Abstract Silica-based glass may possess paradoxically high resistance to hypervelocity impact due to the experimentally observed phase change emanating from high pressure characteristic to hypervelocity impact combined with irreversible densification of the material, which leads to a highly efficient kinetic energy-absorption mechanism. In order to capture this extraordinary behavior of silica glass in hypervelocity impact, a coupled thermo-mechanical model is developed in the framework of thermodynamics with internal state variables. In addition to pressure induced densification (phase change), the proposed model is aimed at capturing the effects of dramatic increase in temperature, strain rate sensitivity and fragmentation/comminution of the material. The proposed model is based on the multiplicative decomposition of the deformation gradient into thermoelastic and plastic parts. The irreversible densification of silica glass is characterized by the plastic volumetric strain which is a basic internal state variable associated with a molecular structure rearrangement due to phase change. Evolution of the plastic deformation is described by a critical state plasticity model combined with damage evolution. In the absence of damage, the elastic domain is fully informed by molecular dynamics simulations of perfectly intact silica glass. With evolving damage, the atomistically informed elastic domain shrinks smoothly to another critical state plasticity elastic domain which serves as a granular description of the fragmented/comminuted state of the material. Thermo-mechanical coupling is considered where temperature rises as a result of mechanical dissipation while mechanical behavior depends on temperature through thermal softening. In addition, the model is capable of capturing both the material’s ductile behavior (featuring significant densification due to high pressure) in the vicinity of projectile–target contact interface and its characteristically brittle behavior exhibited elsewhere. This is achieved by introducing a brittle damage initial criterion based on the thermodynamic driving force for damage that is analogous to the energy release rate-based criterion for crack growth. Constitutive functions and material parameters in the model are determined from the molecular dynamics simulations. The proposed model has been implemented in the explicit coupled thermo-mechanical finite element code and validated against hypervelocity impact experiments.

中文翻译：

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石英玻璃在超高速撞击下的热力学一致热机械耦合模型

摘要 由于实验观察到从高压特性到超高速冲击的相变与材料的不可逆致密化相结合，二氧化硅基玻璃可能对超高速冲击具有自相矛盾的高抵抗力，这导致了高效的动能吸收机制。为了捕捉石英玻璃在超高速撞击中的这种非凡行为，在具有内部状态变量的热力学框架内开发了一种耦合热机械模型。除了压力引起的致密化（相变）之外，所提出的模型旨在捕捉温度急剧升高、应变率敏感性和材料破碎/粉碎的影响。所提出的模型基于将变形梯度乘法分解为热弹性部件和塑料部件。石英玻璃的不可逆致密化以塑性体积应变为特征，塑性体积应变是与由于相变引起的分子结构重排相关的基本内部状态变量。塑性变形的演变由结合损伤演变的临界状态塑性模型来描述。在没有损坏的情况下，完全完整的石英玻璃的分子动力学模拟完全了解弹性域。随着损伤的演变，原子学上的弹性域平滑地收缩到另一个临界状态塑性弹性域，作为材料破碎/粉碎状态的粒度描述。在温度因机械耗散而升高而机械行为通过热软化取决于温度的情况下，考虑了热机械耦合。此外，该模型能够捕捉弹丸-目标接触界面附近材料的延展行为（由于高压而显着致密化）及其在其他地方表现出的特征性脆性行为。这是通过引入基于热力学驱动力的脆性损伤初始准则来实现的，类似于基于能量释放速率的裂纹扩展准则。模型中的本构函数和材料参数由分子动力学模拟确定。