Carbon Fiber-reinforced Plate Research Articles

Defect Detection in Carbon Fiber-Reinforced Plate by Imaging of Mechanical Nonlinearity-Induced Sideband Vibrations

Laser Doppler scanning vibrometry is used for imaging spectral vibration components in a carbon fiber-reinforced composite plate that contains a sub-surface delamination defect caused by hammer impact. The images reveal sideband generation at the location of the defect, reflecting mechanical nonlinearity-induced mixing between a high amplitude, low-frequency vibration that modulates the stress–strain behavior near the defect and a low amplitude, high-frequency probe vibration. In this work, a multifrequency probe is used to tackle the problem that the mixing coefficients are, in practice, frequency dependent. Based on the measured sideband amplitudes, a study is presented on the expected feasibility of detecting defects by a full field imaging scheme based on a photorefractive interferometer that is configured as a vibrometer acting as a bandpass filter around a sideband frequency of interest.

Double-Stage DMAS With Fresnel Zone Filtering in Guided Waves Damage Imaging.

Digital beamforming methods in plate-like structures are widely exploited for Lamb waves-based damage imaging. Among them, the delay and sum (DAS) imaging technique is the most popular thanks to its low-computational cost and ease of implementation. However, the imaging outputs are low quality due to the high levels of side lobes and limited off-axis signal rejection, which leads to limited image resolution and contrast. Recently, the delay multiply and sum (DMAS) beamforming has been applied to nondestructive testing (NDT) field as a promising DAS alternative able to enhance the imaging reconstruction in terms of contrast and damage detectability. However, DMAS is still affected by high levels of artifacts. To tackle this aspect, literature offers a beamforming algorithm called double-stage DMAS (DS-DMAS), first introduced in photoacoustic imaging and medical ultrasound imaging. In this article, the DS-DMAS performance is analyzed for Lamb waves inspection, to provide an exhaustive comparison between DAS, DMAS, and DS-DMAS. As a further step, a filtering process addressed as Fresnel zone filtering (FZF) is used to restrict the beamforming partial sums in a physical way to the area around the scattering point. The proposed approach is an adaptation of a well-established technique in seismic data processing called Fresnel migration, able to suppress artifacts and enhance the quality of the imaging. The algorithms have been compared and characterized by exploiting an online free dataset for guided waves inspection (ht.tp://openguidedwaves.de/) which collects piezo pitch-catch signals traveling through a quasi-isotropic carbon fiber-reinforced plate (CFRP) at different actuated frequencies and damage positions.

Deep learning for impact detection in composite plates with sparsely integrated sensors

In this paper, both location and energy of impacts on an anisotropic carbon fiber reinforced plate (CFRP) are detected with the help of deep learning. We introduce sparse low-cost sensor array integration in CFRP plates that allows for structural monitoring of lightweight structures. Using a resin transfer moulding process microelectromechanical systems (MEMS) and piezoelectric transducers (PZT) sensors are integrated into CFRP plates. We developed an automated test bench to perform weight drop impact loadings with impact energies ranging between 0.22–0.56 mJ on a 1 × 1 cm2-grid with 441 locations. The obtained sensor signals were processed by means of a short-time fourier transformation and used as input for the training of a deep learning model. This model was implemented with a convolutional neural network. To accelerate the training phase we introduce a coarse analytical model that generates artificial sensor signals we use for pretraining of the neural network. Yielding high prediction accuracies of 99.82% and 98.68% for a correct classification of impact location and energy, respectively, the capability of the proposed approach was demonstrated. Despite their limited resolution the low-cost MEMS accelerometers were able to correctly locate an impact and its energy with 99.76% and 97.04%, respectively. The pretraining led to an increased robustness of the training process. Additionally, for the case of PZT sensors, it also reduced the number of required epochs for convergence significantly.

A Macro-Meso Correlation Model for Numerical Simulation of CFRP Tensile Notched Strength

In this paper, the tensile mechanical behavior of Carbon Fiber Reinforced Plates (CFRP) with central open-holes was studied by experimental and simulation ways. A correlation model was built by macromechanical analysis and mesodamage analysis to form a progressive analysis architecture. Composite laminates were disassembled into two kinds: Representative Volume Element (RVE), which were 3D intralayer orthotropic, and the 2D interlayer cohesive element. The macromechanical analysis built connections between external loading cases and RVE stress distribution filed. The mesodamage analysis aimed to determine multimode damage initiation and evolution inside RVE. By comparing simulation results with experimental data, the prediction accuracy on failure mode, ultimate load, and fracture morphology were good enough to show the effectiveness and rationality of this new model. In addition, this model’s applicability to different material and geometrical parameters was also verified by simulating the experiment results in the literature.

