Biaxial Fiber Research Articles

Multiscale shear failure mechanisms within a prestrained composite

AbstractThe elastic fiber prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite, where continuous fibers were prestretched under either constant stress or constant strain throughout the curing process. The tension was only removed after the resin was fully cured. It has been demonstrated that EFP is able to enhance the shear properties of the composite, while the underlying mechanics is still unknown. Here, we investigated the multiscale shear failure mechanisms induced by the EFP within a carbon composite. A bespoke biaxial fiber prestressing rig was developed to apply biaxial tension to a plain‐weave carbon prepreg, where the constant strain‐based EFP method was employed to produce prestrained composites with different prestrain levels. Effects of EFP on macro‐scale shear failure were subsequently characterized through mechanical tests and micro‐morphological analysis. Both the micro‐ and meso‐scale representative volume element (RVE) finite element models were established and experimentally verified. These were then employed to reveal the underlying stress evolution mechanics induced by EFP. It is found that EFP would improve the shear performance of a composite by enhancing the fiber/matrix interfacial bonding strength. This attributes to the elastic strain recoveries of the prestrained fibers locked within a polymeric composite, which generate compressive stresses to counterbalance the external loading. The multiscale shear failure mechanisms were then proposed. These findings are expected to facilitate structural design and application of the EFP for aerospace composites.Highlights Biaxial tension is applied to produce prestrained woven composite. Prestrain effects on microstructural stress evolution mechanics are revealed. Multiscale shear failure mechanisms are proposed for prestrained composites.

An anisotropic topology optimization procedure for continuous fiber reinforced polymer structures with biaxial fiber layout for improved intersection point design

Fiber placement technologies allow for manufacturing of complex-shaped composite parts with load-adapted fiber orientation. For design of corresponding structures, topology optimization is well-established. However, anisotropic topology optimization approaches are often limited to unidirectional fiber orientations. In truss-like topology optimized structures, the intersections between the individual trusses are subject to multiaxial stress states. For those, a unidirectional fiber orientation is not appropriate and may not be suitable for manufacturing.In this work we propose a topology optimization procedure that allows for unidirectional but also biaxial fiber orientations. The choice between unidirectional and biaxial fiber layout is based on the stress state within the finite elements. For the biaxial fiber layout, the first fiber angle is aligned with the maximum absolute principal stress direction, while the second fiber orientation is calculated using composite net theory.Results show that considering biaxial fiber orientations leads to fiber orientations that can be better manufactured by fiber placement technologies and are considered suitable for automatic derivation of manufacturing-tolerant placement paths. Furthermore, the stress state at intersections is improved reducing the probability of inter fiber failure. In addition, consideration of biaxial fiber orientations could increase the stiffness at constant weight compared to purely unidirectional topology optimization.

Research on Biaxial Damage Evolution Characteristics of Flexible Woven Composite Film

The flexible braided composite film structures have been widely used in many fields such as near space aerostats, inflatable wings, flexible spacecraft due to their unique advantages such as small folding volume, light weight, high specific strength, excellent comprehensive performance, etc. However, the space environment is so harsh, and the flexible film structure composite material could be easily affected by various environmental factors such as long-term sunlight, ultraviolet radiation and space particle impact. So the weathering damage evolution characteristics directly determine the use life and working efficiency. The typical biaxial fiber reinforced laminated flexible composite material was studied with the damage mode, and the composite meso-mechanical theory was also used to construct the braided composite mechanics model during the damage process. The damage model of the warp and weft fiber bundles with the base film layer was introduced into the independent flexible film composite component damage degree, and the damage evolution model of the damage-containing composite material characterized by the mesoscopic component parameters was also established. Moreover, the load-bearing stress characteristics of each component under different damage conditions were calculated and analysed. The research results could provide an effective theoretical reference for the weathering optimization design and the improvement of the service life of flexible film woven composite structures.

