Mechanical Properties Of Laminates Research Articles

Parametric analysis on explosion resistance of composite with finite element and artificial neural network

To analyze the factors influencing the explosion resistance of composite laminates subjected to explosive blasts in air, a finite element analysis (FEA) model was utilized. The out-of-plane displacement of composite laminates under far-field airborne explosions could be accurately simulated based on the model. Additionally, an artificial neural network (ANN) model was established to train the data obtained from the FEA model, which allowed for accurate predictions of maximum deflection and its arrival time of laminates with varying parameters, such as impulse of blast, side length, thickness, and mechanical properties of laminates. The results highlighted that the thickness and side length of the composite laminates were critical factors affecting the deformation of laminates under explosive blasts. This research provided a valuable insight aimed at optimizing the design of composite structures to enhance their explosion resistance.

Evaluation and Defect Detection in L-Shaped GFRP Laminates by Infrared Thermography.

Glass fiber-reinforced polymer (GFRP) laminates are used in many applications because of their availability, high mechanical properties, and cost-effectiveness. Fiber defects in the form of waviness or wrinkles can occur during the production of multilayered laminates. When curved laminates of significant thickness are produced, the likelihood of such defects increases. Studies have confirmed that fiber deformation during manufacture leads to a reduction in the mechanical properties of laminates. Therefore, early detection of such defects is essential. The main part of this paper deals with research into the possibility of using active infrared thermography to detect wrinkles in curved multilayered GFRP laminates. The size of the artificial wrinkles was assessed by analyzing scans and microimages. The shape deformations of the samples were evaluated by comparing the samples with the mold and the assumed nominal shape. The influence of the out-of-autoclave manufacturing process on the reduction in wrinkles formed without significantly affecting the internal structure of the laminate is presented in this work. This research demonstrated the ability to detect wrinkles in thick curved laminates using active infrared thermography. However, it also showed how the interpretation of the thermographic results is affected by the curvature of the structure, the lack of uniform heating, and the configuration of the thermographic setup.

Cure path dependency of damage resistance in interlayer toughened composite laminates subjected to quasi-static indentation and low-velocity impact

Cure cycle optimization reduces exotherms, defects and cycle times for thermoset composites, but may change the interlayer microstructure of toughened systems. The question remains, however, how the cure-dependent interlayer microstructure affects laminate mechanical properties. This work studies the effects of cure cycle heating rates on interlayer microstructure and damage resistance of interlayer toughened T800SC/3900-2 laminates, subjected to quasi-static indentation (QSI) and low-velocity impact (LVI). Results show that QSI damage resistance is affected by heating rate and interlaminar microstructure due to the cure-dependent delamination migration. Specifically, a lower heating rate causes separated particles, a thicker interlayer, and more fibre migration into the interlayer, which promotes delamination migration from toughened interlayer to brittle intralayer and consequently weakens the toughening effect. Less delamination migration retains the toughening effect for higher heating rates. In contrast, LVI damage resistance is independent of the cure cycle because delaminations remain in the toughened interlayer for all interlaminar microstructures.

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes.

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the forming pressure, the mass fraction of fiber is reduced and lots of air bubbles are trapped inside, resulting in low-quality laminates (low stiffness and strength). The wet hand lay-up/vacuum bag (WLVB) process for the fabrication of composite laminates is based on the traditional wet hand lay-up process, using a vacuum bag to remove air bubbles and provide pressure, and then carrying out the heating and curing process. Compared with the traditional hand lay-up process, laminates manufactured by the WLVB process show superior mechanical properties, including better strength and stiffness, higher fiber volume fraction, and lower void volume fraction, which are all benefits for composite laminates. This process is completely manual, and it is greatly influenced by the skills of the preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to finely describe the WLVB process, finely control steps, and quantify material ratios, in order to ensure the mechanical properties of laminates. This paper describes the meticulous process of the WLVB process for preparing woven plain patterned glass fiber reinforcement composite laminates (GFRPs). The fiber volume content of laminates was calculated using the formula method, and the calculated results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of the laminates were characterized using tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

Composite Laminates for Aerospace and Packaging Fields

Composite materials have become increasingly popular and widely used in the present world due to their unique combination of properties that cannot be achieved by any single material. In the current study the mechanical properties of composite laminates (Jute, palm and banana fibers) were fabricated by varying groundnut husk and seashell powders quantities (5, 10, 15 and 20gms) in epoxy resin using hand layup technique. In according to the ASTM standards, a mixture of Epoxy (LY556) and Hardener (araldite) HY951 is used. The ratio of epoxy to hardener is 10:1. The material will be properly mixed for some time before being used to create laminates. Samples were fabricated with different compositions of jute, palm and banana fibers. Tensile, Compression properties of laminates were analyzed by testing composite laminates on universal testing machine. In this context the weight ratio of groundnut husk to seashell powder is 2:1. Analysis states that both the powders have impact on the mechanical properties of laminates. The impact of groundnut husk powder is slightly more on the laminates mechanical properties (tensile, compression) when related to seashell powder.

