Shear behavior and strain transmission mechanism in bonding interface of robust toughened epoxy/flattened bamboo composites

Abstract

To improve the brittle bonding interface of epoxy/flattened bamboo composite (EFB) and expand its application in bamboo buildings, the effects of bonding structures, alkali-treated surface, and toughened epoxy on shear bonding behavior of EFB were systemically investigated to completely understand bonding interface mechanism and novelly simulated models was analyzed. The microstructure and chemical bonding group of the EFB bonding interface were characterized to reveal the toughening bonding mechanisms. The tensile shear behavior of the bonding interface was analyzed by digital image correlation (DIC) and the strain transfer mechanism was simulated by finite element analysis (FEA). Results indicated that the bonding interphase between epoxy and flattened bamboo primarily involved mechanical interlocking in the bonding interface and chemical bonding in the parenchyma cells. The alkali-treated surface and toughened epoxy group (ATEG) improved epoxy penetration on flattened bamboo surface changing the interphase between epoxy and bamboo interface. Alkali-treated surface and toughened epoxy significantly enhanced shear strength and fracture energy of EFB. The maximum dry shear strength of ATEG was higher than control group, with increases varying across the three bonding structures. Under hygrothermal conditions, ATEG achieved the highest wet shear strength in core-reinforced structure with bamboo failure of 60 %. DIC analysis revealed the improvement of strain continuity and dispersion in ATEG under dry conditions, while strain concentration occurred mainly in interphase of EFB bonding interface under hygrothermal conditions leading to the debonding failure. FEA illustrated that alkali-treated surface and toughened epoxy reduced strain concentration in the interphase of bonding interface and improved strain distribution of EFB, consistent with DIC analysis.