Julia de Castro

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.

Effect of Natural Weathering on Durability of Pultruded Glass Fiber–Reinforced Bridge and Building Structures

After 17 and 15years of use, respectively, a detailed inspection of a pedestrian bridge and a 5-story building structure composed of partly adhesively bonded pultruded glass fiber-reinforced polymer (GFRP) profiles was conducted accompanied by full-scale serviceability and destructive coupon testing on exchangeable profiles. The bridge is exposed to a harsh Alpine climate and the building to a mild plateau climate. The system and material stiffness of the bridge remained unchanged during the 17years. The material strength of the bridge, however, was significantly affected by combined freeze-thaw cycles and ultraviolet (UV) irradiation. The latter accelerated the strength degradation by uncovering the fibers (fiber blooming) and thus inducing humidity ingress into the material by wicking effects. A large majority of the small-area adhesive bonds in the bridge were intact, although a few small cracks were observed in some joints at the surface. The large-area bonds of the building did not show any damage. Based on results of the inspection of the bridge, the application of an appropriate coating on pultruded GFRP structures exposed to harsh environments is recommended

Total light transmittance of glass fiber-reinforced polymer laminates for multifunctional load-bearing structures

The total light transmittance of hand lay-up glass fiber-reinforced polymer laminates for building construction was investigated with a view to two architectural applications: translucent load-bearing structures and the encapsulation of photovoltaic cells into glass fiber-reinforced polymer building skins of sandwich structures. Spectrophotometric experiments on unidirectional and cross-ply glass fiber-reinforced polymer specimens in the range from 0.20 to 0.45 fiber volume fraction and artificial sunlight exposure experiments on encapsulated amorphous silicon photovoltaic cells were performed. Analytical models have been developed to predict light transmittance through glass fiber-reinforced polymer structures and the percentage of solar radiation reaching encapsulated photovoltaic cells. The total amount of fibers in the laminates was the major parameter influencing light transmittance, with fiber architecture having little effect and regardless of fiber volume fraction. Eight-three percent of solar irradiance in the band of 300–800 nm reached the surface of amorphous silicon photovoltaic cells encapsulated below structural glass fiber-reinforced polymer laminates with a fiber reinforcement weight of 820 g/m2, demonstrating the feasibility of conceiving multifunctional glass fiber-reinforced polymer structures.

Integration of dye solar cells in load- bearing translucent glass fiber- reinforced polymer laminates

The encapsulation of dye solar cells in translucent, structural and lightweight glass fiber-reinforced polymer laminates was investigated with a view to designing multifunctional envelopes for daylit buildings. Small and large integrating sphere experiments and solar radiation experiments were performed to determine the light transmittance of the laminates and the electrical efficiency of the encapsulated cells. An overall cell efficiency of 3.9% (before encapsulation) only decreased to 3.4% after encapsulation below laminates of around 3-mm thickness. Thermal cycle experiments and finite element analysis allowed the thermal performance of the encapsulation for two types of cell substrates (glass and acrylic polymer) to be evaluated. Contrary to glass substrates, no delaminations were observed on acrylic substrates after 300 h of cycles +60/−20℃. A design for integrating dye solar cells into multifunctional sandwich building envelopes is proposed. A light transmittance of around 0.35 was estimated through a sandwich envelope with cell modules occupying 50% of the external face sheet. Research on the manufacturability of cells on polymeric substrates is encouraged.

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.

Optically-derived mechanical properties of glass fiber-reinforced polymer laminates for multifunctional load-bearing structures:

This paper demonstrates how the translucency of glass fiber-reinforced polymer (GFRP) laminates allows the derivation of their mechanical properties through optical measurements. Spectrophotometric, goniophotometric and tensile experiments were performed on unidirectional and cross-ply hand lay-up GFRP laminates with fiber volume fractions ranging from 0.15 to 0.45. An analytical model to predict the directional fiber volume fractions—and thus the mechanical properties of GFRP laminates—has been developed based on the total and diffuse transmittance and directional light scattering of the laminates. It is demonstrated that structurally optimized GFRP laminates can meet the requirements for GFRP skylights and the encapsulation of photovoltaic cells into translucent GFRP laminates.