Delamination Characteristics Research Articles

AVG delamination: a cause of early cannulation arteriovenous graft dysfunction in hemodialysis patients

Background A series of cases have reported graft delamination as a rare complication of early-cannulation arteriovenous graft (ecAVG). The unique multilayer structure of ecAVGs contributes to the property of cannulation as early as hours after implantation, but on other hand it takes the risk of graft delamination. However, the underlying mechanism and management of graft delamination as well as its effects on the long-term patency of ecAVGs have not been systemically analyzed. Methodsz A retrospective study was conducted in a cohort of patients who required an ecAVG for hemodialysis (HD) access in our center between April 2017 and December 2021. The characteristics of graft delamination and the outcomes of its different treatments were analyzed. Results A total of 144 ecAVGs were established in 141 end-stage renal disease (ESRD) patients, including 124 (86.1%) Acuseal grafts and 20 (13.9%) Flixene grafts. During follow-up 24.5(11.5, 45.8) months, 11 (7.6%) subjects had graft infection with an incidence of 0.03 patient-year. Thirteen (9.0%) subjects had graft delamination at 9.3(5.0,12.4) months after ecAVG implantation, with an incidence of 0.04 per patient-year. ecAVG delamination was observed in both Acuseal grafts (0.037 per patient-year) and Flixene grafts (0.055 per patient-year). Thrombosis or venous hypertension was the most common complaints. Seven delamination was observed at 1.3 (0.1, 4.2) months after an endovascular procedure. The primary patency, primary assistant patency and secondary patency in delamination group were significantly lower than that in non-delamination group (p < 0.05). Post-procedure primary patency of group A (percutaneous transluminal angioplasty, PTA), group B (stenting) and group C (partial graft replacement, PGR) were 1.3 (0.45,4.22) months, 5.3 (3.05,6.85) months and 8.45 (4.78,14.53) months respectively (p = 0.029). Conclusions Graft delamination was not a rare complication of ecAVGs in this cohort. It significantly reduced the long-term patency of AVGs. PGR might be a more effective therapeutic way than endovascular treatments.

Investigation of Delamination Characteristics in 3D-Printed Hybrid Curved Composite Beams.

This study focuses on understanding the impact of different material compositions and printing parameters on the structural integrity of hybrid curved composite beams. Using the continuous filament fabrication technique, which is an advanced fused deposition modelling process, composite curved beams made of short carbon and various continuous fibre-reinforced nylon laminae were fabricated and subjected to four-point bending tests to assess their delamination characteristics. The results show that the presence of five flat zones in the curved region of a curved beam achieves 10% and 6% increases in maximum load and delamination strength, respectively, against a smooth curved region. The delamination response of a curved composite beam design consisting of unidirectional carbon/nylon laminae is superior to that of a curved beam made of glass fibre/nylon laminae, while the existence of highly strengthened glass fibre bundles is alternatively quite competitive. Doubling the number of continuous fibre-reinforced laminae results in an increase of up to 36% in strength by achieving a total increase in the beam thickness of 50%, although increases in mass and material cost are serious concerns. The hybrid curved beam design has a decrease in the maximum load and the strength by 11% and 13%, respectively, when compared with a non-hybrid design, which consists of some type of stronger and stiffer nylon laminae instead of short carbon fibre-reinforced conventional nylon laminae. Two-dimensional surface-based cohesive finite element models, which have a good agreement with experimental results, were also established for searching for the availability of useful virtual testing. The results from this study will greatly contribute to the design and numerical modelling of additively manufactured hybrid composite curved beams, brackets, and fittings.

Study on delamination characteristics and mechanical properties of cemented waste rock backfill with rubber aggregation

Since some phosphorus mines use raw ore as a product and do not conduct beneficiation around the mines. This makes it difficult for the amount of waste rock to prepare enough backfill for the filling of underground mined-out areas. Using rubber particles made of waste tires to replace part of the waste rock aggregate (WRA) can not only solve the problem of insufficient WRA, but also improve the environmental problems caused by the large accumulation of waste tires. However, due to the small density of rubber and high density of waste rock, the phenomenon of segregation delamination may occur in the cemented backfill, thus affecting the mechanical properties of cemented waste rock backfill (CWRB). To this end, the effect of rubber aggregate (RA) on the segregation delamination of CWRB was determined by using the section image analysis method of specimens, and the quantitative index of segregation delamination of cemented waste rock backfill with rubber (CWRB-R) was constructed. The mechanical properties and failure characteristics of CWRB-R were studied by acoustic emission (AE) test under uniaxial compression condition. The experimental results showed that the segregation delamination characteristics of CWRB-R were related to the mass concentration. The higher the mass concentration, the weaker the degree of segregation stratification of the aggregate, the more uniform the distribution of the aggregate, and the less the strength loss of CWRB caused by the incorporation of RA. The incorporation of RA in CWRB not only reduced the uniaxial compressive strength (UCS) of the backfill, but also caused more cracks to be produced during the failure process of the backfill, and the failure form changes from brittle failure to ductile failure.

