Fiber Layout Research Articles

From Fiber Layout to the Sensor: Preparation Methods as Key Factors for High-Quality Coupled-Core-Fiber Sensors.

During recent years, the optical-fiber-based simultaneous sensing of strain and temperature has attracted increased interest for different applications, e.g., in medicine, architecture, and aerospace. Specialized fiber layouts further enlarge the field of applications at much lower costs and with easier handling. Today, the performance of many sensors fabricated from conventional fibers suffers from cross-sensitivity (temperature and strain) and relatively high interrogation costs. In contrast, customized fiber architectures would make it possible to circumvent such sensor drawbacks. Here, we report on the development of a high-quality coupled-core fiber and its performance for sensors-from the initial fiber layout via elaboration of the preform and fiber up to the sensor evaluation. A compact, high-speed, and cost-effective interrogation unit using such a specialized coupled-core fiber has been designed to monitor reflectivity changes while even being able to distinguish the direction of the force or impact. Several fiber core material techniques and approaches were investigated, which made it possible to obtain a sufficient volume of material for the required fiber core number and a specialized fiber core geometry in terms of core distances and radial refractive index profile, whilst handling the non-symmetrical fiber architectures of such modeled, complex structures and balancing resources and efforts.

A strategy for the improvement of the bonding performance of 3D-printed concrete interlayer interfaces

3D-printed concrete, as an intelligent building technology, has enormous potential in construction. However, the weak bond interfaces between two adjacent layers of concrete are still a well-known problem affecting the mechanical properties of printed structures, with reduced interlayer shear and tensile properties. The reinforcement method of inserting steel bars in vertically printed layers is crucial and requires research and exploration of suitable methods, as well as finding the optimal reinforcement scheme that satisfies the interlayer interface when facing different loads. This study proposes a method of interlayer reinforcement by vertically laying steel fibers between layers, and investigates the effects of steel fiber offset, deployment density, and cross-sectional area on interlayer bonding strength. The strengthening effect of steel fiber on interlayer shear and tensile strength was tested through shear and splitting tests. Microscopic numerical models are used to study the evolution process of interlayer cracking. The correlation between different steel fiber variables and interlayer bonding strength was studied using a Generalized Grey Relational Analysis (GGRA). The results showed that the shear strength and tensile strength of the interlayer interface could be improved by 256.32 % and 353.61 %, respectively, through a reasonable fiber layout scheme. It is recommended to lay steel fibers with small offsets. When the interlayer interface is subjected to shear loads, priority should be given to increasing the cross-sectional area. When the interlayer interface is subjected to tensile loads, the deployment density should be increased first to achieve the best improvement in interlayer strength.

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.

Effect of fiber layout on low-velocity impact response of intralaminar hybrid carbon/glass fiber braided composite pipes under internal pressure

This study investigated the low-velocity impact behaviors of intralaminar hybrid carbon/glass braided composite pipes under internal pressure. The effects of intralaminar fiber layout and internal pressure on the mechanical responses, damage extension, and material cost-effectiveness were analyzed. The internal damage distribution of composite pipes with different hybrid fiber alternating numbers but identical mix ratios was evaluated through Micro-CT three-dimensional damage reconstructions. The yarn splitting of brittle carbon fiber materials was mutually prevented by the induction of intra-yarn debonding and delamination damages by hybridization with ductile glass fiber materials, which were prone to produce out-of-plane displacement and shear stresses under impact loading. A smaller hybrid fiber alternating unit was conducive to exploiting the hybrid impact toughening effect by avoiding pure reinforced fiber materials aggregated under the impactor. Internal pressure had a supporting effect on the composite pipe and was effectively synergistic with the hybridization effect. The change in the dominant damage mode resulted in significant reductions in impact deformation and damage severity compared to the unpressurized case.

Absolute Nodal Coordinate Formulation-Based Shape-Sensing Approach for Large Deformation: Three-Dimensional Beam

In recent years, fiber-optic shape sensing, which means reconstructing the deformation state of structures from strain information measured by fiber-optic sensors, has attracted interest from many fields. Most of the existing shape-sensing research for flexible three-dimensional (3D) slender structures is based on simple strain-curvature transformation, relying on standardized substrates with a circular cross section and particular forms of fiber layouts. To develop a more general shape-sensing method that can be applied to a wider range of practical engineering conditions, in this paper, the strain–displacement relationship of 3D slender structures under the effect of multiple deformation modes coupling is described by introducing absolute nodal coordinate formulation element, and the deformation reconstruction problem is reorganized into a nonlinear optimization problem that can be applied to large deformation and accommodates different cross-sectional shapes and optical fiber layouts. Due to the rapid increase in the calculation difficulties of nonlinear optimization problems with the number of variables, an element-by-element solving strategy is adopted, and nodal degrees of freedom that have less influence on the overall shape of the structure are merged. In addition, in order to address the issue of local strain anomalies caused by unmodeled factors such as section warping, the pointwise matching between the theoretical strains and measured strains is relaxed to an average matching in subregions to capture the overall deformation, improving the robustness and computational efficiency of the solution process. The accuracy and computational performance of the proposed method are verified through numerical simulation and experiment.

