Carbon Fiber Panels Research Articles

Reverse design and application of phononic crystals based on deep learning

Abstract This paper reverse-design phononic crystals with band gaps within a targeted frequency band using the trained Conditional Variational Autoencoder (CVAE) and further studies the vibro-acoustic characteristics of a composite sandwich plate with a phononic crystal panel as the core layer. Firstly, a matrix composed of 0s and 1s, representing scatterers and substrates, is randomly generated by MATLAB to represent two-dimensional phononic crystals. The three-dimensional phononic crystals are obtained by stretching the two-dimensional phononic crystals along the average direction, and COMSOL Multiphysics is used to calculate the band gap. In order to maximize the production of phononic crystals with a band gap distribution, the Convolutional Neural Network (CNN) is trained to predict whether the generated phononic crystals have band gaps. Finally, using data on the structures of phononic crystals and their band gap distributions, the CVAE is trained to achieve the reverse design of artificial periodic structures based on the target band gap. To verify the effectiveness of the structures obtained through the reverse design method on vibration and noise reduction, the submerged vibro-acoustic characteristics of a composite sandwich plate consisting of a phononic crystal panel and carbon fiber panels are studied. The model of the composite sandwich plate is fabricated, and its submerged vibro-acoustic characteristics are tested and compared with numerical results. Finally, the submerged vibro-acoustic response levels of composite sandwich plates with phononic crystal panels and honeycomb panels as core layers are compared using numerical methods to assess the phononic crystal panel's vibration and noise reduction effects.

Research on seismic performance of reinforced concrete structures reinforced with CFRP plates

In the modern construction industry, natural disasters such as earthquakes pose an increasingly prominent threat to reinforced concrete structures, which often lead to serious damage to the structures. Therefore, how to enhance the seismic performance of reinforced concrete structures has become an urgent problem to be solved in the field of construction. This study delves into the seismic performance of CFRP plates in strengthening reinforced concrete structures. Firstly, the material characteristics of CFRP panels were analyzed, including the mechanical and adhesive performance indicators of carbon fiber panels, and corresponding specimens were made. Subsequently, through specimen loading experiments, the performance of reinforced specimens and unreinforced specimens under load was compared. The experimental results show that prestressed CFRP plates can significantly increase the cracking load and enhance the seismic resistance of reinforced concrete structures. In addition, simulation tests were conducted using a finite element model. Through simulation testing, the load deflection curve of the specimen was obtained, revealing the influence of CFRP plates on beam stiffness. Especially in the critical stages of concrete cracking and yielding of tensile steel bars, carbon fiber board has a particularly significant effect on improving the stiffness of beams.

A high-performance, sensitive, low-cost LIG/PDMS strain sensor for impact damage monitoring and localization in composite structures

Health monitoring of composite structures in aircraft is critical, as these structures are commonly utilized in weight-sensitive areas and innovative designs that directly impact flight safety and reliability. Traditional monitoring methods have limitations in monitoring area, strain limit, and signal processing. In this paper, a multifunctional sensor has been developed using acid-treated laser-induced graphene (A-LIG) with a multi-layer three-dimensional conductive network. Compared to untreated laser-induced graphene, the sensitivity of A-LIG sensor is increased by 100%. Furthermore, PDMS is used to fill the pores, which improves the fatigue performance of the A-LIG sensor. To obtain clear monitoring results, a data conversion algorithm is provided to convert the electrical signal obtained by the sensor into a strain field contour cloud map. The impact test of the A-LIG/PDMS sensor on the carbon fiber panel of the aircraft wing box segment verifies the effectiveness of its strain sensing. This work introduces a novel approach to fabricating flexible sensors with improved sensitivity, extended strain range, and cost-effectiveness. The sensor exhibits high sensitivity (gauge factor, GF ≈ 387), is low hysteresis (∼53 ms), and has a wide working range (up to 47%), and a highly stable and reproducible response over multiple test cycles (>18 000) with good switching response. It presents a promising and innovative direction for utilizing flexible sensors in the field of aircraft structural health monitoring.

