Types Of Layups Research Articles

Torque loading tests on the rolling shear strength of cross-laminated timber

In this study , torque loading tests on small shear blocks were performed to evaluate the rolling shear strength of cross-laminated timber (CLT). The CLT plates in the tests were manufactured with Mountain Pine Beetle-afflicted lumber boards and glued with polyurethane adhesive; two types of layups (five-layer and three-layer) with a clamping pressure 0.4 MPa were studied. The small block specimens were sampled from full-size CLT plates and the cross layers were processed to have an annular cross section. These specimens were tested under torque loading until brittle shear failure occurred in the middle cross layers. Based on the test results, the brittle shear failure in the specimens was evaluated by detailed finite element models to confirm the observed failure mode was rolling shear. Furthermore, a Monte Carlo simulation procedure was performed to investigate the occurrence probability of different shear failure modes in the tests considering the randomness of the rolling shear strength and longitudinal shear strength properties in the wood material. The result also suggested the probability of rolling shear failure is very high, which gives more confident proof that the specimens failed dominantly in rolling shear. It was also found that the torque loading test method yielded different rolling shear strength values compared to the previous research from short-span beam bending tests; such a difference may mainly be due to the different stressed volumes of material under different testing methods, which can be further investigated using the size effect theory in the future.

Postbuckling analysis of laminated composite shells under shear loads

The postbuckling behavior of laminated composite plates and shells, subjected to various shear loadings, is presented, using a modified 8-ANS method. The finite element, based on a modified first-order shear deformation theory, is further improved by the combined use of assumed natural strain method. We analyze the influence of the shell element with the various location and number of enhanced membrane and shear interpolation. Using the assumed natural strain method with proper interpolation functions, the present shell element generates neither membrane nor shear locking behavior even when full integration is used in the formulation. The effects of various types of lay-ups, materials and number of layers on initial buckling and postbuckling response of the laminated composite plates and shells for various shear loading have been discussed. In addition, the effect of direction of shear load on the postbuckling behavior is studied. Numerical results and comparisons of the present results with those found in the literature for typical benchmark problems involving symmetric cross-ply laminated composites are found to be excellent and show the validity of the developed finite element model. The study is relevant to the simulation of barrels, pipes, wing surfaces, aircrafts, rockets and missile structures subjected to intense complex loading.

Experimental study of compression after impact of asymmetrically tapered composite laminate

This paper presents an experimental study of CAI (compression after impact) of tapered composite laminate. Two types of layup with thickness changing from 4mm to 6mm are considered. A new CAI testing rig, suitable for the specimens and a brief description of impact damage are presented first. Then, the behavior of impacted specimens under compressive loading is discussed along with the effects of ply drop-off parameters (taper angle, ply drop-off disposition and configuration) and impact point location on the failure mechanism. Finally, the residual strength in CAI of tapered laminates is compared with equivalent flat laminates. The results show that compressive behavior of the specimens is mostly governed by a coupling between compression and bending, generated by the discontinuity of the neutral axis in the tapered region. Despite this difference of behavior with flat laminates, the presence of ply drop-off has little effect on the residual strength in CAI.

Experimental Strength of Woven Fabric Kenaf Composite Plates with Different Stacking Sequences

Awareness on implementing sustainable construction materials has risen significantly leading to increased renewable materials used commercially. Kenaf fibers are potentially used as composite reinforcements and combined with epoxy polymer to produce an advanced engineering material that may offer superior specific stiffness (and strength) to its density. Other advantages include renewability, easy during fabrication handling stage and relatively cheaper than commercial fibers counterparts. Current project aims to investigate mechanical strength of woven fabric kenaf composites coupons with different stacking orientations. Testing series under investigation includes different lay-up types with variation of plate thickness. Mechanical testing is conducted referred to relevant code of practice and associated damage observations during testing will be recorded. It is suggested that these materials are potential to provide an alternative reinforcing materials in composite fabrications and enhanced its applicability to a greater extent in local sector.

