Plastic Laminates Research Articles

Delamination and thrust force mitigation during drilling of unidirectional carbon fibre-reinforced plastic laminate using magnetorheological elastomer

Abstract In new improvements to the aviation industry, carbon fibre-reinforced plastic (CFRP) is a buoyant material due to its noteworthy and application-friendly properties. The behaviour of transversely isotropic CFRP, which prompts drilling-induced delamination, causes critical damage that leads to the rejection of the final product. The cause of the delamination damage is the thrust force generated by the drilling tool during the machining operation. The present work proposes an indigenous approach to suppress delamination significantly using magnetorheological elastomer (MRE). The thrust force generated by the drilling tool is recorded for varying magnetic field strengths. Delamination damage was computed using the MATLAB script. Meanwhile, specific focus was given to studying the interlaminar mechanics of a drilled hole through scanning electron microscopy. The results show that nearly 45% of the thrust force is reduced using this MRE at a maximum field strength of 0.4T compared to a conventional one. The results are further supported by a 22% and 30% smoothening of the delamination at the hole’s entry and exit, respectively. Thus, this approach helps to reduce delamination during drilling.

Behavior of laminated timber portal frames reinforced with fiber-reinforced plastic laminates under cyclic lateral load

This study aimed to enhance the structural performance of a drift joint with a slotted-in steel plate using laminated timber made from small- to medium-diameter timbers. An analysis was conducted to compare and evaluate the structural performance and seismic behavior of laminated timber portal frames reinforced with fiber-reinforced plastic (FRP) laminates, such as glass fiber cloth (GFC), glass fiber reinforced plastic sheet (GS), and carbon-reinforced plastic sheet (CS), under low amplitude cyclic lateral loads, in comparison to unreinforced portal frames (UR). The reinforced portal frame, strengthened by FRP laminates, exhibited higher resistance to strength and stiffness strength degradation due to cyclic loading-induced degradation at low drift angles compared to the unreinforced frame affected by heterogeneous timber. The reinforced portal frame, particularly the GFC and GS, exhibited energy dissipation rates 32% and 17% higher than UR, respectively, making them the most effective in vibration damping. FRP laminates mitigated fiber direction cleavage from drift pin holes. The average maximum moment and average yield moment of the reinforced portal frame increased by 18% and 21%, respectively, due to the alleviation of joint failure. Finally, CS significantly affected the maximum moment, while GFC significantly influenced the yield moment.

An agent-based modeling approach for infection prevention predesign: simulating the spread of pathogens between humans and the environment in an Intensive Care Unit

ABSTRACT This study aims to investigate infection prevention measures in healthcare environments, focusing on the role of surface materials and hand hygiene compliance. To address this goal, an Agent-Based Model was developed to examine the combined effects of human factors and environmental interventions on the transmission of three types of healthcare-associated bacteria in an Intensive Care Unit (ICU). The model evaluates five key prevention measures: surface material selection, daily and terminal cleaning, hand hygiene compliance, and the use of personal protective equipment (PPE). Hand hygiene was chosen as the primary variable for model validation due to the extensive computational and field research available in this area. It also serves as a bridge between material design and human factors in infection transmission risk. Simulation data were compiled from each run by gathering the average value for the number of infected patients and contaminated environment over different scenarios. After validating the model, patients infectivity and environmental contamination associated with commonly used surface materials; namely quartz, copper-impregnated surfaces, plastic laminate, and stainless steel; were assessed under two scenarios of baseline and enhanced hand hygiene compliance. The findings underscore the importance of surface material choices in healthcare settings, suggesting that the most effective infection control strategies combine improved hand hygiene practices with the strategic use of materials in areas prone to bacterial contamination. These insights advise healthcare designers to adopt strategies that integrate both behavioral interventions and environmental components to minimize the risk of contamination and pathogen spread within healthcare environments.

Bonding positional accuracy of attachments and marginal adaptation of in-house aligners - A quality improvement laboratory study.

