Ballistic performance of spaced multi-ply soft fabrics: Experimental and numerical investigation

It has been reported that the ply gap influences the ballistic resistance of spaced multi-ply fabric systems,but its working mechanism was not well-understood. This paper reports the experimental and numerical approaches and results of an investigation on the mechanisms that enable the improved ballistic performance of spaced multi-ply systems. Penetration tests were performed over a range of impact velocities ranging from 200 m/s to 400 m/s. The results confirmed that the ply gap is beneficial to the energy absorption capability of the systems. This is because the front plies tend to absorb more energy when they are not immediately constrained by the rear plies. During a ballistic event, the gap relieves the reflection of the compressive pulse, prolonging the projectile engagement time with the front plies;on the other hand, the rear plies become increasingly less active in dissipating energy as the gap increases.When the gap is sufficiently widened to avoid any interference between the plies before the failure of the front ply, the responses of the whole system no longer vary. It was also found that the ballistic performance of the spaced systems is influenced by ply thickness, impact velocity, and the stacking order of the ply gap.

Effect of dynamic loading conditions on the dynamic performance of MP1 energy-absorbing rockbolts:Insight from laboratory drop test

Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support, and their serviceability is closely related to the frequency and magnitude of seismic events. In this research, the splittube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1rockbolts under a wide range of seismic event magnitudes. The test results showed that the impact process could be subdivided into four distinct stages, i.e. mobilization, strain hardening, plastic flow(ductile), and rebound stage, of which strain hardening and plastic flow are the primary energy absorbing stages. As the impact energy per drop increases from 8.1 to 46.7 k J, the strain rate of the shank varies between 1.20 and 2.70 s^(-1), and the average impact load is between 240 and 270kN, which may be considered as constant. The MP1 rockbolt has a cumulative maximum energy absorption(CMEA) of 31.9–40.0 k J/m, with an average of 35.0 k J/m, and the elongation rate is 11.4%–14.7%, with an average of 12.7%, both of which are negatively correlated with the impact energy per drop. Regression analysis shows that energy absorption and shank elongation, as well as momentum input and impact duration,conform to the linear relationship. The complete dynamic capacity envelope of MP1 rockbolts is proposed, which reflects the dynamic bearing capacity, elongation, and distinct stages. This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engineers in robust reinforcement systems design to mitigate rockburst damage in seismically active underground excavations.

Performance of a Refrigeration Absorption Cycle Driven by Different Power Sources

In this study, performance assessment of absorption refrigeration cycle has been carried out under variable power sources namely electric, conventional fuel and renewable energy sources. The ammonia-water absorption cycle was used in this work, the temperatures at each point in the cycle such as generator, absorber, evaporator and condenser have been measured and with using absorption device system. The coefficient of performance and efficiency of the plant were measured and then compared. The results showed that when the cycle driven by electricity, the coefficient of performance varied 0.694 to 1.032 along the test time and the generator temperature changes from 48.1°C to 101.5°C with the average efficiency of 57.1% and average coefficient of performance of 0.78. When methane used as a fuel to generate power the coefficient of performance varied between 0.686 and 0.94 under the generator temperature of 123.3°C and 127.4°C and average efficiency of 40.02% with coefficient of performance of 0.735. Solar energy used as the alternative source of power which is the clean and safe power source and when the plant driven by the solar thermal energy, the coefficient of performance reached to 0.801 under the generator temperature of 91°C, but the system efficiency about 11.68% along the test time. Solar energy can be used efficiently and replaced the conventional power sources to drive the absorption refrigeration unit.

Experimental study on the shear performance of quasi-NPR steel bolted rock joints

Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics,which is of high value in deep rock and soil support engineering.However,research on the shear resistance of quasi-NPR steel has not been carried out.To study the shear performance of quasi-NPR steel bolted rock joints,indoor shear tests of bolted rock joints under different normal stress conditions were carried out.Q235 steel and#45 steel,two representative ordinary bolt steels,were set up as a control group for comparative tests to compare and analyze the shear strength,deformation and instability mode,shear energy absorption characteristics,and bolting contribution of different types of bolts.The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load,while the bolted jointed rock masses show obvious ductile failure characteristics.The shear deformation ca-pacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and#45 steel.No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance.However,the other two types of control bolts become fractured under the same conditions.Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel.In particular,the shear force plays a major role in resisting the shear deformation of Q235 steel and#45 steel,therefore,fracture failure occurs under small bolt deformation.However,the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation;the steel itself does not break when large shear deformation occurs,and the supporting effect of the jointed rock mass is effectively guaranteed.

Parametric study on the ballistic performance of seamed woven fabrics

The ballistic perforation response of composite fabrics made by combining plain weaves with seaming technology is reported and compared with conventional unseamed plain fabrics.The effect of the seaming technique on the ballistic resistance of aramid plain fabrics is investigated by varying the seaming process.The ballistic experiment uses 8 mm diameter spherical projectiles to impact different fabric sample targets with velocities of 230 m/s and 400 m/s.The ballistic performance of seamed and unseamed fabrics is characterized by the specific energy absorption(SEA)values of the fabrics.The results show that the seamed fabric has a better energy absorption capacity than the unseamed fabric,e.g.,the SEA of sample 5(seaming lines on every four yarns in a single-ply fabric system)is 135%of sample 1(plain weave without thread seaming).In the single-layer system,the effect of the seaming technique on the energy absorption of the fabric in significant when considering seaming density,seaming orientation,seaming distance,and seaming material on the plain fabric;In addition,it is found that in multi-layer systems,seamed panels(e.g.,sample 7)exhibit better ballistic performance than multi-layer fabrics(e.g.,sample 2),and the specific energy absorption of sample 7 is approximately 156%and 200%of sample 6 and sample 2,respectively.Meanwhile,the energy absorption of the fabric decreases with the increase of impact velocity,which is related to the energy absorption mechanism of the soft fabric system at high impact velocities.The yarn pull-out tests shows that the constraint provided by the seaming thread increases the friction between the fabric-forming yarns.However,when the constraint exceeds a certain level,it is detrimental to the energy absorption of the fabric,which may be due to the overconstraint of yarn mobility.

Relationships between distribution characteristics of ceramic fragments and anti-penetration performance of ceramic composite bulletproof insert plates

Through quantitative statistics and morphological characterization of ceramic fragments for ceramic composite bulletproof insert plates(CCBIPs),distribution characteristics of ceramic fragments within a specific size range were analyzed for different Armor Piercing Incendiary(API)and shot times.To quantitatively evaluate the effect of energy absorption for ceramic plates,a model of energy absorption during penetration for CCBIPs was established based on statistics of the size distribution of ceramic fragments(SDCF).Variation in the SDCF and its influence on energy absorption for CCBIPs were investigated.The results indicate that the distribution feature of ceramic fragments in the range of 0.25-2.25 mm is Gaussian distribution.Compared with Type 56 of API(56-API),ceramic fragments formed by 53-API with higher kinetic energy possess more quantity and more concentrated distribution,whose average equivalence size decreases by 6.5%,corresponding to increasing by 83.9%of estimated energy absorption.Besides,the ability of CCBIPs to resist the third shot is significantly weakened,whose estimated energy absorption decreases by 58.8%compared with the first shot.More concentrated distribution and fewer fragments are formed after the third shot,the average equivalence size of ceramic fragments increases by 6.9%,which may attribute to the micro-cracks induced by the previous two shots.

高速冲击加载下碳纤维复合材料层合结构抗侵彻特性及响应机理

碳纤维复合材料层合结构在高冲击服役环境中常遭受外来物体冲击作用,使之出现一些不可预测的各种损伤形式,甚至会出现不可控的损伤模式。为确保这些结构的安全性和可靠性,对碳纤维复合材料层合结构抗冲击响应及防护机理展开了研究。以碳纤维复合材料层合结构作为研究对象,基于一级轻气炮构建高速冲击加载试验装置,探明了碳纤维复合材料层合结构能量吸收特性与冲击能量之间的联系规律,结合弹道极限方程,确定了其弹道极限,并明确了不同冲击速度作用下的损伤模式。同时引入内聚力单元进行数值模拟仿真研究,探明了碳纤维复合材料层合结构层与层之间内聚力单元的损伤模式,揭示了其在高速冲击加载环境下的损伤机制。研究结果为反向设计适用于高速冲击加载环境复合材料层合结构提供理论依据。

玻璃砂超高性能水泥基复合材料的制备及性能

为实现超高性能水泥基复合材料(ultra-high performance cementitious composite,UHPCC)的可持续性和环保性,以玻璃砂替代UHPCC中的河砂,制作玻璃砂超高性能水泥基复合材料(glass sand ultrahigh-performance cementitious composite,GS-UHPCC),通过开展力学性能试验,探讨不同玻璃砂替代率和玻璃砂粒径对GS-UHPCC抗压、抗折性能的影响,定量表征GS-UHPCC的弯曲韧性和能量吸收能力,并通过X射线衍射和扫描电镜试验,分析了玻璃砂的增韧机理.结果表明,以平均粒径为0.27 mm的玻璃砂替代河砂,当体积替代率为40%时效果最好,替代后GS-UHPCC在养护28 d时的抗压强度相较于未掺时提升了17.0%,抗折强度提升了14.8%,能量吸收能力最优,微观结构致密,水化反应最为完全.本研究得出的最优玻璃砂替代率与粒径,可为GS-UHPCC的应用提供可行性支持.

弹道冲击下石墨烯和聚乙烯改性芳纶织物的钝伤防护性能

芳纶凭借其轻质高强的特点广泛应用于防弹领域。为提高单层芳纶织物的抗钝伤能力,采用热塑性树脂聚乙烯(Polythene,PE)与石墨烯纳米粒子表面改性方法提升芳纶织物的抗钝伤性能。以背衬凹陷为标准,对不同质量配比改性芳纶织物的抗钝伤能力和能量吸收特性进行测试对比。对比结果表明:石墨烯和PE两种改性方法均可提升芳纶织物的抗钝伤能力,其中PE改性方法使得改性织物面密度增加较小但抗钝伤能力显著提升,10%PE的防弹能力和比吸能值较纯芳纶分别提升了18.0%和30.8%;石墨烯改性织物刚性的增加使其低速抗钝伤能力增强,但是过大的纱线间摩擦使其高速防护能力减弱,2%石墨烯粉体为石墨烯改性织物的最佳配比。此外,优化验证得到了2层10%PE和13层的6层正交超高分子量PE无纬布防弹衣组合设计。

基于熔体发泡法泡沫铝填充管力学性能研究

采用熔体发泡法制备闭孔泡沫铝,研究泡沫铝填充密度对铝合金薄壁管的压缩及吸能性能提升作用,对比提升效果,确定最佳密度参数;并在最佳密度的基础上设计三类不同截面的复合结构,研究填充管的截面结构对压缩性能及吸能性能的影响,确定最佳结构参数。采用万能试验机进行准静态压缩试验,并利用有限元模拟结果与试验结果相对比,验证数据准确性。结果表明:填充梯度泡沫铝会增加薄壁管的力学性能,如屈服强度、平均压溃载荷和吸能性能,降低曲线波动性,密度为0.480 5 g/cm3的闭孔泡沫铝表现出最优结果;二次试验中,复合结构能进一步提升薄壁管的力学性能,其中外方管内圆管的复合结构具有最高的屈服强度、平均压溃载荷以及吸能效果。

高温环境下多壁管增强泡沫铝压溃行为的理论分析与数值模拟研究

通过理论和数值模拟方法研究了新型高效吸能结构——多壁管增强泡沫铝在高温环境下的压溃特性及能量吸收性能。采用能量法预测了多壁管增强泡沫铝的轴向压缩平均力,在此基础上研究了温度以及泡沫铝与多壁管材料流动应力之比对结构吸能效率的影响。结果表明:理论预测值与有限元结果吻合较好,最大误差值为-6.7%;环境温度从室温上升至350℃,温度升高导致材料力学性能下降,多壁管增强泡沫铝平均力下降了1/3;另外,流动应力之比会影响多壁管半折叠波长或塑性铰数目,因此通过控制合适的流动应力之比可以提高结构吸能效率。

热处理对选区激光熔化制备的点阵结构性能影响研究

选区激光熔化(SLM)技术因其独特的成形原理成为制备复杂点阵结构的理想工艺。以钛合金骨架和片状结构为研究对象,通过数值仿真和试验相结合的方法,分析了热处理工艺对结构微观组织、力学性能、断裂机制及吸能特性的影响规律。结果表明,固溶时效热处理后钛合金中α+β相均匀分布,固溶温度的增加会使片状α'相马氏体逐渐减少而β相增多;不同热处理状态下片状结构压缩强度为骨架结构的1.81~2.17倍,平台应力为后者的3.1倍,但两者弹性模量相当,同时热处理工艺对骨架结构力学性能影响较小而对片状结构影响较大;两类结构都表现出了45°结对角剪切断裂和断裂带传递的现象;骨架结构能量吸收效率远大于片状结构,但累积能量吸收量较低,热处理工艺没有提高被测结构的吸能性能。

纤维增强复合材料缠绕管桩弯曲冲击吸能试验与模拟

纤维增强复合材料(fiber reinforced polymer, FRP)具有较高的比强度、优异的耐腐蚀性、灵活的可设计性等优点。为解决桥梁防船撞难题,提出一种缠绕成型的FRP管桩抵御船舶撞击。分别改变管桩的壁厚、缠绕角度和冲击能量,开展弯曲冲击试验,对比分析各试件的破坏模式、动力时程响应及撞击过程中能量耗散情况。结果表明,纤维缠绕角度会改变试件的破坏模式,±75°缠绕角度的试件发生了剪切破坏,而±45°缠绕角度的试件仅在冲击区域发生局部破坏,且能恢复变形;增大壁厚能有效减小试件变形,但撞击力峰值会随之增大。采用ANSYS/LS-DYNA建立了冲击试验模型并进行有限元分析,数值模拟结果与试验值吻合较好。

飞行保护头盔用复合材料结构吸收碰撞能量性能研究

针对碳纤维头盔和超高分子量聚乙烯(PE)头盔,采用坠落式冲击试验台和基于冲击加速度及头部损伤指数(HIC)评价方法,系统研究了材料种类、缓冲垫密度和服役环境温度对头盔吸收碰撞能量的影响。结果表明:随着缓冲垫密度的增加,两种头盔在低温(-20℃)条件下的冲击加速度幅值均表现出增加趋势,在常温(20℃)及高温(50℃)下,碳纤维和PE头盔壳体的冲击加速度幅值均表现出明显的降低趋势。升高温度有利于降低头盔的加速度幅值,对于80g/L和90g/L的缓冲垫,两种头盔的冲击加速度幅值随温度升高都表现出降低趋势。缓冲垫密度和温度显著影响头部损伤指数,随着温度从-20℃升高至50℃,PE头盔的头部损伤指数均表现出增加趋势,然而,碳纤维头盔在50℃表现出与常温和低温相反的趋势,即随着缓冲垫密度增加,其头部损伤指数逐渐降低,但PE头盔的头部损伤指数数值低于碳纤维头盔。两种材料在冲击载荷下的损伤形貌不同:PE头盔有明显的基体凹陷形变特征但均无裂纹形成,而碳纤维头盔均表现出明显的基体开裂及纤维断裂。碳纤维由于其高刚度,在冲击力大于破坏强度后容易产生裂纹,无法通过结构系统塑性形变吸收冲击能量,是导致其在不同缓冲垫密度和不同温度条件下,头部损伤指数以及加速度幅值均高于PE的主要原因。PE具有较高的缓冲作用和吸收冲击能量能力,因此,虽然均表现出较大基体凹陷,但均无裂纹形成,采用PE头盔,头部损伤指数和加速度幅值都低于同等条件下的碳纤维头盔。

功能梯度三周期极小曲面静动态力学特性

功能梯度设计能够有效提高结构的力学特性及吸能性能.为探讨功能梯度极小曲面结构在静动态载荷下的力学响应以及梯度壁厚分布方式对其力学特性的影响规律,构建了包含线性梯度和多种非线性梯度(对数梯度、Sigmoid梯度以及指数梯度)Gyroid结构,通过3D打印光敏树脂制备样件开展了准静态压缩试验,采用LS-DYNA构建仿真模型并与试验结果对比,验证了仿真方法的有效性.研究发现,功能梯度壁厚分布方式显著影响结构力学性能及变形模式.在准静态压缩下,功能梯度结构呈现逐层压溃的变形模式,在接触端产生局部的致密化带,这一模式导致梯度结构吸能特性有一定提升.基于准静态测试数据以及试验变形模式分析,构建了Gibson-Ashby模型,揭示了均质结构弹性模量和屈服强度随等效密度的变化规律;利用该Gibson-Ashby模型,预测了功能梯度结构屈服强度,并构建等应力模型预测了梯度结构的弹性模量,预测结果与实验值具有良好的一致性.对于其动态力学性能,构建了4种冲击速度仿真模型,深入探讨不同冲击速度对梯度结构力学性能的影响规律.功能梯度结构在高速冲击下,由于其壁厚逐层递增的特性,其局部压溃现象更为明显,导致其在高速冲击下的致密化应变显著增大,其吸能特性也有所提升.其中,对数梯度结构具有最高的屈服强度,而Sigmoid梯度结构具有最高的平均平台应力和吸能特性,其比吸能特性为13.01 J/g,相较于相对密度为45%的均质结构而言提升了45%.此外,基于刚性-完美塑性-锁定模型对梯度结构的动态平台应力进行拟合预测,拟合结果与仿真结果吻合度较高,为预测功能梯度结构的动态力学响应提供了计算方法.

