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Abstract Many paper products are coated with plastic to improve their quality and stability. However, this limits recycling and recovery options and the plastic-coated waste paper is mostly disposed in landfills. Such practices are uneconomical and contrary to sustainable waste management. In this work enzymes of the white rot fungus Dichomitus squalens were investigated for possible delamination of plastic-coated waste paper. Enzymes were found capable to release the polyethylene foil from plastic-coated paper which resulted in 88.6–91.5% mass loss. The delamination rate, however, was depended on the ratio between plastic-coated paper and volume of enzyme filtrate. Results of a consequent experiment showed that enzymes are also efficient when plastic-coated paper is treated in a sequencing batch reactor resulting in 88.2–90.6% mass loss. The system was fully functional up to the 5th cycle; afterwards, the delamination rate reduced due to high thickness of the waste paper sludge. The enzyme activity, however, was still very high; with the laccase activity at the end of the experiment above 900 U/L and manganese peroxidase above 250 U/L. Our results demonstrated, that plastic-coated waste paper has the potential to be efficiently recovered instead of being disposed in landfills. Graphical abstract Image 1 Highlights • Enzymatic delamination of waste paper was investigated. • Enzymes were capable to release the polyethylene foil from the plastic-coated paper. • Treatment in a sequencing batch reactor is also possible. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) paper is an attracting structural material because of its high stiffness and light-weight. In order to exploit the high strength and stiffness of individual GO nanosheet into GO paper, the fabrication process must be optimized. In this study we fabricated ultra-stiff and strong GO paper by directed-flow vacuum filtration and compared its mechanical properties under different loading conditions. We also explored the effect of cross-linking with borax, thermal annealing and sonication to further enhance mechanical properties. The stiffest GO paper reported here has a tensile modulus of 109.9 GPa and a flexural modulus of 45.7 GPa. We also found that the flexural modulus of GO paper is significantly lower than the tensile modulus because of interlayer shearing, micro-buckling and delamination during flexural deformation. The properties of GO papers therefore need to be carefully selected for mechanical structures where flexion is the major deformation. This study provides significant insights about improving mechanical properties of GO paper and selecting GO paper for different loading conditions. Image 1095 [ABSTRACT FROM AUTHOR]

Fibre morphology and its evolution during refining and fractionation at low consistency were studied to understand the key relationships between the mechanical properties of paper and those of fibres. A broad analysis is presented on the physical and mechanical properties characterising the intrinsic morphological properties of fibres. The experimental refining process involved a primary stage at high consistency (HC), a fractionation stage with a small aperture basket, a low consistency (LC) refining stage, and a final high consistency refining (HCR) stage. The idea was to benefit from the pulp already being at low consistency following the screening step. Using a higher proportion of low consistency refining (LCR) tended to lower the tensile strength at 100 mL CSF, but some intermediate values did exhibit better responses to refining. Fractionation permits the use of LCR to retain fibre length and to develop additional long fibre bonding. The net gain remains even with energy reduction. It is believed, among other things, that a greater number or greater intensity of fibre-to-bar contacts would help increase internal delamination of the fibre structure. [ABSTRACT FROM AUTHOR]

This study investigates roll paper fire using laboratory-scale experiments, with emphasis on water transport on burning surfaces for sprinkler suppression. Freeburn, water transport and suppression experiments were conducted using different types of paper with various basis weight and water absorptivity. For fire suppression, the experimental results showed different water transport patterns that are sensitive to the burning surface conditions. This is in contrast to the water transport under no fire conditions in straight vertical rivulets exhibiting highly non-uniform distribution along the roll perimeter. For roll paper fire growth, both surface delamination and exfoliation play a crucial role, with the delamination length increasing either linearly or exponentially with time and the exfoliation rates strongly dependent on paper basis weight. Although the effects observed at the small scale in this work may have differences from those at large scales, the experimental results yield insights for better understanding of fire growth and suppression mechanisms and provide extensive data for numerical model development and validation. [ABSTRACT FROM AUTHOR]

The paper focuses on the cutting behavior of Glass Fiber Reinforced Polymer (GFRP) composites and GNP–GFRP composites that contain varying amounts of Graphene Nano Platelets (GNP). GFRP composites are increasingly being used in a variety of industrial applications due to their excellent mechanical properties, such as high strength, stiffness, and low weight. However, their machining and cutting behavior can be challenging due to the presence of the reinforcing fibers. Therefore, the study aims to investigate the machining behavior of GFRP composites and the effect of adding GNP on their cutting behavior. The effect of different parameters such as cutting speed, feed rate and reinforcement rate on cutting forces and delamination factor is investigated. In addition, the tensile strength and fatigue behavior of the composite materials with the best and worst delamination factors were also determined. Addition of up to 0.2 wt.% of GNP to GFRP composites resulted in an increase in cutting forces and delamination factor when drilling GFRP composites. While the cutting force and delamination factor decreased with the increase in cutting speed, the cutting force and delamination factor increased with the increase in the feed rate. Analysis of variance (ANOVA) was performed to determine the effects of drilling parameters and reinforcement ratio on cutting force and delamination factor according to full factorial experimental design. The most efficient factor on the cutting forces is found to be feed rate (84.97%), followed by the reinforced rate (6.48%) and cutting speed (6.13%). The most efficient factor on the delamination factor is determined to be feed rate for (44.49%), followed by the reinforced rate (29.20%) and cutting speed (21.73%). [ABSTRACT FROM AUTHOR]

The crucial obstacle to design an electrically conducting device is the poor and heterogeneous dispersion of the pristine CNTs in polymer matrices. The best method to overcome these problems is to create a CNT core-polymer shell structure, allowing a dense close-packing of the CNT core-polymer shell units, expecting in the formation of completely homogeneous CNT-polymer films and a big improvement in their physicochemical properties including the electrical conductivity. Poly[3-(5-carboxylpentyl)thiophene-2,5-diyl] wrapped multi-walled carbon nanotubes (P3PT-COOH/CNTs) in core-shell structure were successfully prepared as a bucky paper by simple pH-control of the aqueous solution containing different weight percentages of the both components (P3PT-COOH/CNTs = 50/50, 60/40, 70/30). The core-shell structure of P3PT-COOH/CNT-50 nanohybrid films showed a significantly high electrical conductivity increase of up to 17 fold compared with those of non-core-shell structure prepared by a simple mixing (e.g. from 1.33 to 1.81 S/cm up to 22 S/cm). The result could be considered to be a consequence of a homogeneous P3PT–COOH–wrapping on the surface of CNTs, the regular shell thickness of individual CNT-core/P3PT–COOH–shell nanohybrid fibers, and their three-dimensional close packing in a film. [ABSTRACT FROM AUTHOR]