ULTRA-JET DIAGNOSTICS OF DAMAGE TO CARBON FIBER PANELS AS A RESULT OF THERMAL CYCLING

The article is devoted to the development of a method of ultra-jet diagnostics of damage to carbon fiber panels, based on the high-speed impact of a liquid jet on the surface of a sample, the results of which are judged on its quality indicators. It is shown that the informative criteria for assessing the quality of carbon fiber panels as a result of ultra-jet diagnostics are the amount of stratification of the composite material and the depth of the cavity. Based on the analysis of experimental data, it is proved that the method of ultra-jet diagnostics makes it possible to assess the level of defectiveness of a carbon fiber panel formed as a result of thermocyclic tests of samples of various durations. Dependences are constructed according to which it is possible to observe a change in the informative (geometric parameters) of samples depending on the formed damage as a result of previously conducted thermocyclic tests. The presented material is part of the ongoing comprehensive research on the assessment of the possibility of using the proposed method of ultra-jet diagnostics to assess the quality of composite materials used in rocket and space technology.

Damage sensitivity studies of composite honeycomb sandwich structures under in-plane compression and 4-point bending: Experiments and numerical simulations

Honeycomb sandwich structures, especially those with carbon-fiber panels and Nomex-honeycomb cores, are widely employed in automobiles and aircraft due to their excellent mechanical properties. Here, in-plane compression and 4-point bending experiments, as well as FEM simulations, are performed for a composite honeycomb sandwich structure with face-core de-bonding defects or impact damage to evaluate the damage sensitivity. It is found that the structure exhibits a higher sensitivity to impact damage than to de-bonding defects. Impact damage caused by an energy of 3 J–5.5 J can alter the failure mode under both in-plane compression and 4-point bending loads, and reduce in-plane compression strength by more than 50 % and 4-point bending strength by 15 %. In comparison, de-bonding defects of the same size can change the failure mode and decrease the strength by only 10 % under in-plane compression. The developed FEM model predicts all failure modes and residual strengths obtained from experiments. The simulation results show that the structural characteristics of producing concaves in the facesheet and core are the dominant contributors to structural failure. Our model, covering all geometric and structural details of the honeycomb core, provides a useful tool for studying the mechanical behaviors of such structures.

Surface Damage in Woven Carbon Composite Panels under Orthogonal and Inclined High-Velocity Impacts

The present research is aimed at the study of the failure analysis of composite panels impacted orthogonally at a high velocity and with an angle. Woven carbon-fibre panels with and without external Kevlar layers were impacted at different energy levels between 1.2 and 39.9 J. Sharp and smooth gravels with a mass from 3.1 to 6.7 g were used to investigate the effects of the mass and the contact area on the damage. Optical microscopy and thermography analyses were carried out to identify internal and surface damage. It was identified that sharp impactors created more damage on the impacted face of the panels, while the presence of a Kevlar layer increased the penetration limit and reduced the damage level in the panel at a higher energy.

Natural fibers replace carbon fibers in Mercedes-AMG GT4 race car composite bumpers

Swiss sustainable lightweighting company, Bcomp, is now supplying its high-performance natural fiber technologies to HWA AG – development partner of Mercedes-AMG – for the new front bumpers on Mercedes-AMG GT4 race cars. Set to be phased in over the coming weeks, Bcomp's bodywork solutions will provide a sustainable alternative to the GT4’s existing carbon fiber panels, which is claimed to offer equivalent mechanical performance in stiffness and weight and improving safety.

