Laminate Structure Research Articles

Investigation of effect of hygrothermal ageing on physical properties of graphene oxide / epoxy nano-composites

The present article investigates the effect of hygrothermal ageing on the physical and mechanical properties of graphene oxide reinforced epoxy/glass composites. Both neat and graphene reinforced composite laminate structures were immersed in hot artificial seawater with different temperatures namely 50 °C and 60 °C for 72 h and then tested for different physical and mechanical properties. Langmuir's model was employed for simulating the physical properties. Fick’s law was proposed for the diffusion coefficient and parameters as a function of temperature and graphene content. The results showed that diffusion coefficient, permeability and moisture absorption decrease with the addition of graphene oxide, but glass transition temperature and hardness increase with graphene. The water uptake of graphene oxide reinforced laminates has significantly decreased due to graphene oxide acting as a water barrier in laminates. The improvement in microhardness of graphene oxide reinforced laminates due to strengthened interface bonding and enhanced epoxy stability.

In Situ Consolidation of Thermoplastic Prepreg by Generating Harmonic Oscillations on the Consolidation Roller

Automation technologies such as Automated Fiber Placement (AFP) or Automated Tape Laying (ATL) are widely used in the aerospace industry today. However, these processes can still be further improved for higher productivity. Fiber-reinforced plastics allow the production of components with extremely high specific strength and stiffness. Regarding the automated manufacturing processes, the thermoplastic tape placement offers efficiency improvements compared to the nowadays more commonly used thermoset tape placement, especially through the substitution of the expensive and time-consuming autoclave process. The consolidation of thermoplastic Prepregs is achieved with an elastic or rigid roller according to the current state of the art. The Prepregs must be consolidated precisely on the substrate or on top of each other. The most important process parameters for high-quality laminate structure with low porosity are the control of heat source, consolidation force, consolidation roll speed, and tape tension. The efficiency of the AFP process can generally be improved by increasing the speed of the consolidation roller. By increasing the speed of the consolidation roller, porosity is increased and mechanical properties of the laminate are reduced significantly due to the short contact time between consolidation roller and Prepregs. This study investigates a process that can reduce these challenges by increasing the contact time and force duration of the consolidation roller on the Prepregs. The consolidation roller in this study is additionally to be driven by the harmonic oscillations. The new method allows the consolidation roller to oscillate forward and backward during the fiber placement process. This creates another force vector in addition to the compressive force of the consolidation roller and increases the bonding strength between the layers.

Low-velocity impact behaviours of AFP manufactured fibre metal laminate structures

This study reports the findings on the impact behaviour of metal-composite structures. Carbon fibre/Epoxy composite laminates were manufactured by using the Automated Fibre Placement (AFP) technique. Subsequently, hybrid structures were fabricated by bonding fibre laminate and aluminium plate together. The hybrids were tested at low velocity impact energies to probe the role of AFP composite laminates on the performance of the hybrid system. Our findings show that the bonding of the composite onto aluminium plate increased the natural frequency (stiffness) of the system and its energy absorption capability by almost 40 %. It was also found that the fibre layout of AFP composite significantly improved the central deflection of the hybrid. For instance, the deflection of cross-ply hybrids was 15% less in comparison to their counterparts with unidirectional fibrous composites. Nevertheless, under the investigated energies, the fibre layout appeared to have a marginal influence on the peak contact force. Post-mortem examination showed that at an impact energy of 150 J there was no fibre failure observed in asymmetric FMLs with unidirectional composite laminates. Conversely, the fibre failure in cross-ply hybrids occurred at 150 J. This suggests that less energy is required to induce fibre failure energy in cross-ply hybrids when compared to their unidirectional hybrid counterparts. Furthermore, it was also found that substrate treatment was successful in preventing excessive delamination, even though its influence on the peak contact force was not significant.

