Application Of Single Overload Research Articles

Fatigue crack growth of composite patch repaired Al-alloy plates under variable amplitude loading

In this paper, fatigue crack growth of edge crack in 2024 T351 aluminum alloy plate repaired with bonded composite patch under constant and variable amplitude loading (VAL) was predicted. The Al-alloy plate was repaired with symmetric patch “Boron/Epoxy”. Additionally to constant amplitude loading (CAL), the effects of single overload and band overload were investigated for repaired and unrepaired Al-alloy plates. The obtained results confirm the improvement in repair performances by composite patch on fatigue lives and crack growth rates for all applied cycles (CAL and VAL) compared to unrepaired plates. A retardation effect was observed in application of single overload compared to band overload with the same stress ratio (R=0.2) for unpatched plate and characterized by instantaneous delays. However, this retardation effect is increased by the presence of the patch repair which leads to the higher fatigue life. Retardation effect was neglected for lower overload ratio (ORL>1.8). Comparison in fatigue life and crack growth rates under the same overload ratio (ORL=2.4) between repaired and unrepaired plates show the supplementary beneficial effects in combination of overloading and patch repair

Effect of yield strength and single tensile overload cycles on effective stress intensity range ratio in 6061-T6 Al-alloy

Crack closure experiments were conducted on 6061-T6 A1 lalloy, using COD gauge for various overload ratios (1.67, 1.88 and 2.06) and different prestrains (0, 3 and 6%). On the basis of these experiments some power laws are developed. The delay period after application of single overload is also increased as magnitude of overload increased. The retardation is less as percentage of prestrain increased for the same over-load ratio. After application of an overload cycle the decrease in U value is less in prestrain material as compared to as received material. Crack growth rate is also decreased after application of overload cycle. It attains the CAL crack growth rate after certain number of cycles. As prestrain value increased the size of plastic zone decreased. It is main reason in decrease of delay cycles in higher prestrained condition.

Effect of prestrain on material and single tensile overload cycles on crack closure

Crack closure experiments were performed on 6063-T6 Al-alloy, using COD gauge for various overload ratios (1.67, 1.87 and 2.06) and different prestrains (0, 3 and 6%). On the basis of these experiments some relations are developed. The delay period after application of single overload is also increased as magnitude of overload is increased. The retardation is less as prestrain increased for the same overload ratio. After overload cycle the decrease in U value is less in prestrain material as compared to as received material. CGR is also decreased after application of overload cycle, it attains the CAL CGR after a certain number of cycles. In general crack closure load increased after overload cycle and after a certain number of cycles it tends to attain its CAL closure value.