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The measurement of damage constants in adhesive bonding has been investigated. Bulk adhesive was used in this study for two reasons: a) stress distribution in bulk adhesive is simpler than adhesive in joints and b) specimen dimensions met fatigue test standard. Bulk adhesive was made from film-form of epoxy resin. In general, the characteristics and the behaviour of bulk adhesive may differ from adhesive in joint because of the presence of voids and the constrains imposed by the substrates. Low cycle fatigue tests with load amplitude ratio of 0.1 at frequency 5 Hz were performed to determine the damage variable as a function of number of cycles. Damage curves, i.e. evolution of damage variable as a function of number of cycles, were derived and plotted using isotropic damage equation. Damage was evaluated using the decrease of stress range during lifecycles of a constant displacement amplitude test. It was found that damage curves were fitted well by low cycle fatigue damage evolution law equation. This equation was derived from a dissipation potential function. Curve fitting was performed using Robust Least Square rather than ordinary linear least square because damage curves have extreme points (usually near failure point). It was found that fitting process could not converge for adhesive fracture at higher cycles (Nf > 9000). Two damage constants A

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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.