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Analysis of the effects of cold expansion of holes using thermoelasticity and image correlation
Author(s) -
BACKMAN D.,
COWAL C.,
PATTERSON E. A.
Publication year - 2010
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.2010.01472.x
Subject(s) - mandrel , digital image correlation , materials science , thermoelastic damping , composite material , crack closure , structural engineering , tension (geology) , ultimate tensile strength , fracture mechanics , engineering , physics , thermal , meteorology
Although cold expansion has been shown to have a positive effect on fatigue life, little work to date has been performed to evaluate the evolution of the strain field surrounding the crack tip on the mandrel entry and exit faces in cold‐expanded coupons. Full‐field strain measurements using both digital image correlation (DIC) and thermoelastic stress analysis (TSA) were used to compare the strains during crack growth around holes that had and had not been cold‐expanded by 4%. Simple rectangular fatigue coupons were machined from 2024‐T3 aluminium sheet, half had simple open, unexpanded holes and half had cold‐expanded open holes. A DIC system was used to monitor the (mandrel) entry face of the coupon while a TSA system was used to monitor the (mandrel) exit face of the coupon during cyclic tensile loading (R‐ratio = 0.1). These two systems provide the first published measurements of the simultaneous mandrel entry and exit surface strains surrounding a crack initiating from a cold‐expanded hole. The cracks originating from the unexpanded hole exhibit a strain field around the crack tip which is characteristic of a mode I fatigue crack while those emanating from the cold‐expanded holes show a significantly lower distribution of strains around the crack tip. Crack opening displacements evaluated from the strain data obtained from DIC, are substantially reduced by the residual compressive stresses from cold expansion, while the overall fatigue data show the life improvement achieved at various applied stress levels.