层间接触对沥青路面粘弹性动力响应影响研究

为分析沥青面层材料粘弹特性及路面各层间接触条件对沥青路面动力响应的影响,基于解析的方法,开展了层间非完全连续沥青路面粘弹性动力响应的求解工作．采用修正的Burgers模型定义沥青面层材料的粘弹性本构关系,考虑沥青路面层间接触条件,在车辆荷载作用下,建立沥青路面的理论计算模型;通过Laplace-Hankel积分变换将偏微分方程组转化为常微分方程组并对问题进行求解;采用转换矩阵表征层间接触条件,求得层间非完全连续沥青路面粘弹性动力响应的解析表达式．从沥青路面实例计算结果发现：修正的Burgers模型中的瞬时弹性模量参数是对弯沉计算结果影响最大的因素之一,路表弯沉随的增大呈下降趋势,特别是当较小时,这种趋势尤为明显;沥青混合料本构模型中的粘弹性修正系数B和黏性参数是影响路面路表弯沉计算结果的另两个重要因素,并且B和对弯沉峰值出现时间的影响具有相反的趋势;层间的非完全连续条件对沥青路面动态弯沉计算结果影响较大,并以面层与基层间的非完全连续对弯沉计算结果影响最为显著．     

残余应力与残余应变的几何作图法

理想弹塑性材料截面受弯达到部分塑性后完全卸载将存在残余应力与残余应变。本介绍了求解这种残余应力与残余应变的几何尺规作图法。     

微凸体碰撞对接触应力应变的影响

基于有限元法建立了单对半球状微凸体的接触、碰撞模型,研究了碰撞对微凸体在完全弹性、弹塑性和完全塑性三种接触状态下的Mises应力分布和等效塑性应变(PEEQ)的影响.结果表明:接触变形状态不同时,微凸体的Mises应力分布在碰撞过程具有不同的变化过程,但碰撞结束后,Mises应力值都降低,仅在完全塑性接触时,个别节点的Mises应力峰值大于屈服极限.碰撞使微凸体的等效塑性应变迅速增加到峰值,并保持到碰撞结束,与接触变形状态无关.完全弹性、弹塑性接触状态和完全塑性接触状态下,微凸体等效塑性应变的峰值分别位于接触中心区域和应变峰值环,这意味着裂纹可能产生的部位也不同.     

循环接触下安定状态问题的研究

基于线性随动强化理论,运用算子分离技术,研究将弹塑性问题转换为弹性问题和残余问题的分析方法,且针对循环载荷接触安定状态,建立了计算机分析程序,该研究能够分析计算弹塑性接触载荷在安定状态下的应力、残余累积应变及残余应力,分析计算了不同载荷的安定状态,并探讨其残余应力场的分析方法。     

变曲率连续滚滑接触安定性的数值方法研究

针对接触表面变曲率的特点,引入局部坐标系,构造出局部坐标下残余应力应变场的分布状态,建立了变曲率连续啮合过程中安定状态残余应力的计算方法。该数值方法将弹塑性问题分解为弹性问题和特征应变决定的残余问题,并采用增量映射方法求解特征应变决定的残余问题,可直接得到接触安定状态下的接触残余应力,并随之进行安定极限的判定。采用该数值方法计算了不同曲率处接触点的安定极限,给出了安定极限与摩擦因数之间的关系,并与有关数值结果相比较,验证了该算法的有效性。     

车辆制动作用下的车辆-路面-桥梁系统随机振动分析

视车辆、路面体系和桥梁为整个系统,将车辆模拟成弹簧和阻尼器连接的多刚体,沥青路面层模拟成Kelvin模型支承的无限长梁,混凝土路面和主梁一起模拟成Euler-Bernoulli梁。应用弹性系统动力学总势能不变值原理和形成矩阵的"对号入座"法则,建立了系统的竖向运动方程;并运用协方差等效方法模拟了车轮随机输入非平稳时域模型。研究了车辆制动作用下的车辆-路面-桥梁耦合系统的振动特性。计算表明:在其他条件相同时,刹车时,混凝土路面层对应的冲击系数为沥青路面层所对应系数的1.31倍;刹车时间为0.3 s时对应的冲击系数为刹车时间0.6 s所对应的1.29倍;路面的不平状况加剧了车辆制动作用时对桥梁冲击系数的影响。     

铁磁梁式板的磁弹塑性动力特征分析

针对典型的矩形磁脉冲,研究了横向磁脉冲作用下线性强化材料铁磁梁式板的磁弹塑性动力响应及其动力失稳特征,给出了线性强化铁磁梁式板的弹塑性动力失稳特征曲线;探讨了塑性应变强化系数对铁磁梁式板的动力响应特征曲线、最终平衡位置、残余构形等的影响.数值结果表明:在同等条件下,塑性应变强化系数越大,其相应铁磁梁式板的动力失稳磁场值越大,其相应的残余构形越小.     