Excellent tension properties of stainless steel with a 316L/17-4PH/17-4PH laminated structure fabricated through laser additive manufacturing

Laminated metal structures (LMS), which are metals with site-specific properties, exhibit great potential for practical applications. In this study, a stainless steel with a laminated structure of alternating 316L/17-4PH/17-4 PH layer is fabricated using a laser additive manufacturing (AM) technique. Heterogeneous structures in the LMS are observed in two distinct areas, the austenite area (AU) and the martensite area (MA), based on optical microscopy and backscattered electron images. In the electron backscattered diffraction images, the AU area can be divided into austenite and mixture layers, while the MA area represents the martensite layer. Owing to the AM fabrication process, heterogeneity of both the micro-hardness and chemical composition exists among the three layers, which leads to different austenite stabilities in each layer. The tension test results reveal an excellent strength-ductility synergy with stronger ultimate strength and larger elongation than the pure 316L structure produced by AM with the same printing process parameters. During tension testing, the laminated structure causes strain partitioning, which evolves with the applied strain and delays the strain localization process. Owing to the change in austenite stability compared with pure AM 316L, the transformation-induced plasticity effect (TRIP) is triggered successively, and the laminate structure extends the TRIP effect to large plastic strains. As a result, the present study verifies the potential of using AM design for LMS stainless steel and may offer a framework for re-exploring LMS materials and components.

CeO2/Ni-Al layered double hydroxide composite electrode for the enhancement of specific capacitance and capacitance retention performance

Layered double hydroxides(LDH) possessed excellent capacitive properties but with poor cycling performance and low specific capacitance at high current density. CeO2/Ni-Al LDH (NAHCe) composite was synthesized by a one-step hydrothermal method to improve the electrochemical performance Ni-Al LDH. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results proved the well distribution of cerium on the surface of the Ni-Al LDH laminate structure. The specific capacitance and capacitance retention after 1000 cycles of the optimal composite NAHCe-2.5 reached 879.63 F·g−1 at 1 A g−1 and 90.36% at 2 A g−1, which was higher than that of NAH (541.82 F·g−1 at 1 A·g−1, 62.9% at 2 A·g−1 after 1000 cycles) under the same conditions. The CeO2 particles loaded on Ni-Al LDH sheets effectively reduce the internal electrochemical resistance of the composite electrode which contributed to the improvement of the specific capacitance and capacitance retention performance of the electrode. The idea of CeO2/LDH composite for the enhancement of electrochemical performance could be of help for the synthesis of other new-type supercapacitors.

Loss of lamin-B1 and defective nuclear morphology are hallmarks of astrocyte senescence in vitro and in the aging human hippocampus.

The increase in senescent cells in tissues, including the brain, is a general feature of normal aging and age‐related pathologies. Senescent cells exhibit a specific phenotype, which includes an altered nuclear morphology and transcriptomic changes. Astrocytes undergo senescence in vitro and in age‐associated neurodegenerative diseases, but little is known about whether this process also occurs in physiological aging, as well as its functional implication. Here, we investigated astrocyte senescence in vitro, in old mouse brains, and in post‐mortem human brain tissue of elderly. We identified a significant loss of lamin‐B1, a major component of the nuclear lamina, as a hallmark of senescent astrocytes. We showed a severe reduction of lamin‐B1 in the dentate gyrus of aged mice, including in hippocampal astrocytes, and in the granular cell layer of the hippocampus of post‐mortem human tissue from non‐demented elderly. The lamin‐B1 reduction was associated with nuclear deformations, represented by an increased incidence of invaginated nuclei and loss of nuclear circularity in senescent astrocytes in vitro and in the aging human hippocampus. We also found differences in lamin‐B1 levels and astrocyte nuclear morphology between the granular cell layer and polymorphic layer in the elderly human hippocampus, suggesting an intra‐regional‐dependent aging response of human astrocytes. Moreover, we described senescence‐associated impaired neuritogenic and synaptogenic capacity of mouse astrocytes. Our findings show that reduction of lamin‐B1 is a conserved feature of hippocampal cells aging, including astrocytes, and shed light on significant defects in nuclear lamina structure which may contribute to astrocyte dysfunctions during aging.

