Fiber Reinforced Plastic Plates Research Articles

Reliability assessment of glass epoxy composite plates due to low velocity impact

Probability of failure estimation of an offshore composite structure under low velocity impact is an essential requirement to incorporate the uncertainties associated with material properties and load due to an impact. The likelihood of this hazard causing a chain of failure events plays an imperative role in risk assessment. The material properties of composites mostly exhibit a scatter due to their in-homogeneity and anisotropic characteristics, brittleness of the matrix and fibre and manufacturing defects. In reality, the possibility of incidence of such a situation is due to large randomness arising in the structure. Stochastic finite element analysis of fibre reinforced plastic plates under low velocity impact is performed to account for the uncertainties of material properties and initial impact velocity. Impact induced failure of fibre reinforced plastic structures are a stochastic process due to scatter arising in material and impact behaviour, since individual faults in the ply are not easy to track. The continuum damage model is implemented in the finite element code by a user-defined material subroutine to overcome these problems. The Gaussian process response surface method is presently adopted to determine the probability of failure. Comparative study is also carried out for different combination of impactor velocities and mass. The stochastic design optimization method is performed to attain superior strength and lighter weight of fibre reinforced plastic structures.

Guided ultrasonic waves for determining effective orthotropic material parameters of continuous-fiber reinforced thermoplastic plates

Ultrasonic methods are widely established in the NDE/NDT community, where they are mostly used for the detection of flaws and structural damage in various components. A different goal, despite the similar technological approach, is non-destructive material characterization, i.e. the determination of parameters like Young’s modulus. Only few works on this topic have considered materials with high damping and strong anisotropy, such as continuous-fiber reinforced plastics, but due to the increasing demand in the industry, appropriate methods are needed. In this contribution, we demonstrate the application of laser-induced ultrasonic Lamb waves for the characterization of fiber-reinforced plastic plates, providing effective parameters for a homogeneous, orthotropic material model.

Accelerated noncontact laser ultrasonic scanning for damage detection using combined binary search and compressed sensing

Laser ultrasonic scanning is attractive for damage detection due to its noncontact nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search and compressed sensing, an accelerated laser scanning technique is developed to localize and visualize damage with reduced scanning points and scanning time. First, the approximate damage location is identified by examining the interactions between the ultrasonic waves and damage at the sparse scanning points that are selected by the binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain using a basis pursuit approach so that the interactions between the ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Second, wavefield images around the damage are reconstructed from the previously selected scanning points using compressed sensing. The performance of the proposed accelerated laser scanning technique is validated using a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a carbon fiber-reinforced plastic plate with delamination. The number of scanning points that is necessary for damage localization and visualization is dramatically reduced from N·M to 2log2N·log2M. N and M represent the number of equally spaced scanning points in the x and y directions, respectively, which are required to obtain full-field wave propagation images of the target inspection region. For example, the number of scanning points in the composite plate experiment is reduced by 97.1% (from 2601 points to 75 points).

Effect of High Velocity Ballistic Impact on Pretensioned Carbon Fibre Reinforced Plastic (CFRP) Plates

This work describes an experimental investigation of the pretensioned thin plates made of Carbon Fibre Reinforced Plastic (CFRP) struck by hemispherical and blunt projectiles at various impact velocities. The experiments were done using a gas gun with combination of pretension equipment positioned at the end of gun barrel near the nozzle. Measurements of the initial and residual velocities were taken, and the ballistic limit velocity were calculated for each procedures. The pretension target results in reduction of ballistic limit compared to non-pretension target for both flat and hemispherical projectiles. Target impacted by hemispherical projectile experience split at earlier impact velocity compared to target by flat projectile. C-Scan images analysis technique was used to show target impact damaged by hemispherical and flat projectiles. The damage area was shown biggest at ballistic limit velocity and target splitting occurred most for pretention plate.

