共查询到19条相似文献,搜索用时 187 毫秒
1.
基于如下假设,给出了层裂过程中的应力松弛方程,并建立了一种基于空穴聚集的延性层裂模型:在层裂早期,微空穴的主要效应是减小应力作用面积;在层裂后期,应力按空穴聚集时的应力-空隙度依赖关系减小。把P.F.Thomason、D.L.Tonks等及S.Cochran等给出的依赖于应力(压力)的层裂空隙度方程分别耦合于守恒方程、计及损伤的状态方程及本构方程,建立了求解所有变量包括损伤的封闭方程组。这种基于空穴聚集的层裂模型已被应用于一维层裂试验的数值模拟。模型中的层裂强度及临界损伤度初始可以估计,最终的确定将使数值模拟结果与实测的速度(或应力)剖面以及观测的层裂面上的损伤基本一致。分别基于D.L.Tonk等及S.Cochran等给出的依赖于压力的层裂空隙度方程所作的一维层裂试验数值模拟结果基本一致,而与基于P.F.Thomason给出的依赖于应力的层裂空隙度方程所作的相应数值模拟结果有明显差异。 相似文献
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三角形波致LY12铝层裂的平板冲击实验研究 总被引:1,自引:1,他引:1
采用基于冲击波衰减动力学的实验技术,使平板碰撞层裂实验的LY12铝样品中,产生三角形冲击脉冲.采用VISAR技术记录样品自由表面历史,获得样品中发生层裂的信号.在经过高应力三角形波实验的软回收样品上,发现了两个层裂面.就样品中呈现三角形脉冲的平板冲击实验而言,样品中可以存在一些高拉伸应力区域并发生多次层裂.将该文提出的基于空穴聚集的层裂模型用于数值模拟这些特定条件的平板冲击试验,并将计算的样品自由面速度历史及样品中的损伤分布与实测的VISAR数据及软回收的样品层裂面等作了比较.研究表明,人为粘性、状态方程、本构方程以及层裂模型对于数值模拟三角形冲击脉冲引起的层裂有严重影响. 相似文献
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初始应力状态对材料层裂破坏特性影响研究 总被引:3,自引:0,他引:3
通过对球面飞片加载条件下的应力/应变状态分析表明采用施加径向应变方法可以近似模拟球面加载的受力过程. 采用过盈配合的热装配方法对平面样品施加了径向预应变,一维平面应变气炮实验结果显示初始预应力(变)明显降低了LY12铝层裂强度. 从空洞长大基本原理出发分析了各向异性受力条件下空洞长大的路径和所消耗能量不同于各向同性应力加载.通过数值模拟对含损伤的材料本构模型进行分析,得到了材料层裂强度与其外部宏观应力场密切相关,也间接的与构型相关的结论. 相似文献
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20#钢动态拉伸断裂行为及其临界损伤度研究 总被引:1,自引:0,他引:1
首先对一维应变平面冲击载荷下20#钢的动态拉伸断裂行为进行了实验研究,考察了加载应力和拉伸应变率影响;然后基于损伤度函数模型,对实验进行了数值模拟研究,结果表明:模型中定义的特征物理量一断裂临界损伤度与外载荷条件(加载应力和拉伸应变率)的无关性或不敏感性;最后,采用Ls-dyna动力有限元程序并嵌入损伤度函数模型,对滑移爆轰下20#钢柱壳内爆驱动层裂进行二维数值模拟研究,结果表明:一维应变平面层裂实验和模型计算确定的损伤模型参数,也适用于描述柱壳构形复杂应力环境下的动态拉伸断裂问题.从而初步证实了断裂临界损伤度可以看作是一个表征延性金属动态拉伸断裂的内禀物性参数. 相似文献
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结合经典强度理论和现代损伤力学对金属屈服和断裂解释的力学原理,给出了高强钢在应力三轴空间广义屈服轨迹方程的新诠释.根据三向等拉伸应力状态下高强钢屈服和宏观脆断的重合性,提出了高强钢在应力三轴空间的开裂准则.通过对高强钢刻痕杆断裂试验的数值模拟分析,对比验证了该开裂准则的普适性及精度.最后,给出了高强钢广义强度理论的物理解释及抗断设防.建议的广义强度理论是解高强钢裂纹体和无裂体断裂的一个尝试. 相似文献
8.
