Experimental and numerical evaluation of the mechanical behavior of diagonally reinforced plates subjected to the effect of residual thermal stresses

Martha L Sanchez,Gil Capote,Julián Carrillo

doi:10.15446/ing.investig.v37n3.60633

Abstract

This paper presents an experimental and numerical study of the effect of residual thermal stresses on the mechanical behavior of diagonally reinforced plates. The study focuses on the analysis of carbon/epoxy square plates onto which diagonal reinforcements were glued. These reinforcements were glued using two different methodologies: the first method was to glue the reinforcements at operating temperature (22 °C), while in the second methodology reinforcements were cured in an autoclave at 177 °C. Mechanical behavior assessment was based on the stiffness, free vibration, and buckling tests. For the study of the stiffness of the plates, an optical technique to determine the transversal displacement caused by the presence of a static load was employed. For the vibration tests, the natural frequencies associated with the first four modes of free vibration were determined by using a dynamic signal analyzer. For the linear and non-linear buckling, compression tests on a universal testing machine were performed, determining the displacements produced during the test using the digital image processing method. All experimental results were compared with results obtained from numerical approximations made with commercial software. The results show the effect of residual thermal stresses caused during the manufacturing process on the mechanical performance of diagonally reinforced plates.

Highlights

The efficient design of composite structures requires proper study of the factors that directly or indirectly influence their performance and can even cause changes in theHow to cite: Sánchez, M.L., Capote, G., Carrillo
It is noteworthy that on applying a load at point 1, located in the center of the plate, it can be seen that the presence of thermal residual stresses does not substantially affect the stiffness of the plate
This response is associated with the fact that this point is located directly on the reinforcement located in the center of the plate, this being an area of high stiffness that is caused by the design of the laminate itself

Summary

Introduction

The efficient design of composite structures requires proper study of the factors that directly or indirectly influence their performance and can even cause changes in theHow to cite: Sánchez, M.L., Capote, G., Carrillo. The strongly anisotropic character and the inhomogeneity of polymer laminates are factors that contribute to the appearance of residual stresses during the curing process of the material (Hosseini-Toudeshky & Mohammadi, 2009) The study of these stresses is all the more relevant because they can lead to negative effects on the strength of the material and on its dimensional stability, and the material may experience overall premature failure, delamination, and fracture mechanics (Kim et al, 2006). It is for this reason that recent research has focused on developing methods to modify the curing processes, seeking thereby to reduce residual thermal stresses in order to help improve the mechanical performance of the laminate (Kim et al, 2012). Reports show that differences in the thermal expansion coefficients of the constituent materials of composite laminates can generate large residual stresses during the curing process, reducing the fatigue resistance of the material. Kim et al (2013) propose a monitoring system based on methods such as the dielectrometric method and the use of sensors based on Bragg networks, which allows monitoring and controlling cure cycles, achieving a reduction in the residual thermal stresses in reinforced carbon fiber composites

Methods

Results

Conclusion