Soccer ball anisotropy modelling

The work presented in this paper details the development of a finite element (FE) model of a soccer ball, allowing for a greater understanding of the performance of soccer balls under dynamic conditions that are representative of play. The model consists of composite shell elements that include a hyperelastic strain energy potential equation to define the latex bladder layer and a plane stress orthotropic elastic material model to define the anisotropic woven fabric outer panels. The model was validated through a series of experimental impact tests whereby the ball was impacted normal to a rigid plate at an inbound velocity of approximately 34 ms⁻¹ (76 mph), with each impact recorded using high speed video (HSV) techniques. It was found that the combined effects of ball design and panel material anisotropy resulted in impact properties such as coefficient of restitution, contact time, deformation and the 2D shape taken up by the ball at maximum deformation, to vary with pre-impact ball orientation. The model showed good agreement with the measurements, and its ability to represent the effects of anisotropy in ball design.     

Multiscale design of a rectangular sandwich plate with viscoelastic core and supported at extents by viscoelastic materials

This work presents a multiscale model of viscoelastic constrained layer damping treatments for vibrating plates/beams. The approach integrates a finite element (FE) model of macroscale vibrations and a micromechanical model to include effects of microscale structure and properties. The FE model captures the shear deformation of the viscoelastic core, rotary inertial effects of all layers, and viscoelastic boundaries of the plate. Comparison with analytical and FE results validates the proposed FE model. A self-consistent (SC) model makes the micro to macro scale transition to approximate the effective behavior a heterogeneous core. Modal damping resulting from the presence of voids and negative stiffness regions in the core material is modeled. Results show that negative stiffness regions in the viscoelastic core material, even at low volume fractions, yield superior macroscopic damping behavior. The coupled SC and FE models provide a powerful multiscale predictive design tool for sandwich beams and plates.     

Dynamic finite element simulation of the gunshot injury to the human forehead protected by polyvinyl alcohol sponge

Although there are some traditional models of the gunshot wounds, there is still a need for more modeling analyses due to the difficulties related to the gunshot wounds to the forehead region of the human skull. In this study, the degree of damage as a consequence of penetrating head injuries due to gunshot wounds was determined using a preliminary finite element (FE) model of the human skull. In addition, the role of polyvinyl alcohol (PVA) sponge, which can be used as an alternative to reinforce the kinetic energy absorption capacity of bulletproof vest and helmet materials, to minimize the amount of skull injury due to penetrating processes was investigated through the FE model. Digital computed tomography along with magnetic resonance imaging data of the human head were employed to launch a three-dimensional (3D) FE model of the skull. Two geometrical shapes of projectiles (steel ball and bullet) were simulated for penetrating with an initial impact velocity of 734 m/s using nonlinear dynamic modeling code, namely LS-DYNA. The role of the damaged/distorted elements were removed during computation when the stress or strain reached their thresholds. The stress distributions in various parts of the forehead and sponge after injury were also computed. The results revealed the same amount of stress for both the steel ball and bullet after hitting the skull. The modeling results also indicated the time that steel ball takes to penetrate into the skull is lower than that of the bullet. In addition, more than 21 % of the steel ball’s kinetic energy was absorbed by the PVA sponge and, subsequently, injury sternness of the forehead was considerably minimized. The findings advise the application of the PVA sponge as a substitute strengthening material to be able to diminish the energy of impact as well as the load transmitted to the object.     

Experimental investigation of high velocity ice impacts on woven carbon/epoxy composite panels

Spherical-shaped ice simulating hailstones were projected onto woven carbon/epoxy composite panels to determine the damage resistance of thin-walled composite structures to ice impact, and to observe the resulting damage modes that occur over a wide range of velocity. To study the behavior of ice in isolation from the complex response of the composite panel targets, impacts onto a dynamic force measurement device were first conducted. These experiments show a linear relationship between the peak measured force and the projectile kinetic energy, regardless of projectile size. Composite panel impact experiments show a linear relationship between the kinetic energy at which failure initiates, referred to as the failure threshold energy (FTE), and the thickness of the panel. Impacts at kinetic energies greater than the FTE produced a multiplicity of damage modes. Glancing impact tests on composite panels show that the FTE can be accurately estimated using a simple trigonometric scaling relationship.     

