Detection of fatigue macrocracks in 1100 aluminum from thermomechanical data

Specimens of commercial purity polycrystalline aluminum were cyclically str ained to final fracture. During testing the temperature response was monito red at five locations along the gage length of the specimens as a function of applied cycles. For much of the Lest, the rates of temperature increase at different locations on the gage section were relatively uniform. However , before final fracture, the rate of temperature rise at one or two of the monitored locations became greater than those observed in the rest of the g age section. Beach marks and striations were observed on the failure surfac es of the specimens. These fractographic features were used to estimate the number of cycles spent growing a macrocrack under cyclic loading. It was f ound that the beginning of localized temperature rises corresponded to the beginning of fatigue crack growth which produced striations and beach marks . The thermomechanical data derived from specimen temperature responses wer e also used to estimate the location of the crack in the gage length of the specimen. (C) 2000 Elsevier Science Ltd. All rights reserved.