Investigation of mechanical properties of cotton stalk based on multi-component analyses**

Abstract

A b s t r a c t. A comprehensive understanding of the uprooting failure mechanism will likely require the accurate characterization of the mechanical properties of cotton stalk. Uprooting failure includes a fractured cotton stalk and peeled phloem sliding along the xylem. The modulus of elasticity of cotton stalk and its tissues (xylem and phloem) were measured using three different modes (tensile, compression and bending), and the reasons for the fractured cotton stalk and the peeled phloem sliding along the xylem were analysed from the perspective of composite mechanics. The results showed that the cotton stalk radially conforms to the properties of the composite with transverse anisotropy. The axial modulus of elasticity was significantly larger than the radial modulus of elasticity (axial modulus of elasticity: cotton stalk is 3181.79 MPa, xylem is 1093.91 MPa, phloem is 249.89 MPa, radial modulus of elasticity: is 91.04 MPa, xylem is 83.77 MPa, phloem is 77.01 MPa). Xylem is the backbone of the stalk that provides 96% of its compressive strength. The direct cause of fractured cotton stalk originated from the load force that exceeded its intrinsic compressive strength. Peeled phloem sliding along the xylem was related for the most part to the different radial modulus of elasticity of the xylem and phloem, and the weak cohesion between these two tissues. Based on the results, some suggestions were provided for the design of a puller.