Triaxial Braid Research Articles

Scatter of mechanical properties of 2D biaxial and triaxial braided reinforced composites and their correlation with visual features

Tensile properties of 2D braid reinforced composites are analyzed with regards to process-induced fiber architecture variations. First, a parametric study concerning the effect of radial braiding parameters on the braid characteristics is performed and a quantitative quality index based on visual attributes is introduced. Second, test laminates are produced with vacuum resin infusion to conduct tensile tests with biaxial and triaxial braids of varying qualities. To correlate fiber architecture variations with mechanical properties, each braided layer is scanned and analyzed by means of gray scale based image processing. This allows for determining specimen-specific fiber orientations and correlating them with mechanical properties. The results show strong correlations of measured fiber architectures and mechanical properties. Thus, the study suggests that detailed information about the (local) fiber architecture should allow for significantly improving the prediction of 2D braided composite properties.

Additive manufacturing of weft knitted and braided fabric structures with fused deposition modeling

Additive manufacturing (AM), also commonly called three-dimensional (3D) printing, allows fabrication of complex objects within a limited time frame with minimal waste production. The purpose of this research is to design, 3D print, and analyze the mechanical properties of fabric structures. Two different fabric types are considered for this work: weft knit fabric and braided fabric structures. A single yarn and weft knitted fabric structure were designed, fabricated and weft knitted fabrics are tested. Different designs of braided structures such as diamond braid, regular braid, Hercules braid, triaxial braid, and bi-furcated braid are designed, fabricated, and tested. Poly(lactic) acid (PLA) filaments were used to print the fabric structures. Mechanical properties and morphological structures were studied using the printed structures. The results showed that weft knitted fabrics possess a good ductile response before failure showing a tensile displacement in the range of 12–15 mm, and the peak force exhibited is nearly 250 N. On the other hand, the maximum flexural displacement is approximately 10 mm, and the load is in the range of 15–22 N in the wale direction, and 85–95 N in the course direction. Braided structures showed that they can bear significant amount of compressive load having displacement at failure of more than 25 mm. Optical microscope (OM) analysis showed that the yarns contain voids and cracks that contributed to the failure of the samples. The additively manufactured weft knitted fabric structures can be used in wearable, filtration, and geotextiles applications whereas the circular braided structures can be used in shock absorption applications.

Low‐velocity impact response and damage tolerance of hybrid biaxial/triaxial braided composite laminates

AbstractThe structural properties of braided composite laminates are significantly affected by the low‐velocity impact (LVI). In this paper, the impact resistance and damage tolerance of triaxial braid structure laminates at different positions were mainly studied. Three hybrid biaxial (B)/triaxial (T) braided composite structures of BBTT, BTTB, and TTBB were designed, and LVI test and post‐impact compression tests were carried out. The results show that the triaxial braided fabric with quasi‐isotropic on the impact side caused more significant matrix cracks along the axis yarn direction, and the matrix damage area and delamination area were larger. For triaxial braided ply with high curl levels, severe fiber fracture and relatively concentrated damage occurred first on the non‐impact side. Interestingly, triaxial braided fabrics exhibited better impact resistance in terms of mechanical response when distributed across the specimen surface. However, a global damage pattern appears at high energy levels, which seriously reduced the residual strength of the structure and showed the worst damage tolerance. The damage quantification analysis of cracks, dent depths, delamination and residual compressive strength caused by the LVI of hybrid shaft number braided laminates was carried out in this work, which provided a valuable reference for engineering failure analysis and rational structure optimization of composite laminates.

An experimentally validated model for predicting the tensile modulus of tubular biaxial and triaxial hybrid braids

AbstractBraiding is a versatile and cost‐effective approach to generating various composite structures for mechanical, sports, and biomedical engineering applications, which are different from each other. For example, a stent is a braided structure and blood penetration in it is essential as much as the right function. Predicting the tensile responses is a prerequisite for the success of implementation of braided structures, and it is usually performed via destructive mechanical testing that might be costly and/or time‐consuming. Therefore, it is essential to provide a model that can accurately predict the tensile modulus. In this research, a theoretical model is developed using the simplification of a braided structure and is validated via testing of biaxial and triaxial braids composed of polyester, glass, and basalt yarns on a 16‐carrier vertical braiding machine. Experimental results not only are used for the model validation but also show the effectiveness of axial yarn presence, hybridization, and the presence of high‐performance yarn in the braided structures on the tensile properties. A good correlation between theoretical values and experimental results is observed approving the high accuracy of the proposed model. This paper is likely to fill a gap in the state of the art and provide pertinent results that are instrumental in the design of hybrid‐braided structures with minimum computational/experimental effort. The research innovation centers on the use of two different yarns to make hybridization, simplicity of the model to be used for biaxial and triaxial braided structures, and a start to omit destructive tests.

