Loading intensity factors

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. 

Lack of accepted stress intensity factors for internally pressurized components has, until recently, limited this appHcation. The factors are a function of the size and shape of both cracks and high pressure components as well as modes of loading (91). Stress intensity factors can be derived analytically for some simple geometries, but most require the appHcation of advanced numerical methods (105—107). Alternatively they may be deterrnined experimentally (108). 

Another important appHcation of LEFM is the rate of growth of a fatigue crack under cycHc loading. This is also controlled by the stress intensity factor through an equation of the following form (110) ... 

For a single-value toughness material, dT/dc = 0. Accordingly, if the applied stress intensity factor is always increasing with crack length, equation 4 is always satisfied. Thus, the condition for fracture is equation 5, where is given by the applied loading conditions. 

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. 

The symmetric stress-intensity factor k, is associated ith the opening mode of crack extension in Figure 6-10. The skew/-symmetric stress-intensity factor l<2 is associated ith the fonward-shear mode. These plane-stress-intensity factors must be supplemented by another stress-intensity factor to describe the parallel-shear mode. The stress-intensity factors depend on the applied loads, body geometry, and crack geometry. For plane loads, the stress distribution around the crack tip can always be separated into symmetric and skew-symmetric distributions. 

The stress corrosion resistance of maraging steel has been evaluated both by the use of smooth specimens loaded to some fraction of the yield strength and taking the time to failure as an indication of resistance, and by the fracture mechanics approach which involves the use of specimens with a pre-existing crack. Using the latter approach it is possible to obtain crack propagation rates at known stress intensity factors (K) and to determine critical stress intensity factors (A iscc) below which a crack will not propagate (see Section 8.9). 

Fracture Mechanics Tests One problem of both sustained load and slow strain-rate tests is that they do not provide a means of predicting the behaviour of components containing defects (other than the inherent defect associated with the notch in a sustained load test). Fracture mechanics provides a basis for such tests (Section 8.9), and measurements of crack velocity as a function of stress intensity factor, K, are widely used. A typical graph of crack velocity as a function of K is shown in Fig. 8.48. Several regions may be seen on this curve. At low stress intensity factors no crack growth is... 

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... 

Fig. 9.33 Critical intensity factors for different ways of loading.

The parameter K is the stress intensity factor, whose level defines the stress field around the crack tip. In the case of a mode I loading, it is denoted as Kj. 

Stresses. The main mechanical properties to consider are maximum stress or stress intensity factor, <7m ix or Kmax, cyclic stress or stress-intensity range, Act or AK, stress ratio R, cyclic loading frequency, cyclic load waveform (constant-amplitude loading), load interactions in variable-amplitude loading, state of stress, residual stress, and crack size and shape, and their relation to component size geometry.31... 

POSTER TITLE Identification of the fatigue stress intensity factor threshold for different load ratios R From fretting fatigue to C(T) fatigue experiments... 

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