Fiber-reinforced Plastic Specimens Research Articles

Reappearance of Typical Characteristics of FRP Core Rods in the Decay-Like Fracture Insulator

In this paper, an artificial accelerated aging platform of Fiber Reinforced Plastic (FRP) core rod with various aging conditions, including high temperature, acid corrosion and high electric field strength, is presented. Based on that, the typical degradation characteristic of FRP core rods in decay-like fracture insulators are simulated and verified. A thermal infrared imager is used to detect the temperature rise when the AC voltage is applied. The results show that the temperature of the FRP specimens under multiple stresses is significantly increased up to 61 °C (177%) compared with the specimen under single aging stress (22 °C). Moreover, Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Thermal Gravimetric Analysis (TGA) are applied to study the physicochemical properties of the aging FRP specimen and the reaction occurred in the degradation process and the influence mechanism among different aging factors. The results show that the epoxy resin matrix is eroded by water and nitric acid. In the presence of a high electric field, the epoxy resin matrix is further degraded and evaporated. Then the interface between the epoxy resin and the glass fiber separates and develops, accompanied by ion-exchange and hydrolysis process. With the development of the degradation process of FRP core rod, obvious carbonized channel can be detected. Finally, electric erosion puncture occurs and breakdown happens. Compared with the FRP core rod extracted from the decay-like fractured composite insulators, the artificial accelerated aging sample shows the similar change trend on physicochemical properties. This work can provide theoretical support for the FRP core rod degradation mechanism and life predicting of high voltage composite insulators or other actual operation environment.

A Versatile Methodology for the Fatigue Life Prediction of Unidirectional Carbon Fiber-reinforced Plastic Specimens by the Micro-stress Analysis of Resins

A Versatile Methodology for the Fatigue Life Prediction of Unidirectional Carbon Fiber-reinforced Plastic Specimens by the Micro-stress Analysis of Resins

Defect Detection in Composite Products Based on Sparse Moving Window Principal Component Thermography

As a nondestructive testing (NDT) technology, pulsed thermography (PT) has been widely used in the defect detection of the composite products due to its efficiency and large detection range. To enhance the distinction between defective and defect-free region and eliminate the influence of the measurement noise and nonuniform background of the thermal image generated by PT, a number of thermographic data analysis approaches have been proposed. However, these traditional methods only consider the correlations among the pixel while leave the time series correlations unmodeled. In this paper, a sparse moving window principal component thermography (SMWPCT) method is proposed to incorporate several thermal images using the moving window strategy. Also, the sparse trick is used to provide clearer and more interpretable results because of the structure sparsity. The effectiveness of the method is verified by the defect detection experiment of carbon fiber-reinforced plastic specimens.

Characterization of Metal Inserts Embedded in Carbon Fiber Reinforced Plastics

The use of fiber-reinforced-plastics (FRP) contributes to an efficient implementation of lightweight design due to their outstanding specific mechanical properties. The RTM process offers great design freedom and allows the integration of functional elements during manufacturing. Embedded metal elements, so-called inserts, can be used to deal with the load transfer to structural parts. These elements have distinctive characteristics in comparison to other joining technologies. For example, detachable connections can be established with the help of inserts. Due to the fiber continuity not being interrupted and, subsequently, the FRP parts not having to be drilled, there is no local bearing stress. This paper aims at the characterization of metal inserts in FRP parts. The parts are manufactured using the RTM process with a specially adapted RTM mold with exchangeable cartridges for different insert geometries. The inserts are made of metal sheets with welded bushings and are embedded during preforming. The cured FRP specimens are tested under different load conditions to evaluate their suitability for various fields of application. Furthermore, the diameter and thickness of the metal sheet of the insert as well as the thickness of the FRP are varied to identify their influence on the failure behavior and load capacity under tensile loads.

An Investigation on Surface Flashover Characteristics of FRP in Several Insulation Gases for the Spacer of Cryogenic Bushing

Abstract —Superconducting equipment has been actively investigated for securing the environment and energy technology (ET) in various parts of the world. Despite these movements, a high voltage cryogenic bushing, which plays an important role of interconnection between the electric power systems and superconducting devices, has not been fully developed due to severe insulation requirements. gas A insulated cryogenic bushing has been investigated as one of our projects since 2010. a basic step to obtain the design As parameters for cryogenic bushing, we focused on the surface flashover characteristics of glass fiber reinforced plastic (FRP) in several insulation gases. the danger of reduction of the dielectric performanceFor the surface flashover tests, several insulation gases including SF6, CF 4 and N 2 gas were prepared. Various length of FRP specimens were fabricated in order to obtain the data for fundamentalcreepage distance of FRP. The first specimen group was from 2 mm to 10 mm with 2 mm intervals and the second specimen group was from 20 mm to 100 mm with 20 mm intervals. And the gas pressure was varied from 1 bar to 4 bar. n AC Aovervoltage test and a lightning impulse test were performed. Then the experimental results of surface flashover were obtained and analyzedBased on these results, it would be . possible to design the optimum creepagedistance of FRP in a cryogenic bushing.

