Effect Of Lay-up Research Articles

Quasi-Static Fracture Toughness and Damage Monitoring in Liquid Metal Reinforced Hybrid Composites

An experimental study is performed to investigate the quasi-static fracture toughness and damage monitoring capabilities of liquid metal (75.5% Gallium/24.5% Indium) reinforced intraply glass/carbon hybrid composites. Two different layups (G-0, where glass fibers are along the crack propagation direction; C-0, where carbon fibers are along the crack propagation direction) and two different weight percentages of liquid metal (1% and 2%) are considered in the fabrication of the composites. A novel four-probe technique is employed to determine the piezo-resistive damage response under mode-I fracture loading conditions. The effect of layups and liquid metal concentrations on fracture toughness and changes in piezo-resistance response is discussed. The C-composite without liquid metal demonstrated higher fracture toughness compared to that of the G-composite due to carbon fiber breakage. The addition of liquid metal decreases the fracture initiation toughness of both G- and C-composites. Scanning electron microscopy images show that liquid metal takes the form of large liquid metal pockets and small spherical droplets on the fracture surfaces. In both C- and G-composites, the peak resistance change of composites with 2% liquid metal is substantially lower than that of both no-liquid metal and 1% liquid metal composites.

Experimental investigation on failure mechanisms of hybrid steel/GFRP hat‐shaped beams under bending loading

AbstractThe bending failure mechanism and energy absorption characteristics of hybrid metal/composite structures are the keys to the side collision safety of automobiles. The purpose of this paper is to investigate the bending behavior and failure mechanism of hybrid Steel/GFRP hat‐shaped beams under three‐point bending. Firstly, both quasi‐static and dynamic three‐point bending tests were conducted on Steel, GFRP and hybrid Steel/GFRP hat‐shaped beams. Then, the effect of layups and loading speeds on the bending failure behaviors of GFRP hat‐shaped beams were investigated, and the five stages of the bending process of GFRP hat‐shaped beams were exposed. Finally, the failure mechanism of hybrid Steel/GFRP hat‐shaped beams under both quasi‐static and dynamic three‐point bending were investigated. It is found that the failure mechanism is related to the interaction effect between the Steel and GFRP parts in the hybrid Steel/GFRP hat‐shaped beam. In the bending failure process, the crack propagation in GFRP parts is delayed by the plastic deformation of the connected Steel parts, which improves the energy absorption and load carrying capacities of the hybrid Steel/GFRP hat‐shaped beam, and this improvement in the whole bending process is quantitatively exposed in this work. Besides, it is found that with the same impact energy, the load carrying capacity of the hybrid Steel/GFRP hat‐shaped beam can be increased by the loading roll diameter increasing.Highlights A bending process with five stages of GFRP hat‐shaped beams is exposed. The loading speed increases impact loads due to the strain rate strengthening. The interaction between Steel and GFRP improves the load carrying capacity. The load carrying improvement is due to crack propagation delay in GFRP parts. The greater loading roll diameter increases the load carrying capacity.

Out-of-plane shear strength of cross-laminated timber made of Japanese Larch (Larix kaempferi) with various layups and spans

