Fiber Reinforced Plastic Laminates Research Articles

Anisomorphic constant fatigue life diagrams for quasi-isotropic woven fabric carbon/epoxy laminates under different hygro-thermal environments

The effect of absorbed moisture on the fatigue strength of a plain-weave roving fabric carbon/epoxy quasi-isotropic laminate under constant amplitude loading at different stress ratios has been examined. First, constant amplitude fatigue tests are performed at room and high temperatures (HT), respectively, on the specimens immersed in hot water until saturation as well as on the specimens kept in a dry place. The results indicate that the fatigue lives of wet specimens are shorter than those of dry specimens, regardless of stress ratio as well as test temperature. The fatigue strength is reduced by about 11% due to water absorption at room temperature (RT), regardless of stress ratio. A similar reduction in fatigue strength can be seen in wet specimens at HT as well. Then, the full shapes of constant fatigue life (CFL) diagrams for the woven carbon fiber-reinforced plastic (CFRP) laminate in dry and wet environments are identified using fatigue test data obtained at different stress ratios and at different test temperatures. The results show that the experimental CFL diagrams are asymmetric and nonlinear, and the shape of CFL envelope gradually changes. Finally, the CFL diagrams for the woven CFRP laminate under uniaxial fatigue loading in different hygro-thermal environments are predicted using the anisomorphic CFL diagram approach for composites that was developed in an earlier study. Comparison with experimental results demonstrates that the anisomorphic CFL diagram approach is a promising step in predicting the CFL diagram for the woven CFRP laminate not only in a dry environment but also in a wet environment, regardless of test temperature.

Free Edge Stress Analysis of Unidirectional CFRP Laminates Based on a Homogenization Theory for Time-Dependent Composites

In this study, distributions of microscopic stress at free edges of unidirectional carbon fiber-reinforced plastic laminates (CFRP laminates) are analyzed three-dimensionally, based on a homogenization theory for time-dependent composites. For this, the homogenization theory is reconstructed for free edge problems using a traction-free boundary condition. Then, an analysis domain is reduced using the point-symmetry of the internal structure of the unidirectional CFRP laminate. Moreover, the substructure method is newly introduced into the theory to reduce the computational costs required for the analysis. The present method is then applied to the elastic-viscoplastic microscopic stress analysis at free edges of unidirectional carbon fiber/epoxy laminates subjected to an in-plane uniaxial tensile load. It is shown that complex microscopic stress distributions occur in the vicinity of the free edge, especially around fiber/matrix interface regions.

Identification of Failure Modes in Composites from Clustered Acoustic Emission Data Using Pattern Recognition and Wavelet Transformation

Acoustic emission (AE) is widely used to characterize damage occurring in composite materials: however, the discrimination between AE signatures due to different damage mechanisms is still an open issue. In this study, the various failure mechanisms in bidirectional glass/epoxy laminates subjected to uni-axial tension are identified using AE monitoring. AE data recorded during the tensile testing of a single-layer specimen are used to identify matrix cracking and fiber failure. In contrast, delamination signals are characterized using a two-layer specimen with a pre-induced defect, produced by artificially inserting a 10 mm wide Teflon tape in the middle portion of the two layers. Twelve-layer Glass fiber reinforced plastics laminates were also tested as a reference for the comparison of results. The procedure leading to signal discrimination involves a number of steps. First, Fuzzy C-means clustering associated with principal component analysis are used to discriminate between failure mechanisms, while parametric studies using AE count rate and cumulative counts allowed damage discrimination at various stages of loading. The two above methods led to AE waveform selection: on the selected waveforms, fast Fourier transform (FFT) enabled calculating the frequency content of each damage mechanism. Continuous wavelet transform (WT) allowed identifying frequency range and time history for failure modes in each signal, while noise content associated with the different failure modes is calculated and removed by discrete WT. Short time FFT (STFFT) finally highlighted the possible failure mechanism associated with each signal.

Shape optimization of high-speed penetrators: a review

Abstract In spite of a large number of publications on shape optimization of penetrating projectiles there are no dedicated surveys of these studies. The goal of the present review is to close this gap. The review includes more than 50 studies published since 1980 and devoted to solving particular problems of shape optimization of high-speed penetrators. We analyze publications which employed analytical and numerical method for shape optimization of high-speed penetrators against concrete, metal, fiber-reinforced plastic laminate and soil shields. We present classification of the mathematical models used for describing interaction between a penetrator and a shield. The reviewed studies are summarized in the table where we display the following information: the model; indicate whether the model accounts for or neglects friction at the surface of penetrator; criterion for optimization (depth of penetration into a semi-infinite shield, ballistic limit velocity for a shield having a finite thickness, several criteria); class of considered shapes of penetrators (bodies of revolution, different classes of 3-D bodies, etc.); method of solution (analytical or numerical); in comments we present additional information on formulation of the optimization problem. The survey also includes discussion on certain methodological facets in formulating shape optimization problems for high-speed penetrators.

