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AbstractCarbon fiber-reinforced polymer (CFRP) is prone to machining defects, including burrs and tearing, during milling. These defects are closely associated with interface delamination while milling force plays a crucial role in their occurrence. In this paper, a nonlinear explicit finite element (FE) model is developed to predict the milling force and analyze the delamination damage occurring during the milling of unidirectional CFRP (UD-CFRP). The proposed FE model is validated through numerical comparison with experimental data for milling force. Moreover, a detailed study is conducted to examine the influences of spindle speed, feed rate and depth-of-cut on the side-milling performance and damage response of UD-CFRP. This study provides valuable insights into the effects of machining parameters on milling force and delamination damage in CFRP, thereby supporting the optimization of machining technology for this composite material system. [ABSTRACT FROM AUTHOR]

Digital image correlation (DIC) is a powerful technique for determining material deformation and damage and currently is viewed as a potential method to study failure and crack propagation in advanced composite materials. Case studies in concrete, epoxy adhesives, and carbon/epoxy laminates demonstrate the effectiveness of the DIC technique in visualizing crack propagation. This review highlights the applications, challenges, and implementation of the DIC technique in the failure and crack propagation of fibre-reinforced polymer (FRP) composites. The important factors such as field of view, speckle pattern, and algorithm choice are discussed while emphasizing the need for careful selection and calibration. The review concludes by highlighting the significance of crack propagation studies for composite behaviour and the role of DIC in calibrating and validating models of composite failure analysis. Future research directions include investigating mixed-mode delamination, improving calibration procedures, assessing DIC accuracy for large deformations, and comparing different DIC algorithms, which are discussed. [ABSTRACT FROM AUTHOR]

High-pressure pure waterjet (WJ) technology is widely used in the hole drilling process for carbon fiber–reinforced polymers (CFRP) laminates because of its high processing efficiency and zero heat affected zones. However, the phenomena of the delamination zone and poor roundness pose significant challenges to the hole processing of CFRP laminates. In this study, the numerical and experimental investigation of a high-pressure pure WJ CFRP laminate drilling process are conducted, to improve the quality of the pure WJ drilling process. A comprehensive coupled fluid–solid numerical model based on the smoothed particle hydrodynamics method is developed to simulate the pure WJ drilling process of CFRP laminates and determine mechanism of the material removal. Thereafter, extensive pure WJ drilling experiments are conducted on two stacking sequence CFRP laminates to obtain a hole with remarkable roundness. The simulation results illustrate that during the WJ drilling of CFRP laminates, the material removal process and damage zones of each inter-laminate interface are mainly extended along the fiber direction (the direction of longitudinal Young's modulus). Water-wedging action is observed to play an important role in the damage of inter-laminate interface and propagation of peel-up and push-down delamination. Furthermore, the experimental results show that an increase in the WJ pressure contributes to the reduced hole taper and surface roughness of sidewalls. Holes with diameters below 2 mm are successfully drilled, and a roundness error of 0.05 mm is obtained for the [0/45/–45/90]2s CFRP laminate, which is 1/6 of that of the [0]16 laminate. [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]

Considering the ever-increasing importance of composite patches applied to repair or reinforce composite structures, radical health monitoring of these patches seems inescapable. Thermography method is one of the most influential non-destructive methods applied to inspect the repaired structures. Since there are many parameters influencing defects detection in repaired composite structures, extracting the most influential method to determine these parameters is significantly important. In the present study, a repaired carbon fiber reinforced plastic (CFRP) composite structure having defects of different dimensions, types and features located in different depths, is investigated by experiment and finite element simulations to assess the influence of the experimental parameters, like the thermal excitation pulse duration and the best image frame. In thermal simulation, two criteria, maximum thermal variations versus time and path length, are developed to derive the most optimum heating duration and the best thermal frames. The obtained results are validated through defining direct and diagonal paths passing through defects demonstrated on thermography images and thermal map images. The average error of thermal variations on different paths displayed on thermography and simulation images is less than 4.5 percent which confirms the correspondence of obtained results of both mentioned methods. [ABSTRACT FROM AUTHOR]

