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Abstract: Fatigue induced from various aeromechanical sources can reach gigacycle regime due to vibratory stress cycles at high frequencies. Composite repairs offer various advantages over mechanical fastening or riveting, including improved long-term durability behavior and reduced corrosion. In this study, by using ultrasonic frequency cyclic loading, fatigue crack growth tests in gigacycle regime were conducted on notched 7075 and 6061 aluminum alloy substrates (in T6 condition) with and without bonded Boron/epoxy patches. A considerable increase in the fatigue life was observed with more number of patch plies. The effect of patch configuration and thickness on enhancing the fatigue strength by orders of magnitude has been demonstrated. [Copyright &y& Elsevier]

In this paper, monotonic tensile and fatigue crack growth (FCG) studies were conducted on 7075-T6 Al substrates with and without bonded boron/epoxy patches. The Al substrates were machined to V-type side notch specimen. The presence of the pre-crack significantly decreased the plastic displacement and caused a slightly higher stiffness compared with the unnotched Al substrate. It was found that the repairs appeared to make the pre-cracked substrates slightly more plastic. The experimental results show that both static strength and fatigue life of the repaired aluminum substrates had been significantly increased for the bonded composite patches. The different patch-ply repairs were found to provide about a 5–14 times improvement in the fatigue life and a 2–4 times decrease in the stress intensity factor. The 4-ply-patch repaired specimen demonstrated its effectiveness in preventing static failure and increasing fatigue life of the cracked substrates. An analytical model, based on Rose''s analytical solution and Paris'' power law, was developed to predict FCG behavior of the repaired substrates. The analytical and experimental results are in good agreement. [Copyright &y& Elsevier]

Discusses the fatigue characterization of a spheroidal graphite cast iron under ultrasonic loading. Uses of spheroidal graphite cast iron; Brief discussion of fatigue crack initiation; Fatigue testing in a piezoelectric resonance system; Investigation of fracture surfaces of tested specimens by scanning electron microscopy.

Abstract: A novel testing methodology on three-point bending fatigue test at 20kHz has been developed based on ultrasonic vibration theory to determine the bending fatigue strength of structural materials in very high cycle regime. In this paper, the working feature of the testing machine has been introduced. On the basis of vibration theory analysis, the differential equation of longitudinal and flexural vibration were given, finite element model was introduced to design and calculate the amplifier, specimen and the connector in the testing system. Furthermore, to produce the shapes of the components necessary to achieve the required displacement and stress states. Longitudinal cyclic load was transferred to transverse vibration of specimen by the tip in the testing system. In order to understand the effect of the tip on the testing system, matching analysis between amplifier and tip in the bending vibration system has been discussed. Finally, a successful application of the methodology is demonstrated by the experimental results from TiAl alloy specimens subjected to three-point bending stress states. [Copyright &y& Elsevier]