A Study of the Mechanical Properties of Biaxial and Triaxial Braided Composites for an Automotive Propeller Shaft

A Study of the Mechanical Properties of Biaxial and Triaxial Braided Composites for an Automotive Propeller Shaft

Investigation on Poisson’s ratio of tubular braid’s structure, considering different structural deformation regimes, Part 1: experimental study

Despite the importance and complexity of Poisson’s effect in tubular braids, it has been overlooked in researches investigating the mechanical properties. In this study, the effect of structural parameters on the Poisson’s Ratio (PR) of tubular braid was investigated. For this purpose, braids with different structural parameters such as braid angle, weave pattern, yarn count and the structural layer and structural axis was produced. Then, the PR of braids was evaluated and expressed in different structural deformation regimes by image processing technique. Results showed that Among the factors studied, braid angle had a prominent effect on the initial PR, in a way as the braid angle increased the magnitude of PR decreased. By increasing the floating length of yarns, initial PR increased. By increasing the yarn’s count and structural layers of tubular braids, initial PR decreased. Triaxial braids have lower initial PR in comparison to biaxial braids.

Numerical analysis of crimping behaviour of triaxial braided structures

The mechanical properties of tubular braided structures influence their inherent performance during application as biomedical materials. In their use as stents, braided structures are forced to conform to the topology of the host tissues. Triaxial braided structures have had limited use in tissue repair and organ support even though they have the potential of offering equal if not better performance compared to bi-axial braided structures. A study of the mechanical dynamics of tri-axial braids would be crucial in the potential design of customised structures for advanced tissue repair and organ support. This study therefore uses Finite Element Methods (FEM) to design and develop triaxial braided structures and investigate their crimping behaviour using parametric modeling and numerical analysis in their potential application as biomedical materials. The results in this study portrayed that the presence of axial yarns in tubular braided structure offers improved performance in terms of stability of the structure.

Experimental and Numerical Impact Analysis of Automotive Bumper Brackets Made of 2D Triaxially Braided CFRP Composites.

The impact behavior of carbon fiber epoxy bumper brackets reinforced with 2D biaxial and 2D triaxial braids was experimentally and numerically analyzed. For this purpose, a phenomenological damage model was modified and implemented as a user material in ABAQUS. It was hypothesized that all input parameters could be determined from a suitable high-speed test program. Therefore, novel impact test device was designed, developed and integrated into a drop tower. Drop tower tests with different impactor masses and impact velocities at different bumper bracket configurations were conducted to compare the numerically predicted deformation and damage behavior with experimental evidence. Good correlations between simulations and tests were found, both for the global structural deformation, including fracture, and local damage entities in the impact zone. It was proven that the developed phenomenological damage models can be fully applied for present-day industrial problems.

Analysis of tow architecture variability in biaxially braided composite tubes

Spatial deviations in composite braid unit cell dimensions limit mechanical performance and are challenging to model. Full-field measurements of the irregular tow placement in biaxially braided composite tubes were obtained by digital image correlation. Analysis of the reconstructed tow paths showed long-range defects along the hoop direction with short-range defects dominating the biased tow direction. A route toward numerical simulation of the composite response is established by developing a 3D model of the composite using the measured tow trajectories. Finally, a comparison to previously-published triaxial braid results indicates axial tows work to constrain unit cells dimensions along the hoop direction.

Design Optimization of a Braided Roof Frame Reinforcement by Process-Integrated Local Customization of Component Properties

In order to use the full potential of fiber-reinforced composite materials, load-compliant fiber architecture and suitable manufacturing technologies are essential. Therefore, multiple approaches to enable customized braided structures for highly stressed structural profiles in high volume applications are introduced and resulting design possibilities for generic parts are described. A methodology for component optimization considering manufacturing restrictions arising from the introduced customization techniques is proposed and applied to an automotive roof frame reinforcement serving as an example use case. Starting from an initial design based on a conventional triaxial braid, high-potential variants are derived by means of finite element simulation. Experimental validation confirms substantial improvements regarding lightweight and cost potential for the component’s main load case by applying the introduced process approaches.