It has been established that exposure to a microwave electromagnetic field with an energy flux density that is rational for each type of composite (carbon-, glass-, organoplastic) contributes to an increase in the specific work of delamination by 18.6, 12 and 20%, respectively, which satisfactorily correlates with an increase in strength of these materials under three-point bending and interlaminar shear. [ABSTRACT FROM AUTHOR]

The main, well-known scientific results were obtained by outstanding scientist Yu. N. Rabotnov in the field of creep theory, hereditary elasticity, damage mechanics, technical theory of shells. However, in the last years of his life, the academician Yu. N. Rabotnov was keen on some problems in the field of mechanics of fiber-reinforced composite materials. He proposed new, original strength criteria, simplified methods for ply-by-ply calculation of composite laminates. One of Yu. N. Rabotnov's scientific passions were connected with description of specific fracture modes of layered fibrous composites having the types of delamination and splitting. On the base of energy fracture criterion, it's possible to estimate the scale effect of strength – the dependence of critical stresses on the absolute sizes of composite members. Such models of specific fracture modes make it possible to estimate the danger of such technological defects as thin polymeric film between composite layers. [ABSTRACT FROM AUTHOR]

The seismic data recorded at 48 broadband stations on an 1,800‐km‐long linear array have been used to image the deep structure and deformation in the intra‐continental collision between the Tarim Basin and the Northern Tibetan Plateau (NTP). Common Conversion Point (CCP) stacking imaging along the linear array and joint inversion of receiver function and surface wave dispersion defined the crustal and upper mantle structure, indicating that the Tarim block underthrusts the Altyn Tagh Range–Qaidam Basin. Whereas Moho is flattened, the lithospheric mantle beneath the Qaidam Basin has unusually low velocity, which is thought to be the consequence of the delamination in the lower crust and mantle lithosphere. Strong positive phase occurring at depths of 150–200 km on the CCP stacking imaging is likely to be associated to the remnant subducted oceanic lithospheric slab or the underthrusting Tianshan lithospheric slab beneath the collision zone. The removal of the Altyn Tagh Range–Qaidam Basin orogenic root may be due to convection‐driven delamination underneath it and subsequent underthrusting of the Tarim block. The spatial variation of the SKS splitting is manifested as the large‐scale pattern of lithospheric deformation and local abrupt changes, transitioning from pure shear on the NTP to simple shear in the Altyn Tagh Range. A comprehensive analysis of SKS splitting and GPS data reveals a simple shear pattern of vertical coherent deformation in the Altyn Tagh Range and its adjacent areas, which is evidence of the lithospheric shear zones. Plain Language Summary: The seismic wave data received by 48 broadband stations on the newly 1,800 km long linear array were used to determine the deep structure and deformation of the crust and upper mantle caused by the intra‐continental collision between the Tarim block and the Northern Tibetan Plateau by the joint inversion of the receiver function and the surface wave dispersion method. The results of this study reveal that the Tarim block underthrusts the Altyn Tagh Range–Qaidam Basin, and the Moho discontinuity below it appears nearly flat, indicating that the underlying orogenic roots have been removed. The mantle lithosphere below the Qaidam Basin is a low‐velocity anomaly zone which is thought to be evidence of the delamination of the lower crust and upper mantle. Convection‐driven delamination underneath the Qaidam Basin and subsequent underthrusting of the Tarim block resulted in the removal of the orogenic roots below the Altyn Tagh Range–Qaidam Basin. The delamination and uplift resulted in the shortening and thickening of the Altyn Tagh Range–Qaidam Basin. A comprehensive analysis of SKS splitting and GPS data reveals the vertical coherent deformation of the Altyn Tagh Range. The consistency between the coherent SKS fast direction and the strike of the crustal faults is considered evidence of simple shear of the Altyn Tagh Range. Key Points: Flat Moho and anomalous low‐velocity lithospheric mantle beneath the Qaidam Basin are thought to be the consequence of delaminationStrong positive phases of receiver function at depth of 150–200 km may be related to the remnant subducted Tarim oceanic lithospheric slabSimple shear pattern of vertical coherent deformation resulting from SKS splitting suggests that the Altyn Tagh Range is a lithospheric shear zone [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study on the low-energy impact fatigue and bending behavior of sandwich panels reinforced with composite laminate glass and carbon fabric facesheets, supported by a honeycomb core made of Nomex. The crushing behavior of honeycomb sandwich specimens subjected to the impact test was compared and discussed. Our results indicate that the carbon composite facesheets have a significant effect on the impact, resulting in an increase in impact resistance and a 157.14% increase in crack depth in the elastic region compared to glass facesheets reinforcement. This increase serves as an indicator of the laminate's ability to resist damage initiation and impact fracture mechanisms. Also, an increasing in flexural strength about 45.72% was observed in carbon facesheets honeycomb specimens compared to glass facesheets reinforcement. Microscopic illustration of the damaged honeycomb sandwich specimens was conducted to evaluate the interfacial characteristics and describe the damage mechanics of the composite facesheets and core adhesion under the impact test. The numerical approach proves to be efficient in terms of accuracy and simplicity compared to existing methods for predicting the damage mechanisms of honeycomb sandwich structures. It was noted that results of numerical study show best agreements with experiment results and the model can be used to predict the low-energy impact fatigue. [ABSTRACT FROM AUTHOR]

