5A06铝合金的动态本构关系实验

运用材料试验机和分离式霍普金森压杆装置(SHPB)对3种不同加工及热处理状态的5A06铝合金在常温~500 C、应变率为10-4~103 s-1 下的力学行为进行了实验研究。基于Johnson-Cook (JC) 本构模型,通过实验数据拟合得到了每种状态下材料的本构模型参量。对Johnson-Cook本构模型中的应变率强化项作了修正,修正后的Johnson-Cook本构模型与实验数据基本吻合,从而确立了3种状态下5A06铝合金的动态本构关系。     

6061-T6铝合金动态拉伸本构关系及失效行为

采用HMH-206高速材料试验机开展了6061-T6铝合金在0.001～100 s-1应变率范围内的静、动态拉伸力学性能实验,分析了其应力-应变响应特征和应变率敏感性,讨论了应变率对6061-T6铝合金流动应力和应变率敏感性指数的影响,并基于实验结果对Johnson-Cook本构模型进行了修正。结合缺口试件的实验结果和模拟数据,得到了材料的Johnson-Cook失效模型参数,并对模型的准确性和适用性进行了验证。结果表明,在拉伸载荷作用下,6061-T6铝合金表现出明显的应变硬化特征和应变率敏感性,其流动应力随应变率的升高而提高,修正的Johnson-Cook本构模型可以描述材料的动态塑性流动行为,建立的Johnson-Cook失效模型能够表征材料的断裂失效行为。     

陶瓷材料动态压缩损伤本构模型

运用细观损伤力学理论,从动态压缩载荷下陶瓷材料内翼型裂纹的产生和扩展的损伤机理出发,建立了陶瓷材料的弹脆性动态损伤本构模型,给出相应的损伤演化方程.假设裂纹成核满足Weibull分布,讨论了成核分布参数、原始缺陷尺寸对材料动态断裂应力、断裂应变的影响,并用动态损伤演化模型计算了冲击载荷下AD90陶瓷的动态应力应变曲线,计算结果和实验结果符合很好.     

基于J-C模型的Q235钢的动态本构关系

采用万能材料试验机、分离式霍普金森压杆和拉杆系统,研究了Q235钢在常温至900 ℃的准静态和动态压缩及拉伸力学性能。基于实验结果,修正了Johnson-Cook（J-C）本构模型中的温度软化项,提出了Q235钢的修正J-C本构模型,并利用Taylor撞击实验和数值仿真验证了其动态本构关系。     

考虑损伤的节理本构模型

本文在弹塑性损伤的理论框架内，讨论了节理等地质间断面的本构模型。这个模型能够反映节理面的损伤弱化，扩容和弹性刚度劣化等复杂特性。这个模型的另一优点是，塑性变形增量与屈服面是非正交的，但本构矩阵具有对称性。这种对称性在岩石力学的理论研究和数值分析中是至关紧要的。     

7A04铝合金的本构关系和失效模型

使用万能材料试验机、扭转试验机和Taylor撞击实验研究了高强铝合金7A04在常温至250 ℃的 准静态、动态本构关系和失效模型。基于实验结果,修改了Johnson-Cook强度模型中的应变强化项以及 Johnson-Cook失效模型中的温度软化项,并结合数值模拟标定了模型参数。实验结果表明,7A04铝合金的 应变和应变率强化效应不显著,失效应变随温度的增加、应力三轴度的减小和应变率的减小而增加。     

一种高强度钢的动态力学本构参数识别和数值模拟

分析了N-1钢在不同应变率条件下(10-3~103s-1)的应力应变关系实验结果,得到了N-1钢的应 变率强化特性。修正了平板试件断裂面中心的真实应力,并通过对真实应变与最小截面的厚度缩减率关系的 研究,得到了断裂面中心的真实应变,从而识别出了N-1钢的修正Johnson-Cook本构模型的参数。利用所确 定的本构关系模型,对N-1钢平板试件的杆-杆型冲击拉伸过程进行了数值模拟,模拟结果与实验结果较吻 合,验证了采用的修正的Johnson-Cook本构模型参数的实验识别方法以及数值模拟方法的正确性。     

混凝土冻融损伤本构模型研究

基于各向同性连续损伤力学理论,以损伤条件下的弹性模量和泊松比为变量,基于Ottosen理论模型建立了混凝土冻融损伤破坏准则,并以Ottosen本构理论模型为基础,利用建立的冻融损伤破坏准则构建了混凝土冻融损伤本构模型,并编制了本构模型有限元程序,经过试验验证模型计算结果较为准确,为有限元计算和冻融作用后混凝土结构模拟应...     