Stress Distribution of Bolted Joints With Different Lay-Up Types

A parametric study of the stress distribution in the composite plates is undertaken to show the effect of different lay-ups. Full 3-D elastic properties are required in the modelling. These properties are calculated using equations taken from the literature and derivation from simple Classical Laminate Plate Theory (CLPT). In previous experimental work, it was shown that tensile failure involved the development of a damage zone at the edge of the hole. In a double-lap joint, it is assumed that uniform stresses are exhibited throughout the plate thickness. Different lay-ups system give different tangential stress distributions and insignificant variation in the radial stress distribution along the hole boundary.

Notched Strength of Woven Fabric Kenaf Composite Plates with Different Stacking Sequences and Hole Sizes

Advantages of using kenaf fibres over synthetic fibres in composites manufacturing are relatively cheap, less abrasive and hazardous during handling, and renewable materials. Current work investigates parametric effects on notched strength of woven fabric kenaf polymer composites plates with variation of lay-up types, notch sizes and plate thickness. Testing coupons are prepared using hand lay-up technique and circular notch were drilled prior to mechanical testing. Stress concentration at the notch edge promotes micro-damage event as tensile loading was applied leading to crack initiation and propagations across the plate width. It is suggested that woven fabric kenaf polymer composites are potentially used in low and medium load bearing applications.

Non-Linear Thermal Stability Analysis of SMA Wire-Embedded Hybrid Laminated Composite Timoshenko Beams on Non-Linear Hardening Elastic Foundation

In the present study, non-linear thermal post-buckling analysis of hybrid laminated composite Timoshenko beams embedded with the shape memory alloy (SMA) wires resting on a non-linear hardening elastic foundation were studied. Mechanical properties of composite media are considered temperature-dependent. The theory of Timoshenko beams and von Kármán's strain-displacement relations are applied simultaneously in virtual work principles to derive the system of non-linear equilibrium equations. Various types of boundary conditions such as clamped, simply supported, and rolled edges were studied for edge supports. Generalized Differential Quadrature Method (GDQM) was utilized to discrete the equilibrium equations in space domain. Different types of lay-ups, such as symmetric and asymmetric, were considered. Post-buckling paths are depicted for different values of non-linear elastic foundation parameters, volume fractions, pre-strains of the SMA fibers, and boundary conditions. The one-dimensional thermo-mechanical constitutive law suggested by Brinson [1] is applied to model the SMA wires. Numerical results make it possible to recognize that increases in the volume fraction and pre-strain of SMA lead to a dramatic enhancement in thermal buckling and post-buckling capacity of the beam. Pre-buckling, buckling, and post-buckling behavior of the beam are totally different and this is due to variations among critical buckling, austenite start and finish temperatures. Due to the recovery stress of SMA wires, particular consequences are shown.

Influence of internally dropped-off plies on the impact damage of asymmetrically tapered laminated CFRP

This paper presents an experimental study of low velocity impact response of carbon/epoxy asymmetrically tapered laminates. The tests are realised at energy between 10 and 30J on two types of layup with multiple terminated plies. The type and localisation of damage are analysed using C-scan and micrographs. Then, the data is compared with the response of corresponding respective plain laminate. The effects of some tapering parameters (taper angle, drop-off disposition and configuration) on the impact damage mechanisms are also investigated. Very similar impact damage phenomena are found between tapered and plain laminates. The presence of material discontinuity due to the resin pocket affects less the damage mechanism than the structural difference between the thick and the thin sections.

Bird strike analysis on a typical helicopter windshield with different lay-ups

In the current paper, bird strike to a typical helicopter windshield is investigated using smoothed particles hydrodynamic (SPH) finite element method. Five types of lay-ups in a windshield (single layer stretch acrylic, single layer glass, two-wall cast acrylic, acrylic with Polyvinyl butyral (PVB) interlayer and glass with PVB interlayer) is considered and in each case the thickness which prevents the bird from perforating the windshield is calculated. Since helicopters can have lateral movement in addition to their longitudinal movement, the effect of incident angle on the integrity of windshield is also investigated. Simulations showed that among the five cases presented, glass with PVB interlayer can be the best choice for being used in windshield against bird strike. Another conclusion is that for the same initial velocity, the angled impact can cause more damage in the windshield than the direct impact.

