Rice stress cracks

A. Lustiger, Understanding Environmental Stress Cracking in Polyethylene, in Medical Plastics Degradation, Resistance Failure Analysis ed. R.C. Portnoy (SPE, Plastic Design Library, Rice RC, Tritsch DE, 1998), pp. 66-71... 

There are several published papers dealing with the modeling of stress cracks in a rice kernel induced by drying. Two complementary approaches are usually used ... 

Stermer, R. A., 1968. Environmental conditions and stress cracks in milled rice. Cereal Chem. 45(4) 365—373. 

Oven-puffed breakfast cereals constitute one of the most important categories. Undoubtedly, the most popular is expanded rice. These products have less expansion compared to products expanded with gun-puffing. The preferred rice is medium or short with intermediate amylose content (15%-20%). Waxy rice is not recommended, nor is milled rice with a high incidence of microfissures or stress cracks and fat content (>0.25%), because it expands less and yields low-quality products. Generally, the kernel expands 2 to 5 times its original volume. The traditional process for oven-puffed rice is depicted in Figure 11.3. The unit operations are practically... 

Rice J.R., Drucker D. (1967) Energy changes in stressed bodies due to void and crack growth. Int. J. Eracture Mech. 3 (1), 19-27. 

Moreover, the decrease of the stress field ahead of the crack tip is explained by the development of a damage zone with load increase (Fig. 9). Loading is made prior to reaching the experimental fracture energy evaluated by the Rice Integral (as a crack stop criterion). Nevertheless, the mesh distortion at the crack tip does not allow to increase more loading because Ottosen model is not usually applied on notched beams. 

This is the contour integral described by Rice wiuch is usually denoted by J for non-linear elastic materials and becomes G for the linear case given here. The result is important since, if a stress analysis for a cracked body is performed in which the stress and displacement fields are found, then G may be determined. 

The elliptical hole prepares our intuition for the more extreme case that is presented by the atomically sharp crack. For the sharp crack tip, the dominant stresses near the crack tip may be shown to have a singular character with the particular form (see Rice (1968) for example). The realization that the crack tip fields within the context of linear elasticity have such a simple singular form has... 

According to Landes and Wei [2], the connection between the steady-state creep rate and the crack-driving force (characterized by K) is derived through the use stress-strain results from elastic-plastic analysis by Hutchinson [9] and Rice and Rosengren [10], According to these models, crack-tip stress and strains in the loading direction (y-direction) are given by Eqn. (6.7). 

The contour integral [17] was applied to fracture analysis in 1968 by Rice [18] to characterize elastic-plastic material behavior ahead of a crack. This nonlinear energy release rate was expressed in the form of a line integral, which was described as the J-integral. evaluated along an arbitrary contour around the crack. The analyses [ 19.20] showed that J can yield a nonlinear stress intensity parameter as well as energy release rate. 

At larger stresses, beyond SSY, for which the plastic zone extends deeper into the undeformed ligament t = D - a as shown in Fig. 12.6(b), the stress and strain distributions at the crack tip inside the yield zone are now very significantly altered, such that the strongly attenuated stresses are accompanied by more concentrated crack-tip plastic strains. To deal with a family of such problems a form of non-linear crack-tip analysis was introduced independently by Hutchinson (1968) and by Rice and Rosengren (1968). This approach is referred to as the HRR crack-tip analysis. 

The problem of a crack meeting an interface in a composite as shown in Fig. 16.6(a) was posed by Cook and Gordon who wrongly concluded that the strength of the interface was important. Zak and Williams followed by Rice and Sih" also studied this problem using elastic stress analysis, but the problem was complicated mathematically and led to strange oscillating stresses near the crack... 

A second approach is that of Rice,(3) who defined a path-independent integral around a crack and denoted it J. It turns out that, for a nonlinear elastic solid, the integral is equivalent to the energy released from the stress field for unit propagation of the crack and is thus essentially the same as the more empirical parameter of Rivlin and Thomas.(2)... 

A number of additional trends can be noted. For example, if the stress concentration factor is larger than 2 - it is approximately 3 for a circular groove in a tension field - then the site is more effective as a source of dislocations. If the configuration of the stress concentrator is a notch with a very high curvature of the notch surface at its root, then the stress concentration factor can be very large compared to 2, but the spatial extent of the localized stress field is significantly reduced from that of the circular stress concentrator. For the case of a planar crack, which is the ultimate sharp notch, the issue of dislocation nucleation has been modeled by Rice and Thomson (1973) and Rice and Beltz (1994). Similar techniques have been adapted for the study of dislocation nucleation at the edge of an epitaxial island (Johnson and Freund 1997). 

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