Dynamic mechanical behavior of shear thickening fluid and its composites

发展具有优异抗冲击性能的先进材料，并揭示相关的耗能机制，一直是冲击防护领域的研究前沿之一。许多材料在高压和高应变率下表现出卓越的抗冲击和防爆特性，但往往在单次冲击加载后失效并丧失防护性能。因此，发展多次冲击吸能的先进材料具有重要的应用需求。剪切增稠流体（STF）是一种应变率越高粘度越大的非牛顿流体，其通常由微纳米颗粒均匀分散在流体介质中形成。当外部载荷作用在STF上时，其粘度会快速增加并耗散一定的能量；当停止加载后，STF会快速恢复到初始状态，因此具有重复吸能的特性。利用STF的流变特性，将其与多孔结构材料进行复合设计，通过STF与结构在冲击加载过程中的强耦合作用，以增强能量耗散效应，从而进一步提升材料的防护能力。 本文围绕STF及其复合材料的动态力学行为展开了以下几个方面的研究工作： 1．研究了高压、超高应变率下STF的动态力学行为，建立了STF可压缩非线性粘性本构模型。制备了不同质量分数的二氧化硅-聚乙二醇（PEG）的STF，并表征了其流变性能。结果表明，随着STF中二氧化硅纳米颗粒质量分数的增加，粘度快速增加。采用强激光诱导冲击加载试验方法，分析了水、PEG、40%二氧化硅质量分数的STF（40wt.%STF）和68%二氧化硅质量分数的STF（68wt.%STF）在冲击载荷下的力学响应规律。研究发现，STF具有高冲击波衰减能力，高质量分数纳米颗粒的STF具有优异的防护性能。同时，建立了PEG、40wt.%STF和68wt.%STF的一阶和二阶Mie-Gr&uuml;neisen状态方程。通过冲击波加载铝板-STF-铝板数值模拟，验证了状态方程的正确性。 2．研究了STF填充点阵夹层板（SPLTC-STF）在低速冲击下的动态力学行为。采用STF本构模型描述其剪切稀化、剪切增稠和体积压缩性等力学行为，结合动态压缩试验和流固耦合数值计算获得了本构模型参数。通过数值模拟，获得了SPLTC-STF的动态力学行为及宏观响应特性，在内部STF靠近点阵夹层板周围快速流动的过程中，与芯材产生了较强的相互作用，引起SPLTC变形模式的转变，从而提高了SPLTC-STF的吸能能力。 3．研究了SPLTC-STF在高速冲击下的力学行为。通过建立数值计算模型，分析了不同填充物点阵夹层板在平板撞击后的变形行为、速度衰减和动能衰减规律。结果表明，随着撞击速度的增加，SPLTC-STF的最大速度衰减能力越强。同时，较高粘度的STF能够进一步增强耦合耗能能力，实现更好的防护性能。通过爆炸加载试验和数值模拟，也表明SPLTC-STF具有良好的防爆性能，在爆炸与冲击防护领域中具有重要的应用价值。 4．制备了STF微胶囊-硅橡胶基复合材料（SR-STF），测量了SR-STF复合材料静态和动态力学行为，发现SR-STF复合材料表现出对加载速率的智能适应性，即在低应变速率下，SR-STF复合材料的刚度随着STF微胶囊含量的增加而减小，而在高应变率下，刚度随着STF微胶囊含量的增加而快速增加。基于试验结果，建立了SR-STF复合材料的超弹性本构模型，准确预测了材料的动力学行为。 本文获得了STF在高压高应变率下应力波衰减和能量吸收规律，并建立了STF的可以缩非线性粘性本构方程。揭示了STF填充点阵夹层板在低速和高速冲击下的动态力学行为和能量耦合耗散机制。首次制备了STF微胶囊填充SR复合材料，并得到了SR-STF在不同载荷条件下的力学性能。</p

Silicone rubber matrix composites with shear thickening fluid microcapsules realizing intelligent adaptation to impact loadings

