泡沫EPS非线性粘弹性本构模型在LS-DYNA空调跌落仿真中的研究

目的 研究泡沫EPS非线性粘弹性本构模型对空调跌落仿真精度的影响。方法 通过动态压缩试验获得泡沫EPS在不同应变率下的应力-应变结果,使用LS-DYNA中的非线性粘弹性本构模型Fu-Chang泡沫准确模拟泡沫在不同应变率下的力学性能,并通过空调跌落仿真进行验证。结果 使用不同应变率下的泡沫EPS非线性粘弹性本构模型进行仿真,空调不同位置的仿真加速度曲线和实际试验加速度曲线相似度在90%以上。结论 不同应变率下的泡沫EPS非线性粘弹性本构模型可以准确模拟EPS泡沫在动态冲击下的材料力学性能,可以更加准确地模拟跌落工况中空调结构的动态反应及泡沫失效状态,提高仿真精度。     

基于损伤模型的2024-O-T42搭接件动态拉伸失效分析

针对高锁螺栓单搭接件所采用的2024-O-T42铝合金,设计狗骨试验件进行准静态与动态拉伸试验,设计六种不同的缺口试验件进行准静态拉伸试验。通过开展拉伸失效仿真,对比Hartley-Srinivasan与Johnson-Cook两种本构模型,以及最大塑性应变失效准则、Johnson-Cook失效模型与GISSMO损伤模型三种失效模型。结果表明,在试验的100 s^-1应变率范围内,2024-O-T42铝合金材料流动应力应变率效应不明显,其最大相差约为5%;在不考虑应变率及温度的情况下,Hartley-Srinivasan本构模型比Johnson-Cook本构模型更能准确表征材料塑性段的力学行为;采用Hartley-Srinivasan本构模型和GISSMO损伤模型,高锁螺栓单搭接件在1 m/s、3 m/s、5 m/s拉伸速度下的仿真结果与试验结果吻合更好,且仿真获得的失效位移相对试验失效位移平均值分别偏大4.7%、偏大4.3%和偏小7.4%。     

基于率相关三维弹塑性损伤模型的复合材料渐进失效分析

建立了一个同时考虑复合材料非线性力学响应、应变率效应和损伤累积导致材料属性退化的弹塑性三维损伤本构模型。采用改进的塑性力学模型表征材料在动态荷载下的非线性力学行为。为准确预测复合材料在动态荷载下的弹塑性力学响应,引入了率相关放大系数对准静态下的塑性强化函数进行修正。采用“断裂带模型”对已开发的本构模型软化段进行规则化,以减轻有限元分析结果的网格敏感性。采用分区反抛物线插值法对基体损伤初始断裂面角度及纤维扭结/劈裂平面角度进行求解。开发包含数值积分算法的用户材料自定义子程序VUMAT,并嵌于有限元程序ABAQUS V6.14中,对力学行为展现显著非线性力学效应和应变率效应的IM7/8552碳纤维/环氧树脂复合材料层合板进行了渐进失效分析,验证本文提出的材料本构模型的有效性。结果显示,预测结果与已报道的试验结果吻合良好,表明已建立的率相关三维弹塑性损伤本构模型能准确预测此类复合材料层合板的在动态荷载下的力学行为,为复合材料构件及其结构设计提供了一种有效的分析方法。     

一种弹芯用聚碳酸酯的动态力学性能研究及本构关系

为了研究一种弹芯用聚碳酸酯材料在冲击作用下的动态力学响应,利用材料试验机和SHPB装置对该材料在不同应变率条件下动静态压缩性能进行测试分析,获得了该聚碳酸酯材料不同应变率下的应力应变曲线,试验结果表明:聚碳酸酯材料的压缩过程呈现明显的黏弹性现象,其动静态屈服强度和模量随着应变率的增加而变大,塑性阶段表现为应变软化与应变硬化相互作用的结果,且不同应变率下塑性阶段的应力应变曲线切向模量近似相等;基于试验结果建立了描述聚碳酸酯材料大变形力学行为的黏弹塑性本构模型,并得到了该材料的本构方程。对比分析显示,该模型可以较准确地描述聚碳酸酯材料动静态压缩行为。     

