Structural and residual strength analysis of metal-to-metal adhesively bonded joints.

Prathuru, Anil

Abstract

The aim of this study is to propose a new simulation/experimental methodology to assess the residual strength of defective adhesive bonds. This incorporates defect detection in adhesive bonds and quantification of the effect of these defects on the adhesive bond failure. Finite element analysis (FEA) was used to simulate the failure behaviour of adhesive bonds. Acoustic emission (AE) was used to monitor the adhesive bond failure experimentally. AE-based pencil lead break (PLB) tests were used to detect the defects in adhesive joints manufactured with two different adhesive types (brittle, ductile) and different defect area distributions (0%, 25% and 40%) along one of the interfaces. The chosen type of defect was kissing bonds, as these are the most difficult to detect. The recorded signals were processed to establish the AE parameters that were used to distinguish between the different defective adhesive bonds. 4-point flexure and plane strain (cylindrical wedge) indentation were chosen as the methodologies for mechanical testing to assess the failure of defective adhesive bonds. Cohesive Zone Model (CZM) was used in conjunction with FEA for indentation testing, to study the effect of adhesive layer thickness, adhesive modulus, interfacial strength and toughness on the adhesive bond failure. Flexure, indentation and single lap joint tension experiments were carried out in selected specimens with AE monitoring to record crack propagation events. FEA of the 4-point flexure of adhesive bonds showed that the failure initiation is at the loading points. Failure propagation is because of the strain mismatch between the adhesive and adherends. FEA analysis of indentation testing showed that the failure initiation is under mode-II adjacent to the indentation compressive zone. Increasing the interfacial strength delays crack initiation under indentation loading, while increasing the interfacial toughness reduces the total crack length for a given indentation depth. AE monitoring of experiments showed that the AE event energy - as well as the number of crack events - can be used to assess the residual strength of defective adhesive bonds. The classification of the AE events into mode-I and mode-II events enabled verification of the nature of crack propagation observed in the simulations. Finally, a correlation is proposed between cumulative AE energy and CZM energy release rate to estimate the adhesive bond interfacial strength.

Citation

PRATHURU, A. 2019. Structural and residual strength analysis of metal-to-metal adhesively bonded joints. Robert Gordon University [online], PhD thesis. Available from: https://openair.rgu.ac.uk

• Thesis Type: Thesis
• Deposit Date: Aug 12, 2019
• Publicly Available Date: Aug 12, 2019
• Keywords: Adhesive bond strength; Adhesive bond toughness; Finite element analysis; Acoustic emission testing
• Public URL: https://rgu-repository.worktribe.com/output/346900
• Award Date: Jan 31, 2019