Investigation of the effect of aging parameters on the mechanical properties of composite materials and optimization by response surface methodology

The heavy structures of metal materials commonly used in marine vehicles and liquid transportation and the corrosion of these metal materials as a result of contact with liquid have led researchers to search for alternative materials. The fact that composite materials have high specific strength, fatigue resistance, yield strength as well as light weight and good corrosion resistance has led to an increase in the use of composite materials in the sector. In this thesis, basically, glass fiber reinforced composite materials were produced by vacuum infusion method at different curing temperatures (20°C, 60°C and 100°C) and the effects of aging parameters (temperature and salinity ratio) on mechanical properties were investigated. researched. researched. researched. researched. researched. Produced composite materials were examined. Experiments were designed with the central composite design method, which is one of the experimental design methods, and these parameters were optimized using the response surface method and optimum parameter values for the aging process were determined. This thesis basically consists of three parts. In the first part, glass fiber reinforced composite sheet was produced at different curing temperatures (20°C, 60°C and 100°C) by vacuum infusion method. Tensile test specimens and low velocity impact test specimens cut from the produced sheets were aged for 1416 hours. The aging parameters are 20°C, 45°C and 70°C water temperature and 3%, 19% and 35% salinity. The aging processes and mechanical tests applied to the samples were carried out in accordance with the experimental design created using the central composite design method. During the aging process, the samples were removed from the brine and the weights of the samples were measured at regular intervals, and the increase in their weights as a result of dehumidification was recorded. After the aging process, tensile and low-speed impact tests were applied to the samples. In addition, the rupture surfaces (damage areas) of the tensile test specimens were examined by scanning electron microscopy (SEM) When the results obtained in this thesis study were examined, it was seen that water temperature and curing temperature had a negative effect on water absorption. The higher the curing temperature and the water temperature, the higher the water absorption. The salinity ratio, on the other hand, has a positive effect on the weight gain caused by the water absorption of the samples, that is, as the salinity rate increases, the amount of water absorbed by the samples decreases. The aging temperature has a quadratic effect on the percent change in tensile strength, while salinity has a linear effect. In the 20°C-40°C aging temperature range, the aging temperature has no significant effect on the change in tensile strength, while further increase in the aging temperature causes a negative increase in tensile strength. power change. tensile strength. Increasing the curing temperature has a positive effect on the percent change of the modulus of elasticity; this indicates that as the curing temperature increases, the modulus of elasticity will be less affected by the aging process. On the contrary, increasing aging temperature has a negative effect on the percent change of the modulus of elasticity, that is, the higher the aging temperature, the more the modulus of elasticity is affected by the aging process. Increasing the curing temperature between 20°C and 45°C has a negative effect on the percent change in peak strength, indicating that the peak strength decreases as the curing temperature increases. At the intermediate curing temperature (60°C), the loss in peak energy is minimal for minimum aging temperature and maximum salinity. As a result of the experiments, a decrease in the mechanical properties of the materials was observed. As a result of the examination made with scanning electron microscopy, microstructure interfacial separations, resin rupture, fiber rupture and fiber outflow were observed. The most important reason for this is the weakening of the interface between the matrix material and the fibers and the deterioration of the chemical properties of the matrix material. The optimum curing temperature, brine temperature and salinity obtained using the response surface method are 100°C, 20°C and 19.8%, respectively. For the verification tests, composite plate production and aging were carried out in accordance with these parameters, and tensile and low-speed impact tests were applied to the samples cut in appropriate sizes from this plate. As a result of the tests, it was seen that the values found were in high level closeness with the predicted values. Keywords:Aging, Optimization, Experimental design, Response surface methodology, Curing temperature