Optimization of Process Parameters for Carbon Fiber Reinforced Polyamide 6 Composites Fabricated by Self-Resistance Electric Heating Technology.

As an energy-saving and efficient composites-forming technology, the properties of carbon fiber self-resistance electric (SRE) heating technology still need to be improved, which is not conducive to the popularization and application of this technology. To deal with this problem, the SRE heating technology was combined with a compression molding process to form carbon-fiber-reinforced polyamide 6 (CF/PA 6) composite laminates in this study. Orthogonal experiments of three factors (temperature, pressure, and impregnation time) were designed to study the effect of process parameters on the impregnation quality and mechanical properties of CF/PA 6 composite laminates and to obtain the optimized set of process parameters. Furthermore, the effect of the cooling rate on crystallization behaviors and mechanical properties of laminates was studied according to the optimized settings. The results show that the laminates possess a good comprehensive forming quality under process parameters using a forming temperature of 270 °C, forming pressure of 2.5 MPa, and an impregnation time of 15 min. The ununiform impregnation rate is due to the ununiform temperature field in the cross-section. When the cooling rate decreases from 29.56 °C/min to 2.64 °C/min, the crystallinity of the PA 6 matrix increases from 25.97% to 37.22%; the α-phase of the matrix crystal phase also increases significantly. The effect of the cooling rate on crystallization properties also further affects the impact properties; laminates with a faster cooling rate have stronger impact resistance.

Modeling the effect of automated fiber placement induced gaps based on serial layer scanned point clouds

The gap is one of the most common defects during the AFP process, which has a nonnegligible impact on the mechanical properties of laminates. This paper proposes a novel three-dimension reconstructive gap model based on the in-process serial layer scanned point clouds, which can characterizes the gap features inside the laminate and pre-determine the mechanical performance before the subsequent procedures. The measured point cloud will be transformed into eligible and processible formats and then be used to generate a finite element grid using the element-based material property assignment method. The local material properties and fiber orientation are defined by previously assigned classes and grid geometries respectively. The effect of gap size on the in-plane tensile strength and damage evolution of laminates is investigated and both the experimental and simulation results find that the ultimate strength and stiffness show a significant decrease with the increase of gap size.

Is Graphene Always Effective in Reinforcing Composites? The Case of Highly Graphene-Modified Thermoplastic Nanofibers and Their Unfortunate Application in CFRP Laminates.

Graphene (G) can effectively enhance polymers' and polymer composites' electric, thermal, and mechanical properties. Nanofibrous mats have been demonstrated to significantly increase the interlaminar fracture toughness of composite laminates, hindering delamination and, consequently, making such materials safer and more sustainable thanks to increased service life. In the present paper, poly(ethylene oxide) (PEO), polycaprolactone (PCL), and Nylon 66 nanofibers, plain or reinforced with G, were integrated into epoxy-matrix Carbon Fiber Reinforced Polymers (CFRPs) to evaluate the effect of polymers and polymers + G on the laminate mechanical properties. The main aim of this work is to compare the reinforcing action of the different nanofibers (polyether, polyester, and polyamide) and to disclose the effect of G addition. The polymers were chosen considering their thermal properties and, consequently, their mechanism of action against delamination. PEO and PCL, displaying a low melting temperature, melt, and mix during the curing cycle, act via matrix toughening; in this context, they are also used as tools to deploy G specifically in the interlaminar region when melting and mixing with epoxy resin. The high extent of modification stems from an attempt to deploy it in the interlaminar layer, thus diluting further in the resin. In contrast, Nylon 66 does not melt and maintain the nanostructure, allowing laminate toughening via nanofiber bridging. The flexural properties of the nanomodifed CFRPs were determined via a three-point bending (3PB) test, while delamination behavior in Mode I and Mode II was carried out using Double Cantilever Beam (DCB) and End-Notched Flexture (ENF) tests, respectively. The lack of a positive contribution of G in this context is an interesting point to raise in the field of nanoreinforced CFRP.

