Fatigue In Tension Perpendicular to the Grain

Traditionally fatigue resistance is quantified as number of cycles to failure at a given stress level. A previous study by the authors showed that fatigue in compression parallel to the grain is governed partly by duration of load and partly by an effect of loading, i.e. a combination of a creep mechanism and a mechanism connected to damage introduced in the loading sequences. The purpose of the present study is to disentangle the effect of duration of load from the effect of load oscillation in fatigue in tension perpendicular to the grain. Fatigue experiments are made on small specimens and on dowel type joints with slotted in steel plates. In series of ten, the small specimens are taken to fatigue failure in uniform tension at square wave shaped load cycles at 0.01 Hz and 0.1 Hz. In arder to test the predictive validity of the result from the small tension specimens, fatigue experiments are made on dowel type connections that have tension perpendicular to the grain as limiting strength parameter. It is concluded that no significant influence of duration of load is observed w hen the fatigue resistance of small specimens at 0.01 Hz and 0.1 Hz are compared. A weak but inconclusive time dependency is observed for the fatigue experiments on dowel type connections