Temperature effect on the flexural deformation and strength of carbon fiber-reinforced plastic laminate

Tests and numerical analysis were conducted to evaluate the flexural deformation and strength of laminated carbon fiber-reinforced plastic under high temperature conditions. First, a series of four-point bending tests in various temperature conditions was conducted, and the results indicated a remarkable temperature effect on the flexural deformation and strength. At high temperature test conditions, above the glass transition temperature ( Tg) of resin materials, the degradation rate of flexural stiffness and strength abruptly accelerated. The failure mode also changed from de-lamination failure to local buckling failure. Next, finite element analyses using a progressive failure model were performed and compared to the test data. A new damage model considering the Weibull distribution of the composite strength was implemented in the user subroutine of the ABAQUS/standard. It was found that the flexural strength and failure mechanism of laminated carbon fiber-reinforced plastic in various test temperature conditions were well explained and predicted by finite element analysis.

Impact localization in composite structures of arbitrary cross section

This article proposes an in situ structural health monitoring method able to locate the impact source and to determine the flexural Lamb mode A0 velocity in composite structures with unknown lay-up and cross section. The algorithm is based on the differences of the stress waves measured by six surface-attached acoustic emission piezoelectric (lead zirconate titanate) sensors and is branched off into two steps. In the first step, the magnitude of the squared modulus of continuous wavelet transform, which guarantees high accuracy in the time–frequency analysis of the acoustic waves, was used to identify the time of arrival of the flexural Lamb wave. Then, the coordinates of the impact location and the group speed values are obtained by solving a set of non-linear equations through a combination of local Newton’s iterative method associated with line search and polynomial backtracking techniques. The proposed method, in contrast to the current impact localization algorithms, does not require a priori knowledge of the anisotropy angular-group velocity pattern of the measured waveforms as well as the mechanical properties of the structure. To validate this method, experimental location testing was conducted on two different composite structures: a quasi-isotropic carbon fibre–reinforced plastic laminate and a sandwich panel. The results showed that source location was achieved with satisfactory accuracy (maximum error in estimation of the impact location was approximately 3 mm for quasi-isotropic carbon fibre–reinforced plastic panel and nearly 2 mm for sandwich plate), requiring little computational time (nearly 1 s). In addition, the values of the fundamental flexural Lamb mode A0 obtained from the optimization algorithm were compared with those determined by a numerical spectral finite element method.

Effect of Grit Size and Wall Thickness of Core Drill on Machining Quality at Hole Exit in Drilling Carbon Fiber Reinforced Plastics Laminate

This article focuses on the drilling of carbon fiber reinforced plastics (CFRP) laminate with brazed diamond core drill under no cooling condition. The effect of grit size, wall thickness of core drill and feed speed on machining quality at the hole exit is studied. The experimental results indicate that the grit size has a significant influence on the diameter of the hole exit. The expanding factor of diameter at hole exit increases with the decrease of grit size. Both large wall thickness and high feed speed lead to serious drilling-induced defects of the hole exit. The drilling-induced defects at hole exit are transformed from broken-edge and burr to local tear.

Flexural behaviour of glass fibre-reinforced plastic laminates with drilled hole

Drilling is one of the most commonly used process for hole making. Drilling of polymer matrix composites (PMCs) causes substantial damage around the drilled hole. Drilling-induced damage not only decreases the strength of the composite laminate with hole, but it also deteriorates the long-term performance of the PMC laminates under different loading conditions. In the present research investigation, the flexural behaviour of the glass fibre-reinforced plastic laminates with drilled hole was experimentally investigated under three-point loading conditions. The results of the experimental investigation were compared with those of the finite element model and were found to be in close agreement.

CM-JP-5 Microscopic Interlaminar Analysis of CFRP Laminates Based on a Multiscale Approach

In this study,the distributions of microscopic interlaminar stress of angle-ply carbon fiber-reinforced plastic(CFRP) laminates subjected to in-plane uniaxial tension are analyzed based on a homogenization theory.In this analysis,an analysis model for angle-ply CFRP laminates and its semiunit cell including interlaminar areas are defined.Then,three kinds of laminate configurations,i.e.,[±30°],[±45°] and [±60°] are considered.It is shown from the analysis results that microscopic shear stress noticeably occurs at the interlaminar areas irrespective of laminate configurations.It is also shown that the magnitude and distribution of such shear stress remarkably vary depending on the laminate configurations.