Damage characterization of CFRP laminates using acoustic emission and digital image correlation: Clustering, damage identification and classification

Damage mechanisms in composite laminates are quite complex, and it is necessary to perceive their effects on the degradation of laminate mechanical properties. This work employs acoustic emission (AE) and digital image correlation (DIC) techniques to describe the evolution of intra/inter-laminar damage modes in the CFRP laminates under in-plane/out-of-plane loading conditions. In this study, laminates of stacking sequences [900]8, [450]8, [450/−450]2s, and [00]8 under tensile load are investigated to distinguish the intra-laminar damages like matrix cracking, fiber–matrix debond, and fiber breakage. Double cantilever beam, end notch flexure, and mixed-mode bending specimens are used to characterize delamination failure in the laminate. An unsupervised k-means clustering technique is used to classify the AE data based on peak frequency and amplitude. The surface displacement and strain data are evaluated using the DIC technique to understand the damage evolution in the laminates. Post failure analysis is carried out using a digital microscope, and fractography studies are used to identify and assign the damages to different AE clusters. This investigation yields a taxonomy of damage modes, their sequence of occurrence, and failure strains that can be used for structural health monitoring and progressive damage modeling of composite laminates.

Identification of Multiple Mechanical Properties of Laminates from a Single Compressive Test.

In-plane elastic and interlaminar properties of composite laminates are commonly obtained through separate experiments. In this paper, a simultaneous identification method for both properties using a single experiment is proposed. The mechanical properties of laminates were treated as uncertainties and Bayesian inference was employed with measured strain-load curves in compression tests of laminates with embedded delamination. The strain–load curves were separated into two stages: the pre-delamination stage and the post-delamination stage. Sensitivity analysis was carried out to determine the critical properties at different stages, in order to alleviate the ill-posed problem in inference. Results showed that the in-plane Young’s modulus and shear modulus in elastic properties are dominant in the pre-delamination stage, and the interlaminar strength and type I fracture toughness in interlaminar properties are dominant in the post-delamination stage. Five times of property identification were carried out; the maximum coefficient of variation of identified properties was less than 1.11%, and the maximum error between the mean values of the identified properties and the ones from standard experiments was less than 5.44%. The proposed method can reduce time and cost in obtaining multiple mechanical properties of laminates.

Variational Stress Analysis of Laminates Containing Regions with Different Material Properties in Loading Direction

In this study, a variational stress analysis was performed on a laminate that contained regions with varying material properties in the loading direction. Investigation of material properties and damage behavior of laminates with fiber discontinuity (resin-rich region) has been the main motivation for this study. The analysis considered an arbitrary number of regions with different material properties. For simplicity, we assumed a plane stress condition or stress distribution, we assumed that the normal stress in the loading direction was constant along the direction of thickness in each ply. The admissible stress state that satisfied both equilibrium and boundary/continuity conditions was constructed with unknown functions that were determined using the principle of minimum complementary energy. The analysis was applied to laminates with single fiber discontinuity and with distributed fiber discontinuities. These results were compared using finite element analyses, which obtained good agreement. The results show the validity of this analysis, which can be used to investigate the effects of fiber discontinuity on the laminate mechanical properties and damage behavior in laminates with fiber discontinuities.

Multiscale analysis of multi-directional composite laminates to predict stiffness and strength in the presence of micro-defects

A methodology is proposed to incorporate spatial distributions of micro-defects within a three dimensional multiscale modeling framework for Carbon Fiber Reinforced Polymer (CFRP) composites to predict stiffness and strength properties of laminates for use in structural design and in establishing nondestructive inspection protocols. Defects in both the fiber and matrix due to variations in the manufacturing process for fiber reinforced composite laminates are considered. Stochastic sampling of micro-defects based on experimental data using Ripley’s K-function is proposed. Three different laminate void volume fractions are used. Spatial statistical analysis is performed for the micro-defects, and then a methodology is presented for predicting stiffness and ultimate strength of three multi-directional composite laminates with distributions of microstructural defects. The results indicate that, in addition to the volume of micro-defects that are present, the spatial distribution of the micro-defects plays a significant role in mechanical properties of laminates, especially the ultimate strength for which a 3.62% reduction is seen in the simulations of laminates containing distributions of micro-defects. Based on these results, it is recommended that the spatial statistics of micro-defects in manufactured composites be incorporated into both design criteria and nondestructive inspection criteria for composite laminates.

