Moisture absorption effects on the mechanical properties of carbon/epoxy composites

Abstract

PurposeThis paper investigates the influence of moisture absorption on the mechanical properties of carbon/epoxy composites.Design/methodology/approachThree types of specimens are prepared, which are for longitudinal, transverse and shear tests. Specimens are immersed in distilled water at 70°C for 1, 3 and 9 months. These correspond to the moisture content of 2.2, 3.8 and 5.3%.FindingsCompared to the values at dry condition, the longitudinal modulus, shear modulus and Poisson's ratio are invariant with the moisture content. However, the transverse modulus, transverse strength and shear strength are sensitive to moisture attack. The maximum degradation is 33%, 76 and 33% for the three properties, respectively. It is also worth to note that the longitudinal tensile strength is stable at 1 and 9 months of immersion. However, at 3-months ageing period, there is only 67% of the longitudinal tensile strength retained.Originality/valueThe experimental results are fitted with a residual property model. Results show comparatively good fit, with a difference within 16% except the longitudinal tensile strength at 9-months immersion. This highlights that the model is not suitable to fit the experimental data with a fluctuated trend.

Moisture Absorption Effects on Mode II Delamination of Carbon/Epoxy Composites

“…To describe the variation of G IIC with respect to moisture content M , the following residual property model (RPM) [ 3 , 6 , 13 ] is adopted where G IIC (M) is the residual mode II fracture toughness at particular moisture content, G IIC,dry is the dry property, G IIC,min is lowest mode II fracture toughness within the range of study, M is the moisture content, M m is the maximum moisture content, and ζ is the degradation parameter. This model assumes that the residual mode II fracture toughness is a function of moisture content only.…”

“…As for the other lamina properties (transverse modulus E 22 , in-plane shear modulus G 12 , out-of-plane shear modulus G 13 , and G 23 ) at wet conditions, they are estimated using the same ratio of the corresponding E 11 with respect to its dry value. The Poisson’s ratio ( ν 12 ) is assumed to be invariant with the moisture content [ 6 ]. It is to note that the transverse and shear properties are generally recognized to be sensitive to moisture attack [ 6 ].…”

“…The Poisson’s ratio ( ν 12 ) is assumed to be invariant with the moisture content [ 6 ]. It is to note that the transverse and shear properties are generally recognized to be sensitive to moisture attack [ 6 ]. However, since the bending behavior of the composite is dominated by E 11 , the accuracy of the transverse and shear properties are therefore not critical in this case.…”

“…Nevertheless, aircraft structures are exposed to different environmental conditions throughout their service lifetime. It is commonly reported that moisture absorption could lead to the degradation in the mechanical properties of composite materials [ 3 , 4 , 5 , 6 ]. Not only that, as the external loadings in real life applications are generally induced in the lateral direction, mode II delamination could be dominant due to the interlaminar shear stress caused by the bending of the structures [ 7 ].…”

An Extended Thickness-Dependent Moisture Absorption Model for Unidirectional Carbon/Epoxy Composites

“…When using carbon/epoxy laminated composites for aircraft applications, the materials are inevitably subjected to various environmental conditions. Upon prolonged moisture and heat attacks, the properties may degrade and lead to premature failure of the structures [ 3 , 4 , 5 , 6 , 7 ]. It is common to relate the residual properties to the absorbed moisture content of the materials [ 3 , 4 , 5 ].…”