Carbon Fiber Reinforced Plastic Panels Research Articles

The Relationship Between the Extent of Indentation and Impact Damage in Carbon-Fibre Reinforced-Plastic Composites after a Low-Velocity Impact

AbstractThe present paper investigates the low-velocity impact behaviour of carbon-fibre reinforced-plastic (CFRP) composite panels and the damage incurred when they are subjected to a single impact. The relationship between the depth of permanent surface indentation that results and the associated area of interlaminar delamination damage is investigated for two different thicknesses of composite panels. In particular, the delamination damage area increases with impact energy for both thicknesses of composite panel that were studied. Likewise, the indentation depth also increases with increasing impact energy, again for both thicknesses of CFRP panels. It is shown that the indentation depth, at the centre of the indentation, may be used to provide an indication of the extent of delamination damage within the CFRP panel after impact. Indeed, from plotting the indentation depth versus the interlaminar delamination normalised by the thickness of the panel area there is shown to be a unique ‘master’ relationship, with a positive intercept indicating that the indentation damage seems to result before delamination damage initiates. Thus, for both thicknesses of CFRP panels, it is suggested that the indentation process is a precursor to interlaminar delamination damage.

Joining Strength of Self-Piercing Riveted Vibration-Damping Steel and Dissimilar Materials

A vibration-damping steel panel is used for lightweight vehicles to block any noise subjected to the passenger cabin replacing heavy fiber-based insulators. Conventional weld joining methods often encounter problems due to the presence of viscoelastic compounds reducing the joint quality and making the joining process unproductive. In this work, we present experimental results that show the self-piercing riveting (SPR) process can be used to produce high-quality joints between vibration-damping steel and (i) commonly used steel alloy (SPFC590DP), (ii) carbon-fiber-reinforced-plastic (CFRP) panels. Various die shapes are used to investigate the resulting interlock width and bottom thickness of the joints and tensile shear load tests were performed to evaluate the joining strength. The results show that high-quality joints between vibration-damping steel and the steel alloy are possible for all the dye types and panel configurations, used in this study, producing up to 6.2 kN of tensile shear load. High-quality joints were also possible with CFRP producing up to 4.0 kN, however, acceptable joints were formed only when the CFRP panels were on top during the riveting process due to severe cracking.

Improving shear strength of carbon fiber composite honeycombs with the surface microprinting technology

Carbon fiber reinforced plastics (CFRP) honeycomb structures are widespreadly applied in aerospace and aeronautical sectors due to their high specific strength and stiffness. However, the low shear strength of CFRP honeycomb structures limits its further application. In this paper, surface treatment methods for improving surface bonding strength of CFRP plates are studied. The results show that the surface microprinting technology (SMT) is a recommended surface treatment method for CFRP panels and can be used to improve the bonding strength among facesheet-core (between facesheets and cores) and core-core (among the honeycomb walls) of honeycomb sandwich structure. Meanwhile, the mechanical model of CFRP honeycomb structure is established, the theoretical prediction formula of shear strength of CFRP honeycomb structure is explicitly deduced. And further analysis and verification were conducted compared to shear tests. The strengthening mechanism of the surface treatment method is then revealed. The experimental results show that the treatment method of SMT can greatly improve the shear strength of CFRP honeycomb sandwich structure and provide technical database and guidelines for its application in the aerospace and aeronautical fields.

The effectiveness of patch repairs to restore the impact properties of carbon-fibre reinforced-plastic composites

The present paper studies the low-velocity impact testing of carbon-fibre reinforced-plastic (CFRP) pristine and patch-repair CFRP panels. Firstly, the effect of repeated impacts on the pristine CFRP damage growth is considered at impact energies of 7.5, 10.5 and 30 J. Secondly, such tests lead to a single-sided, patch-repair panel being manufactured by removing a 40 mm diameter central hole, to act as the ‘damaged area’, from the parent CFRP panel and then adhesively-bonding a circular CFRP patch-repair over the hole so generated. Various diameters and thicknesses for the CFRP patch-repair are employed and, in some cases, a CFRP circular plug is also used to fill the hole created by removal of the parent composite. The measured load versus time, and load versus displacement, traces are compared. Further, the extent and location of any interlaminar damage, i.e. delaminations between the plies of the CFRP, caused by the impact event are mapped using an ultrasonic C-scan technique. It is shown that single-sided patch repairs can be very effective in restoring the impact performance of damaged CFRP panels.

