Viscoelasticity of multi-layer textile reinforced polymer composites used in soccer balls

This paper gives details of a comprehensive dynamic mechanical analysis (DMA) material characterisation activity for all constituent layers of two modern-day thermoformed soccer balls. The resulting material data were used to define a series of viscoelastic finite element (FE) models of each ball design which incorporated the through-thickness composite material properties, including an internal latex bladder, woven fabric-based carcass and polymer based outer panels. The developed FE modelling methodology was found to accurately describe the viscoelastic kinetic energy loss characteristics apparent throughout a soccer ball impact at velocities which are typical of those experienced throughout play. The models have been validated by means of experimental impact testing under dynamic loading conditions. It was found that the viscoelastic material properties of the outer panels significantly affected ball impact characteristics, with outer panel materials exhibiting higher levels of viscous damping resulting in higher losses of kinetic energy.     

Oblique impact of inflated balls at large deflections

A planar theory for oblique impact of thin-walled spherical balls against a rough rigid surface has been developed on the basis of an assumed deformation field—an initially spherical ball is assumed to flatten against the constraint surface while the remainder of the ball remains undeformed. For inflated thin-walled balls, which are represented by these assumptions (basketballs, soccer balls, volleyballs, etc) the normal reaction force acting on the flattened contact patch is predominately due to the internal gas pressure—the reaction due to shell bending is insignificant in comparison with this gas force. During impact of a thin-walled ball there also is a non-conservative momentum flux reaction that is caused by the flow of momentum into and out-of the flattened contact patch. If the ball is translating as well as rotating about an axis perpendicular to the plane of motion, the distribution of the normal component of velocity for material entering and exiting the flattened contact patch results in a distribution of momentum flux force intensity around the periphery of the contact patch and consequently, a momentum flux torque acting on the flattened sphere. The effect of these reaction forces and torque on oblique impact of thin-walled spherical balls is calculated as a function of the ball deflection (or normal component of impact velocity). In comparison with rigid body calculations for oblique impact of a spinning ball against a rough surface at angles<45° from normal, the effect of maximum deflections as large as half the initial radius is to slightly accentuate the effect of friction on angle of rebound and moderately decrease the angular velocity of the ball. However, for angles >45° from normal, the final angular velocity can be as small as 40% of that predicted by rigid body theory. The most significant changes in rebound angle are for cases with initial backspin—a technique commonly used in many ball sports.     

Plastic deformation of high-purity α-titanium: Model development and validation using the Taylor cylinder impact test

In this paper, results of an experimental study on the quasi-static and high-rate plastic deformation due to impact of a high-purity, polycrystalline, α-titanium material are presented. It was found that the material is transversely isotropic and displays strong strength differential effects. Split Hopkinson Pressure Bar tests in tension and compression and Taylor impact tests were conducted. For an impact velocity of 196 m/s, plastic deformation extended to 64% of the length of the deformed specimen, with little radial spreading. A three-dimensional constitutive model was developed. Key in the formulation was the use of a macroscopic yield function that incorporates the specificities of the plastic flow, namely the combined effects of anisotropy and tension–compression asymmetry. Comparison between model predictions and data show the capabilities of the model to describe with accuracy the plastic behavior of the α-titanium material for both quasi-static and high-rate loadings. In particular, the three-dimensional simulations of the Taylor impact test show a very good agreement with data, both the post-test major and minor side profiles and impact interface footprints are very well described.     

超高强钢制电池包底部球击试验与仿真方法研究

目的 研究超高强钢电池包底部球击工况的仿真分析方法,通过实物试验验证仿真分析方法的准确性。方法 通过建立电池包底部球击的仿真模型,对底部球击工况进行数值模拟,分析球击过程中应力–应变分布和底板承受变形的能量情况。开展底部球击实物试验,并与模拟结果进行对比分析。结果 在球击过程中,随着球击头撞击底板位移的增大,挤压力逐渐增加,底板变形能量也逐渐增加;当挤压力达到10 k N时,仿真位移为19.127 mm,试验结果位移为20 mm。当位移达到20 mm时,仿真底板变形能量为73.716 J,试验结果为70.581J,仿真与试验结果较为一致。结论 超高强钢电池包在底部球击试验中未发生开裂,满足标准要求,数值模拟方法可以为电池包底部球击工况提供指导。     

