Finite element modeling of impact, damage evolution and penetration of thick-section composites

Impact, damage evolution and penetration of thick-section composites are investigated using explicit finite element (FE) analysis. A full 3D FE model of impact on thick-section composites is developed. The analysis includes initiation and progressive damage of the composite during impact and penetration over a wide range of impact velocities, i.e., from 50 m/s to 1000 m/s. Low velocity impact damage is modeled using a set of computational parameters determined through parametric simulation of quasi-static punch shear experiments. At intermediate and high impact velocities, complete penetration of the composite plate is predicted with higher residual velocities than experiments. This observation revealed that the penetration-erosion phenomenology is a function of post-damage material softening parameters, strain rate dependent parameters and erosion strain parameters. With the correct choice of these parameters, the finite element model accurately correlates with ballistic impact experiments. The validated FE model is then used to generate the time history of projectile velocity, displacement and penetration resistance force. Based on the experimental and computational results, the impact and penetration process is divided into two phases, i.e., short time Phase I - shock compression, and long time Phase II - penetration. Detailed damage and penetration mechanisms during these phases are presented.     

Dynamic penetration of graphite/epoxy laminates impacted by a blunt-ended projectile

The dynamic penetration of graphite/epoxy laminates as a result of impact by a blunt-ended projectile is investigated in the present study. The ballistic limit is determined by a series of high-velocity impact tests. A dynamic finite element analysis is performed to simulate the penetration process in composite laminates. A previously developed static penetration model is incorporated into the analysis to predict the ballistic limit. The ballistic characteristics are represented by the relationship between the striking and residual velocities of the projectile. Good agreement between experimental data and computational results implies that the ballistic limit of graphite/epoxy laminates can be predicted by the present analysis without performing dynamic impact tests.     

Prediction of low velocity impact damage in carbon–epoxy laminates

It is well known that composite laminates are easily damaged by low velocity impact. This event causes internal delaminations that can drastically reduce the compressive strength of laminates. In this study, numerical and experimental analyses for predicting the damage in carbon–epoxy laminates, subjected to low velocity impact, were performed. Two different laminates (0₄,90₄)_s and (0₂,±45₂,90₂)_s were tested using a drop weight testing machine. Damage characterisation was carried out using X-rays radiography and the deply technique. The developed numerical model is based on a special shell finite element that guarantees interlaminar shear stresses continuity between different oriented layers, which was considered fundamental to predict delaminations. In order to predict the occurrence of matrix failure and the delaminated areas, a new failure criterion based on experimental observations and on other developed criteria, is included. A good agreement between experimental and numerical analysis for shape and orientation of delaminations was obtained. For delaminated areas, reasonable agreement was obtained.     

含分层损伤复合材料加筋层合板的动承载能力

采用有限元方法研究了含穿透分层损伤复合材料加筋层合板的动力响应和承载能力。根据复合材料层合板一阶剪切理论, 推导了复合材料层合板单元的刚度阵和质量阵列式;同时采用Adams 应变能法与Rayleigh阻尼模型相结合的方法, 构造了相应的阻尼阵列式;为了防止在低阶模态中分层处出现的上、下子板不合理的嵌入现象, 建立了含分层损伤复合材料加筋层合板动力分析中分层分析模型和虚拟界面联接模型。并采用Tsai提出的刚度退化准则和动力响应分析的精细积分法, 对在动荷载作用下含分层损伤复合材料加筋层合板结构进行了破坏和承载能力分析。通过典型算例分析, 分别讨论了外载频率、分层深度、筋的位置以及破坏过程中刚度退化对含损伤复合材料加筋层合板动力响应特征和承载能力的影响, 得到了一些具有理论和工程价值的结论。     

动荷载作用下含损伤复合材料层合板承载能力

研究了含分层损伤层合板的动力响应和承载能力。基于层合板的一阶剪切理论,采用分项等参插值方法推导了复合材料层合板刚度阵、质量阵列式,在瑞利阻尼的基础上构造了相应的阻尼阵列式;建立了用于含分层损伤复合材料层合板动力分析的分层模型和虚拟界面联接单元,以防止低阶模态中在分层处出现的上、下子板不合理的脱离和嵌入现象;同时又采用Tsai提出的0.44刚度退化准则和动力分析的Newmark法,对含分层损伤复合材料层合板结构进行了在动荷载作用下的破坏和承载能力分析;通过典型算例,分别讨论了外载频率,分层位置,以及刚度退化对含损伤复合材料动力响应特征和承载能力的影响。本文中提出的方法和得到的结论对复合材料工程设计具有参考价值。      

