Home About us Contact
|
Home About us Contact | ||
|
|
||
Crack Branching (crack + branching)
Selected AbstractsREAL-TIME EXPERIMENTAL INVESTIGATION OF DYNAMIC CRACK BRANCHING USING HIGH-SPEED OPTICAL DIAGNOSTICSEXPERIMENTAL TECHNIQUES, Issue 2 2003L.R. Xu First page of article [source] Environmental and frequency effects on fatigue crack growth rate and paths in aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005S. A. MICHEL ABSTRACT The environmental and frequency effects on fatigue crack growth in aluminium alloys are studied theoretically and experimentally. 2024-T351 and 7075-T651 tested in corrosive environments (humid air or technically purified nitrogen) show a constant crack growth rate (da/dN) at low values of the effective stress intensity range (,Keff). Typical well-known fits of this curve (da/dN vs ,Keff) do not reflect the plateau-like region. A new model of crack growth is presented, which physically attributes this region to the formation and subsequent fracture of a crack tip oxide layer. The thickness of this layer is measured with X-ray photon electron spectroscopy. At higher loads, other mechanisms are understood to be active. The model parameters are determined from constant amplitude tests, and are valid for a given material and environment. In 7075-T651 tested in nitrogen, with R= 0.1 and 83 Hz, unexpected macroscopical crack branching is observed when ,Keff reaches approximately 3.0 MPa ,m. [source] Dynamic crack propagation with cohesive elements: a methodology to address mesh dependencyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2004F. Zhou Abstract In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three-dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effect of cooling rate and crack propagation direction on the mode 1 interlaminar fracture toughness of biaxial noncrimp warp-knitted fabric composites made of glass/PP commingled yarnPOLYMER COMPOSITES, Issue 3 2008Yantao Wang The mode 1 interlaminar fracture toughness of biaxial (±45°) noncrimp warp-knitted fabric composites made of glass/PP commingled yarn was investigated. The crack propagation along the warp and weft directions, respectively, was considered for the composites cooled at two different rates during laminate molding. The interlaminar fracture toughness was characterized by determining the critical strain energy release rate (GIC) of initiation and propagation measured from the double cantilever beam tests. In the case of a slow cooling rate (1°C/min), most specimens possess pure interlaminar crack propagation and direction-independence characteristics. Nevertheless, the high-cooled (10°C/min) specimens fractured in both directions suffer extensive intraply damage (crack branching, debonding, and bridging of 45°-oriented interfacial yarns) and knit thread breakage, leading to GIC of propagation two times higher than that of the slow-cooled specimens, and the clear difference in the GIC values of initiation between the two directions may be due to the contribution of the knit thread breakage to the fracture energy. POLYM. COMPOS., 2008 © 2007 Society of Plastics Engineers [source] | |||||||||||||