Selective laser melting with changing input energy periodically for production of partially hardened laminate structure in H13 steel

We produced a sub-millimeter-order periodic laminate structure exhibiting different hardness values, phase constituents, and microstructures for an AISI H13 hot work tool steel using a selective laser melting (SLM) process under a combination of different processing conditions applied periodically and continuously (under the concept of “scan strategy”). SLM-scanning with a high energy input beam, which was periodically inserted once every 1.5 mm in the building direction in combination with a low energy input, results in the formation of deep quench-hardened areas and produces a laminate structure possessing different hardness distributions. The surface area (corresponding to the top area) of the SLM product consists of untempered hard martensite because of the rapid cooling of the final heated layer. The local hardened area (corresponding to the intermediate area) and the surrounding area (corresponding to the matrix area) are subjected to tempering due to subsequent reheating to different degrees during the SLM process. Microstructures in all the regions of the top, intermediate, and matrix areas in the laminate structure consist of α'-martensite and austenite (γ) phases. A large amount of retained austenite is also present in the matrix area. The difference in hardness, depending on the area in the laminate structure, is caused by the difference in dislocation densities (related to the degree of tempering depending on the area) and the different amounts of retained austenite. Thus, the results of this study suggest a methodology as well as optimum SLM process conditions (by the “scan strategy”) for producing the laminate structure by controlling the difference in the degree of tempering and altering the Vickers hardness.

Ultrasonic autofocus imaging of internal voids in multilayer polymer composite structures

Multilayer polymer composite structures have been playing important roles in various fields, but the voids inside are not allowed in most scenarios. Ultrasonic technology has been widely used to inspect voids in concrete and metal structures. However, the application of ultrasonic imaging in polymer composite structures is severely blocked by the coating and lamination structures and unstable manufacturing induced sound speed variations. In this paper, a method to autofocus imaging of internal voids in multilayer polymer composite structures with ultrasonic phased array is firstly proposed. The method processes the full matrix capture (FMC) and focuses all voids in the multilayer structure automatically without the prior information of the speed of sound (SOS). The method utilizes the focus criterions to evaluate the focusing quality and then estimates the SOS with differential evolution layer by layer from surface to deep, which improves the robustness and computational efficiency. The method was examined with simulation data from three multilayer structures and well-focused all voids with position error less than 0.6 mm and SOS error less than 6 %. Moreover, the method was verified with the experimental data and focused voids with position error less than 1 mm.

Layered 3D structure derived from MXene/magnetic carbon nanotubes for ultra-broadband electromagnetic wave absorption

The widespread use of communication equipment has exacerbated the deterioration of the electromagnetic environment, urgently requiring the development of more efficient electromagnetic wave (EMW) absorption materials. Two-dimensional metal carbides are highly regarded for their characteristic structure and excellent electrical conductivity. Here, to break the single way of designing Ti3C2Tx MXene composites and to compensate for their lack of magnetic loss capability, an attempt was made to prepare composites with magnetic NiCo/Carbon nanotubes (CNTs) modification to achieve EMW absorption. Such CNTs-encapsulated Ni and Co metal particles anchored in the matrix, coupled with a multilayer laminate structure, enable the composite to have enhanced EMW absorption. Remarkably, the NiCo/TiC/TiO/CNTs composites exhibit excellent EMW absorption performance at a filling level of only 14.2 wt%. The minimum reflection loss (RL) of −51.98 dB and the maximum effective absorption bandwidth of 7.76 GHz were obtained at thicknesses of 1.9 mm and 2.1 mm, respectively. In addition to this, the possible mechanisms involved in EMW absorption have been elucidated in detail. These results demonstrate an environmentally friendly and simple strategy for the preparation of EMW absorbers based on Ti3C2Tx MXene substrate.