弹体高速侵彻陶瓷复合厚靶的计算模型研究

针对平头弹高速撞击陶瓷复合厚靶的问题,以集中质量法为基础并考虑靶体的内摩擦效应对Fellows模型加以改进,建立侵彻过程的理论计算模型并利用Matlab编程求得不同撞击速度下弹体侵彻复合靶体的侵彻深度,模型得到了试验结果和数值计算结果的验证。参数分析的结果表明,陶瓷厚度的增加可提高复合靶体的抗侵彻能力,但随着初始撞击速度的提高,弹体的侵彻深度增长曲线趋于平缓。     

Instrumented Tablet Press Studies on the Effect of Some Formulation and Processing Variables on the Compaction Process

Using an instrumented tablet press, compression force-time measurements were used to evaluate the effects of formulation and processing variables on the compaction process. The effects of tablet press speed, punch size, depth of upper punch penetration (into the die), and the setting of the overload spring mechanism were studied. The effects of tablet weight, particle size and amount of lubrication were also studied. Several direct compression materials which are believed to compact by different mechanisms were used in the study. The results indicate the sensitivity of the area under the compression force-time curve and the Area/Height ratio. Some of the changes seen in the area and A/H ratio were those which would be expected from a relatively simple model of compaction/compression. The results clearly show the usefulness of the instrumented tablet press as an analytical tool in the development of tablet formulations, the evaluation of processing requirements, and the remedy of tablet production problems.     

Mechanical properties of model ice ridge keels

Rubble ice presents pressure dependent yield strength and its behaviour can be described by mathematical models based on several mechanical parameters. They are investigated for HSVA model rubble ice through the analysis of three different tests: the oedometer test, the pile test and the punch test. This last test is analysed with the non-linear Eulerian finite element method. The tests were performed on 4 ice ridges with two different submersion times. A 0.5 to 1.2 kPa model scale Mohr-Coulomb cohesion (0.6 to 1.5 kPa Drucker-Prager cohesion), depending on the ridge history, was used in the simulations of the model scale punch tests. The friction angle is estimated between 30 and 45° (40 and 50° Drucker-Prager friction angle). The upper value was used in the punch test simulations. A 0.9 MPa Young modulus was derived and the hydrostatic compressive yield curve was determined. The numerical model is able to estimate the rubble action during the entire penetration of the punch test in the keel and it is shown that a cohesive softening occurs in the rubble. In order to reproduce the experimental load time series for the short submersion time ridges it was necessary to use a vertical distribution of the cohesion representing the vertical distribution of the freeze-bond strength. A sensitivity analysis of the punch test shows that the keel depth and the ice density are the main parameters governing the keel frictional resistance. A precise determination of these parameters is therefore crucial for a correct determination of the rubble mechanical properties from the numerical simulation of experimental punch tests. The punch test is not appropriate for the determination of the friction angle due to the low confinement pressure at the failure plane. The numerical analysis of the punch test allows the estimation of different assumptions used in analytical models for the rubble failure: the cohesion averaging is an under-conservative approximation, and the non-simultaneity of the cohesive and shear resistance maximum values can be considered in the peak load estimation by the computation of their quadratic mean. The comparison with full scale values shows a reasonably good scaling of the cohesion for the model ice ridges with a long submersion time.     

基于加速度测试及模糊模型的弹丸侵彻混凝土深度实时预测方法

为了对卵形弹垂直侵彻半无限厚混凝土目标的侵深进行实时预测,提出了一种基于实测加速度值及模糊模型的计算方法。该方法根据瞬时速度的不同将侵彻过程分成了高速侵彻、中速侵彻和低速侵彻三个阶段,并分别采用不同的模型对每个阶段的减加速度、速度和侵彻深度进行了描述。通过判断减加速度的计算误差,自动确定了高速侵彻阶段与中速侵彻阶段以及中速侵彻阶段与低速侵彻阶段的截点速度。同时,利用实测的全弹道加速度曲线,实时计算了侵彻过程的初始冲击速度。将实验后所测得的侵彻深度与模型预测的侵彻深度进行比较,结果表明该预测方法可以对侵彻深度进行准确地实时计算。     