Developing constitutive models that can be used to model composite structural systems subjected to impact loads where modeling damage, failure, and delamination are critical is a challenging task. Often processing experimental data to develop the composite material model and, especially, the delamination model can be tedious, subjective, and error prone. In this paper, procedures for characterizing the behavior of laminated unidirectional composites (UDCs) are explained. First, laboratory tests are conducted to obtain the orthotropic material properties of a commonly used composite, IM7-8552. The obtained data are used in the MAT_213 model in LS-DYNA. Second, fracture-related tests, i.e., double-cantilever beam (DCB) and end-notched flexure (ENF) tests, are conducted to obtain the load-displacement responses. Finally, an inverse analysis approach is used by combining response surface methodology (RSM) and gradient-based numerical optimization to find the optimal values of the traction-separation law (TSL) parameters to build the constitutive model for modeling delamination. The developed cohesive zone element (CZE) model is then validated using the experimental results of a quasi-isotropic tension test. It is shown that the overall process of analyzing the experimental data and building a finite-element model is simpler, and the results from the validation test indicate that the developed methodology can yield accurate predictions. [ABSTRACT FROM AUTHOR]

The radial displacement of hydrogen storage composite overwrapped pressure vessel (COPV) is a key factor related to the collapse failure and burst pressure. However, there is still lack of effective method to monitor the radial displacement during the hydrostatic test and service process of the vessels. This paper proposed a method to measure the radial displacement based on fringe projection profilometry (FPP). Hydrostatic test with a composite overwrapped pressure vessel verifies the proposed method. The variation of displacement changing with inner pressures observed in the experiments is in agreement with that obtained from finite element analysis. Also Computed Tomography (CT) scanning is conducted and a widely spread micro defects is found in the composite layer of the cylinder. 78.9% of the total observed defects are small (<1000 mm2). In regions where large-sized defects (>1000 mm2) are concentrated, the total area of defects reaches 16,200 mm2. According to the statistical analysis, the strong correlation is found between the defects area and radial displacement. • Presented a novel method based on fringe projection profilometry (FPP) for monitoring the deformation of composite overwrapped pressure vessels (COPVs) during hydrostatic testing. • Employing 3D point clouds from FPP to reconstruct the cylinder and measure radial displacement. • The variation trend of radial displacement with pressure obtained by experiments is consistent with the finite element results. • Utilized Computed Tomography (CT) to detect and quantify micro delamination defects in the cylinders. • A significant correlation was found between the area of defects and radial displacement, while the relationship between the number of defects and radial displacement was less pronounced. [ABSTRACT FROM AUTHOR]

Cellulose acetate (CA) lamination, a technique to strengthen documents by sealing them between sheets of thermoplastic film, was widespread from the 1930s to the 1990s. Its use gradually stopped in the 1980s amid concerns about the physical and chemical instability of the laminate and the degradation risks posed to the treated document. Despite concerns about CA lamination, no coordinated effort has taken place to establish the various materials and techniques used in cellulose acetate laminations or to determine the number and present condition of CA laminated documents in US collections. In this paper, we review the chemistry and methods used in CA lamination. We then report results of a survey of 52 US institutions with significant laminated collections. We find that at least 2.9 million laminated documents exist in US collections, and most of those documents are observed to be in stable condition. A majority of the institutions used cellulose diacetate (CDA) as the laminating film and as few as 0.6% CDA laminated documents have been delaminated. The results should aid institutions in determining the cost benefit in the management of these significant collections. [ABSTRACT FROM AUTHOR]

Highlights This paper presents the effect of varying the type of Z‐pin on the delamination bridging performance of unidirectional composite laminates. Carbon and Kevlar Z‐pins were inserted in thick composite laminates using the pre‐hole insertion Z‐pinning process and their bridging performance characterized across the different mode‐mixity range. The bridging response indicated that Kevlar Z‐pin experienced load reduction driven by interfacial friction (Stage III), which was absent in the Carbon Z‐pin. When Mode II dominated the bridging crack, Kevlar Z‐pin showed partial pullout and fiber shear cracking, while the Carbon Z‐pin exhibited clean transverse fracture. Although the bridging load obtained by the Carbon Z‐pin was twice that of Kevlar Z‐pin, the Kevlar Z‐pin provided a higher interlaminar fracture energy. The superior bridging performance of Kevlar Z‐pin is correlated with the enhanced ductility. Moreover, the resin‐rich area was involved in deformation and provided the extra axial load of Z‐pin. The comparison of mixed‐mode bridging mechanism between Kevlar Z‐pin and Carbon Z‐pin. Reveal the variation of multi‐directional load and energy consumption with mixed‐mode angle in thick laminates. Detailed scanning electron microscope observation to understand failure characteristics of ductile Z‐pin. Evidence that the extra axial load of Z‐pin provided by resin‐rich area. [ABSTRACT FROM AUTHOR]

This paper comprehensively investigated the effect of the tool geometries on heat transfer and special crystallization characteristics in the drilling of carbon fiber‐reinforced polyetheretherketone (CF/PEEK) composite for the first time. Three tools with different geometries (twist, brad, and dagger drill) are carried out on CF/PEEK drilling experiments, and temperature, as well as crystallinity and surface roughness, are introduced to make a comparative evaluation on the effect of the tool geometries. The results show that the drilling temperature is determined by the contact length of the profile between the drill and the material. Correspondingly, better surface quality with lower surface roughness and smoother surface is obtained by using a twist drill due to the heat‐induced PEEK smearing effect. Further, in situ XRD and differential scanning calorimeter (DSC) were used to characterize the crystallization characteristics where crystal phase transformation at different temperatures was measured. The occurring temperature of the strongest crystallization characteristics for CF/PEEK is basically not affected by tool geometries, all at 300°C, and the limiting crystallization temperature is 344.5 ± 0.7°C. The crystallinity is found to be affected by drilling temperature and cooling rate and gradually decreases along the heat transfer direction. This work provides a new sight into the improvement of CF/PEEK drilling. Highlights: The effect of tool geometries on thermal and crystallization for CF/PEEK is provided.In situ XRD and DSC are used to characterize crystallization characteristics.The drilling temperature and cooling rate are both determinants of crystallinity.The limiting crystallization temperature of the CF/PEEK composite is 344.5 ± 0.7°C.Heat‐induced PEEK smearing effect improves the surface quality of CF/PEEK drilling. [ABSTRACT FROM AUTHOR]