Cross-laminated timber (CLT) is a promising construction material. When CLT is used for horizontal applications, shear stress occurs in the out-of-plane direction and can fracture the transverse layers owing to the rolling shear. The out-of-plane shear strength of the CLT can be evaluated by an out-of-plane loading test and is affected by the CLT layups and/or span conditions. In this study, we conducted out-of-plane loading tests on 3-layer 4-ply, 5-layer 7-ply, 7-layer 7-ply, and 9-layer 9-ply CLT made of Japanese larch (Larix kaempferi) under various spans and investigated the effect of layups and spans on the out-of-shear strength. The fracture modes of the specimens were classified into three types: shear fracture, shear fracture accompanied by bending fracture, and bending fracture. The out-of-plane shear strength of the specimens except for the 9-layer 9-ply ones decreased as the span increased, and then converged to a constant value (1.0–1.5 kN/mm2). In addition, the shear strength decreased exponentially as the number of laminae in the transverse layers increased and then converged to a constant value (1.0–1.5 kN/mm2). The out-of-plane shear strength of the 9-layer 9-ply specimens decreased as the shear span increased; however, the converged value with a longer span could not be calculated because the tests were conducted under only three-span conditions. The shear strength of 3-layer 4-ply specimens was lower than that of the other layups. The results of the Monte Carlo simulation of the shear strength of the laminae in the transverse layers showed that a model, which assumed that the minimum shear strength of the laminae in the transverse layers determined the shear strength of a specimen, tended to correspond with the decreasing tendency of shear strength with longer spans. The results showed that the weakest link model for the out-of-plane shear fracture of the CLT would relate to a specimen with long span.

Experimental investigation on translaminar fracture behavior of cross-laminated bamboo

Cross-laminated bamboo (CLB) is a bamboo-based construction product with bamboo's advantages, which are green, environmentally protective, and sustainable. However, bamboo is easy to crack. Structural elements in bamboo constructions are assembled onsite, making splitting cracks easily form at joints and bolt connections. Therefore, it is essential to assess cracked structure safety with fracture mechanics. However, rare studies are addressed on fracture properties of bidirectional laminated bamboo, especially the translaminar fracture resistance, which represents the ability to arrest a catastrophic crack in structures. This paper studies the translaminar fracture properties of CLB composite using three-point bending beam tests. Load-displacement and load-CMOD curve characteristics, fracture process, and the failure modes of bidirectional laminated bamboo are analyzed. The R-curve expressed by the energy release rate is calculated by three methods. Results demonstrate that the R-curves obtained by the three different methods show similar results. The methods to determine R-curves employed in this study are simple and can describe the translaminar fracture toughness of laminated bamboo. The methods are validated by comparing the traction-separation relations calculated from the R-curves to those measured by double-edge notched tests (DENT). A comparison of the bidirectional laminated bamboo's energy release rate to the matrix-dominated energy release rate of unidirectional laminated bamboo reveals that bidirectional fiber arrangement has a remarkable improvement on the toughening of laminated bamboo at and after crack initiation. Moreover, the lay-up effects of CLB are analyzed by relating the energy release rate results to the failure pattern of fractured specimens. It is found that fiber pullout/bridging caused by 90°direction crack propagation around fiber bundles is the dominant toughening mechanism of CLB. The lay-up sequence of 0° and 90° plies also has an effect on 90°direction crack propagation; therefore, it will influence the toughness of CLB.

Lay-up effect on the open-hole shear strength of composite laminates

The effect of lay-up on the open-hole shear (OHS) strength of quasi-isotropic carbon fibre/epoxy composite laminates was investigated. It was found that laminates with equivalent specific stiffness but different laminate lay-up, i.e. with different arrangements of plies and ply thicknesses, exhibit significant differences in ultimate OHS strength of up to 16.3% and 27.9% for the prepreg material systems IM7/8552 and T800/epoxy, respectively. Using Digital Image Correlation (DIC), X-ray Computed Tomography (CT), and Finite Element Analysis (FEA), it is shown that the lay-up dependent OHS strengths were associated with distinctly different failure modes. These lay-up dependent failure modes are challenging to predict. It is therefore proposed that the OHS test could be used for material screening, and as a new benchmark case for the development and validation of advanced progressive damage modelling frameworks for laminated composites, complementing the commonly used open-hole tensile (OHT) test.