Analysis of Carbon Fiber-Reinforced Polymer Composites Delamination during Vibration Assisted Trimming using Historical Data Design

Delamination is one of the main issues during the CFRP cutting process. This problem attracts researchers to investigate to meet the stringent quality need. This paper evaluates the influence of Rotary Ultrasonic Assisted Trimming (RUAT) when slotting carbon fiber reinforced plastic (CFRP). The study investigates rotation speed, vibration amplitude, and frequency particularly. The correlation effect of these parameters is to be evaluated by response surface methodology (RSM) to identify the minimum delamination. Seventeen trials were conducted with 38 plies of multi-directional CFRP panel. The trimming quality was determined by the minimum delamination damage of the slotting area analyzed by the ImageJ software. The best slotting quality can be achieved by applying spindle speed, amplitude, and frequency of 5305 rpm, 2.75 µm, and 26.79 kHz.

Statistical guided-waves-based structural health monitoring via stochastic non-parametric time series models

Damage detection in active-sensing, guided-waves-based structural health monitoring (SHM) has evolved through multiple eras of development during the past decades. Nevertheless, there still exist a number of challenges facing the current state-of-the-art approaches, both in the industry as well as in research and development, including low damage sensitivity, lack of robustness to uncertainties, need for user-defined thresholds, and non-uniform response across a sensor network. In this work, a novel statistical framework is proposed for active-sensing SHM based on the use of ultrasonic guided waves. This framework is based on stochastic non-parametric time series models and their corresponding statistical properties in order to readily provide healthy confidence bounds and enable accurate and robust damage detection via the use of appropriate statistical decision-making tests. Three such methods and corresponding statistical quantities (test statistics) along with decision-making schemes are formulated and experimentally assessed via the use of three coupons with different levels of complexity: an Al plate with a growing notch, a carbon fiber-reinforced plastic (CFRP) plate with added weights to simulate local damage, and the CFRP panel used in the Open Guided Waves project, all fitted with piezoelectric transducers under a pitch-catch configuration. The performance of the proposed methods is compared to that of state-of-the-art time-domain damage indices (DIs). The results demonstrate the increased detection sensitivity and robustness of the proposed methods, with better tracking capability of damage evolution compared to conventional approaches, even for damage-non-intersecting actuator–sensor paths. In particular, the Z statistic emerges as the best damage detection metric compared to conventional DIs, as well as the other proposed statistics. Overall, the proposed statistics in this study promise greater damage sensitivity across different components, with enhanced robustness to uncertainties, as well as user-friendly application.

Drilling carbon fiber reinforced plastics with pre-cooling treatment by cryogenic fluid

The high technological properties of carbon fiber reinforced plastics (CFRPs) have led to their ever-increasing use in recent decades for industrial applications, especially in the aerospace and automotive sectors, where the demand for lightweight structures is high. The panels of composite, to be assembled with other materials, may require repeated realization of holes, making the final quality of the union highly dependent on the drilling process. However, the heterogeneity of the composite material may lead to several inconveniencies, such as rapid tool wear and hole delamination, as during machining the drill bit encounters fiber and matrix alternatively, which have different properties. These damages could be reduced through cryogenic drilling, as demonstrated in the related literature, mainly because the machining behavior of composite changes at low temperatures. Starting from this evidence, the present paper proposes an experimental study conducted on CFRP panels using a new methodology of cryogenic drilling, based on the pre-cooling of the composite before starting the machining process, in order to create a uniformly refrigerated material. The analysis is aimed at comparing the hole quality obtained under dry and pre-cooled cryogenic conditions in terms of delamination, surface roughness and dimensional accuracy and at evaluating thrust force, tool wear and the influence of feed rate.

