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451.
H.L. Yu 《Theoretical and Applied Fracture Mechanics》2010,54(1):54-62
Nonlinear dynamic finite element analysis (FEA) is conducted to simulate the fracture of unnotched Charpy specimens of steel under pendulum impact loading by a dedicated, oversized and nonstandard Bulk Fracture Charpy Machine (BFCM). The impact energy needed to fracture an unnotched Charpy specimen in a BFCM test can be two orders of magnitude higher than the typical impact energy of a Charpy V-notch specimen. To predict material failure, a phenomenological, stress triaxiality dependent fracture initiation criterion and a fracture evolution law in the form of strain softening are incorporated in the constitutive relations. The BFCM impact energy results obtained from the FEA simulations compare favorably with the corresponding experimental data. In particular, the FEA predicts accurately the correlations of the BFCM impact energy with such factors as specimen geometry, impactor tup width and material type. The analyses show that a specimen’s progressive deterioration through the thickness dimension displays a range of shear to ductile fracture modes, demonstrating the necessity of applying a stress state dependent fracture initiation criterion. Modeling the strain softening behavior helps to capture the residual load carrying capability of a ductile metal or alloy beyond the onset of damage. The total impact energy can be significantly under predicted if a softening branch is not included in the stress-strain curve. This research supports a study of the puncture failure of railroad tank cars under dynamic impact loading. Applications of the presented fracture model in failure analyses of other structures are further discussed. 相似文献
452.
疲劳短裂纹萌生及发展的细观过程和理论 总被引:20,自引:1,他引:20
本文综述了疲劳短裂纹研究的进展和现状,包括关于短裂纹的属性,短裂纹萌生和发展的细观过程以及描述短裂纹行为的若干模型。 相似文献
453.
通过构造反向传播神经网络,对裂纹尖端的应力场进行模拟,进而实现对裂纹尖端应力场甬数的逼近。得到的网络具有较高的联想、记忆能力和相当的稳定性,并且可以快速、准确地得到带裂纹构件的裂纹尖端应力场,从而确定裂纹尖端的塑性区和分析裂纹的扩展。数值计算给出了LY12-CZ材料裂纹扩展方向的计算结果,与实验结果吻合较好,还给出了两相材料含界面裂纹在复合型载荷作用下的塑性区形状的变化情况,并对两相材料含界面裂纹在复合型载荷作用下裂纹的扩展方向进行了预测。 相似文献
454.
455.
结合材料的破坏通常都是从界面或其附近发生的,但界面破坏的机理及其评价准则尚未十分清楚.采用分子动力学模拟方法,可以对结合材料的界面破坏过程进行模拟,从而获得结合材料的界面应力和界面破坏之间的关系.界面破坏可以分为奇异应力场作用下的破坏,和界面应力集中引起的破坏两种.虽然在分子动力学模拟中采用了高度简化的界面模型,但对界面破坏过程的模拟,仍可以帮助人们获得结合材料界面破坏过程的规律性认识.分别模拟远场作用下界面上存在初始裂纹和界面附近存在初始裂纹两种情况下的界面破坏,根据分子动力学模拟结果,提出了一个结合材料界面破坏的准则. 相似文献
456.
本文提出了一种准一维拉氏分析方法,用二维拉氏实验方法测得的不同拉氏位置上的压力和径向位移的变化曲线作为输入量,就能求解二维冲击波起爆过程中对称轴附近的流场。作为初步应用,文中列出了在两种加载条件下,压装TNT的二维冲击波起爆过程的分析结果。 相似文献
457.
M. V. Mir-Salim-zade 《Journal of Applied Mechanics and Technical Physics》2007,48(4):562-570
The fracture mechanics problem of crack initiation in a stiffened plate is considered. The crack nucleus is modeled by a prefracture
zone with bonds between the crack faces, which is treated as a region of weakened interparticle bonds of the material. The
boundary-value problem of the equilibrium of a stiffened plate with a crack nucleus reduces to a nonlinear singular integrodifferential
equation with a Cauchy type kernel. The strains in the crack initiation zone are found by solving this equation. The case
of the stress state of the plate with a periodic system of prefracture zones is considered.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 111–120, July–August, 2007. 相似文献
458.
Dynamics of flame kernel evolution with and without external energy addition has been investigated analytically and numerically. Emphasis is placed on the effects of radiation heat loss, ignition power and Lewis number on the correlation and transition between the initial flame kernel, the self-extinguishing flame, the flame ball, the outwardly propagating spherical flame and the propagating planar flame. The present study extends previous results by bridging the theories of the non-adiabatic stationary flame balls and travelling flames and allowing rigorous consideration of radiation heat losses. The results show that the effects of radiation heat loss play an important role in flame regimes and flame transition and result in a new isolated self-extinguishing flame. Furthermore, it is found that radiation heat losses significantly increase the critical ignition radius and result in three different dependences of the minimum ignition power on the Lewis number. Comparisons between the results from the transient numerical simulation and those from the quasi-steady state analysis show a good agreement. The results suggest that prediction of flame initiation without appropriate consideration of radiation is not acceptable. 相似文献
459.
M. Buback R. G. Gilbert G. T. Russell D. J. T. Hill G. Moad K. F. O'Driscoll J. Shen M. A. Winnik 《Journal of polymer science. Part A, Polymer chemistry》1992,30(5):851-863
The problems of determining reliable, well-characterized values of kinetic parameters in free-radical polymerizations are discussed. The origins of the fact that experimental determinations of rate coefficients of ostensibly identical systems often result in quite different values being reported can be ascribed to subtle mechanistic assumptions made in data interpretation, which are considered in detail. A series of recommendations to assist in overcoming these problems, and to highlight their origins, are presented, with emphasis placed on new techniques including those employing laser photolysis and EPR. 相似文献
460.
The behavior of nonlinear vibration for symmetric angle-ply laminated plates including the material viscoelasticity and damage
evolution is investigated. By employing the von Karman's nonlinear theory, strain energy equivalence principle and Boltzmann
superposition principle, a set of governing equations of nonlinear integro-differential type are derived. By applying the
finite difference method, Newmark method and iterative procedure, the governing equations are solved. The effects of loading
amplitudes, exciting frequencies and different ply orientations on the critical time to failure initiation and nonlinear vibration
amplitudes of the structures are discussed. Numerical results are presented for the different parameters and compared with
the available data.
The project supported by the National Natural Science Foundation of China (10272042) and the Special Science Fund of the Doctoral
Discipline of the Ministry of Education, China (20020532018)
The English text was polished by Ron Marshall. 相似文献