Hai Fang

Behavior of sandwich wall panels with GFRP face sheets and a foam-GFRP web core loaded under four-point bending

In this paper, a simple and innovative sandwich panel with GFRP face sheets and a foam-GFRP web core (GFFW panels) is developed. An experimental study was carried out to validate the effectiveness of this panel for increasing the bending strength. The effects of web thickness, web spacing, web height and face sheet thickness on bending stiffness and energy dissipation were also investigated. Test results demonstrate that compared to the normal foam-core sandwich panels, a maximum of approximately 640% increase in the ultimate bending strength can be achieved. Meanwhile, the bending stiffness and energy dissipation can be enhanced by increasing web thickness, web height and face sheet thickness. An analytical model was developed to predict the ultimate bending strength of GFFW panels. The formulae to calculate the equivalent bending stiffness, shear modulus and mid-span deflection were also derived. A comparison of the analytical and experimental results showed that the analytical model accurately predicted the ultimate bending strengths and min-span deflections of the GFFW panels under four-point bending. Furthermore, the finite element analysis was extended to nvestigate the effects of foam density and shear span-to-depth ratio which were not considered in the tests. The numerical results revealed that increasing foam density and decreasing the shear span-to-depth ratio can improve the bending strength and stiffness of the panels.

Flexural behavior of hybrid composite beams with a bamboo layer and lattice ribs

This paper presents an experimental investigation of flexural behavior of hybrid composite beams with glass fiber reinforced plastics box skins, a polyurethane foam core, a bamboo layer, and lattice ribs. The bamboo layer was placed on the top of a wrapped polyurethane foam core. The lattice ribs were distributed along the longitudinal direction of the beam. Four beams, involving a control specimen, were loaded in four-point bending to validate the effectiveness of the bamboo layer and lattice ribs for increasing the ultimate bending strength of the hybrid composite beams. Compared to the control specimen, a maximum of an approximately 85% increase in the ultimate bending strength can be achieved. The beam with bamboo layer reinforcement and without lattice ribs exhibits the highest stiffness-to-weight ratio, while the beam with both bamboo layer and lattice ribs exhibits the highest strength-to-weight ratio. Meanwhile, various failure modes were summarized, including compressive and crushing failures. Finally, an analytical model to predict the bending stiffness and ultimate bending strength of the hybrid composite beams was proposed. Furthermore, the analytical results were agreed well with test results.

Experimental and Theoretical Study of Sandwich Panels with Steel Facesheets and GFRP Core

This study presented a new form of composite sandwich panels, with steel plates as facesheets and bonded glass fiber-reinforced polymer (GFRP) pultruded hollow square tubes as core. In this novel panel, GFRP and steel were optimally combined to obtain high bending stiffness, strength, and good ductility. Four-point bending test was implemented to analyze the distribution of the stress, strain, mid-span deflection, and the ultimate failure mode. A section transformation method was used to evaluate the stress and the mid-span deflection of the sandwich panels. The theoretical values, experimental results, and FEM simulation values are compared and appeared to be in good agreement. The influence of thickness of steel facesheet on mid-span deflection and stress was simulated. The results showed that the mid-span deflection and stress decreased and the decent speed was getting smaller as the thickness of steel facesheet increases. A most effective thickness of steel facesheet was advised.

Experimental Study of the Bending Properties and Deformation Analysis of Web-Reinforced Composite Sandwich Floor Slabs with Four Simply Supported Edges

Web-reinforced composite sandwich panels exhibit good mechanical properties in one-way bending, but few studies have investigated their flexural behavior and deformation calculation methods under conditions of four simply supported edges. This paper studies the bending performance of and deformation calculation methods for two-way web-reinforced composite sandwich panels with different web spacing and heights. Polyurethane foam, two-way orthogonal glass-fiber woven cloth and unsaturated resin were used as raw materials in this study. Vacuum infusion molding was used to prepare an ordinary composite sandwich panel and 5 web-reinforced composite sandwich panels with different spacing and web heights. The panels were subjected to two-way panel bending tests with simple support for all four edges. The mechanical properties of these sandwich panels during the elastic stage were determined by applying uniformly distributed loads. The non-linear mechanical characteristics and failure modes were obtained under centrally concentrated loading. Finally, simulations of the sandwich panels, which used the mechanical model established herein, were used to deduce the formulae for the deflection deformation for this type of sandwich panel. The experimental results show that webs can significantly improve the limit bearing capacity and flexural rigidity of sandwich panels, with smaller web spacing producing a stronger effect. When the web spacing is 75 mm, the limit bearing capacity is 4.63 times that of an ordinary sandwich panel. The deduced deflection calculation formulae provide values that agree well with the measurements (maximum error <15%). The results that are obtained herein can provide a foundation for the structural design of this type of panel.

Experimental Study of the Flexural and Compression Performance of an Innovative Pultruded Glass-Fiber-Reinforced Polymer-Wood Composite Profile

The plate of a pultruded fiber-reinforced polymer or fiber-reinforced plastic (FRP) profile produced via a pultrusion process is likely to undergo local buckling and cracking along the fiber direction under an external load. In this study, we constructed a pultruded glass-fiber-reinforced polymer-light wood composite (PGWC) profile to explore its mechanical performance. A rectangular cross-sectional PGWC profile was fabricated with a paulownia wood core, alkali-free glass fiber filaments, and unsaturated phthalate resin. Three-point bending and short column axial compression tests were conducted. Then, the stress calculation for the PGWC profile in the bending and axial compression tests was performed using the Timoshenko beam theory and the composite component analysis method to derive the flexural and axial compression rigidity of the profile during the elastic stress stage. The flexural capacity for this type of PGWC profile is 3.3-fold the sum of the flexural capacities of the wood core and the glass-fiber-reinforced polymer (GFRP) shell. The equivalent flexural rigidity is 1.5-fold the summed flexural rigidity of the wood core and GFRP shell. The maximum axial compressive bearing capacity for this type of PGWC profile can reach 1.79-fold the sum of those of the wood core and GFRP shell, and its elastic flexural rigidity is 1.2-fold the sum of their rigidities. These results indicate that in PGWC profiles, GFRP and wood materials have a positive combined effect. This study produced a pultruded composite material product with excellent mechanical performance for application in structures that require a large bearing capacity.