Damping and mechanical behaviour of composite laminates interleaved with rubbery nanofibers

The development of composite components with superior damping capacity is welcome in fields like automotive and aerospace for improving comfort and reducing composite damages. Here, a structural composite with improved damping and unaffected overall mechanical properties is presented. Vibration hampering is achieved by interleaving electrospun Nitrile Butadiene Rubber/poly(∊-caprolactone) (NBR/PCL) blend nanofibrous mats into epoxy unidirectional Carbon Fiber Reinforced Polymer (CFRP) prepregs. Three laminate configurations were produced using rubbery nonwoven layers with different thicknesses (5, 10 and 20 μm) for evaluating the effect of grammage layer on CFRP damping and mechanical properties. A preliminary thermomechanical behaviour of modified CFRPs was evaluated via Dynamic Mechanical Analysis (DMA), while the influence of both interleaved mat grammage and testing temperature was more deeply investigated via destructive three-point bending (3PB) analyses. Flexural elastic modulus and strength of rubbery-modified CFPSs are comparable to unmodified laminate. Some lowering occurs only at relatively high temperature when present the highest mat grammage.Damping behaviour was evaluated by single cantilever beam vibration tests using the advanced Modified-Coulomb-Model (MCM). The interleaved NBR/PCL mats improved the composite damping up to +77%, without significantly affecting the laminate mechanical properties, weight, and thickness.

Multiphase Flow Coupling Behavior of Bubbles Based on Computational Fluid Dynamics during AFP Process: The Behavior Characteristics of Bubbles during AFP Process

To investigate the mechanism of the effect of process parameters on bubble flow behavior during automated fiber placement (AFP) and the relationship between the bubble and voids, mechanical properties of laminates, this paper analyzes the multiphase flow coupling behavior of the bubble and fiber formation using computational fluid dynamics (CFD) and finite element (FE) method under different AFP process parameters. The effects of AFP process parameters on bubble characteristics and fiber deformation are then discussed, respectively, including bubble displacement, maximum cross‐sectional area, the lowest internal temperature of the bubble, bubble breakup, and maximum deformation of the fiber. Furthermore, the AFP and corresponding test experiments are performed to investigate the relationships between different bubble characteristics and void content, mechanical properties, mainly interlaminar shear strength (ILSS) and flexural strength (FS). The results show that the maximum cross‐sectional area of bubbles is closely related to the AFP process parameters. The FS and ILSS are positively correlated with the maximum cross‐sectional area. With the increase of bubble displacement and fiber maximum deformation, FS and ILSS are first increased and then decreased.

Characterization of banana and E glass fiber reinforced hybrid epoxy composites

In this paper Fibers of banana and Eglass used as a reinforcement because if its low cost and its abundancy. Normally density of fibre is calculated by using water displacement methods. Fiber were intially treated with 5% concentration of NaOH and NaCl solution to improve adhesion property between fibres. These fibers are again treated with Hardner -HY951. 20% and 30% of volume fraction of fibres are teken and fabricated using Hand lay up method for the dimension 300*300 mm2. Change in the volume fraction of FRC’s changes the value of young’s modulus by making material stiffer. The testing was carried out by the computer integrated universal testing machine (UTM) which has the capacity of 100KN Kalpak software is used for the data acquisition the testing. Specimen is cut into as per standards for Tension test, three point bending test and hardness test. Tensile and hardness tests are conducted on 30% of volume fraction of fibers (Banana and E glass). Results of tensile test is obtained experimentally results reveal that hybrid combination of banana and E glass fibers are 56% stiffer and intern increases the elasticity and UTS. It was observed that by combining the E-glass fabric with the banana fabric in the composite laminate mechanical properties of the laminate are improved.

Characteristics of the mechanical behavior of Ti–6Al–4V multilayer laminate under impact loading

Multilayer laminates comprising thirteen layers of Ti–6Al–4V alloy were produced by diffusion bonding. The influence of the processing conditions on the microstructure and mechanical properties of laminates were determined. The multilayer laminates were tested at room and liquid-nitrogen temperatures under impact bending tests with recording of dynamic loading diagrams. The influence of the interfaces pores on the total energy of fracture, the energy of crack initiation and the energy of crack propagation was analyzed. The impact strength value of the laminate decreased by 1.7 times for the crack divider orientation, and it increased by 14 times for the crack arrester orientation with the relative length of pores increasing from 1 to 30%.

