Papers by Keyword: Damage Measurement

Abstract: This paper describes a new technique allowing the monitoring of damage in metallic freestanding thin films during micro-tensile test by using electrical characterization. After a presentation of the set-up, results obtained on Aluminium thin coatings by using two calculation methods for damage variable are presented and commented.

Abstract: Adhesive in joints will have complex stress state rather than bulk adhesives. This will lead to the assumption behind bulk adhesive that triaxiality function (Rv) is equal to one (uni-axial stress state) is not valid anymore. In this paper, new procedure to find damage parameters α and β for single-lap joints has been developed based on global damage of adhesive joints. With this procedure, damage parameters α and β have been found. Validating the procedure by calculating the number of cycles to failure (Nf) has been performed successfully. The accuracy of the damage evolution equation is less than 2 %.

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.