Investigation on sensor layout of optical fiber d istributed acoustic sensing technology for flow velocity measurement in pipes

Investigation on sensor layout of optical fiber d istributed acoustic sensing technology for flow velocity measurement in pipes

Design and angular robustness test of chirped periodically poled lithium niobate crystal for 1064 nm second-harmonic generation experiment

A 532-nm solid-state laser, generated by second-harmonic generation (SHG) technology, has become one of the most extensively used lasers in various applications today. In the traditional scheme, the most prevalent SHG crystal of the 532-nm solid-state is lithium borate (LBO), and continues to exhibit insufficient angular robustness and SHG efficiency. In order to overcome these limitations and obtain SHG crystals with better angular robustness, this study starts with a comprehensive theoretical analysis of angular robustness. On this basis, the structure of a chirped periodically poled lithium niobate (CPPLN) crystal is designed by taking into account the desired properties for improving its performance, and then the theoretical simulations and experimental tests are implemented to validate the effectiveness of the designed crystal. The simulation results corroborate the superior angular robustness of the CPPLN crystal. In a range from <inline-formula><tex-math id="M4">\begin{document}$ - {3^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M4.png"/></alternatives></inline-formula> to <inline-formula><tex-math id="M5">\begin{document}$ + {3^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M5.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M5.png"/></alternatives></inline-formula>, the designed CPPLN crystal exhibits a maximum SHG efficiency of 0.80% and a minimum one of 0.51%, which indicates that the SHG efficiency of this crystal in this range can be maintained at 60% of the maximum efficiency. The experimental results show that the SHG efficiency can be more than 11 times that of LBO crystal. Moreover, the study indicates that the half width of the actual SHG efficiency near the incident angle of the designed CPPLN crystal can exceed <inline-formula><tex-math id="M6">\begin{document}$ {6^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M6.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M6.png"/></alternatives></inline-formula>, demonstrating its excellent tolerance for changes in incident angle. Furthermore, the output spot of the SHG light generated by the designed CPPLN crystal exhibits a standard Gaussian profile, which remains virtually unaffected by the incident angle. In summary, the findings of this research highlight the CPPLN crystal as a promising alternative to LBO, with markedly higher SHG efficiency and better angular robustness. These superior characteristics make the CPPLN crystal a highly attractive candidate for a wide range of laser applications.

Affordable lab-scale electrospinning setup with interchangeable collectors for targeted fiber formation

The electrospinning method is increasingly in demand due to its capability to produce fibers in the nanometer to micrometer range, with applications in diverse fields including biomedical, filtration, energy storage, and sensing. Many of these applications demand control over fiber layout and diameter. However, a standard flat plate collector yields random fibers with limited control over diameter and density. Other viable solutions offering a higher level of control are either scarce or substantially expensive, impeding the accessibility of this vital technique. This study addresses the challenge by designing an affordable laboratory-scale electrospinning setup with interchangeable collectors, enabling the creation of targeted fibers from random, aligned, and coiled. The collectors include the standard flat plate and two additional designs, which are a rotating drum and a spinneret tip collector. The rotating drum collector has adjustable speed control to collect aligned fibers and exhibits stability even at high rotational speeds. The spinneret tip collector was designed to produce helically coiled fibers. The setup was validated by directed fiber formation using polycaprolactone (PCL), a biodegradable and FDA-approved polymer. Overall, the uniqueness of the design lies in its affordability, modifiability, and replicability using readily available materials, thus extending the reach of the electrospinning technique.

Effects of fiber layout on strength and failure of 3D printed notched composites

This study investigates the effect of printing strategies on the strength of additively manufactured notched fiber reinforced composite specimens. Specimens with varying notch geometries (two radii and two opening angles) and fiber layouts (unreinforced, unidirectional, quasi-isotropic and concentric) were 3D printed and tested under tension. Digital image correlation provided surface strain field data. Results showed that fiber deposition patterns significantly impact notch sensitivity, failure loads and mechanisms, with notch geometry being of secondary importance. The unidirectional layout achieved the highest strength but with progressive failure, while quasi-isotropic specimens failed abruptly from the notch. The concentric layout shielded the notch region but induced premature failure away from the notch due to transverse stress. Stress concentration factor approaches, which work well for conventional laminates, have limitations for 3D printed composites due to local differences and complex interactions. Optimizing fiber deposition, instead of geometry, emerges as a promising design route. Combining unidirectional and contouring algorithms may improve performance. However, further studies utilizing multiscale modelling and local failure analyses are needed to fully understand failure mechanisms and guide optimal notch designs for 3D printed composites. With improved understanding and design methods, 3D printing promises to unlock new possibilities for structurally efficient notched composite parts.

