An Apparatus to Measure the Relaxation of Crop Samples following Compression

An apparatus has been constructed to obtain a fundamental understanding of the relaxation, after compression, of small samples of straw or other plant material, and to allow measurement of the influence of material properties such as age and moisture content. The device has been used to apply pressures of up to 150 MPa to straw samples of 5 mm diameter and typically of 0·3 to 0·5 mm thickness and, after the load was removed, to measure the recovery or change in thickness with time to an accuracy of better than 0·01 mm. The accuracy of the measurement system was confirmed by the consistent results obtained when a steel reference plate was used in place of the sample. In over 50 tests carried out on straw samples to test the potential of the device, moisture content was found to have a greater effect on relaxation than did the age of the material or the position on the plant from which the sample was taken.