Glass Fiber Reinforced Polymer (GFRP) materials are extensively used in the aerospace and marine industries because of their high strength and stiffness to weight ratio and excellent corrosion resistance. Stiffened panels are commonly used in aircraft wing and fuselage parts. The present study focuses on the behavior of composite stiffened panels under compressive loading. With the introduction of stiffeners to unstiffened composite plates, the structural stiffness of the panel increases resulting in higher strength and stiffness. Studies in the past have shown that the critical structural failure mode under compressive loading of a stiffened composite panel is by local buckling. The present study attempts to evaluate the mechanical behavior of composite stiffened panels under compression using blade stiffener configuration and in particular on the behavior of the skin- stiffener interface through experimental testing. A novel test fixture is developed for experimental testing of GFRP stiffened panels. A non-contact whole field strain analysis technique called digital image correlation (DIC) is used for capturing the strain and damage mechanisms. Blade stiffeners increased the strength, stiffness and reduced the out-of plane displacement at failure. The failure of both the unstiffened and stiffened panels was through local buckling rather than through material failure. DIC was able to capture the strain localization and buckling failure modes.
In the present work, the behavior of thin adhesively layer in patch repaired carbon fiber reinforced polymer (CFRP) panel under tensile load is investigated experimentally using digital image correlation (DIC) technique. The panel is made of Carbon/epoxy composite laminate and the stacking sequence in the panel is [0º]4. A circular hole of 10 mm diameter (d) is drilled at the center of the panel to mimic the case of low velocity impact damage removal. The panel with open hole is repaired with double sided (symmetrical) and single sided (unsymmetrical) rectangular patch made of same panel material having stacking sequence of [0º]3. Araldite 2011 is used for bonding the patch onto the panel over the damaged area. The global behavior of thin adhesive layer is examined by analyzing whole field strain distribution using DIC. Longitudinal, peel and shear strain field in both double and single sided repair configuration is studied and a compression is made between them. An estimate of shear transfer length which is an essential parameter in arriving at an appropriate overlap length in patch design is proposed from DIC and FEA. Damage development, failure mechanism and load displacement behavior is also investigated. The experimental results are compared with the numerical predictions.