含脱层损伤复合材料层合梁冲击动力响应实验研究

对纤维增强复合材料层合梁在受轴向冲击时的动力响应问题进行了实验研究。实验以单向玻璃纤维布和环氧树脂材料制作试件,在层间预埋薄铜箔模拟脱层损伤。采用激光测速仪测量子弹速度,动态应变仪和TDS420A数字示波器记录应变时程曲线进行动力响应分析。实验结果表明铺层角度是决定材料性能的主要原因,脱层损伤的存在及大小对动力响应和发生动力屈曲有重要影响。此外,初始缺陷的影响也是不可忽视的重要因素。     

现场实测结构温度对半刚性沥青路面性能的影响

针对中国特色的半刚性基层沥青路面,在广韶高速公路瓮城段进行为期一个月高温期的现场温度观测。运用三维有限元方法,结合现场实测温度,分析了半刚性沥青路面结构的最大拉应力、最大剪应力和最大路表弯沉在荷载和荷载耦合作用下的变化情况。结果表明,随着路面深度增加,温度波动的幅度逐渐减小;路面内的最高温度相对大气和路表温度滞后约1小时;沥青路面内部温度高于表面温度;大气、路表和路面内部温度变化基本同步,温度波峰与波谷的出现频率相同;在温度和荷载综合作用下,路表以下2cm深度范围内易出现因拉应力不足造成的开裂破坏;路表以下10cm深度范围内,较易出现剪切破坏;高温温度场的存在虽不会明显增大路面结构各层的拉应力与剪应力,但会明显增大路表弯沉,故易产生车辙破坏。     

多体系统碰撞动力学中接触力模型的研究进展

接触碰撞行为作为大自然与多体系统中的常见现象,其接触力模型对于多体系统的碰撞行为机理研究与性能预测至关重要.静态弹塑性接触模型与考虑能量耗散的连续接触力模型是研究接触碰撞行为的两类不同方法,在多体系统碰撞动力学中存在诸多共性与差异.本文分别从上述两类接触模型的发展历程入手,详细介绍了两类模型的区别与联系.首先,根据阻尼项分母中是否含有初始碰撞速度将连续接触力模型分为黏性接触力模型与迟滞接触力模型,讨论了能量指数与Hertz接触刚度之间的关系,阐述了现有连续接触力模型在计算弹塑性材料接触碰撞行为时存在的问题.其次,着重介绍了分段连续的准静态弹塑性接触力模型(可连续从完全弹性转换到完全塑性接触阶段),分析了利用此类弹塑性接触力模型计算碰撞行为的技术特点.同时,以恢复系数为桥梁和借助线性化的弹塑性接触刚度,避免了Hertz刚度对弹塑性接触刚度的计算误差,根据碰撞前后多体系统的能量与动能守恒推导了弹塑性接触模型等效的迟滞阻尼因子.探索了连续接触力模型与准静态弹塑性接触力模型之间的内在联系,数值计算结果定量说明了人为阻尼项代表的能量耗散与弹塑性接触力模型中加卸载路径代表的能量耗散具有等效性.另外...     

Delamination of an elastic film from an elastic–plastic substrate during adhesive contact loading and unloading

Adhesive contact between a rigid sphere and an elastic film on an elastic–perfectly plastic substrate was examined in the context of finite element simulation results. Surface adhesion was modeled by nonlinear springs obeying a force-displacement relationship governed by the Lennard–Jones potential. A bilinear cohesive zone law with prescribed cohesive strength and work of adhesion was used to simulate crack initiation and growth at the film/substrate interface. It is shown that the unloading response consists of five sequential stages: elastic recovery, interface damage (crack) initiation, damage evolution (delamination), film elastic bending, and abrupt surface separation (jump-out), with plastic deformation in the substrate occurring only during damage initiation. Substrate plasticity produces partial closure of the cohesive zone upon full unloading (jump-out), residual tensile stresses at the front of the crack tip, and irreversible downward bending of the elastic film. Finite element simulations illustrate the effects of minimum surface separation (i.e., maximum compressive surface force), work of adhesion and cohesive strength of the film/substrate interface, substrate yield strength, and initial crack size on the evolution of the surface force, residual deflection of the elastic film, film-substrate separation (debonding), crack-tip opening displacement, and contact instabilities (jump-in and jump-out) during a full load–unload cycle. The results of this study provide insight into the interdependence of contact instabilities and interfacial damage (cracking) encountered in layered media during adhesive contact loading and unloading.     

