【作者】 王宝珍；

【导师】 胡时胜；

【作者基本信息】 中国科学技术大学 ， 工程力学， 2010， 博士

【摘要】 人体组织和防弹衣之类人体防护系统中的软材料在使用中不可避免会承受冲击载荷。为了设计用于抵御来自不同方向飞来的重物利器损害的人体防护系统,必须对其防护能力予以准确的模拟评估,并能进行优化设计。这种模拟评估和优化设计要求了解所有相关材料的动态力学性能。这些材料既包括人体组织生物材料,又包括制备人体防护系统的软材料。然而,与金属、陶瓷等工程装甲材料相比,人们对这些软材料、尤其是人体组织生物材料的动态力学性能了解甚少,这主要是因为软组织材料在冲击加载条件下的动态性能测试难度较大。鉴于以上情况,本研究以实验研究为主,提出了一套能准确、可靠测定这些生物材料动态力学性能的霍普金森压杆(SHPB)和拉杆(SHTB)实验技术,成功的获得了肌肉材料沿纤维方向和垂直纤维方向的动态压缩和拉伸应力应变曲线,并且发展了能够描述肌肉材料在很宽应变率范围内力学性能的横向同性超粘弹性本构模型。本文首先针对霍普金森压杆(SHPB)和拉杆(SHTB)进行软材料实验室存在的透射信号小,应力均匀难以达到等问题进行了系统的讨论。针对透射信号小的问题,可采用选用广义波阻抗低的杆件和高灵敏度传感器的方法。低波阻抗的粘弹性杆在提高透射信号上具有很大的优势,但是应力波在粘弹性杆中传播会发生弥散和衰减,通过DFT算法编写了计算粘弹性杆波传播系数的程序,并由实验和程序计算得到了尼龙杆的衰减系数和相速度,通过验证发现该程序在修正弥散和衰减效应问题上结果可信。半导体应变片和石英压电传感器在检测微弱信号方面发挥着重大作用,尤其是石英压电传感器,不但检测微弱信号的能力很强,还可用于检测试样的应力均匀性,在SHPB实验中占据重要地位。传感器在使用中会存在一些问题,如各类传感器的灵敏度系数标定、半导体应变片的非线性及石英片检测应力均匀时惯性力信号的干扰,本文对这些问题都进行了讨论,并提出了解决办法。试样的应力均匀条件是决定试样结果是否可靠的一个必要条件,本文从量纲分析出发,利用LS-DYNA软件进行数值模拟,考察了五个无量纲β,θ/τs,Eα/Es,tr/τs,νr/Cs对粘弹性试样应力和应变均匀性的影响。发现2τs升时的梯形波加载最利于低波阻抗比的粘弹性试样的应力和应变均匀。对于某一确定的材料,2τs升时的梯形波加载下,β越小,θ/τs越大,Eα/Es越大,应力均匀所需的时间越短,而νr/Cs则存在一个极限值,并且发现在小于或等于2τs升时的梯形波加载,应变较应力更易均匀。通过传感器检测应力的均匀性也可判断应变的均匀性是否满足。肌肉软组织具有一定的生命意义,离体实验只要尽量模拟正常的生理状态才能反映活体组织的性能,文中采用新鲜的生猪猪肉为研究对象,通过合理的保存和加工,摒除了离体组织死后时间对实验结果的影响。并利用岛津试验机和生物材料实验机对其进行了准静态压缩和拉伸测试。发现在kreb溶液保存下,死后17小时肌肉力学性能基本无变化。结合已有文献的结果与本实验结果进行比较发现,实验数据尽管存在一些差异,但是还是有一定的可比性。实验结果表明,压缩时垂直纤维方向的强度比纤维方向要大,而拉伸时则相反,通过纤维向和垂直纤维向压缩和拉伸的变形特性,对此进行了分析。并且对拉伸时断裂性能也进行了分析。采用改进的SHPB和SHTB实验装置对猪后腿肌肉进行了一系列实验,得到了高应变率下猪后腿肌肉沿纤维方向和垂直纤维方向的压缩和拉伸应力应变曲线。结果表明,在很宽的应变率范围,肌肉具有明显的应变率效应,高应变率下的流动应力远远高于准静态下的流动应力。而且加载方向也对力学性能有影响,垂直纤维方向压缩时强度要高于纤维向压缩。拉伸时,低应变率下,纤维向的拉伸强度要高于垂直于纤维方向,高应变率出现了异常：应变较小时,垂直于纤维方向的应力反而比纤维方向要大,但是当变形逐渐增加后,两方向的强度则无显著不同,纤维方向流动应力有逐渐高于垂直纤维方向的趋势。本文首次发展了一个可用于描述肌肉类软组织准静态及高应变率下力学性能的横向同性超粘弹性本构模型,并通过对实验数据进行拟合得出了模型中的材料参数,拟合的结果与实验结果重复较好,可为以后进行人体数值模拟提供了肌肉组织的材料参数。更多还原