Removing fiber orientation uncertainty from the finite element model of a composite lamina with direct updating algorithm

In this paper, a direct updating algorithm is proposed to remove the uncertainties present in the simulated/analytical finite element (FE) model of a composite material lamina. There are number of possible uncertainties present in the composite materials such as its constituent properties and its orientations, boundary conditions and its assumed dimensions etc It is observed from this analytical study that the uncertainty present in the fiber orientation in the matrix put its direct effect on the modal-model (natural frequencies and corresponding mode shapes) of the composite material lamina. The direct updating algorithm has been already used for many isotropic structures. However, for anisotropic structures like composite materials, the application to accurate the simulated-finite element model by using finite element model updating techniques is a new area of research. In this regard, to remove these uncertainties from the simulated-finite element model of a composite lamina, the application of direct updating algorithm is proposed. It is observed from the present study that by updating the mass and the stiffness matrices through direct updating algorithm, the vibration pattern of the mode shapes are updated. It is found that the maximum percentage error in the constituent properties and in the fiber orientation is 22.58% and 100% respectively that are reduced to 0% in the modal-model of the lamina by the application of direct updating algorithm. This represents the novelty of the application of direct updating method for composite lamina structures. The overlay of frequency response function (FRF) curves are plotted to authenticate the results. Also, it is found that the application of the direct updating algorithm increases the tracking performance of the simulated FE model response when excited at different resonant frequencies.

Predicting interlaminar damage behaviour of fibre-metal laminates containing adhesive joints under bending loads

This study includes experimental and numerical investigations on fibre-metal laminate structures containing adhesive joints under static bending loads. Experimental tests were carried out on Glare® 4B specimens manufactured in-house and containing doubler joint features. Numerical analyses were performed using Abaqus software including damage in the glass fibre reinforced polymer layers, ductile damage in the resin pockets (FM94 epoxy) and plasticity in the metal layers. A new cohesive zone model coupling friction and interfacial shear under through-thickness compressive stress has been developed to simulate delamination initiation and growth at the metal/fibre interfaces with the adhesive joint under flexural loading. This model is implemented through a user-defined VUMAT subroutine in the Abaqus/Explicit software and includes two main approaches, firstly, combining friction and interfacial shear stresses created in the interlaminar layers of the fibre-metal laminate as a result of through-thickness stresses and secondly, considering elastic-plastic damage behaviour using a new cohesive zone model based on the trapezoidal law (which provides more accurate results for the simulation of toughened epoxy matrices than the commonly used bilinear cohesive zone model). Numerical results have been validated against experimental data from 4-point bending tests and a good correlation observed with respect to both crack initiation and evolution. Delamination and shear failure were noted to be the predominant failure modes under bending stresses as expected. This is due to the higher mode-II stresses introduced during bending which cause different damage evolution behaviour to that seen for axial stresses. Finite element results revealed that both friction and shear strength parameters generated from through-thickness compression stresses have a significant effect in predicting damage in fibre-metal laminate structures under this type of loading.

Core Cracking in Advanced Organic Substrates Due to Free Edge Effect at Cold Temperatures

Advanced FPGAs utilizing substrates with thick organic core showed substrate core cracking after thermal cycling. These substrates are laminate structures with a core made from stacked layers of glass fiber and resin with routing layers made of copper and dielectric build-up polymer. This type of cracking typically occurs on the glass fiber-resin interface, can penetrate several millimeters and across thru-vias to cause electrical failure, and was found on several test vehicles, four of which are detailed here. This work observed numerous examples to identify the characteristics of the cracking and notes the best observation practices. We hypothesize this cracking is due to free edge effect at cold temperature. Since the free edge cannot have normal stress, a large out-of-plane stress exists at the edge and concentrates at the corner. Models were built to study the effects of various package parameters on the failure mode. The primary contributions to the free edge effect are the low-CTE glass fiber, the high-CTE resin, and the high-CTE build-up layers. The trend toward lower CTE substrates has demanded lower CTE glass fiber material, which exacerbates this problem. Increasing complexity of routing demands additional layers, which also increases the out-of-plane stress at the corner. Other less significant factors that increase the stress include lower resin CTE, higher build-up CTE, and decreasing core thickness. Thru-via placement and dicing optimization had small impact and substrate had negligible impact.