To evaluate the 3D accuracy of attachment positioning and the adaptation of aligners to attachments using in-house templates made with either polyethylene terephthalate glycol (PETG) or ethylene-vinyl acetate (EVA) and either pressure or vacuum thermoforming machines. Overall, 140 test specimens were resin-printed. Templates for the attachment bonding were made with 1-mm EVA or 0.5-mm PETG laminates. Orthodontic aligners were manufactured with 0.75-mm PETG. The thermoplastification process was carried out using either vacuum or pressure machines. The positional differences between the virtual and bonded attachments were assessed in the X, Y and Z coordinates. The marginal adaptation between the aligners and the attachments was measured. Minor inaccuracies in the positioning of the attachments were observed in all combinations of thermoforming machines and plastic laminates used to fabricate the templates, mainly in the superior-inferior (Z) dimension. PETG performed better than EVA in the anterior region (p < .05). No association was found between thermoplastification machines and the accuracy of the positioning of the attachments (p > .05). While small misadaptations between the aligners and the attachments were observed, the EVA templates performed better than the PETG templates. The inaccuracy of the attachment positioning and the misadaptation of the aligners to the attachments were slight. The vacuum and pressure thermoplastification machines showed no difference in attachment positioning accuracy. The PETG template was better than the EVA template in the anterior region, but the EVA attachments presented a better adaptation to the aligners than the PETG attachments.

Failure analysis of Fiber Metal Laminate channel section column under axial compressive pulse loading

The study aims to analyse the dynamic buckling phenomenon and assess the role of the stress tensor components in the failure process of a short Fiber Metal Laminate column under axial compressive dynamic loading. The investigation is focused on a channel-section profile composed of three aluminium layers and two doubled composite plies [Al/0/90/Al/90/0/Al]. The numerical analysis was performed on the finite element model, which was validated by experimental static buckling tests. Employing a progressive failure algorithm, this analysis incorporated the material property degradation method and Hashin’s criterion as the damage initiation criterion. Failure initiation in metal layers was based on the HuberMises-Hencky failure criterion. Based on the conducted analyses, it was concluded that the dominant forms of destruction in the FML structure are yielding in the metal layers due to excessive compressive stresses and the failure of the matrix in composite plies as a result of compressive and shear stresses. Through a thorough examination of the stress tensor components, critical stresses contributing to aluminum plastic deformation and laminate failure mechanisms were identified.

Mechanical and failure analysis of “outer single lap” adhesive joints of carbon fiber reinforced plastics under hygrothermal conditions

Carbon fiber reinforced plastics (CFRP)laminates are widely used in aircrafts. The laminates are often assembled into components by adhesive joints, which will be affected by elevated temperature and humidity during use, resulting in performance degradation. In this study, a compression test of “Outer Single Lap” adhesive joints of CFRP on the rear fuselage of a certain type of navigable aircraft was carried out to investigate the influence of hygrothermal conditions on their performance. The experimental environment includes the elevated temperature and wet condition (ETW) (71 °C, 85%RH) and Room temperature drying (RTD) (23 %, 30%RH). The test results show that RTD specimens have different stages, and the initial stage has good plasticity and no damage. However, when the load reached 50 %, the initial opening pattern damage occurred, which eventually led to the failure of the 20° opening. Compared with RTD samples, the compression properties of ETW samples decreased by 47.7 %, and the opening damage disappeared. Fracture features and stain analysis were performed. The findings suggest the fracture characteristic can change from a brittle fracture to a ductile fracture in different testing conditions, and the influence of the humid and thermal environment on the resin structural adhesive layer itself, the compression state of the carbon fiber laminates, the interface between the carbon fiber laminates and the resin structural adhesive layer should be fully considered in the design.

