冲击块与金属圆柱壳相互作用的缓冲吸能分析

应用Johnson Cook本构方程, 结合Singace叠缩模型,考虑冲击作用引起材料的应变强化效应、应变率强化效应和温度效应,研究了冲击物体和金属圆柱壳相互作用的能量转化过程。运用角度增量叠缩法计算了圆柱壳的塑性变形能,根据冲击块和圆柱壳所组成系统能量守恒得到了冲击块速度位移、冲击块和圆柱壳之间瞬时载荷的解析表达式,以及圆柱壳塑性变形引起的温度分布函数。通过对不同材质的金属圆柱壳在冲击作用下塑性变形过程的计算分析,并和有限元计算结果比较,证明了本文计算方法的正确性。     

非轴对称移动载荷下有限长圆柱厚壳的动力响应

本文在介绍圆柱厚壳应力与位移理论分析发展的前提下,建立了有限长圆柱厚壳在非轴对称移动载荷作用下的三维力学模型,假设沿厚度方向径向剪切应变二次分布、径向正应变线性分布,且建立了为满足边界条件待定的位移表达式,采用Heaviside函数和Dirac函数表达移动和作用变化着的移动载荷的基础上,用最小势能原理建立了该圆柱厚壳的动力学微分方程组,应用Galerkin法和修正的Runge–Kutta–Fehlberg法,求得了非轴对称移动载荷作用下的圆柱厚壳的动力响应。通过具体算例,对有限长圆柱厚壳的位移响应和应力状态进行了分析,并将动态响应的理论解与ANSYS数值解进行了对比,从而相互印证了解的可靠性。     

金属圆柱壳参数变化对缓冲吸能的影响

根据能量守恒以及角度增量叠缩法研究得到了圆柱壳在采用不同的材料以及不同几何参数时的冲击块的速度位移曲线、圆柱壳的载荷以及瞬时载荷位移历程曲线，计算结果说明改变圆柱壳的材料以及几何参数可以确定合理的平均载荷以及瞬时载荷位移历程曲线，还可以通过增加圆柱壳的数量减少圆柱壳在塑性变形叠缩过程中的垂直位移。     

载荷脉宽对圆柱壳瞬态响应的影响分析

为认识载荷脉宽对圆柱壳瞬态响应及其对X射线冲击响应模拟等效性的影响规律,定义了等效性评价指标即平均应变差异。以四种不同尺寸的典型圆柱壳为对象,分别加载六种冲量相同、脉宽不同的三角形脉冲载荷,通过数值模拟,获得了平均应变差异Δε随脉宽变化的关系,从结构特性角度分析了变化的原因。发现Δε主要受t/τ(脉宽占比)控制,t/τ≤0.45时,平均应变差异在20%以内。所得结果可为模拟X射线冲击环境的试验设计、结果评估和数值模拟提供参考。     

循环压缩和冲击下聚氨酯发泡塑料的能量吸收

基于聚氨酯发泡塑料的准静态压缩和落锤冲击试验,分析其在中低应变率下的力学性能和能量吸收性能,得到了该材料的应力-应变曲线和能量吸收图,研究了不同应变率和循环静动态试验对该材料缓冲性能的影响。随着初始应变率由2.56×10-3s-1(准静态)增加至4.01×101s-1、5.08×101s-1和5.68×101s-1,材料的应力和能量吸收明显增大,应变为0.4时动态应力分别比静态应力增加了54.34%、79.35%和114.49%,所吸收的能量分别比静态增加了18.98%、30.09%和65.74%。对同一试样先后进行五次循环准静态压缩或落锤冲击试验,与首次试验相比第二、三、四、五次试验应力和能量吸收明显下降,应变为0.4时静态应力分别下降了18.48%、32.97%、36.59%和39.49%,动态应力分别下降了20.81%、28.48%、34.75%和34.75%,准静态压缩能量吸收分别下降了24.54%、37.50%、40.74%和43.52%,落锤冲击能量吸收分别下降了15.30%、24.20%、30.25%和30.96%。中低应变率下,聚氨酯发泡塑料的应变率效应十分明显,循环准静态压缩和落锤冲击效应同样十分明显。循环试验达到一定次数后,材料缓冲性能基本保持不变,可用此数据作为缓冲包装设计的依据。研究结果对于聚氨酯发泡塑料的合理缓冲包装设计有指导意义。     