Study of the decrease in print-through phenomenon on fiber-reinforced plastic material

Fiber-reinforced plastic (FRP) is a general kind of composite material used in many industries. This study examines the print-through phenomenon (PTP) via quantitative measurements on the gel-coated surface of FRP specimens. Moreover, finite element analysis is also adopted in this investigation. Based on a large number of experiments and computations, an average parameter, the arithmetic mean deviation is utilized to determine the degree of the PTP. Further, the reflections of a light image on a FRP surface were observed in photographs. Experimental results show that insulating residual stress can reduce PTP. Adding a core-mat layer to the FRP stacking scheme is a good solution for minimizing the PTP. In addition to using the core-mat materials, substitute materials used to prevent the PTP are also investigated.

A New Method for Predicting the Fatigue Life of Fiber-reinforced Plastic Laminates

This article introduces a new methodology for predicting the fatigue life of fiber-reinforced plastic (FRP) laminates at various stress levels. This method is based on the evolution of the center of gravity (CG) of the hysteresis loops (HL), and is termed the CG method. The CG method provides precise information regarding the fatigue behavior and damage situation within FRPs, offering highly accurate predictability of fatigue failure. Furthermore, the CG method can be constructed by tests performed on only one specimen by utilizing a new periodic function that represents the response of FRP specimens under dynamic loading fatigue tests - either in displacement control mode or load control mode. The authors originated the CG method in (Momenkhani, K. (2003). Using Geometric Properties of Hysteresis Loops for Predicting Fatigue Damage Accumulation in Fiber Reinforced Plastic Laminates, Doctoral Dissertation, The George Washington University, pp. 49-130), and published it in (Momenkhani, K., Sarkani, S. and Jones, D.L. (2005). Development and Application of a Model Using Center of Gravity of Hysteresis Loops to Predict Fatigue Damage Accumulation in Fiber Reinforced Plastic Laminates, Journal of Composite Materials, 39(6): 557-575). The present article applies the CG method as an alternative model to replace and supersede S-N curve methods for fatigue life predictions of FRPs.

On the experimental investigation of crash energy absorption in laminate splaying collapse mode of FRP tubular components

In this experimental work the crash energy absorption of fibre reinforced plastic (FRP) tubular components that collapse in laminate splaying mode is investigated by means of a new testing method, the “curling test”. This test method was used trying rectangular carbon, aramid and glass FRP strips—in which the reinforcing fibres were in the form of reinforcing woven fabric (carbon and aramid FRP specimens) and multi-axial fibre reinforcements (glass FRP specimens). Apart from the analysis of the system of bending and friction forces acting on the specimens during the curling tests in comparison with the forces acting in the case the laminate splaying collapse mode and the observations related to the deformation and crushing induced on the FRP specimens by this force combination, the analysis of the test results focused on the influence of the most important geometric and laminate material properties—such as thickness, flexural rigidity, number of reinforcing fibre layers, laminate stacking sequence and constituent material mechanical properties—on the specific energy absorption and the peak load.

Investigation of the Durability Characteristics of Fiber Reinforced Plastic (FRP) Materials in Concrete Environment

Commercially available fiber reinforced plastic (FRP) materials were used in this investigation. Accelerated laboratory tests were performed mostly on samples conditioned in simulated concrete pore solution to evaluate the long-term durability characteristics. Most glass fiber reinforced plastic (GFRP) bars were tested after conditioning to evaluate the changes in tensile strength and stiffness with respect to the unconditioned samples. Mass uptake/absorption of alkaline solution and morphological changes of FRP specimens were also studied. The acceleration test regime used in this investigation can be used as a method for determining the durability characteristics of FRP materials in a concrete environment and for the selection of FRP products for demonstration projects before finalizing the design codes and specifications. A simple mass uptake measurement under accelerated test conditions can be used as a first-step screening procedure to eliminate poor-quality products from further testing.

EXAMINATION OF FUNDAMENTAL ASSUMPTIONS OF ANALYTICAL MODELING OF FIBER PULLOUT TEST

Some of the simplifying assumptions fundamental to shear lag theory-based models of the fiber pullout test are compared with results from a detailed finite-element (FE) model to examine their validity. A range of material and geometric parameters representative of glass- and carbon fiber-reinforced plastic specimens are examined. The FE model strongly contradicts shear lag theory's assumptions that the axial stress gradient in the matrix can be neglected in the equilibrium equation, and that the radial and hoop stresses can be neglected in the constitutive relations of the matrix. Shear lag's assumptions that the shear strain in the matrix is dominated by the variation of axial displacement, and that the fiber end transmits no load appear to be in better agreement with the FE results. It is speculated that the questionable validity of these assumptions leads to inaccurate predictions for the energy release rate, G.