Study on the Flexural Design for Strengthening Reinforced Concrete Beams with Quasi-isotropic Laminate Structure Reinforcement

Study on the Flexural Design for Strengthening Reinforced Concrete Beams with Quasi-isotropic Laminate Structure Reinforcement

Regression analysis of bonding strength of sprayed coatings based on acoustic emission signal

Abstract The aim of this paper was to obtain the regression equation of the bonding strength of sprayed coatings vs. acoustic emission (AE) signal. FeCrBSi coating, Al2O3-40 wt.% TiO2 (AT40) coating and Al2O3 coating were prepared using an atmospheric plasma spraying system. The microstructures and properties of the coatings were characterized. The coatings exhibited typical laminate structure with low porosity and good bonding interface. The AE signals during indentation testing were abstracted and investigated. AE energy was more sensitive to the coating cracking failure than AE amplitude. Moreover, the energy of AE burst signal had a close positive relationship with coating bonding strength. The distribution characteristic of AE peak energy was discussed based on the Weibull distribution. The best regression equations for the three coatings were obtained to predict the bonding strengths of sprayed coatings based on AE burst signal energy for similar coating/substrate systems.

Heat insulating materials based on vermiculite

Vermiculite, a hydrated Mg/Al/Fe silicate mica-like clay mineral with a laminate structure. Vermiculite is a very versatile material. It has a remarkable ability to expand to many times its original volume (exfoliation) when heated (>300°C). The majority of applications call for vermiculite in its exfoliated form, and it has a wide range of applications that take advantage of its significant properties such as low bulk density, low thermal conductivity, odor-free, chemical inertness, easy handle and fire resistance. These properties make vermiculite a promising material for use as high-temperature insulating refractory material in the metallurgical industry.

Enhancing Impact Energy Absorption, Flexural and Crash Performance Properties of Automotive Composite Laminates by Adjusting the Stacking Sequences Layup

In response to the high demand for light automotive, manufacturers are showing a vital interest in replacing heavy metallic components with composite materials that exhibit unparalleled strength-to-weight ratios and excellent properties. Unidirectional carbon/epoxy prepreg was suitable for automotive applications such as the front part of the vehicle (hood) due to its excellent crash performance. In this study, UD carbon/epoxy prepreg with 70% and 30% volume fraction of reinforcement and resin, respectively, was used to fabricate the composite laminates. The responses of different three stacking sequences of automotive composite laminates to low-velocity impact damage and flexural and crash performance properties were investigated. Three-point bending and drop-weight impact tests were carried out to determine the flexural modulus, strength, and impact damage behavior of selected materials. Optical microscopy analysis was used to identify the failure modes in the composites. Scanning electron microscopy (SEM) and C-scan non-destructive methods were utilized to explore the fractures in the composites after impact tests. Moreover, the performance index and absorbed energy of the tested structures were studied. The results showed that the flexural strength and modulus of automotive composite laminates strongly depended on the stacking sequence. The highest crash resistance was noticed in the laminate with a stacking sequence of [[0, 90, 45, −45]2, 0, 90]S. Therefore, the fabrication of a composite laminate structure enhanced by selected stacking sequences is an excellent way to improve the crash performance properties of automotive composite structures.

In-process monitoring of total organic volatiles during packaging film manufacturing using portable sensors

Organic solvents are widely used to facilitate ink and coating applications during the lamination of packaging substrates using adhesives. These solvents may remain sequestered between the laminated layers due to their slow diffusion through the laminate structure. This diffusion increases the potential for subsequent migration into food. The residual solvents (also referred to as volatile organic compounds (VOCs)) in laminated films are a significant concern due to heightened regulatory, consumer, and environmental pressure in domestic and global markets. There is a need to develop in-process detection systems for packaging materials as conventional benchtop laboratory analyses are time-consuming, costly, and do not allow for 100% inspection. This work demonstrates an in-process detection system for monitoring VOCs on a commercial food grade film lamination line. This in-process detection system consists of portable sensors including photoionization detector, semiconducting metal oxide sensor, infrared sensor, and electrochemical sensor. Correlations were found between the sensor signals generated from VOC detection during the lamination process and post-conversion benchtop gas chromatography-flame ionization detector (GC-FID) analyses for several solventless and solvent based adhesives. The correlation coefficients between the readings of the electrochemical sensor and GC data were 0.75 and 0.91 for the solventless and Matte Lacquer Ethyl Acetate based adhesive, respectively. Strong positive correlations were also found among the response signals from most sensors for each type of adhesive. Linear regression modeling was completed to predict GC results from the sensor data measured in-process during the lamination process. Results showed that the sensor readings can predict the total amount of VOCs detected by GC-FID with high coefficients of determination (R 2 > 0.90) for the solventless adhesive, ethyl alcohol based adhesive and ethyl acetate based adhesive formulation two. This study is among the first that utilized portable sensors for the detection of VOCs during the film lamination process in the food packaging industry and compared the sensor readings with the results of laboratory GC-FID. Findings of this study demonstrate potential to decrease cost of laboratory analysis, improve solvent and adhesive application control, and increase traceability with nearly 100% inspection of packaging substrates utilizing in-process monitoring technologies. This study also demonstrated viability of in-process regulatory compliance for laminated packaging. • Use of portable sensors including PID and EC were used to monitor VOCs released during film lamination. • VOCs detected by the sensors correlated with GC-FID concentrations for different adhesive formulations. • Mathematical models built predicted GC values from sensor readings for several adhesives.

