高低温环境对剪切硬化胶改性乙烯-醋酸乙烯酯泡沫的防护性能影响

乙烯-醋酸乙烯酯泡沫（ethylene-vinyl acetate foam,EVA）广泛应用于防弹衣缓冲层、护膝护肘中作为缓冲材料。文章利用剪切硬化胶（shear stiffening gel,SSG）对EVA进行改性，得到了具备更高冲击防护性能的EVA/SSG复合缓冲泡沫。为研究高低温环境对EVA/SSG泡沫材料缓冲性能的影响，利用动态热机械分析、万能压缩机对EVA/SSG泡沫在–50℃～50℃下的力学性能进行了研究，得到了EVA/SSG材料的损耗模量、储能模量、屈服强度随温度变化的规律；同时借助落球试验平台系统研究了高低温环境（–50℃～50℃）对EVA/SSG泡沫材料冲击防护性能的影响。通过分析落球冲击试验结果与材料的力学性能测试结果，系统总结了高低温环境对EVA/SSG复合泡沫材料防护性能的影响规律

Enhancing impact resistance of CFRP by incorporating dynamic non-covalent bonds into epoxy resin networks

Carbon fiber reinforced epoxy composites have gained widespread application in aerospace and automotive industries due to their exceptional mechanical properties and chemical stability. However, the inherent brittleness of epoxy matrices and the relatively weak interfacial adhesion to carbon fibers significantly constrain the further utilization in extreme conditions. To overcome these obstacles, this study introduced an innovative approach to modify epoxy-based resin by employing polyethylene glycol 200/nano-silica suspensions as dispersion media to incorporate boric acid into the epoxy molecular system. This methodology successfully constructed boron-contained side-chain structures during epoxy curing, where dynamic boron-oxygen (B-O) and boron-nitrogen (B-N) crosslinked networks were established in the epoxy molecular chains and at the resin-fiber interface simultaneously. The dynamic crosslinked network-induced performance enhancement is attributed to three synergistic mechanisms: (1) dynamic bonds participate in the epoxy curing process moderately and thus reduce crosslinking density, which contributed to the improvement of material toughness; (2) the reversible breakage-reformation behavior of dynamic B-O/B-N bonds effectively dissipates impact energy; (3) dynamic covalent bonds at resin-fiber interfaces significantly strengthen adhesive performance and optimize stress transfer efficiency. Experimental results demonstrated that the impact fracture strength of modified epoxy resin was promoted by over 30 %. Furthermore, the novel composite system exhibited outstanding impact damage resistance, where the post-impact residual compressive strength and the fracture strength were improved by 37.2 % and 60.7 %, respectively. This study proposes new design principles to develop high-performance fiberreinforced composites with substantial engineering application potential in aerospace and transportation fields

Micromechanical properties of shear stiffening gel reinforced ethylene-vinyl acetate foam

In previous study, a novel composite foam that possesses cushioning properties is developed by incorporating shear stiffening gel (SSG) into Ethylene-vinyl (EVA) foam. In this work, uniaxial compression is used to obtain the mechanical properties of the proposed material under static loading. The test results demonstrate the additive SSG could effectively enhance the energy absorption capacity. With the aid of in-situ Scanning Electron Microscope (SEM), two characteristics, the homogeneous microstructural morphology and phase separation between SSG and EVA, are found that played dominant roles in the improvement of cushioning properties

Protective performance of shear thickening gel modified epoxy sealant on lithium-ion batteries under mechanical abuse

The popularity of electric vehicles leads to more attention drawn to the safety of Lithium-ion batteries in traffic crashes. In this study, a novel epoxy-based sealant was proposed by incorporating shear-thickening gel (STG) into the matrix material. The material properties including morphological characteristics and chemical compositions were determined via microscopic analysis techniques. Mechanical properties of the newly proposed material under different loading conditions were determined using corresponding testing methods. The experimental results confirmed the contribution of the STG to dampness, ductility, and toughness. To examine the protective effectiveness of the proposed encapsulating material, indentation tests on individual cell units and drop weight tests on battery packs were carried out. It was found that the modified sealant could improve the failure strength as well as delay the onset of internal short-circuit under lateral compression. In comparison with the conventional sealant, the deformations of cell units and the acceleration at the central region of the battery pack were remarkedly reduced by using the modified material under drop weight impact, which were detected by the strain gauges and accelerometers. The experimental observations and test results in this study could support the potential application of STG-modified epoxy material in battery systems of electric vehicles

Protective performance of shear stiffening gel-modified foam against ballistic impact: Experimental and numerical study

As one of the most widely used personal protective equipment (PPE), body armors play an important role in protecting the human body from the high-velocity impact of bullets or projectiles. The body torso and critical organs of the wear may suffer severe behind-armor blunt trauma (BABT) even though the impactor is stopped by the body armor. A type of novel composite material through incorporating shear stiffening gel (STG) into ethylene-vinyl acetate (EVA) foam is developed and used as buffer layers to reduce BABT. In this paper, the protective performance of body armors composed of fabric bulletproof layers and a buffer layer made of foam material is investigated both experimentally and numerically. The effectiveness of STG-modified EVA in damage relief is verified by ballistic tests. In parallel with the experimental study, numerical simulations are conducted by LS-DYNA (R) to investigate the dynamic response of each component and capture the key mechanical parameters, which are hardly obtained from field tests. To fully describe the material behavior under the transient impact, the selected constitutive models take the failure and strain rate effect into consideration. A good agreement between the experimental observations and numerical results is achieved to prove the validity of the modelling method. The tests and simulations show that the impact-induced deformation on the human body is significantly reduced by using STG-modified EVA as the buffering material. The improvement of protective performance is attributed to better dynamic properties and more outstanding energy absorption capability of the composite foam. (c) 2023 China Ordnance Society. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/)

Prediction of Energy Resolution in the JUNO Experiment

International audienceThis paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors