Transient impact responses of laminated composite cylindrical shells

The generalized ray method(GRM) has been successfully used to study the transient elastic wave transmitting in the beams,planar trusses,space frames and infinite layered media.In this letter,the GRM is extended to investigate the early short time transient responses of laminated composite cylindrical shells under impact load.By using the Laplace transformation and referring to the boundary conditions,the ray groups transmitting in the finite laminated cylindrical shells under the shock load are obtained and the transient response related to each ray group can be derived via FFT algorithm.From the numerical results,it is shown that the early short time transient accelerations of the laminated composite cylindrical shell under impact loads are very large.But the short time transient shear strain and displacement are very small.

Axial impact response of composite cylindrical shell

Following Love's shell theory and classical lamination theory, governing equation of composite cylindrical shell in the axisymmetric deformation was established with radial displacements expressed in terms of Fourier series, and numerical results given for axial impact response of laminated shell with simple support will be used to further study of dynamic stability of composite shell.

Low velocity impact response and energy absorption behavior on glass fibre reinforced epoxy composites

A study was undertaken to determine the effects of several key geometry influencing factors on the impact response and energy absorption behavior of the glass fibre reinforced epoxy composites at low and intermediate energies.The energy-balance model was employed for characterising the energy absorption behavior and it depends strongly on the plate diameter and thickness.In addition,the damage vs.energy and force maps is effective in monitoring damage growth within the composite panel.The response of the composite laminate configurations characterized by different stacking sequences subjected to low velocity impacts with different impact energies have also been studied to estimate the damage initiation of composites.

Experimental Study on the Energy Absorption Properties of MWK Reinforced Composites

The energy absorption properties of MWK fabric reinforced composite plates were studied. Low velocity and low energy impact experiments were carried out for MWK fabric reinforced Glassfibre/Epoxy composite plate, by setting up a drop weight impact test system. Using this system, the drop weight velocity during impacting was obtained and recorded by transducer and corresponding signal processing system. Based on the velocity record, the impact energy and dissipated impact energy (energy absorption) were obtained. The influences of structure parameters of MWK on the impact behavior and energy absorption properties were then investigated.

Performance study of jute-epoxy composites/sandwiches under normal ballistic impact

This study is undertaken to explore the use of natural fiber Jute-epoxy(JE),Jute-epoxy-rubber(JRE)sandwich composite for ballistic energy absorption.Energy absorbed and residual velocities for these composites are evaluated analytically and through Finite Element Analysis(FEA).FE analysis of JE plates is carried out for different thicknesses(3,5,10 and 15 mm).JE plates and JRE sandwiches having the same thickness(15 mm) are fabricated and tested to measure residual velocity and energy absorbed.The analytical results are found to agree well with the results of FE analysis with a maximum error of 9%.The study on JE composite plate reveals that thickness influences the energy absorption.Experimental and FE analysis study showed that JRE sandwiches have better energy absorption than JE plates.Energy absorption of a JRE sandwich is about 71% greater than JE plates.Damages obtained from FEA and testing are in good agreement,SEM analysis confirms composites failed by fiber rupture and fragmentation.

Mechanical characteristics of composite honeycomb sandwichstructures under oblique impact

Carbon fiber reinforced polymer(CFRP)and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact.The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment.The oblique impact model is established,and the reliability of the model is verified by the oblique impact test.To further analyze the influence of structural parameters on energy absorption under oblique impact,the influence of impact angle,face sheet thickness and wall thickness of the honeycomb is numerically studied.The results show that the impact angle has an important effect on energy distribution.The structural parameters also have an effect on the peak contact force,contact time,and energy absorption,and the effect is different from normal impact due to the presence of frictional dissipation energy.Compared with normal impact,the debonding of oblique impact will be reduced,but the buckling range of the honeycomb core will be expanded.