Response of fabric insert injection overmolding PP based composites subjected to single and muti-impact

This paper presents the results of a current study on the development and impact response of composite plates manufactured by injection overmolding on the two sides of a single reinforcement fibre mat. The injection polymer is a talc-filled polypropylene, nowadays used for structural purposes. Three configurations with different insert fibre mats were used: Kevlar, biaxial and multiaxial glass fibre mats. The parameters studied were the fibre mat type and the impact energy. For single impact tests, it was concluded that the highest impact energy required to achieve impactor perforation is obtained with Kevlar insert, while the highest percentage of energy recovered is achieved with biaxial glass fibre netting. Kevlar insert also allows for the maximum impact stiffness. For the multi-impact tests, the recovered energy and the dynamic stiffness show the same tendencies of the single impact tests. On low energy impacts, the effect of the insert fibre and of the previous impact are quite reduced, while for impact energies above 6J, previous impacts reduce significantly the recovered energy and the impact energy for which the perforation was achieved.

Mechanical properties of 3D printed composites with ABS/ASA substrate and glass fiber inserts

3D printed specimens (ASTM D638 Type I) were manufactured from ABS and ASA material via additive manufacturing through material extrusion 3D printing (ME3DP). During manufacturing, the printing process has been paused, pre-impregnated biaxial or uniaxial glass fiber mesh has been placed onto the ABS/ASA substrate and then the printing process has been resumed. The obtained composite specimens have been subjected to tensile strength testing and results have been compared to those of specimens printed from homogenous material. The influence of raster angle, glass fiber direction and mesh density on resulting toughness has also been analyzed. It was found that inserting uniaxial glass fiber increases toughness of specimens in the axial direction, with a drop in layer adhesion if biaxial fiber is used. Test specimens manufactured with 30 uniaxial fiber strands embedded in a 0o raster angle 3D printed thermoplastic matrix match mechanical characteristics of injection-molded parts. The maximum mesh density without leading to delamination is one layer of glass fiber every two layers of thermoplastic matrix.

Plain para-aramid/phenolic multiwall carbon nanotubes prepreg/multistiched preform composites: Experimental characterization of mode-I toughness

The fracture toughness (mode-I) properties of nanostitched para-aramid/phenolic multiwall carbon nanotube prepreg composites were investigated. The fracture toughness (GIC) of the stitching and nanostitched composites showed 42-fold and 41-fold (beam theory), 18-fold and 21-fold (modified beam theory) increase compared to the control, respectively. The prepreg para-aramid stitching yarn and nanostitched yarn were dominant parameters. The toughness resistance to arrest crack growth in the nanostitched composite was primarily due to nanostitching fiber bridging and pull-out, and was secondarily due to nanotubes and biaxial fiber bridging and pull-out. The failed surfaces of the nanostitched and stitching composites had tensile filament failures in the aramid stitching fibers where filament/matrix/nanotube debonding and axial filament fibrillar splitting were found. The results indicated that stitching yarn and the nanotubes arrested the crack propagation. Therefore, the nanostitched and stitched para-aramid/phenolic composites displayed a better damage resistance performance compared to those of the control or nanotube composites.

Experimental determination of fracture toughness properties of nanostitched and nanoprepreg carbon/epoxy composites

The interlaminar fracture toughness properties based on the double cantilever beam test of the multilayered stitched carbon/epoxy/multiwall carbon nanotube prepreg woven composites was investigated. The fracture toughness based on beam theory and modified beam theory of the stitched/nano and stitched composites showed 3-fold and 2-fold increases compared to the base and base/nano composites, respectively. The fracture toughness resistance to arrest the crack propagation in the stitched/nano composite was primarily due to out-of-plane directional stitching fiber bridging and was secondarily due to in-plane directional biaxial fiber bridging and multiwall carbon nanotubes. Fracture surfaces of the stitched/nano had multiple matrix and brittle tensile filament breakages in carbon stitching yarn and ductile filament breakages in the para-aramid stitching yarns where filament/matrix debonding and filament pull-out were identified.

