Near- threshold fatigue crack growth in copper and alpha- brass: Grain- size and environmental effects

Fatigue Crack Resistance of Ultrafine-Grained Copper Structures

“…It can be concluded that the ACR model rationalises the R-ratio effect in FCG stage II with discrete approximation, while it fails when applied to the threshold regime, where, as already known, the role of the microstructure achieves greater importance. This result is in partial accordance with FCG tests made on conventional CG copper, where it has been observed that by decreasing the grain size the threshold K increases, suggesting that in copper crack tip plasticity considerations are more important in determining the threshold values than crack closure effects (Marchand et al, 1988).…”

On the growth of nanoscale fatigue cracks

“…First, nanocracks exhibit growth rates that are comparable to those of fatigue cracks from the other two length scales. However, the computed da/dN for nano-cracks range between 10 À11 and 10 À8 m/cycle, while long cracks were found to grow at rates lower than 10 À11 m/cycle in the experiments of Marchand et al [15] in the near-threshold regime, for copper with two grain sizes of 12 and 120 mm, respectively. In polycrystalline copper, Liaw et al [9] recorded da/dN for copper at two heat-treatment conditions ranging from approximately 10 À10 to values larger than 10 À7 m/cycle.…”

“…However, a more systematic study, using at least one of the well-known methods (constant K max or constant R) will be required for a rigorous characterization of ÁK th for nanocracks. Small cracks -ε appl = 2 × 10 −4 [10] Small cracks -ε appl = 4.5 × 10 −4 [10] Small cracks -ε appl = 7 × 10 −5 [10] Long cracks -Cu single crystal [16] Long cracks -Cu polycrystal [10] Long cracks -Cu polycrystal -120 µm [15] Long cracks -Cu polycrystal -12 µm [15] Long cracks -Annealed Cu, R = 0.7 [9] Long cracks -Quarter-Hard Cu, R = 0.7 [9] The growth rates for nanocracks computed from atomistic simulations indicated that as the applied ÁK is lowered toward a value of approximately 0.05 MPa/m 1/2 , the scatter in the growth data increases considerably. On the contrary, for larger ÁK values, the crack growth rates do not exhibit significant scatter and the data tends to be positioned on a well-defined line on the da/dN versus ÁK plot.…”

Development of <i>ΔK</i>-decreasing test method of the metal film by displacement constraint along the elliptical through hole-edge

“…The threshold stress intensity factor ranges, DKth, are obtained 2.3MPa m, 3.3 MPa m and 3.5 MPa m for the aluminum, the copper and the titanium films, respectively. The value of DKth is smaller for the copper film than for the bulk one with the comparable poof stress (Liaw, et al, 1982 andMarchand, et al, 1988). On the other hand, the DKth for the titanium film has about the same value with the bulk one (Ogawa et al, 1988).…”