A computational micromechanics constitutive model for the unloading behavior of paper

In this study, a computational micromechanics material model for the unloading behavior of paper and other nonwoven materials is presented. The asymptotic fiber and bond (AFB) model for paper elastic–plastic behavior [Sinha, S.K., Perkins, R.W., 1995. Micromechanics constitutive model for use in finite element analysis, In: Proceedings of the 1995, Joint ASME Applied Mechanics and Materials Summer Meeting, Los Angeles, CA, USA, Jun 28–30, 1995] has been extended to model the unloading process through a computational algorithm and implemented using the UMAT subroutine in ABAQUS finite element code. For every unloading increment, the material model assumes elastic unloading with a slope equal to the initial elastic modulus. The Jacobian matrix of the constitutive model is updated at every unloading increment by applying the incremental form of AFB model for a planar element with an elastic fiber and bond condition. A uniaxial tensile and a biaxial Mullen burst loading–unloading experiments were carried out for a paperboard sample and simulated using the model. The stress–strain curve and residual strain for the uniaxial loading were in good agreement with experimental results. The finite element model of the burst test with the AFB unloading material model predicted the general shape of the pressure versus deflection curve. However, the model over predicted the residual deflection by more than 50%. The loading portion of the pressure–deflection curve had a significant offset from experimental curves, and the nonlinearity in the unloading curve towards the end was not predicted. The discrepancies with experimental results are attributed to the burst test itself, model parameter estimation inadequacies, boundary conditions used in the FEA, and neglecting time-dependant effects. Nevertheless, the model can be useful in parametric studies relating microstructure to unloading behavior in structural problems.     

A finite strain elastic-viscoplastic self-consistent model for polycrystalline materials

A large strain elastic-viscoplastic self-consistent (EVPSC) model for polycrystalline materials is developed. At single crystal level, both the rate sensitive slip and twinning are included as the plastic deformation mechanisms, while elastic anisotropy is accounted for in the elastic moduli. The transition from single crystal plasticity to polycrystal plasticity is based on a completely self-consistent approach. It is shown that the differences in the predicted stress-strain curves and texture evolutions based on the EVPSC and the viscoplastic self-consistent (VPSC) model proposed by Lebensohn and Tomé (1993) are negligible at large strains for monotonic loadings. For the deformations involving unloading and strain path changes, the EVPSC predicts a smooth elasto-plastic transition, while the VPSC model gives a discontinuous response due to lack of elastic deformation. It is also demonstrated that the EVPSC model can capture some important experimental features which cannot be simulated by using the VPSC model.     

基于显式有限元方法的两相介质弹塑性动力反应计算分析

针对增量形式的流体饱和两相多孔介质弹塑性波动方程组,运用基于显式逐步积分格式的时域显式有限元方法对该波动方程组进行求解,并应用基于SMP破坏准则的弹塑性动力本构模型描述两相介质的动力反应性质,对两相介质在输入地震波作用下的弹塑性动力反应进行计算和分析,将计算结果与相应的弹性动力反应的计算结果进行对比;对本文应用的弹塑性...     

Unloading of an elastic–plastic loaded spherical contact

The process of unloading of an elastic–plastic loaded sphere in contact with a rigid flat is studied by finite element method. The sphere material is assumed isotropic with elastic-linear hardening. The numerical simulations cover a wide range of material properties and sphere radius. The contact load, stresses, and deformation in the sphere during both loading and unloading, are calculated for a wide range of interferences. Analytical dimensionless expressions are presented for the unloading load–deformation relation, the residual interference and the residual curvature of the sphere after complete unloading. A new measure termed elastic–plastic loading index is introduced to indicate the plasticity level of the loaded sphere. Some ideas regarding reversibility of the unloading process and elasticity of multiple loading unloading are also presented.     

移动载荷作用下沥青路面稳态响应与计算

为了研究移动载荷作用下沥青路面稳态响应,将沥青路面看作为作用在Kelvin黏弹性地基 上不仅具有弹性而且具有黏滞性的无限长梁,建立了梁的稳态响应数学模型. 找到了稳态响 应与瞬态响应的关系,由瞬态响应解析解得到了稳态响应近似解析解,并进行了实例计算. 从而解决了稳态数学模型难以求解和计算的问题. 计算结果表明,依所给的道路参数和车辆 载荷,只要响应位置距初始位置一定距离,移动载荷作用下沥青路面的瞬态响应即为稳态 响应.     

Unloading of an elastic–plastic spherical contact under stick contact condition

The unloading process of an elastic–plastic spherical contact under stick contact condition is analyzed for various material properties. The evolution of normal and shear stress distribution at the contact area as well as the residual profile of the sphere and residual von Mises stresses inside the sphere are presented. Empirical expressions for the residual interference and for the evolution of the interference and contact area during the unloading are provided. Good agreement with experimental results is shown.