Fatigue in wood-based panels. Part 2: property changes during fatigue cycling of OSB, chipboard and MDF

Wood-based panels are viscoelastic so when a load (stress) is applied to them there is a time lag before a deflection (strain) is produced, which results in hysteresis (a loss of energy). The capture of stress versus strain hysteresis loops is a non-interruptive method of monitoring the damage produced during fatigue testing. Hysteresis loops were captured throughout the flexural fatigue testing of OSB, chipboard and MDF in four-point bending allowing the development of fatigue damage to be followed. The MDF tested had a greater mean bending strength than the OSB and chipboard. When stresses were applied to the materials as a percentage of their bending strengths, the stresses applied to the MDF samples were larger than those applied to the OSB and chipboard samples. As a result the microstrains were greater for MDF than for the chipboard and OSB. The OSB was stiffer than the chipboard and MDF, which were both of similar stiffness. The information gained from the hysteresis loops indicates that the OSB, chipboard and MDF all had fatigue limits just below 20% of their bending strengths. The fatigue limit for the MDF is likely to be slightly lower than for the chipboard and the OSB.