Search

Strengthening and repairing infrastructure with fiber‐reinforced polymers while achieving low‐cost, real‐time monitoring of cracks in engineering structures is highly challenging. Herein, a piezoelectric glass‐fiber‐reinforced polymer (piezo‐GFRP) sensor is used to monitor the mechanical behavior of cement beams with cracks under cyclic bending. The output voltage and frequency of the sensor are shown to be effective feedback signals for determining the mechanical behavior. The thin piezo‐GFRP sensor shows sufficient piezoelectric sensitivity to monitor the slight variations in the mechanical behavior of the cement beams during the early stages of cracking. It is indicated in this result that such sensors have the potential for the multifunctional structural health monitoring of engineering structures. [ABSTRACT FROM AUTHOR]

Many structural health monitoring (SHM) techniques have been investigated for damage detection in woven glass fiber reinforced polymer (GFRP) laminates. Recently, the GFRP composites integrated with sensors have received attention because the composite material can transmit information about the structural condition during operation. Magnetostrictive materials are considered as feasible candidates to realize the contactless SHM techniques by exploiting the Villari effect, but the theoretical modeling to correlate a magnetostrictive response with structural conditions is a critical issue. In this study, the analytical procedure considering the mechanics of materials and electromagnetism was proposed to model the magnetic induction by the Villari effect of magnetostrictive GFRP laminates under bending. The magnetostrictive Fe–Co fiber/GFRP composites were then developed, and the four-point bending tests were carried out to evaluate the fabricated composites' stress monitoring capability. The magnetic flux density behavior corresponded to the bending stress fluctuation. The maximum magnetic flux density change was 70.7 mT subjected to the peak bending stress of 158 MPa. The analytical solutions showed reasonable agreement with the experimental results. The applied stress and measured magnetic flux density were correlated by the theoretical models. Thus, these results suggest an important step in realizing the novel contactless SHM technique utilizing magnetostrictive materials. [ABSTRACT FROM AUTHOR]

This paper investigates the through-thickness tensile behavior of woven glass fiber reinforced polymer (GFRP) composite laminates at cryogenic temperatures. Tensile tests were carried out with cross specimens at room temperature and liquid nitrogen temperature (77 K), and the through-thickness elastic and strength properties of the woven GFRP laminates were evaluated. The failure characteristics of the woven GFRP laminates were also studied by optical and laser scanning microscopy observations. A three-dimensional finite element analysis was performed to calculate the stress distributions in the cross specimens, and the failure conditions of the specimens were examined. It is found that the cross specimen is suitable for the cryogenic through-thickness tensile characterization of laminated composite materials. In addition, the through-thickness Young's modulus of the woven GFRP composite laminates is dominated by the properties of the matrix polymer in the given temperature, while the tensile strength is characterized by both, the fiber to matrix interface energy and the cohesion energy of the matrix polymer. [ABSTRACT FROM AUTHOR]

In this article, we investigate the strength characteristics of woven glass fiber reinforced polymer composite laminates subjected to tensile fatigue loading at cryogenic temperatures using the open hole specimens. Tension–tension fatigue tests were conducted on the open hole specimens of the woven glass fiber reinforced polymer laminates at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K), and microscopic observations of damage around the hole were made on failed specimens. A numerical procedure based on the finite element method was then applied to evaluate the fatigue strength of the unnotched woven glass fiber reinforced polymer laminates using the experimentally applied load and the length of the hole edge damage zone. The obtained results were compared with the existing experimental data from the unnotched specimens. It was demonstrated that the presented combined numerical–experimental method was effective for the determination of the fatigue properties of the woven glass fiber reinforced polymer laminates at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work is to investigate the interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates loaded in a mixed-mode bending (MMB) apparatus at cryogenic temperatures. The finite element analysis (FEA) is used to determine the mixed-mode interlaminar fracture toughness of MMB specimen at room temperature (RT), liquid nitrogen temperature (77K) and liquid helium temperature (4K). A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen and to examine the effect of damage on the mixed-mode energy release rate. The technique presented can be efficiently used for characterization of mixed-mode interlaminar fracture and damage behavior of woven laminate specimens at cryogenic temperatures. [Copyright &y& Elsevier]