Influence of Textile Parameters on the Out-of-Plane Permeability of Carbon Fiber Non-Crimp Fabrics

Within the last years, liquid composite molding (LCM) is gaining more and more importance for the automotive industry due to weight saving of (semi-)structural car parts. In order to make carbon fibre parts economically more interesting for this area, short cycle times are necessary. Hence, one concept is the impregnation of carbon fibre parts in through-the-thickness direction. The behaviour of the impregnability depends mainly on the out-of-plane permeability of the fabric. The permeability of the fabric is mainly influenced by the fibre type, orientation of the fibres, and the stitching parameters. In this study the influence of textile parameters on the out-of-plane permeability of 45° and 0°/90° biaxial carbon fibre non-crimp fabrics (NCF) was investigated. The stitching yarn parameters (linear mass density and stitch length) were varied to see the influence on the out-of-plane permeability. The out-of-plane permeability was measured using a measurement cell based on flow front monitoring with ultrasonic technology at a minimum of three different fibre volume contents between 47 % and 63 % to show the decrease of permeability with respect to the fibre volume content. The results show that the out-of-plane permeability of the 0°/90° carbon fibre NCF are not significantly affected by the yarn linear mass density and the stitch length. Conversely the 45° carbon fibre NCF is affected by the stitch length, but not by the yarn linear mass density.

Monitoring Poisson’s ratio of glass fiber reinforced composites as damage index using biaxial Fiber Bragg Grating sensors

Damage accumulation in Glass Fiber Reinforced Polymer (GFRP) composites is monitored based on Poisson’s ratio measurements for three different fiber stacking sequences subjected to both quasi-static and quasi-static cyclic tensile loadings. The sensor systems utilized include a dual-extensometer, a biaxial strain gage and a novel embedded-biaxial Fiber Bragg Grating (FBG) sensor. These sensors are used concurrently to measure biaxial strain whereby the evolution of Poisson’s ratio as a function of the applied axial strain is evaluated. It is observed that each sensor system indicates a non-constant Poisson’s ratio, which is a sign of damage accumulation under the applied tensile loading. As the number of off-axis plies increases, transverse strain indicates a notable deviation from linearity due to the formation of transverse cracking, thereby leading to a larger reduction in Poisson’s ratio as a function of applied axial strain. Here, it is demonstrated that biaxially embedded FBG sensors are reliable to monitor the evolution of Poisson’s ratio, unlike biaxial strain gages which record strain values that can be significantly influenced by the cracks formed on the surface of the specimen.

Research of long-term properties of high-strength fiberglasses by means of the built-in FBG sensors

In this work the possibility of use of the built-in fiber-optical sensors (Bragg's sensors) of deformation for control of a condition of polymeric fiberglasses on epoxy polymer matrix ED-I cured at the increased temperature was investigated. Sensors were inserted in different layers of the layered plastic reinforced by biaxial fiber glass fabric. The package of layers had quasiisotropic structure. The sample made by method of vacuum impregnation was affected by saturated steam (90 °C) within 6 months. Operability of system of measurement has been as a result shown and swelling parameters in different layers of FGRP were recorded. For measurement measuring systems of two types — on a superbright light-emitting diode and on the tunable laser were used.

Torsional Behaviour and Finite Element Analysis of the Hybrid Laminated Composite Shafts: Comparison of VARTM with Vacuum Bagging Manufacturing Method

Braided sleeve composite shafts are produced and their torsional behavior is investigated. The braided sleeves are slid over an Al tube to create very strong and rigid tubular form shafts and they are in the form of 2/2 twill biaxial fiber fabric that has been woven into a continuous sleeve. Carbon and glass fibers braided sleeves are used for the fabrication of the composite shafts. VARTM (vacuum assisted resin transfer molding) and Vacuum Bagging are the two different types of manufacturing methods used in the study. Torsional behaviors of the shafts are investigated experimentally in terms of fabrication methods and various composite materials parameters such as fiber types, layer thickness, and ply angles. Comparing the two methods in terms of the torque forces and strain angles, the shafts producing entirely carbon fiber show the highest torque capacities; however, considering the cost and performance criteria, the hybrid shaft made up of carbon and glass fibers is the optimum solution for average demanded properties. Additionally, FE (finite element) model of the shafts was created and analyzed by using ANSYS workbench environment. Results of finite element analysis are compared with the values of twisting angle and torque obtained by experimental tests.

Resonant fiber scanner with optical feedback.

