Abstract
Carbon fiber-reinforced polymer (CFRP) materials have been effectively used as externally bonded sheets to repair damaged steel structures such as airplanes and ships. In this study, a series of double strap joints with different bonding lengths are considered and examined to experimentally and theoretically assess the effective bond length. Various models exist in the literature which are used to predict the strength of steel and CFRP joints under various loading conditions. Non-linear Lagrange stress method (NLS) which is a novel stress-based method for predicting the failure load values is presented for the first time. This approach is based on 2D and 3D linear elastic finite element analysis. Relying only on two experimental tests, the new approach proposed here can quickly and easily predict the failure load in steel/CFRP samples. In this methodology, it is assumed that the adhesive joint will fail as the normal stress along the adhesive mid-line reaches a predetermined value at a critical distance. In addition, experimental data on steel/CFRP joints gathered from the literature are compared to predictions using the NLS method. It was found that results from the theoretical predictions (NLS) were in good agreement with experimental tests conducted on double strap joints. It was also revealed that the average accuracy of the NLS method is superior to other methods such as cohesive zone model and Hart-Smith. The results revealed that under the best conditions, the NLS model is 5 times more accurate than existing models.
Highlights
Polymeric composite materials (PMC) show superior properties such as high specific strength and stiffness making them versatile materials with various applications in military, civilian aircrafts, space, and automobile industries
It was found that results from the theoretical predictions (NLS) were in good agreement with experimental tests conducted on double strap joints
A new method, namely the non-linear Lagrange stress method, was presented for failure load prediction in steel/Carbon fiber reinforced polymer (CFRP) adhesively bonded double strap joints (DSJ) based on longitudinal stress along the adhesive mid-plane
Summary
Polymeric composite materials (PMC) show superior properties such as high specific strength and stiffness making them versatile materials with various applications in military, civilian aircrafts, space, and automobile industries. Lee et al used an experimental approach to obtain the joint strength and the failure modes in steel and GFRP bonded DSJs [30]. The researchers modified the Hart-smith model and predicted the failure load in steel/CFRP DSJs and obtained reasonable results when compared to experimental data. In this paper the bond characteristics between CFRP laminate and steel members under quasi-static loading are investigated experimentally and theoretically in a series of DSJs. The presented criterion is based on normal (peel) stress along the midplane of the adhesive layer. Finite element analysis is performed on the DSJs in order to predict the failure loads and to obtain the stress distribution across the adhesive mid-plane in the 2D model of the specimens. The NLS method is described in order to directly determine the value of failure strength and the effective bond length before performing any other experiments
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