Comparative design of E-glass and flax structures based on reliability

Flax fibres are often documented as having equivalent properties to E-glass ones. Based on these comparisons they have been proposed as a suitable replacement for E-glass in structural applications. However, some recent experimental studies demonstrate that flax behaves differently to conventional composites at the structural scale, which indicates that the capabilities of flax need to be better understood at this scale. This paper therefore uses reliability analysis to generate flax structures with an equivalent safety to those in E-glass, accounting for the change in behaviour. An extensive literature review of flax laminate mechanical properties is performed to define their range and variations. These values are used to simulate probabilities of failure which demonstrate that flax structure needs to be 2.4 times heavier than the E-glass structures to have an equivalent safety. It concludes that flax fibres might be used in some applications but cannot replace E-glass in volume constrained structures.

Influence of consolidation process on voids and mechanical properties of powdered and commingled carbon/PPS laminates

Relations between autoclave consolidation process, microstructure and mechanical properties of thermoplastic composite laminates were investigated. For this purpose, two different carbon fibers/PPS semi-pregs were used for laminate manufacturing: a powdered fabric and a commingled fabric with stretch broken fibers. Laminates with [0°]6stacking sequence were consolidated in autoclave. Several consolidation levels were established by varying process parameters which are external pressure, vacuum level and consolidation duration. Microstructural characterization was performed by using matrix digestion and CT-scanning to identify void content and morphology. Laminate mechanical properties in tensile, bending, compressive and interlaminar shear were also assessed. External pressure increase by 0.5 MPa leads to void content reduction of 2.1% for powdered system and 5.4% for commingled system. The rising consolidation duration contributes slightly to void content decrease. Bending and interlaminar failure stress are the most sensitive to void level with a dependency on void size and location. Results acquired allow to identify main settings for optimized consolidation cycles which could be used for thermoplastic composite part manufacturing with complex shape.

A general B-Spline surfaces theoretical framework for optimisation of variable angle-tow laminates

This work deals with the optimum design of variable angle-tow (VAT) composites in the theoretical framework of B-Spline surfaces. The design problem is formulated as a constrained optimisation problem in the context of the multi-scale two-level (MS2L) optimisation methodology. The proposed approach aims at optimising all parameters characterising the VAT laminate at each pertinent scale (mesoscopic and macroscopic ones). In particular, this study focuses on the first level of the MS2L optimisation strategy that aims at determining, at the VAT laminate macroscopic scale, the optimum distribution of the laminate mechanical properties over the structure. At this stage, the behaviour of the VAT composite is described by means of the polar formalism and the spatial distribution of the polar parameters is represented through a set of suitable B-Spline surfaces. The expression of the gradient of objective and constraint functions is determined in a closed form by exploiting the properties of the B-Spline surfaces. Moreover, the effect of the discrete variables tuning the shape of the B-Spline surfaces (mainly the number of control points) on the quality of the optimum solution is investigated. The effectiveness of the proposed approach is tested through some meaningful benchmarks taken from literature.

The Influence of Uneven Temperature Distributions on Local Shear and Interlaminar Fracture Toughness Properties of a Thick Composite Laminate

Abstract Because wind turbine blade length has increased over the years, so have the root and spar cap thicknesses. Temperature gradients and residual strains related to the manufacturing process of thick laminates are factors that determine the final laminate mechanical properties. The aim of this study is to investigate the manufacturing process influence on shear and fracture toughness properties for an epoxy glass fiber-reinforced polymer. Epoxy-infused laminates of 84 layers (55–60 mm) thick were manufactured. The laminate was manufactured using vacuum infusion on a single-sided mold. Thermocouples and strain gauges were embedded at different thickness positions to monitor temperature and residual strain during the curing process. The laminate was manufactured using the sublaminate technique: with the help of peel plies at different thickness positions, sublaminates were extracted and separately tested as standard coupons. Shear coupons were tested according to ASTM D7078-12, Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method, and fracture toughness double-cantilever beam coupons were tested in Mode I according to ASTM D5528-13, Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites. Based on the extracted sublaminates, the relations between local curing cycles, residual strains, and the influence on the shear and fracture toughness were studied. This work reports temperature profiles and residual strain measurements that were monitored during thick laminate manufacturing. In addition, experimental data from shear and fracture toughness tests (static and fatigue) are correlated with the local residual strains and temperature measurements.