This article presents high‐fidelity observations of the time evolution of unstable delamination growth in tapered composite beams under tensile loading via ultra‐high‐speed camera in conjunction with digital image correlation. Asymmetrically tapered GFRP laminates, with a thickness drop from 18 plies to 12 plies, are manufactured in three different layup configurations with grouped drop‐offs: [06/(02)3/06], [06/06/06], and [06/(±45)3/06]. Beam specimens are subjected to quasi‐static tensile loading in a servo‐hydraulic axial testing machine, and the damage evolution on one edge of the tapered beam is monitored in situ at 124,000 fps with a high‐speed camera (HSC). In selected tests, digital image correlation (DIC) analyses are conducted either on the edge or on the tapered surface to obtain the full‐field strain and elucidate failure mechanisms. Real‐time HSC observations of the damage sequence consistently affirm that the initial failure mechanism is a transverse crack at the nearest drop‐off to the thin section, which is followed by delaminations at interfaces of sublaminates. Unstable delamination growth is characterized by measurements of lower bounds of crack tip speeds. The unique crack speed data provide evidence for the existing effect of through‐the‐thickness stresses on delamination growth. The detailed sequence and patterns of dynamic failure presented in this paper can serve as a benchmark to validate damage models used in simulations of tapered laminates. Highlights: The sequence of unstable delamination growth in tapered GFRP beams is investigated experimentally.Characterized unstable delamination growth based on crack tip speed measurements.Strain fields are evaluated along beam edges using DIC in real‐time.In‐situ observations of dynamic failure can serve as a benchmark to validate damage models. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to assess the hydrogen embrittlement sensitivity of carbon gradient heterostructure materials and to verify the reliability of the scratch method. Design/methodology/approach: The surface-modified layer of 18CrNiMo7-6 alloy steel was delaminated to study its hydrogen embrittlement characteristics via hydrogen permeation, electrochemical hydrogen charging and scratch experiments. Findings: The results showed that the diffusion coefficients of hydrogen in the surface and matrix layers are 3.28 × 10−7 and 16.67 × 10−7 cm2/s, respectively. The diffusible-hydrogen concentration of the material increases with increasing hydrogen-charging current density. For a given hydrogen-charging current density, the diffusible-hydrogen concentration gradually decreases with increasing depth in the surface-modified layer. Fracture toughness decreases with increasing diffusible-hydrogen concentration, so the susceptibility to hydrogen embrittlement decreases with increasing depth in the surface-modified layer. Originality/value: The reliability of the scratch method in evaluating the fracture toughness of the surface-modified layer material is verified. An empirical formula is given for fracture toughness as a function of diffused-hydrogen concentration. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced composites acquire widespread use in the technologically advanced sectors on account of their lightweight and outstanding strength. Considering the significant connection between component quality and durability, bearing strength is a critical factor in the mechanically assembled parts during the manufacturing process. Therefore, in this paper, an experimental study was performed on hybrid glass fiber/aluminum‐mesh composites to assess the impact of abrasive water jet (AWJ) drilling on delamination and bearing strength. The samples were drilled, and the delamination damage was assessed. Finally, the bearing test was conducted on the sample in conformity with ASTM D5961M. The impact of stress distribution on the specimen's failure patterns was studied. Experimental outcomes reveal that the GFA specimen had a 2.9% higher average bearing strength than the AGF specimen. The drilling‐induced damage was determined to be the primary factor responsible for a 27% reduction in bearing strength. The optimization of operational parameters yields improved bearing load and lower damage. A significant level of conformity was detected by the regression accuracy and validation test results with a residual error of less than 10%. Highlights: A comparison of two hybrid composites utilizing various layouts for damage and load bearing.Delamination damage is a key factor in predicting the efficiency of bolted connections.Using optimized operation parameters enhances drilling output response significantly. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to examine how the thickness of layers and printing speed impact the energy absorption capacity of honeycomb structures through drop-weight experiments. In addition, the effect of printing orientation on the resulting microstructure and mechanical performance was targeted to be examined. Design/methodology/approach: In this paper, after manufacturing test specimens using fused deposition modeling technique with three distinct layer thicknesses (0.16 mm, 0.20 mm and 0.28 mm) and printing speeds (40 mm/min, 50 mm/min and 70 mm/min), drop weight tests were carried out. Then to see the effect of printing orientation on mechanical performance, three-point-bending tests were performed and damage mechanisms were comparatively examined through scanning electron microscopy. Findings: An increase in layer thickness from 0.16 mm to 0.28 mm resulted in a notable 37% decrease in the impact resistance of the printed part. In addition, increasing the printing speed from 50 to 70 mm/min reduced the energy absorption capacity of the printed part by approximately 36.5%. Moreover, in terms of printing direction, transversely printed specimens showed 10% lower flexural strength than longitudinally printed specimens. Finally, scanning electron microscopy (SEM) observation showed that internal defects were more prominent in transversely printed specimens, resulting in premature failure. Furthermore, delamination was also detected in transversely printed specimens as another damage mechanism accelerating material failure. Originality/value: It is seen that the effect of printing parameters on the fundamental mechanical properties including tensile strength, strain at break, ductility and elastic modulus were studied by various researchers. However, to the best of authors' knowledge, the effect of printing speed and layer thickness on the energy absorption of polylactic acid based hexagonal honeycomb was not encountered. In addition, in-depth SEM analysis to discover the influence of printing direction significantly contributes to the literature. [ABSTRACT FROM AUTHOR]