The addition of an apertured mirror before the imaging lens is proposed as a method of providing feedback in a single-axis resonant fiber scanner. Reflection at the scan extremities generates timing signals interlaced with back-scattered data, and a phase locked loop and a proportional controller then adjust the drive frequency and amplitude. The capture range and stability of the system are examined. Verification is obtained using a confocal scanner based on mechanically biaxial fiber.

Comparative Study on Tribological Behavior of Biaxial Glass Fiber/Al2O3/SiC Epoxy Journal Bearing Under Various Test Conditions

Composite journal bearings are becoming more popular now a day because they eliminate the possibility of seizure failure to the bearings. The major drawback of the gun metal bearings is the seizure failure. To overcome this problem, the composite journal bearings are widely used by the industries. In this study, the fiber reinforced plastic composed of glass fiber with epoxy resin composite /Al_2O_3/SiC journal bearing having the composition of 10-20% are tested under various operating conditions and the results are compared with gun metal journal bearing. This study focuses on the dimensional stability, temperature, friction, surface roughness and surface topography behavior of biaxial glass fiber epoxy composite with and without lubrication at different speeds and loads. It has been observed that the friction and temperature increases with increase in load but it's very less when compared to gun metal bearing. It is found that there is loss in weight due to increase in temperature and friction but the loss in weight is very less which is approximately 1 g. In the earlier research, most of the bearings are tested under very low speed with more catastrophic failure due to various loading conditions. Therefore in this study the composite journal bearing is tested from low speed to high speed with different loading conditions and their effects has been studied. This composite journal will save the significant cost to the industries by reducing the coefficient of friction, temperature, lubrication etc.

Biaxial Fiber Bragg Grating Accelerometer Using Axial and Transverse Forces

We demonstrate the first biaxial fiber Bragg grating (FBG) accelerometer using axial and transverse forces. An inertial object is fixed at the middle of two FBGs inscribed in one fiber. The difference between the resonant wavelengths of the two FBGs can distinguish the acceleration in the axial direction, while being insensitive in the transverse direction. The average of the resonant wavelengths of the two FBGs can distinguish the acceleration in the transverse direction, while being insensitive in the axial direction. In the experiments, when the transverse direction was vertical, the crest-to-trough sensitivity at 5 Hz and resonant frequency of the average were 0.545 nm/g and 34.42 Hz, respectively. When the axial direction was vertical, those of the difference were 0.0454 nm/g and 900 Hz, respectively. For each FBG, the crest-to-trough sensitivity at 5 Hz and resonant frequency in the transverse/vertical direction were 24 and 1/26 times those in the axial/vertical direction, respectively.

A fibre flexure–shear model for seismic analysis of RC‐framed structures

AbstractWhile currently existing modelling approaches of reinforced concrete (RC) behaviour allow a reasonably accurate prediction of flexural response, the determination of its shear counterpart needs further developments. There are various modelling strategies in the literature able to predict the shear response and the shear–flexure coupling under monotonic loading conditions. However, very few are the reported models that have demonstrated successful results under cyclic loading, as in the seismic load case. These considerations lead to this research work focused on the development of a flexure–shear model for RC beam–column elements. A reliable constitutive model for cracked RC subjected to cyclic loading was implemented as bi‐axial fibre constitutive model into a two‐dimensional Timoshenko beam–column element. Aim of this research work is to arrive at the definition of a numerical model sufficiently accurate and, at the same time, computationally efficient, which will enable implementation within a finite element package for nonlinear dynamic analysis of existing non‐seismically designed RC structures that are prone to shear‐induced damage and collapse. Copyright © 2009 John Wiley & Sons, Ltd.

