Thermophysical and thermomechanical properties of basalt-phenolic FRP rebars under high temperature

Thomas Keller, Ting Li, Jiahui Shen, Hongwei Zhu
ELSEVIER SCI LTD, 2022
Article

Résumé

An experimental investigation was conducted on the thermophysical and thermomechanical properties of phenolic-basalt fiber-reinforced polymer (P-BFRP) rebars subjected to high temperature. As a comparison, vinylBFRP (V-BFRP) and epoxy-BFRP (E-BFRP) rebars were also investigated within the same program. The mass variation of all BFRP rebar types was similar in air atmosphere while P-BFRP rebars decomposed more slowly in nitrogen atmosphere. All BFRP rebar types were found to have a similar specific heat and thermal conductivity up to 350 degrees C. P-BFRP rebars exhibited a much higher glass transition temperature compared with the other two types of BFRP rebars. Three failure modes could be differentiated for all BFRP rebar types according to three temperature ranges, the latter were shifted to higher values for P-BFRP rebars. No reduction in tensile strength occurred in P-BFRP rebars up to 300 degrees C, while V-BFRP and E-BFRP rebars experienced a significant degradation of tensile strength at around 100 degrees C already. This advantage of P-BFRP rebars was mainly caused by the much higher Tg which delayed the initiation of interfacial bonding failure up to 300 degrees C. The elastic modulus of all BFRP rebar types exhibited a similar degradation, which was caused by progressive fiber and fiber bundle failure due to non-uniform stress distributions.

Official source

https://infoscience.epfl.ch/record/295244?ln=fr

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Concepts associés

Chargement

Publications associées

Chargement

Corrosion testing of solar cells: Wear-out degradation behavior

Christophe Ballif, Andrew Wayne Fairbrother, Luca Gnocchi, Alessandro Francesco Aldo Virtuani

Corrosion is one of the main end-of-life degradation and failure modes in photovoltaic (PV) modules. However, it is a gradual process and can take many years to become a major risk factor because of the slow accumulation of water and acetic acid (from encapsulant ethylene vinyl acetate (EVA) degradation). In this work, an accelerated aging test for acetic acid corrosion was developed to probe wear-out and end-of-life behavior and facilitate screening of new cell, passivation, metallization, and interconnection technologies. In the tests, the top glass and EVA layers were removed from PV modules to expose the solar cells and interconnects. These "opened" modules were then placed in acid baths under varying conditions, including acid concentration, temperature, and elec-trical bias. Three cell technologies were tested, including Al-back surface field (BSF), passivated emitter and rear contact (PERC), and silicon heterojunction (SHJ). For all conditions, the presence of acid accelerated module power loss compared to control tests with water baths. Increased temperature accelerated the rate of degradation by several times. Application of electrical bias led to an initial drop in short circuit current, but these modules eventually outperformed the non-biased modules. In all tests, lead oxides were the primary degradation products detected, and found to accumulate mostly along the printed metallization, especially in proximity to the busbar. SHJ cells with a silver paste-based interconnection outperformed Al-BSF and PERC cells with a solder-based interconnection. The accelerated corrosion test methods can be optimized to match corrosion behavior observed in field modules with greater precision and shorter times than standard damp heat tests, and is espe-cially useful to assess the long-term durability of the continuously increasing variety of corrosion sensitive PV materials and components.

ELSEVIER2022

Chargement

Structural behavior and durability of multifunctional fiber-reinforced polymer components