In recent years, composite structures have been used in a large number of applications in aerospace, machinery, marine, and civil engineering. However, there are inevitably many uncertainties in the whole life cycle of composite structures, which can easily lead to structural damage and failure. Therefore, it is important to analyze the reliability and sensitivity of composite structures. At present, most of the contributions use the first-order reliability method (FORM) and the second-order reliability method (SORM) to study the reliability of composite structures and compare them with the results of the Monte Carlo simulation. However, both methods have their limitations. FORM cannot guarantee the calculation accuracy for the highly nonlinear limit state equation, and the calculation efficiency of SORM is too low. Therefore, this paper proposes to use importance sampling (IS) and backpropagation neural network-based Monte Carlo (MC-BPNN) to study the reliability, sensitivity, and dispersion of delamination growth of composite laminates. The results show that compared with FORM and SORM, IS and MC-BPNN have higher calculation accuracy and efficiency and can more accurately evaluate the failure degree of composite structures and ensure their safe operation in the field of aerospace equipment. The universality of this method can make it being widely used in the reliability and sensitivity analysis of different composite materials as well as dispersion analysis. [ABSTRACT FROM AUTHOR]

The Scott bond test method has been used extensively in the paper industry over the years as a means to assess the bond strength of paper. The method has been a subject of some controversy lately since it does not always correlate to the sensitivity of the material to fracture by delamination. To gain some further insight into which parameters govern the fracture process in a Scott bond test a simplified approach has been chosen in order to formulate an analytical mathematical/mechanical model of the test. The model is dynamic in the sense that inertia effects are included. The material model utilised is a simple cohesive theory that assumes a linear behaviour between stress and crack opening when the material has started to degrade. This choice of material model makes the mathematical model very nonlinear. In fact, a system of three coupled nonlinear second order partial differential equations have to be solved and adjusted to the correct initial conditions. The material parameters needed for the model are the elastic modulus in the thickness direction, the transverse shear (elastic) modulus, the tensile strength (in the thickness direction) and the fracture work (per unit area) for a delamination crack. To investigate the ability of the model, a Scott bond testing apparatus have been equipped with a piezoelectric load sensor. The load cell was mounted on the apparatus’ pendulum so that the load acting on the sample holder could be recorded during the whole impact stage. This was done for a number of different initial velocities of the pendulum and it is found that the model gives a fair prediction of the contact load. [ABSTRACT FROM AUTHOR]

In this paper, a novel statistical vibration-based damage detection method is developed considering uncertainties in measured resonance frequencies. The proposed method is based on the application of resonance frequencies as the most accurate and easiest measurable vibration feature. For proof of efficiency of the proposed method, case studies were undertaken using two identical composite plates, one delaminated and the other pristine. In this respect, the frequency response functions (FRFs) were measured and used as the main input to the Resonance Detection Algorithm as the proposed method. Applying these FRFs to a Resonance Detector Function can determine the resonant frequencies and their statistical distribution. Through the statistical distributions of the corresponding resonant frequencies, their reliability of detecting damage has been obtained via the beta distribution. By observing the damage detection reliability of the two sets of corresponding resonant frequencies, it has been determined that the changes in natural frequencies are due to structural changes and not random errors through measurement. [ABSTRACT FROM AUTHOR]

Delamination is one of the most feared failure modes in laminated composites and yet there is a lack of well established procedures to find the ply configuration with the highest delamination resistance for a given geometry of the component and a set of elastic and strength constraints. This paper presents a methodology for determining the quasi-isotropic ply sequence more resistant to delamination under off-axis uniaxial tension. Delamination is considered to be triggered by interlaminar stresses at free-edges or by matrix cracks. Two different ply thicknesses (standard and thin) and two sets of ply orientations (multiples of π /4 or π /8) are considered. The results show that the use of thin plies enlarges the design domain by up to 70% and generates a practically isotropic safe space. The methodology presented is also suitable for optimizing the delamination resistance of other load cases with stress singularities. [ABSTRACT FROM AUTHOR]

This study concerns several possible ways of computing the J-integral in the cases of laminated composite plate structures containing delamination. On the one hand, two special types of plate finite element families are provided for advanced fracture mechanical analyses. On the other hand, a numerical algorithm is introduced also that utilizes results derived from solid element models built in commercial finite element software. In order to create plate elements, the first-order (FSDT) and the third-order shear deformation theories (TSDT) are applied with two equivalent single layers. A subparametric element family is created by using the Hermite interpolation with the FSDT that grants the continuity of the derivatives at the element borders. Besides, an isoparametric family is created also with the TSDT employing the Lagrange interpolation scheme. This paper aims to present the compact formulations of calculating the J-integral around the delamination fronts for both plate element families. The calculation of the J-integral is implemented as a matrix multiplication by taking advantage of the properties of plate transition elements. The models yield improved fracture mechanical analyses for delaminated composite plates with linear elastic material behaviour. In addition, computing the J-integral is not available in most commercial finite element software for laminated orthotropic materials, therefore, an appropriate algorithm is presented here for this purpose. To conclude, the models and algorithms are applied to two case studies and subjected to a comprehensive comparison with analytical and formerly used finite element solutions. • A subparametric FSDT plate element family with granted continuity of the derivatives for delaminated plates. • An isoparametric TSDT plate element family that is appropriate for modelling curved delamination fronts. • A robust algorithm for computing the J-integral numerically in solid element models. [ABSTRACT FROM AUTHOR]

Delamination is one of the most common types of damage in fiber-reinforced composites. In this paper, borrowing from the concept of defect modes in imperfect phononic crystals, we propose a method for identifying delamination damages in composite materials. Specifically, by periodically arranging concentrated masses on the surface of a finite carbon fiber beam, the carbon fiber beam becomes a phononic crystal, and defect modes in Bragg bandgaps can be observed when there is delamination. With the spectral element method formulation, we show that the frequencies of defect modes are directly related to the length and location of the delamination. By performing algebraic addition and subtraction on the generated defect mode frequencies when applying excitations at the two ends of a defected carbon fiber composite beam, an approximately linear correlation with the length and location of delamination can be obtained. Our analytical and experimental results indicate that, by introducing periodicity on the carbon fiber composite beam and applying appropriate post-processing algorithm to the generated defect modes, rapid and accurate identification of the delamination length and location can be achieved based on the bandgap characteristics of the imperfect phononic crystals. [ABSTRACT FROM AUTHOR]

The article lists non-destructive testing (NDT)-related papers including "Update on ISO standards in condition monitoring and vibration," "AI for NDE 4.0--recent use cases," and "Principles for successful deployment of NDE 4.0."

