Location Of Delamination Research Articles

Efficient layerwise multiphysics spectral element model for delaminated composite strips with PWAS transducers

Efficient structural element-based models are essential for fast simulations of wave propagation in composite structures for model-based and physics-informed data-driven structural health monitoring. This article introduces the first efficient multiphysics time-domain spectral structural element for wave propagation analysis of beam and panel-type composite structures with piezoelectric transducers (patch or full layers) containing delaminations. A general framework is presented to model multiple delaminations and transducer patches located arbitrarily. The intact host and patch transducer-bonded laminates and sub-laminates between delaminations are modelled separately using an electromechanically coupled efficient layerwise zigzag theory (ZIGT) for kinematics and a piecewise quadratic variation for the electric potential across piezoelectric layers. The high-order spectral element (SE) features a virtual electric node to model equipotential surfaces of piezoelectric transducers apart from the usual physical nodes having mechanical and internal electric degrees of freedom. A hybrid point-least squares continuity approach is employed to maintain continuity at the intersections of delaminated sub-laminates or the patch-bonded laminate with the host laminate. The model’s performance in capturing electroelastic waves’ interaction with delamination is examined with reference to the conventional finite element (FE) solution based on the ZIGT, continuum-based FE solutions, and the SE solution based on a non-layerwise version of the laminate theory. Finally, the model is used to examine the impact of interfacial location and size of delaminations on wave propagation behaviour.

Predicting delamination in composite laminates through semi-analytical dynamic analysis and vibration-based quantitative assessment

Delamination is a frequent failure mode of laminated fiber-reinforced polymer (FRP) composites structure in aeronautical and other industries, leading to changes in vibration characteristics. Vibration-based techniques evaluate and compare the dynamic response between damaged and undamaged structures, and guarantee the non-destructive measurement with reliability and repeatability. Previous studies typically concentrate on using finite element method to obtain vibration characteristics and enhance the database for intelligent algorithms. This paper presents a semi-analytical result using the Chebyshev−Ritz method to expand delamination prediction. Vibration frequency serves as a global damage indicator, and multi-order frequency characteristics are utilized to identify the delamination length and location of FRP composite plates. A database of natural frequencies corresponding to damage parameters for FRP laminated plates is generated based on the established model using the region approach. An intelligent approach, known as a genetic algorithm optimization-based back-propagation (GA-BP) artificial neural network, is utilized for system identification. The network model is subjected to a sensitivity analysis, where artificial noise is added to vibration frequency to distinguish between the actual structure and the numerical model. The results indicate that the GA-BP algorithm shows good accuracy and stable performance against the standard neural networks for delamination analysis.

The Influence of the Delamination Location on the Bending Behavior of E-Glass Fiber EWR Flat Plates

The paper presents a study on the stresses and deformations induced by the transversal loading of some flat plates made of E Glass EWR Fiberglass Woven Roving type, having delamination type defects. The parametric analysis of the delamination influence on the stresses and displacements occurring in the plate material is performed. The results of the static calculation are compared with the experimental tests of the flat plates subjected to bending, highlighting the concordance of the variation of the stresses and displacements versus to the position of the delamination position.

Terahertz nondestructive layer thickness measurement and delamination characterization of GFRP laminates

Three-dimensional nondestructive location of defects, such as delaminations, in glass fiber-reinforced polymer (GFRP) laminates remains a challenge. Terahertz techniques have shown promise, but their success relies on advanced signal-processing techniques applied to the raw data. The current work presents an advance in the quantitative three-dimensional nondestructive location of delaminations in GFRP laminates. Namely, terahertz time-of-flight tomography, together with adaptive sparse deconvolution based on a two-step iterative shrinkage-thresholding algorithm, as well as the Canny edge-detection operator, are employed in nondestructive measurement of layer thicknesses and to extract the edges of delaminations in GFRP laminates. Compared with the commonly used frequency wavelet-domain deconvolution method or previous implementations of sparse deconvolution, the adaptive sparse deconvolution approach provides a clearer and rapid stratigraphic reconstruction of GFRP laminates while yielding accurate thickness information for each resin layer and low sensitivity to noise. In addition, the proposed edge-detection algorithm presents better performance in estimating the transverse size of delaminations, compared to the common −6 dB drop approach. Finally, our experiments verify the effectiveness of the proposed signal and image processing approaches for three-dimensional localization of delamination defects in GFRP laminates and the quantitative characterization of layer thickness.

