Crack Growth-Theory

Milella, P.P. A fatigue crack growth theory based upon energy considerations, further development on small crack behavior and R ratio effect. Fatigue and fracture mechanics, Twenty-Ninth Volume. ASTM-STP 1332 (1999)... 

It is envisaged that the degradation of the frictional interface properties and the corresponding increase in the relative displacements eventually lead to debond crack growth once the debond criterion is satisfied. The debond criterion based on the energy balance theory given by Eq. (4,35) under monotonic loading can be rewritten as... 

The basic tenet of continuum fracture mechanics is,- therefore, that the strength of most real solids is governed by the presence of flaws and, since the various theories enable the manner in which the flaws propagate under stress to be analysed mathematically, the application of fracture mechanics to crack growth in polymers has received considerable attention. Two main, inter-relatable, conditions for fracture are proposed. 

If results are obtained as a function of ozone concentration, in theory it should be possible to make extrapolations to ambient conditions by empirically fitting a relation to the concentration against time to cracking/crack growth rate. For natural rubber, there has been evidence that that the relation is broadly linear. 

The following simplified explanation for the observed power-law behaviour during stick-slip crack growth is a limiting case of a more general approach to SCG [43] based on crack layer theory [40, 41]. The crack layer in... 

This behavior is characterized by a plateau region, which prevails above a definite threshold K. It is often referred to as stress-corrosion fatigue because SCC systems usually exhibit this behavior, and the most common theory assumes that the crack growth rate results from the addition of SCC, and pure fatigue crack advance. This is a type of... 

Sandoz, G., A unified theory for some effects of hydrogen source, alloying elements, and potential on crack growth in martensitic AlSl 4340 steel. Metallurgical Transactions, 3, 1169-1176, 1972. 

Recent experiments and theory of truly steady state crack growth indicate that there is a threshold K and V and that the exponent m., changes to become nearly infinite just above the threshold. These complications are ignored in this treatment... 

The aim of this review is to concentrate mainly on these fundamental aspects of the fracture behavior of glassy thermoplastics. In the first Section, following an outline of the relevant fracture mechanics theory, the optical interference method is described and the nature of the results obtainable from it is discussed. The next Section then considers the behavior of cracks and crazes in specimens subjected to quasistatic loading, whilst the final Section examines the role of crazing associated with fatigue crack growth. 

Paris, P.C., Tada, H., Zahoor, A. and Ernst, H., (1979), The theory of instability of the tearing mode of elastic-plastic crack growth. In J.D. Landes, J.A. Begley and G.A. Clarke (Eds), Elastic-Plastic Fracture, ASTM STP 668. American Society for Testing Materials, Philadelphia, 5. 

Let us return to consider the properties of the critical stress intensity for environmentally induced crack growth ( Tiscc)- The fact that /sTiscc for sensitized TVpe 304SS apparently depends on the applied potential can be gleaned from the data shown in Fig. 42. Fur ermore, both experiment and theory have established that the crack growth rate for A bcc solution conductivity, temperature, ECP, flow rate, and possible ion type (e.g., sulfate versus nitrate). The most comprehensive database for the effect of conductivity on crack growth rate is probably that of Kassner et al. [82] at the Argonne National Laboratory. Their data... 

Linear elastic fracture mechanics (LEFM) describes the behaviour of sharp cracks in linear, perfectly elastic materials. Since polymers are neither linear nor elastic, the utility of the theory may, at first sight, seem doubtful. In fact, the deviations from the theoretical assumptions are such that quite minor modifications to the analysis produce a precise description of crack growth in polymers within the framework of the conventional theory. The considerable resources of the subject may thus be utilised in that testing experience on other materials may be employed, together with the available analytical work. 

M.O. Speidel, Current Understanding of Stress Corrosion Crack Growth in Aluminum Alloys, The Theory of Stress Corrosion Cracking in Alloys, S.C. Scully, Ed., NATO Scientific Affairs Division, Brussels, 1971, p 289-354... 

Most of the crack problems that have been solved are based on two-dimensional, linear elasticity (i.e., the infinitesimal or small strain theory for elasticity). Some three-dimensional problems have also been solved however, they are limited principally to axisymmetric cases. Complex variable techniques have served well in the solution of these problems. To gain a better appreciation of the problems of fracture and crack growth, it is important to understand the basic assumptions and ramifications that underlie the stress analysis of cracks. 

K/-V relations observed in this study are shown in Figure 3, where results obtained under two different water vapor pressures were shown. It can be seen that the reproducibility of testing results of Kumamoto andesite under the same environmental condition is very high from this figure. In addition, it can be seen that the crack growth behaviors are facilitated under high water vapor pressure. This is in harmony with the theory of stress corrosion cracking in rocks. The obtained results are summarized in Table 1, where K/ means K, at V = 10 [m/s], and v means v at Ki = 1.6 [MN/m ]. Ki and v were determined in order to compare the stress intensity factor... 

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