基于GISSMO断裂准则的6016铝合金断裂行为研究

目的 研究零部件在成形与碰撞过程中,6016铝合金在不同应力状态下的断裂行为。方法 通过准静态拉伸实验,获得了6016铝合金的基本力学性能。利用Nakajima成形极限实验,获得了6016铝合金材料的断裂成形极限曲线。设计了7种涵盖成形及碰撞过程中应力状态的断裂极限测试试样,采用数字图像相关技术(DIC)记录了试样在变形过程中的全场应变。利用实验-有限元反求方法标定了6016铝合金的GISSMO断裂准则的参数,并用帽形件三点弯曲实验验证了模型的合理性。结果 相比于传统断裂成形极限图的预测结果,基于GISSMO断裂准则的仿真结果与实验具有更好的一致性。结论 所建立的GISSMO模型可以用于预测6016铝合金在复杂应力状态下的断裂行为。     

聚脲材料动态压缩力学行为的数值模拟研究

以聚脲材料动态压缩力学特性为研究对象,提出了考虑动态弹性模量、动态强度因子和动态切线模量的简化三直线弹塑性本构模型;基于ANSYS/LS-DYNA有限元分析软件,建立了低、中、高不同应变率下聚脲材料压缩有限元模型,并与实验结果进行对比分析。结果表明：动态弹性模量增大因子、动态强度因子和动态切线模量因子随应变率增加而有规律的增大,均和应变率的对数呈双线性关系。在中低应变率下,三者的线性关系斜率都比较平缓;在高应变率下,三者的线性关系斜率都比较陡,且弹性模量动态增大因子的斜率比动态强度因子的更大,而第二阶段动态切线模量因子的斜率与动态强度因子的基本一致,但第三阶段动态切线模量因子的斜率是动态强度因子的2.3倍左右,说明高应变率下聚脲材料的后期应力强化效应更加显著。聚脲材料的简化三直线弹塑性本构模型可以在ANSYS/LS-DYNA有限元软件中较好地实现。该文建立的有限元模型能较为准确地模拟聚脲材料压缩实验,进一步验证了简化弹塑性本构模型在不同应变率压缩加载下的有效性。该研究可以为聚脲涂覆加固防护结构有限元模型提供材料模型参数依据。     

液晶显示屏包装件跌落仿真分析及结构优化

目的 探究液晶显示屏包装件的跌落仿真分析方法,根据仿真分析和辅助结构设计进行优化改善.方法 根据液晶显示屏的包装形式,创建显示屏包装件的3D模型,运用Ansys LS-DYNA动力学模块对包装件进行z向面跌落仿真.通过材料所受等效应力识别存在失效风险的材料,并对材料结构进行优化改善.结果 通过跌落仿真分析,发现托盘挡墙位置承受了较大应力.其中最大等效应力为67.9 MPa,大于材料屈服强度;有效塑性应变为0.046,大于材料屈服点对应塑性应变,材料存在一定破损失效风险,需要对托盘结构进行优化来增加其支撑强度.结论 通过跌落仿真分析与跌落试验对比,验证了跌落仿真方法的可靠性,通过仿真分析找到托盘较优力学结构,通过试验验证了结构的合理性.     

橡胶压缩Mooney-Rivilin本构模型参数拟合分析

橡胶制品因其优异的超弹性能在工业界得到了广泛的应用。为了准确模拟空调室外机跌落过程中压缩机和管路的振动幅度,需要选取合适的橡胶本构模型以及材料参数。首先通过单轴压缩实验获取橡胶的应力-应变曲线,然后采用Mooney-Rivilin本构模型对曲线进行拟合,获取C_(01)和C_(10)值。最后利用有限元仿真再现单轴压缩实验过程,结果发现通过模拟得到的应力-应变曲线和实验获得的应力-应变曲线基本重合,最大误差4.9%,表明所获取的材料参数基本准确,为后续包装跌落、模态分析等仿真类别提供了数据支撑。     