Research on size effects in the low‐velocity impact (LVI) and compression after impact (CAI) characteristics of composite laminates

AbstractThe load‐bearing capacity and failure characteristics of composite structures are closely related to their dimensions. In this study, low‐velocity impact, ultrasonic non‐destructive testing, and compression after impact tests were conducted on composite laminates of varying widths to investigate the influence of size effects. Distinct impact response profiles and compression failure modes were characterized. The results indicate that under impact loading, the delamination threshold load (6700 N ~ 7200 N) and the knee‐point energy (40 J) are not affected by width. However, variations in width lead to differences in indentation depth, impact duration, peak load, delamination characteristics, and energy absorption. Furthermore, increasing impact energy further magnifies these differences. Under compression loading, wider laminates exhibit lower residual strength, with the influence of impact energy on residual strength decreasing as width increases. Importantly, the observed compression failure deformation mode transitions from localized buckling to widespread sub‐layer delamination‐induced compression failure. This suggests that changes in width alter the governing mechanical mechanisms of CAI failure. Consequently, the use of a single‐size laminate to represent both LVI and CAI processes is not recommended. Based on experimental results, the reliability of the equivalent damage method in predicting the residual compression strength of laminates of different widths was confirmed, providing valuable insights for practical engineering applications.Highlights Assess the variations in the low‐velocity impact process of laminates with different widths. Evaluate the delamination damage of laminates after impacts by ultrasonic C‐scan techniques. Investigate the effect of variation in widths on the compression behavior of laminates after impact. Validate the feasibility of equivalent damage modeling for calculating residual strength.

Vibration-based detection of non-overlapping delaminations in FRP beams using frequency shifts

Extensive research has been carried out on the detection of single delamination in fibre-reinforced polymer (FRP) structures using different structural health monitoring (SHM) approaches, including the vibration-based assessment methods. However, there are limited studies that on the detection of multiple delaminations, which could occur in many real-world scenarios. To address this research gap, this paper aims at developing a vibration-based method to assess the two non-overlapping delaminations in FRP beams based on changes in natural frequencies. A theoretical model of vibrating FRP beams with two non-overlapping delaminations was constructed and used for generating the multiple frequencies of the delaminated beams. By analysing the frequency shifts of the FRP beams before and after the occurrence of damage, the delamination characteristics (location and severity) can be inversely predicted using optimisation algorithms. The accuracy and efficiency of the frequency-based inverse algorithm were verified experimentally by modal testing on FRP beam specimens with one and two non-overlapping delaminations. It is interesting to observe that using the proposed vibration-based method, the single delamination in FRP specimens can also be predicted as two non-overlapping delaminations, with a major one matching the original single delamination and a minor one that can be neglected. Thus, the current vibration-based delamination assessment approach is flexible in identifying the prediction of either single or double non-overlapping delaminations in FRP beams, and therefore, it potentially has wider applicability than the existing single delamination detection methods.

Numerical analysis of delamination behavior in an impregnated HTS Roebel cable during cooling

The delamination failures of REBCO tapes inside impregnated HTS Roebel cables during cooling have been observed in existing experiments. In this work, the finite element analysis (FEA) based on the cohesive zone model (CZM) is applied to simulate the delamination failure within impregnated Roebel cable during cooling from 300 K to 4.2 K. The modified three-dimensional (3D) Roebel geometric model is adopted. Simplified calculation strategies are developed to reduce the modeling complexity and computational cost. As a result, delamination characteristics observed in previous experiments can be captured based on the numerical simulation. Parametric analyses indicate that the mismatch in thermal expansion between impregnating materials and REBCO tapes has a more severe impact on the delamination than the edge pre-crack during cooling. Meanwhile, the various levels of delamination damage among REBCO tapes are observed, and the effects of delamination strength on the numerical results are discussed.

