金属玻璃及其复合材料的剪切变形与破坏

发布时间：2018-04-17 03:37

本文选题：金属玻璃 + 复合材料　；参考：《北京理工大学》2016年博士论文

【摘要】：块体金属玻璃及其复合材料具有优异的力学、物理和化学性能,特别是在玻璃转变温度以下和高应力或高应变率条件下变形时,容易发生局域剪切带,具有极高的剪切敏感性。因此,该类材料有可能应用于新型穿甲弹芯,逐渐成为高速穿甲及装甲防护研究领域的前沿热点。本文基于有限元模拟开展针对金属玻璃及其复合材料剪切带行为的研究,包括剪切带的形核、传播以及剪切带诱导的断裂等,深入讨论材料的剪切变形和破坏特征以及复合材料弹体穿甲的“自锐”特性。首先基于热力耦合模型,考虑自由体积、热和静水应力对材料变形和破坏的影响,推导了块体金属玻璃材料的三维本构模型;基于自由体积聚集和结合的微观机理,引入了临界自由体积浓度的材料破坏准则。将建立的本构模型和破坏准则写入LS-DYNA软件的用户自定义材料子程序(UMAT)中,对不同受力状态和不同温度条件下金属玻璃的变形响应特性进行了有限元模拟研究,具体分析材料内部物理参量的演化特性及其所导致的材料宏观表象。研究发现初始自由体积浓度、应变率、初始温度和静水应力等内外部条件对金属玻璃的变形和破坏具有重要影响:变形和破坏受材料的微观结构即自由体积主控,而温度则起辅助的促进作用;应变率和初始温度均产生明显影响,应变率的作用尤为显著,而静水应力将导致变形的拉压不对称特征。进一步考虑金属玻璃材料内部结构的不均匀性,建立了包含随机分布材料弱区的有限元几何模型。针对块体金属玻璃在准静态拉伸、压缩、弯曲以及高速冲击等不同加载条件下的变形和破坏特性进行了分析。结果表明金属玻璃在常温条件下的变形表现为局域化的剪切特征,呈现出显著的非均匀特性。在准静态加载条件下,剪切带的生成和扩展同时受应力条件和弱区分布特性的影响;而在冲击条件下,弱区的影响减弱。结合纤维/颗粒增强金属玻璃复合材料内部结构特征建立相应有限元几何模型,利用修正的热力耦合本构模型来描述金属玻璃基体的高强度和高剪切敏感性,系统开展了针对复合材料静动态拉压试验和高速冲击试验的研究。结果显示,复合材料的压缩塑性较纯金属玻璃得到明显提高,而拉伸塑性则相对难以改善。在压缩变形过程中,纤维增强复合材料的变形和破坏模式随纤维体积分数和应变率等内外部因素的改变而发生变化,颗粒增强复合材料则主要表现为剪切特征;在拉伸条件下,材料均主要发生脆性断裂,断面基本垂直于加载方向。相应变形和破坏特性同复合材料内部的剪切带行为密切相关。最后结合穿甲试验开展了针对钨纤维/钨颗粒增强金属玻璃复合材料长杆弹穿甲靶板的有限元模拟研究。具体分析复合材料弹体的穿甲“自锐”性能,详细讨论撞击速度、靶材强度和初始弹头形状等因素对弹体的“自锐”行为以及相应穿甲性能的影响,同时对比分析了两种复合材料长杆弹之间的异同。
[Abstract]:Bulk metallic glass and its composites have excellent mechanical, physical and chemical properties, especially in the glass transition temperature and high stress or high strain rate deformation, prone to local shear zone with high shear sensitivity. Therefore, this kind of material can be applied in the new type of penetrator. Gradually become the hotspots of high-speed penetration and armor protection research field. This paper based on finite element simulation of metallic glass and its composites on shear behavior, including shear band nucleation, propagation and induction of shear band fracture, in-depth discussion of "self sharpening characteristics of material shear deformation and failure characteristics of composite materials the penetrating". Based on the coupled thermo mechanical model, considering the free volume, heat and hydrostatic stress effects on material deformation and failure. The formulas of three-dimensional bulk metallic glass material Constitutive model; mechanism of free volume aggregation and based on introduction of critical concentration of free volume of material failure criterion. The constitutive model and failure criterion of writing LS-DYNA software subroutine will be established (UMAT), the deformation response characteristics in different stress state and different temperature conditions of metallic glass a finite element simulation of materials macro representation evolution properties of concrete analysis material physical parameters and its causes. It is found that initial free volume concentration, strain rate, initial temperature and hydrostatic stress has an important influence on the deformation of the internal and external conditions of metallic glass and destruction: the deformation and destruction of the microstructure by material that is the free volume control, while the temperature plays an auxiliary role; has obvious effects of strain rate and initial temperature, strain rate effect is particularly significant, and hydrostatic stress Will lead to tension compression asymmetry deformation. Further considering the inhomogeneity of the internal structure of metallic glass material, a finite element model with random geometric distribution of the material. In the weak area of bulk metallic glass under quasi-static tensile, compression, bending and high impact deformation and failure characteristics under different loading conditions are analyzed the results showed that the deformation of metallic glass. Under normal temperature conditions for shear localization features, showing a significant nonuniformity. Under the quasi-static loading condition, the shear band formation and expansion also affected by stress conditions and weak characteristic distribution; while under impact conditions, weakening the influence of weak areas. Combined with the characteristics of the internal structure of fiber / particle reinforced metal glass composites established finite element model, constitutive model to describe the high strength metallic glass substrate using the modified thermal coupling The degree of sensitivity and high shear, the system carried out for composite materials of static and dynamic tension compression test and high speed impact test. The results showed that the composite compressive plastic than the pure metallic glass has been significantly improved, while the tensile ductility is relatively difficult to improve. In the compression deformation, deformation and failure mode of fiber reinforced composite materials with the fiber volume fraction and strain rate of internal and external factors change, particle reinforced composites are mainly for shear characteristics; under tensile conditions, materials are mainly brittle fracture section perpendicular to the loading direction. The deformation and failure characteristics of shear with composite materials is closely related with the behavior. Finally, the armour test carried out against the finite element simulation of metallic glass composite long rod projectile penetrating target plate of tungsten fiber / tungsten particle reinforced concrete composite material analysis. The self piercing performance of projectile penetrating armor is discussed. The influence of impact velocity, target strength and initial warhead shape on the self sharpening behavior and the corresponding piercing performance of the projectile are discussed in detail. Meanwhile, the similarities and differences between two kinds of composite long rod projectiles are compared and analyzed.

【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8;TB33

【参考文献】