Residual strength and failure mechanism of CF/PPS composites with delamination damage

AbstractDelamination is one form of damage in composite laminates. The effects of delamination damage locations (thickness direction of laminates) on the residual compressive strength and failure mechanism of carbon fiber/polyphenylene sulfide (CF/PPS) composites are studied by damage morphology, full‐field strain and finite element simulation. The closer the delamination is to the center of the composite, the lower the residual compressive strength. The failure mode of composites is dominated by 0° fiber fracture, which is divided into bulging, delamination propagation, and fracture. The delamination locations significantly affect the first two stages.Highlights Constructing delamination damage in composites by interlayer preset defects. Simulation and damage analysis to reveal the mechanism of compression failure. The relationship between delamination depth and damage stage is revealed.

Contact acoustic nonlinearity and damping properties of completely free vibrating curved and delaminated CFRP plates

This study reports an experimental investigation on the effect of plate curvature and circular inter-ply delamination on the completely free vibration properties of carbon fiber reinforced polymer (CFRP) plates. Impact tests on wire suspended plates were performed and variations in measured natural frequencies and modal damping are reported. Delamination clapping type contact acoustic nonlinearity (CAN) was observed in the presence of a series of higher harmonics in the vibration spectrum. These higher harmonics consisted of five to seven equally distanced peaks grouped in a frequency range of around the double of odd mode M (5,0). Modal damping was highly sensitive to delamination which caused a 33% average increase in damping loss factors. Odd mode M (3,0) was the most affected with an average increase of 51% in damping loss factor, explained by the delamination location relative to the wavelength of that mode shape. Natural frequencies were less sensitive to delamination, on average decreasing 1.0% in flat plates and increasing 3.1% in curved plates. The modal frequencies calculated from embedded fiber optic sensor (FOS) or electrical resistance strain gauge signals agreed with finite element modeling (FEM) to within a 3.1% difference for all modes considered. The damping loss factors deducted from suspended plate tests were consistent with complementary results from dynamic mechanical analysis (DMA). The measured delamination clapping CAN and its related influence on damping can serve to enhance structural health monitoring (SHM) methods.

Lamb wave-based damage assessment for composite laminates using a deep learning approach

With the increasing utilization of composite materials due to their superior properties, the need for efficient structural health monitoring techniques rises rapidly to ensure the integrity and reliability of composite structures. Deep learning approaches have great potential applications for Lamb wave-based damage detection. However, it remains challenging to quantitatively detect and characterize damage such as delamination in multi-layered structures. These deep learning architectures still lack a certain degree of physical interpretability. In this study, a convolutional sparse coding-based UNet (CSCUNet) is proposed for ultrasonic Lamb wave-based damage assessment in composite laminates. A low-resolution image is generated using delay-and-sum algorithm based on Lamb waves acquired by transducer array. The encoder-decoder framework in the proposed CSCUNet enables the transformation of low-resolution input image to high-resolution damage image. In addition, the multi-layer convolutional sparse coding block is introduced into encoder of the CSCUNet to improve both performance and interpretability of the model. The proposed method is tested on both numerical and experimental data acquired on the surface of composite specimen. The results demonstrate its effectiveness in identifying the delamination location, size, and shape. The network has powerful feature extraction capability and enhanced interpretability, enabling high-resolution imaging and contour evaluation of composite material damage.

Fractographic justification of fracture resistance loss in steel elements of overloaded machinery metal constructions

The problem related to the loss of resistance to brittle fracture in steel elements of the metal structure of loading equipment has been investigated. A fracto- graphic analysis was conducted at macro and micro levels on samples taken from two sections of the crane that underwent testing to determine their impact toughness. The selected samples covered the least and most loaded areas of the crane's metal structure to reflect the minimum and maximum levels of operational steel degradation. The assessment of metal degradation was carried out based on its resistance to brittle fracture. A correlation was established between the nature of the fracture, energy absorption, and indicators of resistance to brittle fracture. Special attention was given to the location of delamination along the direction of rolling during macro and microfracto- graphic studies. Macrofractographic analysis confirmed the general tendency of the metal to delaminate, especially along the fibers of the texture. This tendency varied for different sections of the crane's metal structure and depended on the level of operational stresses in the structural elements. It was found that longitudinal samples exhibited fractographic signs of delamination in the form of secondary cracks perpendicular to the fracture plane. The macrofracture of a sample from a loaded area revealed a significant amount of delamination, indicating their role in the propagation of fractures during impact tests. These results allow establishing a connection between the material's structure, its mechanical properties, and operational degra-dation, which is crucial for improving the reliability and safety of crane metal structures