Transient response of pretwisted delaminated stiffened shell under low velocity impact

The paper presents the study of low velocity impact response of delaminated composite stiffened shell with pretwist employing finite element method for different combination of stiffeners. An eight noded isoparametric shell element along with a three noded isoparametric beam element are employed to model the shell and the stiffener, respectively. The modified Hertzian contact law is considered to compute the contact force, while the Newmark's time integration algorithm is used to solve the time dependent equations of both impactor and shell. The multipoint constraint algorithm is used to model delamination. Finally, the parametric studies are reported.     

Discrete element method simulation of properties of a 3D conical hopper with mono-sized spheres

The velocity distribution and flow pattern of particles in hoppers during discharging process are of great significance when granular materials are handled in the industry, e.g., in the charging of the ironmaking blast furnace. This paper studies the flow of mono-sized glass particles and the effect of the coefficient of static friction of particle-wall on flow pattern and velocity distribution in a 3D conical hopper using the discrete element method (DEM). The validity of the calculated results was confirmed by comparing them with experimental results reported in the literature. The results show that DEM can be used to predict the behavior of the particles during hopper discharging. Particles were found to have the same velocity in almost the whole area of the hopper except in the conical orifice zone and the movement was controlled by the angular velocity during the discharging process. The flow pattern changes from mass flow to funnel flow and the wall shear layer becomes larger and wider with the increase of coefficient of static friction of particle-wall. The effect of coefficient of static friction of particle-wall on velocity distribution at wall area is obvious.     

带脱层复合材料层板的低速冲击响应

研究了含脱层损伤的复合材料层板在低速冲击下的瞬态响应问题。首先,用基于Mindlin板理论的有限元法来描述层板的运动和变形,并同时考虑了层板大变形的影响。另外,用一种修正的Hertzian压痕法则来计算层板和刚球间的冲击力。同时为了有效地处理脱层间的动态接触问题,采用了由笔者以前提出的一种修正的Lagrange multiplier乘子法来提高计算精度和效率;为了研究脱层的扩展机理,提出了一种基于Mindlin板模型的应变能释放率的计算方法,用于计算脱层前沿的应变能释放率的分布。最后,算例研究了刚球的初始冲击速度、脱层面积和脱层位置对计算结果的影响,算例中提供的信息为人们更好地理解脱层损伤的扩展机理和它对复合材料层板的低速冲击响应的影响提供了依据。     

Instrumented Tablet Press Studies on the Effect of Some Formulation and Processing Variables on the Compaction Process

Abstract

Using an instrumented tablet press, compression force-time measurements were used to evaluate the effects of formulation and processing variables on the compaction process. The effects of tablet press speed, punch size, depth of upper punch penetration (into the die), and the setting of the overload spring mechanism were studied. The effects of tablet weight, particle size and amount of lubrication were also studied. Several direct compression materials which are believed to compact by different mechanisms were used in the study. The results indicate the sensitivity of the area under the compression force-time curve and the Area/Height ratio. Some of the changes seen in the area and A/H ratio were those which would be expected from a relatively simple model of compaction/compression. The results clearly show the usefulness of the instrumented tablet press as an analytical tool in the development of tablet formulations, the evaluation of processing requirements, and the remedy of tablet production problems.     

Prediction of Impact-Induced Fibre Damage in Circular Composite Plates

A simple analytical impact damage model for preliminary design analysis is developed on the basis of experimental findings observed from quasi-static lateral load and low velocity impact tests. The analytical model uses a non-linear approximation method (Rayleigh–Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point load at its centre. It is assumed that the deformation due to a static transverse load is similar to that occurred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with finite element (FE) predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture model developed by the second investigator to estimate the compression after impact strength of such laminates. This approach could save significant running time when compared to FE numerical solutions. Corresponding author.     

