Modeling of single-lap joints with auxetic adhesive utilizing homogeneous and heterogeneous bondline microstructures.

Producing lightweight structures can be effectively achieved using adhesive bonding that incorporates a high-performance adhesive, eliminating the mechanical joints (rivet, bolts). Here, the proof-of-concept of tailoring the high-performance adhesive using microstructures exhibiting a negative Poisson's ratio (auxetic) is investigated using two single lap joint (SLJ) models developed in ABAQUS/Standard. The SLJ models consist of two rigid adherends that are bonded using either homogeneous or heterogeneous adhesive that produces auxetic response. In homogeneous adhesive, a negative value of Poisson's ratio is defined in the adhesive part of the models. In heterogeneous adhesive, the negative Poisson's ratio is obtained by explicitly building orthogonally-arranged elliptical voids in the adhesive part of the models. In addition, the adherend-adhesive interface is represented by cohesive elements with bi-linear traction-separation rule. The effects of using two different adhesive models and thickness on peel and shear stresses, as well as failure mechanism and joint strength, are evaluated. We found that the effect of auxetic adhesive on SLJ response is more profound in the model using heterogeneous adhesive rather than the homogeneous one, where the joint strength enhancement could achieve 45 % in reference to the baseline model. The heterogeneous adhesive embedded between adherends is able to activate ligaments, the mechanism that could not be obtained using merely homogeneous adhesive. Our proposed modeling strategy can be a starting point to further the modeling approach of bonded joints utilizing auxetic adhesive.

Experimental flatwise tensile strength dataset of carbon fibre reinforced plastic sandwich panels with different core material preparations.

Flatwise tension strength of sandwich structure is important for designing a sandwich construction since it provides failure mechanism and debonding strength between the skin faces and the core, as well as (i) core strength and (ii) face strength of the sandwich structures. The flatwise tension strength is affected by many factores: method of core preparation, test environment, testing speed, etc. In this paper, the ambient test temperature was 23 deg C and the humidity was 65%. The testing speed was 0.5 mm/min. Four different core preparations were investigated. ASTM C297 was used as a standard method to get the strength values. Two processes were employed to cure the adhesive during core-to-face bonding. It was found out that cleaning the core with Methyl-ethyl-ketone (MEK) and drying further in an oven gives maximum flatwise tension strength of the sandwich structures, with the value of 5.9 MPa. The data base is important for both the manufacturing and design engineers. For the manufacturing engineers, the data provides a value for process qualification, while for design engineers it gives a maximum allowable strength for designing sandwich construction for tensile loads.