Cyclic creep response of adhesively bonded steel lap joints

Abstract

ABSTRACTThe viscoelastic nature of polymeric adhesives means that the effect of fatigue frequency has to be treated cautiously. However, this subject has received limited attention and very few studies can be found. Therefore, this work aims at investigating the cyclic creep response of adhesively bonded steel lap joints. Load-controlled fatigue tests were performed with shear stresses of 9.1, 7.4, and 6.3 MPa, which are typically low cycle fatigue stresses. Only during the last 20% of fatigue life can we observe an increase in the cycle hysteresis area due to the decrease of the shear stiffness caused by the failure mechanisms. Under fatigue load, the maximum/minimum strain curves exhibit a shape being similar to that of the steady creep curves, in which occurs a second stage with nearly constant strain rate, independently of the number of cycles and increasing with the load range. A linear relationship between the log cyclic creep rate and the log of the number of cycles to failure was observed, indicating that fatigue behaviour is strictly related to cyclic creep.