Al基含能结构材料的Johnson-Cook本构模型及失效参数研究

利用万能实验机和Hopkinson杆装置测试了Al基含能结构材料在不同温度下的静动态力学性能,分析实验结果得到了温度效应和应变率效应对材料力学性能的影响及该合金的Johnson-Cook本构模型参数.结合二维数字图像相关(DIC)方法,研究了Al基含能结构材料的失效应变与应力三轴度及温度之间的关系,得到了该合金的Johnson-Cook失效模型参数.通过平面撞击实验获得了Al基含能结构材料粒子速度和应力波波速之间的经验线性关系和该合金的Grüneisen系数.基于实验获得的材料本构关系和状态方程参数,完成了Al基含能结构材料超高速撞击多层间隔薄钢板的数值模拟,结果表明,数值模拟中靶板的毁伤模式、破孔直径及弹坑主要散布区和实验结果吻合.     

考虑残余强度影响的岩石损伤本构模型

基于岩石微元强度服从Weibull分布规律,引入损伤变量修正因子,建立了考虑残余强度影响的岩石损伤本构模型.运用多元函数求极值的方法,推导了含修正系数的模型参数\(m\)和\(F_{0}\)的理论表达式;对模型修正因子的选取进行了讨论分析. 结果表明：本文修正模型的实质是增加了一个含有修正系数的线性项;修正系数 \(\delta \)主要反映岩石的残余强度特征,选取合适的 \(\delta \) 值可以提高修正后本构模型的准确性.     

Nonlinear dynamic responses of high-speed railway vehicles under combined self-excitation and forced excitation considering the influence of unsteady aerodynamic loads

The dynamic characteristics of a railway vehicle system under unsteady aerodynamic loads are examined in this study. A dynamic analysis model of the railway vehicle considering the influences of aerodynamic loads was established. The model not only considers the forced excitation effect of unsteady aerodynamic loads but also accounts for the effect of unsteady aerodynamic loads on the change of the wheel–rail contact normal forces as well as changes of the wheelset creep coefficients and creep forces/moments. Therefore, this model also considers the influences of unsteady aerodynamic loads on the self-excited vibration characteristics of the vehicle system. The time-history curves, phase trajectory diagrams, Poincaré sections, and Lyapunov exponents of the vehicle system running on a smooth straight track under unsteady aerodynamic loads were determined. The results show that when the critical speed is exceeded, the vehicle system usually performs quasi-periodic motion under unsteady aerodynamic loads, which is significantly different from the periodic motion under steady aerodynamic loads. In different cases, the amplitude and phase of motion are significantly different. The amplitude of the motions can be increased by more than 159%, and the difference of phase can be up to 173°. (The phase is almost reversed.) The dynamic responses of the vehicle system under unsteady aerodynamic loads contain abundant frequency components, including the frequency of the self-excited vibration, the frequency of the forced excitation, and combinations of their integer multiples. The vibration forms corresponding to the main harmonic components under unsteady and steady aerodynamic loads were compared, and the self-excited vibration component of the vehicle system under unsteady aerodynamic loads was identified. The variations in the critical speed with various parameter combinations were computed. The variation range of the critical velocity can reach 73%.

     

宽应变率范围下2A16-T4铝合金动态力学性能

为了研究2A16-T4铝合金的动态力学性能,利用电子万能试验机、高速液压伺服试验机及霍普金森压杆(SHPB)装置进行常温下准静态、中应变率和高应变率的动态力学性能实验,得到不同应变率下的应力应变曲线,基于修正的Johnson-Cook本构模型对它进行拟合,并分析材料中应变率力学特性对模型应变率敏感参量的影响。结果表明:2A16-T4铝合金在应变率10-4~102 s-1范围内应变率敏感性较弱,而在102~103 s-1范围内应变率敏感性较强,且应变率强化效应随塑性应变的增大而减小;同时,在10-4~103 s-1范围内具有较强的应变硬化效应,且应变硬化效应随应变率的增大而减小;此外,修正Johnson-Cook本构模型的拟合结果与实验结果吻合很好,能够很好表征材料的动态力学行为,且考虑材料中应变率力学特性可提高本构模型参量的准确性。     

