Effect of the defect concentration on the impact fatigue endurance of untreated and alkali treated jute–vinylester composites under normal and liquid nitrogen atmosphere

A comparative impact fatigue study has been made for the first time on the untreated and alkali treated, 35% jute fibres in the vinylester resin composites under normal room temperature and liquid nitrogen atmosphere respectively. The jute fibres were alkali treated in a 5% concentration for 4 and 8 h before preparing the longitudinally aligned pultruded composites. The calculated defect concentrations in the composites reinforced with the untreated, 4 and 8 h alkali treated jute fibres were 30%, 18.5%, and 28.5%, respectively. Under normal room temperature the presence of such defects proportionately improved the endurance of the composites acting as a damper to the shock waves produced by the repeated impacts. Whereas, under the liquid nitrogen atmosphere the defects with higher concentration in particular, displayed an inverse role having provided more sites for the adsorbed moisture to form ice facilitating the initiation of cracks, thus lowering its endured number of cycles. A relationship in the form of nlogEI=C−logN was established to describe the impact fatigue curves of the composites. From the relationship, the value of the material character (C) was obtained. The value of the fatigue resistance parameter (n) were found to vary considerably with the defect concentration between the samples tested under the normal and the liquid nitrogen environment.