Modular Multifunctional Composite Structure for CubeSat Applications: Preliminary Design and Structural Analysis

CubeSats usually adopt aluminum alloys for primary structures, and a number of studies exist on Carbon Fiber Reinforced Plastic (CFRP) primary structures. The internal volume of a spacecraft is usually occupied by battery arrays, reducing the volume available to the payload. In this paper, a CFRP structural/battery array configuration has been designed in order to integrate the electrical power system with the spacecraft bus primary structure. The configuration has been designed according to the modular design philosophy introduced in the AraMiS project. The structure fits on an external face of a 1U CubeSat. Its external side houses two solar cells and the opposite side houses power system circuitry. An innovative cellular structure concept has been adopted and a set of commercial LiPo batteries has been embedded between two CFRP panels and spaced out with CFRP ribs. Compatibility with launch mechanical loads and vibrations has been shown with a finite element analysis. The results suggest that, even with a low degree of structural integration applied to a composite structural battery, more volume and mass can be made available for the payload, with respect to traditional, functionally separated structures employing aluminum alloy. The low degree of integration is introduced to allow the use of relatively cheap and commercial-off-the-shelf components.

On the Directivity of Lamb Waves Generated by Wedge PZT Actuator in Thin CFRP Panel.

This paper addresses investigation of guided-wave excitation by angle-beam wedge piezoelectric (PZT) transducers in multilayered composite plate structure with orthotropic symmetry of the material. The aim of the present study is to determine the capability of such actuators to provide the controlled generation of an acoustic wave of a desirable type with the necessary wavelength, propagation distance and directivity. The studied CFRP (Carbon Fiber Reinforced Plastic) panel is considered to be homogenous, with effective elastic moduli and anisotropic structural damping, whose parameters were determined experimentally. According to the results of dispersion analysis and taking into account the data of wave attenuation in a highly damping CFRP composite, the two types of propagating waves A0 and S0 were considered theoretically and experimentally in the frequency range of 10–100 kHz. Using the results of a previous study, we reconstructed the structure of the wedge actuator, to develop its finite-element (FE) model, and a modal analysis was carried out that revealed the most intense natural vibration modes and their eigenfrequencies within the frequency range used. Both experimental and numerical studies of the generation, propagation, directivity and attenuation of waves in the orthotropic composite panel under study revealed the influence of the angular orientation of the actuator on the formation of wave patterns and allowed to determine the capabilities of the wave’s directivity control.

Mixed-Mode Delamination Growth Prediction in Stiffened CFRP Panels by Means of a Novel Fast Procedure

Carbon fiber reinforced plastic (CFRP) structures are highly sensitive to delaminations, resulting from low energy impacts or manufacturing defects. Non-linear numerical algorithms are mandatory to investigate the complex mechanisms governing the delamination growth phenomena. Although the high computational costs associated to the non-linear algorithms are acceptable in a detail verification design stage, less expensive procedures are desired in a preliminary design stage or during optimization procedure. In this work, a fast numerical procedure, able to determine the delamination growth initiation in composite structures in the framework of a damage tolerant design approach when mixed mode I and II growth is expected, is introduced. The state of the art of the fast delamination growth procedures is critically discussed and improvements to the existing approaches are proposed to extend their applicability and to increase their accuracy. Comparisons with the standard non-linear delamination growth approaches are presented to assess the effectiveness of the proposed novel Fast approach. The results of the proposed fast approach are comparable with the ones obtained by means of standard numerical non-linear technique, allowing up to 95% computational cost saving.

Electromagnetic and thermal analysis of a multilayer CFRP panel struck by lightning with the FDTD method

The transient distribution of heat generated in a 16‐layer carbon fiber‐reinforced plastic (CFRP) panel, in which a lightning current with a magnitude of 3 kA, a rise time of 6.4 µs, and a time to half‐peak value of 69 µs is injected, has been computed. Each layer of the CFRP panel has a fiber axis direction of 45, 90, −45, or 0° and, therefore, has anisotropic electrical and thermal conductivities. This multilayer CFRP panel has been represented with a conductivity matrix consisting of off‐diagonal elements in the finite‐difference time domain (FDTD) simulation. The heat is computed, on the basis of FDTD‐computed conduction current densities, using a discretized heat equation. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Piezoelectric Based Lamb Waves Generation and Propagation in Orthotropic CFRP Plates: I. Influence of Material Damping

