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Abstract: This paper presents results of the feasibility of carbon/epoxy composites (CFRP) as a future helicopter flexbeam material. Torsional behaviors of unidirectional CFRP and glass/epoxy composites (GFRP) with the same resin matrix were investigated. The initial torsional rigidity of CFRP was almost identical to that of GFRP. The torsional rigidities calculated using finite element analyses (FEA) agreed with the experimental results: the torsional rigidities are governed mainly by the material’s shear stiffness. Torsion fatigue tests were also conducted by controlling the angle of twist of the sinusoidal wave under a constant tensile axial load. No catastrophic failure occurred with either GFRP or CFRP, although decreased amplitudes of torque and torsional rigidities were observed according to the number of cycles. Results of X-ray CT inspections and numerical calculation by FEA revealed that degradation of a torsional rigidity is caused mainly by splitting crack propagation along the fiber direction. The torsion fatigue life of CFRP was superior to that of GFRP. Consequently, results confirmed that CFRP exhibits excellent properties as a torsional element of a helicopter flexbeam in terms of torsional rigidity and tension–torsion fatigue behaviors. [Copyright &y& Elsevier]

The compressive fracture aspect for the thick quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates was investigated using a high-speed camera to clarify the progress of the brooming fracture. The compressive fracture types of the laminates could be classified into two groups, i.e., the fractures initiating from the innermost 0 ∘ ply and those initiating from the fixed sections of the specimen. The standard deviation of the compressive strength for the innermost 0 ∘ ply-initiated fracture type was larger than that for the fixed-section fracture type, although the average compressive strengths for each fracture mode were similar. The initial fracture in the innermost 0 ∘ ply was caused by the microbuckling of the fibers. The numerical results demonstrated a considerable out-of-plane shear stress around the free edges of the specimen, especially for the innermost 0 ∘ ply. Such a shear stress is thought to cause the microbuckling at the innermost 0 ∘ ply, with the crack subsequently propagating toward the outer plies of the specimen. The compressive strength of the innermost 0 ∘ ply was an important factor affecting the fracture behavior of the thick quasi-isotropic CFRP laminates. [ABSTRACT FROM AUTHOR]