Abstract
Composite materials manufactured by overlapping plies with certain specific geometries are likely to lose part of their strength due to the presence of internally delaminated regions. The aim of this paper is to experimentally evaluate the generation and propagation of these interlaminar cracks in a carbon-epoxy composite material subjected to fatigue loading under mixed mode I/II fracture. Two different test methods were used for this purpose: The standardized mixed-mode bending (MMB) test and the asymmetric double cantilever beam (ADCB) test, with the goal of exploring the viability of the ADCB test as a simpler alternative to perform than the MMB test, especially in fatigue testing. With this aim in mind and after prior static characterization of the material in which the critical values of the energy release rate were determined under both test methods, the levels of the energy release rate to be applied in fatigue tests were defined for two mode mixity ratios, GII/Gc = 0.2 and 0.4 (0.34 ADCB), and a fatigue loading ratio, R = Gmin/Gmax = 0.1. The G-N fatigue onset curves were subsequently obtained from these experimental data. The most relevant result of the study is that the fatigue limits obtained using the MMB method are generally more conservative than those obtained via the ADCB method.
Highlights
High performance composite materials are commonly being used in a wide variety of industries, such as the naval, aeronautical, and sports sectors, among others
The most significant conclusions regarding the influence of the test method (MMB or asymmetric double cantilever beam (ADCB)) on the fatigue behavior of a composite material submitted to mixed I/II loading for two mode mixity the fatigue behavior of a composite material submitted to mixed I/II loading for two mode mixity ratios are presented below
Regarding the experimental results for the two test methods under static loading, slightly values were obtained for the two mode mixity ratios studied in this paper when the trials were higher values were obtained for the two mode mixity ratios studied in this paper when the trials performed using the ADCB test
Summary
High performance composite materials are commonly being used in a wide variety of industries, such as the naval, aeronautical, and sports sectors, among others. The reason for this resides in their excellent mechanical properties, especially their high strength and specific modulus (stiffness). Many polymer matrix composite materials reinforced with continuous fibers are manufactured by successive stacked plies of the material This configuration means that one of the major faults they may suffer, both during the manufacturing process and throughout their in-service life, is delamination, i.e., the generation of cracks or fissures between two adjacent plies.
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