【Abstract】 Soft materials of human tissues and bullet-proof vests will inevitably be subject to impact loading. In order to design to a body-protection system that can withstand impacts from various directions, the protective ability of the system must be simulated and evaluated accurately, then be optimized. In such simulation-based evaluation and optimization, dynamic mechanical properties of used materials are required. These materials include both biological materials of human tissues and soft materials of body-protection systems. However, compared to metals and ceramics used in a body-protection system, dynamic mechanical properties of soft materials, especially biological materials of human tissues are poorly understood, mainly because of the difficulty in testing their dynamic behavior under impact loadings.With regard to the difficulty, this study mainly based on experimental research and has proposed a set of accurate, reliable Split Hopkinson Pressure Bar (SHPB) and Split HopkinsonTensile Bar (SHTB) experimental techniques to test dynamic mechanical properties of biological materials. Using these techniques, we have obtained dynamic compression and tensile stress-strain curves of muscles, along their fiber direction and perpendicular to the fiber. Further, a transverse isotropic hyperviscoelastic constitutive model has been built to describe the behavior of muscles at a wide range of strain rate.In this paper, analysis has been performed systematically on weak transmission signal and stress uniformity in SHPB and SHTB experiments on soft materials. With respect to weak transmission signal, we selected bars of small wave impedance and very sensitive sensors. Viscoelastic bars of small wave impedance show advantage in improving the transmission signal, but the dispersion and attenuation of a stress wave occur in viscoelastic bars. A code to compute propagation coefficient in viscoelastic bars has then been compiled based on DFT algorithm. The code has been validated by comparing calculation results with propagation coefficient and phase velocity obtained experimentally. Semiconductor gauges and quartz piezoelectric sensors have bee applied to detect weak signals, particularly the latter not only be used to detect weak signal but also to detect the stress uniformity of the specimen in SHPB experiments. Solutions to the problems in using these sensors, such as the calibration of various sensors, non-linearity of semiconductor gauge and signal interference in due to inertia signal in detecting the stress uniformity, have been proposed in this thesis.Stress uniformity of a sample is a necessary to the validity of SHPB and SHTB. In this study, we analyze the influence of five dimensionless parameters (β,θ/τs, Eα/Es, tr/τs, vr/Cs) on stress or strain uniformity of viscoelastic materials, based on dimensional analysis and numerical simulation using LS-DYNA. We find that the loading with trapezoidal wave of rise time of 2τs easily leads to stress or strain uniformity of a viscoelastic specimen of small wave impedance. To a certain material loaded with trapezoidal wave of rise time of 2τs, the smallerβ, the largerθ/τs and Ea/Es, the shorter duration to achieve stress uniformity. And there is a limit of vr/Cs, when loading with trapezoidal wave of rise time no longer than 2τs, it is much easier to achieve stress uniformity. Both stress or strain uniformity is detected by using sensors.To analyze the properties of muscle tissues of living creatures, fresh porcine muscle being properly preserved and processed has been taken as the research object of this study, and the effect of the duration after the death on experiments has been neglected. Quasi-static compression and tensile experiments have been conducted by using Shimadzu testing machine and biological testing machine. It has been found that the mechanical properties of the porcine muscle preserved in kreb liquid are almost unchanged after the death of 17-hour. Combining existing researches and experiments of this study, we consider that the experimental data is comparable although some difference. Our experiments show that compression strength vertical to fibers is much larger than that along them wherever opposite result will be obtained in tensile. The deformation of specimens has been analyzed based compression/tensile along fibers or vertical to them. Fracture of specimens under tensile has also been discussed.Using improved SHPB and SHTB devices, we have conducted a series of experiments on the muscles of porcine hams. The compression and tensile stress-strain curves of the muscles along their fiber and perpendicular to the fiber at high strain rates have been obtained. The experiments shows that the muscle has a significant strain rate effect at a very wide range of strain rates, flow stress at a high strain rate is much larger than that under a quasi-static loading. Loading direction also affects their mechanical behaviors. Compression strength vertical to fibers is much larger than that along them. Tensile strength along fibers at a low strain rate is larger than that vertical to fibers. But at high strain rates tensile strength vertical to fibers is larger than that along fibers at a small strain. When strain increases, the strength of these two directions are not obviously different. Flow stress along fibers seems to become larger than that vertical to fibers.This thesis firstly developed a transverse isotropic hyperviscoelastic constitutive model to describe the behavior of soft tissues like muscles under quasi-static loadings or high strain-rate loadings. Through experiments and experimental data processing, the parameters of the constitutive have been obtained and well cover the experimental results. Consequently, this study can provide material data to numerical simulation of the behavior of the tissue of human muscles.更多还原