Time-Dependent Deformation of CFRP Quasi-Isotropic Laminates Caused by Relaxation of Thermal Residual Stress and Physical Aging

Abstract

In this paper, time-dependent dimensional change in quasi-isotropic laminates induced by relaxation of thermal residual stress and physical aging was predicted by the classical lamination theory. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic properties were investigated by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage strain induced by physical aging was studied by measuring the strain change of unidirectional laminates as well. Shrinkage strain in off-axis layers was calculated by using the coordinate-transform method. Shrinkage strain in 60° and 45° laminates were measured and the results were compared with the calculation. From the comparison, it was found that shrinkage strain of off-axis layers can be calculated by using the coordinate-transform method. Experimental results were applied to the classical theory in order to predict the time-dependent dimensional change of quasi-isotropic laminates. The strain change in quasi-isotropic laminates was obtained experimentally, and the result was compared with the prediction. It was verified that the time-dependent deformation of quasi-isotropic laminates can be predicted with a -order by using proposed prediction method.

Dimensional stability of epoxy-based and cyanate-based carbon fiber-reinforced plastics

“…The creep modulus decreased 3.2% for CF/epoxy and 4.2% for CF/cyanate after 1000 h at 40 C. It was predicted that the CF/cyanate would show larger creep deformation than the creep deformation of CF/epoxy at 40 C in contrast to the results at 80 C. Based on these parameters, the deformation caused by the thermal residual stress relaxation at 40 C was calculated using equations ( 1)-( 4). The validity of the prediction was confirmed by Niwa et al 12 They performed the analysis with the same procedure and confirmed that the analytical results showed good agreement with the experimental results. Figure 7 shows the amount of deformation caused by the relaxation of thermal residual stress in the quasiisotropic laminates at 40 C. We assumed that the cooling time from the curing temperature to 40 C was 3 h. The thermal residual stress relaxes during the cooling process.…”

“…This analysis targets the interlaminar thermal residual stress and is applicable for cross-ply and quasi-isotropic laminates that have high interlaminar stress. 12 In addition, the acceleration test is effective in determining the temperature dependency of the viscoelastic properties. [15][16][17] Therefore, it is possible to predict the deformation at an arbitrary temperature by investigating the acceleration through the dynamic mechanical analysis (DMA).…”

“…Moreover, investigations on time-dependent deformations such as the deformation induced by moisture absorption and that caused by internal thermal residual stress have also been conducted. 11,12 In designing precise structures, it is important to quantify each time-dependent deformation and to reduce the dominant deformation by conducting suitable treatments. For example, if minimizing moisture absorption is deemed critical for the dimensional stability of CFRPs, then the amount of moisture absorption should be reduced by using a cyanate resin, which has poor moisture-absorption properties.…”