Experimental and numerical investigation of strain distributions within the adhesive layer in bonded joints

We present the results of investigations into the strain distributions in the adhesive layers of epoxy-bonded aluminium–aluminium and aluminium–carbon fibre reinforced polymer (Al/CFRP) double-lap shear joints. The area of the adhesive at the end of the overlap region, where high stresses are predicted and failure generally initiates, has been studied at high magnification. 2-D maps of the longitudinal and engineering shear strains in this region have been obtained experimentally by using high magnification moiré interferometry (HMMI). These results have been compared with the strain maps predicted by 3D elastic and elasto-plastic finite element (FE) modelling. Excellent agreement is seen between the experimentally measured and FE-predicted strain distributions, thus validating both methods. In some cases, quantitative comparison of the strains along certain profiles is compromised by noise in the measurements, especially for the Al/CFRP joints, which experienced lower overall strains. The source of such errors is discussed in the paper.