新型矩形蜂窝夹芯夹层加筋圆柱壳抗水下爆炸冲击载荷分析

提出了一种新型矩形蜂窝夹芯夹层加筋圆柱壳结构形式。分析了其在水下爆炸冲击载荷下的动力响应特征及     

一般边界条件下受轴向冲击圆柱壳的动力特性计算分析

在受轴向冲击圆柱壳的非冲击端引入轴向、周向、径向和径向旋转4个方向边界弹簧模拟一般边界条件。根据Love薄壳理论得到圆柱壳变形过程中的应力应变,并采用一种改进的Fourier级数方法表示圆柱壳沿坐标轴方向的位移。将应力应变以及位移代入圆柱壳的能量表达式,采用基于Hamilton方程的一阶变分法对能量表达式进行推导和变换,得到一般边界条件下受轴向冲击圆柱壳的自然频率以及动力屈曲临界载荷的判别式。计算分析了一般边界条件对受轴向冲击圆柱壳的自然频率和屈曲临界载荷的影响,以及不同边界条件圆柱壳屈曲模态的类型特点。结果表明：一般边界条件下自然频率随着冲击载荷增大而降低;随着轴向波数的增加圆柱壳自然频率及屈曲临界载荷增大,随着周向波数的增加屈曲临界载荷也增大;轴向、周向、径向和径向旋转各个方向边界刚度对圆柱壳自然频率和屈曲临界载荷的影响都是刚度系数越小,自然频率越低而临界载荷越大;圆柱壳受轴向冲击,边界条件的改变会影响屈曲模态。     

流体作用下正交各向异性圆锥壳的自由振动

给出了流体载荷作用下正交各向异性圆锥壳体的自由振动理论模型。通过波传播法和Galerkin法得到了流体载荷作用下截锥壳体自由振动的解。流体载荷作用下的锥壳被划分为好几段,并且每个小圆锥段被当作一个小圆柱段。通过确定每个小圆柱段的流体载荷,来确定锥壳的流体载荷。这样,作用在锥壳上的流体载荷逐段加载。流体载何以及没有流体载荷作用的各向同性和正交各向异性圆锥壳的数值结果被计算出来阐述求解过程的有效性。     

钢质圆柱壳在侧向局部冲击荷载下的变形及失效破坏

基于动力有限元程序LS-DYNA及随动塑性Cowper-Symonds模型,对两端固支钢质薄壁圆柱壳经受半球头弹体侧向局部冲击的非线性动力响应问题进行数值模拟,获得了不同冲击条件下圆柱壳的变形及破坏模态,并研究了弹体在不同周向冲击倾角时壳壁产生穿透性破裂的最小速度（临界破裂速度）。研究表明,圆柱壳破坏模式与弹体冲击倾角θ0、冲击速度V等因素密切相关,将发生局部凹陷、碟形变形及穿透现象,且临界破裂速度随冲击倾角的增大而增大。研究结果可应用于圆柱壳在侧向局部冲击作用下的毁伤预测,从而为圆柱壳结构的安全防护设计提供理论依据。     

冲击载荷识别的瞬态统计能量分析方法

提出了一种基于瞬态统计能量分析理论的冲击载荷识别新方法。利用该方法,首先由系统能量平衡方程确定冲击载荷的作用位置及相应的输入能量,在常值假设条件下根据识别的输入能量反演得到冲击载荷的幅值谱,在此基础上,对于给定的冲击载荷时域波形形式,提出一种参数拟合方法用于最终重建冲击载荷的时间历程。通过一个两板耦合结构系统的冲击载荷识别对识别方法进行了实验验证研究。结果表明冲击载荷识别的瞬态统计能量分析法能够准确地识别冲击载荷的作用位置和输入能量,在冲击波形已知的假设条件下可以较为准确地重建冲击载荷的时间历程,从而为实际工程中的冲击载荷识别提供了一条可行途径。     

Energy absorption mechanisms during dynamic fracturing of fibre-reinforced composites

Dynamic photoelastic experiments were conducted to study crack propagation in fibrereinforced materials and, in particular, to determine the energy losses occurring during the crack growth and arrest process. This study utilized modified compact tension specimens which were fabricated from polyester matrix and different reinforcing fibres. The effect of the fibre-matrix interface on energy absorbed was also studied. The energy absorbed was partitioned into two parts: that absorbed in the fracture process zone associated with the crack tip, and the energy lost outside this zone. Results show that fibre reinforcement reduces the energy absorbed in the fracture process zone by about 10% for well-bonded and 15% for partly debonded fibres. For the same initial strain energy, this reduction in fracture energy manifests itself in reduced K _ID and lower crack-jump distance as compared to monolithic specimens. Reinforced specimens are found to retain a higher strain energy after crack arrest. The energy absorbed outside the fracture process zone for monolithic and well-bonded fibres is about 45% of the initial strain energy, while for partly debonded fibres it is about 55%.     