This research paper presents a novel investigation into optimizing the milling process of S-GFRP composites using a combination of spindle speed, cutting depth, and feed rate. The study utilizes the Taguchi method and a unique Orthogonal Array L9 design to examine the impact of different parameter combinations on cutting force, surface roughness, and delamination. The results of this study are further analyzed through a combination of Grey Relational Analysis and ANOVA to determine the significance of each input parameter. The findings of this work demonstrate that the speed of the spindle is the most influential factor with largest contribution of 66.64% on all three responses, followed by feed with 26.12% contribution and cutting depth contribution 5.78%. this research provides a valuable insights for the optimization of end milling processes in S-GFRP composite materials. The findings can be used to improve the performance and quality of machined S-GFRP composite parts. [ABSTRACT FROM AUTHOR]

Naturally derived fibers/fillers-based polymers have gained much attention in many industrial applications due to the requirement for renewable and biodegradable components. Machining is sometimes needed to simplify the assembly of pieces in a finished product. Here, this article reports how drill machining affects polymer composites made with 5 wt.% jute filler that has undergone alkaline treatment. The experimental tests have been conducted to explore the impact of tool bit diameter, cutting speed and feed on the various generated responses (thrust force, surface roughness, delamination peel-up and delamination push-out). The results reveal that the appropriate responses are achieved when the cutting speed of the tool is at its maximum while the feed and tool diameter are at their minimal amounts. The response surface methodology (RSM) and support vector machine (SVM) algorithms have been devised to anticipate the drilling performance of produced composites, and both strategies have shown high agreement with experimentally acquired findings. However, the ML tool algorithm proven more reliable than RSM models because of the superior correlation of determination coefficients. [ABSTRACT FROM AUTHOR]

Glass-fiber-reinforced polymers' (GFRP), as compared to metallic materials, require more intricate machining. The composite construction experiences delamination as a result of this machining operation. Delamination at the exit and entrance of holes drilled is a significant flaw in composite materials. Superior-drilled holes can be produced by optimizing the drilling process's governing factors. This study's goal is to maximize the drilling settings using entropy weight-coupled gray relational analysis with fuzzy logic to account for multiple performance factors. Taguchi's L25 5-level orthogonal array is used to increase the accuracy of the results in this study. Feed rate and spindle speed are considered the control variables, and torque, thrust force, and delamination at both the exit and entry are the responses. The results show that drilling performance is enhanced by lower feed rates and elevated spindle speeds. Additionally, the present findings show that feed rate has a stronger influence on drilling hole quality. These results also proved that increasing the number of levels increases the accuracy of the results. Entropy-based gray relational analysis with fuzzy logic using more levels of factors can be effectively used for the optimization of the drilling process. [ABSTRACT FROM AUTHOR]