Monitoring fatigue delamination growth in a wind turbine blade using passive thermography and acoustic emission

Damage monitoring is an essential step to understand fatigue damage growth in composite wind turbine blades and for reliable lifetime prediction. The current study is an experimental investigation of fatigue delamination induced by an intentionally embedded defect in the spar cap of a 31 m wind turbine blade. A constant cyclic flap-wise bending was applied to the blade for 320,000 cycles. Delamination growth is identified and measured by visual inspection, acoustic emission (AE), and infrared thermography of the blade surface. It was observed that the area of delaminated regions grew faster during the early cycles, then their growth rates decreased, and the interlayer cracks reached stable growth. The experiment shows fatigue delamination develops gradually in the spar cap and allows monitoring of the damage before reaching a critical stage. The ability of AE and thermography methods to detect subsurface damage is demonstrated by the identification of steady delamination growth during cyclic load. Damage localization by both methods is in good agreement with the delamination location. Most acoustic activities are spotted in the boundaries of delaminated regions, and the position of a significant number of acoustic activities with the highest energy content correlates with the location of delamination crack fronts. It is shown that the surface temperature distribution contour indicates the shape of the largest delaminated region, and the growth of the hot region area correlates with damage propagation. However, multiple delaminations through the thickness cannot be discriminated from the thermal images.

Deep learning enhanced metamodel design based on reduced mode shapes for delamination identification in composite structures

Structures requiring robust maintenance and accessibility pose challenges for structural integrity monitoring. This monitoring, crucial in various engineering applications, enables corrective actions to ensure machinery and equipment safety. Laminated composite materials, prevalent in aeronautical structures, often exhibit imperceptible delaminations or cracks, demanding the use of artificial intelligence for damage characterization. This study employs a numerical-experimental methodology, integrating artificial neural networks, to identify delaminations. Delamination, a structural damage form, was intentionally induced in epoxy-fiberglass composite structures. Modal tests captured characteristics in damaged and undamaged structures, revealing artificial intelligence effectiveness in pinpointing damage location and size. Damage significantly altered beam mode shapes, generating complex modes. Induced delaminations led to a measurable 15% reduction in natural frequencies, and damping ratios increased by approximately 10% in damaged structures. Artificial neural networks achieved an impressive 92% accuracy in predicting delamination location and size. Quantitative analysis of mode shape alterations validated the proposed methodology’s efficacy. This study provides valuable quantitative insights into damage detection in laminated composite structures, highlighting AI's potential for enhanced structural health monitoring. The numerical–experimental approach, supported by quantitative results, emphasizes the importance of advanced techniques for precise and efficient damage characterization in critical engineering applications.

Effects of Delamination Shapes, Sizes, Locations, and Boundary Conditions Using Modal Analysis of Composite Structure

Effects of Delamination Shapes, Sizes, Locations, and Boundary Conditions Using Modal Analysis of Composite Structure

Detection of Delamination in Composite Laminate Using Mode Shape Processing Method and YOLOv8

In this study, a novel delamination detection method for composite materials is proposed through the innovative use of You Only Look Once v8 (YOLOv8), vibration analysis, and 2D continuous wavelet transform techniques. The method detects the location and size of damage more accurately than existing methods and avoids manual intervention in the detection process. Damage detection performed on the simulation dataset shows that the method is able to accurately identify the delamination location with IoU = 0.9906 and an average accuracy of 91.32%. The proposed method is then compared with the widely used YOLOv5 model, and the superior performance of the YOLOv8 model is verified, with a 37.93% improvement in training speed and 0.81% improvement in detection accuracy. In addition, an experimental dataset of four composite laminates with delamination damage is constructed. By using transfer learning, the performance of the pretrained network achieves a good precision up to 1. The method proposed in this study expands the range of tasks that can be accomplished by mode shape analysis and is very effective in real experiments.

Automated Quantification of Interlaminar Delaminations in Carbon-Fiber-Reinforced Polymers via High-Resolution Ultrasonic Testing.