In this paper, silicone rubber matrix composites with shear thickening fluid microcapsules (SR-STF) with intelligent adaptation to impact loadings are fabricated for advanced impact protective structure. The composites exhibit more flexibility at low strain rates but higher stiffness at high loading rates, indicating significant strain -rate sensitivity. In addition, the initial flexibility and the strain-rate sensitivity of the composite increase with increasing the mass fraction of the STF microcapsules, which should be ascribed to the shear thickening and compressive jamming of the STF microcapsules in the composite during impulse loadings. Based on experimental results, a hyper-viscoelastic constitutive model is developed, in which the influence of the mass fraction of STF microcapsules, the strain-rate sensitivity, and the strain-hardening effect are taken into account. The paper develops a practical strategy for applications of STF in soft protective structures and provides a reliable pre-diction of the dynamic mechanical behavior of the SR-STF composites

Dynamic compressive behaviour of sandwich panels with lattice truss core filled by shear thickening fluid

The compressive behaviour of sandwich panels with lattice truss core filled by shear thickening fluid (SPLTCSTF) at high strain-rates is performed analytically and numerically. Firstly, a hydrodynamic constitutive model for the shear thickening fluid (STF) involving shear thinning, shear thickening, and hydrostatic compressibility is undertaken to describe the dynamic behaviour of the STF. Then an analytical model based on the squeezing flow of viscous fluids is proposed. The squeezing resistance of the STF between the two panels of the SPLTC under various loading velocities is analysed using a fluid-structure interaction (FSI) simulation, by which the constitutive parameters of the STF are obtained. Finally, the dynamic response of the SPLTC-STF involving buckling and post-buckling of core struts in the STF is investigated using the FSI method. The enhanced energy absorption capacity of the SPLTC-STF observed in Ref [1] is numerically interpreted. The effects of shear thickening behaviour of STF on the dynamic response of SPLTC-STF are predicted, providing a method of optimal design for STF filled sandwich panels over a wide range of impulse loadings for dynamic energy absorption

Geometrical scaling law for laser-induced micro-projectile impact testing

Laser-induced micro-projectile impact testing (LIPIT) is a useful experimental method for exploring the dynamic behavior of materials at microscale. It has been a key issue to obtain a scaling law of launch velocity of LIPIT to simplify experimental design and improve experimental configuration. This paper obtains a geometrical scaling law of launch velocity for LIPIT with relative thick metallic film (30-80 mu m thick aluminum) using dimensional analysis, experimental measurements, and numerical simulations. Firstly, the dimensional analyses of LIPIT with and without elastomer film configuration are performed, and the dimensionless parameters controlling the launch velocity of the micro-projectile are deduced, from which the geometrical scaling laws of launch velocity for the LIPIT are obtained. Then, the numerical simulation models of the LIPIT are established and validated by LIPIT experimental results, providing a numerical validation for the geometrical scaling laws. In addition, the influences of the dimensionless parameters on the dimensionless launch velocity of micro-projectiles are analyzed by numerical simulations, and the dimensionless formulas for predicting the launch velocities of micro-projectiles in a LIPIT are given, providing an effective method for analyzing and optimizing the LIPIT experiments

Ultrahigh cavitation erosion resistant metal-matrix composites with biomimetic hierarchical structure

Cavitation erosion significantly impairs the serviceability of hydroelectric turbines and causes tremendous economic loss. Therefore, the demand for materials with effective resistance to cavitation erosion is imperative. Here, a novel nickel (Ni)-tungsten carbide (WC) composite coating with biomimetic hierarchical structure (BHS) is proposed. The BHS imitates cuttlebone in microscale and abalone nacre in nanoscale. In microscale, a threedimensional cross-linking eutectic network of Ni-WC sandwiches divides Ni matrix into many small cells, which effectively inhibits crack propagation to an individual cell, controlling the damage caused by cavitation erosion. In nanoscale, numerical modelling results further reveal that the Ni-WC sandwiches can reduce the tensile stress triggered by cavitation impact and dissipate the impact energy, giving rise to ultrahigh cavitation erosion resistance behaviour. The design of similar structures may promote the development of other metal-matrix composites, establishing new methods for developing material systems with advanced properties