The application of carbon fiber reinforced plastics (CFRP) to airframes has been expanding to reduce weight of aircraft. In addition, by replacing mechanical fastening with adhesive bonding, it is possible to achieve further weight saving of the airframe. In this study, we investigated the effect of curing conditions on the strength of CFRP single lap adhesive joint using epoxy resin adhesive. Specimens with different curing conditions such as curing temperature and curing time were prepared. The reaction ratio of the adhesive samples under each curing condition was evaluated by differential scanning calorimetry (DSC) measurements. Further, tensile shear adhesive strength and failure process of the joints were evaluated by performing tensile shear tests and acoustic emission (AE) measurements on specimens. After the test, failure mode was distinguished by observing the failure surface. From the above, the relationship among the reaction ratio of the adhesive, the strength of the joint and the failure mode was clarified.
The primary objective of this study is to predict the coefficient of thermal expansion (CTE) for carbon fiber reinforced thermoplastic (CFRTP) having temperature dependency and anisotropy by employing the strain transformation matrix and numerical material testing (NMT) based on the homogenization theory. The accuracy of the proposed technique was verified through comparisons between the calculated and measured values. Firstly, the CTE value for CFRTP in the principal direction was calculated through NMT based on the homogenization method. The CTE value for CFRTP in an arbitrary direction was then calculated by incorporating the strain transformation matrix. Measurement of CTE values for CFRTP with plain woven textile was conducted along the longitudinal direction and at an angle of forty-five degrees. The CTE value calculated for the principal direction by employing NMT and the CTE value calculated for an arbitrary direction by incorporating the strain transformation matrix are found to be in good agreement with the CTE values measured along the longitudinal direction and at an angle of forty-five degrees, respectively. The aforementioned results thus corroborate that the CTE value for CFRTP having temperature dependency and anisotropy in the principal and arbitrary directions can be effectively predicted by applying the strain transformation matrix and NMT.
Measurement of the elastic moduli of carbon fiber reinforced plastics (CFRP) can be difficult owing to the anisotropic and viscoelastic characteristics of CFRP. In this study, a technique based on resonant ultrasound spectroscopy is proposed that can identify the viscoelastic moduli of CFRP by measuring the resonant frequencies. The resonant frequencies of a CFRP specimen were measured by employing an experimental device comprising a pair of piezoelectric transducers and the spectrum analyzer software. The viscoelastic moduli were thereby identified by applying genetic algorithms. Considering the viscoelastic properties, it is possible to conduct highly accurate analysis as compared to the case in which the viscoelastic properties are not considered. Furthermore, by measuring the resonance modes that are significantly affected by the three independent viscoelastic moduli (EL, ET, GLT), each modulus can be identified with constant precision.