Fracture mechanics nonlinear effects

These analyses and associated experiments demonstrate that fracture mechanics can be used to provide information and insight into the value of the failure load, the locus of likely crack growth, and the path along which the crack will then grow. Where analytical analyses of stress, strain, and energy release rates are difficult or impossible, modern numerical methods can be very useful. In the opinion of the authors, the utility of these combined tools has hardly been exploited. The inclusion of nonlinear, nonelastic effects in the analyses is feasible is such materials are carefully characterized and/or properties become available. 

In special cases, such as elastomers or other high-elongation materials, bulk plastic or nonlinear behavior of the material does occur. For these cases there have been theories proposed. Chapter 1 discussed the generalized fracture mechanics theory developed by Andrews in which the effect of variables such as crack speed, temperature, and magnitude of strain on the strain energy release rate is considered. ... 

The problem of secondary flexure in axial tensile tests is considered in view of the tension-softening process. The procedures aimed at elimination of that parasite effect were studied by Akita et al. (2001) and Novak et al. (2006) who have shown possibilities of nonlinear fracture mechanics simulation in analysis of the experimental data, including post-peak descending branch of the load-displacement curves, taking into consideration material imperfections and heterogeneities. 

The early researches were mainly concentrated on the calculation of the fracture toughness of concrete in Mode I by testing notched beam specimens. It has been observed that when Kx is calculated from the measured values of the maximum load, the initial notch length and the formulas developed from linear elastic fracture mechanics, the value of is dependent on the dimensions of the beam. This size and geometry dependency can be attributed to slow crack growth and nonlinearity due to random and geometrical interlock effects. 

As shown in Fig.3, the interfacial debonding can be clearly observed. This fracture behavior will be more effective for improving the mechanical properties of the composites through the stress transfer and crack deflection mechanism. Load-displacement curve from bending test of the as prepared 3D C(/SiC composite shows the typically linear and nonlinear parts. 

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