Performance assessment of wood, metal and composite baseball bats

The purpose of this investigation was to develop and verify a predictive capability of determining baseball bat performance. The technique employs a dynamic finite element code with time dependent baseball properties. The viscoelastic model accommodates energy loss associated with the baseball's speed dependent coefficient of restitution (COR). An experimental test machine was constructed to simulate the ball–bat impact conditions in a controlled environment and determine the dynamic properties of the baseball. The model has found good agreement with the experimental data for a number of impact locations, impact speeds, bat models and ball types. The increased hitting speed generally associated with aluminum bats is apparent, but not for impacts inside of the sweet spot. A reinforcing strategy is proposed to improve the durability of wood bats and is shown to have a minimal effect on its hitting performance. The utility of using a constant bat swing speed to compare response of different bat types is also discussed.     

Viscoelastic composite materials for noise reduction and damage tolerance

This paper describes the concept of viscoelastic composites and how their dynamic physical characteristics may be exploited for ship applications where high vibrational damping and damage tolerance is a requirement. A mathematical model is used to describe the effect of fibre alignment on viscoelastic composite dynamic Young's Moduli and loss factors. The model, supported by experimental validation, requires the dynamic physical properties of the matrix resin for the range of operational temperatures and frequencies of interest. The model predicts that the resulting loss factor of a fibre reinforced viscoelastic resin composite behaves in an anisotropic fashion, however, damping optimisation may be achieved in two different ways dependant on the angle of fibre alignment. The implications of these findings and how the fibre alignment in a viscoelastic composite may be exploited for noise free ship and submarine machinery rafts are also discussed. Empirical studies on viscoelastic composites of this type using a drop weight impact tester have shown that their damage tolerance is superior to conventional glass reinforced polyester GRP. Although a theoretical analysis has not been made, it is implied that the viscoelastic nature of the matrix resin and its optimisation over the typical damaging impact frequencies is an important factor in absorbing the impact energy in much the same way as it is for absorbing vibrational energy. In this case the impact impluse is considered to be one particular extreme form of vibrational source. Provided the impact force can do work on the matrix, the energy will be absorbed by it if the viscoelastic nature of matrix is correct with little or no resulting damage to the composite.     

Motorcyclist helmet composite outer shell characterisation and modelling

In this study a new finite element model of composite outer shell of motorcyclist helmet is proposed, by modelling each layer of the composite material that builds the laminated structure of the outer shell of the helmet. Elastic and rupture properties of the laminate are taken into account for developing the finite element (FE) model and are extracted experimentally. A coupled experimental–numerical method combined with experimental modal analysis on beam samples is used to obtain the elastic characteristics of each layer of the outer shell. The rupture properties for each layer are extracted by experimental impact tests. The FE model of the outer shell is then validated with experimental data for elastic and rupture behaviour.     

嵌入式共固化复合材料阻尼结构低速冲击性能的数值模拟

Abstract：Embedded and co-cured composite damping structure is a new damping processing structure, which can be widely used in high-tech fields such as aviation, aerospace, high-speed train, etc. Explicit dynamic analysis software LS-DYNA was used to simulate low velocity impact on embedded and co-cured composite damping structure panels. The simulation results are compared with the experimental data to illustrate the validity of modeling and calculation method. The result of simulation shows that the impact resistance of embedded and co-cured composite damping structure is much higher than composite structure without viscoelastic damping material.     