Effect of layups on the mechanical properties of overlaid laminated bamboo lumber made of radial bamboo slices

Radial bamboo strips are being widely used for structural applications due to the higher yield and high strength. However, there was a sharp taper at the top of bamboo which made nodal diaphragm removed incompletely during the process of stripping. The residual bump could bring about poor bonding strength between adjacent radial bamboo strips. In addition, the traditional radial bamboo strips should be weaved before the next step of processing, which caused a lot of material wastes and consumed a lot of labor and time. In order to address these problems, a novel lumber product made of laminated radial bamboo slices was developed by the proper arrangement of core layer and surface layer. The major and minor directions of a panel were defined as the parallel- and perpendicular-to-its arrangement ones in the core layer, respectively. It was found that (1) the layups with double-layer bamboo mats and radial bamboo slices could produce better mechanical properties. The effective modulus of elasticity in major and minor direction was about 7032.5 MPa and 5016.0 MPa, respectively. The effective modulus of rupture in major and minor direction was about 81.0 MPa and 43.6 MPa, respectively; (2) the density distribution tended to be uniform, with a density of about 0.7 g/cm3 that was lower than other similar bamboo-based materials (about 1.0 g/cm3); and (3) the failures occurred in bamboo slices rather than along the bond lines, suggesting good bond quality achieved in this study.

Mode I translaminar fracture toughness of high performance laminated biocomposites reinforced by sisal fibers: Accurate measurement approach and lay-up effects

The present work performs a systematic experimental analysis of the translaminar fracture behavior of high performance biocomposites constituted by green epoxy reinforced by sisal fibers, by varying the main influence parameters as fiber concentration and lay-up. Despite the corrective function properly introduced to take into account the anisotropy as well as the use of the equivalent crack length, the study shows that the LEFM does not give accurate estimations of the fracture toughness, because the extension of the near tip damaged zone is higher than the singular dominated one. Accurate estimations can be obtained instead by the proposed modified area method that takes into account both the local damage and the fiber bridging that occurs during crack propagation, that lead to R-curves whose asymptotic values constitute the true fracture toughness of the biocomposites examined. The constancy of the damage mechanisms observed by varying the fiber concentration, allows the user to compute the fracture toughness of a generic laminate from the specific fracture energy of the unidirectional lamina. Finally, the relatively high fracture toughness of the examined laminates allows to state that they can advantageously replace not only other composites having lower toughness, but also metals as steel, aluminum and titanium.

Elastic Behavior of Lay-Ups Angles of Laminated Composite Beam with Material Property Grading

The article discusses the study of Vibration Analysis of Generally layered Graphite-Epoxy with lay-up [300 /500 /300 /500 ]. The finite element method is utilized in the study, to analyze the effect of lay-up on the natural frequency and comparing the results with the article[1]. Method: The study is done using Ansys. Graphite-epoxy is considered for the study. The model is prepared from SHELL 281 element which is well-suited for composite shells and sandwiched construction. The accuracy in modeling composite shells is governed by the first-order MindlinReissner shell theory. The element has 8 nodes with 6 degrees of freedom at each node translations in the x, y, and z axes, and rotations about the x, y, and z-axes respectively. Finding: The study concludes that the values of natural frequency decreased when increased the difference between angles of lay-up. Novelty/Applications: Vibration Analysis study has been done in aspects, like sandwiched beam in which different materials are sandhwiched in a layer by layer fashion. Many studies also covers composite material with lay-up in great detail, but there is acute study about the comparision of the different lay-up angles at given boundary condition. These articles cover the same at a greater extent, and conclude that the strength and capacity of composite beams can be enhanced not only by blending composites together, but also giving importance to the arrangement of layers of composite materials.

Interrogating failure mechanisms of notched composites through a discrete crack modeling approach

The prediction of compressive failure of composite laminates is generally more challenging than tensile failure, due to more complex failure mechanisms and nonlinear effects. This work presents an extension of a previously developed numerical framework utilizing discontinuous solid-shell elements and enriched cohesive elements for the simulation of damage growth of open-hole laminates under compression. Unlike tension, compressive loading may result in inclined matrix cracks due to localized shear damage. An approximate but efficient modeling technology was adopted by formulating an assumed vertical cohesive crack with the inclined crack coordinate system. The proposed approach explicitly represents damage as discrete cracks and leads to more accurate prediction of brittle and push-out failure patterns for sublaminate-scaled and ply-scaled laminates, respectively, including size and lay-up effects. These failure events of open-hole compression are believed to be captured with discrete crack analysis for the first time.