Застосування методу головних компонент в задачі аналізу спектрів вільних коливань

This article addresses the main methods used for analysis, distribution, and classification of input data space. The main aspects of applying these methods are analyzed and determined. In this study it is found that the method of the principal components analysis (PCA) is the most suitable. Possible principal components analysis algorithms are described. A combination of these algorithms is used to distribute the input data in the analysis of signals and their spectra obtained by non-destructive testing after applying a free oscillations method. The article aims to study the possibility of reducing the vector of informative features after applying principal components analysis without losing the quality of recognition of the state of objects. The objects of study may be components of electric motors (shunt magnetic conductor), parts of aircraft made of composite materials and other structures that require analysis by non-destructive testing methods. Spectra taken during non-destructive testing by the method of free oscillations of samples of carbon fiber panels from defective and defect-free zones were studied. The analysis of three, five and ten harmonics was conducted and the maximum number of the principal components and the values of maximum dispersions of these components for the input values set of amplitudes were determined. The Mahalanobis distance was used to analyze the quality of the distribution of the input data space into classes (defect-free and defect zones of the sample). The quality of the separation of values from the damaged and undamaged zones of the sample into two classes was improved. Therefore, the use of principal component analysis, in this study, can increase the reliability of the recognition of the state of objects.

Characterization of Woven Composite Material Properties by Using an Inverse Technique Based on Vibration Tests

A mixed numerical-experimental technique based on vibration tests is modified and applied to determine the elastic material properties of woven composites. This non-destructive technique consists of physical experiments, numerical modelling and material identification procedure. For the purpose of characterization, two carbon fiber panels were prepared by manual layout technology. An evaluation of the accuracy of woven composite elastic properties is executed comparing the numerical and experimentally obtained resonant frequencies.

Investigation on low velocity impact damage identification with ultrasonic techniques under different sensor network conditions

Direct or indirect damages due to foreign object impacts on aeronautical structures, represent a major concern. The problem potentially intensifies with the adoption of composite materials, especially due to Barely Visible Impact Damage (BVID). In this context, understanding whether an impact event gives rise to delamination or debonding is highly desirable in view of the optimization of the maintenance strategies and, at the same time, of the safety margins associated to the operation of the structures. One possible method to achieve this goal is that of integrating damage monitoring systems within the vehicle architecture itself. By doing so, in fact, the enhanced structural health state awareness allows the implementation of Predictive Maintenance philosophies and the possibility to detect damage with size/severity and indentation smaller than the BVID currently applied by design and certification. In this work, a simple and a stiffened carbon fiber panel are subjected to Low Velocity Impacts using falling masses to generate a structural damage. A sensor network made of Piezoelectric elements (PZT) allows the application of Ultrasonic techniques, to monitor the damaged structure and calculate signal related features called Damage Indexes (DIs). The DI capability to identify the damage is then thoroughly investigated, with specific reference to: (i) effect of signal averaging, (ii) effect of reduced sensor network configurations and (iii) effect of sensor faults.

Lightning Performance of Copper-Mesh Clad Composite Panels: Test and Simulation

：According to simulation lightning experiments and eddy current analysis results, a three-dimensional finite element model of composite laminated plates with shield is established. By applying electric-thermal boundary and the coupling relationship between them, the lightning strike damage results under the protection of shield are realistically simulated with the commercial finite element analysis software, ABAQUS. Considering the coupling effect of heat, electricity, and force during lightning strike, the load distribution field of copper mesh and carbon fiber panel with lightning current inducted is analyzed. Comparing the thermal stress distribution of the specimen surface under various current loads, it is shown that the stress of carbon fiber panel is significantly lower than the one of the copper screen when the specimen structure suffers heavy current, since the copper network plays a role of endergonic protection. Simulation data are consistent with the test results, thus the method can be used for other similar research.

Mechanical Properties Analysis of Carbon Fiber Panels Sandwich Structure Containing Aluminum Alloy Corrugated Core

Carbon Fiber Reinforced Polymer (CFRP)is widely used in industry and construction. In this paper, three-point bending test was used to analyze the mechanical properties of CFRP by introducing aluminum alloy corrugated core. The numerical simulation is fairly consistent with the experimental analysis. We found that more than 95% of energy consumption comes from corrugated cores. The attenuation of bending failure stress is 38.83%. It fully shows that corrugated core has outstanding buffer capacity for objects hitting. In addition, two kinds of material are bonded by the adhesive. We also found that increasing the thickness of the adhesive will reduce the contact stress, enhance the stability of the structure and promoteelastic-plastic damage deformation.