Ballistic impact response of flexible and rigid UHMWPE textile composites:Experiments and simulations

This study elaborates on the effects of matrix rigidity on the high-velocity impact behaviour of UHMWPE textile composites using experimental and numerical methods.Textile composite samples were manufactured of a plain-weave fabric(comprising Spectra?1000 fibres)and four different matrix materials.High-velocity impact tests were conducted by launching a spherical steel projectile to strike on the prepared samples via a gas gun.The experimental results showed that the textile composites gradually changed from a membrane stretching mode to a plate bending mode as the matrix rigidity and thickness increased.The composites deformed in the membrane stretching mode had higher impact resistance and energy absorption capacity,and it was found that the average energy absorption per ply was much higher in this mode,although the number of broken yarns was smaller in the perforated samples.Moreover,the flexible matrix composites always had higher perforation resistance but larger deformation than the rigid matrix counterparts in the tested thickness and velocity range.A novel numerical modelling approach with enhanced computational efficiency was proposed to simulate textile composites in mesoscale resolution.The simulation results revealed that stress and strain development in the more rigid matrix composite was localised in the vicinity of the impact location,leading to larger local deformation and inferior perforation resistance.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites(GFRP)subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance.Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities,which is confirmed as a sensitive factor for the failure modes and mechanisms.The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%,but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit.The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect.The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities.Based on the energy absorption mechanisms,analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy,the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

Analysis of energy release rate for composite delaminated cylindrical shells subjected to axial compression

In this paper, the postbuckling governing equations and the analytical expression of the energy release rates associated with delamination growth in a compression-loaded cylindrical shell are derived by using the variational principle of moving boundary and the Griffith fracture criterion. The finite difference method is used to generate the postbuckling solutions of the delaminated cylindrical shells, and with these solutions, the values of the energy release rates are determined. In simulational examples, the effects of a wide range of parameters, such as delamination sizes and depths, boundary conditions, geometrical parameters, material properties and laminate stacking sequences on the energy release rates of axisymmetrical laminated cylindrical shells are intensively discussed.

Delamination growth for composite laminated cylindrical shells under external pressure

The delamination growth may occur in delaminated cylindrical shells＇under external pressure. This will lead to failure of structure. By using the variational principle of moving boundary and considering the contact effect between delamination regions, in this work, the delamination growth was investigated for cylindrical shells under the action of external pressure. At the same time, according to the Griffith criterion, the formulas of energy release rate along the delamination front were obtained. In the numerical calculation, the delamination growth of axisymmetrical laminated cylindrical shells was analyzed, and the effects of delamination sizes and depths, the geometrical parameters, the material properties, and the laminate stacking sequences on delamination growth were discussed.

Ballistic Penetration Damage of Hybrid Thermoplastic Composites Reinforced with Kevlar and UHMWPE Fabrics

Polymer matrix types of fiber hybrid composites are key factors to improve ballistic impact damage tolerances.Here we report ballistic penetration damages of Kevlar/ultra-high molecular weight polyethylene(UHMWPE)hybrid composites with thermoplastic polyurethane(PU)matrix.The hybrid composites were penetrated by fragment-simulating projectiles(FSPs)using an air gun impact system.The effects of stacking sequences on the ballistic performance of hybrid composites were analyzed.Two types of specific energy absorption(the energy absorption per unit area density and the energy absorption per unit thickness)were investigated.It was found that the main damage modes of PU hybrid composites were fiber breakage,matrix damage,fiber pullout and interlayer delamination.The instantaneous deformation could not be used as a reference index for evaluating the ballistic performance of the target plate.The energy absorption process of the PU hybrid composites showed a nonlinear pattern.The hybrid structure affected the specific energy absorption of the materials.

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。

金属薄锥壳冲击响应行为及载荷特征研究进展综述

目的系统总结薄锥壳冲击试验方法和数值模拟方法,并分析其响应行为和载荷特征,以发展基于薄锥壳塑性变形的冲击载荷等效加载技术。方法全面调研国内外关于薄锥壳结构冲击响应的工作,总结其冲击试验加载技术和数值模拟方法,主要利用冲击块加速度变化以及载荷-位移曲线对薄锥壳力学响应及能量吸收特性进行表征,并结合弹塑性应力波进行理论分析。结论金属薄锥壳冲击试验加载方法主要有落锤冲击、化爆脉冲加载和气压推动质量块进行撞击等,数值模拟中通常采用刚性板挤压金属壳单元的方法进行验证。除对薄锥壳轴向加载外,还有斜向加载、引入刻槽、泡沫材料填充和复合材料夹层等试验设计。该领域研究仍处于初期发展阶段,今后有必要结合试验测试与数值模拟分析,全面而深入地研究薄锥壳参数变化对其冲击响应行为和载荷特征的影响规律及其物理机制。