Factors influencing properties of parallel laminated binderless bonded plywood manufactured from rotary cut birch (Betula pendula L.)

In this study, the moisture resistance properties of self-bonded plywood were enhanced by thermal modification. The plywood was prepared without any adhesive, using only heat, moisture and mechanical compression. It is known that self-bonded plywood or the wood welding joints suffer from delamination under moist conditions. The results show that the moisture resistance of the joints can be enhanced, i.e. the tendency of delamination can be reduced or eliminated (almost totally) by post-manufacture thermal modification. This was most probably caused by lowered water absorption, relaxation of stored strain energy and formation of crosslinks within the lignin–hemicellulose matrix. The changes in bond integrity in moist conditions as affected by different lay-up types and initial veneer moisture contents were also evaluated. Plywood from initially wet veneers was found to have greater bond stability when soaked. This might be caused by increased crosslinks, because the lignin–hemicellulose matrix is more mobile in wet conditions.

Shear buckling responses of laminated composite shells using a modified 8-node ANS shell element

In this study a numerical investigation is presented for initial buckling response of laminated composite plates and shells under the combined in-plane loading using a modified 8-ANS method. The finite element, based on a modified first-order shear deformation theory, is further improved by the combined use of assumed natural strain method. We analyze the influence of the shell element with the various location and number of enhanced membrane and shear interpolation. Using the assumed natural strain method with proper interpolation functions, the present shell element generates neither membrane nor shear locking behavior even when full integration is used in the formulation. The effect of various types of lay-ups, materials and number of layers on initial buckling response is discussed. In addition, the effect of direction of shear load on the initial buckling response is studied. The interaction curves (between in-plane compression and shear for different parameters of the laminates) are presented. The numerical results obtained are in good agreement with those reported by other researchers.

Co-curing process combining resin film infusion with prepreg and co-cured interlaminar properties of carbon fiber composites

In this article, the carbon fiber/epoxy resin matrix composite laminates were fabricated using a co-curing process combining resin film infusion (RFI) process with prepreg-autoclave process, called co-resin film infusion. A kind of unidirectional prepreg and its corresponding resin film were adopted. The compaction and defects of laminates cured by different processing were studied. Mode I and mode II interlaminar fracture toughness were adopted to evaluate the co-cured interlaminar properties of the co-curing laminates and were compared with those of laminates processed by the prepreg-autoclave process and the resin film infusion process. Moreover, the effects of lay-up type of prepreg part and resin film infusion part, isothermal dwell and epoxy tackifier of fiber preform were also studied. The results show that these factors have important effects on the processing qualities of the laminates cured by co-curing process, including resin-rich regions and voids, resulting in different interlaminar fracture toughness at the co-cured interface. Affected by the prepreg part and the resin film infusion part in the co-resin film infusion laminates, the mode I and mode II initial interlaminar fracture toughness of co-cured laminate lie between those of the prepreg laminate and resin film infusion laminate, and GIC at crack propagation stage for co-resin film infusion laminate are higher due to fiber bridging and deflection of crack. These results have close relationships with the compacting structure of fibers in prepreg and resin film infusion parts and the interfacial bonding between the two kinds of fiber and the matrix.

Cantilevered single walled boron nitride nanotube based nanomechanical resonators of zigzag and armchair forms