Characterization of discontinuous carbon fiber liquid molded PA-6 composites via strategic placement of additional reinforcements

The flexibility of processing PA6-based discontinuous carbon fiber panels using vacuum-assisted resin transfer molding was studied. The ease of incorporating various reinforcements namely baseline, tow in the center of preform, fabric in the center of preform and fabric on the outside as skin was investigated. Mechanical characterization was conducted on all the variations made. There was an average increase of about 3%, 20% and 47% in the tensile properties of tow in the center, fabric in the center and fabric on the outside as skin, respectively, as compared to the baseline. A similar increase in properties was noticed in its flexural and impact strength. The data showed a correlation between the mechanical properties and the total surface area of additional reinforcements used. As the surface area of the reinforcement increased, the mechanical properties increased as well. It also showed that reinforcements on the surface of the preform as a skin performed the best. DMA analysis showed the effect of reinforcement on the storage modulus and tan delta across temperatures ranging from 30°C to 150°C. SEM analysis showed that the fibers and the additional reinforcements were coated with PA6 which translated into consistent mechanical performance.

VZLUSAT‐1: Health monitoring system, preliminary results

The health monitoring (HM) system placed on VZLUSAT‐1 nondestructively measures the mechanical and thermal properties of the newly developed carbon fiber material for space usage. The carbon material is exposed to the vacuum, radiation, and temperature changes in space. It can be used as a substitute for the currently used aluminum alloys because it has lower mass density and better mechanical properties compared to aluminum. The HM payload evaluates the quality changes of a material according to the difference in Young's modulus. Young's modulus of elasticity is a characteristic property of every solid material, and on VZLUSAT‐1 it is measured in terms of the eigenfrequencies of a free‐hanging beam. In this paper we present the first data measured in orbit – the eigenfrequencies, attenuation, and six temperatures from a carbon fiber panel. Based on these data, the quality of the mechanical properties and time stability are determined over the VZLUSAT‐1's life span.

Implementation of Automatic Sample and Composite Element Cutting Technologies

Abstract The article presents the methodology of introducing automatic carbon fiber panel cutting technologies at the Composite Testing Laboratory of the Institute of Aviation. It describes the process of implementing the new cutting technology which boosts the efficiency of preparing composite samples for strength testing, with the requirements applicable to edge smoothness and dimension tolerances taken into consideration. It also reviews the literature concerned with three most popular composite material cutting methods: laser cutting, abrasive water jet cutting and machining, presenting the strong and the weak points of each one of them. After selecting the machining technology relying on a disc, cutting tests have been performed. Cutting discs coated with diamond particles, and carbon fiber panels were used during the tests. The tests were performed with the use of the INFOTEC CNC machine, with an adapter enabling the installation of cutting discs with the maximum diameter of 150 mm.

Acoustic emission based damage localization in composites structures using Bayesian identification

Acoustic emission based damage detection in composite structures is based on detection of ultra high frequency packets of acoustic waves emitted from damage sources (such as fibre breakage, fatigue fracture, amongst others) with a network of distributed sensors. This non-destructive monitoring scheme requires solving an inverse problem where the measured signals are linked back to the location of the source. This in turn enables rapid deployment of mitigative measures. The presence of significant amount of uncertainty associated with the operating conditions and measurements makes the problem of damage identification quite challenging. The uncertainties stem from the fact that the measured signals are affected by the irregular geometries, manufacturing imprecision, imperfect boundary conditions, existing damages/structural degradation, amongst others. This work aims to tackle these uncertainties within a framework of automated probabilistic damage detection. The method trains a probabilistic model of the parametrized input and output model of the acoustic emission system with experimental data to give probabilistic descriptors of damage locations. A response surface modelling the acoustic emission as a function of parametrized damage signals collected from sensors would be calibrated with a training dataset using Bayesian inference. This is used to deduce damage locations in the online monitoring phase. During online monitoring, the spatially correlated time data is utilized in conjunction with the calibrated acoustic emissions model to infer the probabilistic description of the acoustic emission source within a hierarchical Bayesian inference framework. The methodology is tested on a composite structure consisting of carbon fibre panel with stiffeners and damage source behaviour has been experimentally simulated using standard H-N sources. The methodology presented in this study would be applicable in the current form to structural damage detection under varying operational loads and would be investigated in future studies.