Modeling multiaxial impact behavior of a glassy polymer

In many applications of polymers, impact performance is a primary concern. Impact tests experimentally performed on molding prototypes yield useful data for a particular structural and impact loading case. But, it is generally not practical in terms of time and cost to experimentally characterize the effects of a wide range of design variables. A successful numerical model for impact deformation and failure of polymers can provide convenient and useful guidelines on product design and therefore decrease the disadvantages that arise from purely experimental trial and error. Since the specimen geometry and loading mode for multiaxial impact test provides a close correlation with practical impact conditions and can conveniently provide experimental data, the first step of validating a numerical model is to simulate this type of test. In this paper, we create a finite element analysis model using ABAQUS/Explicit to simulate the deformation and failure of a glassy ABS (acrylonitrile-butadiene-styrene) polymer in the standard ASTM D3763 multiaxial impact test. Since polymers often exhibit different behavior in uniaxial tensile and compression tests, the uniaxial compression or tensile tests are generally not representative of the three-dimensional deformation behavior under impact loading. A hydrostatic pressure effect (controlled by the parameter γ) is used to generalize a previously developed constitutive model ("DSGZ" model) so that it can describe the entire range of deformation behavior of polymers under any monotonic loading modes. The generalized DSGZ model and a failure criterion are incorporated in the FEA model as a user material subroutine. The phenomenon of thermomechanical coupling during plastic deformation is considered in the analysis. Impact load vs. displacement and impact energy vs. displacement curves from FEA simulation are compared with experimental data. The results show good agreement. Finally, equivalent stress, strain, strain rate and temperature distributions in the polymer disk are presented. Electronic Publication     

Energy dissipation in collision of two balls covered by fine particles

A new fine particle impact damper (FPID) is composed of a spherical impactor and a small quantity of fine particles as damping agent. The model of energy dissipation in the collision between two balls covered by fine particles is necessary to investigate the mechanism and performance of FPID. In this study, a simplified model verified by FEA simulations is proposed to estimate the energy dissipation in collision between two balls covered by fine particles. In addition, the energy dissipation in the collision between two balls covered by fine particles is compared with that in the impact between two balls without fine particles, by means of theoretical predictions. FEA simulations are also carried out to discuss the effects of diameter ratio of particle to ball, particle material and particle amount on the energetic expression of the elastic–plastic loading (EPL) index (EPL_E). The results from the FEA simulations agree well with the estimations from the model proposed in this paper. It is concluded that the energy dissipation in the collision between two balls covered by fine particles can be predicted by classical collision models of two particles through the substitution of several parameters from balls; the plastic deformation of fine particles affixed on balls can exhaust much more energy than that of the two balls without particles, which is the reason for the good performance of FPID; the diameter ratio of particle to ball and the material of particles do not have significant effects on the EPL_E when the ratio is limited to the range of [1/200 – 1/10]. A correlation of the EPL_E and dimensionless initial relative velocity is also found for the collisions between two balls, which is independent not only of the particle size and material properties but also of the particles presence.     

Determining particulate–solid interphase strength using shear-induced anisotropy

The resistance to shear deformation developed by a granular material layer in contact with a topographically rough natural or manufactured solid material surface is critical to the stability of a variety of composite systems. By using discrete-element method numerical simulations, we show that evolution of fabric and contact force anisotropy at the boundary between the surface and the granular media controls shear behavior. Full mobilization of granular material strength occurs when the contact force anisotropy developed at the interface is equal to the maximum contact force anisotropy of the granular media.     

Application of digital speckle photography to flash X-ray studies of internal deformation fields in impact experiments

A technique to measure two-dimensional deformation fields of a layer inside materials during dynamic events such as impact experiments is presented. Even optically opaque materials like cement can be evaluated when flash x rays are used. Blocks of polyester and cement were prepared with a layer of x-ray-absorbing lead particles. The specimens were then hit by a 9-mm-diameter steel sphere (ball bearing) fired from a 9-mm-bore gas gun at a velocity of 373.5 +/- 3.0 ms(-1). A 30-ns-long x-ray pulse exposed one radiograph before impact; another radiograph was exposed a short time after the impact on the specimen. The two-dimensional displacement field was obtained when the x-ray radiographs were digitized by a conventional flatbed scanner, and a digital speckle photography algorithm was used to calculate the displacements. The flash x-ray technique allowed examination of the deformation at the layer inside the material during failure, thus giving interesting data about the material flow field around the impactor.     

Modelling dynamic failure of concrete with meshfree methods

This paper studies the dynamic failure of concrete structures under blast and impact loading. We will propose a model which can capture many important effects when concrete is subjected to high dynamic loading conditions and large deformations. These effects are the strength increase which we attribute to inertia effects, the compaction of the material under high hydrostatic pressure and the anisotropy of the material in tension. A Lagrangian particle method is used which can easily handle large deformations and fracture. Fragmentation occurs naturally governed by the constitutive model due to separation of the particles. Comparisons between experiments and the simulations are discussed and show good agreement.     