Analysis on power flow of Lamb waves generated by laser illumination in carbon fiber reinforced plastic laminates

Abstract The laser ultrasonics using guided waves excited by laser irradiation has attracted attention as an efficient non-destructive inspection method for carbon fiber reinforced plastic (CFRP) composite laminates. In this paper, to clarify the properties of laser-excited Lamb waves, we investigate the power flow of Lamb waves in an anisotropic CFRP laminate. The temperature rising caused by laser absorption is analytically calculated, and the derived thermal force is input to a finite element model to simulate the generation of Lamb waves. It is found that the power flow has an obvious directivity in a quasi-isotropic CFRP laminate. The power flow is smaller in the direction parallel to the carbon fibers of the surface layer and is larger in the perpendicular direction, but the maximum is in slightly different direction; this result was validated by an experiment. Such directivity pattern is determined by two factors: the distribution of thermal force and the stacking sequence of CFRP laminates. Moreover, we investigate the different simulation models (metal-coated CFRP and cross-ply CFRP) to discuss the influence of each factor on the distribution of power flow separately.

Effects of Carbon Fiber Reinforced Plastic Laminate on the Strength of Adhesive Joints

Carbon fiber composites are being widely considered for many classes of heavily loaded components. A common feature of such components is the need to introduce local or global loads into the composite structure. The use of adhesive bonding rather than mechanical fasteners offers the potential for reduced weight and cost. The use of carbon fiber reinforced plastics (CFRP) for the repair of steel structure is also advantageous, for example to avoid welding or bolting which can weaken structure and add fire risk. This study is based on adhesive bonded double lap shear (DLS) joints where the inner adherend is steel and the outer adherend is cross plies unidirectional (UD) CFRP. Overlap lengths of 25-125 mm with CFRP thickness of 3 and 6 mm were considered and two different orientation angles [0o,90o] and [90o,0o] laminates have been considered. The overall objectives of the paper are to investigate the delamination of the CFRP laminates within the DLS joints under quasi-static loading and both experimental and numerical techniques were used. The numerical study was based on 2-D model using strength-limit method, taking into consideration the UD properties of the plies and the resin layers separating these. As a result, it was concluded that the data obtained from 2-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the laminate markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite

Exploring the Impact of Drilling Parameters on Damage Morphology and Strength of Carbon Fiber-Reinforced Plastic Laminates

Exploring the Impact of Drilling Parameters on Damage Morphology and Strength of Carbon Fiber-Reinforced Plastic Laminates

Investigating Twist Drill Design Influence on Thrust Force and Surface Roughness in Drilling AFRP/ Al7075-T6 Stacks Materials

Drilling Aramid Fiber-Reinforced Plastic (AFRP) presents unique challenges when compared to drilling other composite panels. These difficulties arise from the high-toughness characteristics of aramid fibers, which exhibit a tendency for ductile deformation during the drilling process. This research explores the influence of drill bit design on the drilling process stack-up materials, which comprise Aramid Fiber Reinforced Plastic Composite Laminates (AFRP) and Aluminum Al7075-T6. Three distinct bit designs were employed in the experiment, conducted on a Computer Numerical Control (CNC) machine operating at a spindle speed of 2000 rev/min and a feed rate of 0.05 mm/rev. To measure thrust force during drilling, a dynamometer was integrated into the setup. Subsequently, a roughness tester was utilized to assess the hole surface roughness of the stack-up materials. For AFRP materials, the w-point drill design emerged as the optimal choice, reducing thrust force by approximately 5% to 13% compared to other drill bit designs. Conversely, for Al7075-T6 panels, the tapered web drill design demonstrated exceptional results, lowering thrust force by approximately 21% and 50% in comparison to burnishing and w-point drill bits, respectively. In terms of hole surface roughness, the burnishing drill type consistently produced the smoothest surfaces, boasting significant improvements of 44% and 82% when compared to the tapered web and w-point drill bits for AFRP panels. Similarly, for Al7075-T6 panels, the burnishing drill type consistently outperformed the tapered web and w-point drill bits by 74% and 88%, respectively, in achieving a superior hole surface finish. These findings underscore the critical importance of selecting the appropriate drill bit design to optimize thrust force reduction and hole surface quality when working with stack-up materials.

