Objective   Oriented strand board (OSB) is composed of cross-oriented layers consisting of thin and rectangular wooden flakes or strands, which are compressed and bonded together with synthetic resins. OSB is an important engineered wood product. The influence of application environment on the bending properties of OSB can provide necessary theoretical support for optimizing the processing technology and application method of OSB.

  Method  Samples prepared from 13 mm thick OSB panel were conditioned under different relative humidity (RH) conditions. Three-point bending tests were performed to measure the fatigue deflection of OSB under cyclic loading, strain distribution was recorded using digital image correlation (DIC) simultaneously. This contributes to reveal the causes of deflection results.

  Result  The increase of RH increased the moisture content and thickness of OSB, and enlarged the voids among wood strands and cracks in wood strands. The deflection of OSB increased significantly after conditioning at (95 ± 3)% RH, and after conditioning the samples at (65 ± 3)% RH, the deflection was still larger than the initial deflection. The samples’ deflection was close to their initial deflection if conditioning them at (95 ± 3)% RH and (65 ± 3)% RH without adding loading. The effect of loading cycles on the deflection was slight when the samples were conditioned at unchanged (65 ± 3)% RH. The deflection of the first cycle loading obviously increased, which was not found as increasing loading cycles. Strain distribution was homogeneous if the samples were conditioned only at (65 ± 3)% RH. The increase of moisture content could hamper the strain transfer and induce strain accumulation. Specifically, bending strain was prone to accumulate on the top and bottom surfaces, and shear strain would occur in the two opposite directions in high moisture content samples.

  Conclusion  The findings of this work explore the effect of application conditions and loading cycles on the bending strength of OSB. The outputs of this work are helpful for optimizing the manufacturing strategies and enlarging application field of OSB.