A STUDY OF THE PHYSICAL AND MECHANICAL-PROPERTIES OF WHEAT-STRAW

A series of experiments was conducted to measure the physical properti es, tensile and shear strengths and elastic moduli of stem between nod es of wheat straw (var Mercia). These stems are referred to subsequent ly as ''stem internodes''. Apparatus is described for the measurements of physical properties, strength and elastic moduli. Young's modulus was measured by applying four point loading transversely to the stem; the rigidity modulus was found by subjecting a stem to torque. The pri ncipal variables investigated were (a) the effects of four stages of p lant maturity for the third stem internode position, (b) position of t he stem internode measured downwards from the ear for the fourth stage of plant maturity and (c) stem moisture in the range 8 to 22% w.b., f or the third stem internode position at the fourth stage of plant matu rity. There was in increase in stem diameter and wall cross-sectional area from the first to the fourth stem internode from the plant ear. T ensile strength was in the range 21.2 to 31.2 MPa and shear strength i n the range 4.91 to 7.26 MPa. Young's modulus was between 4.76 and 6.5 8 GPa and the rigidity modulus in the range 267 to 547 MPa. Plant matu rity had some significant effects on shear strength, which was highest for the first stage of maturity and for Young's modulus which increas ed with maturity, but had no effect on rigidity modulus. The stem inte rnode position for the fourth stage of maturity had some significant e ffects on both the strengths and elastic moduli, but consistent trends were not evident. Moisture content for the fourth stage of maturity, at the third stem internode position, affected both shear strength whi ch increased and rigidity modulus which decreased with increasing mois ture content. It had no effect on Young's modulus, however, or any con sistent influence on tensile strength. Stem conservation by freezing a t -20 degrees C had a significant effect on strength and elastic modul i. Young's modulus was larger for samples which had been frozen and sh ear strength and rigidity modulus were smaller. Storage of stems for 3 months had no significant effect on the elastic moduli. (C) 1995 Sils oe Research Institute