A constitutive model for shear thickening fluid (STF) impregnated Kevlar fabric subjected to impact loading

A constitutive model is presented herein to predict the response and failure of STF impregnated Kevlar fabric under impact loading on the basis of the progressive damage model for fibre reinforced plastic (FRP) laminates. In the constitutive model, the strain rate effect of shear strength is innovatively connected with the rheological property of STF. In order to verify the validity and accuracy of the model, numerical simulations of both ballistic and low-velocity impact experiments of STF impregnated Kevlar fabric are conducted. Furthermore, parametric study is carried out on the influences of impact velocity and rheological behavior of STF. It transpires that the numerical results using the constitutive model are in good agreement with the experimental data in terms of residual velocity, load-displacement curve, energy absorption, global deformation and failure patterns. It also transpires that, with the same impact energy, STF impregnated Kevlar fabric shows stronger resistance to lower velocity ballistic impact. In addition, the maximum viscosity and shear thickening interval of the STF have a significant effect on the ballistic performance of the STF impregnated Kevlar fabric.

Evaluation of matrix crack growth in interlaminar toughened quasi-isotropic carbon-fiber reinforced plastic laminates up to the very-high cycle regime by ultrasonic fatigue testing

It is time-consuming to conduct conventional hydraulic fatigue testing up to the very-high cycle fatigue (VHCF, N (number of cycles) ≥ 108) regime. Ultrasonic fatigue testing has been proposed as an accelerated alternative method. In this study, ultrasonic fatigue testing was conducted on interlaminar toughened quasi-isotropic carbon-fiber reinforced plastic (CFRP) laminates to evaluate the characteristics and mechanism of fatigue up to the VHCF regime. Hydraulic fatigue tests were conducted at the same stress ratio as a comparison. The resulting S–N diagrams showed a lower fatigue strength and different fatigue mechanisms for specimens subjected to ultrasonic fatigue tests compared with those subjected to hydraulic fatigue tests. The observed growth of the matrix crack density in each laminate layer was used to perform a shear-lag analysis to calculate the energy release rate considering off-axis matrix cracks. The results suggested different damage growth behaviors for specimens subjected to ultrasonic and conventional fatigue tests.

Stress and energy release rate analysis of cross-ply carbon fiber-reinforced plastic laminate with transverse cracks subjected to ultrasonic vibration using a variational approach

Application of carbon fiber reinforced plastics (CFRP) to structures that are subjected to increasingly high numbers of cyclic loads is expected to expand, so evaluation of fatigue properties up to the very-high cycle regime is essential to prove their long-term reliability. Conventional fatigue testing is not practical for such conditions owing to the excessive time required; ultrasonic fatigue testing, which can be performed at a frequency of 20 kHz, is an effective alternative. Stress distribution in ultrasonic fatigue testing differs from that in conventional fatigue testing because the specimen is resonated. The stress distribution of cross-ply laminates with transverse cracks subjected to resonance was calculated using a variational approach. The energy release rate was calculated based on the results of a previous study on transverse crack initiation. The results of the stress analysis are in good agreement with those of finite-element analysis. Quantitative evaluation of transverse crack initiation was also conducted.

Effect of nanosecond laser pulse width and energy on damage characteristics in carbon fibre reinforced plastic (CFRP) laminates

AbstractThis study explores the effects of laser pulse width and energy on CFRP laminates damage in laser bond inspection technology. Three testing programs were used, including varying laser energy while keeping pulse width constant, altering pulse width while maintaining constant power density, and modifying pulse width while keeping energy constant. The results show that when the pulse width remains constant, increased laser energy has a minimal effect on the initial damage location but leads to gradual interlayer delamination and fiber fracture propagation toward the impact surface. With constant laser energy, a specific threshold for pulse width is observed. When the laser pulse width is below this threshold, it exhibits a positive correlation with the damage characteristics of CFRP laminates, whereas when it exceeds this threshold, it shows a negative correlation. Power density correlates with damage when pulse width is constant, but there is no direct correlation when pulse width varies.Highlights CFRP laminates underwent laser shock tests with varying pulse widths. Power density is positively correlated with damage under specific conditions. There exists a specific threshold for laser pulse width. In single‐sided laser shock, initial damage spreads within a specified range.