铝制包装箱搬运过程跌落分析

针对某铝制包装箱,对其进行跌落仿真分析,研究其跌落过程中的应力与变形。本文采用ANSYS/LS-DYNA对其进行弹塑性条件下的跌落模拟分析,采用应力失效与应变失效相结合的方法进行安全评定,证明该产品结构满足设计要求。     

基于Johnson-cook本构模型的EPE包装跌落冲击模拟

目的将聚乙烯泡沫塑料在动态压缩试验下得到的力学性能引入有限元中,创建材料模型,并应用于跌落冲击仿真分析,以提高仿真的精确度。方法通过聚乙烯泡沫塑料在不同速率下的压缩试验,得到真实的应力-应变曲线,并基于Johnson-cook本构模型在有限元中建立EPE的材料模型。最后用AnsysWorkbench中的LS-DYNA模块对聚乙烯泡沫缓冲包装的跌落过程进行仿真分析,用LS-PREPOST软件进行后处理。在此基础上,对比分析仿真结果和实验结果。结果仿真结果的误差分别为0.85%,1.6%,2.97%,与实验结果基本一致。结论基于Johnson-cook本构模型构建的聚乙烯泡沫塑料有限元材料模型能有效提高低速冲击的仿真精度,为非线性材料和应变率敏感材料的有限元动态冲击分析提供了参考。     

Modeling of Nonlinear Mechanical Behavior for 3D Needled C/C-SiC Composites Under Tensile Load

This paper established a macroscopic constitutive model to describe the nonlinear stress–strain behavior of 3D needled C/C-SiC composites under tensile load. Extensive on- and off-axis tensile tests were performed to investigate the macroscopic mechanical behavior and damage characteristics of the composites. The nonlinear mechanical behavior of the material was mainly induced by matrix tensile cracking and fiber/matrix debonding. Permanent deformations and secant modulus degradation were observed in cyclic loading-unloading tests. The nonlinear stress–strain relationship of the material could be described macroscopically by plasticity deformation and stiffness degradation. In the proposed model, we employed a plasticity theory with associated plastic flow rule to describe the evolution of plastic strains. A novel damage variable was also introduced to characterize the stiffness degradation of the material. The damage evolution law was derived from the statistical distribution of material strength. Parameters of the proposed model can be determined from off-axis tensile tests. Stress–strain curves predicted by this model showed reasonable agreement with experimental results.     

Deformation response and constitutive modeling of vinyl ester polymer including strain rate and temperature effects

The deformation behavior of vinyl ester polymer under monotonic tensile loading is characterized and modeled. The Standard Linear Solid model, which is a physical model, was used and modified to represent the stress–strain behavior of this polymer over a wide range of strain rates and temperatures. This model was also used to predict the stress-relaxation and short-term creep behavior of this material. The comparisons between the predictions and experimental data from tensile and relaxation tests demonstrate that this model can represent the deformation behavior of the material reasonably well.     

Investigating the transverse behavior of Glass–Epoxy composites under intermediate strain rates

In this study, the strain rate effects on transverse tensile and compressive properties of unidirectional Glass fiber reinforced polymeric composites are investigated. To demonstrate strain rate effects, the tensile and compressive composite specimens with identical configuration are fabricated and tested to failure in the transverse direction at quasi-static strain rate of approximately 0.001 s⁻¹ and intermediate strain rates of 1–100 s⁻¹. The tensile and compressive tests are performed using a servo-hydraulic testing apparatus equipped with strain rate increasing mechanisms. For performing the practical tests, a jig and a fixture and other test supplies are designed and manufactured. The performance of the test jig is evaluated and showed that it is adequate for composites testing under tension and compression loads. The effects of strain rate on mechanical properties (maximum strength, modulus, and strain to failure) are considered. The characteristic results for the transverse properties indicate that damage evolution is strain-rate-dependent for the examined material. Also, a strain-rate-dependent empirical material model associated with different regression constants is proposed based on the experimental results obtained to characterize the rate dependent behavior of Glass/Epoxy composite material.     

