Duncan, B C; Ogilvie-Robb, K (1999) Creep of flexible adhesive joints. NPL Report. CMMT(A)225

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Abstract

Commercial finite element analysis (FEA)software packages are used extensively for the prediction of the performance of adhesive joints.The accuracy of any prediction will depend on the validity of the material model employed and the reliability of the test data input into the chosen model.he aim of this work was to carry out an initial investigation into the creep properties of flexible adhesives.
FE software packages incorporate visco-elastic models for describing time-dependent material properties.Data are required from either creep tests or stress relaxation in order to calculate the relaxation constants for the models.Creep measurements have been carried out on bulk specimens to derive input data for the FE models and to investigate the failure of such materials under long-term loads.Despite the scatter in the data there is some evidence to suggest that there may be simple rules to predict long-term performance.In particular,constant rate tests performed at elevated temperatures may give information relating to the long-term failure criteria for the joint.
FE predictions of the behaviour of lap joints under constant loads have been compared with experimental measurements.The relaxation model used in the FE software relies on normalised input data.This means that the long-term FE predictions are critically dependent on the accuracy of the initial ‘elastic ’extension of the joint under load. Since the joint is rarely loaded at the same rate at which the elastic properties are obtained the accuracy can be poor.This is an area requiring further research.More suitable models making use of actual material properties such as compliance and incorporating stress dependence of the visco-elastic function are likely to increase the reliability of the predictions.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	CMMT(A)225
Subjects:	Advanced Materials Advanced Materials > Adhesives
Last Modified:	02 Feb 2018 13:18
URI:	http://eprintspublications.npl.co.uk/id/eprint/1242

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