Florian Riebel

In the context of sustainable development, building insulation represents a major concern as a means of increasing energy efficiency. In order to comply with new norms such as the Passive House standard, locations where load-bearing components must penetrate the building's insulating envelope, such as when cantilevered slabs (e.g. balconies) are anchored to building walls, constitute a particular challenge. With conventional steel reinforcement, thermal bridges are inevitable and insulation is weakened. To overcome this deficiency, a multifunctional joint has been developed in which GFRP (glass-fiber reinforced polymer) elements performthe necessary structural functions without compromising the continuity of the building's insulating envelope. This is due to GFRP materials' low thermal conductivity, which is magnitudes smaller than that of concrete and steel, making them particularly suitable. The anchorage of balconies requires linkages that can resist shear as well as tensile and compression forces in the upper and lower parts of the slab. In a first step, a hybrid joint was created in which the lower compression steel reinforcement was replaced by a compression-shear (CS-)element made of GFRP. This consisted of a short pultruded profile with cap plates bonded to its cut ends. In addition to compression forces, the element was intended to bear parts of the shear load. The joint was investigated in various full-scale beam specimens each representing a section of the slab. Based on the results, the joint's structural behavior was modeled analytically and structural requirements for the CS-element were determined. It was seen that shear transfer through the element increased with increasing shear-to-moment ratios. In a second step, an all-GFRP joint was created in which, in addition to the element in the compression zone, a tension-shear (TS-)element replaced the remaining steel reinforcement. This element consisted of the same pultruded profile cut to longer sections and penetrating the concrete. To anchor the tensile forces in the concrete, ribs were bonded to its surface. This joint type was also investigated through full-scale beam experiments similar to the hybrid-joint beams. The load transfer through the joint and into the concrete was studied and modeled analytically. The behavior of the all-GFRP joint was as ductile as that of the hybrid joints. The TS-element bore the main portion of the shear load independently of the shear-to-moment ratio however. The CS-element used in both joint types was of special interest with regard to remaining strength and stiffness after long-term service life. Exposure to alkaline concrete-pore solution represents a particular threat to the polyester matrix and glass fibers inside the GFRP material. Therefore, CS-elements were immersed in alkaline liquids at different temperatures and their compression strength and stiffness were studied during a period of eighteen months. Material degradation was investigated by SEM-microscopic images and EDX-analysis. The observed loss of compressive strength was ascribed to moisture diffusion and chemical degradation of the fibers, matrix, and fiber-matrix interface. It was shown that the strength degradation rate at different temperatures followed the Arrhenius rate law and that remaining strength after long time spans could therefore be projected by extrapolating the measurements. Remaining strength after 70 years of service life was found to be sufficient for the element never to become the critical failure location and classic concrete theory can be applied to verify the joint. Since stiffness at high temperatures was observed to already remain constant after short exposure times, this value could directly be extrapolated to apply to a 70-year service lifespan.

EPFL2006

Chargement

As the range of applications for fiber-reinforced polymer (FRP) composite materials in civil engineering constantly increases, there is more and more concern with regard to their performance in critical environments. The fire behavior of composite materials is especially important since complex physical and chemical processes such as the glass transition and decomposition occur when these materials are subjected to elevated and high temperatures, possibly leading to considerable loss of stiffness and strength. This stiffness and strength degradation in composite materials under elevated and high temperatures is the result of changes in polymer molecular structures. When polyester thermosets are subjected to elevated and high temperatures, they undergo three transitions (glass transition, leathery-to-rubbery transition, and rubbery-to-decomposed transition), corresponding to four different states (glassy, leathery, rubbery and decomposed). At a certain temperature, a composite material can therefore be considered as a mixture of materials that are in different states. As the content of each state varies with temperature, the composite material exhibits temperature-dependent properties. Since these changes in state can be described using kinetic theory, the quantity of material in each state can be estimated and the thermophysical and thermomechanical properties of the mixture can thus be determined. These concepts formed a basis for the development of thermophysical and thermomechanical property sub-models for composites at elevated and high temperatures and even for the description of post-fire status. Incorporating these thermophysical property sub-models into a heat transfer governing equation, thermal responses were calculated using a finite difference method. Integrating the thermomechanical property sub-models within structural theory, the mechanical responses were described using a finite element method and the time-to-failure was also predicted by defining a failure criterion. The modeling results for temperature responses, mechanical responses and post-fire behavior were compared with those obtained from structural endurance experiments on full-scale cellular GFRP (glass fiber-reinforced polymer, in this case polyester resin) panels subjected to a four-point bending configuration and fire from one side. The modeling results for time-to-failure were compared with those from the experiments carried out on GFRP tubes under combined compressive and thermal loadings. In each experimental setup, two different thermal boundary conditions were investigated – with and without water cooling through specimen cells – and good agreement was found. The understanding gained and modeling of the behavior of GFRP composites under elevated and high temperatures carried out in this thesis could be applicable for different composite materials, and also benefit investigations regarding both active and passive fire protection techniques in order to improve the fire resistance of structures made of such materials.

EPFL2009

Chargement

Structural behavior and durability of multifunctional fiber-reinforced polymer components

Florian Riebel

EPFL2006

EPFL2009

Corrosion testing of solar cells: Wear-out degradation behavior

Christophe Ballif, Andrew Wayne Fairbrother, Luca Gnocchi, Alessandro Francesco Aldo Virtuani

ELSEVIER2022