High Through-thickness Thermal Conductivity Composites Based on Three-Dimensional Woven Fiber Architectures

Composites based on laminates of uniaxial or biaxial fiber reinforcements exhibit low through-thickness thermal conductivity, due to low matrix thermal conductivity and the number of interfaces in the thermal path. For applications near heat-generating components, the use of laminate composites in the surrounding structure can be limited by this inability to transport heat through the thickness. Three-dimensional orthogonal weaving provides an efficient, cost-effective method of placing high thermal conductivity yarns in the through-thickness Z direction of a preform to yield structural composites with high through-thickness thermal conductivity and with in-plane strength or stiffness comparable to laminates. Three basic research efforts investigated the efficacy of this approach: 1) weaving trials to determine the ability to three-dimensional orthogonal weave pitch carbon fibers and plied copper wires in the Z direction of the preforms, 2) through-thickness thermal conductivity testing of composites based on three-dimensional preforms, and 3) thermal modeling to describe several of the phenomena observed during thermal conductivity tests. During the testing, composites based on the three-dimensional orthogonal preforms with Z fiber volume fractions of only 5.5% measured a 12-fold increase in through-thickness thermal conductivity over a laminate composite, 8.4 versus 0.7 W/m K.

Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films

AbstractSeveral methods to induce grain alignment in polycrystalline thin films are discussed, in which directional effects can dominate over the normal evolution of fiber texture during thin film growth. Early experiments with ion beam assisted deposition showed the importance of channeling directions in selecting grain orientations with low sputtering yield or low ion damage energy density. Examples of this approach include the formation of biaxial fiber textures in Nb, Al and AlN. Grain orientations may also be selected by the release of stored energy during abnormal grain growth initiated by solute precipitation (Cu-Co) or phase transformation (TiSi2). Other energy sources such as mechanical deformation, crystallization or compound formation may also contribute to producing desired grain alignments. In multicomponent thin films, combinations of these mechanisms provide opportunities for more specific control of grain orientations.

Automatic Recognition and Analysis of Scanned Non-crimp Fabrics for Calculation of their Fluid Flow Permeability

Automatic recognition of scanned images of distorted bi-axial fiber bundle arrangements is considered in order to obtain the overall permeability of the formed fiber network. Scanned images are pre-processed with color normalization followed by usage of a threshold to find the pixels belonging to the bundles, the threads keeping the bundles together, and the distinct gaps formed between the bundles. Since the scanned images virtually have a perfect grayscale, the intensity can be treated as a corresponding signal of the image. Next the regular character of the fiber network is investigated using Fourier analysis on the fiber bundles as well as on the threads. The direction, position, and spatial separation of the fiber bundle and the threads are obtained in this way. In order to recognize the bottom fiber bundle layer a fine structure technique is used. Small clusters falsely identified as belonging to the bottom bundle layer are removed by application of a threshold to the perimeter of the cluster. The gaps in the top bundle layer are identified more clearly in this way. Next, a local Fourier analysis is applied to obtain the local distortion of the bundle and the thread structure yielding the characteristic distribution of the gaps between the bundles. Finally the distribution of the width of the threads is obtained by simply identifying the minimal distance between the sides of the threads.

BEHAVIOUR OF REHABILITATED STRUCTURAL WALLS

An experimental program for identifying the causes of failures in structural walls under earthquake loading and investigating potential rehabilitation schemes was undertaken. Large-scale models of the plastic hinge region of the walls were tested. An innovative test setup that provides the possibility of controlling the ratio of the shear force to both bending moment and axial load was constructed. A control wall was tested and failed prematurely in shear reproducing the failure observed in the field. Two different rehabilitation schemes to improve the behaviour of the wall using biaxial fibre reinforced polymer (FRP) sheets were designed to prevent the shear failure. To improve the ductility, the end column elements of the walls were confined using anchored FRP. The two schemes were tested and proved to be effective in increasing shear strength, ductility, and energy dissipation capacity of the walls.

Fracture Propagation in Composites with Biaxial Fiber Reinforcement

Fracture characteristics such as damage progression, work of fracture, ultimate fracture loads, and failure modes are evaluated by computational simulation for composites with biaxial braided fiber reinforcements. Several Graphite–Epoxy Mode I compact tension (C(T)) specimens with different biaxial fiber orientations are modeled and simulated. Damage initiation, growth, and propagation processes at the microscopic level are tracked, enabling a more insightful interpretation of the test results. The effects of ply-layup with various orientations of the braid axis with reference to the notch directions are investigated with respect to their influences on damage and fracture progression characteristics. Results validate the computational simulation method and identify fracture characteristics for biaxially reinforced composites.