matching principle. Two dimensionless parameters α and β are defined, which describe the impedance match between bars and specimen. The range of α and β is gained.③ Analysis of parallelism requirement for bar ends in SHPB system. The effects of the ends parallelism on experimental results are analyzed by numerical simulation, and the quantified requirement of parallelism of the ends is obtained. Otherwise, the simulation results are also helpful for choice of measurements and analysis of abnormal waves in experiments.④ Analysis of stress and strain uniformities in bars and specimen. The stress and strain uniformities in bars and specimen are analyzed by numerical simulation under condition that specimen is elastic or elastic-plastic. In the analysis the contact state between the bars and specimen is ideal, and the elastic-plastic behavior of specimen is emphasized in the analysis. In SHPB experiments, cross-sectional areas and the materials of the bars andspecimen are usually different, the effect of these differences on the stress and strain uniformities in bars and specimen is analyzed by changing the parameters of specimen such as.- diameter, elastic modulus, yield strength and hardening modulus. The diameter ratio between specimen and bars is obtained, which satisfies the stress and strain uniformities of bars and specimen. The relation between results obtained by method of experimental data processes and results output by numerical analysis is analyzed.(5) Investigation on constant strain rate experimental technique. Two methods to realize constant strain rate of specimen in SHPB are proposed. They are proved and compared by experiment and numerical simulation. The effect of strain rate-time history on the stress-strain curves is studied. The results indicate that the effect should be considered in the investigations of dynamic material properties and constitutive relations. When the strain rate of specimen keeps constant in SHPB experiment, the comparability of SHPB testing results obtained by different investigators can be improved.? Investigation on other experimental methods of SHPB. The SHPB with bars of small diameter (the diameter is small or equal 5mm) and Direct Impact Hopkinson Pressure Bar system (DIHPB) are investigated. The dynamic compression stress-strain curves of some materials with the strain rate up to 10V are obtained. Some questions should be further researched are pointed out. Otherwise, the dynamic unloading experimental method is explored by prolonging the unloading time of incident pulse by the help of the cylinder-cone striker instead of the cylinder striker of SHPB.更多还原