This study presents a novel approach to conducting the electromechanical impedance (EMI) technique for delamination detection in composite structures without the need for permanently attaching PZT (Lead Zirconate Titanate) transducers to the surface. Instead, a device is created that can be simply placed on top of the composite structure, enabling one to perform the EMI technique for detecting damage. The primary objective is to investigate the effectiveness of this device in detecting delamination within composite materials. Additionally, this study explores the impact of placing additional weight on top of the transducer to investigate the performance of the device subjected to higher pressure. Experimental results and analysis will be presented to evaluate the feasibility and reliability of this approach for non-destructive testing and structural health monitoring of composite components. This research is significant as it lays the groundwork for developing automated damage detection systems using robotics in the near future. By demonstrating the proposed concept that can be easily integrated into robotic platforms, this study contributes to the advancement of automation in structural health monitoring. Implementing this technique in robotic systems has the potential to revolutionize maintenance practices by enabling continuous, real-time monitoring of composite structures, enhancing safety, and minimizing downtime due to structural defects. Moreover, the investigation into the impact of additional weight on the transducer's performance is crucial for setting minimum weight limits in robotic systems, ensuring optimal functionality and accuracy during automated damage detection tasks. [ABSTRACT FROM AUTHOR]

The ductile-to-brittle transition (DBT) is an important characteristic that restricts the use of body-centered cubic metals as structural materials at low temperatures. This study shows a design of heterogenous lamellar microstructure (HLM), which is implemented in a low-density steel to promote the occurrence of delamination parallel to the direction of the main crack propagation, and result in delamination toughening effect. When the Charpy impact test temperature was reduced from room temperature to −196°C, the impact absorbed energy displayed a linear decline. The design of HLM brings a new pathway for developing economical BCC-structured metal plates with reliable low-temperature toughness. This is the first time of utilizing 'delamination toughening' to fully suppress the ductile-to-brittle transition in a body-centered cubic metal plate. [ABSTRACT FROM AUTHOR]

Composite structures are optimized in shape by terminating specific plies gradually. However, stress concentration at the ply drop-off can cause interlaminar delamination from the ply edge. In this study, Ply Curving Termination (PCT), which is introduced by locally curving fibers at 0° ply edges, is used to enhance tensile strength of the ply drop-off. To clarify the dependence of the PCT strength on the curved fiber angle (PCT angle), static tensile tests using ply drop-off specimens are conducted, followed by detailed damage observations using X-ray CT. The results indicates that the strength significantly increases with PCT but the fracture behavior differs depending on the PCT angle. Interestingly, specimens with large PCT angles fail from the position where the fibers curve, away from the ply edge. This PCT-specific failure mechanism is then elucidated using finite element analysis and the virtual crack closure technique, indicating that shear lag caused by the stiffness change due to fiber curving is important. Finally, using the revealed PCT failure mechanism, PCT angles that are the most effective in enhancing tensile strength is discussed. [ABSTRACT FROM AUTHOR]

In this paper, nine different carbon fiber laminates containing clusters are designed using the ant colony ACO algorithm, which have similar equivalent bending stiffnesses and B‐matrices, with the differences being the fiber orientation of the clusters and the position of the clusters in the laminates. The dynamic mechanical characterization of laminates for low velocity impact (LVI) at three different energies was carried out by means of a falling weight impact experiment. The experimental results show that the main form of failure of the laminate is delamination failure at low energy impacts, and shear fracture becomes more and more obvious with the elevation of the impact energy, which was observed in detail by the stereo microscope and electron microscope. The damage area of the laminate and the force and displacement curves after 30 J energy impact were compared by x‐ray scanning to derive the effects of the angle of the ply cluster fibers and the different positions of the ply clusters in the laminate on the impact resistance of the laminate. In conclusion, when designing the laminate, consideration should be given to designing 45° clusters on the impacted side and 90° clusters in the middle layer of the laminate to obtain the best impact resistance. Highlights: Designed 9 types of laminates with different laminate structures based on ACO algorithm.Different laminates have similar equivalent bending stiffnesses and the B matrix as close to 0 as possible.LVI tests at three energies were performed on 9 types of laminates.The effects of different orientations of the clusters and the position of the clusters in the laminate on the impact resistance of the laminate were investigated. [ABSTRACT FROM AUTHOR]

