Journal of the Japan Society for Composite Materials

Research paper

Experimental Evaluation of the Damage Growth Restraining in 90° Layer of Thin-ply CFRP Cross-ply Laminates

Hiroki TAKEUCHI, Hiroshi SAITO, Isao KIMPARA

2011 Volume 37 Issue 4 Pages 121-129
Published: 2011
Released on J-STAGE: March 25, 2012

DOIhttps://doi.org/10.6089/jscm.37.121

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In this study, a systematic detailed experimental observation was made on the damage growth behavior in 90° layer of cross-ply CFRP laminates. It is generally known that the crack initiation strain is increased with decreasing the thickness of 90° layer. However the mechanism has not been well clarified in the case of very thin thickness such as less than 0.100 mm. We used a thin-ply prepreg developed by SAKAI OVEX CO., LTD with the theoretical minimum thickness of 0.040 mm. As a result of observation, the mode and the growth behavior of the damage were different depending on the ply thickness of 90° layer. It is shown that the damage growth is faster with the 90° layer to be thicker and vice versa. It is suggested that the damage growth behavior can be controlled with the ply thickness of 90° layer based on energy release rates by the FEM simulation.

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Mode II Fracture Toughness of CFRP Adhesive Bonded Structure at Cryogenic Temperature

Akinori YOSHIMURA, Yohei NOJI, Toshio OGASAWARA, Tomohiro YOKOZEKI, Sh ...

2011 Volume 37 Issue 4 Pages 130-137
Published: 2011
Released on J-STAGE: March 25, 2012

DOIhttps://doi.org/10.6089/jscm.37.130

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In the present paper, end notched flexure (ENF) tests are conducted for CFRP/CFRP, CFRP/aluminum sheet adhesive bonded specimens at room temperature (296 K), at low temperature (223 K) and at cryogenic temperature (77 K) in order to investigate the mode II adhesive fracture toughnesses. Large difference of the coefficients of thermal expansion (CTE) between the CFRP and the aluminum sheet derives considerable thermal stress at the cryogenic temperature. Therefore, in the ENF tests, the effect of thermal stress must be considered. In the present paper, first the effect of thermal deformation is analytically discussed, and ENF tests are then carried out. The test results reveal that the fracture toughness is much higher at the low temperature than at the room temperature. However, the toughness is significantly lower at the cryogenic temperature than at the low temperature. Moreover, the results show that the crack extends in the adhesive film (cohesive failure) at the room and the low temperatures, whereas it extends at the interface between adhesive film and CFRP (adhesive failure) at the cryogenic. These results imply that the transition of the crack surface caused the degraded adhesive fracture toughness.

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Development of Thermoplastic Press Sheet with In-Plane Randomly Oriented and Dispersed Carbon Mono-Fibers and Evaluation of the Mechanical Property

Masahiro HASHIMOTO, Tomonaga OKABE, Masaaki NISHIKAWA

2011 Volume 37 Issue 4 Pages 138-146
Published: 2011
Released on J-STAGE: March 25, 2012

DOIhttps://doi.org/10.6089/jscm.37.138

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We have developed a novel stampable sheet composed of discontinuous carbon mono-fibers and thermoplastic resin for press molding of composite materials. This sheet enables in-plane random orientation and dispersion of carbon fibers in composites. Therefore, complexly shaped products, such as rib structures, are easily fabricated. Moreover, composites having superior mechanical properties can be obtained because the fiber length in composite is easily controlled to be long. This study addressed the effect of fiber length on strength and fracture modes of composites made of the sheet, using tensile tests and micromechanical analyses. To investigate the influential damage for the fracture mode, our analysis utilized Duva-Curtin model for fiber breakage. We incorporated this damage model into an equivalent inclusion model combined with the Mori-Tanaka theory to predict the tensile strength of the composites. The predicted results agreed well with those of the experiments when the fiber length and orientation in the composites were appropriately considered. Our analyses also indicated that 3 mm as the lower-limit fiber length in the composite, below which the damage mode is no longer dominated by fiber breakage and superior strength of the composites cannot be obtained.

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