Shape memory alloy (SMA) tufted composites have shown a significant improvement of the mechanical strength, fracture toughness, and delamination resistance of structural joints. This paper investigated the self-sensing functionality of SMA tufted carbon/epoxy composite T-joints to enable in situ strain monitoring for the detection of low-velocity impacts. Indeed, large deformations in the tufted composite due to impacts caused abrupt changes in electrical resistance of SMA filaments, which were used to trigger the detection system. An Arduino Mega controller was programmed to simultaneously extract and process real-time electrical resistance recordings from SMA tufts during impact tests conducted at 5 J and 10 J. Experimental results showed that the proposed SMA-enabled detection system can capture accurately the time of the impact and localise the delamination onset, thus demonstrating the truly multifunctional capabilities of proposed SMA tufted composites. [ABSTRACT FROM AUTHOR]

Delaminations and cracks are detrimental phenomena that hinder the quality of the final product in metal additive manufacturing. The effective use of other online monitoring systems that can detect these deformations and delaminations during the manufacturing process is currently being developed and implemented in practice. In this paper, gas-borne acoustic emission is used to show that cracks/delaminations that occur during the metal laser powder bed fusion build process can be detected and distinguished from other machine noise. The peaks in the amplitude of the signal emitted in the time domain could be used to indicate the occurrence of cracks during the build process. The frequency characteristics of the signal could also clearly indicate the occurrence of the macro cracks and differentiate between the signals from the cracks and the machine noise. [ABSTRACT FROM AUTHOR]

The aim of the research presented in this paper was to simulate the relationship between selected technological drilling parameters (cutting speed, vc, and feed per tooth, fz) and cutting forces and the delamination in machining of a new glass-fiber-reinforced polymer (GFRP) composite. Four different types of new materials were manufactured with the use of a specially designed pressing device and differed in the fiber type (plain and twill woven materials) and weight fraction (wf) ratio, but they had the same number of layers and the same stacking sequence. A vertical machining center Avia VMC800HS was used for drilling holes with a two-edge carbide diamond coated drill. Measurements of the cutting force Fz in the drilling process conducted with variable technological parameters were carried out on a special test stand, 9257B, from Kistler. The new ink penetration method, involving covering the drilled hole surface with a colored liquid that spreads over the inner surface of the hole showing damage, was used to determine the delamination area. The cause-and-effect relationship between the drilling parameters was simulated with the use of five machine learning (ML) regression models (Linear Regression; Decision Tree Regressor; Decision Tree Regressor with Ada Boost; XGBRF Regressor; Gradient Boosting Regressor). Gradient Boosting Regressor results showed that the feed per tooth had the greatest impact on delamination—the higher the feed was, the greater the delamination became. Push-out delamination factors had higher values for materials that were made of plain woven fibers. The lowest amplitude of the cutting force component Fz was obtained for the lowest tested feed per tooth of 0.04 mm for all tested materials, with the lowest values obtained for the materials with twill fibers. [ABSTRACT FROM AUTHOR]

• Energy-based formulation of delamination by a quasi-static evolutionary process. • Enhanced formulation of the delamination model using an interface damage variable. • Experimental verification by the interlaminar stiffness test for Mode I delamination – DCB Test. • Providing the best experimental estimate to the stress–strain relation in the computational model. The paper presents methods and procedures of computational and experimental approach of modeling and analysis of problems with Mode I delamination. One of the main goals of the work is to focus on the interface between anisotropic materials in a computational model and its consideration under stress. The paper presents a numerical method for the prediction of a damaged interface based on a variational formulation that is implemented using the symmetric Galerkin boundary element method. The calculation part consists of interface analysis considering the cohesive type of contact. The damaged interface between anisotropic domains is analyzed under loading in Mode I. Stress, deformation quantities and damage are calculated using methods of nonlinear programming. The experimental evaluation of the Mode I delamination is presented in a comparison with the values obtained from the computations. The experience and recommendations related to the use of carbon fiber reinforced polymer composite materials are presented. [ABSTRACT FROM AUTHOR]

In this paper, the two‐dimensional (2D) (0°/90°) plain‐woven Amosic‐3 SiC/SiC turbine guide vane (TGV) was fabricated using the chemical vapor infiltration method. Thermal and stress analysis of the TGV was conducted using the finite element method analysis. Multiple thermal shock tests at T = 1250, 1350, 1400, 1420, 1450, 1470, and 1480°C were conducted for N = 100, 100, 400, 300, 200, 200, and 700 cycles. After thermal shock tests, the surface damage of the TGV was observed visually, and the micro damage mechanism was analyzed using the scanning electronic microscopy. Micro X‐ray computed tomography was adopted to characterize the internal damages in the SiC/SiC guide vanes. The delamination occurred at the positions approaching internal hollow, due to the weak binding force along the thickness direction and the high thermal shock stress caused by the temperature change. The diameter, area, volume, and sphericity distributions of the pores inside of the guide vanes were also obtained. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The GIC reached a maximum of 1412.42 J/m2 at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the GIIC reached a maximum value of 983.73 J/m2, approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed. [ABSTRACT FROM AUTHOR]

This paper proposes a low-in-plane damage ZPI (Z-pin pre-hole insertion) process. The delamination growth behavior and the influence of Z-pin insertion density on the mode I interlaminar fracture toughness of laminate was explored experimentally and numerically. Meanwhile, Z-pin pull-out and shear tests were conducted in order to provide accurate data for the DCB simulation test. What's more, an infinite-focus microscope was used to scan the specimen's defect caused by the ZPI process. It can be found that the ZPI process can lead to less Z-pin inclination, fibre breaking, and crack initiation at the bonded interface. The DCB test results show that the load-displacement curve can be distinguished into four stages for the pinned specimen. In addition, a specimen pinned with a higher Z-pin volume fraction to more suitable for increasing the G IC . The simulation results show that the simulated maximum load and the G IC of the specimen are 286.63 N and 940.06 J·m−2, with a 0.56% and 10.10% error from the experimental result, indicating that the proposed FE model is validated by comparing the predictions with the experimental results. These results can provide some guidance for fabricating the reinforced laminates via the ZPI process. [ABSTRACT FROM AUTHOR]

Tests of welds are carried out inter-operatively, during the execution of the steel structure, as well as after the structure is welded, but even before its assembly. Steel structures already in service are also examined to detect potential cracks, delamination, or corrosion loss of thickness having the effect of weakening the mechanical strength of the structure. Such examinations are some the elements that comprise a structural health assessment. In this paper, the metal memory method was used to evaluate the effect of the welding method and weld temperature on the change in magnetic field strength. S235JR structural steel was used for the study, which was subjected to milling and MMA, TIG, and MIG welding. The results of measurement experiments carried out for each welding method are presented as graphs. [ABSTRACT FROM AUTHOR]