Flexure Behaviour of Foamed Concrete Incorporating Banana Skin Powder and Palm Oil Fuel Ash Strengthened with Carbon Fibre Reinforced Plate

This paper investigated the chemical properties of banana skin powder (BSP) and palm oil fuel ash (POFA), and mechanical properties of lightweight foamed concrete (LFC) incorporating BSP and POFA strengthened with carbon fibre reinforce polymer (CFRP) plate. The BSP and POFA are added in the LFC mixture at various percentages as cement and sand replacement, respectively. LFC cubes incorporating BSP and POFA, LFC-BSP-POFA, were cast and tested under compression to determine its compressive strength. LFC-BSP-POFA prisms strengthened with 100 mm and 150 mm length of CFRP plates glued on its bottom mid-span surface were cast and tested under four point bending load to determine its flexure behaviour. From the chemical test, it was found that BSP and POFA each contain pozzolan materials, which are 55.98% and 51.83% silicon dioxide, and 2.71% and 2.32% aluminium oxide, respectively. From the mechanical property tests, compressive and flexural strength increased when percentage of BSP and POFA incorporated in the LFC increased. Meanwhile, CFRP plate managed to strengthen the LFC prism further where higher ultimate load recorded when longer CFRP plate was used.

Non-Linear Vibro-Acoustic Wave Modulations - Analysis of Different Types of Low-Frequency Excitation

Signal processing method based on wavelet transform used in non-linear acoustic test is presented in the paper. The method is applied for sidebands identification in response signal acquired during vibro-acoustic modulation test of impacted carbon fiber reinforced plate (CFRP). The plate was impacted with known energy using drop-weight testing machine. The modulation effect in investigated specimen results from the interaction of low and high frequency excitation with damage. The paper investigates different than mono-harmonic low-frequency excitation usually used in non-linear acoustics tests. Application of aperiodic low-frequency excitation signal allows to omit the modal test, where natural frequency of the structure are estimated. However, this requires the use of dedicated signal processing methods.

Smart monitoring of aeronautical composites plates based on electromechanical impedance measurements and artificial neural networks

This paper presents a structural health monitoring (SHM) method for in situ damage detection and localization in carbon fiber reinforced plates (CFRPs). The detection is achieved using the electromechanical impedance (EMI) technique employing piezoelectric transducers as high-frequency modal sensors. Numerical simulations based on the finite element method are carried out so as to simulate more than a hundred damage scenarios. Damage metrics are then used to quantify and detect changes between the electromechanical impedance spectrum of a pristine and damaged structure. The localization process relies on artificial neural networks (ANNs) whose inputs are derived from a principal component analysis of the damage metrics. It is shown that the resulting ANN can be used as a tool to predict the in-plane position of a single damage in a laminated composite plate.

Fire-Damage or Freeze-Thaw of Strengthening Concrete Using Ultra High Performance Concrete

There are some reinforced concrete structures exposed to severe environmental conditions might require maintenance or strengthening. Many of these severe circumstances are the result of extreme climate conditions such as low temperature, freeze–thaw action, fire attack, and exposure to deicing salts. Because of this, the environmental durability of both the repair materials and methods used in rehabilitation applications are of utmost importance. A small fire can reach 250°C, while a common blaze can easily produce temperatures of around 800°C. In major conflagrations the temperature can even reach 1100°C. At this level, the heat affects most materials, provoking the spontaneous combustion of some of them and affecting the resistance of others. However, very little research has been performed in evaluating the environmental durability of strengthening materials for concrete members. Very little work has been done on the effects of freeze–thaw cycling on bonding and repair materials. In this study, ultra high performance concrete (UHPC) was used to investigate the effect of strengthening concrete members by fire-damage test or freeze-thaw test. The results show that the mechanical properties of UHPC possess high strength, toughness, and freeze-thaw resistance. The CFRP (carbon fiber reinforced plates) wrapping specimens exposed at 300 °C showed totally failure with the deterioration of the adhesive. The UHPC with bonding 10 mm thickness specimens exposed at 400 °C and duration of 1 hour still in good shape. The UHPC with 1-cm or 2-cm thickness on strengthening concrete members could be obtained specific retrofit effects. The performance of UHPC specimens is better than those of CFRP wrapping specimens during high temperature exposure. The results of slant shear tests show that the bond strength of PC/PC, UHPC/PC and UHPC/UHPC decreased significantly after 600 freeze–thaw cycles or high temperature exposure.

A preliminary study of RPC for repair and retrofitting materials

This study aims to assess the performances of reactive powder concrete, RPC, as a new repair and retrofitting material and evaluate its durability in concrete members. One accelerated aging environment, namely a freeze‐thaw cycle acceleration deterioration test, was selected for the durability study of the repair materials. Before and after aging, the samples were evaluated by the bond strength (slant shear test), rebar pull out strength, and relative dynamic modulus NDT tests. The test results show that the RPC displayed excellent repair and retrofit potentials, as it possessed high strengthening effect, bond strength, dynamic modulus and durability, as compared with other concretes. Using RPC or CFRP (carbon fiber reinforced plates) for strengthening concrete members one can obtain specific retrofit effects, but the costs are extremely different for these two materials.

Assessment of the Exit Defects in Carbon Fibre-Reinforced Plastic Plates Caused by Drilling

This paper investigates the formation of the exit defects in carbon fibre-reinforced plates and characterizes their features in terms of drilling conditions. It was found that spalling and fuzzing are the major mechanisms of exit defects. The spalling, consisting of a main region and a secondary region, is caused by chisel and cutting edge actions, in which the former plays a key role. The fuzzing, however, exists in the cutting region where the included angle between the fibre direction of the surface layer and that of the cutting speed is acute. A severer spalling damage corresponds to a high spindle speed, a large feed rate and a great thrust force. Some empirical relationships, including a dimensionless formula, were developed for assessing the characteristic dimension of the spalling damage based on the known drilling conditions.