Application of Fiber Reinforced Polymer Overlays to Extend Steel Fatigue Life

Abstract

An experimental and analytical study was conducted to investigate the effectiveness of applying carbon fiber reinforced polymer (CFRP) overlays to steel fatigue tension coupons to prolong fatigue life. Specimens were either notched or center hole specimens and tested in uniaxial tension. Variables studied were CFRP system, bond length, bond area, one and two sided applications, and applications prior or subsequent to crack propagation. Two sided applications were very effective, prolonging fatigue life by as much as 115%. Similar application of CFRP materials subsequent to crack propagation extended the remaining fatigue life by approximately 170% without any other means of crack arrest. The method therefore showed promise as both a preventive technique and repair method. The epoxy performance was critical to the effectiveness of the system, with all failures initiated by debonding of the CFRP. Overlays were most effective when the system was applied directly to the potential crack trajectory. One-sided applications introduced bending and did not significantly improve performance. CFRP materials with a moderate modulus of elasticity performed best. FEM was performed to estimate stress factors and effectiveness of overlays.