Mode I fracture toughness of CFRP as a function of temperature and strain rate

Composite structures currently used in the automotive industry must meet strict requirements for safety reasons. They need to maintain strength under varied temperatures and strain rates, including impact. It is therefore critical to fully understand the impact behaviour of composites. This work presents experimental results regarding the influence of a range of temperature and strain rates on the fracture energy in mode I, GIC, of carbon fibre reinforced plastic plates. To determine GICas a function of temperature and strain rate, double cantilever beam specimens were tested at 20, 80 and −30℃, with strain rates of 0.2 and 11 s−1. A complementary numerical study was performed with the aim of predicting strength using the measured values. This work has demonstrated a significant influence of the strain rate and temperature on GICof the composite materials, with higher strain rates and lower temperatures causing a decrease in the GICvalues.

Estimation of statistical energy analysis loss factor for fiber reinforced plastics plate of yachts

Loss factor is one of the most significant parameters of Statistical Energy Analysis (SEA) which represents the damping loss characteristics of a system and indicates the ability of its vibration energy consumption. In order to estimate it, the power input method (PIM) and the impulse response decay method (IRDM) have become widely used especially when the object of study is made of Fiber Reinforced Plastics (FRP) of which dynamic interaction is really complicated. Numerical simulation is also applied to analyze the loss factor of the spring-damping-system with single degree of freedom (SDOF) using MATLAB to introduce the identification procedure of PIM and IRDM. With the comparison of the methods, the analytical study indicates these techniques are effective for the estimation of loss factor. This paper focuses on an experimental approach to get the SEA loss factor of FRP plate and the test investigations are performed in detail. The requirements and limitations of each method applied are discussed and PIM is a better solution dealing with this kind of the composite material. The loss factor of test specimen is obtained to provide a valuable reference for the prediction and control of vibration and noise of yachts with SEA.

Bond behavior of FRP carbon plates externally bonded over steel and concrete elements: Experimental outcomes and numerical investigations

Abstract The paper is firstly aimed to furnish a review of the current knowledge about the bond behavior of Fiber Reinforced Plastic (FRP)-steel joints with reference to: a) experimental results of bond tests available in the technical literature, and b) existing strength model for estimating the debonding load. In order to assess the influence of geometrical and mechanical properties of the adhesive on the debonding load, parametric analyses have been carried out by means of some selected bond strength models. The effectiveness of these models has been also checked by means of comparisons with experimental debonding loads collected from technical literature. The second objective of the paper is the comparison of the bond behavior of FRP-steel and FRP-concrete joints in order to identify the role of the adhesive on the bond behavior separately from the concrete. The comparison is aimed to assess bond laws for FRP-concrete joints taking into account the only nonlinearities of the adhesive and to model the concrete as a nonlinear material. To this purpose few experimental bond tests were carried out by the Authors on carbon FRP plates bonded over both steel and concrete support according to the same lay-out and set-up. Finally, basing on the experimental bond law assessed for the FRP-steel joints, a Finite Element (FE) plane model with interface elements is developed for validating the experimental results of bond tests.

Evaluation of porosity effects on the mechanical properties of carbon fiber-reinforced plastic unidirectional laminates by X-ray computed tomography and mechanical testing

The effects of porosity on the matrix-dominated mechanical properties of unidirectional carbon fiber-reinforced plastic composites were evaluated using X-ray computed tomography and mechanical testing. Carbon fiber-reinforced plastic plates of four porosity levels were manufactured by implementing different curing cycles. Porosity was detected by X-ray computed tomography tests, conducted on samples taken from the plates, and quantified by analyzing the computed tomography scans using the VGStudio Max software. Four different types of mechanical tests were conducted; namely, transverse tension, V-notched rail shear, three-point bending, and short-beam shear tests. The porosity analysis showed that with increasing the porosity volume fraction, the number of pores decreases, their volume increases while their shape changes from spherical or ellipsoidal to a needle-shape. The results from mechanical tests reveal that the presence of pores reduces all matrix-dominated material properties of the UniDirectional (UD) carbon fiber-reinforced plastic material. The reduction in strength is greater than the reduction in the elastic properties. Moreover, the reduction in the in-plane shear and interlaminar properties is greater than the tensile properties of the UD carbon fiber-reinforced plastic material. Between porosity contents of similar volume fraction, the one with the few large pores proved more severe than the one with the many small pores. The large standard deviation observed for some of the tests is attributed to the non-uniform dispersion of pores.