Effects of strain rate and high temperature environment on the mechanical performance of carbon fiber reinforced thermoplastic composites fabricated by hot press molding

The mechanical performance of continuous large tow carbon fiber reinforced polyamide 6 laminates fabricated by hot press molding was studied using quasi-static and dynamic tests. The effects of layup, strain rate and high temperature were discussed. The results show that the thermoplastic composites possess strain rate strengthening effects and high temperature weakening dependence. Different layup laminates exhibit different sensitivities. The elastic modulus difference of unidirection/cross-ply laminates decreases but that of unidirection/quasi-isotropic or unidirection/angle-ply laminates increases with the increasing strain rate. However, the failure strength difference changes insignificantly as the strain rate increases. The modulus or strength difference between unidirectional laminate and the other laminates decreases with the increasing temperature. The weakening effect of high temperature is stronger than the strengthening effect of strain rate for tensile mechanical properties. Furthermore, the failure behavior and mechanism were analyzed. These experimental data and research results could provide some insight for high-performance thermoplastic composites.

Three-dimensional modelling of interlaminar normal stresses in curved laminate components

This paper presents the interlaminar normal stress distribution across the width of L-shaped composite components in bending, with special emphasis on the free edge effects and the induced loading due to boundary conditions. As L-shaped composite components are becoming more commonplace in engineering applications, it is of vital importance to understand their failure mechanisms and stress fields. An extensive literature review reveals that interlaminar delamination is the critical failure mode for curved composite components. Despite this, most literature only provides a two-dimensional analysis of the interlaminar stresses and the free edge effects and asymmetry due to induced torsion are not considered. This paper uses three-dimensional finite element modelling to address the following with respect to L-shaped laminate components in bending: (i) radial stress due to the presence of curvature, (ii) effect of lay-up on the free edge effect, (iii) determining how induced torsion affects the interlaminar normal stress distribution. The necessity of using a three-dimensional model to analyse the interlaminar normal stress across the width of a curved composite component is discussed. It was concluded that using a two-dimensional model could underpredict the interlaminar normal stresses by up to 37% for the lay-ups analysed in this research.

J-integral evaluation of repaired cracks in AA7075-T6 structures subjected to uniaxial tensile stresses

Bonded repairs using composite patches over metallic structures have been evaluated as a cost effective method to increase the life of damaged structures. The J-integral is a widely applied fracture mechanics parameter relating to the energy release associated with crack growth and is a measure of the deformation intensity at the crack tip. In practice, the calculated J-integral can be compared with a critical value for the material under consideration to predict fracture. This study aimed at providing an overview of the behavior of a cracked plate of AA7075-T6 alloy repaired with a boron-epoxy patch bonded with FM73 Adhesive layer. The Finite Element Method (FEM) using Abaqus Software 6.14 predicted the performance. The results show a considerable decrease in the value of the J-integral. This is due to the beneficial effect of the patch on the stress state at the crack tip. The best results were obtained from a uni-directional composite fibres orientation of 0°, where the fibers oriented parallel to the direction of load. A parametric analysis has been carried out to evaluate the effect of lay-up, load variation and crack mouth opening on the J-integral. It was found that the crack mouth opening displacement (CMOD) was reduced by 90–97%.

