A Study of the Physical and Mechanical Properties of Wheat Straw

Abstract

A series of experiments was conducted to measure the physical properties, tensile and shear strengths and elastic moduli of stem between nodes of wheat straw (var Mercia). These stems are referred to subsequently 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 principal variables investigated were (a) the effects of four stages of plant maturity for the third stem internode position, (b) position of the 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., for the third stem internode position at the fourth stage of plant maturity. There was in increase in stem diameter and wall cross-sectional area from the first to the fourth stem internode from the plant ear. Tensile strength was in the range 21·2 to 31·2MPa and shear strength in the range 4·91 to 7·26MPa. Young's modulus was between 4·76 and 6·58 GPa and the rigidity modulus in the range 267 to 547 MPa. Plant maturity had some significant effects on shear strength, which was highest for the first stage of maturity and for Young's modulus which increased with maturity, but had no effect on rigidity modulus. The stem internode position for the fourth stage of maturity had some significant effects 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 which increased and rigidity modulus which decreased with increasing moisture content. It had no effect on Young's modulus, however, or any consistent influence on tensile strength. Stem conservation by freezing at -20°C had a significant effect on strength and elastic moduli. Young's modulus was larger for samples which had been frozen and shear strength and rigidity modulus were smaller. Storage of stems for 3 months had no significant effect on the elastic moduli.