Salih Akpinar

The Effect of Moment and Flexural Rigidity of Adherend on the Strength of Adhesively Bonded Single Lap Joints

In the present study, mechanical properties of different single lap joint configurations derived from adherends with different thicknesses subjected to tensile loading were investigated experimentally and numerically. For this purpose, experimental studies were conducted on two different types of SLJ samples, the first type with identical upper and lower adherend thicknesses and the second with different upper and lower adherend thicknesses. For the first type, five different thickness values were tested. For the second type, the lower adherend thickness was constant while five different upper adherend thickness values were tested. The adhesive was prepared from a two-part paste. After the experimental studies, stress analyses on the SLJs were performed with three-dimensional finite element analysis by considering the geometrical non-linearity and the material non-linearities of the adhesive (DP460) and adherend (AA2024-T3). It was observed that, in single lap joint geometry, variation in the thickness of the adherend and the use of lower and upper adherends with different thickness values changed the stress concentrations at the edges of the overlap regions, affecting the experimental failure load of the joints.

Effect of the Spew Fillet on Adhesively Bonded Single-Lap Joint Subjected to Tensile Loading: Experimental and 3-D Non-Linear Stress Analysis

In the single-lap joint (SLJ) geometry, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. In the present study, the mechanical behavior of the SLJ geometry of various widths having spew fillets, which was subjected to tensile loading, were investigated experimentally and numerically. For this purpose, firstly, four different types of SLJ samples (without spew fillet, with spew fillet at joint edges, with spew fillet at joint ends, and with spew fillet at all edges) were produced for experimental studies by using two-part paste adhesive. Then, stress analyses in the SLJ were performed with a three-dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesive (DP460) and adherend (AA2024-T3). It was concluded that the spew fillet in the SLJ geometry with variable widths decreases stress concentrations and increases the load carrying capacity of the joint.

An experimental study on composite adhesives reinforced with different types of organo-clays

ABSTRACT In this study, the mechanical properties of single lap joints prepared by adding nanoclays with different properties into adhesives with different characteristics (toughened, flexible, paste-type, and rigid) were experimentally investigated. Single lap joints and bulk specimens were produced using DP460, DP125, Araldite 2015, and AV138 as adhesives. High-concentration hydrocarbon-doped organo-clay (HDOC-1) obtained from Çankırı, low-concentration hydrocarbon-doped organo-clay (HDOC-2) obtained from Erzurum, and organo-clay (OC) were incorporated into the adhesives as reinforcements at two different concentrations (1% and 2% wt.). The aluminum alloy AA2024-T3 was used as the adherend material. Evaluation of experiment results showed that both the characteristics of the adhesive (toughened, flexible, paste-type, and rigid) and the different forms of clays significantly influenced failure loads of the joints. Moreover, increasing or decreasing the amount of clay added into the adhesive also affected failure loads of the joints; 1% wt. reinforcement provided the best results.

Investigation of mechanical and thermal properties of nanostructure-doped bulk nanocomposite adhesives

ABSTRACT In recent years, findings in nanoscience and nanotechnology have deeply influenced many disciplines including the material and mechanical sciences. Polymers including nanostructures have attracted attention as their adoptions in general engineering composites have yielded efficient results. In this study, three different two-component (epoxy-hardener) adhesives were doped with graphene nanoplatelets, graphene oxide nanoplatelets, carbon nanotube, and fullerene C60 at three different rates (0.5%, 1%, and 2% by weight) and the mechanical and thermal properties of the nanocomposite adhesives were examined. The nanocomposite adhesives’ mechanical properties were analyzed via tensile tests and thermal properties were analyzed via Differential Scanning Calorimeter (DSC) thermograms and Fourier Transform Infrared Spectroscopy (FT-IR) spectra. Results showed that doping nanostructures improve the stress-strain capacity of the adhesives. Both mechanical and thermal properties of the nanocomposite adhesives seem to change depending on the amount of nanostructure. Additionally, DSC and FT-IR curves showed an agreement with these improvements in the adhesives’ mechanical properties.

Effects of unbalance on the adhesively bonded composites-aluminium joints

ABSTRACT This article presents the experimental and numerical results of adhesively bonded hybrid single-lap joint (SLJ) geometry with different configurations of lower and upper adherends subject to a four-point bending test. AA2024-T3 aluminium alloy and carbon/epoxy composites with different lamina numbers and four different stacking angles as adherend and two-part liquid, structural adhesive DP 125 as paste adhesive were used. In the experimental studies, three different types of SLJs were produced using lower material that had a constant thickness of AA2024-T3 aluminium alloy and upper material of composite material that had different numbers of layers and four different stacking sequences ([0], [0/90], [45/−45], [0/45/−45/90]). In the numerical analysis, stress analyses of the SLJs were performed with a three-dimensional non-linear finite element method and the composite adherends were assumed to behave as linearly elastic materials, while the adhesive and aluminium adherend were assumed to be non-linear. Consequently, the change of stacking sequence and thickness of the composite in adhesively bonded SLJs altered the location of the neutral axis in the joint. This situation substantially influences the load-carrying capacity of the joint.