Mechanical behavior and damage monitoring of pultruded wood-cored GFRP sandwich components

This study presents the efficient manufacturing of rectangular wood-cored GFRP sandwich components by pultrusion process. Unlike the traditional pultruded sections by use of the roving, three types of mats (strand mat, uni-axial fabric and tri-axial fabric) were adopted to improve the web-flange junction integrity of GFRP hollow-section (HS) and sandwich section (SS) specimens. The mechanical behavior of glue-laminated Douglasfir (DF), HS, and SS specimens under four-point bending was investigated. The test results showed that DF and HS specimens failed by tensile rupture and web buckling, respectively. The SS specimens exhibited excellent ductility and load-carrying capacity resulting from three main reasons: a) the step-by-step wrinkling of GFRP web, b) the plastic deformation capacity of the timber under the local compression parallel and perpendicular to the grain and c) the bond-slip between the timber core and the GFRP inner surface. Meanwhile, the acoustic emission (AE) system was applied to detect the damage signals. Comparisons between failure progressions and AE signal analysis suggest that cumulative AE energy was more effective than hits to characterise the damage stages. A 2-D damage location model was also developed. The predicted damage locations agreed well with the experimental failure modes.