GFRP Layers Research Articles

Influences of Stress Ratio on the Fatigue Strength of Unidirectional Hybrid Composite GFRP/Al

Effects of stress ratio on the off-axis fatigue strength of a unidirectional fiber-metal laminate GFRP/Al have been studied at room temperature. Tension-tension and tension-compression fatigue tests for three kinds of stress ratio: R=0.4, 0.1 and -0.2 are performed on GFRP/Al coupon specimens with different fiber orientations in the GFRP layers: θ=0, 5, 10, 15, 20, 30, 45, 60 and 90°. Also, a fatigue damage mechanics model is formulated which considers the effect of stress ratio. It is clearly observed that the fatigue strength is affected by stress ratio for every off-axis angle. Effects of the mean stress on the fatigue strength of GFRP/Al are examined on the basis of the constant fatigue life diagrams, and those diagrams are approximately described by the linear relationships of the Goodman type. Failure morphology of specimens indicates the fatigue failure of GFRP/Al is substantially governed by the fatigue strength of GFRP for the fiber orientations θ=0∼10°, while it is done by that of Al alloy for θ=30∼90°. It is demonstrated that the proposed fatigue damage mechanics model adequately describes the effect of stress ratio on the off-axis fatigue strengths of the unidirectional fiber-metal laminate.

Impact Performance of Macrocomposite Laminates-1. Evaluation of Energy Absorbed in Non-Penetration Impact Test

Cladding of dissimilar materials is one of the several methods for improving the mechanical properties of composite materials. In this investigation, low impact energy test (non-penetration test) was carried out on GFRP/metal composites. The behavior at three energy levels (4, 8, and 12 J) was studied. The samples were divided into three types: Type 1 consisting of GFRP, Type 2 is GFRP with stainless steel (not bonded) and Type 3 is GFRP bonded to stainless steel. The GFRP contains chopped strand mat (CSM), biaxial system (BX) and quasiaxial system (QX). Both force at the initial peak (Fi) and maximum force (Fmax) increased due to the presence of stainless steel in the composite. However, Fmis increases with respect to impact energy whilst Fi was independent of impact energy. A slight improvement on the energy absorption of GFRP layer in the macrocomposite system was achieved at all energy levels except for CSM-GFRP which shows a significant brittle failure.

Inelastic behavior and strength of fiber-metal hybrid composite: Glare

Off-axis inelastic and fracture behavior of a new type of fiber-metal composite called GLARE 2, a hybrid laminate of unidirectional glass/epoxy laminae (GFRP) and aluminum-alloy sheets, have been examined under static tensile-loading conditions. The classical laminated plate theory (CLT) was applied for describing the off-axis inelastic behavior of GLARE 2 laminate. Irrespective of the off-axis angle, a sharptransition caused by the yielding of aluminum alloy layers appears in the stress-strain relations. The nonlinearity of the behavior of GLARE 2 after this transition increases more significantly as the off-axis angle becomes larger. The tensile-fracture strength of the GLARE 2 laminate is almost two times as large as that of the monolithic aluminum alloy in the fiber direction, and it is about five times the value of the GFRP in the transverse direction. The anisotropy for the tensile fracture strength of the GLARE 2 laminate can be predicted using the Tsai-Hill theory. For the off-axis angles > 5°, transverse cracks develop in the GFRP layers before the GLARE 2 laminate fractures. A CLT-based model, which takes into account the transverse failure in the GFRP layers to cause an instantaneous degradation of transverse and shear elastic moduli, accurately describes the characteristic deformation behavior of the GLARE 2 laminate.