Impact resistance analysis of flexible fabric by 3D shape of impact basin in low-speed impact test

Hopkinson non-penetrating low-speed impact test was carried out on Kevlar flexible fabrics. The impact basin was formed by the clay on the back of the fabric, and the ultimate deformation of the fabric was recorded completely. The 3D shape of the clay impact basin was measured by fringe projection profilometry and converted into the impact basin volume. At the same time, the relationship between the indentation volume and the deformation energy of the clay was calibrated using the clay intrusion test. The clay impact basin volume is then converted into the residual energy of the flexible fabric subjected to the low-speed impact, and a new index of the impact basin volume is established to evaluate the energy absorption efficiency of fabric under the low-speed impact. Finally, combined with the deformation of single-layer fabric, the stress wave propagation in the impact deformation process of fabric is discussed, which is helpful to understand the impact energy absorption mechanism of flexible fabric.     

Enhancing toughness of poly (lactic acid)/Thermoplastic polyurethane blends via increasing interface compatibility by polyurethane elastomer prepolymer and its toughening mechanism

Due to the environmental pollution caused by the petroleum-based polymer, poly (lactic acid) (PLA), a biodegradable and biocompatible polymer that obtained from natural and renewable sources, has attracted widespread attention. However, the brittleness of PLA greatly limits its application. In this study, the super toughened PLA-based blends were obtained by compatibilizing the PLA/thermoplastic polyurethane (TPU) blends with the polyurethane elastomer prepolymer (PUEP) as an active compatibilizer. The mechanical properties, thermal properties and corresponding toughening mechanism of PLA/TPU/PUEP system were studied by tensile test, instrumented impact test, dynamic mechanical analysis (DMA), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All the results demonstrate that the isocyanate (−NCO) group in PUEP is successfully reacted with the –OH groups at both sides of the PLA and the obtained polyurethane (PU)~PLA copolymer (PU ~ cõ PLA) significantly improves the interfacial compatibility of PLA/TPU blends. The gradually refined dispersed phase size and fuzzy phase interface as displayed in SEM images suggest a good interfacial compatibilization in the PLA/TPU/PUEP blends, probably due to the isocyanate reaction between PLA and PUEP. And the interfacial reaction and compatibilization among the components led to the formation of super toughened PLA/TPU/PUEP blends. And the instrumented impact results indicate that most of the impact toughness is provided by the crack propagation rather than the crack initiation during the entire fracture process.     

Dynamic fracture testing of polymethyl-methacrylate (PMMA) single-edge notched beam

Dynamic fracture in single-edge notched polymethyl-methacrylate (PMMA) beams have been investigated by three-point-bending impact testing with a drop-weight machine. A high-speed camera combined with the digital image correlation (DIC) method is used to capture the impact-induced crack initiation and propagation, as well as the beam deformation fields and the open mode strain at the original notch tip. The crack propagation length is recorded and the instantaneous crack velocity is calculated. Furthermore, the dynamic fracture toughness K_Id is quantified from the loading-displacement relations at different impact velocities. The effects of the impact velocity and impact energy on dynamic fracture toughness, fracture initiation strain, as well as the corresponding influences on the fracture propagation velocity, are discussed.     

Performance of high-temperature thermosetting polyimide composites modified with thermoplastic polyimide

The preparation of polyimide (PI) resin with high heat resistance and toughness is a significant challenge. In this study, thermoplastic PI (TPI) was used to toughen thermosetting PIs, and toughened PI (TPI/PI) blends were prepared. The modified PI resin system exhibited good thermal stability, excellent heat resistance, and high toughness. The results indicated that the TPI/PI blends maintained the curing behavior and characteristics of the PI oligomer. The T_g of the cured TPI/PI blend exceeded 395 °C, and the T_5% values were in the range of 533–563 °C, suggesting excellent thermal stability and heat resistance. The maximum impact strength was increased by 46% compared with that of pure PI, indicating the excellent toughening effect of the TPI. Carbon fiber-reinforced PI composites were prepared using the toughening system as a matrix. The compression-after-impact values of the carbon fiber-reinforced PI composites were up to 190 MPa, indicating the excellent toughness of the materials.     

Structural behaviour of fibre metal laminates subjected to a low velocity impact

Structural impact tests were first presented to cover typical fibre metal laminates (FMLs) subjected a low velocity projectile impact,which produced the corresponding load-displacement traces and deformation/failure modes for the validation of numerical models.Finite element (FE) models were then developed to simulate the impact behaviour of FMLs tested.The aluminium (alloy grade 2024-0) layer was modelled as an isotropic elasto-plastic material up to the on-set of post failure stage,followed by shear failu...     

泡沫铝冲击吸能器被动冲击隔离技术研究

对隔振系统中引入泡沫铝冲击吸能器进行探讨.首先,在综合考虑最大加速度和最大相对位移这2个影响舰船设备防护的重要指标情况下,对舰船单层隔振系统中引入泡沫铝冲击吸能器进行了理论分析,在此基础上进行了实验验证.通过实验结果可知,泡沫铝冲击吸能器能有效消除舰船设备的二次冲击.实验结果与理论结果吻合较好,可为泡沫铝冲击吸能器的应...     

时一空守恒元解元（CE／SE）方法综述

时一空守恒元解元方法是近年来兴起的一种全新的高分辨率守恒型方程计算方法．它具有物理概念清晰、计算精度高和格式构造简单等优点,是一种具有广阔发展前景的计算方法．本文详细地介绍了cE／ss方法的基本原理、发展历史、应用情况和最新进展、并指出了当前研究的不足和发展方向．     

杆弹侵彻钢纤维混凝土实验研究

采用DOP实验方法,进行了35CrMnSiA杆弹对不同钢纤维体积含量的钢纤维混凝土的侵彻实验.分别研究了杆弹着速和钢纤维体积含量对钢纤维混凝土杭侵彻性能的影响.实验表明,随着弹速增加,不同钢纤维含量的钢纤维混凝土侵彻深度都会增加,但钢纤维混凝土中弹体便深增加较素混凝土缓慢;而钢纤维能增强混凝土的抗侵彻性能,且随钢纤维体...     

基于J-C本构模型的Comp.B炸药落锤冲击数值模拟

为研究Comp.B炸药在惯性冲击下的力学响应特性, 基于Johnson-Cook本构模型, 对 点火前的Comp.B炸药大落锤(400kg)冲击实验进行了数值模拟. 在不同应力加载条件下模 拟计算得到了用状态方程和不用状态方程的$\sigma$-$t$曲线, 对比应力峰值、应 力上升时间等主要力学参数, 结果表明考虑了状态方程的数值模 拟结果与实验吻合最好, 可以很好地模拟炸药惯性冲击下的力学响应.     

7A04铝合金的本构关系和失效模型

使用万能材料试验机、扭转试验机和Taylor撞击实验研究了高强铝合金7A04在常温至250 ℃的 准静态、动态本构关系和失效模型。基于实验结果,修改了Johnson-Cook强度模型中的应变强化项以及 Johnson-Cook失效模型中的温度软化项,并结合数值模拟标定了模型参数。实验结果表明,7A04铝合金的 应变和应变率强化效应不显著,失效应变随温度的增加、应力三轴度的减小和应变率的减小而增加。