Akar Dogan

Variation of the mechanical properties of E-glass/epoxy composites subjected to hygrothermal aging:

In this study, the effects of hygrothermal aging on the mechanical properties and impact behavior of glass-epoxy composites were investigated experimentally. The vacuum-assisted resin infusion molding was used to manufacture composites. In manufacturing of composites, unidirectional E-glass fabrics with areal density of 300 g/m2 and a resin system (Araldite LY 564/Aradur 3487 BD) were used. In order to determine mechanical properties such as modulus of elasticity, longitudinal and transverse strengths, shear strength, and Poisson’s ratio, the composite samples were prepared according to the ASTM standards. Then, the samples were conditioned at a constant temperature (95℃) and a constant humidity (70%) for different periods of times, ranging from 0 h to 1200 h. The conditioning temperature was chosen due to the glass transition temperature (Tg) of the intact composites which is determined as 78℃. It is noted that the most affected mechanical property via material degradation is modulus of elasticity in transverse direction (E2) while the least affected one is shear modulus (G12). The perforation threshold of the composite materials also decreases with increase of conditioning time.

Effects of axial impacts at different temperatures on failure response of adhesively bonded woven fabric glass fiber/epoxy composite joints

Evaluating post-impact failure responses of single-lap adhesively bonded composite-to-composite joints in uniaxial static tensile loading was the main objective of the current experimental study. At first, axial tensile impacts having various energy levels (10, 15, 20, and 25 J) were applied to the joints at different temperatures (−20, 0, room temperature, 50, and 80℃). Afterward, the samples were secondarily subjected to static tensile loading at ambient temperature, so that reductions in joint strengths arising from the impacts performed under different loading conditions could be assessed. Consequently, it was definitely proved that each of the axial impacts performed in any loading case has a noticeable effect on ultimate joint strengths, proportionally to the acting condition. Besides, the combination of high energy and temperature sometimes appeared to be the reason of impact failure, which occurs instantly without being able to perform axial static tests. When applied energy and/or absolute difference from room temperature is increased, lower joint resistances could be measured during secondary tensile tests.

Effects of Temperature and Hole Drilling on Adhesively Bonded Single-Lap Joints

In this study, the load-carrying capacity of a single-lap joint bonded by an adhesive was determined experimentally. Glass fiber-epoxy composite material was chosen as adherends and Loctite® 9466 A&B2 was used as adhesive. The vacuum assisted resin infusion method (VARIM) was used to manufacture composites. In this experimental study, the effects of hole drilling and temperature were investigated. Five hole configurations and three temperatures (room temperature, 50°C, and 80°C) were considered. The results show that hole drilling elevate the failure load and when the temperature increases the load-carrying capacity decreases.

Multi-linear stress analysis in adhesively bonded double-lap joint

In this study, an elastic–plastic stress analysis is carried out in fiber glass-epoxy adherends with DP460 ductile adhesive. Multi-linear plastic solution is applied to the joints. Analytical results are checked using a multi-linear finite element solution, ANSYS 12. Analytical and numerical solutions are found to be in good agreement. The thickness of the adherend is chosen as 1.8 mm, 2.5 mm and 3 mm. It is observed that when the thickness of the adherend is increased, the intensity of the peel stress raises. Shear and peel stresses are found to be the highest at or around the free ends of the adhesive. The multi-linear solution yields a closer solution with respect to the bilinear solution since it follows the stress–strain diagram.

Effects of temperature and impactor nose diameter on the impact behavior of PA6 and PP thermoplastic composites

In this study, the effects of temperature and impactor nose diameter on the impact behavior of woven glass-reinforced polyamide 6 (PA6) and polypropylene (PP) thermoplastic composites were investigated experimentally. Impact energies are chosen as 10, 30, 50, 70, 90, 110, 130, and 170 J. The thickness of composite materials is 4 mm. Impact tests were performed using a drop weight impact testing machine, CEAST-Fractovis Plus, and the load capacity of test machine is 22 kN. Hemispherical impactor nose diameter of 12, 7, and 20 mm were used as an impactor. The tests are conducted at room temperature (20°C and 75°C). As a result, the PP composites of the same thickness absorbed more energy than PA6 composites. The amount of absorbed energy of PP and PA6 composites decreased with temperature.