Micromechanical finite element framework for predicting viscoelastic properties of asphalt mixtures

A micromechanical finite element (FE) framework was developed to predict the viscoelastic properties (complex modulus and creep stiffness) of the asphalt mixtures. The two-dimensional (2D) microstructure of an asphalt mixture was obtained from the scanned image. In the mixture microstructure, irregular aggregates and sand mastic were divided into different subdomains. The FE mesh was generated within each aggregate and mastic subdomain. The aggregate and mastic elements share nodes on the aggregate boundaries for deformation connectivity. Then the viscoelastic mastic with specified properties was incorporated with elastic aggregates to predict the viscoelastic properties of asphalt mixtures. The viscoelastic sand mastic and elastic aggregate properties were inputted into micromechanical FE models. The FE simulation was conducted on a computational sample to predict complex (dynamic) modulus and creep stiffness. The complex modulus predictions have good correlations with laboratory uniaxial compression test under a range of loading frequencies. The creep stiffness prediction over a period of reduced time yields favorable comparison with specimen test data. These comparison results indicate that this micromechanical model is capable of predicting the viscoelastic mixture behavior based on ingredient properties.     

The low velocity impact response of foam-based sandwich panels

This paper describes the results of a combined experimental/numerical study to investigate the perforation resistance of sandwich structures. The impact response of plain foam samples and their associated sandwich panels was characterised by determining the energy required to perforate the panels. The dynamic response of the panels was predicted using the finite element analysis package ABAQUS/Explicit. The experimental arrangement, as well as the FE model were also used to investigate, for the first time, the effect of oblique loading on sandwich structures and also to study the impact response of sandwich panels on an aqueous support.     

Evaluation of impact assessment methodologies. Part I: Applied methods

The present paper is the first part of a comparative evaluation of two methodologies for the analysis of damage in composites. The subject of the investigation is low-velocity impact and residual compression strength of monolithic composite panels. One of the methodologies is implemented in the tool CODAC, which is a stand-alone software that aims to be a fast tool and works with specialized finite element (FE) and material models. The other methodology IDAT parametrically generates the FE models by using MSC.Patran and performs the analysis by the FE code ABAQUS/Standard. The evaluation in regard to accuracy and efficiency is performed by comparing and judging the models and techniques, which are applied for stress analysis, failure detection, material degradation and time integration. Part I of the paper describes the applied methodologies. In Part II, the methodologies are validated by comparing computational results against experimental results.     

嵌入式共固化复合材料阻尼结构低速冲击性能数值模拟

嵌入式共固化复合材料阻尼结构是一种新型阻尼处理结构,在航空、航天、高速列车等高科技领域有广阔的应用前景。采用LS-DYNA显式动力学软件建立了该结构的有限元分析模型,对这种新型阻尼结构的低速冲击性能进行数值模拟,并将数值模拟结果与实验数据进行比较以说明模拟方法的有效性。结果表明这种新型复合材料阻尼结构的抗冲击性能大大优于相同材质的复合材料结构。     

Experimental study and numerical simulation of the vertical bounce of a polymer ball over a wide temperature range

The dependence to temperature of the rebound of a solid polymer ball on a rigid slab is investigated. An acrylate polymer ball is brought to a wide range of temperatures, covering its glass to rubbery transition, and let fall on a granite slab while the coefficient of restitution, duration of contact, and force history are measured experimentally. The ball fabrication is controlled in the lab, allowing the mechanical characterization of the material by classic dynamic mechanical analysis. Finite element simulations of the rebound at various temperatures are run, considering the material as viscoelastic and as satisfying a WLF equation for its time–temperature superposition property. A comparison between the experiments and the simulations shows the strong link between viscoelasticity and time–temperature superposition properties of the material and the bounce characteristics of the ball.     

Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

A numerical study of ply orientation on ballistic impact resistance of multi-ply fabric panels

This paper presents a detailed finite element (FE) analysis aiming to investigate numerically the impact deformation of multi-ply fabric panels with angled plies. The purpose of the investigation described in this paper is to study numerically the way in which the multi-ply panels deform and to identify the energy absorption in different panel constructions. The FE model was created using ABAQUS to simulate the transverse impact of a projectile onto various woven fabric panels. Influencing factors such as the impact velocity, panel construction and the number of plies are taken into account in the FE simulations. The numerical predictions show that the orientation of plies significantly affects the energy-absorbing capacity of the multi-ply fabric panels. The angled panels always increase the energy-absorbing capacity, compared with the aligned panel, by as much as 20%, depending on the number of plies in the panel. In addition, the stacking sequence of oriented plies also plays an important role in absorbing the energy. For the multi-ply fabric panel with large numbers of plies, there is an optimised sequence of plies which can maximise the energy-absorbing capacity of the panel. An important aspect of the work is validation of the numerical technique. It is shown that the FE predictions are highly consistent with the experimental study [1].     

Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.     

明胶鸟弹撞击复合材料蜂窝夹芯板试验

开展明胶鸟弹撞击复合材料蜂窝夹芯板试验,研究夹芯结构在软体高速冲击下的损伤形式,分析相关因素对结构动态响应结果的影响。通过CT扫描对复合材料蜂窝夹芯板内部进行检测可知,面板出现分层、基体开裂、纤维断裂、凹陷、向胞内屈曲等损伤形式,蜂窝芯出现芯材压溃、与面板脱粘的损伤形式;分析复合材料蜂窝夹芯板后面板的动态变形过程及撞击中心处位移-时间数据可知,复合材料蜂窝夹芯板在撞击过程中出现由全局弯曲变形主导和局部变形主导的两种变形模式;通过对比不同工况下的复合材料蜂窝夹芯板损伤程度可知,复合材料蜂窝夹芯板损伤程度随鸟弹撞击速度的增加而增大;蜂窝芯高度为10 mm的复合材料蜂窝夹芯板较蜂窝芯高度为5 mm的复合材料蜂窝夹芯板的损伤程度大;初始动能较大的球形鸟弹较圆柱形鸟弹对复合材料蜂窝夹芯板造成的冲击损伤程度更大。      

Numerical investigation on steel fibre reinforced cementitious composite panels subjected to high velocity impact loading

Steel fibre reinforced cementitious composite (SFRCC) panels are numerically investigated for their performances under high velocity impact of short projectiles. Numerical responses are obtained using advanced constitutive material model of Riedel–Hiermaier–Thoma (RHT) for cementitious materials and adopting appropriate modelling techniques. Effects of steel fibre volume and the thickness of panels on the impact performance are mainly highlighted in this paper. Various characteristics phenomenon during impact on cementitious composite panels namely, spalling, cracking, scabbing and perforation, are captured which is a difficult task. Scabbing is likely to occur when tensile stresses at the back face of the panel exceed dynamic tensile strength of the material. Various critical aspects in numerical modelling like boundary conditions, material input parameters, and handling severe distortion of the Lagrangian based finite elements are appropriately explained. Design chart is also developed to determine optimum fibre volume and thickness for an impact energy level up to 2.2 kJ. The numerically predicted impact responses are found to corroborate well with experimental results.     

The effect of geometric scale on impact induced fragmentation, and its application to the design of dual plate armor

An analysis is presented which predicts that, for a fixed impact velocity, impact induced fragmentation becomes more severe as geometric scale increases. Test data is presented which supports this prediction, and which allows calculation of material dependent coefficients. The analysis was based on a minimization with respect to radius, for an expanding body, of a total energy density term (expansion kinetic energy per unit volume plus surface energy per unit volume). The test configuration was a steel sphere impacting an aluminum plate, with fragmentation recorded by a stack of spaced witness panels. The tests were run at full and half scale. Correlation between testing and analysis was achieved for the number of fragments perforating the front witness panel when a term analogous to a threshold energy was introduced. While the fragment count showed a dependence on geometric scale, the relative depth of penetration (number of witness panels perforated) did not. This suggested that the targets were fragmented, but that the projectile remained in one piece. A reduction in penetration depth with increasing impact velocity was seen, and was attributed to increased projectile deformation. For cases where the projectile would fragment (for example, if a harder target material were used), the effect of geometric scale on the performance of dual plate armor is predicted by analysis. The prediction is that, for impact velocities where projectile breakup at the outer plate of dual plate armor is a factor, the armor required to stop a large scale projectile can be lighter, on a relative basis, than the armor required to stop a small scale projectile.