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Project PAJ2, Report No. 7, An evaluation of yield criteria for adhesives for finite element analysis.

Dean, G; Read, B E; Duncan, B C (1999) Project PAJ2, Report No. 7, An evaluation of yield criteria for adhesives for finite element analysis. NPL Report. CMMT(A)117

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Tensile and shear tests on bulk specimens of adhesives and tensile tests on butt-joint specimens have been employed to obtain stress/strain data for use with elastic-plastic models in finite element analyses of bonded joints. The adhesives investigated were a toughened epoxy and a toughened acrylic. The tests were carried out in an Instron machine at different crosshead speeds chosen to give the same effective plastic strain-rate for each mode of deformation.
The results of the tensile and shear tests reveal that the von Mises yield criterion is not applicable to these materials except possibly at small plastic strains. The test results were therefore used to derive parameters for the linear Drucker-Prager and the exponent Drucker-Prager materials models. These models were then used in finite element analyses to predict force-extension curves for the butt-joint specimens. It was observed that the exponent Drucker-Prager model appeared to accurately describe the deformation behaviour of the epoxy whilst the linear Drucker-Prager model was more appropriate for the acrylic.
These are believed to be chance observations, and a more detailed analysis of results has indicated that none of these models are suitable for toughened adhesives under all stress states. It is concluded that the von Mises criterion, possibly modified to include a small dependence on hydrostatic stress, is suitable for stress states and magnitudes in which the hydrostatic tensile stress is insufficient to initiate cavitation in the rubber or crazing in the matrix polymer. When the stress state and magnitude induce cavitation or crazing in the adhesive, then an alternative or modified model must be used to describe the influence of these mechanisms on deformation behaviour.
The basis for the development of a new model is briefly discussed.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CMMT(A)117
Subjects: Advanced Materials
Advanced Materials > Adhesives
Advanced Materials > Polymers
Last Modified: 07 Sep 2018 14:30
URI: http://eprintspublications.npl.co.uk/id/eprint/1063

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