Anti-bird-strike behavior of M40J carbon fiber reinforced plastic laminates

In this paper the anti-bird-strike behavior of M40J 12 K/7901 carbon fiber reinforced plastic (CFRP) laminates was investigated numerically and experimentally. Gelatin artificial birds were used to perform the bird-strike tests on various M40J CFRP laminated square plates with a wide range of impact velocities. Ultrasonic C-scan was utilized to measure the damage of the tested plates. Finite Element (FE) Models were created to simulate the bird-strike tests and the numerical predictions agreed well with the experimental results. The threshold values of bird’s impact velocity V0 when fibers begin to break were studied for 4 types of plates under normal and oblique bird-strikes to evaluate the anti-bird-strike capability of the laminates. The fiber damage after a flock-strike of two small birds was then investigated and the results suggest that the investigation of one large bird strike is more convincing in qualifying the anti-bird-strike resistance than that of a flock-strike of two small birds. Finally, a ply stacking sequence optimization in anti-bird-strike stiffness was obtained by the global optimization method.

Ballistic performance of thin CFRP laminates under complex in-plane preload

In this research, we explore the effects of complex in-plane quasi-static loads on the high-velocity impact response of Carbon Fiber Reinforced Plastic (CFRP) composite laminates, grounded in the practical context of various working loads combined with potential high-velocity impacts experienced by aircraft. The specific complex in-plane loads studied include uniaxial tension and compression, biaxial tension and compression, and a combination of tension and compression preloading. The results show that the complexity of in-plane preloads, along with pre-compression, reduces the ballistic limit velocity. Biaxial preloading, especially in compression, greatly compromises the specimen's ballistic resistance. The study also proposes a theoretical model based on energy conservation principles to predict the ballistic limit velocity of CFRP laminates under various preloading conditions. The research provides valuable insights for designing composite structures and highlights the importance of considering in-plane preloads in assessing thin CFRP ability to withstand ballistic impacts.

Strength degradation of GFRP cross-ply laminates in hydrothermal conditions

The changes in mechanical properties of glass fiber reinforced plastic cross-ply laminates as a result of hydrothermal aging were studied theoretically. The composite specimens have been immersed in distilled water at 25, 40, and 70 °C for 60 days for aging testing. Based on Fick’s law and the Arrhenius theorem, the moisture absorption data under different environments was analyzed, and the method for determining the diffusivity and the equilibrium moisture content was obtained. The relationship model between the moisture absorption behavior of the composite material and the ambient temperature was proposed and verified by finite element analysis. The mechanical behavior of the composites was studied by tensile, compression, and three-point bending tests. Under the condition of ultimate moisture absorption, the tensile, compressive, and bending strengths of the composite decreased by 31.663%, 12.948%, and 26.985%, respectively. A variety of empirical models were used for data analysis, which confirmed the strong correlation between strength degradation and moisture absorption of composite cross-ply laminates. The scanning electron microscope observation results of different moisture absorption levels showed that matrix cracking and fiber/matrix interface debonding caused by moisture absorption are the fundamental reasons for the strength degradation of the composites.

