Effective stress intensity factor

Correspondingly, the effective stress intensity factor range, may be expressed as... 

Fig. 7.15 A comparison of the normalized effective stress intensity factor, Ke K, as a function of the normalized time, tltc, for static loading and for different waveforms in cyclic loading. After Lin et al.M See text for details.

Figure 3.23. Stress components at a point near a hollow microsphere in the vicinity of the crack (a) before superposition, (b) after superposition, and (c) effective stress intensity factor Kj) [31]...

The computational process of analysis is hidden from the user, and visually the analysis is conducted in terms of M-02-91 or R6 [6] assessment procedure On the basis of data of stress state and defect configuration the necessary assessment parameters (limit load, stress intensity factor variation along the crack-like defect edge) are determined. Special attention is devoted to realization of sensitivity analysis. Effect of variations in calculated stress distribution and defect configuration are estimated by built-in way. 

Figure 7 shows these results schematically for both twist and tilt crack deflections. Thus, for the stress intensity factor required to drive a crack at a tilt or twist angle, the appHed driving force must be increased over and above that required to propagate the crack under pure mode 1 loading conditions. Twist deflection out of plane is a more effective toughening mechanism than a simple tilt deflection out of plane. 

An analysis of loading mode effects has also provided evidence of the critical role of hydrogen. A stress-intensity factor (K) can be achieved in either a tensile loading mode (mode I) or a shearing mode (mode III) (Section 8.9). Under mode I conditions the volume of metal immediately in... 

The last issue that remains to be addressed is whether the MBL results are sensitive to the characteristic diffusion distance L one assumes to fix the outer boundary of the domain of analysis. In the calculations so far, we took the size L of the MBL domain to be equal to the size h - a of the uncracked ligament in the pipeline. To investigate the effect of the size L on the steady state concentration profiles, in particular within the fracture process zone, we performed additional transient hydrogen transport calculations using the MBL approach with L = 8(/i — a) = 60.96 mm under the same stress intensity factor Kf =34.12 MPa /m and normalized T-stress T /steady state distributions of the NILS concentration ahead of the crack tip are plotted in Fig. 8 for the two boundary conditions, i.e. / = 0 and C, =0 on the outer boundary. The concentration profiles for the zero flux boundary condition are identical for both domain sizes. For the zero concentration boundary condition CL = 0 on the outer boundary, although the concentration profiles for the two domain sizes L = h - a and L = 8(/i - a) differ substantially away from the crack tip. they are very close in the region near the crack tip, and notably their maxima differ by less than... 

Using the MBL formulation, we performed additional transient hydrogen transport calculations with L — 5.10, 9.96, 16.04, 21.36. 31.28. 41.63, 50.38 mm, stress intensity factor K, =34.12 MPaVm. T Icsa =-0.316, and zero hydrogen concentration C, prescribed on the outer boundary. For these domain sizes, we found the values of the effective time to steady state r to be 240. 608. 1105. 1538. 2297, 2976. and 3450 sec, respectively. Although the MBL approach does not predict the effective time to steady state accurately in comparison to the full-field solution, it can be used to provide a rough approximation. The non-dimensional effective times to steady-state r = Dl jb and the... 

The third example of time effects in elastic fracture concerns accelerated crack growth. Up to the early 80 s it has been assumed that a unique relation exists between the stress intensity factor K and the rate of crack growth da/dt. This contention had been confirmed in many steady crack growth experiments. Using three point bending specimens Chan and Williams [33] obtained for HDPE in water the following relation between da/dt, and the acting stress intensity factor Kc ... 

If the crack tip is considered to be located at the end of the zone of bridging or cohesion (see Fig. 10.6), then the cohesive forces exist in the wake of the crack. Under these circumstances, the cohesive forces essentially reduce the effective value of the stress intensity factor at the crack tip, Keff. Accordingly, the crack tip in this case is shielded. When the shielding is only partial, Keff is finite, whereas for complete shielding, Keff = 0. Both cases are valid fracture mechanics representations for cracks that include cohesive zones. We consider partial shielding first. 

The approach here is that of partial shielding with a finite value of the effective crack tip stress intensity factor, Keff. The crack growth rate law assumed was of the form... 

Kawada H, Srivastava VK (2001) The effect of an acidic stress environment on the stress-intensity factor for GRP laminates. Compos Sci Technol 61(8) 1109—1114... 

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