Pesticides effectively manage fungal diseases in fruits and vegetables; however, their toxicity poses significant environmental risks to human beings. Consequently, the chemical industry faces a daunting challenge in controlling or eliminating the presence of pesticides in the natural environment. The present work reports the synthesis of zeolitic materials with distinct structural properties (starting from the layered precursor PREFER and 3D-faujasite) and their use for the removal of the pesticide myclobutanil. The PREFER sample underwent two distinct treatments: external functionalization with CTAB and layers separation (delamination). On the other hand, external functionalization of the faujasite surface with different CTAB contents was performed. The results showed that the potentially delaminated PREFER sample (PREFER-CTAB-90ºC) performed better in removing the pesticide among all the samples due to the higher availability of CTAB on their exposed lamellae. In contrast, the samples with a double-layered arrangement of CTAB chains presented better pesticide removal performance in comparison with the samples with a single CTAB arrangement. DFT calculations were performed to elucidate the interaction mechanism occurring between myclobutanil and CTAB. The obtained results indicate that the adsorption of myclobutanil by two CTAB molecules is more efficient than a single CTAB; the calculated binding energy considering two CTAB molecules in the process was nearly four times larger than for a single CTAB. The theoretical data provided validation for the adsorbent performances, including a detailed discussion of molecular mechanisms (with and without solvent effects). This proof-of-principle study emphasizes the significant potential of CTAB-functionalized zeolite in removing myclobutanil. This represents an important advancement toward better understanding and harnessing the capabilities of this material for effective and efficient pesticide removal. [ABSTRACT FROM AUTHOR]

A novel damage tolerance design method of discrete interleaved toughening for laminated composite was proposed. In this paper, discrete thermoplastic Polyamide-6,6 (PA 66) films were deployed at between the selected adjected layers, and three toughening dimensions were considered. Besides, three impact positions of specimens were tested under 5 J, 10 J, and 15 J, respectively. The impact behavior and compression after impact (CAI) of specimens were discussed and compared. Experimental results showed that delamination damage was suppressed in the process of propagation outwards across the toughened region, and the path of delamination crack propagation was changed and swerved. Therefore, the delamination damage projected area (DDPA) of all specimens were reduced by 21.09%–62.85%, compared with the non-toughened plate (base plate). In addition, the finding demonstrated that CAI strength is influenced by the delamination position and DDPA. The proposed method could improve the CAI strength by suppressing delamination and swerving the propagation path of delamination. Moreover, the CAI strength of all toughened plates were improved by 16.35%–61.94% in contrast to the related base plates. [ABSTRACT FROM AUTHOR]

The impact-echo method (IE) is a non-destructive testing method commonly used in civil engineering. We propose a completely new approach for air-coupled actuation based on supersonic jet flow. The impinging jet sound generates continuously high sound pressures with a broad frequency bandwidth. This novel concept of utilising aeroacoustic sound for air-coupled IE was evaluated on two concrete specimens and validated using a classical IE device with physical contact. The results show a high agreement with the expected frequencies. Delaminations are correctly detected in depth and size. This proves the high reliability of air-coupled IE based on supersonic jet flow. [ABSTRACT FROM AUTHOR]