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads：the aerodynamic loads can change the position of vehicle system（consequently the contact relations）,the wheel/rail normal contact forces,the gravitational restoring forces/moments and the creep forces/moments.A mathematical model for hunting stability incorporating such influences was developed.A computer program capable of incorporating the effects of aerodynamic loads based on the model was written,and the critical speeds were calculated using this program.The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method,the results were also compared with the situations without aerodynamic loads.It is shown that the most dominant factors a ff ecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not.The damping of yaw damper is the most dominant influencing factor for linear critical speeds,while the damping of lateral damper is most dominant for nonlinear ones.When the influences of aerodynamic loads are considered,the linear critical speeds decrease with the rise of cross wind velocity,whereas it is not the case for the nonlinear critical speeds.The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads.Combined actions of aerodynamic loads and suspension parameters also a ff ect the critical speeds.The effects of such joint action are more obvious for nonlinear critical speeds.     

Analytical track models for ride dynamic simulation of tracked vehicles

This paper presents various modelling strategies to account for track in the ride dynamic simulation of high mobility tracked vehicles negotiating rough off-road terrains. Four analytical track representations of varying complexities are formulated in conjuction with an in-plane ride dynamic model of a typical tracked vehicle. These track models are conceived in view of the tracked vehicle kinematics while ignoring the track belt vibrations. The ride dynamic response of a conventional armoured personnel carrier is evaluated in conjunction with different track methods, and validated against field-measured ride data. The relative performances of these track models are thus assessed based on the accuracy of response predictions, and associated computational time.     

泡沫铝材料动态本构参数的实验确定

基于泡沫材料的动态刚性-线性硬化塑性-刚性卸载(D-R-LHP-R)模型,结合连续性方程,动量守恒方程及刚体的运动方程,得到了激波在泡沫材料中的量纲一消失位置X_s/L₀和动态屈服应力Y_i、激波波速c_p、冲击初始应变ε_i之间的如下关系式: $\frac{X_{\mathrm{s}}}{L_{0}}=\exp \left(-\frac{\rho_{0} c_{\mathrm{p}} v_{\mathrm{i}}}{Y}\right)=\exp \left(1-\frac{\sigma_{\mathrm{i}}}{Y}\right)=\exp \left(-\frac{\rho_{0} c_{\mathrm{p}}^{2} \varepsilon_{\mathrm{i}}}{Y}\right)$ 采用Taylor-Hopkinson装置进行实验,当直接测得泡沫铝试样密度ρ₀、边界初始应力σ_i、初始打击速度v_i、泡沫铝杆原长L₀及激波在泡沫铝杆中消失长度X_s后,利用方程式(a)可反演求得D-R-LHP-R模型下的泡沫铝动态应力应变曲线。最后通过与泡沫铝准静态实验数据对比,表明该泡沫铝是应变率敏感性材料。     

On the fidelity of high-speed photographic systems for dynamic photoelasticity

A general theory has been developed which predicts the influence of the characteristics of a high-speed recording system on the fidelity of a dynamic photoelastic-fringe pattern. The general theory was applied to recording systems currently employed in dynamic photoelasticity which include the high-speed framing camera, the spark-gap camera and the Q-spoiled laser system. Equations for a nondimensional form of the exposure as a function of normalized position have been developed for each of these three recording systems. From these equations, criteria to measure the fidelity of the recording systems were established. The methods developed are applied to the spark-gap system and examples of resolution limits, time shift and distortion are illustrated.     

On the optimal strategy of stochastic-based reliability assessment of railway bridges for high-speed trains

Meccanica - The scope of this paper is to evaluate the performance and computational efficiency of various stochastic simulation methods for a stochastic based reliability assessment of railway...     

Revised damage evolution equation for high cycle fatigue life prediction of aluminum alloy LC4 under uniaxial loading

The fatigue life prediction for components is a difficult task since many factors can affect the final fatigue life. Based on the damage evolution equation of Lemaitre and Desmorat, a revised two-scale damage evolution equation for high cycle fatigue is presented according to the experimental data, in which factors such as the stress amplitude and mean stress are taken into account. Then, a method is proposed to obtain the material parameters of the revised equation from the present fatigue experimental data. Finally, with the utilization of the ANSYS parametric design language (APDL) on the ANSYS platform, the coupling effect between the fatigue damage of materials and the stress distribution in structures is taken into account, and the fatigue life of specimens is predicted. The outcome shows that the numerical prediction is in accord with the experimental results, indicating that the revised two-scale damage evolution model can be well applied for the high cycle fatigue life prediction under uniaxial loading.