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     

Effect of PVD coatings on the strain and low-cycle fatigue resistance of stainless steel and titanium alloys

The effect of different PVD coatings and their thickness on the tensile and cyclic elastoplastic strain resistance of Kh18N10T stainless steel and VT1 and VT20 titanium alloys was experimentally substantiated. The application of PVD coatings, also after tension or cyclic loading, enhances tensile and cyclic elastoplastic strain resistance and leads to the change in fracture behavior (quasistatic to fatigue) and cyclic properties of the material.     

Analytical approach to the strain rate effect on the dynamic tensile strength of brittle materials

An explicit mathematical expression for the dynamic load-carrying capacity of brittle materials under dynamic tensile loads is derived based on a kind of structural-temporal failure criterion [1] and the one-dimensional longitudinal plane wave propagation model. It is shown that the dependence of the dynamic load-carrying capacity on the strain rate can be determined only by the static material parameters such as tensile strength, density, incubation time, critical failure length and constitutive constants, which verifies that the well known strain rate effect on material strength can be considered as an structural rather than material behavior, as pointed out by Cotsovos and Pavlovi? [2] recently. Moreover, it is found that, under constant strain rate, the dynamic load-carrying capacity depends also on the amplitudes of imposed boundary loads, which explains, to a significant extent, the scatter that characterizes the available experimental data. Furthermore, the derived expression can also be used as a foundation of theoretical analyses on other problems involving the strain rate effect such as dynamic size effect, dynamic failure of quasi-brittle materials and composites.     

碳纤维静、动态加载下拉伸力学性能的试验研究

利用岛津试验机和自行研制的旋转盘式击拉伸试验装置,对Ｔ３００和Ｍ４０Ｊ两种碳纤维实施了应变速率范围为０．００１－１３００ｓ＾－１的静、动态拉伸试验,获得了两种材料在不同应变速率下的完整的应力变曲线。     

An unusual elastoplastic response of thermoplastic elastomers at cyclic deformation

Observations are reported on a thermoplastic elastomer (ethylene–octene copolymer) in uniaxial tensile tests. The experimental data reveal a rather unusual mechanical response: unlike particle-reinforced rubbers, for which preconditioning causes a monotonic decrease in tensile stress compared with that in a virgin specimen, cyclic preloading of the thermoplastic elastomer induces a reduction in stress at small strains and its noticeable growth at relatively large elongation ratios.A constitutive model is derived for the elastoplastic behavior of a polymer network with constrained chains at three-dimensional deformations with finite strains. The stress–strain relations involve five adjustable parameters that are found by fitting the experimental data. Good agreement is demonstrated between the observations and the results of numerical simulation. It is shown that the material parameters are affected by intensity of preloading in a physically plausible way.     

骨料粒径对混凝土动态拉伸强度及尺寸效应影响分析

骨料粒径是影响混凝土力学性能及破坏机理的重要因素。从细观角度出发,将混凝土看作由骨料颗粒、砂浆基质及界面过渡区组成的三相复合材料,考虑细观组分的应变率效应,建立了混凝土动态拉伸破坏行为研究的细观力学分析模型,模拟研究了不同骨料粒径下混凝土动态拉伸破坏行为,并揭示了动态拉伸强度的尺寸效应规律。研究表明:低应变率下骨料不发生破坏,骨料粒径对混凝土动态拉伸破坏模式及拉伸强度影响显著,且拉伸强度的尺寸效应随骨料粒径的减小而削弱;高应变率下裂缝将贯穿骨料,骨料粒径的大小对混凝土动态拉伸强度及尺寸效应影响可忽略。最后,结合应变率效应的影响机制,建立了混凝土拉伸强度的"静动态统一"尺寸效应理论公式,该公式可以较好描述各骨料粒径下混凝土动态拉伸强度与试件尺寸的定量关系。