Delamination Characteristics of Aluminum-Composite Bonds: Impact of Reinforcements and Matrices

Adhesion properties of metal-composite bonds are crucial in defining composite capability with other metallic components, and failures could lead to severe accidents. Hence, the study is aimed at the development and characterization of metal-composite bonds using different rigid adherends and adhesive materials (thermoset and thermoplastics). Among natural fibers, jute was used, while aramid, carbon, and glass woven reinforcements were employed from synthetic fibers. A simultaneous comparison of both thermoset and thermoplastic matrices was done using epoxy, polypropylene (PP), and polyvinyl butadiene (PVB) as adhesive materials. Floating roller delamination characterization proved variation in adhesion qualities governing different failure modes by varying adhesive even in a single rigid adherend. The highest fracture toughness was observed for aluminum-jute bonds made with PP and PVB that was due to toughness of matrix and intralaminar failure. Carbon being brittle in nature showed the most fluctuated performance with a 90% difference between the highest value of carbon-PVB and the lowest value of carbon-epoxy. Thermoplastic matrices owing to plasticity offered overall more fracture toughness than brittle thermoset resin. Furthermore, intralaminar was the dominant failure mechanism in the jute-based bond made with thermoplastic matrix.

Analysis of Geometric Characteristics of Cracks and Delamination in Aerated Concrete Products Using Convolutional Neural Networks

Currently, artificial intelligence (AI) technologies are becoming a strategic vector for the development of companies in the construction sector. The introduction of “smart solutions” at all stages of the life cycle of building materials, products and structures is observed everywhere. Among the variety of applications of AI methods, a special place is occupied by the development of the theory and technology of creating artificial systems that process information from images obtained during construction monitoring of the structural state of objects. This paper discusses the process of developing an innovative method for analyzing the presence of cracks that arose after applying a load and delamination as a result of the technological process, followed by estimating the length of cracks and delamination using convolutional neural networks (CNN) when assessing the condition of aerated concrete products. The application of four models of convolutional neural networks in solving a problem in the field of construction flaw detection using computer vision is shown; the models are based on the U-Net and LinkNet architecture. These solutions are able to detect changes in the structure of the material, which may indicate the presence of a defect. The developed intelligent models make it possible to segment cracks and delamination and calculate their lengths using the author’s SCALE technique. It was found that the best segmentation quality was shown by a model based on the LinkNet architecture with static augmentation: precision = 0.73, recall = 0.80, F1 = 0.73 and IoU = 0.84. The use of the considered algorithms for segmentation and analysis of cracks and delamination in aerated concrete products using various convolutional neural network architectures makes it possible to improve the quality management process in the production of building materials, products and structures.

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

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

Low-velocity impact damage detection in cfrp laminates based on ultrasonic phased-array ndt technique

To investigate the delamination characteristics of CFRP laminates in Barely Visible Impact Damage (BVID) state, Low-Velocity Impact Tests (LVIT) and Non-Destructive Testing (NDT) were employed. The energy thresholds of six diverse ply-stacking sequences of laminates in the BVID state were established utilizing visual inspection and contact measurement methods. Ultrasonic phased-array NDT techniques were employed to evaluate quantitatively the magnitude of delamination damage from different viewpoints, including delamination area, shape, and trend variation. Furthermore, the impact resistance of laminates was qualitatively evaluated by analyzing the distinctive delamination damage forms of various specimens to identify the effects of the ply-stacking sequence. The findings of this study demonstrate that reducing the angle disparity between adjacent plies and minimizing the repetition of identical plies can mitigate delamination damage. Additionally, enhancing the ratio of ±45 and 0° plies can improve the flexural stiffness of the structure. Specifically, the ultrasonic phased-array NDT technique was shown to effectively detect delamination damage within the laminate in the BVID state.

Characterization of Electromechanical Delamination Behaviors in Practical REBCO Coated Conductor Tapes Under Transverse Tension at 77 K

In high-temperature superconducting coils, the high transport current density and magnetic field generate a large electromagnetic force on REBCO-coated conductor (CC) tapes. A large Lorentz force can cause interlayer delamination damage to the CC tape under radial or transverse tensile loads. The structural delamination characteristics of multilayered REBCO CC tape are essential for the fabrication of mechanically reliable CC coils. In this study, the electromechanical delamination behaviors of practical REBCO CC tapes were characterized using an anvil test method. Our recently established continuous critical current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurement system was used to minimize the test time and can directly evaluate the effect of the transverse tensile load on I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> behavior without time-consuming intermittent I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurements during testing. Characterization of the delamination mechanism, including damage initiation, was performed through scanning electron microscopy observation of the fractured sample. Two-parameter Weibull distribution analysis was used to specify the data scattering of the electromechanical delamination strength.

