Reversible Rail Shear Apparatus Applied to the Study of Woven Laminate Shear Behavior

Abstract

The multitude of in-plane shear tests existing in the literature seems to demonstrate the complexity of developing a test adapted to all experimental works. In a general framework of investigation of translaminar cracks in thin laminates, a test able to reproduce a pure in-plane shear loading was required. The laminate studied is notably employed as helicopter blade skin, and cyclic torsion induced by aerodynamic load involves cyclic in-plane shear. This particular application established some specifications for the test needed to carry out this study. To comply with them, an original technological solution has been developed from a three-rail shear test apparatus. This paper describes the resulting "reversible rail shear test" solution and its application to the study of in-plane shear behavior of a thin glass-epoxy laminate. The results concern plain and notched coupons under quasi-static loading, and crack growth tests under cyclic loading.

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

“…The same general trends were observed for 2-and 4-ply specimens ([0] n and [90] n ) made of the material of the study and submitted to quasi-static tensile tests [14][15][16]. So, interrupted tensile tests (on an electromechanical tension machine: INSTRON, capacity: 10 kN) were performed on [0] 2 specimens to highlight the damage scenario using micrograph SEM analysis [7].…”

“…6. Shearing behaviour-controlled by the resin-is initially linear then followed, from approximately c = 0.9 %, by a nonlinear phase (progressive ''strain hardening'') where inelastic strains develop [14]. We can also note a hysteresis effect as well as partial relaxation of the inelastic strains at zero stress, translating the typical visco-elastic behaviour of an epoxy resin [23,24].…”

“…11b for the warp face. For both faces, the thermo-elastic cooling observed until a shear strain of around 1.0 % (&threshold of plasticity observed by [14][15][16]) is homogeneous in the area. It is however slightly higher on the weft face, but the variation is relatively weak.…”

“…The macroscopic behaviour of the glass/epoxy fabric was previously studied in the laboratory by [15][16][17], using the offaxis tensile test, and more recently by [14] via a rail shear test. The stress/strain graph of a [0°] 4 specimen for a rail shear test is presented in Fig.…”

“…6b for two different specimens. The initial shear modulus G 0 is estimated at approximately 3.54 GPa by [15] (off-axis tensile test) and 3.82 GPa by [14] (rail shear test). The modulus reduction observed with the criterion of secant modulus (up to 60 %) is higher than with the tangent modulus (20 %).…”