矩形泡沫铝填充镀锌钢管静态压缩性能研究

采用94个试验方案,研究了泡沫铝填充矩形镀锌钢管在静态压缩下的性能。对试验结果进行分析可知,矩形泡沫铝填充镀锌钢管在静态压缩过程中经历了弹性阶段和屈服平台阶段,其平均压溃载荷、极限压溃载荷和吸能能力随着泡沫铝相对密度和钢管厚度的增加而增加,而其受构件长度的影响较小,特别是平均压溃载荷几乎无变化,极限压溃载荷随构件长度增大而略有减少。同时将试验结果与理论公式进行了比较,两者数值非常吻合。

高温环境下碳纤维层合板的抗弹性能分析

碳纤维增强复合材料(CFRP)层合板的轻质防护结构设计需要考虑其在极端环境下的抗冲击性能,尤其是高温环境特征。方法采用实验和数值模拟相结合的方式开展了CFRP层合板在高温下的抗弹性能和损伤机制分析。结果结果发现,在25(常温)、75和125℃下,2mm厚度的CFRP层合板的弹道极限分别是191、176和189 m/s。由此可知,CFRP层合板的弹道极限随着温度的升高呈先降后升趋势。随着冲击能量的增加,层合板能量吸收呈线性增加。在冲击能量较低时,CFRP层合板能量吸收随温度升高而增大;随着冲击能量的增加,温度对能量吸收的影响逐渐减小。在球弹的高速撞击下,层合板正面出现凹陷,背面出现凸起,损伤模式主要为纤维断裂、基体压溃和纤维分层等。其中,相比常温环境,高温下层合板的背面凸起显著减小,但侵彻通道附近的分层损伤会加重,产生的纤维碎屑会减少。对比层合板的分层失效特征,发现环境温度为75℃时损伤最严重。结论研究结果可为CFRP层合板在航空航天、民用等轻型装甲防护结构中的设计和应用提供依据和参考。

组合减震技术在加固改造项目中的应用

以新冠肺炎疫情期间的应急项目加固改造为例,主要探究组合减震技术在加固改造项目中的应用。鉴于既有结构抗震性能以及防震缝宽度不足、结构整体扭转和局部抗震承载力不足的问题,兼顾加固工程量、最大限度减轻对原有建筑影响以及加固成本,最终采用组合减震技术(VFW+BRB)对原有框架进行加固设计。根据项目实际情况,按照不同的部位和重要程度制定了性能目标和设计。计算结果表明,采用组合减震技术加固后的结构在遭遇地震作用时,可以显著减少顶点位移和水平加速度,降低地震响应,提高结构抗震冗余度。

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针对普通金属材料密度大、易生锈、易磨损及吸能效果差等问题,文章以自然界的淡水龙虾和螃蟹螯作为仿生原型,设计了一种纤维增强复合材料模型。利用有限元模拟的方法对设计的复合材料模型进行了数值模拟对比分析,对复合材料模型的抗压性能、抗扭性能、吸能性能和表面摩擦性能进行了研究。

植筋连接对既有结构的消能减震效果分析

针对传统抗震加固法建设工期长、工程费用高、现场湿作业较多的问题,以过去的施工经验为依据,采用植筋连接将黏滞阻尼器连接墙安装在既有建筑结构上,提出了一种新的消能减震框架子结构施工方案。解决了如何将墙式连接消能减震技术应用到既有建筑结构上的问题,实现了既有建筑结构抗震加固的设计要求。