In this paper, the dynamic response analysis of single walled boron nitride nanotubes (SWBNNTs) has been done using a finite element method (FEM). To this end, different types of zigzag and armchair layups of SWBNNTs are considered with cantilever configuration to analyze the mass detection application, as a SWBNNT based nanomechanical resonator. Using three dimensional elastic beams and point masses, single walled boron nitride nanotubes are approximated as atomistic finite element models. Implementing the finite element simulation approach, the resonant frequency of cantilevered nanotubes obtained and observed the shifts in it mainly due to an additional nanoscale mass to the nanotube tip. The effect on resonant frequency shift due to dimensional variation in terms of length as well as diameter is explored by considering different aspect ratios of nanotubes. The effect of intermediate landing positions of added mass on resonant frequency shift is also analyzed by considering excitations of different modes of vibration. Also, the effect of chiralities compared for resonant frequency variations to check the effect on sensitivity due to different forms of SWBNNTs. The present approach is found to be effectual in terms of dealing different chiralities, boundary conditions and consideration of added mass to analyze the dynamic behavior of cantilevered SWBNNT based nanomechanical resonators. The simulation results are compared with the analytical results based on continuum mechanics and found in good agreement as one of the toolkits for systematic analysis approach for novel design of SWBNNT based nanomechanical resonators for wide range of applications.

AN EFFICIENT FINITE ELEMENT MODEL FOR ANALYSIS OF SINGLE WALLED BORON NITRIDE NANOTUBE-BASED RESONANT NANOMECHANICAL SENSORS

In this paper, the dynamics analysis of single walled boron nitride nanotubes (SWBNNT) as a resonant nanomechanical sensor by using the finite element method has been reported. Molecular structural mechanics-based finite element model (FEM) has been developed by using three-dimensional elastic beams and point masses, such that the proximity of the model to the actual atomic structure of nanotube is significantly retained. Different types of armchair layups of SWBNNTs are considered with cantilevered and bridged end constraints. By implementing the finite element simulation approach, the resonant frequency shift-based mass sensitivity analysis is performed for both types of end constraints for considered armchair form of the SWBNNTs with different aspect ratios. For both types of end constraint, continuum mechanics-based analytical formulations, considering effective wall thickness of nanotubes are used to validate the present FEM-based simulation approach. The intermediate landing position of the added mass is analyzed, considering variations in resonant frequency shifts of the different fundamental modes of vibrations for both types of end constraints. The FEM-based simulation results for both types of end constraints found in good agreement with the continuum mechanics-based analytical results for the aspect ratio of range of 9–15. The mass sensitivity limit of 10-1 zg is achieved for SWBNNT-based resonant nanomechanical sensors. The resonant frequency shift for higher-order fundamental vibrational modes become stable as the attached mass moves away from the fixed ends for particular magnitude of attached mass. The present finite element-based approach is found to be effectual in terms of dealing different atomic structures, boundary conditions and consideration of added mass to analyze the dynamic behavior of the SWBNNT-based resonant nanomechanical sensors.

NUMERICAL AND EXPERIMENTAL STUDY OF BUCKLING OF ADVANCED FIBER COMPOSITE CYLINDERS UNDER AXIAL COMPRESSION

Advanced lightweight laminated composite shells are increasingly being used in modern aerospace structures, for enhancing their structural efficiency and performance. Such thin-walled structures are susceptible to buckling when subjected to static and dynamic compressive stresses. In this paper, details of a numerical (FEM) and an experimental study on buckling of carbon fiber reinforced plastics (CFRP) layered composite cylinders under displacement and load controlled static and dynamic axial compression are reported. The effects of different types of loadings, geometric properties, lamina lay-up and amplitudes of imperfection on the strength of the cylinders under compression are studied. Accurate measurement of imperfections in the cylindrical surface is carried out in the specimens tested. It is shown that the buckling behavior of thin composite cylindrical shells can be evaluated accurately by modeling measured imperfections and material properties in FEM.

The use of an artificial neural network for modeling the moisture absorption and thickness swelling of oriented strand board

In this study, an artificial neural network (ANN) approach was employed for modeling the moisture absorption (MA) and thickness swelling (TS) properties of oriented strand board (OSB) in various applications. A series of ANN models were developed for the analysis and prediction of correlations between processing parameters and MA and TS of OSB. An ANN model was found for modeling the effects of OSB treatment variables on the MA and TS. The required data for training and testing of the model were obtained from the experimental results of Salay (2010). In designing this model, the MA and TS of the OSB were determined using OSB treatment variables, including board layup type, resin type, application rate of resin, and wax content. When experimental data and results obtained from the ANN were compared by regression analysis using Matlab, it was determined that both groups of data (test and train) were consistent. It was demonstrated that the well-trained feed forward and back propagation multilayer ANN model is a powerful and sufficient tool for the prediction of MA and TS; therefore, by using ANN outputs, satisfactory results can be estimated, rather than measured and hence time and cost are reduced in all the required experimental activities.

