Fracture mechanics-based models

Underfill fracture mechanics-based model N = D MC)" where A AT = range of stress intensity and D = constant 15... 

In many fracture mechanics-based approaches, crack advance is taken to occur when K reaches some critical value Kc (equivalent energy-based criteria are also widely used). Kc may then be measured using a pre-cracked specimen, in which a and hence K are well defined. In some cases (PMMA, for example) crack advance is observed to proceed via breakdown of a single craze at the crack tip. By modeling a craze as an orthotropic linear elastic body it has been shown that Kc is given by Eq. (72), where v is Poisson s ratio, a is related to the craze anisotropy, C7c is the draw stress normal to the craze-bulk interface, Vf is the fibril volume fraction in the craze, and oy is the stress to break a craze fibril [33]. 

Assessment of the elemental mechanistic and synergistic effects for a complex process such as SCC of austenitic stainless steels in SCW will require systematic work and in particular mechanistic fracture mechanics-based crack growth rate tests. More work, especially multiscale modeling based on fundamental mechanisms, is required. 

Finite element mesh for a fracture mechanics-based failure model... 

It is somewhat disconcerting that the MYD analysis seems to present a sharp transition between the JKR and DMT regimes. Specifieally, in light of the vastly different response predicted by these two theories, one must ponder if there would be a sharp demarcation around /x = 1. This topic was recently explored by Maugis and Gauthier-Manuel [46-48]. Basing their analysis on the Dugdale fracture mechanics model [49], they concluded that the JKR-DMT transition is smooth and continuous. 

An improved model based on a fracture mechanics approach... 

There are many features in the analysis of the fiber push-out test which are similar to fiber pull-out. Typically, the conditions for interfacial debonding are formulated based on the two distinct approaches, i.e., the shear strength criterion and the fracture mechanics approach. The fiber push-out test can be analyzed in exactly the same way as the fiber pull-out test using the shear lag model with some modifications. These include the change in the sign of the IFSS and the increase in the interfacial radial stress, (o,z), which is positive in fiber push-out due to expansion of the fiber. These modifications are required as a result of the change in the direction of the external stress from tension in fiber pull-out to compression in fiber push-out. 

Zhou, L.M.. Kim, J.K. and Mai, Y.W. (1992a). Interfacial debonding and fiber pull-out stresses Part II. A new model based on tbe fracture mechanics approach. J. Mater. Sci. 11, 3155-3166. 

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