Determination of static and fracture behavior of S-cam / epoxy laminated composites at different temperatures and deformation speeds

Currently, structures containing S glass can be used as reinforcing elements in composite applications that require high strength, from marine, aviation, energy sector to transportation sector. These composites can sometimes be used in a cold storage or a wind power plant wing in cold climate regions. Sometimes, they can serve as a coating material or a tool in warm environments at temperatures close to the glassy transition temperature in a stracture. These structures can be exposed to different loading conditions that are likely to come over them together with the variable temperature ambient conditions. However, structures such as holes, channels or slits are formed on these materials, especially during their manufacture or assembly. These structures are the factors that shorten the service life of the material. Therefore, it is important to know the fracture behavior of S glass reinforced composite structures as well as their mechanical behavior under different temperature and deformation conditions. In order to understand these behaviors, composite plates were obtained by combining S glass fabric consisting with epoxy resin and curing agent. Experimental samples obtained from the plates were subjected to static tests depending on the production orientation of the laminates (x axis, y axis and 45 degree angle). Static tests were performed under four temperatures (-20°C, 0°C, 20°C, 80°C) to observe ambient temperature variability. Variable loading conditions were investigated with the help of tests performed at three deformation speeds (0,5 mm/min, 5mm/min, 50mm/min) under these temperatures. Mechanical properties have increased in both axes of the sheet with the increase of the deformation rate. This increased to 22,15% in tensile strength and 26,53% in compression strength. S glass/epoxy laminated composites have displayed behaviors that are sensitive to temperature changes with static tests. The composite structure, which has durable structure in cold conditions, lost these strength properties with the increase in temperature. With the increase in temperature, the modulus of elasticity by 21,09%, tensile strength by 30,37% and compressive strength by 31,69% decreased. The results obtained as a result of all experimental conditions were entered as material data in the ANSYS finite element program and formed 12 material libraries that simulated the experimental conditions of fracture tests. As a result of the burning test performed to define the S glass/epoxy laminated composite structure, it was found that the structures that negative affect in the the composite production are less and the composite production is quite successful. In order to examine the viscoelastic behavior of the S glass/epoxy laminated composite structure, it was also examined by dynamic mechanical analysis (DMA) tests. By examining the temperature-dependent change of fiber mass conservation in the composite structure with the TGA test, the temperature at which the pure fiber remains was determined. The fracture mechanics behavior of S glass/epoxy laminated composite structure was also investigated depending on the ambient temperature and drawing speed. Fractudre has been evaluated for Mode I and Mode I/II conditions. Fracture mechanics behavior was also performed at three drawing speeds of 0,5mm/min, 5mm/min and 50mm/min under temperatures of -20°C, 0°C, 20°C and 80°C, as in static tests. In fracture mechanics tests, single edge notched experimental samples with 5mm, 10mm and 15mm crack lengths were used. As a result of the tests, fracture toughness and strain energy release rates were calculated. The fracture toughness and strain energy release rate obtained experimentally were compared with the toughness and J integral values obtained from the ANSYS finite element program. Fracture toughness studies were carried out in three stages. In the first stage, the effect of temperature change under constant crack length on toughness and strain energy release rate depending on drawing speed was studied. In the second stage of the study, the effect of change in crack length under constant temperature on fracture toughness and strain energy release rate depending on the drawing speed was investigated. In the third stage of the fracture mechanics studies, two crack lengths with 50% difference between them and the change in toughness and energy due to the drawing speed in the coldest (-20°C) and the hottest (80°C) environment conditions were investigated. In general, when both the toughness value and the energy value were examined, it was found that the change in crack length was more effective than the change in temperature. In today's world, especially advances in computer technologies have introduced concepts such as artificial intelligence and machine learning into our lives. These concepts allow you to make close predictions about similar but not happened situations yet with the information they learn with programs that can learn. In the thesis study in this context, the fracture behavior of the S glass/epoxy laminated composite structure was also evaluated with the machine learning approach. Experimentally obtained fracture toughness data were taught to four machine learning algorithms, namely Decision Trees (DT), Random Forest (RF), Support Vector Machine (SVM), Artificial Neural Network (ANN). Learning successes of these algorithms have been obtained. Next stage, the toughness value estimates were obtained for the crack lengths that were not tested by these four algorithms and in both fracture modes. The machine learning study also formed the last part of the thesis and the study was concluded.