Measuring of Damage Parameters in Adhesive Bonding

Abstract

In this paper, the characterisation of damage in an epoxy adhesive has been investigated. Bulk adhesive samples were used in this study for two reasons; firstly the stress distribution in the bulk adhesive sample is simpler than that in a joint, secondly, the specimen’s dimensions meet fatigue test specimen standards. Low cycle fatigue (LCF) tests with a load ratio of 0.1 and a frequency of 5 Hz were performed on bulk adhesive dumbbell specimens. Damage curves, relating damage in the specimen to number of cycles to failure, were plotted using an isotropic damage equation in which damage is a function of stress, which decreases as damage progresses. The damage curves were then fitted using a LCF damage evolution law. This equation was derived from a dissipation potential function using Continuum Damage Mechanics (CDM) theory. Curve fitting was performed using a Robust Least Square technique rather than ordinary linear least square because the damage curve has extreme points (usually at the breaking point). Two damage parameters α and β were found from the curve fitting process. This process resulted in different values of α and β for different stress levels. The logarithmic α and β points were then plotted respect against stress level and linear regression was used to determine α and β as a function of stress. With this function, damage parameters for other stress level can be predicted.

Review of fatigue of bulk structural adhesives and thick adhesive joints

“…Dumbbell specimens were also employed see, e.g. [205] presenting results from low cycle fatigue tests on bulk adhesive dumbbell specimens aiming at the development of a damage mechanics model to predict damage curves. Other specimen types were also used, e.g.…”

Predicting fatigue damage in adhesively bonded joints using a cohesive zone model

“…Wahab et al [11], Imanaka et al [12], Hilmy et al [13,14]) employed continuum damage mechanics to predict the fatigue in adhesively bonded joints. In this method, a damage parameter (D) is defined which modifies the constitutive response of the adhesive.…”