We study the delamination induced by the growth of a thin adhesive sheet from a cylindrical, rigid substrate. Neglecting the deformations along the axis of the cylinder, we treat the sheet as a one-dimensional flexible and compressible ring, which adheres to the substrate by capillary adhesion. Using the calculus of variations, we obtain the equilibrium equations and in particular arrive at a transversality condition involving in a non-trivial way the curvature of the substrate, the extensibility of the ring and capillary adhesion. By numerically solving the equilibrium equations, we show that delamination by growth occurs through a discontinuous transition from the fully adherent solution to the partially delaminated one. The shape of the delaminated part can take the form either of a ruck, with a small slope, or a fold, with a large slope. Furthermore, in the weak adhesion regime, complete delamination may occur. We construct the phase diagram between the different solutions in the parameter space. In the quasi-incompressible limit, numerical results are also supported by asymptotic calculations both in the strong and weak adhesion regimes. [ABSTRACT FROM AUTHOR]

The use of Atmospheric Pressure Plasma Jet (APPJ) technology for surface treatment of carbon fabrics is investigated to estimate the increase in the fracture toughness of carbon-fiber composite materials. Nitrogen and a nitrogen–hydrogen gas mixture were used to size the carbon fabrics by preliminarily optimizing the process parameters. The effects of the APPJ on the carbon fabrics were investigated by using optical and chemical characterizations. Optical Emission Spectroscopy, Fourier Transform Infrared-Attenuated Total Reflection, X-ray Photoelectron Spectroscopy and micro-Raman spectroscopy were adopted to assess the effectiveness of ablation and etching effects of the treatment, in terms of grafting of new functional groups and active sites. The treated samples showed an increase in chemical groups grafted onto the surfaces, and a change in carbon structure was influential in the case of chemical interaction with epoxy groups of the epoxy resin adopted. Flexural test, Double Cantilever Beam and End-Notched Flexure tests were then carried out to characterize the composite and evaluate the fracture toughness in Mode I and Mode II, respectively. N2/H2 specimens showed significant increases in GIC and GIIC, compared to the untreated specimens, and slight increases in Pmax at the first crack propagation. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) is a greenhouse gas which is mainly found in natural gas (NG), biogas, and flue gas. Anthropogenic CO2 emissions are the direct result of burning fossil fuels. Meanwhile, pre‐ and postcombustion CO2 separation is a current state of CO2 removal method in an extensive manner. From environmental, economic, and transportation perspectives, removal of CO2 has driven the development of its separation process technology. Among the reported technologies, membrane‐based gas separation technologies have grown substantially, breakthroughs and advances in past decades. This review paper aims to provide an overview on competitive gas separation processes, different types of membranes available, gas transport mechanisms, and fabrication process of hollow fiber membranes, particularly dual‐layer hollow fiber membrane. The performance of the membranes in CO2 separation and effect of spinning parameters on the formation of hollow fiber membranes are highlighted. In addition, approaches to improve the dual‐layer adhesion, strategies to enhance the filler compatibility in the development of dual‐layer hollow fiber mixed‐matrix membranes, and effect of post‐treatments on the gas separation performance of membrane are also discussed. Finally, challenges and future perspectives of dual‐layer hollow fiber mixed‐matrix membranes toward CO2 capture, particularly on CO2/CH4 and CO2/N2 separation, are also included, due to its substantial and direct relevance to the gas separation industry. [ABSTRACT FROM AUTHOR]

In foldable display products, an adhesive is affected by the fatigue delamination force. F‐d curve and Gc value of dynamic and static test do not exhibit a significant difference, but microbubbles are observed in dynamic folding. In this study, the fatigue delamination of adhesive in real user scene is investigated and its measurement methodology is constructed. [ABSTRACT FROM AUTHOR]

Adhesive failure as a result of the development of delamination or splitting is one of the most common types of strength loss in composite structural materials. Delaminations of fiberglass panels, pipes, and pressure vessels can occur under the influence of bending and torsional moments, as well as compressive loads. In composite pipes, under the action of temperature stresses or external compressive pressure, the inner layer or liner may peel off with a simultaneous loss of stability. To analyze the critical stresses when adhesive failure occurs, an energy criterion is used, but, however not in a differential form, but in the form of a comparison of the difference between the initial and final elastic energy of the layer with the work of adhesive destruction proportional to the delamination area. The solution to the problem of large deflections of the layer after loss of stability is reduced to elliptic integrals of the first and second kind. The introduction of the parameter of specific work of adhesive destruction into the energy criterion with a dimension different from the dimension of stress makes it possible to describe the scale effect of strength—the dependence of critical stresses on the radius of the pipe and the characteristic thickness of the layer, the delamination of which is associated with the minimum critical stress. The given estimate of this thickness indicates the most dangerous depth of location of a technological defect, such as nongluing, and can serve as a justification for interpreting the results of nondestructive testing of composite pipes. [ABSTRACT FROM AUTHOR]