Composite layup effect on the failure mechanism of single lap bonded joints

Single lap bonded joints with four different composite adherend stacking sequences were tested and numerically simulated. The aim was to evaluate the effect of the layups on the quasi-static tensile failure of the bonded joints. The study shows that increasing the adherends bending stiffness postpones the damage initiation in the joint. However, this is no longer valid for final failure. The ultimate load is influenced by how the damage progresses. For similar bending stiffness, a layup that leads to the crack propagating from the adhesive towards the inside layers of the composite increases the ultimate load. The failure mode is highly influenced by the orientation of the interface lamina in contact with the adhesive, such that, a 0° interface ply causes failure within the bond line, while a 90° interface ply causes failure inside the composite adherend.Finally, it is concluded that a quasi-isotropic layup may not be the best choice in terms of tensile joint strength. In order to improve tensile strength up to damage initiation, the layup should be optimized for bending stiffness, while up to final failure, a stacking sequence that yields to a complex crack path inside the composite can lead to higher ultimate loads.

Staking lay-up effect on dynamic compression behaviour of e-glass/epoxy composite materials: experimental and numerical investigation

Several industrial applications have exposed polymer matrix composite materials to a very high strain rate loading conditions, requiring an ability to understand and predict the material behaviour under these extreme conditions. Many composite aircraft structures such as fuselage, wing skins, engine nacelles and fan blades are situated such that impacts at high strain rates are a realistic threat. To investigate this threat, high velocity impact experiments and subsequent numerical analysis were performed in order to study the compressive loading of composite materials at high strain rates. Specimens are subjected with various orientations from low to high strain rates to determine the compressive material properties. Three fibre orientations such as: ±20°, ±60° and 90° of cubic geometry are tested in in-plane direction. The tests show a strong material sensitivity to dynamic loading and fibre direction. In the second part, the FEA results of the dynamic tests resulting in no damage appeared satisfactory. The FEA gives results which are in coherence with the experimental data. The improved understanding of these phenomena and the development of predictive tools is part of an ongoing effort to improve the long-term integrity of composite structures under dynamic loads.

Wave propagation analysis in viscoelastic thick composite plates resting on Visco-Pasternak foundation by means of quasi-3D sinusoidal shear deformation theory

In this research, the wave propagation in a viscoelastic composite thick plate resting on a Visco-Pasternak foundation is analyzed by means of sinusoidal shear deformation theory (SSDT). The viscoelastic properties of the plate are considered by using Kelvin-Voigt model. The material properties of composite plate are assumed viscoelastic based on Kelvin-Voigt model. The governing equations of motion are derived by Hamilton's principle. The analytical solution is applied to obtain the effects of the structural and foundation damping coefficients, wave number, aspect ratios, elastic properties and number of layers on the wave propagation behavior of the viscoelastic composite plate including the dimensionless phase velocity, cut-off and escape frequencies. The obtained results indicate that the dimensionless phase velocity and natural frequency decrease with increasing the damping coefficient. Also, it is observed that the effect of layups on the phase velocity becomes more sensible for small wave numbers. However, the effect of the damping coefficient on the dimensionless phase velocity and natural frequency is only observed at large dimensionless wave numbers.

Static strength and damage evaluation of high speed drilled composite material using acoustic emission and finite element techniques

In this paper, a very promising procedure to evaluate damage initiation and propagation of high speed drilled composite laminates base on Acoustic Emission (AE) and Finite Element (FE) techniques is proposed. First, the extent of delamination after high speed drilling was measured in unidirectional and woven composite specimens under different feed rate and cutting speed parameters. Three point bending tests were then performed to investigate the effect of drilling-induced delamination on static strength and the damage mechanisms in the drilled specimens. FE simulation including Cohesive Zone Modeling (CZM) and an improved Continuum Damage Mechanics (CDM) approaches was conducted to predict damage initiation and propagation of each distinct damage. Besides, AE was also used to notice the damage emergence and investigate these damage mechanisms. The results showed that the effect of drilling parameters on static strength is insignificant, however the main accomplishment of this work is illustrating a good consistency between experimental procedure, exhaustive FEM and AE techniques. FEM and AE can be used as efficient ways to predict damage initiation and failure of composite structures and also to evaluate damage mechanisms in drilled composite materials with two kinds of lay-up. Consequently, it is feasible to understand the effect of lay-up on occurring different damage mechanisms.