Analysis of a Process Approach for Production of Triaxial Braids with Locally Customized Filler Yarn Count

In order to enhance lightweight potential and fabrication efficiency of structural parts from carbon fiber-reinforced plastics, the approach of locally tailored component properties has proven effective. For braided hollow profiles, however, technical possibilities to achieve process integrated adaption of a components’ mechanical properties are limited. Therefore, a novel braiding process approach for cycle-time-neutral adjustment of a triaxial braids filler yarn count is examined and its advantages for component design are illustrated. The main objective of this study is to evaluate the approaches applicability with regard to process stability and disturbance of product quality. Two consecutive test series are carried out to identify the most influential process variables and to link the variation of these variables with multiple criteria of process quality. A clear dependency between quality and braid angle, braid yarn tension as well as the number of filler yarns the approach is applied on is derived. On that basis a set of process variables for faultless application of the concept is pointed out.

Multiscale Modeling of a Notched Coupon Test for Triaxially Braided Composites

Braided composites have been widely used in aerospace and automotive structures due to their light weight and high strength. Unlike metal or laminated composite material, the complex braided structure brings a lot of challenges when conducting numerical simulation. In this paper, a finite element analysis based meso-mechanical modeling for the two dimensional triaxially braided composite was developed. This mesoscale modeling method is capable of considering the detailed braiding geometry and architecture as well as the mechanical behavior of fiber tows, matrix and the fiber tow interface. Furthermore, a multiscale model combined both macroscale and mesoscale approaches and it is realized within LS-DYNA environment through Interface_components and Interface_linking. This combined multiscale modeling approach enables the full advantage of both the macroscale and mesoscale approaches, which can describe the details of local deformation and the global overall response features of the entire structure with the minimum computational expense. The evaluation and verification of the mesoscale approach and combined multiscale modeling method is through a notched coupon tensile tests conducted by Kohlman in both axial and transverse direction. The multiscale modeling method captures the response feature accurately so it has the ability to analyze large scale structures.

Test and Analysis of Triaxially Braided Composite Circular Arch under Three-Point Bending

In this paper, the buckling behavior of triaxially braided circular arch with monosymmetric open section subjected to three-point bending was studied experimentally and numerically. First, test specimens were manufactured using vacuum assisted resin transfer molding (VARTM). Then the specimen was tested under three-point bending to determine the ultimate buckling strength. Before performing the numerical analysis, effective material properties of the braided composite were obtained through micro-meso scale analysis virtual testing validated with available test results. Then linear buckling analysis and geometrically non-linear post buckling analysis, established to simulate the test setup, were performed to study the buckling behavior of the composite frame. Analysis results were compared with experimentally obtained ones for verification. The effect of manufacturing defects of tow misalignment, irregular surface and resin rich region, and uncertainties during test setup were studied using numerical models. From the numerical analyses performed it was observed that both manufacturing defect and uncertainties had effect on the buckling behavior and strength.

Mechanical and thermal behaviors of ultra-high molecular weight polyethylene triaxial braids: the influence of structural parameters

Recently, triaxial braids made from ultra-high molecular weight polyethylene (UHMWPE) have been recognized as one of the most popular composite reinforcements in the aerospace and defense fields. To further explore the mechanical characteristics of this material, a detailed experimental study on tensile behavior is reported in this paper. The triaxial braids show a “double-peak” phenomenon in tensile strength and deformation, caused by axial yarns and the in-plane shearing of bias yarns. The evolution of the braiding angle, measured during these tensile tests, is discussed according to the braiding parameters (initial braiding angle, number of axial yarns). Using the high conductivity properties of the UHMWPE material, the temperature caused by inter-yarn friction during tensile tests is also studied. This temperature is related to the evolution of the braiding angle. The temperature increases with the increasing number of axial yarns and decreases with increasing braiding angle. This study provides an experimental database on the influence of braiding parameters on the tensile behavior of triaxial braids.

Experimental Investigation and Numerical Analysis of the In-Plane Tensile Behavior of a Triaxially Braided Composite with Subcell Modeling Approach

AbstractTo improve the prediction of the response of braided composite structures, a subcell approach is under development. This method has shown successes in predicting the moduli of braided compo...

