冲击作用下多孔金属的动力学及热力学响应

发布时间：2018-04-22 09:15

本文选题：冲击动力学 + 多孔材料　；参考：《中北大学》2017年硕士论文

【摘要】：多孔金属有良好的冲击缓冲功能,在军用民用两方面都有重要的应用背景,它涉及到冲击动力力学等多个领域,还有许多值得深入研究的问题。本文首先对多孔金属在冲击作用下的本构关系进行了研究,重点讨论了多孔金属的冲击Hugoniot方程与孔隙率的关系,以及多孔金属在Hugoniot弹性限及以以下的冲击行为。详细分析了多孔材料冲击绝热线的三种不同的计算方法的算法和精度,并提出了一种三段式多孔金属冲击本构关系的计算方法。应用应力波的特征线法对爆炸加载方式下多孔金属的冲击响应进行了研究。主要分析了冲击波的初始参数及冲击波的衰减过程及衰减程度。结果表明,在相同的爆炸加载条件下,多孔金属大大减小初始冲击波的峰值压力。多孔金属的基体材料对冲击的衰减程度有所区别,冲击阻抗越大的金属其相应的多孔材料对冲击波的衰减也越强。炸药的种类、长度及约束情况对爆炸加载下多孔金属的冲击响应也有影响。炸药性质主要影响多孔金属中初始冲击波的强度,爆速越大,初始冲击波强度越大。炸药长度及约束情况影响多孔金属中冲击波的衰减速度,炸药长度越大,侧向约束越强,则多孔金属中冲击波的衰减速度越慢。在对多孔材料均相材料模型和应力波特征线法不足的分析基础上,研究了可将多孔金属看作均相材料的临界指标。该指标可定义为多孔金属内部孔洞的平均直径,其临界尺寸与冲击波的上升沿宽度在同一量级,其范围大致10~(-3)mm~10~(-1)mm之间。孔洞的连通性对多孔金属的缓冲吸能性能也有重要影响。影响的机理主要在于孔内气体的冲击压缩性及开孔的闭合。用显式动力学软件对孔洞形状的影响进行了数值模拟研究。结果表明,对于圆形、正方形、六边形和三角形等简单形状的孔洞,六边形和三角形孔洞的多孔金属对冲击波的误差效果最好,圆形的稍差,而正方形的最差。对多孔金属的冲击升温进行了分析。升温能量来源包括基体金属的绝热塑性变形,孔洞壁面的摩擦,孔洞闭合气体绝热压缩,以及孔洞闭合引起的表面能释放。以钨颗粒为代表的多孔金属的冲击过程进行了数值模拟,得到冲击过程中孔隙闭合的速度与特征时间,并依据模拟结果对摩擦表面的升温进行了计算。计算结果与理论分析结果一致。分析了金属熔点变化与压力间的关系,并对比了多孔钨中摩擦表面局部的温度与其在高压下的熔点数据。结果表明,在冲击作用下多孔金属内可发生局部熔化。对多孔材料的中冲击能量的沉积机理进行了简单讨论,主要有塑性功、缺陷生成、相变等方式的能量沉积。由于多孔结构的性质,这些能量沉积机理的作用强度高于密实介质。
[Abstract]:Porous metals have good shock buffering function and have important application background in both military and civil fields. They are involved in many fields such as impact dynamic mechanics and so on. In this paper, the constitutive relation of porous metal under impact is studied, and the relation between the Hugoniot equation and porosity, the elastic limit of porous metal under Hugoniot and the impact behavior of porous metal are discussed. The algorithm and accuracy of three different calculation methods for porous material impact hot wire are analyzed in detail. A calculation method for the constitutive relation of three-segment porous metal impact is proposed. The impact response of porous metal under explosive loading was studied by means of the characteristic line method of stress wave. The initial parameters of shock wave, the attenuation process and attenuation degree of shock wave are analyzed. The results show that the peak pressure of initial shock wave is greatly reduced by porous metal under the same explosion loading condition. The attenuation of shock wave is different in the matrix of porous metal, and the higher the impact impedance is, the stronger the attenuation of shock wave is with the corresponding porous material. The type, length and constraint of explosive also affect the shock response of porous metal under explosive loading. The strength of the initial shock wave in porous metal is mainly affected by the explosive properties, and the larger the detonation velocity is, the greater the initial shock wave intensity is. The length and confinement of explosive affect the attenuation rate of shock wave in porous metal. The longer the length of explosive, the stronger the lateral constraint, the slower the attenuation rate of shock wave in porous metal is. Based on the analysis of the shortage of homogeneous material model and stress wave characteristic line method, the critical index of porous metal as homogeneous material is studied. This index can be defined as the average diameter of the pores in the porous metal. The critical size is about the same order of magnitude as the rising edge width of the shock wave, and its range is approximately 10~(-3)mm~10~(-1)mm. The connectivity of pores also has an important effect on the energy absorption performance of porous metals. The mechanism of influence mainly lies in the impact compressibility of gas in the pore and the closure of the opening. The influence of the hole shape was simulated by explicit dynamics software. The results show that for the holes with simple shapes such as circular square hexagon and triangle the error of shock wave of hexagonal and triangular holes is the best the circle is slightly worse and the square is the worst. The impact heating of porous metals was analyzed. The sources of heating energy include adiabatic plastic deformation of the matrix metal, friction on the wall of the cavity, adiabatic compression of the closed gas, and the release of surface energy due to the closure of the hole. The impact process of porous metal represented by tungsten particles was numerically simulated, and the velocity and characteristic time of pore closure during impact process were obtained, and the temperature rise of friction surface was calculated based on the simulation results. The calculated results are in agreement with the theoretical analysis results. The relationship between melting point change and pressure was analyzed, and the local temperature of friction surface in porous tungsten was compared with the melting point data at high pressure. The results show that local melting can occur in the porous metal under impact. The deposition mechanism of impact energy in porous materials is briefly discussed, including plastic work, defect generation, phase transformation and so on. Due to the properties of porous structure, the action intensity of these energy deposition mechanisms is higher than that of dense medium.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG14;TB383.4

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