Analysis of the plastic zone under mixed mode fracture in bonded composite repair of aircraft structures

Material fracture by opening (mode I) is not the only failure criteria responsible for fracture propagation. Many industrial examples show the presence of mode II and mixed mode I + II. In the present work, numerical analyses of the three-dimensional and non-linear finite element method are used to estimate the performance of the bonded composite repair of metallic aircraft structures with a pre-existent damage by analyzing the plastic zone size ahead of repaired cracks under mixed mode loading, to assess the effect of the composite repair system on the plastic zone. The Von Mises stress is used to predict yielding of materials under this loading condition. The extension of the plastic zone, which takes place at the tip of a crack, strictly depends on many variables, such as the yield stress of the material, the loading conditions, the crack size and the thickness of the cracked component.The obtained results have demonstrated that the plastic zone ahead of the crack is significantly reduced by the presence of composite patch materials. Furthermore, parametric analysis has been carried out to evaluate the effect of lay-up and material system variation on the J integral.

Effect of Stacking Layup on Spring-back Deformation of Symmetrical Flat Laminate Composites Manufactured through Autoclave Processing

The residual stresses that develop within fibre-reinforced laminate composites during autoclave processing lead to dimensional warpage known as spring-back deformation. A number of experiments have been conducted on flat laminate composites with unidirectional fibre orientation to examine the effects of both the intrinsic and extrinsic parameters on the warpage. This paper extends the study on to the symmetrical layup effect on spring-back for flat laminate composites. Plies stacked at various symmetrical sequences were fabricated to observe the severity of the resulting warpage. Essentially, the experimental results demonstrated that the symmetrical layups reduce the laminate stiffness in its principal direction compared to the unidirectional laminate thus, raising the spring-back warpage with the exception of the [45/-45]S layup due to its quasi-isotropic property.

Investigation of the effect of temperature and layup on the press forming of polyvinyl chloride-based composite laminates and fiber metal laminates

Semi-crystalline thermoplastic-based composite laminates and fiber metal laminates have a narrow forming temperature window, which limits formability of these products. The intention of this study was investigation of non-melting amorphous polyvinyl chloride as a proper matrix to increase the formability and forming temperature window of these products. For this, [45/−45] and [0/90] layups of polyvinyl chloride-based composite laminates and fiber metal laminates were produced using the film-stacking procedure and later press formed into channel sections at six temperatures in the range of 80 to 200 °C. The effects of the layups and forming temperatures on the forming loads and spring back of the formed profiles were measured, and their effects on the fiber buckling, wrinkling, and delamination of the profiles were evaluated using optical microscope images. The effects of layups and forming temperatures on the deformation mechanisms were also analyzed using the grid strain analysis method. Of the fiber metal laminates, 160 °C was found as the minimum forming temperature, and for the composite laminates, 120 and 160 °C were found as the minimum proper forming temperatures of [45/−45] and [0/90] layups, respectively. Finally, the forming temperature windows and formability of polyvinyl chloride matrix composite laminates and fiber metal laminates were found higher than semi-crystalline matrices.

Effect of lay-up of sub-waveguide on transmission of So mode from main waveguide to sub-waveguides

This paper focuses on transmission characteristics of fundamental symmetric Lamb mode (So) at the junction of a main waveguide and sub-waveguides in composite laminates. Numerical simulations on transmission of So from the main to sub-waveguide revealed that transmission factors of the modes depend on stacking sequence of plies in the waveguides. Experiments were carried out to verify the observations made in numerical simulations. This work gives an insight on the transmission characteristics of So mode while it propagates from a healthy to a delaminated region in a composite laminate.