An Investigation of Cutting Mechanisms and Strain Fields during Orthogonal Cutting in CFRPs

Fiber-reinforced plastics (FRPs) are typically difficult to machine due to their highly heterogeneous and anisotropic nature and the presence of two phases (fiber and matrix) with vastly different strengths and stiffnesses. Typical machining damage mechanisms in FRPs include series of brittle fractures (especially for thermosets) due to shearing and cracking of matrix material, fiber pull-outs, burring, fuzzing, fiber-matrix debonding, etc. With the aim of understanding the influence of the pronounced heterogeneity and anisotropy observed in FRPs, “Idealized” Carbon FRP (I-CFRP) plates were prepared using epoxy resin with embedded equispaced tows of carbon fibers. Orthogonal cutting of these I-CFRPs was carried out, and the chip formation characteristics, cutting force signals and strain distributions obtained during machining were analyzed using the Digital Image Correlation (DIC) technique. In addition, the same procedure was repeated on Uni-Directional CFRPs (UD-CFRPs). Chip formation mechanisms in FRPs were found to depend on the depth of cut and fiber orientation with pure epoxy showing a pronounced “size effect.” Experimental results indicate that in-situ full field strain measurements from DIC coupled with force measurements using dynamometry provide an adequate measure of anisotropy and heterogeneity during orthogonal cutting.

Compression modulus and vertical vibration isolation efficiency of FRP rubber isolators

Fibre-reinforced plastic rubber isolators are composed of rubber layers glued to interleaving fibre-reinforced plastic plates. It is a novel rubber isolator and has the capacity to isolate vibration in both the vertical and horizontal directions. In this paper, the compression modulus and vertical vibration isolation efficiency of the fibre-reinforced plastic isolator were investigated. Compression tests of three specimens were introduced and their results were presented. Then, finite element models were constructed, and compression moduli from compression tests and numerical simulations were compared to validate the modelling method. Influences of parameters of planar dimensions, rubber layers and fibre-reinforced plastic plates were investigated with finite element models, and it was found that the vibration isolation efficiency of fibre-reinforced plastic rubber isolators increased with the increase of the aspect ratio and thickness of each rubber layer.

Evaluation of effective elastic properties of layered composite fiber-reinforced plastic plates by piezoelectrically induced guided waves and laser Doppler vibrometry

An approach to non-destructive evaluation of laminate composite plate elastic properties based on piezoelectrically induced elastic guided waves and laser Doppler vibrometry is presented and discussed. The reconstruction procedure is based on the genetic algorithm minimization of an objective function defined by the set of elastic moduli of the composite prepregs. The objective function defines discrepancy between theoretically calculated and experimentally measured dispersion characteristics of guided waves generated in the laminate anisotropic plate by piezoelectric wafer active sensors. The input data used for the identification are group velocities or wavelengths of the fundamental Lamb waves measured at varying excitation frequencies and propagation directions. The proposed approach has been experimentally tested on unidirectional and cross-ply carbon-fiber reinforced plastic plates and validated by conventional tensile tests.

Determination of Material Parameters of FRP Plates With Rotational Flexibility at Boundaries Using Experimental Modal Testing and Model Updating

Inverse identification of material properties of Fiber Reinforced Plastics (FRP) composite plates from the experimental modal testing using finite element model updating is an active area of research. In this approach, measured dynamic responses are correlated with finite element predictions to estimate the material property parameters using optimization techniques. The current practice of modal testing advocates the free-free boundary conditions, as clamped or simply supported boundaries are difficult to realise in experiments. This restricts the application of this technique to small scale specimens, whereas there are plenty of structural applications of FRP with clamped or elastically supported boundary conditions. To extend the application of the existing technique for material parameter estimation, partial fixity at boundaries should also be taken as parameters. The present experimental study estimates varying rotational elastic boundary restraints of a rectangular FRP plate to correctly identify the in-plane material constants which otherwise would be grossly misleading.

