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961.
The important role of the entanglements in the deformation of high-molecular-weight glassy polymers is demonstrated by two phenomena: the build-up of material resistance in polymethylmethacrylate after chain interpenetration and the intrinsic crazing of polycarbonate which is observed when the entanglement network reaches its limits of extension.Dedicated to Prof. Dr. F. H. Müller. 相似文献
962.
This paper deals with the use of finite element for numerically simulating two-dimensional stable crack growth with mode I. A special model called moving tip node model is developed for this purpose, in which the node at crack tip is arbitrarily moved within one element's dimension by sequentially relaxing nodal forces thus reducing the discreteness of simulation to the lowest extent and making it closer to the real physical process. A reliable FORTRAN program based upon the incremental theory of plasticity is developed wherein an elastic-plastic finite deformation hybrid finite element is employed. The results obtained for an aluminum center crack plate treated as a linear hardening material are compared with the experimental results provided by [11] and the simulation is shown to be successful on the whole. 相似文献
963.
60CrMnMo钢热疲劳裂纹生成与长大及稀土的作用 总被引:11,自引:3,他引:11
采用金相和扫描电镜等手段对60CrMnMo钢热疲劳裂纹的萌生和长大规律进行了分析,并考查了稀土在钢中的作用。结果表明:热疲劳裂纹萌生于钢中夹杂物处,热疲劳裂纹的生长,不仅是裂纹自身发展的结果,更主要的是裂纹的相互联接。钢中加入稀土后,可以变质钢中夹杂物,从而抑制了热疲劳裂纹的生成与长大。 相似文献
964.
In a Small Scale Steady State (S4) test apparatus of ISO 13477, instrumentations were designed and successfully adapted to determine decompression wave speed and crack velocity during rapid crack propagation event in water-filled plastic pipes. The basic design for decompression wave speed measurement involved the use of high-frequency dynamic pressure transmitters, located external to the water-filled pipe and connected to pressure measurement positions inside the pipe, by means of stainless steel tubes. For the crack velocity measurements, timing wire system with the required circuitry capable of giving the precise temporal indication of the propagating crack was designed and employed. In this paper, detailed design of instrumentations adapted to the S4 test apparatus and the assessment techniques used to obtain decompression wave speed and crack velocity are described. It was also demonstrated that the methods developed were viable for these measurements which are known to affect the rapid crack propagation behavior in water-filled plastic pipes. 相似文献
965.
Shiqun Guo 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(8):709-723
This paper is concerned with the elastic wave scattering induced by a penny-shaped interface crack in coated materials. Using
the integral transform, the problem of wave scattering is reduced to a set of singular integral equations in matrix form.
The singular integral equations are solved by the asymptotic analysis and contour integral technique, and the expressions
for the stress and displacement as well as the dynamic stress intensity factors (SIFs) are obtained. Using numerical analysis,
this approach is verified by the finite element method (FEM), and the numerical results agree well with the theoretical results.
For various crack sizes and material combinations, the relations between the SIFs and the incident frequency are analyzed,
and the amplitudes of the crack opening displacements (CODs) are plotted versus incident wavenumber. The investigation provides
a theoretical basis for the dynamic failure analysis and nondestructive evaluation of coated materials. 相似文献
966.
Emin Ergun Kubilay Aslantas Süleyman Tasgetiren 《Mechanics Research Communications》2008,35(4):209-218
In this study, a numerical model was developed to study the effects of mechanical properties of the particle and matrix materials, the crack position (in particle/in matrix) and loading conditions (mode 1 and mixed-mode) in particle-reinforced metal-matrix composites. The finite element technique was used to calculate the stress intensity factors for crack at and near-interface. The Displacement Correlation Method was used to calculate the stress intensity factors K1 and K2. In the present model, the particle and matrix materials were modeled in linear elastic conditions. The interface crack was considered between the particle and matrix, without the presence of the interface. For near-interface crack problem, two different crack positions (in particle/in matrix) were selected. The obtained results show the key role on the stress intensity factors played by the relative elastic properties of the particle and matrix. The results also show that loading condition has an important effect on the K2 stress intensity factor and the crack deflection angle. 相似文献
967.
AbstractAn analytical model is proposed to analyze the vibration and buckling problem of partially cracked thin orthotropic microplate in the presence of thermal environment. The differential governing equation for the cracked plate is derived using the classical plate theory in conjunction with the strain gradient theory of elasticity. The crack is modeled using appropriate crack compliance coefficients based on the simplified line spring model. The influence of thermal environment is incorporated in governing equation in form thermal moments and in-plane compressive forces. The governing equation for cracked plate has been solved analytically to get fundamental frequency and central deflection of plate. To demonstrate the accuracy of the present model, few comparison studies are carried out with the published literature. The stability and dynamic characteristics of the cracked plate are studied considering various parameters such as crack length, plate thickness, change in temperature, and internal length scale of microstructure. It has been concluded that the frequency and deflection are affected by crack length, temperature, and internal length scale of microstructure. Furthermore, to study the buckling behavior of cracked plate, the classical relations for critical buckling load and critical buckling temperature is also proposed considering the effect of crack length, temperature, and internal length scale of microstructure. 相似文献
968.
Bhabani Kumar Satapathy Ulrike Staudinger Roland Weidisch Ralf Lach Andreas Janke Konrad Knoll 《Macromolecular rapid communications》2006,27(4):266-273
Summary: The crack toughness behaviour of binary styrene‐butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer (LN3) and a thermoplastic elastomer (LN4) with different molecular architecture was studied using essential work of fracture (EWF) concept and was correlated to the morphological features from transmission electron microscopy (TEM). An increase in the crack toughness behaviour between 60 and 80 wt.‐% LN3 has been observed and is attributed to a change from cylindrical to lamellar morphology. The time‐resolved crack propagation studies have offered new dimensions to understand the kinetic aspects of fracture behaviour while the strain field analysis has explained the time‐dependent deformation behaviour to characterise the time dependence of the strain energy dissipation modes.
969.
采用线场分析方法对理想弹塑性材料偏心裂纹板在裂纹面受两对反平面点力的情形进行弹塑性分析,分析不受小范围屈服条件的限制,求得了裂纹线附近应力场和位移场的弹塑性解析解、裂纹线上的塑性区长度随外荷载的变化规律及有限宽板具有偏心裂纹的承载力. 相似文献
970.