闭孔泡沫铝动态材料参数的实验测试和分析

发布时间：2018-04-06 23:05

本文选题：泡沫铝　切入点：泰勒冲击　出处：《中国科学技术大学》2017年硕士论文

【摘要】：泡沫金属材料由于其特殊的细观结构,使其具有优越的力学性能,诸如高比强度和高比刚度,以及良好的吸能特性,因此被广泛地应用于汽车、航空航天以及军事防护等领域,尤其是在缓冲吸能的结构设计方面,表现相当突出。而泡沫金属材料的功能可设计性也为其能够被广泛应用提供了保障,例如可改变其相对密度,孔径的类型和大小以达到实际应用的要求。泡沫金属的动态力学性能与其细观结构参数的关系尚不明确,实验研究相对较少。对泡沫金属实验研究的主要困难是泡沫金属在高速加载下的非均匀变形特征并不能满足传统Hopkinson压杆技术的均匀性假定,故而在实验中测得的动态压缩性能可能不准确。此外,对细观结构参数的影响的研究也同样存在着实验技术的困难,需要发展合适的实验方法以得到较为准确的动态力学性能与细观结构参数的关系。首先研究了泡沫铝材料在准静态压缩下的应力-应变行为和材料参数的确定方法。采用刚性-塑性硬化(R-PH)材料模型拟合泡沫铝的工程应力-应变关系,讨论了四种拟合方式,并且最终确定从材料参数本身的物理意义出发,采用独立确定材料参数的方法,可以很好地表征泡沫铝在准静态下的应力-应变关系。本文利用直接冲击的方式,基于泡沫铝的动态力学性能,并考察关于泡沫铝动态理论模型的研究,介绍了一种动态、刚性-塑性硬化(D-R-PH)模型,通过跨波阵面的守恒关系以及刚性体的牛顿运动定律,可以得到一种时间关于速度的函数表达关系,如下式所示:式中,L为泡沫铝试件原始长度,v0为初始冲击速度,v为撞击过程中的瞬时速度,t为时间,b和c为材料参数。可以通过实验测定冲击速度的历史曲线,通过(a)式拟合得到材料参数b和c,进而可以给出D-R-PH模型中的两个材料参数:初始压溃应力σ0d和应变硬化参数D。并通过对比拟合得到的应力时程曲线和由Hopkinson杆测得的应力时程曲线,验证了 D-R-PH模型在研究泡沫铝动态力学性能方面的有效性和正确性。通过对比准静态实验的应力应变曲线可观察到泡沫铝是一种加载率敏感的材料。通过实验研究泡沫铝的相对密度对D-R-PH模型参数的影响,得到一种显含有相对密度的泡沫铝的应力应变关系。分别对不同性质的泡沫铝材料进行动态实验,并且通过两种拟合方案对比,得出适用于确定脆性泡沫铝材料或者非脆性泡沫铝材料的理论模型参数的方案。并对相关的原因进行了分析。结果表明,两种实验的拟合方案均可以对动态材料参数进行确定,对于应力的测量出现较大震荡或者不够准确的情况下,应该采取速度时间拟合;若速度和应力均能准确测量,用应力速度拟合方法将会更加准确。
[Abstract]:Foamed metal materials are widely used in automotive, aerospace, military protection and other fields because of their special meso-structure, which makes them have superior mechanical properties, such as high specific strength and high specific stiffness, and good energy absorption characteristics.Especially in the structural design of buffer energy absorption, the performance is quite outstanding.The functional designability of metal foam materials also provides a guarantee that they can be widely used, such as changing the relative density, the type and size of pore size to meet the requirements of practical application.The relationship between the dynamic mechanical properties of foam metals and their meso-structure parameters is not clear, and the experimental studies are relatively few.The main difficulty in the experimental study of foam metal is that the inhomogeneous deformation characteristics of foam metal under high speed loading can not meet the assumption of uniformity of traditional Hopkinson compression bar technology, so the dynamic compression performance measured in the experiment may not be accurate.In addition, it is difficult to study the influence of microstructural parameters on the microstructural parameters, so it is necessary to develop an appropriate experimental method to obtain a more accurate relationship between the dynamic mechanical properties and the meso-structural parameters.Firstly, the stress-strain behavior of aluminum foams under quasi-static compression and the determination of material parameters are studied.The rigid-plastic hardening R-PHM model is used to fit the engineering stress-strain relationship of aluminum foam, and four fitting methods are discussed. Finally, the method of independent determination of material parameters is adopted to determine the physical meaning of the material parameters.The stress-strain relationship of aluminum foam under quasi-static condition can be well characterized.In this paper, based on the dynamic mechanical properties of aluminum foam, a dynamic, rigid and plastic hardening D-R-PHM model is introduced based on the study of the dynamic theoretical model of aluminum foam.By means of the conservation relation of the cross wave front and Newton's law of motion of rigid body, a function expression relation of time and velocity can be obtained.It is shown as follows: in formula L, the original length of the aluminum foam specimen is V _ 0, the initial impact velocity v _ v is the instantaneous velocity t during the impact process, and the time b and c are the material parameters.The historical curve of impact velocity can be measured by experiments, and the material parameters b and c can be obtained by fitting the formula, and two material parameters in D-R-PH model: initial crushing stress 蟽 0d and strain hardening parameter D can be obtained.The validity and correctness of the D-R-PH model in studying the dynamic mechanical properties of aluminum foams are verified by comparing the stress time history curves obtained from the fitting and the stress history curves measured by the Hopkinson rod.By comparing the stress-strain curves of quasi-static experiments, it is observed that aluminum foam is a material sensitive to loading rate.The influence of the relative density of aluminum foam on the parameters of D-R-PH model is studied experimentally, and a stress-strain relationship of aluminum foam with relative density is obtained.The dynamic experiments of aluminum foam materials with different properties were carried out, and through the comparison of two fitting schemes, a scheme suitable for determining the theoretical model parameters of brittle aluminum foam materials or non-brittle aluminum foam materials was obtained.The related reasons are analyzed.The results show that the parameters of dynamic materials can be determined by the fitting schemes of the two experiments, and the velocity time fitting should be taken in the case of large oscillation or inaccuracy in the measurement of stress, if both the velocity and stress can be accurately measured,The method of stress velocity fitting will be more accurate.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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