Dynamic behavior of delaminated plates considering progressive failure process

The paper is to study on dynamic response behavior of the delaminated composite plates considering progressive failure process. A formula of element stiffness and mass matrices for the composite laminates is deduced by using the first-order shear deformation theory combined with the selecting numerical integration scheme. A damping model is constituted by a generalized orthogonal damping model on basis of Adams' strain energy method. A virtual interface linear spring element is also employing for avoiding the overlap and penetration phenomenon between the upper and lower sublaminates at the delamination region. The failure analysis method for the delaminated plates under dynamic loading is established by a modified Newmark direct integral method in conjunction with Tsai's failure criterion and corresponding stiffness degradation scheme. By some numerical examples, the effects of frequency of dynamic load, delamination length and location, and reduction of structure stiffness during the progressive failure process upon dynamic behavior of the delaminated composite plates are discussed. The method and conclusions would be useful for composite structures designers.     

止裂层对陶瓷复合防弹插板冲击损伤行为研究

目的 研究冲击载荷下迎弹面覆盖止裂层的复合防弹插板陶瓷面板碎裂机理和抗侵彻性能。方法 对所设计的复合防弹插板进行空气炮打靶试验,构建冲击仿真有限元计算模型。结合试验和数值模拟,研究覆盖环氧树脂、凯夫拉平纹织物止裂层及无止裂层复合防弹插板的抗侵彻性能,分析不同冲击速度下复合防弹插板陶瓷损伤失效过程。采用内聚力单元对止裂层和陶瓷之间的黏结区域进行建模,分析黏结程度对陶瓷损伤和失效的影响。结果 止裂层表面约束的陶瓷在冲击过程中产生的径向裂纹随着撞击点附近的环向拉应力波的传播而延伸。止裂层黏结作用增强时,陶瓷的冲击缺口面积增大,但质量损失基本不变;迎弹面止裂层未对侵彻过程中子弹动能和复合防弹插板背凸情况产生显著影响。结论 止裂层在一定程度上能减少陶瓷质量损失,但也会造成更多的损伤,这种现象在高速情况下较为明显,且凯夫拉平纹织物止裂层所造成的损伤更多。相关研究工作可为陶瓷复合防弹板的设计提供参考。     

纤维增强复合材料层板高速倾斜冲击损伤数值模拟

根据复合材料三维黏弹性本构关系, 建立了纤维增强复合材料层板高速倾斜冲击损伤的数值分析模型。该模型在复合材料层间引入界面单元模拟层间分层, 结合三维Hashin失效准则进行单层板面内损伤识别, 引入材料刚度折减方案, 采用非线性有限元方法, 研究高速倾斜冲击下复合材料层板的破坏过程和损伤特性。研究结果表明: 层板的主要损伤形式是层间分层、 基体微裂纹和纤维断裂; 冲击速度不变而入射角度增大时, 剩余速度减小, 层板损伤面积在一定入射角度范围内有明显变化; 入射角度不变而冲击速度增大时, 剩余速度增大, 层板损伤面积在一定速度范围内也有明显变化。     

带脱层的复合材料层板的屈曲分析

用基于Mindlin 板理论的有限元方法进行了带脱层损伤的复合材料层板的屈曲载荷分析。为了获得物理上可能的屈曲模态, 即避免上下脱层的相互贯穿, 在接触区域引入一些假想弹簧, 并给出了这些假想弹簧刚度系数的计算公式和接触计算的迭代格式, 通过这些弹簧对原始刚度矩阵进行修正可以有效地求解屈曲载荷特征值分析中的接触问题。数值计算结果表明了本算法的有效性和引入接触分析对这类屈曲分析的重要性。同时, 还对脱层的大小、形状、位置和脱层的纤维铺层方向对屈曲载荷的影响进行了研究。      

Transient analysis and control of delaminated composite plates in hygrothermal environment using active fiber composite actuator

Abstract

In the present article, the transient analysis and control of delaminated composite plates under hazardous environmental conditions using active fiber composite (AFC) is discussed. Top and bottom layers of the laminated composite plate are embedded AFC layers. The present investigation utilizes AFC as an actuator and sensor. A finite element model for centrally located delamination is developed and coded in Matlab. The proportional controller is used to control the undesirable response in real time. The transient response of the smart delaminated plate is studied for different temperatures and moisture conditions. The feedback control of the dynamic response is performed with the help of velocity and displacement feedback gain to the AFC actuator. The key observations from the numerical studies are; the dynamic response and the frequency response of composite plate increase due to delamination and also with the increase of the temperature and moisture concentrations. The response reduces when the feedback control loop is activated. So, the overall performance of the delaminated plate structure in hygrothermal environment may be enhanced.