Stress Intensity Reduction to Enhance Fatigue Resistance of Steel Wind Turbine Towers

Abstract

In this study the fatigue behavior of cruciform welded joint strengthened by carbon fiber reinforced polymer (CFRP) has been investigated experimentally and numerically. To achieve this aim several investigations were considered in the study, these included: (1) Numerical analysis to study the effect of using only CFRP sheets in enhancing the resistance of cruciform welded joints to fatigue failure. According to analysis results, CFRP sheets were not sufficient to enhance fatigue resistance for root crack propagation. Therefore, CFRP stiffener overlapped with CFRP sheets were proposed to be studied experimentally and numerically. (2) Experimental test were conducted to study the effect of using CFRP stiffener overlapped with CFRP Sheet on fatigue life of cruciform welded joint. (3) Finite element analysis to study the effect of using CFRP stiffener overlapped with CFRP Sheet on fatigue life. A parametric study concerning several parameters as Young's modulus of adhesives, Young's modulus of carbon fiber, layers of carbon fibers, and CFRP stiffener dimensions was conducted using Finite Element. (4) Linear Elastic Fracture Mechanics analysis to predict S-N curves of retrofitted cruciform welded joint considering the different parameters and residual stresses result from welding process. Curves were compared with experimental results. Cf and m values of the different S-N curves were compared with that of AWS2002 different categories to evaluate fatigue life enhancement.