梯度多胞牺牲层的抗爆炸分析及设计

发布时间：2018-03-22 13:03

本文选题：梯度多胞金属　切入点：牺牲层　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：梯度多胞金属材料由于其可设计性受到广泛关注,引入密度梯度可望获得更加优异的抗爆炸、抗冲击性能,在工程防护领域有着广阔的应用前景。多胞牺牲层是一种多胞材料夹芯复合结构,通过多胞材料的压溃行为大量地吸收爆炸/冲击能量。已有多胞牺牲层抗冲击行为的研究中,多采用形式简单的刚性-理想塑性-锁定(R-PP-L)冲击波模型来表征多胞材料的动态压溃行为,其与实际的应力-应变曲线还存在较大的差异。此外,在梯度多胞材料的能量吸收和消波性能优越性的问题上尚有争议。本文运用一维非线性塑性冲击波模型和细观有限元模型研究密度梯度多胞牺牲层的抗爆炸性能。通过量纲分析方法得出影响临界厚度的主导因素。针对临界厚度偏于保守的设计,发展了考虑反射波二次加载的分析方法,有效减小芯层厚度以提高多胞金属材料的利用率。基于率无关的、刚性-塑性硬化(R-PH)模型,建立了描述冲击波在梯度多胞牺牲层中传播的控制方程,得到了密度线性分布的梯度多胞金属在指数型爆炸脉冲下的响应特性。多胞牺牲层的临界厚度为爆炸能量恰好被吸收时的芯层最小厚度,在工程上是一个重要的设计指标。分析了临界厚度与载荷强度、覆盖层质量、多胞材料的密度梯度等参数之间的关系,给出了以临界厚度和支撑端应力峰值为指标的密度梯度设计图。结果表明,吸收同等强度的爆炸载荷,正梯度牺牲层需要的厚度小于负梯度牺牲层。通过增大梯度参数值,正梯度能够有效地降低芯层厚度,但是会带来更大的支撑端应力峰值;实现应力峰值最小,均匀密度和负梯度是较理想的选择。本文还进一步给出了特定的支撑端应力峰值下,负梯度牺牲层临界厚度与相关参数的设计图。通过量纲分析的方法,建立梯度多胞牺牲层无量纲临界厚度与三个无量纲参数之间的关系,利用控制变量法给出了无量纲临界厚度的经验公式,并且满足一定的精度要求。分析结果表明,冲击增强因子的平方根S01/2是影响无量纲临界厚度的主导因素,密度梯度参数对其影响相对较小,进而给出临界厚度的一阶近似解。动态加载下,多胞材料的压实应变对冲击速度具有依赖性,依据冲击波衰减设计出的牺牲层临界厚度偏于保守。研究了反射波在有初始变形的正梯度多胞金属中的传播规律,数值求解得到牺牲层响应特性。结果显示,在支撑端应力不超过被保护许可应力的前提下,进一步缩短芯层厚度使得反射波后方的应变从0.4增加到0.7附近,提高了材料的利用率。最后,采用二维Voronoi技术构建了梯度多胞金属的细观有限元模型,检验了一维非线性塑性冲击波模型的抗爆炸分析的有效性。
[Abstract]:Gradient polycellular metal materials have attracted extensive attention due to their designability. The introduction of density gradient is expected to achieve better explosion and impact resistance. It has a wide application prospect in the field of engineering protection. The polycellular sacrificial layer is a kind of polycellular material sandwich composite structure, which absorbs the explosion / impact energy greatly through the crushing behavior of the polycellular material, and has been studied in the research of the impact resistance of the sacrificial layer. A simple rigid-ideal plastic locked R-PP-L shock wave model is used to characterize the dynamic collapsing behavior of polycellular materials, which is quite different from the actual stress-strain curves. The superiority of energy absorption and wave dissipation of gradient polycell materials is controversial. In this paper, the explosion resistance of density gradient polycell sacrificial layer is studied by using one-dimensional nonlinear plastic shock wave model and mesoscopic finite element model. . the main factors influencing critical thickness are obtained by dimensional analysis. For the conservative design of critical thickness, An analytical method considering the secondary loading of reflected wave is developed to reduce the thickness of core layer effectively to improve the utilization ratio of polymetallic materials. Based on the rate-independent rigid plastic hardening R-PHmodel, A governing equation describing the propagation of shock waves in gradient sacrificial layers is established. The response characteristics of gradient polycellular metal with linear density distribution under exponential explosion pulse are obtained. The critical thickness of the sacrificial layer is the minimum thickness of the core layer when the explosion energy is exactly absorbed. It is an important design index in engineering. The relationship between critical thickness and load strength, mass of overlay, density gradient of polycell material is analyzed. The density gradient design diagram with the index of critical thickness and peak stress at the support end is given. The results show that the thickness of the positive gradient sacrificial layer is smaller than that of the negative gradient sacrificial layer by increasing the gradient parameter value. The positive gradient can effectively reduce the thickness of the core layer, but it will bring greater stress peak at the support end, and the minimum stress peak value, the uniform density and the negative gradient are the ideal choices. The relationship between the dimensionless critical thickness of gradient polycell sacrificial layer and three dimensionless parameters is established by dimensional analysis. The empirical formula of dimensionless critical thickness is given by using the control variable method, and the accuracy requirement is satisfied. The analysis results show that the square root S01 / 2 of the impact enhancement factor is the dominant factor affecting the dimensionless critical thickness. The density gradient parameter has relatively little effect on it, and then gives the first order approximate solution of the critical thickness. Under dynamic loading, the compaction strain of the polycellular material is dependent on the impact velocity. The critical thickness of the sacrificial layer designed according to the attenuation of shock wave is conservative. The propagation law of the reflected wave in the positive gradient polymetallic with initial deformation is studied. The response characteristics of the sacrificial layer are obtained by numerical solution. Under the condition that the stress at the support end does not exceed the protected allowable stress, further shortening the thickness of the core layer causes the strain behind the reflection wave to increase from 0.4 to around 0.7, which improves the material utilization ratio. The mesoscale finite element model of gradient polycell metals was constructed by using two-dimensional Voronoi technique, and the effectiveness of the one-dimensional nonlinear plastic shock wave model was tested.
【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】：TG139

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