The article investigates the Lamb wave generation by the surface bonded circular actuator and wave propagation within the orthotropic Carbon Fiber Reinforced Plastic (CFRP) plate considering the anisotropy of the material elastic and damping properties. The first part of our investigation includes experimental determination of the elastic properties of CFRP, the wave attenuation, determination of the waves type that can be excited in the studied CFRP panel using a given frequency range. The model of anisotropic material damping has been proposed, which was further used in the Finite Element (FE) implementation of transient wave generation, propagation and attenuation that is present in the second part of the reported study. The proposed results can be used at the design of SHM for the composite structures with the structural anisotropy and damping, and for making a reasonable choice of the frequency and amplitude of excitation to provide the desired propagation distance and orientation of generated waves.

Tooling materials compatible with carbon fibre composites in a microwave environment

Although metals are the most commonly used tooling materials to cure composites, they do not provide optimal results in a microwave environment. Following a selection process based on the properties of the materials, an alternative tooling material in carbon fibre reinforced plastic (CFRP) was successfully utilised to cure CFRP panels in laboratory and industrial microwaves. The conductive carbon fibres in the tool facilitated the fast heat transfer across the part. Other tooling materials including a glass fibre cyanate ester prepreg and tooling board were trialled, although the latter exhibited damage during cure. These advantages demonstrate that the CFRP tool is a compatible material that can be used when microwave curing composites.

Reliability assessment of pulsed thermography and ultrasonic testing for impact damage of CFRP panels

In order to quantitatively compare the reliability of pulsed thermography and ultrasonic testing techniques, a set of thirty-five Carbon Fiber Reinforced Plastic (CFRP) composite panels with impact damages are inspected by pulsed thermography and ultrasonic C-scan. The comparative experimental results and Probability of Detection (PoD) analysis results are presented. The quantitative comparison shows that pulsed thermography testing has smaller defect size at 90% PoD with 95% confidence level, i.e. a90/95 values than ultrasonic testing for the parameters and setup used in the inspections of these thirty-five CFRP composite panels.

Effect of through-thickness electrical conductivity of CFRPs on lightning strike damages

Making carbon fiber reinforced plastics electrically conductive is an amended solution to the current lightning strike protection technology. However, optimization of the through-thickness electrical conductivity to meet a safety requirement of aircraft against lightning strikes remains unexplored. In this work, four carbon fiber reinforced plastics panels with different through-thickness electrical conductivity were fabricated using a polyaniline-based conductive resin. Their through-thickness electrical conductivity was tailored to achieve specific values using a controlled thermal treatment. The fabricated carbon fiber reinforced plastics panels were tested against a simulated lightning current of 40 kA, and the influence of through-thickness electrical properties on the performance of lightning strike protection was studied. Thermography data and ultrasonic non-destructive testing images confirmed least damage on the sample with higher electrical conductivity. Specimen with through-thickness electrical conductivity of around 110 S/m was able to retain about 92% of the residual flexural strength after the lightning test.

Experimental and numerical analysis of repaired stiffened carbon fiber-reinforced plastics panels under compression

Stiffened carbon fiber reinforced plastics (CFRP) panels have been widely used in the aerospace industry due to their high weight-specific mechanical properties but they are also susceptible to impact damage. Therefore, the research on the effects of various defects and repair methods on the damaged stiffened CFRP panels is of paramount importance. This paper presents an experimental and numerical study on the compression behavior of stiffened CFRP panels containing two types of initial defects with three repair methods i.e. mechanical repair, adhesively bonded repair, and scarf patch repair. Quasi-static compression mechanical tests were first performed on physical specimens. The buckling and post-buckling behaviors of the specimens were analyzed through experimental results. The finite element models were developed and validated through experimental results, based on which parametric studies on the influences of various delamination and repairing parameters to the load-carrying capacity of the stiffened CFRP panel were performed. The experimental and numerical results reported in this paper can serve as a general guideline for the selection of the most suitable repair method for various defected stiffened CFRP panels.