Multi-scale Progressive Failure Analysis of Triaxially Braided Textile Composites

Multi-scale Progressive Failure Analysis of Triaxially Braided Textile Composites

Damage and failure of triaxial braided composites under multi-axial stress states

Damage and failure of triaxial braided composites under multi-axial stress states was investigated. In order to introduce different multi-axial stress states in the material, uni-axial tensile tests were performed at different off-axis orientations. Three braid architectures, comprising braiding angles of 30°, 45° and 60° were each loaded parallel to their axial, transverse and braid yarn direction. Digital image correlation measurement techniques were used to quantify the effects of the textile architecture and its heterogeneity on the strain field, to identify and locate constituent failure mechanisms and to investigate damage initiation and development. In order to identify the driving physical mechanisms behind the material non-linearity, the evolution of the damage variable and the accumulated inelastic strain was quantified using incremental loading/unloading experiments. A high-speed camera was employed in order to study the dynamic nature of catastrophic failure. The triaxial braids within this study exhibited severe non-linearities in the mechanical response before final failure as a result of extensive matrix cracking. While we found the underlying textile architecture to slightly reduce the elastic properties compared to equivalent tape laminates, it functions as a natural crack arresting grid. As a result of this mechanism, braids under certain load conditions were capable of withstanding a higher strain to failure, even if a large portion of the specimen surface was saturated with matrix cracks. The accompanying mechanical behaviour can be desirable in the design of crash absorbing or pseudo-ductile materials. An additional failure mode intrinsic to the textile architecture was encountered for loading in the heavily undulated braid yarn direction. Due to yarn straightening and out-of-plane movements, braided composites were found to fail as a result of large scale delaminations accompanied by progressive fibre bundle pull-out.

Development of a generalized analytical model for tubular braided-architecture composites

Tubular braided composites are manufactured using a Maypole braiding machine which interlaces yarns in order to manufacture a braided structure. Braids can be produced in Diamond (1/1), Regular (2/2) and Hercules (3/3) patterns. In addition, axial yarns can be included in order to produce triaxial braid structures. Several analytical and finite element analysis models have been developed in order to predict the elastic properties of braided composites. Despite the fact that many models exist for braided composites, a comprehensive model has not been presented that can capture the variety of braiding patterns which can be manufactured using the braiding process. In this study, a new analytical model has been developed that can describe the elastic properties of Diamond, Regular and Hercules braids. The proposed analytical model uses a volume averaging stiffness method in order to account for yarn undulations and the orientation of braid yarns within the braid structure. The model presented here has been compared with the existing FEA and analytical models and has also been validated experimentally. Experimental validation comprised tensile and torsional tests in order to predict the longitudinal and shear moduli for both Diamond and Regular braid geometries. The experimental and proposed model results highlight the effect of braiding pattern and braiding angle on the mechanical properties.

Tensile Response of Hoop Reinforced Multiaxially Braided Thin Wall Composite Tubes

This paper presents the tensile response of thin-walled composite tubes with multi-axial fibre architecture. A hybrid braid-wound layup has the potential to optimise the composite tube properties, however, stacking sequence plays a role in the failure mechanism. A braid-winding method has been used to produce stacked overwound braid layup [(±45°/0°)5/90°4]T. Influence of stacking sequence on premature failure of hoop layers has been reported. Under tensile loading, a cross-ply composite tube with the alternate stacking of hoop and axial fibre show hoop plies splitting similar to the overwound braided composite tube. However, splitting has been restricted by the surrounding axial plies and contained between the adjacent axial fibre tows. This observation suggests hoop layers sandwiched between braid layers will improve structural integrity. A near net shape architecture with three fibre orientation in a triaxial braid will provide additional support to prevent extensive damage for plies loaded in off-axis. Several notable observations for relatively open braid structures such as tow scissoring, high Poisson’s ratio and influence of axial tow crimp on the strain to failure have been reported. Digital Image Correlation (DIC) in conjunction with surface strain gauging has been employed to capture the strain pattern.

Influence of the cover factor of 2D biaxial and triaxial braided carbon composites on their in-plane mechanical properties

The effect of the cover factor on the in-plane mechanical properties of biaxial and triaxial braided carbon fiber composites is investigated. Low braid coverage occurs if the mandrel circumference exceeds a specific length, so that gaps occur in between the different yarn systems.Braids are manufactured on different mandrel sizes with a braid angle of ±45°. The cover factor is calculated analytically and measured by means of gray scale analysis of scanned samples. A new analytical model is presented which allows for calculating the cover factor of triaxial braids in good approximation with real results, taking into account the off-centered alignment of the axial yarns. Tensile and compression test results are presented for the thermoset resin systems EPIKOTE MGS® RIM 235 and HexFlow® RTM6. The results show that there is a significant influence of decreased cover factors on the mechanical properties, especially in case of triaxial braids tested in axial direction. Micro computed tomography images based on synchrotron radiation reveal that low coverage leads to an increased fiber undulation of the axial yarns, which mainly determine the mechanical properties of triaxial braids. An influence of the different resin systems is observed for matrix-dominated properties of biaxial braids, where the composite failure strain is in the range of neat resin failure strain.