The impact-echo (IE) method is effective for evaluating invisible defects. However, it might return misleading results when its signals are invalid. This challenge aggravates when the tests are conducted using robotic devices that automatically collect massive data. This study proposes an automatic method to eliminate invalid signals based on the ResNet model. First, the signals are visualized into two-dimensional images as the input for ResNet. The input data can then be classified into valid and invalid data via the ResNet model, which is trained with 11,290 signals and tested with 5664 signals. Finally, defects can be detected using the dominant frequencies of the valid-class data. A case study with IE data from two concrete bridges was employed to validate the feasibility of the proposed approach. The results indicate that the method can achieve an average accuracy of 90.6% for eliminating invalid signals and significantly improve the IE test accuracy.

A quasi-static approach for an interface damage model, incorporating Rayleigh damping for viscoelastic carbon fiber reinforced polymer composites, is introduced. The interface traction-relative displacement behavior is modeled using a thin adhesive layer, similar to cohesive zone models. The problem is solved numerically with a semi-implicit time-stepping method. The cohesive interface model, integrated into the Finite Element Method, was applied to determine the critical force away from the crack tip. Results showed that the numerical delamination under mode I conditions aligned well with experimental data for the cohesive zone formulations studied. The numerical example demonstrates the effectiveness of the proposed model.

The current work investigates the effects of drilling parameters on hole quality, including delamination and circularity, produced in hybrid composite materials consisting of neat glass fibre (NG) and hybrid glass fibre/Al-wire mesh in two distinct sequences, the first one being with Al-mesh in the outermost layers (AG) and the other with Al-mesh in the central layer (GA). The operation's process parameters are feed rate (F = 20, 40, and 60 mm/min), spindle speed (N = 1000, 2000, and 3000 rpm), and drill point angle (Ɵ = 90°, 120°, and 135°). Taguchi's L9 orthogonal array is used for the study. The optimal levels and effects of the process parameters were determined. Gray relational analysis (GRA) was employed to examine the complicated interactions influencing the results and ANOVA was used to evaluate the influence of process parameters. The results indicated that for all specimens, push-out delamination was more severe than peel-up. Circularity is minimized by using N = 3000 rpm, F = 20 mm/min, and Ɵ = 90°. At speed (N) of 3000 rpm circularity reduces by 83.5% and 76.5% compared to 1000 or 2000 rpm, respectively. Compared to other specimens, AG-specimen produced minimal delamination and circularity by an average of 6% and17.38%. The results of the confirmation test and regression model provide good agreement between the experimental and predicted results.

This study discusses the experimental results of the ballistic impact on thick-layered carbon fibre-reinforced polymer (CFRP), glass-based FRP (GFRP), and Kevlar-based FRP (KFRP) composite plates. Ten 10 mm plates of each type were manufactured via the hand lay-up and vacuum bagging techniques to produce plates with a thickness of 2 mm each, which were bonded together using epoxy adhesive and hot pressed at 75°C to obtain thick layered plates with a total thickness of 20 mm each. The specimen plates were tested according to the NIJ 0108.01 standard in a special firing room using a 9 mm G2 Elite handgun with a full metal jacketed round nose 9 mm × 19 mm Mu1-TJ bullets moving at a velocity of approximately 358 m/s. The results indicated that no total penetration occurred on any of the plates. The bullets were destroyed by impact, and the penetration depths of the CFRP, GFRP, and KFRP plates were 11.10, 9.95, and 22.22%, respectively. The layered structures in these plates appear to have changed the penetration behaviour compared with previous studies. In this study, delamination was the primary failure mode.