Hygrothermal exposure and residual strength after cyclic loading on epoxy composites reinforced with sisal fibers

Abstract

The fatigue behavior of epoxy/sisal composites with hygrothermal exposure was investigated. However, their mechanical characterization under cyclic loading associated with aging from hygrothermal exposure is necessary to expand their use in consumer goods and automotive parts. This work used untreated and NaOH-treated sisal fibers (30% in volume) to reinforce epoxy composites in unidirectional and cross-ply orientations. The composites were submitted to cyclic loading tests before and after hygrothermal exposure and submitted to hot water absorption test, tensile strength, residual tensile strength, and scanning electron microscopy (SEM) analyses. The results show that unidirectional NaOH-treated sisal/epoxy composites outperformed the untreated composites, with approximately 40% less water absorption after the hygrothermal exposure and a 1.4 times improvement in tensile strength. This performance enhancement resulted from the efficient transfer of stresses between the components, stemming from adhesion between the fibers and the epoxy matrix. The tensile strength of unidirectional treated sisal composites showed a minor decrease following cyclic loading (approximately 6%), in contrast to the untreated composites, which experienced a significant decline of 20%. As a result, the treated sisal improved the composites mechanical behavior compared to the untreated ones, which underwent a more significant loss due to weaker interactions between the fibers and the matrix. The SEM images showed that the fiber/matrix interface played a central role in the composites' performance in all tests. Overall, this study highlights the potential of unidirectional NaOH-treated sisal/epoxy composites, an environmentally friendly material, for applications subjected to cyclic loading and hygrothermal exposure.

Keywords

• Functional fatigue
• Residual strength
• Hygrothermal exposure
• Aging