A Study on the Bonded Flush Patch Repair Method for Aircraft Composite Solid Laminates

An evaluation was performed by applying repair technology of composite solid laminates to airframe composite structures. Damage and defects in the composite laminate structure of an aircraft are caused by events occurring during vehicle movement, such as lightning, tide collisions, and runway collisions during takeoff and landing along with damage caused during aircraft movement and maintenance, fuel injection, and cargo loading. After the damaged part was removed, the damaged composite solid laminated structure was repaired using the bonded flush patch repair method. In the bonded flush patch repair method, the molded patch is joined to the base material using an adhesive. To determine the damage caused by external impact, the test results of the repaired specimen and those of the specimen before damage were compared.

An FEM-Based Peridynamic Model for Failure Analysis of Unidirectional Fiber-Reinforced Laminates

To predict the mixed damage modes of unidirectional fiber-reinforced polymer (FRP) laminates under dynamic loading, an FEM-based peridynamic model is introduced in this paper. Based on its geometric structure and material composition, a long fiber lamina is considered a transversely isotropic medium as a result of homogenization at the meso-scale. The laminated structure is modeled by stacking surface mesh layers with arbitrary fiber angles along the thickness direction. The peridynamic bonds between Gauss points connect the separated elements. These bonds are classified as inner-layer bonds and inter-layer bonds. To represent the anisotropy of a laminate, the micro-elastic modulus of the inner-layer and inter-layer bonds is calculated from the anisotropic engineering material constants separately. To capture complex failure behaviors of laminate structures, an empirical damage model is proposed for the tension/ compression breakage of peridynamic bonds. This damage model can control the in-plane and delamination failure process. Benchmark tests are conducted to validate the elastic response of laminates under dynamic loading. In terms of damage analysis, the proposed model can capture the complex damage modes and resistive force of laminate structures.

Quality assessment and structural health monitoring of CNT reinforced CFRP and Ti6Al4V multi-material joints

Hybrid multi-material joints of titanium alloy (Ti6Al4V) bonded to carbon fibre reinforced polymer (CFRP) are really interesting for lightweight high-performance structures, i.e., aeronautical and marine applications. Co-bonding technique, in which the joining takes place at the same time as the manufacturing of the CFRP, could be a great solution for easy manufacturing fibre metal laminate (FML) and complex structures, or a time saving process. One of the biggest challenges in this type of multi-material structures is to be able to confirm the structural health in service. The present work deals with the use, as matrix, of an epoxy resin reinforced with multiwalled carbon nanotubes (MWCNT) for manufacturing of Ti-CFRP joints by co-bonding. The aim is the structural health monitoring (SHM) of these hybrid structures, enhancing their mechanical properties.The obtained results show an improvement of more than 140% in fracture resistance of the multi-material joints with optimal surface preparation, by incorporating CNT. Furthermore, electrical monitoring makes it possible to discern the quality of the manufactured joints, increasing their reliability and performance. Besides, the ability to localize crack propagation and stresses prior to joint failure has been confirmed, so CNT addition results in a powerful tool for SHM multi-material joints.