In this paper, pultruded GFRP bars are investigated to determine their fracture properties. The double cantilever beam test (DCB) is used to assess fracture behavior under mode I loading conditions. However, due to the presence of the R-curve effect (variable fracture energy dependent on the length of the crack), it is necessary to introduce a nonstandard approach to determine fracture properties. The mixed experimental–numerical approach is proposed to deal with this issue. Numerical simulations were carried out in Simulia Abaqus, and with Python scripting it was possible to generate models and obtain R-curve for the material. The numerical model built based on the experimental results has very good agreement with it (force–displacement and delamination length–time characteristics) which allows the use of the mentioned model in the analysis of more complex structures. Acoustic emission analysis was introduced as an auxiliary technique. The delamination obtained from both the numerical model and the experiment complies with the registered acoustic emission events. The proposed method can be used in preparing a material model for other composite materials, which display the presence of the R-curve effect. [ABSTRACT FROM AUTHOR]

This paper presents a new analytical approach to the embedding of delamination in the layerwise theory, which can be applied to determine the stress–strain state in the cross-section of laminated plates with internal delamination. The new approach is based on the layerwise theory, which transfers considerations from the level of the laminated plate to the level of the lamina. The paper presents a mathematical model and defines a calculation procedure for determining the state of the stress and strain in a cross-section with an internal delamination that occurred during plate production. The convergence and stability of the computational procedure, based on a new approach to the embedding of delamination in layerwise theory, are proven. It is also proven that the existence of internal delamination on the bond between layers of laminated plates significantly changes the stress-strain state of the cross-section, in relation to a cross-section without delamination. In numerical examples, the value of delamination in the plane (x, y) is determined and considered. The initial state after a static load or "zero state" of stress and strain in a cross-section with delamination represent the input for further and future nonlinear analyses that involve the growth, development, and propagation of delamination. [ABSTRACT FROM AUTHOR]

Drilling in synthetic fiber-reinforced polymer composites is facing challenges due to their anisotropic, inhomogeneity, and abrasive machining behavior. The joining of composite parts using fasteners is commonly done by the drilling, and the generated heat is one of the main causes to damage the drilled hole in the composite. Moreover, the quality of drilled hole is crucial for joining parts effectively. The paper presents the design, fabrication, and drilling of a hybrid fiber-reinforced polymer (HFRP) based on insulative coating. These composites were fabricated using vacuum infusion molding (VIM) and coated with different thicknesses to investigate the influence of drilling parameters and associated damages. Cutting speed, feed rate, and coating thicknesses were varied, and a full factorial design of the experiment was formulated. High-speed steel (HSS) twist drill bit was used to drill the coated composite and test samples, and delamination factor and surface roughness were measured. ANOVA and full factorial response optimizer were used to evaluate the influence and optimum drilling parameters. The delamination factor (DF) at the entry and surface roughness were found to decrease with the increasing cutting speed. However, the DF at the exit showed the opposite. Coating thickness influenced the delamination at the entry whereas delamination at the exit has been found insignificant. For drilling HFRP composite with 1 mm coating thickness, 3000 RPM spindle speed and 0.08 mm/rev feed rate were found optimum parameters in minimizing surface roughness and delamination damage. However, 6000 RPM and 0.02 mm/rev were found optimum parameters for drilling HFRP composite with 1.5 mm coating thickness. [ABSTRACT FROM AUTHOR]

In this paper, three-dimension failure behaviour of L-shaped composite beam with manufacturing defects was studied under four-point bending test condition. First, X-ray computed tomography scan was performed for L-shape laminated composite beam specimen to detect manufacturing defects such as voids, pre-delamination, and wrinkles or ply waviness. The scan images were then converted to three-dimensional volumetric entity through image processing, from which finite element mesh was generated with the detected defects directly incorporated. Next, three-dimensional progressive failure analysis was performed for the finite element model of the L-shaped laminate composite simulating four-point bending test condition with delamination and matrix failure in 90 degree plies accounted for by using cohesive zone modelling. The predicted maximum load was well matched to that obtained by tests validating the analysis modeling. Then a series of parametric studies were performed to investigate the effect of defect size and location on the failure load and delamination propagation pattern. It was found that the maximum load reduction was the largest when the pre-defect was located at the center of the symmetrical portion of the L-beam. In addition, the maximum load and delamination development behavior varied significantly depending on the interlayer and in-plane position of the pre-defect. [ABSTRACT FROM AUTHOR]

Cohesive elements are routinely used to simulate delamination between plies in composites. However, the allowable maximum size of these elements is limited, owing to the presence of a very small process zone ahead of the cohesive crack-tip, which needs to be discretised with multiple elements for obtaining an accurate failure response. This restricts their applicability beyond analysing delamination in coupon scale problems, due to the need for a very fine mesh and associated large problem size. In this paper, a novel hp cohesive element is developed to address this problem. This element is capable of simultaneous mesh refinement and elevation of interpolation order, locally and adaptively around the propagating cohesive crack tip. Additional degrees of freedom associated with the hp refinement are handled by extra nodes already supplied in the initial mesh file, that are selectively activated by the program as required. Several example problems are presented showing the ability of this method to improve the prediction of delamination onset and growth in extremely coarse meshes with a reduced computational time. [ABSTRACT FROM AUTHOR]

• Based upon a novel meshless method-the Fragile Point Method (FPM), an initially rigid interface debonding model incorporating mixed-mode damage and varying damage behaviors based on interface tension or compression is proposed. • Either intra- or inter-ply cracks in composite laminates can be explicitly modelled by the proposed method within a same numerical framework. • Delamination migration of composite laminates is simulated and results agree well with published test data. • A new mechanism of delamination migration is discussed according to FPM's simulation. Predicting damage in composite laminates is essential for a better utilization of the material, but it is challenging especially when the inter- and intra-ply damages are coupled. In this paper, a Fragile Points Method (FPM) with a numerical-flux-based interface debonding model is proposed to simulate the laminates' damage. The FPM is a novel meshless method using the discontinuous Galerkin weak formulations and the point-based discontinuous polynomial trial functions. In this work, an orthotropic interface debonding model has been developed based on the numerical fluxes to simulate the mixed-mode inter- and intra-ply damage. For any interior interface in an FPM model, the interface damage is triggered when the damage criterion is satisfied and the interface is separated when the fracture energy is reached. Due to the discontinuous characteristics of the FPM, the inter- and intra-ply damage modes are introduced explicitly, and thus the coupling between them can be naturally captured. In this paper, the proposed FPM is verified by four benchmark examples for Mode I, Mode II and Mixed Mode delamination. Then the proposed method is applied to simulate the delamination migration, used as an example for the inter- and intra-ply damage. The FPM results show that this method is able to provide reliable prediction on the load–displacement curves as well as the damage and crack patterns, and the mechanism governing the delamination migration is also discussed based on the FPM results. [ABSTRACT FROM AUTHOR]