This article presents a method of ultrasonic testing (UT) that detects and quantifies interlaminar delaminations in CFRP composites with high resolution in terms of both spatial resolution in the planar dimension and depth into the laminate. Unidirectional and woven CFRP laminates were fabricated for this study, with a PTFE film inserted at various depths throughout the laminate to act as intentional crack initiation sites. All samples were mechanically tested via a three-point, end-notched flexure (ENF) test, followed by a quantification of the extent of the induced interlaminar delaminations using UT and X-ray computed tomography (CT). UT analysis for unidirectional CFRP samples was able to show a clear contrast between the delaminated area and the non-delaminated area. UT analysis of the woven CFRP samples yielded comparable results but required finer tuning of analysis parameters due to the interlocking woven fabric. CT results revealed a significant contrast between the crack and composite; thus, fine geometrical features of the crack front could be observed. UT and CT measurements were then compared, revealing an average difference of 1.09% in the delamination area, with UT overestimating as compared to CT. A UT depth study was also performed to automatically locate the interlaminar delamination at different depths throughout the components, with the delamination being predicted within one lamina interface for all samples. These results demonstrate UT's ability to accurately detect and quantify the extent and location of interlaminar delaminations due to bending.

Effect of delamination on the dynamic characteristics of thin‐walled carbon fiber‐reinforced polymer tube

AbstractThin‐walled carbon fiber‐reinforced‐polymer (CFRP) tubes are susceptible to damage, which impacts their dynamic characteristics. This paper investigates the influence of delamination damage on the dynamic properties of thin‐walled CFRP tubes through finite element simulation and experimental methods. A transversely isotropic principal model is employed to establish the geometric model. Delamination damage is induced using the cohesive zone model and the secondary stress criterion. Both circumferential and elliptical delamination cases are studied. The modal test is conducted using the hammer excitation method. It is observed that the finite element model aligns with the experimental results. It is discovered that the larger the delamination size, the lower the natural frequency for a given damage location. The location of the delamination within a single layer has minimal effect on the natural frequency. The natural frequency exhibits a symmetrical pattern of decreasing and then increasing as the delamination shifts from the sides toward the center layer. Positional information is discernible in the modal shape, which can be utilized for delamination detection and localization.Highlights The damage model is built by transversal isotropic equation and cohesive unit. Finite element model is built with various delamination sizes and locations for two cases. Modal tests are performed on CFRP tubes and obtained good accuracy. Effect of delamination size and location on dynamic parameters is discussed.

Simulation and experimental studies of mechanical delamination characteristics of REBCO tapes and lap joints under transverse tension

In this study, we investigate the delamination properties of high-temperature superconducting REBa2Cu3O7−x (REBCO) coated conductor (CC) tapes and lap joints under transverse tension by a finite element model (FEM) based on the cohesive zone model. The interfacial cohesive strength and the initial penalty stiffness used in the FEM calculations are adopted based on the experimental data obtained from the anvil tensile tests. Compared to previous theoretical studies, our calculation results of the delamination behaviors for the REBCO CC tapes and the lap joints are more approaching to the experimental data, and the abrupt failure behavior of the transverse load–displacement curves, which appears in the anvil tests, is reproduced by the simulations. Moreover, the effects of welding strength between the upper and lower tapes and internal tape damage during the welding process on the delamination characteristics, including the delamination strength, initial separation, delamination locations, and damage distribution of the CC lap joints, are presented.

Efficient zigzag theory-based spectral element model for guided waves in composite structures containing delaminations

Lamb wave-based structural health monitoring offers excellent potential for real-time delamination detection in laminated structures. It necessitates fast and accurate numerical simulation of guided wave interaction with delaminations. Towards this objective, we present an efficient layerwise zigzag theory (ZIGT) based time-domain spectral element for wave propagation analysis of composite beam- and panel-type structures (strips) containing delamination at arbitrary locations. The ZIGT delivers accuracy like layerwise theories by allowing slope discontinuities in the in-plane displacement field at layer interfaces while maintaining computational efficiency like equivalent single-layer (ESL) theories, making it ideal for such analyses. The high-order elemental nodes at Lobatto points have only four displacement variables, irrespective of the number of layers in the laminate. Delamination is modelled using the region approach, adapting the recently proposed hybrid point-least squares continuity method to satisfy the nonlinear displacement field continuity at the delamination fronts. The model’s efficacy is examined vis-à-vis elasticity-based elements, ESL theory-based elements, and the ZIGT-based standard finite element for free vibration and guided wave propagation responses of composite strips featuring multiple delaminations. The present model shows superior overall efficiency, accuracy, and convergence. An application of the model is also explored for identifying delamination locations from Lamb wave velocity fields.

