FATIGUE BEHAVIOR OF OSB IN SHEAR

A five-point bending test was used to investigate shear fatigue proper ties of 18.26-mm- (23/32-in.-) thick commercial oriented strandboard ( OSB) under repeated sinusoidal load. The test was found to be an effec tive low-cost method of determining shear fatigue behavior of OSB. Max imum applied stress was controlled between 70 and 100 percent of the m aterial's average static strength, and loading frequencies of 0.5 and 1 Hz were used. Fatigue behavior in shear using a five-point bending t est is described as a three-stage process in the plot of load-deflecti on ratio versus cycles. Fatigue failure in shear is defined as the sha rp loss of the load-deflection ratio that initiates stage II. Prior to this sharp reduction, there was a gradual decline in the ratio. The f atigue properties (S-N curve (stress-number of cycles)) for OSB are pr oduced, where the stress level percent is based on a predicted static strength. A linear regression closely fits the S-N data. A stress leve l of 60 percent (based on the predicted strength of the materials) wit h an associated fatigue life of 10(5) cycles was the smallest load lev el tested. The trend of the data indicates that the endurance limit (i nfinite life) of the OSB is well below this stress level. Although the average fatigue life for material tested at 80 percent stress level a nd 0.5 Hz is 19 percent greater than for 1 Hz, there was no statistica lly significant difference between the fatigue lives at the two freque ncies.