Perforation of FRP laminates under impact by flat-nosed projectiles

A theoretical study is performed herein on the perforation of fibre-reinforced plastic laminates subjected to impact by flat-nosed projectiles in a wide range of velocities. Ballistic impact on FRP laminates is a very complex problem and it can be generally classified into two categories, i.e. global deformation with local rupture and wave-dominated local failure. Simple analytical models for both global deformation failure as well as wave-dominated local failure are first given, and a shear failure criterion is employed to predict the perforation of FRP laminates which fail in global deformation mode. By combining the wave-dominated local failure model and the concept of Von Karman’s critical impact velocity, a condition for the transition of the above mentioned two failure modes is obtained. It is shown that the model predictions are in good agreement with available experimental observations in terms of ballistic limits and critical conditions for the transition of failure modes.

Investigation of Bulk Damage Progression and Inspection for GFRP Laminate Properties

A study has been accomplished to compare bulk material degradation in two graphite fiber-reinforced plastic (GFRP) laminates under cyclical fatigue. This study is the first in a series of experiments to characterize and quantify acoustic response to large-area bulk properties of field systems with hybrid structural composite-metallic systems. Long before failure of load-bearing composite components, stiffness reduction creates loading path changes, potentially overloading or fatiguing metallic substructure. The composite materials used in this study represent potential components and their respective correlation of stiffness changes to acoustic signal degradation through direct area measurement techniques. Specimens tested were fatigued using a sinusoidal waveform at continuous max loading and stress range at 30, 50, 60, and 70% of each layup, and UTS and cyclic stress-strain data were collected over 100,000 cycles to generate discrete levels of stiffness change. Additional specimens were cycled to one million cycles to generate higher levels of damage and determine failure life in specimens examined. All the specimens in this study were 8-ply, woven, 30.5-cm-long, 2.54-cm-wide, 0.297-cm-thick, rectangular specimens. A damage parameter based on material stiffness, as determined by changes in Young’s modulus (D = 1 − E/E0), was employed to compare the overall stiffness changes in the specimens. This damage parameter was correlated to ultrasonic scan results to provide a basis for field characterization of bulk material damage and, subsequently, life estimates of in-use structural parts. Examination of these effects showed a strong correlation of back-face signal strength to stiffness degradation in both laminates.

An experimental assessment of open-hole tension–tension fatigue behaviour of a GFRP laminate

The drive to improve predictive models and design methodologies of fibre-reinforced polymer composites subjected to fatigue loading is reliant on more accurate and reliable methods for monitoring and assessing material degradation and fatigue life. This paper presents the results of an experimental study carried out to evaluate the applicability of various measurement techniques including digital image correlation (DIC) and multiplexed fibre Bragg grating (FBG) sensors for this purpose. The study focused on the open-hole tension (OHT) fatigue behaviour of a quasi-isotropic glass fibre-reinforced plastic (GFRP) laminate under constant and block amplitude loading. Constant amplitude tests were conducted at two different R-ratios ( R = σ min/ σ max) and the block amplitude tests involved two or more stress levels. Longitudinal strain and stiffness, and surface temperature are used to assess damage progression and fatigue life. These parameters are shown to be interrelated and potentially suitable for predicting notch fatigue performance.

A Prediction Method for In-Plane Permeability and Manufacturing Applications in the VARTM Process

VARTM (Vacuum Assisted Resin Transfer Molding) is a popular method for manufacturing large-scaled, single-sided mold composite structures, such as wind turbine blades and yachts. Simulation to find the proper infusion scenario before manufacturing is essential to avoid dry spots as well as incomplete saturation and various fiber weaves with different permeability affect numerical simulation tremendously. This study focused on deriving the in-plane permeability prediction method for FRP (Fiber Reinforced Plastics) laminates in the VARTM process by experimental measurements and numerical analysis. The method provided an efficient way to determine the permeability of laminates without conducting lots of experiments in the future. In-plane permeability imported into the software, RTM-Worx, to simulate resin flowing pattern before the infusion experiments of a 3D ship hull with two different infusion scenarios. The close agreement between experiments and simulations proved the correctness and applicability of the prediction method for the in-plane permeability.

