Determination of fatigue damage level of glass fiber reinforced epoxy based nanocomposites by electrical resistance change method

The purpose of this thesis is to monitor the damage level of fiber reinforced composites (FRPs) subjected to fatigue loading by using the electrical resistance change method and to prevent fatigue failures of FRPs by obtaining an electrical resistance change value with 95% reliability using Weibull analysis. Thus, it is aimed to develop a method to reduce the economic and safety risks of FRPs caused by fatigue damage. First, the woven glass fiber reinforced epoxy composite laminates were manufactured by vacuum bagging method. Multi walled carbon nanotubes (MWCNTs) were employed as filler materials to obtain electrical conductivity in composites. The distribution of MWCNTs in epoxy matrix was achieved by ultrasonication. Then, tensile strength of composites was determined by conducting static tensile tests. In-situ damage monitoring of composite specimens during fatigue tests by electrical resistance change method was carried out. Finally, Weibull analysis was applied to obtain a critical electrical resistance change ratio with % 95 reliability to be used as a reference value to prevent FRP composites from fatigue failures. Fatigue tests were conducted at two different stress amplitudes. The critical cycles at the fatigue failure and the corresponding critical electrical resistance change value for two different stress amplitudes were determined. An electrical resistance change value with 95% reliability using Weibull analysis was obtained to prevent fatigue failure for a particular stress amplitude.