Behzad D. Manshadi

Thermomechanical behavior of multifunctional GFRP sandwich structures with encapsulated photovoltaic cells

The feasibility of encapsulating solar cells into the glass fiber-reinforced polymer (GFRP) skins of load-bearing and thermally insulating sandwich elements with foam cores has been evaluated. Exposure of the encapsulated cells to artificial sunlight led to a significant temperature increase on the top sandwich surface, which almost reached the glass transition temperature of the resin. Mechanical loading up to serviceability limit loads did not cause any damage to the solar cells. Stresses of less than 20% of the material strength arose in the face sheets due to thermal and mechanical loading up to failure. Composite action through the face sheets with encapsulated cells was maintained and no debonding between face sheets and foam core was observed. Thanks to the superior mechanical and thermal sandwich behavior, thin-film silicon cells are more appropriate than polycrystalline silicon cells for use in multifunctional GFRP sandwich structures, although they are less efficient.

Shear Buckling Resistance of GFRP Plate Girders

Thin webs of glass-fiber-reinforced polymer (GFRP) girders are sensitive to shear buckling, which can be considered an in-plane biaxial compression-tension buckling problem, according to the rotated stress field theory. An extensive experimental study was performed, which shows that an increasing transverse tension load significantly increases the buckling and ultimate loads caused by a decrease in the initial imperfections and additional stabilizing effects. The stacking sequence also greatly influenced the buckling behavior. Higher bending stiffness in the compression direction increased the buckling and ultimate loads, while higher bending stiffness in the tension direction changed the buckling mode shape. The general solution obtained using the Fok model accurately modeled the experimental results, while the simplified solution (modified Southwell method) provided accurate results only at higher tension loads.

Contribution to Shear Wrinkling of GFRP Webs in Cell-Core Sandwiches

Glass-fiber-reinforced polymer (GFRP) cell-core sandwiches are composed of outer GFRP face sheets, a foam core, and a grid of GFRP webs integrated into the core to reinforce the shear load capacity. One of the critical failure modes of cell-core sandwich structures is shear wrinkling, a local buckling failure in the sandwich webs because of shear loading. The shear wrinkling behavior of GFRP laminates with different laminate sequences, stabilized by a polyurethane foam core, was experimentally and numerically investigated. Shear wrinkling was simulated by a biaxial compression–tension setup. The results show that an increasing transverse tension load significantly decreases the wrinkling load. The decreasing effect of tension is explained by the lateral contraction because of Poisson’s effect, which causes an increase in the initial imperfections and subsequent accelerated bending.

Shear Wrinkling of GFRP Webs in Cell-Core Sandwiches

Glass fiber-reinforced (GFRP) cell-core sandwich structures are increasingly used in bridge deck and roof construction. GFRP cell-core sandwiches are composed of the outer GFRP face sheets, a foam core and a grid of GFRP webs integrated into the core in order to reinforce the shear load capacity. One of the critical failure modes is shear wrinkling, a local buckling failure in the sandwich webs due to shear loading. Shear wrinkling is a biaxial compression-tension wrinkling problem and, for this reason, the numerous results of pure compressive wrinkling research are not necessarily applicable. The details and results of in-plane biaxial compression-tension wrinkling experiments on GFRP sandwich laminates, stabilized by a polyurethane foam core, are presented. It is shown that an increasing transverse tension load significantly decreases the wrinkling load. These results are confirmed by finite element calculations.

Shear buckling of GFRP beams webs

Slender webs of glass fiber-reinforced polymer (GFRP) beams are sensitive to shear buckling. Shear buckling can bee seen as an in-plane biaxial compression-tension buckling problem. The transverse tensile load thereby delays the onset of buckling and increases the ultimate load. Thin-walled GFRP plates of two different fiber stacking sequences, [0/90]S and [90/0]S, were subjected to in-plane biaxial compression-tension loading. The buckling loads were almost duplicated by increasing the tensile load while the ultimate loads were increased by up to 20%. The fiber stacking sequence thereby had significant effects on buckling mode shape and buckling and ultimate loads.