Abstract
In recent years, structural composites manufactured by carbon fiber/epoxy laminates have been employed in large scale in aircraft industries. These structures require high strength under severe temperature changes of -56° until 80 °C. Regarding this scenario, the aim of this research was to reproduce thermal stress in the laminate plate developed by temperature changes and tracking possible cumulative damages on the laminate using ultrasonic C-scan inspection. The evaluation was based on attenuation signals and the C-scan map of the composite plate. The carbon fiber/epoxy plain weave laminate underwent temperatures of -60° to 80 °C, kept during 10 minutes and repeated for 1000, 2000, 3000 and 4000 times. After 1000 cycles, the specimens were inspected by C-scanning. A few changes in the laminate were observed using the inspection methodology only in specimens cycled 3000 times, or so. According to the found results, the used temperature range did not present enough conditions to cumulative damage in this type of laminate, which is in agreement with the macro - and micromechanical theory.
Highlights
Differential in the coefficient of thermal expansion (CTE) is a primary cause of thermal shock in composite materials, in which carbon fiber and polymeric matrix have a large difference in values, contributing to stresses at the interface, and a thermal shock which is related to rapid temperature changes, high temperatures, and stress gradients[1,2]
Composites Under Thermal Cycling drop or raise was considered as a potential defect)
According to the results obtained in this work, microstructural changes could be observed using the ultrasonic inspection in the laminates cycled 3000 times, or so
Summary
Differential in the coefficient of thermal expansion (CTE) is a primary cause of thermal shock in composite materials, in which carbon fiber and polymeric matrix have a large difference in values, contributing to stresses at the interface, and a thermal shock which is related to rapid temperature changes, high temperatures, and stress gradients[1,2]. A very large CTE mismatch may result in debonding at the fiber/matrix interface and/or possible matrix cracking due to thermal stresses[2,3]. The fiber/matrix interface is likely to affect the overall mechanical behavior of fiber-reinforced composites. The performance of fiber reinforced composite is often controlled by the chemical adhesion at the fiber/matrix interface[4]. The temperature changes in a laminate generate stresses that can be predicted by Equation 1, one of the mostly used expressions. Simplifying Equation 1, considering a cross ply laminate, with subscription L as the reinforcement, and by cooling the composite will induce to a compressive stress (σL)[1]
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