Modulus of Elasticity and Moment of Inertia of Grass Hedge Stems

Abstract

The ability of grass hedges to remain erect where runoff concentrates is critical to their control of ephemeral gully erosion. Hedge resistance to failure depends on the mechanical properties of its stems. We measured moment of inertia (I), modulus of elasticity (E), yield strength (Y), and the bending angle (V) at the elastic limit of stems of switchgrass (Panicum virgatum L.), vetiver (Vetiveria zizaniodes L.), miscanthus (Miscanthus sinensis Cv. gracillimus), and tall fescue (Festuca arundinacae). The stems were sorted into morphological age groups—vegetative, green internode, and woody internode. Moment of inertia was determined from stem geometry and modulus of elasticity from stem deflection from load increments applied in a cantilever arrangement. Yield strength and bending angle were calculated from the displacement of the stem at the last load increment before the elastic limit was exceeded. Grass internodes had I values between 8 and 272 mm4. Their modulii of elasticity were between 2.6 and 8.5 GPa, similar to certain plastics, but their yield strengths of 7 to 30 MPa were generally lower than those of the same plastics. The bending angle at the elastic limit for all grasses was between 2 and 8°.