Different responses of wheel–rail interface adhesion and wheel surface damage induced by an out–of–round wheel tread

The out–of–roundness of wheel treads are an inherent degradation characteristic of the wheels of railway vehicles, and the interface behaviour of the wheel and rail caused by out–of–roundness features has essential research value in high–speed train running safety and quality. Sliding–rolling contact wear testing was conducted to evaluate the effect of the out–of–round wheel on the wheel–rail damage behaviour, by using a twin–disc setup. The effects of four wheels, three wheels of different eccentricities and one normal wheel were taken as a control group. The characteristics of the wheel–rail interface adhesion, wheel surface damage and compressive residual stress (CRS) distribution were compared and analysed. The results showed a dramatic increase in the fluctuation amplitude of the wheel–rail vertical force of the eccentric wheels, and the adhesion coefficient of the wheel–rail interface significantly decreased. Furthermore, eccentric wheels dramatically accelerate the wear loss of the rail used as a counterpart during wheel–rail rolling contact. The surface damage behaviour of the eccentric wheels is obviously different along the circumferential direction, and non–uniform wear was observed. The damage mechanism of the worn surface presented varying characteristics, which could be divided into a severely damaged zone (located at the maximum of the rolling radius rmax) and a slightly damaged zone (located at the minimum of the rolling radius rmin). The surface contact stress of the severely damaged zone was high, this finding can be explained by the extremely rough worn surface caused by the severe fatigue delamination characteristics and the initiation and propagation of fatigue cracks in the severely damaged zone. Furthermore, the values of surface hardness and residual stress were relatively low. By contrary, an adhesion layer was observed on the worn surface of the slightly damaged zone. The adhesion layer protects worn surface in the slightly damaged zone was relatively flat, and the CRS was relatively high.

Analisis Kekuatan Bending Komposit Lamina Serat Ijuk Anyam dan Serat Ijuk Acak bermatriks Polyester

The current automotive industry uses composite materials as an alternative material to replace metal or plastic, due to the advantages of composite materials that have biodegradable properties and support environmental sustainability. Composite materials can be used as car body protectors, as a protector composite materials must withstand compressive loads. Referring to this, the research will be carried out through flexural testing. Study aim is to analyze variations of fiber volume fraction effect to the flexural strength. Method of making composite materials using hand layup then press mold, variations in fiber volume fraction 25%, 30%, 35%, 40%, and 45%. Flexural testing is carried out according to ASTM D-790. The morphology analysis was also carried out on the fractures of result of flexural test. Flexural testing results show that the highest flexural strength is founded in the fiber volume fraction 50% and the lowest flexural strength is founded in the fiber volume fraction 25%, 724.4 MPa and 435.8 MPa, respectively. A suitable composition in the fiber volume fraction of 40% can produce an optimal bond between the matrix and the fiber. Observing the morphology of the fracture and the cross-section of the fracture flexural testing results, it was found that there were fiber fractures with the characteristics of fiber pullout and delamination in each test specimen.

Математическое моделирование потери устойчивости локальных расслоений, полученных в результате скоростного удара

Delamination of a composite may occur as a result of high-speed impact under the action of shock-wave unloading. Delamination could grow further under operation with the subsequent composite destruction. This paper presents analytical expressions for values characterizing the delamination critical loss of stability and describing their non-linear delaminating deformation resulting from the impact. Elastic characteristics of the thin-walled delamination of a multilayer package, elastic characteristics of separate layers included in it depending on the shear modulus, elastic moduli, Poisson ratio, thickness, and orientation angle of fibers of the unidirectional layer were determined. A technique for numerical simulation and calculation of the structural elements made of layered composite materials with allowable defects such as delamination was developed in the ANSYS Mechanical system to solve problems of the plates’ supercritical behavior.

