Mechanical behavior of rotary friction welding joints composed of laminated veneer bamboo substrate and bamboo dowel

Abstract

Rotary friction welding is a new connecting technique to produce joints by melting and re-solidification processes of substances, which has been pioneered in wooden furniture and structures due to the high interface strength. Bamboo has similar chemical components to wood and is a practical supplement to timber for applications. In this regard, the bamboo dowel was explored in this work to connect laminated veneer bamboo substrates using the rotary friction welding technique. The bond strength and shear strength of the proposed joints were experimentally evaluated by pull-out tests and single-shear tests based on the orthogonal array testing methodology. The effects of pre-drilled hole diameter, rotation rate, welding angle and substrate thickness on the mechanical behavior were investigated. The failure modes and load-carrying capacity were analyzed and discussed. Two failure modes including the pull-out failure and dowel fractured failure in pull-out tests and three failure modes including the pull-out failure, shear failure and hybrid failure of dowels in single-shear tests, were observed. It was found that the bond strength and shear strength of joints were primarily influenced by the pre-drilled hole diameter and the welding angle, respectively. The maximum bond strength of 4.40 MPa and maximum shear strength of 4.24 kN were achieved with the pre-drilled hole diameter of 8 mm and the welding angle of 45°, respectively. Furthermore, the results of scanning electron microscope observation and Fourier transform infrared spectroscopy analysis indicated that the bamboo fibers wound on the dowel surface and the relative contents of lignin increased. The research would provide the theoretical and technical basis for the application of bamboo rotary friction welding.