Dry and Residue-Free Cutting with High-Pressure CO<sub>2</sub>-Blasting

Jet cutting with high-pressure CO2 jets has the potential for a dry and residue-free machining of materials. However, a high-pressure CO2 blasting plant as well as experimental expertise for the continuous jet cutting with high-pressure CO2 at atmospheric conditions are not available. A pilot plant for the continuous jet cutting with liquid carbon dioxide was developed and realized at the Fraunhofer-Institute for Production Systems and Design Technology. Identical cutting tests were carried out in polyurethane blocks of different Shore D-hardness and density with high-pressure CO2 and water jets. Based on the first results in polyurethane blocks the tests were extended to cutting carbon fibre reinforced plastic plates with the high-pressure CO2 jet. Finally the possibilities and limits of the high-pressure CO2 jet cutting were summarised.

Flaw Inspection of Aluminum Pipes by Non-Contact Visualization of Circumferential Guided Waves using Laser Ultrasound Generation and an Air-Coupled Sensor

Our group had previously proposed a generation laser scanning system for visualizing ultrasound propagation on an object as an animate image, which provided visible and quick flaw inspection. Recently, we improved this system to make it completely non-contact by employing an air-coupled ultrasound transducer as a receiver instead of a contact transducer, and demonstrated the successful visualization of Lamb waves propagating on aluminum and carbon fiber reinforced plastic plates, as well as the detection of flaws. In this research, we applied this system to the non-contact visualization of circumferential guided waves on aluminum pipes. It was shown that circumferential guided waves propagating in opposite directions could be visualized separately, and that a flaw such as a slit or thinning on the inside surface of the pipe could be successfully detected even when it existed outside the scanning area.

An Analysis of Interfacial Stresses in Steel Beams Bonded With a Thin Composite Plate Under Thermomechanical Loading

The strengthening of steel structures in situ with externally bonded fiber-reinforced plastic (FRP) composite sheets is increasingly being used for the repair and rehabilitation of existing structures. The previous researchers have developed several analytical methods to predict the interface performance of bonded repairs. An important feature of a reinforced steel beam is the significant stress concentration in the adhesive at the ends of the FRP plate. In this paper, a closed-form solution for the interfacial shear and normal stresses in simply supported steel beams strengthened with a bonded FRP plate and subjected to thermomechanical loadings is presented. The shear strains of the adherends are included in the present theoretical analysis by assuming a parabolic distribution of shear stress across their thickness. Contrary to some existing studies, the assumption that both adherends have the same curvature is not used in the present study. The results of this numerical study are beneficial for understanding the mechanical behavior of material interfaces and for the design of hybrid FRP-reinforced steel structures.

Determination of fracture parameters of FRP composites: A combined experimental and numerical investigation

Fibre-reinforced plastic (FRP) composites are used in weight-sensitive aerospace type of applications as well as in infrastructure where durability is of real concern. FRP structures are prone to fracture at interfaces or within the matrix which may not be visible from outside. Thus, a thorough knowledge of initiation and propagation of crack in FRP composites is necessary. The present investigation focuses on a combined experimental and numerical investigation to understand the fracture behavior of FRP properly. The finite element modeling of FRP plate type of specimen is done using ABAQUS to estimate the fracture parameters, such as fracture toughness, fracture energy, etc. The same parameters are also measured experimentally by three-point bending tests as per American Society for Testing and Materials (ASTM) standards. The mode-I fracture behavior seems to be predicted very closely, whereas the observed mode II behavior does not match closely and the reasons for discrepancies are explored.