Texture development in the cold rolling of IF steel

The development of deformation texture in ferrite has been measured in cold rolled IF steel. This has been compared, in a quantitative way, to the predictions of Taylor models—including those with relaxed constraints—and a finite element model with crystal plasticity constitutive laws. The finite element model gave much better prediction of the overall levels of orientation density but failed to predict the relatively high level of {0 0 1}1 1 0 texture which occurred at strains greater than about unity. That feature was predicted by relaxed constraint Taylor models. It is argued that that prediction is a coincidence, and either the finite element model cannot readily deal with the intragranular inhomogeneity of deformation in an adequate way, or that factors such as high-angle boundary migration may be important in the development of deformation texture.     

An analytical model for predicting springback and side wall curl of sheet after U-bending

An analytical model for predicting sheet springback after U-bending is proposed in this paper based on Hill48 yielding criterion and plane strain condition. The model takes into account of the effects of deformation history, thickness thinning and neutral surface shift on the sheet springback of U-bending. Three rules for material hardening – kinematic, isotropic and combined hardening – have been used to consider the effect of complex deformation history that has undergone stretching, bending, and unbending deformations on the sheet springback. The model is applied to the benchmark of NUMISHEET’93 2-D draw bending problem. It indicates that the springback is overestimated when isotropic hardening is applied, while is underestimated when kinematic hardening is applied. For reverse loading problem, the combined hardening is a good approach to the practical material. In addition to that, the effects of blank holding force, friction coefficient between sheet and tools, sheet thickness and anisotropy have been investigated. When the shifting distance of neutral surface exceeds one-fourth of sheet thickness, the springback can be reduced effectively by increasing the blank holding force and friction between sheet and die. And the springback increases with anisotropy and friction between sheet and punch, and decreases with the sheet thickness.     

Failure initiation and propagation characteristics of honeycomb sandwich composites

The energy absorbed during the failure of a variety of structural shapes is influenced by material, geometry and the failure mode. Failure initiation and propagation of the honeycomb sandwich under loading involves not only non-linear behavior of the constituent materials, but also complex interactions between various failure mechanisms. Therefore, there is a need for an improved understanding of the material characteristics and energy absorption modes to facilitate the design of sandwich performance. In the present study, failure initiation and propagation characteristics of sandwich beams and panels subjected to quasi-static and impact loadings were investigated. Experimental studies involved a series of penetration and perforation tests on 2D beam and 3D panel configurations using a truncated cone impactor with impact velocities up to 10 m/s. Preliminary tests were also performed on the sandwich beams subjected to the three-point bending. Load-carrying, energy-absorbing characteristics and failure mechanisms under quasi-static and impact loading were determined. Dominant deformation modes involved upper skin compression failure in the vicinity of the indenter, core crushing and lower skin tensile failure.     

单层和双层足尺度海底管道抗冲击性能分析

海底管道在服役过程中除了受到常规荷载作用外,还会受到各种意外的冲击载荷作用而失效.为了研究承受横向冲击载荷作用下海底管道的动态特性,对三个单层和一个双层的足尺度管道进行了落锤冲击试验,获得了横向冲击作用下管道的破坏形态、冲击力时程曲线、位移时程曲线及应变时程曲线.建立了分析冲击荷载作用下海底管道失效过程的有限元模型,并...     

Critical stresses and strains at the spall edge of a case hardened bearing due to ball impact

Short spall propagation times of failing main shaft ball bearings of aircraft engines are a serious safety concern for single engine aircraft. Bearing designers would like to understand the impact of four variables namely (i) ball material density, (ii) subsurface residual stress, (iii) gradient in yield strength with depth (case hardening), and (iv) raceway surface hardness/yield strength that are thought to affect spall propagation. Extensive spall propagation experiments have been conducted at AFRL, Ohio in the past few years to address this issue. However, a detailed mechanistic analysis of these experiments has not been performed. This work presents an elastic–plastic finite element (FE) model that simulates a ball impacting a spall edge to determine the relative contributions of the four material variables on spall propagation. The magnitude and extent of damage of the spall edge material is determined based on critical stresses and plastic strains induced by the ball impact. The results indicate that the influence of ball density is greatest on inducing damage at the impacted spall edge when compared to the other three properties, which also agrees with the hybrid bearing spall propagation tests conducted at AFRL.     

Phenomenological and crystal plasticity approaches to describe the mechanical behaviour of Ti6Al4V titanium alloy

This paper presents a multiscale study of the quasi-static behaviour of a Ti6Al4V titanium alloy sheet. Tensile and compressive tests were carried out on specimens along several orientations from the rolling direction in order to characterise the material anisotropy. In parallel, X-Ray diffraction texture measurements were performed before and after deformation in tension. A phenomenological model (CPB06exn) and a multiscale crystal plasticity model (Multisite) were investigated to describe the mechanical behaviour of the tested material. The identification of the material parameters provides good predictions of the plastic anisotropy using both tensile and compressive data. The crystal plasticity model is in good agreement with the experiments in tension but it was observed that some improvements should be done to take into account the tension-compression asymmetry displayed by the material. Moreover both models lead to a good prediction of the Lankford’s coefficients and yield strength.     