Effects of material property variation in composite panels

PurposeThe purpose of this paper is to determine which of the ten material properties of the Hashin progressive damage model significantly affect the maximum load-carrying ability of center-notched carbon fiber panels under in-plane tension and out-of-plane bending.Design/methodology/approachThe approach used is to calculate the maximum load using a finite element model for a range of material property values as specified by a fraction factorial design. The finite element model used has been experimentally validated in prior work.FindingsResults showed that for the laminates considered, at most three and as few as one of the ten Hashin material properties significantly affected the magnitude of the maximum load.Practical implicationsWhile the results of this paper only specifically apply to the laminates included in the study, the results suggest that, in general, only a small number of the Hashin material properties affect laminate load-carrying ability.Originality/valueKnowing which properties are significant is of value in selecting materials to optimize performance and also in determining which properties need to be known to a high accuracy.

Distributed internal strain measurement during composite manufacturing using optical fibre sensors

After manufacturing a composite laminate, it is expected to store residual stresses that might affect the mechanical response of the plate. An optical fibre sensor was embedded in an epoxy carbon fibre panel, measuring the development of residual strain by monitoring in-situ and in real-time the manufacturing process, from the resin infusion to the curing cycle, and the changes experienced within. An optical sensor interrogator detects and measures changes in strain and temperature along the optical fibre length with high precision and accuracy, making it possible to obtain a full strain/temperature profile. Data acquired from the embedded sensor led to track and characterize the strain profile at every stage of the manufacturing process. This work showed that the infusion stage is highly related to the residual strain after the curing process. Moreover, the residual strain is 40% higher near the edge compared to the mean value measured in the laminate.

Mode III Loading of Composite Panels

Efficient design of modern aircraft requires an understanding of the mechanical behavior of carbon fiber panels under both in-plane and out-of-plane loading conditions. Currently, relatively little published literature exists for out-of-plane shear (mode III) loading. This paper presents both experimental and computational results for strain fields showing damage initiation, and propagation of notched carbon fiber panels under mode III loading. Experimentally, strain fields were measured using digital image correlation. Computationally, the commercial finite element package Abaqus, using typical composite analysis techniques, was used to calculate strain fields. Comparisons were made between measured and calculated values. Experimental results indicated that areas of both tensile and compressive strain concentrations existed at the notch tip. Damage initiation occurred in these areas, typically only in one or the other. Subsequent damage propagation occurred both in areas of elevated tensile strain and in areas of elevated compressive strain. Computational results showed differences of typically to as compared with experimental results for notch tip strain concentrations before damage and with larger differences after damage had occurred. Overall, these results provide information on how notched carbon fiber panels behave under mode III loading and the effectiveness of a commonly used computational approach in predicating this behavior.

Study on Dynamic Responses and Reinforcement of Reinforced Concrete Columns Subjected to Blast Loading

The terrorism and regional conflicts posed a threat to the world peace. Some terrorist explosions caused collapse of the buildings, which brought heavy tragedies to the human components. Therefore research on damage of structural components and resistance to damage have become the focus of our attention. Finite element software LS-DYNA was applied to simulating the response of reinforced concrete columns under blast loading. And analysis on dynamic response under different loading period was carried out. By studying on the stress and strain of reinforced concrete columns subjected to blast loading, the possible failure modes were obtained. In addition, the bearing capacities of concrete columns that are reinforced with carbon fiber and steel panel were analyzed, and the reinforcement effects were compared to provide reasonable reinforcement schemes for structures blast-resistant design.