Enhanced strength-ductility-toughness synergy in an HSLA steel with multi-gradient ultrafine grained structure by adopting a two-stage rolling coupling inter-pass ultra-fast cooling process

In this work, a multi-gradient ultrafine grain (GUFG) structured high strength low alloy (HSLA) steel was successfully prepared by adopting a two-stage rolling coupling ultra-fast cooling process. The heterogeneous microstructure with gradients in grain size, shape, and texture across the thickness direction of the GUFG HSLA steel was characterized by large area electron backscattered diffraction (LA-EBSD) technique, and the quasi-static tensile properties, dynamic Charpy impact toughness, and its anisotropy were evaluated at ambient temperature. Results show that optimal matching of strength and ductility can be attained in the GUFG steel compared to the ultrafine grain (UFG) and coarse grain (CG) uniformed grain-sized structures. Furthermore, the GUFG specimens have a significantly enhanced toughness under dynamic impact loading, which was, respectively, 1.6 and 5.9 times that presented in uniform UFG and CG structures when impacted along the rolling direction. The refined grains and synergistic deformation of heterogeneous microstructures can contribute to the high strength without compromising ductility and toughness in GUFG specimens. In addition, the GUFG, UFG, and CG structures all exhibit obvious anisotropy in mechanical properties, which originate from distinct microstructure, texture, and delamination characteristics. This work not only reveals that the quasi-static/dynamic fracture resistance can be markedly improved by heterogenous structure-design strategies but also provide a realistic preparation technology for the exploitation of superior steel for engineering applications.

Research on laser ultrasonic propagation characteristics and quantitative detection of delamination of carbon fiber composite

Aiming at the problems of low signal-to-noise ratio (SNR) and low detection accuracy in the non-destructive testing of composites with anisotropic and multilayer structure, the delamination detection of composite materials is studied by using the advantages of laser ultrasonic micro defect detection combined with phased array technology. Firstly, through finite element simulation, the propagation characteristics of laser ultrasound when the delamination evolves are obtained, and a time-modulated phased array laser ultrasound test platform is designed to improve the SNR and detection efficiency of the delamination signal. Then, a laser ultrasonic feature extraction method based on the improved Hilbert-Huang transform is proposed. It includes optimizing the decomposition process of CEEMDAN (Complete Ensemble Empirical Mode Decomposition with Adaptive Noise), searching for the sensitive IMF components through correlation coefficient between the decomposed signal and the original signal, and extracting the feature parameters by Hilbert transform. Finally, the maximum amplitude imaging of the delamination defects is performed using the extracted feature parameters. Experiments show that the proposed method can characterize the delamination characteristics with high accuracy, effectively solve the interference of resin layer on the delamination characteristic signal, and can visualize the delamination in composites.

Titanium nitride concentration and coordination effect with hexagonal boron nitride enhancing the reciprocating wear behavior of AZ91D alloy-based composites

The influence of TiN hard ceramic concentration and coordination effect of hBN solid lubricant particulates on reciprocating wear and friction behavior of AZ91D alloy-based magnesium matrix composites is investigated in this work. A unique stir-ultrasonication-squeeze casting procedure was employed to fabricate the composites. The fine dispersion of reinforcing particulates in matrix was examined using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM). The X Ray Diffraction (XRD) analysis confirmed the existence of reinforcements in composites and formation of intermetallic phases demonstrating the thermal stability of matrix reinforcement materials. The hardness of fabricated AZ91D/5 wt.% TiN (AT), AZ91D/5 wt.% hBN (AH), AZ91D/5 wt.% TiN/5 wt.% hBN (ATH), and AZ91D/10 wt.% TiN/5 wt.% hBN (ATTH) composites were increased by 18.37%, 8.14%, 11.68%, and 25.2% in comparison with as-cast alloy “A”. The tribo-properties of single and dual ceramic particles reinforced materials were investigated using a linear reciprocating tribometer at an unchanged sliding distance of 200 mm and stroke length of 10 mm under varied loads (7.5, 15, 22.5, and 30 N), reciprocating frequencies (2, 4, 6, and 8 Hz), and temperature conditions (50°C, 100°C, 150°C, and 200°C). Compared to material “A,”“ATTH” composite performs well in terms of wear behavior, with performance increasing by 42.63% and 54.33% respectively, under ambient and enhanced conditions. At low load, increased frequency accelerates material removal from the plate’s surface due to direct abrasion and plowing action caused by rough asperities on the counterface. The increase in applied load under high-frequency settings increases the pin’s contact pressure with the sample surface, which raises the temperature and causes the shallow grooves to severe delamination. At increased temperatures, the wear characteristics of intense oxidation, plastic deformation, and significant delamination were discovered on manufactured materials.

