A Sensor for Direct Measurement of Internal Stress in Wood During Drying: Experimental Tests Toward Industrial Application

In this study, an internal drying stress sensor was developed based on a silicon micromachined pressure gauge inserted in a cylindrical Teflon shell. Teflon provides protection and works as a medium between the gauge and wood. In this configuration, the pressure gauge has unidirectional, axis-selective sensitivity. When inserted in a drill hole at a given depth in the wood, the sensor can directly measure the compressive stress produced by shrinkage in the diameter of the hole. Based on research in the last 5 years, a preindustrial version has been developed that has been tested in laboratory drying experiments. Results show that the trend of the stress during the drying process can be visualized, and critical points can be determined such as stress reversal time and the effect of the conditioning phase on the internal stress. The sensors thus have potential to be used in the drying control on industrial scale once the remaining problems are solved.