Heat Transfer Mechanism And Post-fire Mechanical Performance Of Wood-cored Composite Sandwich Beams

The applications of glass fiber-reinforced polymer(GFRP)composite sandwich members are seriously restricted due to the problems of inflammable and poor fire-resistance.In this study,the wood-cored composite sandwich beams were selected as the research objects.The mechanical performance,heat transfer mechanisms and fire-resistance capacity of the sandwich beams were investigated by the combination of experimental analysis,analytical calculation and numerical simulation from the material to the member level.The main research work conducted is summarized as follows.(1)The compare investigation of four-point bending behavior of timber beams,composite hollow tube beams and wood-cored sandwich beams in ambient temperature.The parameters include the sections,multi-orientation fabrics.The failure modes,stiffness,deflections,ductility were investigated by the experiments.The developed 2D acoustic emission damage monitoring model could be used to monitor effectively the damage evolution of the sandwich beams.(2)The experimental investigation of mechanical properties of the component materials at elevated temperatures.The parameters of composite compression include temperatures and off-axis angles.The parameters of composite shear include temperatures,multi-orientation fabrics and shear planes.The parameters of douglas-fir shear include temperatures and shear planes.The developments of temperature-dependent strength,modulus and failure modes were studied.Based on the thermal kinetic theory and mixture laws,the strength and modulus of composites were predicted.The parameter of Henkinson model regarding the estimation of off-axis compressive properties were suggested.(3)The effect of fiber orientation on thermal conductivity were considered to modify the apparent thermos-physical model for composites.Based on the thermal kinetic theory and thermal analysis experiments,the apparent thermos-physical model for wood was developed.The developed thermos-physical model has clear physical meaning.(4)Using the 1D implicit and 2D alternative direction implicit(ADI)scheme,finite differential heat transfer models of component materials were developed to solve the heat transfer equations with variable thermos-physical parameters.The models were validated by three experiments,including the bottom-side fire experiment of composite square tube,the one-side heating of paulownia wood and the four-side heating of douglas-fir.(5)The ISO-834 standard fire experiments on 8 sandwich beams were conducted.The parameters include calcium silica board,exposed faces and endurance time.Based on ABAQUS,the user subroutine UMATHT was coded to develop the 2D finite element heat transfer model which was validated by the experimental data.(6)The investigation of post-fire four-point bending performance of sandwich beams.The development of failure modes,ultimate load-carrying capacity,deflections were studied.Based on the analytical theory,the bending stiffness and the shear stress distribution in composite webs were investigated.The user subroutine UMAT regarding to the constitutive model was coded.With the combination of UMATHT and UMAT,the thermos-mechanical finite element analysis model was developed and the model was validated by the experimental data.