In-plane impact behavior of honeycomb structures randomly filled with rigid inclusions

The in-plane impact behavior of honeycomb structures randomly filled with rigid inclusions was studied by using the finite element method to clarify the effect of inclusions on the deformation process, mean stress, densification strain, and absorbed energy. The deformation processes of the models were disturbed by inclusions; shear bands were pinned, and the cell regions surrounded by inclusions were shielded. Mean stress, densification strain, and absorbed energy per unit volume normalized by the values of the model without inclusions were found to be only dependent on the fraction of inclusions. As the volume fraction of inclusions increased, the normalized mean stress linearly increased and the normalized densification strain linearly decreased. The normalized absorbed energy per unit volume could be approximated by an inverted parabolic equation. The energy absorption of models with inclusions having volume fractions from 0 to 0.25 was larger than that of the models without inclusions. In particular, honeycomb models with fractions of inclusion from 0.1 to 0.2 exhibited the maximum absorbed energy. The model with a volume fraction larger than 0.4 could not be compressed because the inclusions in the model had already percolated before deformation. The in-plane impact behavior of honeycomb structures as energy absorbing materials can be designed by using the approximate equation and selecting the volume fraction of inclusions.     

Considerations in straight fold analysis of thin tubes under axial compression

A straight fold model for the analysis of the tubes under axial compression is reconsidered. Based on experiments, the tube is assumed to fold partly inside and partly outside the mean diameter of tube. The model considers the variation of circumferential strain during the formation of a fold, change in thickness of the tube during the deformation, and the influence of change in the yield strength of material in tension and compression. The first fold ends at the mean diameter and all subsequent folds initiate and end at the mean diameter. Some parameters have been introduced for making the expressions valid for first as well as the subsequent folds. The size of fold, load–compression curves, variation of inside and outside fold lengths and mean crushing load have been computed. All the variables involved in the analysis such as, the size of fold, folding parameter, mean crushing load, and the peak load have been obtained analytically. The model developed has been validated with the experiments.     

On the response of thin-walled CFRP composite tubular components subjected to static and dynamic axial compressive loading: experimental

In this work the crushing response and crashworthiness characteristics of thin-wall square FRP (fibre reinforced plastic) tubes that were impact tested at high compressive strain rate are compared to the response of the same tubes in static axial compressive loading. The material combination of the tested specimens was carbon fibres in the form of reinforcing woven fabric in epoxy resin, and the tested tubes were constructed trying three different laminate stacking sequences and fibre volume contents on approximately the same square cross-section. Comparison of the static and dynamic crushing characteristics is made by examining the collapse modes, the shape of the load–displacement curves, the peak and average compressive load and the absorbed amount of crushing energy in both loading cases. In addition, the influence of the tube geometry (axial length, aspect ratio and wall thickness), the laminate material properties-such as the fibre volume content and stacking sequence-and the compressive strain rate on the compressive response, the collapse modes, the size of the peak load and the energy absorbing capability of the thin-wall tubes is extensively analysed.     

Hygrothermal effects on the dynamic compressive properties of graphite/epoxy composite material

The effects of temperature and moisture on the response of graphite/epoxy laminated composites to high strain rate penetration loading using the Split Hopkinson Pressure Bar apparatus was investigated. The results show that in the thickness direction loading under extreme temperature, moisture and combined moisture and temperature conditions, the compressive strength, elastic modulus, and energy absorbed decrease exponentially. Failure strain and displacement increase linearly with temperature and moisture with particle velocity increasing linearly with temperature but independent of moisture content. The combined effect of temperature and moisture on the damage process was more apparent than the effect of temperature or moisture acting alone. At the same impact energy, the results show the failure properties to be sensitive to the strain rate, with energy absorbed increasing linearly with strain rate at low temperature and remaining relatively constant at high temperature. The compressive yield strength increases as the strain rate increases both at low and high temperatures while the ultimate strength (maximum strength) decreases slightly with strain rate.     