Dynamic crash responses of bio-inspired aluminum honeycomb sandwich structures with CFRP panels

Abstract Nature has provided us with extraordinary resources to tackle design challenges facing in modern society nowadays. The multistate structures inspired by animal shell have proven effective to improve the impact resistance of composite laminate. This study aims to identify the crash responses and crashworthiness characteristics of bio-inspired sandwich structures composed of carbon fiber reinforced plastic (CFRP) panels and aluminum honeycomb. The crash responses, failure mode as well as the effects of core side length, height and impact velocity on peak load and energy absorption were explored herein. The differences of crashworthiness characteristics between the CFRP aluminum honeycomb sandwiches and bare CFRP panel were quantified. Two typical load-displacement relations, namely single-peak and double-hump curves, were observed in the tests. It was noted in the energy-displacement curve, where the slopes corresponding to the failure stages of the upper and lower face-sheets, were greater than that in the honeycomb failure stage, indicating that the bare aluminum honeycomb was of lower energy absorption capacity than the CFRP face-sheet. By comparison, the honeycomb filling was an effective way to improve the impact resistance of CFRP structure, yielding higher energy absorption and lower peak load during the impact. It was also found that the crashworthiness characteristics were more sensitive to the core length than to the core height; and the specific energy absorption (SEA) varied insignificantly with the increase in the core height. It was noted that the peak load, absorbed energy and SEA increased significantly under high impact velocity.

FDTD Simulation of Lightning Current in a CFRP Panel: Comparison of the Use of Conductivity Matrix Approach With That of Triangular Prism Cells

The transient distribution of lightning current, which flows in a multilayer carbon-fiber-reinforced plastic (CFRP) material of aircraft, has been studied using the finite-difference time-domain (FDTD) method. Each layer of the multilayer CFRP panel has a fiber direction of 45°, 90°, –45° or 0°, and, therefore, has an anisotropic conductivity: the conductivity is high in the fiber axial direction and low in other directions. It is impossible to represent such an anisotropic layered panel using the FDTD method with common rectangular prism or cubic cells. In this letter, two approaches are employed: one is the application of conductivity matrix having off-diagonal elements and the other is the application of triangular-prism cells. The transient distribution of the magnetic field over the surface of the CFRP panel, computed with the former approach, is compared with that computed with the latter approach. Also, the results are compared with the corresponding measured ones.

FDTD Simulation of Lightning Current in a Multilayer CFRP Panel With Triangular Prism Cells

Transient distribution of lightning current, which flows in a multilayer carbon fiber reinforced plastic (CFRP) material of aircraft, has been studied using the finite difference time domain (FDTD) method with triangular prism cells. The use of triangular prism cells allows us to represent a multilayer CFRP panel, each layer of which has a fiber direction of 45, 90, 45 or 0 and, therefore, has an anisotropic conductivity. An experiment for evaluating the transient distribution of magnetic field over the surface of a multilayer CFRP panel has also been carried out. The FDTD-computed distribution of magnetic field agrees reasonably well with the corresponding measured one. This shows that the present FDTD simulation with triangular prism cells is valid and effective in analyzing lighting current in a CFRP aircraft.

Experimental Validation on Time Base Analysis of Various Aircraft CFRP Panel Conditions for Structural Health Monitoring

This paper evaluates the feasibility and effectiveness, within controlled conditions of an active pitch catch sensing PZT sensors on two panels and an aircraft structure made from carbon fiber reinforced plastic (CFRP) pre-impregnated materials. Once cured, the exhibits were subjected to partial and full penetration damages. Two PZT sensors each acting as an actuator and receiver were placed across the investigated region at 100mm apart. Three conditions were set on each panel for each undamaged, damaged and repaired area. Fifty readings were carried out on each panel for each condition. Feature extraction of the wavelet propagations were applied for the post processing from the captured Lamb wave data. The aircraft structure was also used to acquire data with the same above condition. A promising result shows that the interrogation of the actuating PZT sensors can differentiate the studied condition for both panels and structure. In addition, distinguished wavelet patterns were contributed by the surface irregularities due to damage and additional repair plies for both panels and aircraft structure.