The problem of failure in the facings of a corrugated board is investigated by means of a mechanical model utilizing the principles of continuum damage mechanics. To evaluate the predictive capability of the model, experiments have been conducted on in-plane isotropic single and two-ply paper sheets manufactured in the laboratory. It is found that there is a qualitative agreement between model and experiments. The model can predict if delamination will occur before the top-ply loses its in-plane load carrying capacity due to material degradation. To circumvent delamination problems, a material with low stiffness should be used in the top-ply (as compared to the bottom-ply) and a very thin top-ply should be avoided. It is exemplified that it is possible to steer the failure mode by optimizing the degree of beating or the ply thickness. It is demonstrated that plasticity may be omitted in the analysis if one is only interested in characterizing the expected type of failure mode. An important key result is that, if the circumstances are that severe damage growth takes place in the crack-tip region, then delamination most likely occur which may be in contradiction to what is anticipated from classical theories of fracture mechanics. [ABSTRACT FROM AUTHOR]

This paper presents a new method of piercing the carbon fibre reinforced polymer (CFRP) with abrasive water jet (AWJ), which can avoid delamination. The method consists of adding the abrasive particles in the water jet at the very beginning of jet formation, thus obtaining a mixed abrasive water jet during the first impact with the composite work piece. A new cutting system was designed and set up based on the proposed piercing method and was compared with a conventional AWJ cutting system. The main added values brought by this paper are: it validates our original concept; provides synthetic analyses, the effects of the AWJ homogeneity, and the abrasive inlet angle on the CFRP delamination, and it brings a complete set of recommendations on how to overcome the industrial difficulties caused by the delamination of the composite materials, during the piercing with AWJ. [ABSTRACT FROM AUTHOR]

Carbon fibre reinforced plastic materials (CFRPs) have a wide range of industrial applications like automobile, aerospace, biomedical, defence, and sports industries because of extraordinary multidimensional properties. Mechanical drilling is a most widely used common secondary machining process for composite laminates. Drilling induced delamination at hole-entry and hole-exit of a drilled hole is frequently occurred due to anisotropic and non-homogeneous structure of a material mechanics. Delamination can be smothered by employing tool design optimisation, upgraded drilling strategies and improving drilling methods. In this paper, various drilling conditions towards damage free drilling of CFRPs are reviewed. The above drilling conditions are categorised under adhesive layer, cryogenic cooling, minimum quantity lubrication (MQL), pilot hole, reverse air suctioning, spring-damper mechanism, support plate mechanism, variable feed strategy, etc. These strategies are extensively reviewed with reference to drill bit geometry, drilling techniques and drilling methods to uncover the significance of drilling conditions and its importance on drilled quality. This common review on various drilling conditions for delamination-free drilling can be referenced as not only a widespread summary from literature survey available till the date but also help researchers to explore new possible ways to achieve delamination-free drilling for composite materials in upcoming years. [ABSTRACT FROM AUTHOR]

Fiber-reinforced resin matrix composites have been widely used in aerospace, construction, transportation and other industries due to their excellent mechanical properties and flexible structural design. However, due to the influence of the molding process, the composites are easily delaminated, which greatly reduces the structural stiffness of the components. This is a common problem in the processing of fiber-reinforced composite components. In this paper, through the combination of finite element simulation analysis and experimental research, drilling parameter analysis was carried out for prefabricated laminated composites, and the influence of different processing parameters on the processing axial force was qualitatively compared. The inhibition rule of variable parameter drilling on the damage propagation of initial laminated drilling was explored, which further improves the drilling connection quality of composite panels with laminated materials. [ABSTRACT FROM AUTHOR]

Large deformations under in-plane compression of paperboard appear in forming processes like hydroforming, pressforming and deep drawing, but the mechanisms of deformation have not been studied on a micromechanical level. A constrained in-plane compression test is presented. This test allows for in-plane compression, buckling, wrinkling and compaction. The constrained compression test is realized using a DEBEN CT-500 in-situ tester for laboratory microtomography and synchrotron microtomography. Experiments with five different materials spanning from laboratory handsheets to commercially available multi-layered paperboards are performed. Image processing is used to observe the local out-of-plane fiber orientation and compaction. A phenomenological investigation of the deformation behavior of these materials is presented. Delamination is found to be the primary mechanisms of failure in the multi-layered boards. Furthermore, a porous network structure, created by using long and minimally refined softwood fibers, is found to facilitate the formation of uniform wrinkles and compaction. [ABSTRACT FROM AUTHOR]

Numerical and experimental research programs have been carried out to investigate the effect of scaling on the tensile strength of notched composites. This paper presents a computational study of scaled open-hole tensile tests using the Discrete Ply Model (DPM) method. This finite element model is discrete, and only a small number of parameters are required from experimental characterization tests. Experimental and numerical strength values are compared here, and reveal that DPM simulations tend to slightly overestimate strength values, with an average discrepancy of 9.7%. However, DPM Results show that such modeling simulates both the reduction in strength when specimen size is increased for sublaminate level scaled specimens, where failure is fiber dominated, and the increase in strength when specimen size is increased for ply level scaled specimens, where failure is delamination dominated. In all cases, increasing the total thickness of the specimen leads to a decrease in strength and this effect is dominant over the effect of increasing hole diameter. As well as the variation in strength, three distinct failure mechanisms are observed: fiber failure with extensive matrix damage (pull-out failure), fiber failure with little or no matrix damage (brittle failure) and delamination failure. Comparisons with experiments demonstrate that tensile strengths, damage propagation scenarios and failure patterns are predicted with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's Mode-I fracture toughness test findings. The MBT technique's GIc values for initiation and propagation are 0.533 and 0.679 KJ/m², respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the -IIc values for the CBBM technique are 1.65 KJ/m² for non-pre cracked and 1.4 KJ/m² for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness. [ABSTRACT FROM AUTHOR]