Free Vibration-Based Delamination Detection in Fiber Metal Laminates Composite Beam

Delamination is a typical flaw in fiber-metal laminated composite structures that, when hidden from view, can significantly lower structural stiffness and alter a structure's ability to respond dynamically to forces like natural frequencies. Delamination is undoubtedly an important topic as it causes the performance of the Fiber Metal Laminate structures in the service to worsen. Delamination detection and severity analysis are essential in the aerospace industry for both safety and cost reasons. Although natural frequencies do not directly reveal the location or extent of damage, they are the most dependable metrics for damage detection. Frequency shifts in various modes are used to solve the inverse problem to pinpoint the damage location and extent. The bending natural frequencies shift brought on by delamination is utilized as an input to predict the delamination parameters. This study used an approach based on machine learning and a regression model to find the delamination parameters, i.e., locations and severity, in fiber metal laminated cantilever beams. FEA simulations using ANSYS were used to get the dataset pertaining to the position, severity, and eigen values (or bending natural frequencies) of the delamination. The results of this study indicate that the delamination locations and severity predictions developed using machine learning and regression models are reasonably accurate and demonstrate good agreement with the observed data.

Minimization of delamination effect on laminated composite plates using functional materials (piezoelectric and magnetostrictive)

In this paper, minimization of delamination effect on laminated composite plates using smart (piezoelectric and magnetostrictive) materials has been investigated. The static and dynamic responses of the smart composite plates with/without delamination have been obtained using the finite element method. The validation and comparison studies of the laminated composite plate have also been performed to show the level of accuracy of the presently adopted model by solving a few examples related to static and frequency cases. For control and minimization of delamination effect, smart materials have been introduced at the various layers of the laminated panel. Further, the influence of delamination size, location, orientation scheme, aspect ratio, modular ratio and different boundary conditions on the dynamic response of the smart delaminated composite plate has been analyzed. Finally, optimization study has been carried out to find the optimal value of these parameters by minimizing the difference between the frequency responses. Here, two optimization algorithms TLBO and PSO have been considered to carry out the optimization study and results obtained from both techniques are validated and compared.

Experimental study on delamination identification in tapered laminated composite plates using damage detection models

Delamination frequently occurs in composite laminates composed of fibre-reinforced polymer (FRP) and is considered a typical type of failure. The structural health monitoring (SHM) of structures with composites can be assessed by utilising changes in dynamic responses caused by a reduction in structural stiffness resulting from delamination. However, to ensure successful SHM, an inverse problem solution is required. Solving inverse problems can be computationally expensive and time-consuming, especially for large and complex structures. This study examined the efficiency of different damage identification techniques in detecting delamination in tapered composite plates. Four damage detection algorithms were tested, including the mode shape curvature (MSC), gapped smoothing method (GSM), mode shape curvature square (MSCS), and the gapped smoothing method square (GSMS) were implemented as damage index (DI) and curvature damage factor (CDF). A tapered composite plate composed of glass-fibre reinforced polymer was subjected to experimental modal analysis, including one undelaminated plate and three artificially delaminated plates. The delamination areas in the artificially damaged composite plates ranged from 1.5% to 8% of the plate area and were located at different interfaces. The results showed that statistical treatment further enhanced the damage identification, the CDF using the GSMS method performed the best overall, particularly in identifying the size and locations of delamination. The study also found that adding more modes to the averaging process increased CDF sensitivity and reduced uncertainty. This study suggests that the CDF method using GSMS is a promising approach for detecting delamination in tapered composite plates, with potential applications in aerospace, automotive, and civil engineering.

Novel Repair Scheme for the Edge Delaminated Composites

Edge delamination refers to those delaminations, which arise at the free edge of a laminate. Although edge delamination in advanced laminated composites is a well-documented phenomenon, the repair of edge delamination is still a gray area. This paper presents an effective novel repair approach to repair edge delamination. Special repair tools have been designed and fabricated for this purpose. It also highlights the fabrication of artificially edge delaminated Carbon Fiber Reinforced (CFRP) specimens. Repair strengths have been evaluated by compression tests and Ultrasonic C-scan is used for validation of the repair scheme. From the tests it has been observed that the repair scheme has no bearing on the location of edge delamination and stacking sequence.