OS1507 CFRP積層板端部における微視的応力分布解析(OS15-2 マルチスケール解析,OS-15 微視構造を有する材料の変形と破壊)

In this study, the distributions of microscopic stresses at a free edge of a cross-ply carbon fiber-reinforced plastic (CFRP) laminate are analyzed three-dimensionally based on a homogenization theory. For this, the mathematical homogenization theory for elastic materials is reconstructed for CFRP laminates with free edges using a traction free boundary condition. This theory is then applied to the analysis of microscopic stress distributions at a free edge of a cross-ply CFRP laminate subjected to in-plane uniaxial tension. It is shown that microscopic in-plane shear stresses noticeably occur at the interlaminar area between 0 ° - and 90 ° - plies, especially around the free edge.

905 アングルプライCFRP積層板の層間における3次元微視的応力分布解析(OS9-(2)オーガナイズドセッション《複合材料の変形と破壊およびマルチスケール計算技術》)

In this study, the distribution of microscopic stress around interlaminar areas of angle-ply carbon fiber-reinforced plastic (CFRP) laminates subjected to in-plane uniaxial tension is analyzed based on a homogenization theory. In this analysis, an analysis model for angle-ply CFRP laminates and its unit cell containing interlaminar areas are defined. Then, three kinds of laminate configurations, i.e., [±30°], [±45°] and [±60°] are considered. It is shown from the analysis results that microscopic shear stress noticeably occurs at the interlaminar areas irrespective of laminate configurations. It is also shown that the magnitude and distribution of such shear stress remarkably vary depending on the laminate configurations.

709 フリーエッジを有する周期材料のための均質化理論およびその応用(OS7.材料の組織・強度に関するマルチスケールアナリシス/OS8.電子・原子・マルチシミュレーションに基づく材料特性評価 合同ポスターセッション,OS・一般セッション講演)

In this study, the distributions of microscopic stresses at a free edge of a cross-ply carbon fiber-reinforced plastic (CFRP) laminate are analyzed three-dimensionally based on a homogenization theory. For this, the mathematical homogenization theory for elastic materials is reconstructed for CFRP laminates with free edges using a traction free boundary condition. This theory is then applied to the analysis of microscopic stress distributions at a free edge of a cross-ply CFRP laminate subjected to in-plane uniaxial tension. It is shown that microscopic in-plane shear stresses noticeably occur at the interlaminar area between 0°- and 90°- plies, especially around the free edge.

Delamination in Fiber Reinforced Plastics: A Finite Element Approach

The fiber reinforced plastics (FRPs) are being used widely in the most diverse applications ranging from the aerospace to the sports goods industry. Drilling in particular is important to facilitate the assembly operations of structurally intricate composite products. The drilling of holes in FRPs leads to drilling induced damage which is an important research area. The researchers worldwide have tried to minimize the damage by optimizing the operating variables, and tool designs as well as by developing unconventional methods of hole making. Most of the work done so far has been experimental in nature with little or no focus on numerical simulation of the drilling behavior of FRPs. In the present research endeavor, a finite element model has been developed to investigate the drilling induced damage of FRP laminates.

An Investigation of Interfacial Stresses in Reinforced Concrete Beams Using FRP Laminates

Reinforcement of reinforced concrete (RC) beams against bending through utilization of bonded fibre-reinforced plastic (FRP) laminates has been accepted as an effective method of strengthening. In this study, the effects of FRP reinforcement over the parameters of interfacial stresses in reinforced concrete beams were examined both experimentally and numerically. Essentially, the main goal of the study was to investigate quantitatively the behaviour of the RC beams strengthened with adhesively bonded FRP. In order to achieve this goal, an experimental study was initially carried out. Afterwards, the ANSYS® WB finite element program was employed to model and analyze the RC beams externally bonded to FRP. The obtained results are expected to demonstrate the main characteristics of interfacial stress distributions inside beams strengthened with FRP. The evaluation of interfacial stresses provides the basis for understanding the main characteristics in such beams and for developing suitable design rules.

Editorial

Editorial

Optimal Strength Design for Fiber-Metal Laminates and Fiber-reinforced Plastic Laminates

Optimal strength design of fiber-reinforced plastic (FRP) laminates and fiber-metal laminates (FML) is studied in this article. An optimization approach that integrates the particle swarm optimization algorithm and a general finite element code ANSYS was developed. ANSYS is utilized to obtain the failure index as fitness function and the optimum fitness is obtained by altering the fiber orientations. The strength behavior of FRP and FML under in-plane load and out-of-plane load is compared based on the optimization results. Results show that for in-plane load, due to the substituting of metal alloy sheet for prepreg layer, the strength behavior in transverse direction is enhanced and FML has better resistance to biaxial load. For out-of-plane point load, FML offers strength performance superior to that of FRP and is more stable for all the boundary conditions investigated.