On the Mode I and Mode II Delamination Characteristics and Surface Morphological Aspects of Composites with Carbon-Thermoplastic Hybrid Fabrics and Innovative Liquid Thermoplastic Resin.

In the current research, the delamination behavior under Mode I and Mode II loading for the hybrid carbon-thermoplastic fabrics in conjunction with novel liquid thermoplastic acrylic Elium® resin processable at ambient conditions was studied. The experimentation by incorporating doublers methodology, studying the performance under Mode I and Mode II loading, and understanding failure mechanisms using surface morphological fractography is deliberated. Hybrid Carbon-Ultra-high molecular weight polyethylene (UHMWPP)/Elium® composite has shown a 22.81% higher GIC and a 22.2% higher GIIC than Carbon-UHMWPP/Epoxy composite. On the contrary, the Carbon_Ultra-high molecular weight polypropylene (UHMWPE)/Elium® has shown an 11.11% higher Mode I critical energy release rate (GIC) and a 7.58% higher Mode II critical energy release rate (GIIC) than Carbon_UHMWPE/Epoxy composite. Hybrid fiber reinforced thermoplastic composites have shown severe plastic deformation of the matrix, rough fracture surface, and micro-cracks on the de-bonding surface, extensive fiber bridging, and crack branching which contributed to the improvement in the delamination behavior. Hybrid fiber architecture is also found to be detrimental by inducing crack arresting mechanisms including the tortuous crack path and the resin-rich pockets path due to the mismatch of the size of the fiber yarns.

A Comparative Study on Drill Tool Effect on Vibration and Delamination Characteristics of FRPs

ABSTRACT Drilling is an inevitable process for component assembly which need appropriate control aiming damage reduction. To study such drill-induced damages, Glass and Natural fiber composites with unidirectional (11) and cross-ply lay-up (12) were drilled using Twist and Annular Core drill tool of varying diameters (6 and 8 mm). The derivative of modal analysis (natural frequency, damping) and delamination are the factors considered for the analysis. In the chosen laminates, maximum variation in the natural frequency was observed to be 8.98% in N12 and 8.60% in G12 for twist drill of 8 mm, whereas the core drill of 8 mm contributes to 0.51% and 0.54%. A similar trend was observed in damping factor showing a maximum variation of 26.98% (N12) and 11.30% (N12) with 8 mm twist and core drill, respectively. Similarly, the maximum delamination factor was observed to be 1 .62 and 1.30 with 8 mm core drill in G12 and N12 which is lower than the 6 and 8 mm twist drills. Further, twist drilling experiences both peel-up and push down delamination in N12, N11 which was eliminated by the core drill. Thus, core drill exhibits distinct advantages with reduced damage and retained structural properties.

Research on entrance delamination characteristics and damage suppression strategy in drilling CFRP/Ti6Al4V stacks

Carbon Fiber Reinforced Polymer (CFRP) and CFRP/Ti6Al4V stacks are now commonly used in the aircraft industry. In the integrated drilling process of CFRP/Ti6Al4V stacks, the entrance delamination defects of CFRP is often more serious than that in drilling single CFRP. Considering the anisotropy of CFRP, this paper analyzed the entrance delamination defects caused by the CFRP drilling phase and the influence of titanium alloy drilling phase on the evolution of entrance delamination defects of CFRP. A series of drilling experiments were carried out on CFRP and CFRP/Ti6Al4V stacks respectively. The causes and differences of entrance delamination defects in the drilling process of CFRP and CFRP/Ti6Al4V stacks were compared from the aspects of drilling force, temperature and titanium alloy chip formation. In addition, the entrance delamination defects suppression strategy called high and low frequency vibration-assisted drilling method (CVAD) in drilling CFRP/Ti6Al4V stacks was investigated. The results indicate that in the single CFRP drilling process, the entrance near 135° cutting angle of CFRP fiber presents slight type I and type III delamination defects due to the tool structure and fiber anisotropy. However, in the CFRP/Ti6Al4V stacks drilling, the thermal-mechanical effect of high temperature titanium alloy chips leads to the evolution of more serious type I elliptical delamination defects at the entrance of CFRP. By using CVAD method to reduce the titanium alloy chip size and drilling temperature, the entrance delamination defects of CFRP/Ti6Al4V stacks can be effectively suppressed. The findings of this paper can contribute to identifying the formation of entrance delamination defects in CFRP and providing guidance for improving the processing quality of CFRP/Ti6Al4V stacks.