Energy absorption during projectile perforation of lightweight sandwich panels with metallic fibre cores

This paper concerns energy absorption during projectile penetration of thin, lightweight sandwich panels with metallic fibre cores. The panels were made entirely of austenitic stainless steel (grade 304). The faceplates were 0.4 mm thick and the core (∼1–2 mm thick) was a random assembly of metallic fibres, consolidated by solid state sintering. The impact tests were simulated using ABAQUS. Faceplate behaviour was modelled using the Johnson and Cook plasticity relation and a strain rate-dependent, critical plastic strain failure criterion. The core was modelled as an anisotropic, compressible continuum, with failure based on a quadratic, shear stress-based criterion. The experimental data show that, with increasing impact velocity, the absorbed energy decreased from the ballistic limit, reached a minimum value, and then underwent a monotonic increase. The FEM modelling demonstrates that this increase arises from the kinetic energy of ejected fragments, while the energy absorbed by plastic deformation and fracture tends to a plateau. Normalised absorbed energies have been compared to values for single faceplates. The sandwich panels are marginally superior to single plates on an areal density basis.     

STRAIN ENERGY ASSOCIATED WITH STRUCTURAL MODIFICATIONS

Modifications to linear elastic structures are considered for which the amount of additional stiffening material is increased proportionally. It is proved that, for fixed loading, the strain energy will not be increased and, for fixed displacements, the strain energy will not be decreased by the addition. Furthermore the graphs of strain energy versus the amount of additional material will be monotonic. Also the strain energy absorbed by an incremental amount of additional material must equal the change in the total strain energy for both the cases of fixed loading and fixed displacements. These behavioural properties have been formulated as three theorems. The paper justifies and discusses these and presents some simple illustrations.     

装甲用镁合金抗弹性能表征体系探讨

介绍了高应变率载荷条件下镁合金的吸能特性及变形特征；论述了对镁合金抗弹性能有重要影响的动态强度、高应变率能量吸收率、高应变率变形断裂特征和动态强度等科学问题；就镁合金在装甲领域的应用研究做了初步探讨。     

Effect of triggering and polyurethane foam-filler on axial crushing of natural flax/epoxy composite tubes

In this study, empty and polyurethane-foam filled flax fabric reinforced epoxy composite tubes were longitudinally crushed under quasi-static compression. The effects of foam-filler (density of 160 kg/m³, two diameters of 64 and 86 mm), tube thickness (2, 4 and 6 plies of laminate), and triggering (45° edge chamfering) and the combination of triggering and foam-filler on the crushing characteristics and energy absorption capacity of these tubes were investigated. The test results indicate that the observed primary failure mode was progressive crushing for all the specimens. Foam-filled tubes have better crashworthiness than empty tubes in total absorbed energy, specific absorbed energy and crush force efficiency. The presence of triggering has no significant effect on total absorbed energy and specific absorbed energy of the empty tubes. However, the crush force efficiency of triggered tube is significantly larger compared to the non-triggered one. In addition, the triggering minimises the force variation of the tubes from the average crush force and in turn a more stable progressive crushing is achieved. The foam-filled and triggered tubes have better crashworthiness than the empty tubes in all the aspects. Compared with either triggered or foam-filled tubes, the triggered and foam-filled tubes have larger values in average crush load and crush force efficiency. In terms of total absorbed energy and specific absorbed energy, the triggered and foam-filled tubes have values always larger than those of the tubes with triggering only, but these values are either larger or smaller than the tubes with foam-filler only.     

裂隙岩体冲击韧性及破坏模式实验

为研究裂隙对岩体冲击韧性及破坏模式的影响规律,以及裂隙岩体在高应变率下的动态破坏特征,采用摆锤式冲击实验机对裂隙及完整岩体进行了不同冲击速度、不同裂隙条件下的冲击实验。实验结果表明,对长度相同的完整试件而言,试件直径越大,即试件体积越大,试件破碎就越充分,断面也越不规整;试件中的裂隙长度越长,试件破坏时的吸收功就越小,冲击韧性也越小,试件吸收功和冲击韧性随裂隙长度的增加而减小;试件裂隙角度越大,试件破坏断面就越不规整,试件破坏后的块度也越不均匀,试件吸收功和冲击韧性随裂隙倾角的增大而减小。