Experimental and analytical assessment of axial crushing of circular hybrid tubes under quasi-static load

In the present article, axial crushing behavior of circular aluminum/glass–epoxy hybrid tubes is studied experimentally and analytically. 48 quasi-static axial crushing experiments are carried out on bare metal and hybrid tubes to evaluate the effect of different parameters such as metal and composite wall thicknesses and stacking sequence of composite layers on the crashworthiness characteristics. The specimens are made in two types of layups including angle ply pattern [±θ]s and multi angle ply pattern (different ply angles). The experimental results reveal that stacking sequence has a considerable effect on crashworthiness characteristics, for example for layup [90/0/0/90], the absorbed energy is more than three times of aluminum tube with the same aluminum wall thickness. Also the aforementioned layup has better energy absorption compared to [90/90/90/90] which has been previously proposed as the best layup.According to considerable effect of stacking sequence on the axial crushing behavior of hybrid tubes, an analytical model is developed by including fiber ply orientation of each composite layer and an expression is derived for the mean crushing load and fold length in terms of thicknesses of metal and composite walls and material properties of metal and composite. This model shows reasonably good agreement with experimental results.

Interlaminar stresses in thick rectangular laminated plates with arbitrary laminations and boundary conditions under transverse loads

In the present study, interlaminar stresses resulting from bending of thick rectangular laminated plates with arbitrary laminations and boundary conditions are analyzed analytically based on a three-dimensional multi-term extended Kantorovich method (3DMTEKM). Using the principle of minimum total potential energy, three systems of coupled ordinary differential equations with non-homogeneous boundary conditions are obtained. Then an iterative procedure is established to achieve analytical solution. The results obtained from this theory are compared with those of analytical solutions existing in the literature. It is found that the present results have excellent agreements with those obtained by layerwise theory. The results show that the multi-term EKM converges within only three terms of trial functions and the single-term EKM is not able to estimate the local interlaminar stresses near the boundaries of laminates. Finally, the power of the present approach in obtaining the interlaminar stresses in thick rectangular laminated plates with general types of boundary conditions and lay-ups is examined.

Strength of concrete columns externally wrapped with composites under compressive static loading

This work describes the experimental results related to several series of circular cross-section concrete columns reinforced by composite materials glass/polyester. The columns have been wrapped externally with several plies, and subjected to classical static uniaxial compression loading, and a novel compressive technique consisting in repeated loading steps. The authors identify in particular two specific composite layups (bidirectional fabrics (0/90)2 and (+30/−60)2), the first providing the highest time to failure, the second showing an increase up to 70% in strengthening efficiency compared with non-reinforced columns. Six hybrid composite jacket configurations have also been investigated. The authors also provide a cost analysis of the different types of layups used to wrap the columns, showing the enhanced mechanical/cost effectiveness of the reinforcements proposed in this article.

Bistable characteristic of laminated shells with graded fibers

Based on an inextensional two-parameter analytical model for cylindrical shells, the relationships between the bistable properties of laminated shells with graded fibers and the distribution patterns of the fibers are studied in this article. The fibers are distributed through-thickness in power law from the middle surface to top or bottom surface. Two types of layup, i.e., antisymmetric and symmetric layups, are considered for obtaining the second stable configuration of laminated shells. The distribution regulation of the constituent volume fraction has been obtained for the availability of the second stable equilibrium configurations for both the symmetric and antisymmetric layups. It is showed that the laminated shells with symmetric layups are more difficult to form the second stable configurations than the shells with antisymmetric layups. The effects of the distribution patterns and Young’s modulus of fibers on the bistable configuration of laminated shells are examined. It is revealed that distributing fibers nearly to the top and bottom surfaces and higher Young’s modulus of the fibers are favorable to form second stable configuration and make it coil tighter.