The Growth of Small Fatigue Cracks in 7075?t6 Aluminum

Abstract

The growth of 'small', half-penny shaped surface fatigue cracks in a precipitation hardened aluminum alloy is compared with the growth of 'large' cracks in fracture mechanics type specimens. I t IS found that the small cracks grow much faster than LEFM equivalent large ones, and also experience growth rate perturbations. It is suggested that localixd microplasticity in nominally elastic specimens IS responsible for the rapid growth of small cracks and that grain size limitations on the microplastic regions cause transient dcceleratioiis and sometimes permanent arrest. in crack growth.

Corrosion Fatigue Crack Propagation Rate Characteristics for Weldable Ship and Offshore Steels with Regard to the Influence of Loading Frequency and Saltwater Temperature

“…The effect is inverse to the short crack length effect, which is well-known (e.g. [4,5]) and will not be considered in the present paper. In the light of later considerations [6], Equation (1) is well-founded theoretically, and therefore the previously [3] proposed alternative form containing the term log(a n ) will not be considered in the present paper.…”

“…For data obtained by Thomas and Wei [23], the activation energy values E act have been calculated directly by Equation (5), that is, by comparison of the ratio of CFCGRs at two different temperatures to the ratio of the above exponential function values at the same temperatures. E act values are shown in Table 3 for different temperature intervals.…”

Fatigue Behavior of Long and Short Cracks in Wrought and Powder Aluminum Alloys.

“…14. In the latter case the progressive deceleration in short crack growth rates was reported in the bsence a notch and attributed to impeded growth at grain boundaries [71].…”

Microstructure-Property Relations in Fatigue of a Cast A356-T6 Aluminum Alloy

“…During typical small fatigue crack growth (incubation, MSC, and PSC regimes in our terminology), microstructure plays an explicit role on the fatigue crack growth behavior for many classes of wrought engineering alloys (Pearson, 1975;Lankford, 1982;Lankford, 1985;Tanaka, 1989;Suresh, 1991;McClung et al, 1996). Furthermore, microstructure has an extremely dominant influence on cracks growing in the small crack regime that are very small with respect to pertinent microstructural features (microstructurally small cracks (Pearson, 1975;Lankford, 1982;Lankford, 1985;Tanaka, 1989;Suresh, 1991;McClung et al, 1996)). As the fatigue crack length and corresponding crack tip driving force increases, cracks are characterized as growing in the Long Crack regime.…”