Novel real-time acousto-ultrasonic sensors using two phase-shifted fiber Bragg gratings

A novel real-time acousto-ultrasonic sensor system using a phase-shifted fiber Bragg grating rather than a normal fiber Bragg grating was investigated. The spectrum of the phase-shifted fiber Bragg grating was simulated and analyzed, which indicates that a phase-shifted fiber Bragg grating has superior properties when compared to a normal fiber Bragg grating. Based on theoretical considerations, a novel real-time acousto-ultrasonic sensor system was proposed. Two identical 5-mm phase-shifted fiber Bragg gratings, with slightly different Bragg wavelengths, were used as the filter and the sensor. An amplified spontaneous emission light source and an apodized fiber Bragg grating were connected to illuminate the phase-shifted fiber Bragg gratings. The design allows the strain resulting from the ultrasonic wave to be precisely received and converted to the fluctuation of the output voltage. An ultrasonic wave generated in a carbon fiber–reinforced plastic plate using a macrofiber composite actuator was detected by both the phase-shifted fiber Bragg grating sensor system and a sensor system based on a normal fiber Bragg grating and arrayed waveguide grating. Comparison of the temporal and spectral responses of these two systems indicates that the phase-shifted fiber Bragg grating sensor system has a higher sensitivity than the fiber Bragg grating system. The results show that the phase-shifted fiber Bragg grating system does not require data averaging for noise reduction to measure the Lamb wave modes in a carbon fiber–reinforced plastic plate.

118 CNT 一方向配向シートを用いた高強度薄肉FRPの創製と評価

Ultra thin fiber reinforced plastic plates, with around l0μm thickness, were fabricated using the uni-directionally aligned carbon nanotube (CNT) sheet. The CNT sheets are drawn wound around the bobbin from the CNT array developed on the silica glass base plate. The CNT used in this study was multi-walled CNT with diameter of around 40 nm. The CNT/epoxy resin prepreg was created by heating the CNT sheet put on the epoxy resin sheet at the temperature of 100℃ for 3 minutes using a hotpress. The CNT/epoxy resin composite material is laminated on the symmetrical cross ply lamination ([90/0]s). To minimize the content of epoxy resin to have thinner thickness, the CNT sheet with out resin were used to 0° layers and the prepreg to 90° layers. The total thickness of the composite became around 40 μm with high volume fraction of ≈ 30 to 50 %. However, the modulus and strength of the composites in tensile test became low. The low modulus attributes from the ply thickness un-uniformity where 0° ply thickness became about 1.5 times larger than 90° ply. Because of this thickness un-uniformity, CNT volume fraction in 0° plies became small to make tensile modulus low To improve mechanical properties of thin CNT composite film, process optimization to have thinner and uniform ply thickness were required as a future work.

Electromechanical impedance method of fiber-reinforced plastic adhesive joints in corrosive environment using a reusable piezoelectric device

Various nondestructive evaluation techniques exist for structural health monitoring of structures such as acoustic emission, ultrasonic impedance, and impact echo testing. However, these techniques often require expensive and sophisticated hardware with expert operators, limiting their applications to a certain aspect. On the other hand, a relatively new technique known as electromechanical impedance–based structural health monitoring has shown promising results as a local nondestructive evaluation method. To date, only a few numbers of studies have been conducted to develop a reusable lead zirconate titanate sensor for the electromechanical impedance method as majority of researchers have focused on damage detection performance. In this study, a reusable method for the electromechanical impedance method was proposed by using a lead zirconate titanate patch to eliminate the trial-and-error approach to minimize the time requirement for the electromechanical impedance method while reducing the cost for multiple measurements. The proposed reusable device was used to evaluate the damage of the adhesive layer between the fiber-reinforced plastic plates subjected to a corrosive solution while investigating the reliability performance of the device.

Experimental Research and Nonlinear Finite Element Analysis of CFRP-Strengthened High-Strength Concrete Structure

The debonding behavior at the interface between fiber-reinforced plastic (FRP) sheet and concrete is a key problem for the application of FRP plate, which has been widely applied in the civil engineering for rehabilitation and retrofitting of conventional structures. This paper presents the experimental and nonlinear finite element analysis results of the CFRP-strengthened high-strength concrete member. On the basis of the test, considering of the adhesive layer, explicit finite element is used for simulating the shear failure of CFRP-strengthened concrete, obtain the whole process of structure deformation development, describe the conformation and development of crack and the failure mode. The FE result coincides with the experimental result.