重复冲击载荷下泡沫铝夹芯壳的动态响应

通过数值模拟研究了泡沫铝夹芯壳在重复冲击载荷作用下的变形和能量耗散机理,分析了曲率半径、前后面板厚度分配、芯层厚度和冲击能量梯度对结构抗重复冲击性能和能量吸收能力的影响规律。结果表明:在重复冲击载荷作用下,泡沫铝夹芯壳结构的变形不断累积,前面板局部弯曲变形,芯层局部压缩,后面板整体弯曲变形。随着冲击次数的增加,冲击力峰值逐渐增大,冲击持续时间缩短,结构能量吸收能力降低,整体抗弯刚度增大。每次冲击能量相同时,泡沫铝夹芯壳结构曲率越大,能量吸收能力越强,同时前、后面板5次重复冲击后的中点挠度大于曲率较小的夹芯壳结构。5次重复冲击载荷作用下,前面板厚度较大且后面板厚度较小时,结构的比吸能较低,但后面板中点挠度较小。泡沫铝芯层厚度越大,结构的后面板挠度越小,但总比吸能降低。3种不同梯度的冲击能量作用下,递增能量工况下结构的吸能最多,前、后面板的挠度较大,递减能量工况下结构的吸能最少,前、后面板的挠度较小。

玻璃-环氧圆柱壳吸能特性的试验研究

主要研究［±θ］５玻璃－环氧圆柱壳在轴向压缩载荷作用下的吸能特性。通过试验研究，分析了纤维缠绕角度对能量吸收性能的影响；比较了不同纤维缠绕角度的圆柱壳在不同加载条件下的压缩过程、压碎破坏模式及吸能能力。

玻璃-环氧圆柱壳的撞击吸能分析

玻璃－环氧圆柱壳（管）的撞击试验表明它的破坏是渐进过程。根据一维应力波传播理论，提出了圆柱壳受轴向撞击破坏的简化模型，分析了这一破坏过程中的能量变化。结果表明本文中所提出的模型能较好地描述圆柱壳受轴向撞击吸能过程。

高速冲击下薄壁组合结构吸能特性研究

研究了高速冲击下组合薄壁结构的吸能特性。采用显式动力有限元方法模拟薄壁结构在轴向冲击下的动态屈曲并分析其吸能特性,通过在结构上增加诱导缺陷和提出新型组合截面来提高其抗冲击吸能性能。同时对多种模型对比分析,研究了不同诱导缺陷、截面形式对吸能特性的影响,以得到最优化的结构。

复合材料的冲击吸能与动态黏弹特性

考察了玻璃纤维、炭纤维、芳纶和UHMWPE纤维复合材料(分别称为GFRP,CFRP,AFRP和DFRP)层板的低速冲击吸能,并采用高载动态热机械分析仪EPLEX-OR500分析了其纤维复丝的动态黏弹性的载荷敏感性.结果表明:冲击吸能明显受纤维性能及层板破坏模式的影响,呈韧性破坏的AFRP和DFRP的冲击吸能明显高于呈脆性破坏的GFRP和CFRP.在动态热机械分析中,静载增大使得储能模量升高但损耗角正切减小,动载增大时正好相反,且在这些影响中有机纤维复丝动态黏弹性较无机纤维复丝表现出更显著的载荷敏感性和非线性.4种层板的吸能大小与其纤维复丝储能模量载荷敏感性的强弱以及损耗角正切大小的顺序相同:DFRP>AFRP>GFRP>CFRP,反映出材料宏观冲击性能与表征其微观结构特征的黏弹性能的相关性.

引发方式、铺层对纤维增强复合材料圆柱壳吸能特性影响的冲击试验研究

对作为吸能元件的纤维增强复合材料圆柱壳的吸能特性进行了试验研究。制备了不同铺层角度和不同引发方式的玻璃纤维/聚酯树脂基圆柱壳,通过对该圆柱壳进行动态试验,探求铺层方式和引发方式对该吸能元件吸能效果的影响,以及该复合材料层合壳体压溃过程的破坏机理。

复合材料结构的能量吸收

针对缠绕成型的 [± 75 ]n玻璃纤维 /聚酯和 [0 /± 75 ]n玻璃纤维 /环氧树脂圆柱管的轴向与非轴向压缩失效行为及能量吸收特性进行了研究 (轴压的倾斜角度变化范围 0～ 2 5°) ,分析了复合材料圆柱管的宏观破坏模式和能量吸收机理 ,比较了轴向与非轴向载荷下能量吸收的特点 .研究表明 :复合材料圆柱管在偏轴角度下其压缩损伤过程可分为 3个阶段 ,即初始引发阶段、稳态渐进阶段以及压实或失稳阶段 ;