Achieving strong interfacial bonding of CFRP and magnesium alloy by modifying magnesium alloy surface via alkaline etching with EDTA addition

The interfacial properties of fibre metal laminates are closely related to the surface microstructure of metals. Herein, a hitherto unreported honeycomb-like micro/nano-porous structure was successfully fabricated on an AZ31B Mg alloy surface by incorporation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) into an alkaline solution and achieved excellent interfacial bonding property between AZ31B and carbon fibre-reinforced plastic. The addition of EDTA-2Na can promote the formation of etched pores. The growing nano-scale etched pores join together to produce micro-scale pores and ultimately lead to the formation of a micro/nano-porous structure. The 60 min etched AZ31B/carbon fibre-reinforced plastic laminate exhibits a bonding strength of 25.87 MPa, which is an increase of 350.7% compared to that of the untreated sample. The significant increase in bonding strength is mostly ascribed to composite mechanical interlocking by the micro/nano-porous structure and chemical bonding through the formation of MgCO3 and MgO1+X. In addition, the characteristics of micro-pores also affect the bonding strength.

Multi-objective optimization of composite sandwich structures using Artificial Neural Networks and Genetic Algorithm

Sandwich structures offer significant opportunities to improve the performance of many industrial applications such as aerospace, automotive, and marine. The design of a composite sandwich structure is often challenging because it is driven by the balance between the weight and cost of these structures. In this paper, a multi-objective optimization model using a Genetic Algorithm (GA) and an Artificial Neural Network (ANN) is presented to evaluate a new optimization approach in terms of weight and cost minimization for the composite sandwich structures. Classical lamination and beam bending theories were used, along with Monte Carlo simulation, to generate the design data for the proposed composite sandwich structure, which is applied as a floor panel for a high-speed train. Multilayer feedforward neural networks were used for predicting safety factors, cost, and weight of the designed structure based on the following inputs: core density, core thickness, face sheet materials’ combinations, and applied load. The trained Neural Network model was able to predict the considered results with a good performance metric, namely the coefficient of determination (R2 = 0.99) and the Mean Square Error (MSE = 1.3·10−5).Multi-objective optimization for cost and weight minimization was performed with a Genetic Algorithm using the derived ANN model. The obtained Pareto front provided several non-dominated optimal points leading to insights on the optimization process. The Finite Element Method (FEM) was used to model the key points of the optimal designs (i.e. the design with the lowest cost, weight, and Pareto optimal points). The FEM and optimization results had a maximum deviation of about 8.9%, indicating a good agreement between the two techniques.The newly elaborated methodology demonstrates a new approach for obtaining the optimum design of the investigated composite sandwich structure constructed from honeycomb core and laminated face sheets in terms the cost and weight. The study concluded that the use of Carbon Fiber-Reinforced Plastic (CFRP) or Fiber-Metal Laminate (FML) face sheets results in significant weight savings of about 59.5% and 48.6%, respectively, compared to an all-aluminum sandwich structure.

Study on the low‐velocity impact response of the repaired carbon fiber‐reinforced plastic laminates: Bonded versus scarf repair

AbstractExperimental and simulation studies of the response of bonded‐repaired and scarf‐repaired carbon fiber‐reinforced polymer laminates under the low‐velocity impact (LVI) were carried out. The center‐ and eccentric‐repaired laminates were prepared for experiments. The experimental results verify the validity of the finite element model in terms of the force response and different modes of damage. The effect of impact energy and the variation of repair position on the impact response of the laminate was investigated based on the benchmark model. The bonded repaired laminates have higher peak impact forces and lower energy absorption than the scarf‐repaired laminates; the damage of the bonded repaired laminate is mainly intralaminar damage and delamination damage of the patch; the adhesive of the scarf repair is prone to failure, leading to poor impact resistance. The relative positions of the impact point and the patch determine the impact response of a laminate repaired at different locations. The impact point at the edge of the patch has a detrimental effect on the repaired laminate. The impact point vertical position near the bottom hole edge of the parent plate in the scarf‐repaired case harms the impact resistance of the laminate.Highlights The low‐velocity impact response of bonded versus scarf‐repaired laminates was compared. Bonding repairs provide superior impact resistance to damaged laminates than scarf repairs. The risk of adhesive failure in scarf repair is significantly higher than in bonded repair. The relative position of the damage (repair) to the impact point critically influences the impact response. Impacts near the edge of the initial damage hole can cause severe damage to scarf‐repaired laminates.