Li Qingzhong 《力学学报》2010,42(5):971
通过逆向加载和等厚对称碰撞实验相结合的方法,确定了FeMnNi合金完整的加卸载物理过程和相变层裂特征。采用修正的Boettger模型与非平衡两相相变理论模型,成功模拟再现了实验过程,解释了冲击相变、卸载逆相变及稀疏冲击波形成的物理机理。实验和数值模拟相结合,从应力波相互作用的角度定量分析了层裂发生的原因,指出层裂发生的机制正是由于受载样品发生了冲击相变和卸载逆相变。 相似文献
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A. Chatterjee 《Shock Waves》1999,9(2):95-105
An initially planar shock wave can undergo significant distortion to its shape along with changes in its strength during
the period of its interaction with a compressible vortex. This phenomenon is studied by numerically simulating the shock wave-vortex
interaction with a high resolution shock-capturing scheme. Incident shock waves of various Mach numbers are made to interact
with a compressible vortex and the dependence of the shock wave distortion on the strength of the incident shock wave is studied
in detail. It is known that the type of complex shock structure formed in the later stages of a compressible vortex-shock
wave interaction is dependent on the Mach number of the incident shock wave. A simple physical model based on the principle
of shock wave reflection is proposed to explain this complex shock structure formation and its dependence on the relative
strengths of the interacting vortex and shock wave.
Received July 28, 1997 / Accepted November 17, 1997 相似文献
12.
Yao Guowen Liu Zhanfang Huang Peiyan 《Acta Mechanica Solida Sinica》2006,19(1):69-74
The failure wave has been observed propagating in glass under impact loading since 1991. It is a continuous fracture zone which may be associated with the damage accumulation process during the propagation of shock waves. A progressive fracture model was proposed to describe the failure wave formation and propagation in shocked glass considering its heterogeneous meso-structures. The original and nucleated microcracks will expand along the pores and other defects with concomitant dilation when shock loading is below the Hugoniot Elastic Limit. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from the collapse of the original pores. Numerical simulation of the free surface velocity was performed and found in good agreement with planar impact experiments on K9 glass at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer. 相似文献
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This paper describes the shock propagation through a dilute gas-particle suspension in an aligned baffle system. Numerical
solution to two-phase flows induced by a planar shock wave is given based on the two-continuum model with interphase coupling.
The governing equations are numerically solved by using high-resolution schemes. The computational results show the shock
reflection and diffraction patterns, and the shock-induced flow fields in the 4-baffle system filled with the dusty gas. 相似文献
14.
We propose a constitutive model to describe the nonlinear viscoelasticity of epoxy resins in the glassy state. Experimental tests have shown that nonlinear viscoelasticity rules the cyclic behaviour of epoxy resins before the material strength is reached. The proposed model allows the simulation of this cyclic behaviour and, in particular, of the flex which characterises the stress–strain curve upon unloading. The consistent integration algorithm, based on the Central Difference Scheme, of the proposed constitutive law is given. As an example, the model is successfully used to numerically homogenize the cyclic behaviour of hollow sphere-filled epoxy resins (i.e., syntactic foams) by means of unit cell models. 相似文献
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The springback phenomenon of strong anisotropic sheet metals with U-channel bending as well as deep-drawing is numerically
studied in detail by using Updating Lagrange FEM based on virtual work-rate principle, Kirchhoff shell element models and
the Barlat-Lian planar anisotropic yield function. Simulation results are compared with a benchamark test. Very good agreement
is obtained between numerical and test results. The focus of the present study is on the numerical simulation of the springback
characteristics of the strong anisotropic sheet metals after unloading. The effects of the planar anisotropy coefficients
and yield function exponent in the B-L yield function on the springback characteristics are discussed in detail. Some conclusions
are given.