This article focuses on understanding the Mode II interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates at cryogenic temperatures. A four point bend, end notched flexure (4ENF) test is performed at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4K), and an R-curve characterization is conducted for determining the mode II cryogenic fracture properties of GFRP woven laminates. The test configuration is also analyzed by finite element analysis coupled with damage. The damage distributions within the 4ENF specimens are predicted, and the effect of damage on the Mode II energy release rate is examined. This work is the first application of failure criteria (Hoffman criterion and maximum strain criterion) to the description of the R-curve behavior and interlaminar fracture toughness values of woven laminate ENF specimens at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical investigation of the effect of specimen geometry on the tensile properties and damage behavior of glass fiber reinforced polymer woven laminates at cryogenic temperatures. Cryogenic tensile tests were performed on three types of specimens, and acoustic emission monitoring was employed to characterize the damage development during loading. A two-dimensional finite element analysis was also carried out for three tensile test specimens in order to have a thorough understanding of the progressive failure behavior. A comparison was made between simulation and experiment. [ABSTRACT FROM AUTHOR]

The interlaminar fracture and damage behavior of glass fiber-reinforced polymer (GFRP) woven laminates at cryogenic temperatures has been investigated theoretically and numerically. The corrected beam theory and finite element analysis (FEA) have been used to calculate the Mode I interlaminar fracture toughness (IFT) of double cantilever beam (DCB) specimens at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). The effect of temperature on the Mode I IFT was investigated. A FEA coupled with damage was also employed to study the damage distributions within the specimen and to examine the effect of damage on the Mode I energy release rate. The corrected beam theory or FEA shows good agreement with the previous experimental compliance of the DCB specimen. The numerical results show that damage causes a decrease in the energy release rate. This work is the first application of failure criteria (Hoffman criterion and maximum strain criterion) to the analysis of the cryogenic behavior of woven laminate DCB specimens. [ABSTRACT FROM AUTHOR]

This paper developed smart composite structures with screen-printed piezoelectric composite energy harvesters. P(VDF-TrFE) based composites with BaTiO 3 particles of different concentrations were deposited via screen printing and studied regarding surface morphology, crystalline structure, piezoelectric, dielectric and mechanical properties. It was identified that P(VDF-TrFE) with 5 wt% BaTiO 3 addition exhibited the best piezoelectric property. Even with a monotonic reduction in the β phase crystallisation as the BaTiO 3 concentration was increased, a 5 wt% inclusion of BaTiO 3 led to the rise of d 33 from −28.63 pC/N to −33.90 pC/N. This was attributed to the enhanced interfacial polarisation and the stress concentration induced by the addition of the ceramic particles. Subsequently, the printed piezoelectric composites were co-cured with glass fibre reinforced composites (GFRPs) and carbon fibre reinforced composites (CFRPs). The assembled harvesters were tested under both sinusoidal excitation and real industrial vibration. It was found that the smart composites with 5 wt% BaTiO 3 always manifested the best energy harvesting performance. For the optimised generator, maximum power of 2 μW and 1.5 μW could be obtained when using GFRPs and CFRPs as substrates under 1 g peak-peak sinusoidal excitation, respectively. The harvested energy could be used to power a commercial accelerometer with the help of a power management system. When exciting the GFRP-based energy harvester with an optimised printed piezoelectric generator at 7 g p-p acceleration, the power harvested was sufficient to maintain the operation of the accelerometer for 0.34 s. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this research is to characterize the cryogenic delamination growth behavior in woven glass fiber reinforced polymer (GFRP) composite laminates subjected to Mode II fatigue loading. Mode II fatigue delamination tests were performed at room temperature, liquid nitrogen temperature (77K) and liquid helium temperature (4K) using the four-point bend end-notched flexure (4ENF) test method, and the delamination growth rate data for the woven GFRP laminates were obtained. The energy release rate range was determined by the finite element method. Microscopic examinations of the specimen sections and fracture surfaces were also carried out. The present results are discussed to obtain an understanding of the fatigue delamination growth mechanisms in the woven GFRP laminates under Mode II loading at cryogenic temperatures. [Copyright &y& Elsevier]

