Fatigue-Crack Propagation

This optimum condition is designed to ensure that the botes of all components yield at the same time. If the cylinder is subjected to fatigue conditions, it has been suggested (39) that a better design criterion would arrange for the maximum normal stress, which controls fatigue crack propagation, to be the same in each component. 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Fatigue Crack Propagation, ASTM STP 415, American Society for Testing and Materials, Philadelphia, Pa., 1967. 

Several theories have been proposed to explain the corrosion-fatigue phenomena. One is that cyclic stressing causes repeated rupture of protective coatings. Corrosion-fatigue cracks propagate as the coating is successively reformed and ruptured along a plane. 

Data on fatigue crack propagation are gathered by cyclically loading specimens containing a sharp crack like that shown in Fig. 15.7. We define... 

Total interpenetration of chains (X approaches Rg) is not necessary to achieve complete strength when M > M and x < 7). However, a word of caution while complete strength may be obtained in terms of critical fracture measures such as G c and A lc, the durability, measured in sub-critical fracture terms, such as the fatigue crack propagation rate da/AN, may be very far from its fully healed state at r. We have shown that while the weld toughness A lc increases linearly with interdiffusion depth X as K f. X, the fatigue crack propagation behavior of partially healed welds behaves as [1]... 

Fig. 8.61 Fatigue crack propagation across specimen section (after Tomkins and Wareing...

Remarkably little has been published on corrosion fatigue crack propagation in copper and its alloys. In general little or no influence of marine environments has been observed in crack propagation experiments on manganese and nickel-aluminium bronzes although the frequencies employed were quite high (> 2.5 Hz) ... 

Stewart, A. T., Effect of hydrogen on fatigue crack propagation in steels , Proc. Int. Conf. on Mechanisms of Environment Sensitive Cracking in Materials, University of Surrey, 4-7 April 1977, The Metals Society, pp. 400-11 (1977)... 

James, L. A., Fatigue crack propagation in Austenitic stainless steel . Atomic Energy Review 14, 37-86 (1976)... 

Barsom, J. M., Effect of cyclic stress waveform on corrosion fatigue crack propagation... 

Ritchie, R. O., Near threshold fatigue crack propagation in steels . International Metals Reviews, Nos. 5 and 6, pp. 205-230 (1979)... 

Brocklehurst [37] has written an exhaustive review of the early work (prior to 1977) on fracture in polycrystalline graphite. Much of this work focused on the fracture behavior of nuclear graphites. In most investigations considered, conventional fracture mechanics tests and analysis were performed for macroscopic cracks. LEFM provided an adequate criterion for failure. Additionally, results on work of fracture, strain energy release rate, and fatigue crack propagation were reported. 

Fatigue crack initiation, in metal-matrix composites, 16 185 Fatigue crack initiation sites, 13 481 Fatigue crack propagation tests, 16 185-187... 

ISO 15850 2002 Plastics - Determination of tension-tension fatigue crack propagation -Linear elastic fracture mechanics (LEFM) approach... 

The vibratory mode most frequently encountered is of the plate type and involves either the shroud or the disc. Fatigue failure generally originates at the impeller outside diameter, adjacent to a vane often dne to the vibratory motion of the shroud or disc. The fatigue crack propagates inward along the nodal line, and finally a section of the shrond or disc tears out. 

This approach using LEFM is a very useful tool for polymer fracture characterization and may be extended to impact characterization (determination of KId, GId, in dynamic conditions), and for fatigue crack propagation studies (see Sec. 12.4.4). 

Figure 13.11 Paris diagrams for fatigue crack propagation of polyldimethyl-siloxane)-modified epoxy networks. (Rey et a/., 1999 with kind permission from Kluwer Academic Publisher.)... 

R.A. Smith et al Experimental and theoretical fatigue-crack propagation lives of variously notched plates. J. Strain Ana. Eng. Dsgn. 9, 61-66 (1974)... 

Stress ratio. Rates of corrosion fatigue crack propagation generally are enhanced by increased stress ratio R, which is the ratio of the minimum stress to the maximum stress. 

Some other factors, including the metallurgical condition of the material (such as composition and heat treatment) and the loading mode (such as uniaxial), affect corrosion fatigue crack propagation. (Glaeser and Wright)5... 

Figure 6.51 Corrosion fatigue crack propagation rate (da/dN) as a function of the cyclic crack tip stress intensity range (AK) (Phull)5...

---