This paper develops a new detection method taking the power function of the modal displacement curvature difference as a damage index to accurately identify the location and degree of the delamination. The 4-layer Poly Tetra Fluoro Ethylene films of size 0.02 m × 0.11 m are embedded between adjacent carbon fiber prepregs being 0.06 m and 0.115 m away from the left edge, respectively. The force-hammer excitation experiment is carried out on the prepared laminates with fixed supports at both ends, and the frequency response curves of measuring points are processed by the Polylscf algorithm in Dong-Hua Data Analysis System. The finite element model of delaminated laminates is established through adding new layers with film properties, and the modal displacements of nodes are compared with experimental data. The number of measuring points in the experiment is limited, making the precise characterization of surface abrupt characteristics difficult. The numerical results are used to calculate the square of the Gaussian curvature difference between the modal displacements of intact and damaged laminates. Significant improvement of the delamination detection accuracy is achieved in this process, confirming that the developed method constitutes a valuable tool for the Non-Destructive Testing of the laminates. [ABSTRACT FROM AUTHOR]

Internal delamination damage in composite connection structures can occur in the process of the overloading of a high-speed bearing, with alternating force loads, high or low temperatures, and the humid or hot environment loads. Mechanical drilling and riveting are usually used at the delamination position and outside its envelope, to inhibit delamination expansion. However, delamination damage can change the structural stress state of the original structure. It is difficult to achieve a better inhibition effect using conventional drilling mechanisms and process methods with intact composite panels, and new damage forms can even be introduced into the drilling process due to unreasonable parameter settings. Therefore, this paper combined finite element simulation technology and experimental processing technology, to analyze the influence of different delamination dimensions and positions on processing quality. The results showed that the feed speed and rotating speed had significant effects on the axial force of composite laminates. In particular, in the case of a low speed and high feed, the axial force will increase significantly. [ABSTRACT FROM AUTHOR]

Delamination is a typical defect of carbon fiber-reinforced composite laminates. Detecting delamination is very important in the performance of laminated composite structures. Structural Health Monitoring (SHM) methods using the latest sensors have been proposed to detect delamination that occurs during the operation of laminated composite structures. However, most sensors used in SHM methods measure data in the contact form and do not provide visual information about delamination. Research into mechanoluminescent sensors (ML) that can address the limitations of existing sensors has been actively conducted for decades. The ML sensor responds to mechanical deformation and emits light proportional to mechanical stimuli, thanks it can provide visual information about changes in the physical quantity of the entire structure. Many researchers focus on detecting cracks in structures and impact damage with the ML sensor. This paper presents a method of detecting the delamination of composites using ML sensors. A Convolutional AutoEncoder (CAE) was used to automatically extract the delamination positions from light emission images, which offers better performance compared to edge detection methods. [ABSTRACT FROM AUTHOR]

This paper aims at experimental and numerical research of delamination process in carbon/epoxy composite laminates with different fiber orientation angles in stacking sequence exhibiting the bending–twisting elastic couplings. Experimental specimens were subjected to the double cantilever beam (DCB) tests according to the ASTM D5528 regulations. Values of the mode I strain energy release rates were calculated by using three different data reduction schemes: the modified beam theory, the compliance calibration method and the modified compliance calibration. Determination of delamination initiation point was conducted in twofold way: by visual observation of crack tip using high resolution camera and by utilization of the acoustic emission technique. Numerical analyss were prepared in Abaqus/CAE Software environment by using the virtual crack closure technique (VCCT). The numerical beam model consisted of SC8R continuum shell elements. Obtained outcomes revealed that extensive fiber bridging phenomenon occurring during delamination process pronouncedly affected propagation values of strain energy release rate (GIprop) and numerically obtained load–displacement curves. Nevertheless, in initial stage of delamination, results obtained by using the VCCT were in agreement with experimental data. The greatest value of the mode I fracture toughness equal 0.56 N/mm was obtained for the BT45 laminate. [ABSTRACT FROM AUTHOR]

This paper investigates delamination detection in composite pipes using higher harmonic generation technique for the first time. The semi-analytical finite element (SAFE) method is developed to analyze the dispersion characteristics of the composite pipe. Then, a flexural mode at low frequency is selected to detect delamination. The three-dimensional (3D) finite element (FE) model is developed to simulate the flexural mode propagating in the composite pipe and its interaction with delamination. By comparing the simulated radial displacement signals with and without delamination, it is observed that the delamination can contribute to the higher harmonic generation. Subsequently, the ultrasonic measurements are conducted to demonstrate the numerical results. Using a relatively simple piezoelectric transducer (PZT) configuration, an almost pure flexural mode can be excited in the experiment. More importantly, experimental results indicate the higher harmonics induced by the delamination can be observed obviously. Finally, extensive parametric studies are performed to reveal the sensitivity of higher harmonics to the delamination with various sizes and at different interface. The proposed higher harmonic generation of flexural waves is promising for the practical application of delamination detection in composite pipes. [ABSTRACT FROM AUTHOR]

• Imaging of delamination in CFRP laminates based on integration of multiple LDR modes. • LDR frequencies calculated by frequency-domain finite element approach. • Quantitative assesment of delamination with various shapes and sizes. Accurately visualizing the geometry and dimensions of internal delamination in fiber-reinforced polymer (CFRP) composites is a challenging endeavor. In this paper, we develop a method to identify and characterize delamination in composites by the integration of multiple local defect resonance (LDR) modes. The proposed method was validated by using T300/M914 CFRP plates containing three distinct defect geometries, employing both numerical simulations and experimental measurements. The approach commences with the application of a frequency-domain finite element method for LDR frequency determination, emphasizing improved computational efficiency. This technique is further corroborated through the use of the defect-to-background ratio (DBR) method, which identifies LDR frequencies in both numerical simulations and experimental testing. The integration of multiple LDR modes (IMLDR) at various frequencies enables precise imaging of delamination defects of diverse geometries and sizes. Experimental results closely align with the numerical findings, confirming that the integrated imaging results accurately correspond to artificial defects. This method furnishes precise descriptions of damage location, geometry, and dimensions. The obtained results indicate that the proposed IMLDR-based technique significantly enhances the accuracy and reliability of delamination imaging in composites. Consequently, it offers an effective approach for quantitatively assessing delamination damage in composites. [ABSTRACT FROM AUTHOR]