Unidirectional Carbon Fiber-reinforced Plastic Laminates Research Articles

Influence of Thermal Environment on Mode I and Mode II Interlaminar Fracture Toughness in Unidirectional CFRP Laminates.

In the present paper, the influence of thermal environment on Mode I and II interlaminar fracture toughnesses in unidirectional carbon fiber reinforced plastic (CFRP) Laminates is considered experimentally based on thermoviscoelastic property of matrix resin. Mode I and II interlaminar fracture toughnesses were measured by double cantilever beam (DCB) test and end notched flexure (ENF) test from-100°C to 200°C, respectively. The specimens were made of prepreg of unidirectional carbon fiber/epoxy resin. As the results, Mode I fracture toughness decreases slightly with increasing temperature. Near the primary glass transition temperature of matrix resin, the fracture toughness has extreme value and over the temperature it falls down rapidly. On the other hand, Mode II interlaminar fracture toughness decreases roughly except primary and secondary glass transition temperature where the fracture toughness has a peak.

An Inelastic Constitutive Equation of Fiber Reinforced Plastic Laminates

A Constitutive model for describing the time dependent inelastic deformation of unidirectional and symmetric angle-ply CFRP (Carbon Fiber Reinforced Plastics) laminates is developed. The kinematic hardening creep law of Malinin and Khadjinsky and the evolution equation of Armstrong and Frederick are extended to describe the creep deformation of initially anisotropic materials. In particular, the evolution equations of the back stresses of the anisotropic material were formulated by introducing a transformed strain tensor, by which the expression of the equivalent strain rate of the an isotropic material has the identical form as that of the isotropic materials. The resulting model is applied to analyze the time dependent inelastic deformation of symmetric angle ply laminates. Comparison between the predictions and the experimental observations shows that the present model can describe well the time dependent inelastic behavior under different loadings.

ＣＦＲＰ積層材に対する時間依存非弾性変形のモデリング

A constitutive model for describing the inelastic deformation of unidirectional and symmetric angle-ply CFRP (Carbon Fiber Reinforced Plastics) laminates is developed. The kinematic hardening creep flow law of Malinin and Khadjinsky and the evolution equation of Armstrong and Frederick are extended to describe the creep deformation of anisotropic materials. In order to express anisotropic hardening, back stress taking account of anisotropic inelastic strain sensitivity is incorporated into the creep constitutive equation. Then, the resulting model is applied to analyze the time-dependent inelastic deformation of symmetric angle-ply laminates. Comparison between the prediction and the experimental observation shows that the present model can describe well the time-dependent inelastic behavior under different loadings.

Evaluation of Dynamic Fracture Toughness of Unidirectional CFRP Laminates.

In the present paper, dynamic inter-laminar fracture toughness are estimated for carbon fiber reinforced plastics (CFRP). In the experiments, split Hopkinson's bar test was applied to dynamic end notched flexure (ENF) test. The dynamic deformation of the specimen is approximated by beam theory with Laplace transform. The mode II fracture toughness of unidirectional CFRP was estimated by the analyzed deflection of the specimen employing the scheme of J-integral with the measured impulsive load and reactions at the supported points. Through some numerical calculations, validity of the J-integral for the dynamic ENF test is confirmed. In addition, as a experimental result, dynamic inter-laminar fracture toughness of CF/EPOXY unidirectional specimens are estimated and it indicates dependency on deflection rate.