Anisotropic viscoplasticity constitutive model for directionally solidified superalloy

Abstract

The macroscopic deformation behaviour of a Ni-based directionally solidified (DS) superalloy was experimentally investigated, and an anisotropic constitutive model of the material was developed. Monotonic and creep tests were performed on uniaxial test specimens machined from DS plates so that the angle between the loading direction and the solidified grain direction varied between 0 and 90°. Tension-torsion creep tests were also conducted to examine the anisotropic behaviour under multiaxial stress conditions. The material exhibited marked anisotropy under elastic and viscous deformation conditions, whereas it showed isotropy under plastic deformation conditions of high strain rates. Then crystal plasticity analyses were carried out to identify slip systems under creep loading conditions, assuming the anisotropic creep behaviour of the DS material. A viscoplastic constitutive model for expressing both the anisotropic elasticity-viscosity and the isotropic plasticity was proposed. The elastic constants were determined using a self-consistent approach, and viscous parameters were modelled by crystal plasticity analyses. The calculation results obtained using the constitutive model were compared with the experimental data to evaluate the validity of the model. It was demonstrated that the constitutive model could satisfactorily describe the anisotropic behaviour under uniaxial and multiaxial stress conditions with a given set of material parameters.     

Structural aspects of ball milled CdS and CdSe

The structural effects of ball milling powders of CdS and CdSe have been investigated by X-ray diffraction. When initially wurtzite-phase material was ball milled, excessive broadening and the selective extinction of certain diffraction lines were observed in Debye-Scherrer diffraction photographs of CdS and diffractometer traces of CdSe. These effects culminated in the disappearance of all but the three reflections from the (00.2), (11.0) and (11.2) planes. The fact that these reflections would coincide with those that would arise from the (111), (220) and (311) planes of the cubic sphalerite phase has led to earlier interpretations of similar effects in these and related materials as arising from a wurtzite to sphalerite transformation. Such a model does not fully account for the effects observed here. However, a careful examination of structure factors suggests an alternative explanation based on randomization due to structure deformation by faulting.     

Mullins effect on incompressible hyperelastic cylindrical tube in finite torsion

The isotropic softening effect in non-homogeneous deformation resulting from combined effect of torsion, extension and inflation of cylindrical rubber tube is discussed. The effects of deformation induced anisotropy, permanent set and hysteresis are neglected. A general neo-Hookean parent material model is illustrated and subsequently the stress-softening effect on the same hyperelastic material is analyzed. Simple torsion of cylindrical tube with neo-Hookean material model is analyzed and the results obtained are shown in various plots. Analytical results are compared with the experimental results of Rivlin and Saunders. Universal relations are also established for incompressible, isotropic, hyperelastic material for non-homogeneous deformation with isotropic damage function in both virgin and stress-softened cases.     

球磨对滑石、绿泥石、菱镁石和刚玉X射线衍射峰强度的影响

采用球磨工艺,获得了不同粒度的滑石、绿泥石、菱镁石和刚玉粉末样品,用来研究球磨时间对试样衍射峰强度的影响.试验表明,采用球磨法制得的样品的X射线衍射峰严重变形,随着球磨时间的延长,变形更加严重.辽宁产滑石和绿泥石,球磨4h,其衍射强度衰减不大,可以满足X射线定量分析的精度要求.菱镁石在球磨条件下迅速粉化,X射线衍射法定量分析时不宜采用.刚玉是一种较好的耐球磨物质,宜优先用作参比物质.     

基于连续球压痕法的45钢强度与韧性测试研究

为研究在役设备的材料强度与韧性测试评价问题,针对工程中常用材料45钢,采用连续球压痕方法,获取了材料的屈服强度、抗拉强度与断裂韧性,通过与常规力学性能试验结果比较,对该方法的可靠性进行了验证。通过研究球压头下压产生的塑性功,与冲击启裂能及断裂韧性之间的关联关系,建立基于仪器化球压痕测试技术的冲击韧性估算评估方法。试验结果表明,利用连续球压痕方法获取的屈服强度、抗拉强度与实际结果的偏差均小于10%,断裂韧性值与试验结果的偏差为12.3%,计算结果在试验值偏差数据范围内。利用连续球压痕技术,建立的断裂韧性与冲击韧性之间的关联公式,所预测的冲击韧性结果与仪器化冲击试验值具有较好的一致性,为在役设备材料的韧性快速评价提供了有效的测试方法。