The project supported by the National Natural Science Foundation of China (No. 19832020) and Provincial Natural Science Foundation
of Jilin China (No.20000519) 相似文献
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We study planar shock wave structure in a two-temperature model of a fully ionized plasma that includes electron heat conduction
and energy exchange between electrons and ions. For steady flow in a reference frame moving with the shock, the model reduces
to an autonomous system of ordinary differential equations which can be numerically integrated. A phase space analysis of
the differential equations provides an additional insight into the structure of the solutions. For example, below a threshold
Mach number, the model produces continuous solutions, while above another threshold Mach number, the solutions contain embedded
hydrodynamic shocks. Between the threshold values, the appearance of embedded shocks depends on the electron diffusivity and
the electron–ion coupling term. We also find that the ion temperature may achieve a maximum value between the upstream and
downstream states and away from the embedded shock. We summarize the methodology for solving for two-temperature shocks and
show results for several values of shock strength and plasma parameters in order to quantify the shock structure and explore
the range of possible solutions. Such solutions may be used to verify hydrodynamic codes that use similar plasma physics models. 相似文献
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激波在自由面卸载后金属内部经常出现层裂现象。若金属内层裂区再次受到冲击加载,则处于拉伸稀疏状态下的金属会逐渐被再次压实为密实介质,直至层裂区消失、再压实过程完成。由于金属层裂区初始拉伸状态的复杂性及再压实后物质状态的不确定性,复杂加载情况下宏观模拟该问题的可靠性验证存在困难。目前,在实验诊断难以准确给出金属层裂区进入再压实过程的初始状态及再压实状态的情况下,具有层裂区内部细节描述能力的直接数值模拟成为了验证宏观模拟可靠性的一种有效手段。首先,在直接数值模拟建模中将金属层裂区初始拉伸状态建模为仅含层裂片、仅含孔洞、同时含有孔洞与层裂片3类情况。然后,通过不同孔隙度、再压实速率、层裂片数及孔洞数下的直接数值模拟,统计得到了对应工况下金属层裂区的再压实状态。最后,在保证直接模拟与宏观模拟具有良好可比性的情况下,对层裂再压实过程进行了宏观建模及模拟分析。分析认为:在宏观网格断裂后处理算法使用全应力置零和温度不变的情况下,宏观模拟能够较好地模拟稀疏区内含层裂片情况下的金属层裂再压实过程及再压实状态;若金属层裂区内部以仅含孔洞的初始状态进入再压实过程,则无论孔洞塌缩是否形成界面喷射,宏观模拟均无法较好模拟该层裂再压实过程及再压实状态。 相似文献
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聚硅氧烷硅胶是一类以Si——O键为主链、硅原子上直接连接有机基团的无色透明高分子聚合物, 因其具有优异的超弹性性能而广泛应用于精密减震结构、柔性电子器件等领域. 在聚硅氧烷硅胶减震结构和柔性电子器件的设计中, 材料在大变形和动态加载下的黏超弹性力学行为的精确描述至关重要. 本文针对该问题进行了系统的研究:首先, 将该硅胶的超弹性和黏弹性行为进行解耦, 确定其黏超弹性本构方程的基本框架;其次, 基于单轴拉压、平面拉伸试验确定其准静态超弹性模型的各项参数;再次, 利用霍普金森压杆冲击试验确定其黏弹性模型的各项参数;在此基础上, 将超弹性和黏弹性模型合并为适用于大应变和大应变率的黏超弹性动态本构模型;最后, 利用落锤冲击试验对该硅胶薄片的冲击变形行为进行了研究, 并利用上述建立的动态本构模型对落锤冲击过程进行了有限元模拟. 结果表明:本文建立的黏超弹性本构模型可有效预测该硅胶在冲击载荷下的力学行为, 从而为聚硅氧烷硅胶减震结构和柔性电子器件的优化设计提供了理论和应用基础. 相似文献
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The influences of the acoustic impedance and shock strength on the jet formation in shock-heavy gas bubble interaction are numerically studied in this work. The process of a shock interacting with a krypton or a SF 6 bubble is studied by the numerical method VAS2D. As a validation, the experiments of a SF 6 bubble accelerated by a planar shock were performed. The results indicate that, due to the mismatch of acoustic impedance, the way of jet formation in heavy gas bubble with different species is diversified under the same initial condition. With respect to the same bubble, the manner of jet formation is also distinctly different under different shock strengths. The disparities of the acoustic impedance result in different effects of shock focusing in the bubble, and different behaviors of shock wave inside and outside the bubble. The analyses of the wave pattern and the pressure variation indicate that the jet formation is closely associated with the pressure perturbation. Moreover, the analysis of the vorticity deposition, and comparisons of circulation and baroclinic torque show that the baroclinic vorticity also contributes to the jet formation. It is concluded that the pressure perturbation and baroclinic vorticity deposition are the two dominant factors for the jet formation in shock-heavy gas bubble interaction. 相似文献