THE FATIGUE AND DURABILITY BEHAVIOR OF AUTOMOTIVE ADHESIVES - PART III - PREDICTING THE SERVICE LIFE

In Part I [1] a fracture mechanics approach has been successfully used to examine the cyclic fatigue behaviour of adhesively-bonded joints, which consisted of aluminium-alloy or electro-galvanised (EG) steel su bstrates bonded using toughened-epoxy structural paste-adhesives. The adhesive systems are typical of those being considered for use, or in use, for bonding load-bearing components in the automobile industry. T he results were plotted in the form of the rate of crack growth per cy cle, da/dN, versus the maximum strain-energy release-rate, G(max) appl ied in the fatigue cycle, using logarithmic axes. In Part II [2] the m echanisms of failure were considered, particularly the mechanisms of e nvironmental attack. The present paper, Part III, discusses the use of the relationship between da/dN and G(max), which can be obtained in a relatively short timescale, to predict the fatigue lifetime of (uncra cked) single-overlap joints cyclically loaded in tension. An analytica l and a finite-element model have been derived to predict the number o f cycles of failure, N-f for lap joints and, particularly when the lat ter model was used to deduce the value of the strain-energy release-ra te, G, in the lap joints, the agreement between the theoretical predic tions and the experimental results is found to be very good.