Abstract: This paper investigates the cryogenic fatigue delamination behavior of glass fiber reinforced polymer woven laminates under Mode III loading. Fatigue delamination tests were conducted using split cantilever beam specimens at room temperature, liquid nitrogen temperature (77K) and liquid helium temperature (4K). A finite element analysis was also employed to calculate the energy release rate. The temperature dependence of the fatigue delamination growth rate vs. energy release rate range is discussed. Fracture surfaces were examined by scanning electron microscopy to identify the delamination mechanisms under fatigue loading. The important conclusion we reach is that the Mode III fatigue delamination growth rates of woven laminates at cryogenic temperatures are lower than that at room temperature. [Copyright &y& Elsevier]

Abstract: This paper describes an experimental and analytical study on the cryogenic fatigue behavior of glass fiber reinforced polymer woven laminates under Mode I loading. Fatigue crack growth rate tests were performed using compact tension specimens at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). The fracture surfaces were also examined by scanning electron microscopy to correlate with the fatigue properties. A finite element method coupled with fatigue damage was adopted for the extensional analysis. The effects of temperature and loading condition on the fatigue crack growth rates are examined. [Copyright &y& Elsevier]

Glass fiber reinforced polymer (GFRP) composites integrated with sensors have received attention because the composite material can transmit information about the structural condition during operation. This study investigated the crack self-sensing capability of GFRP composites with magnetostrictive Fe–Co fibers under mixed-mode bending. The mixed-mode bending (MMB) test was performed using GFRP composites with a certain number of Fe–Co fibers introduced. Three different mixed-mode I/II ratios for MMB tests were selected and tested. The self-sensing capability of crack propagation was discussed by measuring the magnetic flux density induced by the inverse magnetostrictive effect using Hall probes. The GFRP composites with Fe–Co fibers fabricated in this study are a promising monitoring technology for non-contact sensing. [Display omitted] [ABSTRACT FROM AUTHOR]

Piezoelectric composites are a significant research field because of their excellent mechanical flexibility and sufficient stress-induced voltage. Furthermore, due to the widespread use of the Internet of Things (IoT) in recent years, small-sized piezoelectric composites have attracted a lot of attention. Also, there is an urgent need to develop evaluation methods for these composites. This paper evaluates the piezoelectric and mechanical properties of potassium sodium niobate (KNN)-epoxy and KNN-glass fiber-reinforced polymer (GFRP) composites using a modified small punch (MSP) and nanoindentation tests in addition to d 33 measurements. An analytical solution for the piezoelectric composite thin plate under bending was obtained for the determination of the bending properties. Due to the glass fiber inclusion, the bending strength increased by about four times, and Young's modulus in the length direction increased by approximately two times (more than that of the KNN-epoxy); however, in the thickness direction, Young's modulus decreased by less than half. An impact energy harvesting test was then performed on the KNN-epoxy and KNN-GFRP composites. As a result, the output voltage of KNN-GFRP was larger than that of KNN-epoxy. Also, the output voltage was about 2.4 V with a compressive stress of 0.2 MPa, although the presence of the glass fibers decreased the piezoelectric constants. Finally, damped flexural vibration energy harvesting test was carried out on the KNN-epoxy and KNN-GFRP composites. The KNN-epoxy was broken during the test, however KNN-GFRP composite with a load resistance of 10 M Ω generated 35 nJ of energy. Overall, through this work, we succeeded in developing piezoelectric energy harvesting composite materials that can withstand impact and bending vibration using glass fibers and also established a method for evaluating the electromechanical properties with small test specimen. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The present research examines experimentally and analytically the mixed-mode interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates at cryogenic temperatures. The mixed-mode bending (MMB) tests were performed with the improved test apparatus, at room temperature, liquid nitrogen temperature (77K) and liquid helium temperature (4K). The energy release rates at the onset of delamination crack propagation were evaluated for the woven GFRP specimens using both beam theory and finite element analysis. The fracture surfaces were also examined to verify the fracture mechanisms. In addition, the initiation and growth of damage in the specimens were predicted by a damage analysis, and the damage effect on the mixed-mode interlaminar fracture properties at cryogenic temperatures was explored. [Copyright &y& Elsevier]