Surface wrinkling of a film on an anisotropic substrate

This paper presents analytical solution for wrinkling of thin film bonded to anisotropic substrate by complex function method and linear perturbation analysis, which is verified by FEM. Effect of material parameters along principal axes on critical strain is illustrated. Furthermore, due to effective modulus determined by Voigt assumption, a fiber-reinforced substrate is considered, and results indicate that both Young’s modulus perpendicular to wrinkling direction and in-plane shear modulus have significant influence on wrinkling onset point. The most effective fiber layout in resisting wrinkling is at about 45°inclined to wrinkling direction and arranging at the upper area of the substrate.

Research on a Space-Time Continuous Sensing System for Overburden Deformation and Failure during Coal Mining.

Underground coal mining can cause the deformation, failure, and collapse of the overlying rock mass of a coal seam. If the mining design, monitoring, early warning, or emergency disposal are improper, in that case, it can often lead to mining disasters such as roof falls, water inrush, surface collapse, and ground fissures, seriously threatening the safety of mine engineering and the geological environment protection in mining areas. To ensure the intrinsic security of the entire coal mining process, aspace-time continuous sensing system of overburden deformation and failure was developed, which breaks through the limitations of traditional monitoring methods that characterize the evolution process of overlying rock deformation and ground subsidence. This paper summarizes the classification of typical overburden deformation and failure modes. It researches the space-time continuous sensing of rock-soil mass above the coal seam based on Distributed Fiber Optic Sensing (DFOS). A multi-range strain optical fiber sensing neural series from micron to meter was developed to achieve synchronous sensing of overburden separation, internal micro-cracks, and large rock mass deformation. The sensing cable-rock mass coupling test verified the reliability of the optical fiber monitoring data. The sensing neural network of overburden deformation was constructed using integrated optical fiber layout technology on the ground and underground. Different sensing nerves' performance and application effects in overburden deformation and failure monitoring were compared and analyzed with field monitoring examples. A physical model was used to carry out the experimental study on the overburden subsidence prediction during coal mining. The results showed that the optical fiber monitoring data were reliable and could be used to predict overburden subsidence. The reliability of the calculation model for overlying rock subsidence based on space-time continuous optical fiber sensing data was verified in the application of mining subsidence evaluation. A systematic review of the shortcomings of current overburden deformation observation technology during coal mining was conducted, and a space-time continuous sensing system for overburden deformation and failure was proposed. This system integrated sensing, transmission, processing, early warning, decision-making, and emergency response. Based on the fusion of multi-parameter sensing, multi-method transmission, multi-algorithm processing, and multi-threshold early warning, the system realized the real-time acquisition of space-time continuous information for the overburden above coal seams. This system utilizes long-term historical monitoring data from the research area for data mining and modeling, realizing the prediction and evaluation of the evolution process of overburden deformation as well as the potential for mining subsidence. This work provides a theoretical reference for the prevention and control of mining disasters and the environmental carrying capacity evaluation of coal development.

Speech Enhancement Based on Array-Processing-Assisted Distributed Fiber Acoustic Sensing

Distributed Fiber acoustic sensing (DAS) based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) has attracted lots of attention due to unique advantages. In security monitoring, speech recognition and other relevant fields, DAS’s ability to acquire speech signals is a key indicator for the practical application. However, the speech signal has broadband and non-stationary characteristics, so the conventional filtering is not sufficient, and the speech enhancement algorithm based on the characteristics of the speech signal is needed; on the other hand, the acoustic sensitivity of conventional fiber layout is not high enough, resulting in poor signal quality. In this paper, speech enhancement based on array-processing-assisted DAS system is proposed to recover speech signal with high-fidelity. Pulse compression Φ-OTDR, combined with multichannel speech enhancement algorithm based on optimally modified log-spectral amplitude (OM-LSA) is used. As far as we know, this is the first time that the multichannel OM-LSA speech enhancement is proposed for DAS. Compared with the signal before processing, the speech signal processed by this method has a great improvement in the signal distortion, background noise intrusiveness and signal overall quality. In addition, other signal enhancement methods, such as wavelet denoising and beamforming are also analyzed and compared. Our scheme outperforms in above three aspects. This scheme does not need to obtain a large number of data sets in advance, and can be transplanted to other DAS systems, which has great significance for realizing high performance speech acquisition.

Structure shape measurement method based on an optical fiber shape sensor

In industry and architecture, real-time and complete measurement of structures has become a research frontier since it is directly related to the safety of life and property. Optical fibers have the potential to monitor constructions due to advantages such as small size, anti-electromagnetic interference, etc. However, existing research on optical fiber sensors pays attention to the sensing fiber itself and ignores the layout of the optical fibers. As a result, currently available fiber sensors are only suitable for monitoring one-dimensional rigid structures such as surgical robots and puncture needles. They may face challenges when measuring the freeform surfaces encountered in industrial and architectural scenarios. In this paper, a cross-orthogonal measurement method based on optical fiber shape sensors is proposed to meet the shape measurement requirements of freeform surfaces. The cross-orthogonal network allows global measurement and performs surface reconstructions more easily as compared to single-fiber arrays. It also divides the sensing fiber into several segments that are reconstructed separately (with different initial frames), avoiding the cumulative error at the end of the sensing fiber. Results of verification experiments using four-core fibers indicate that the presented method can improve measurement accuracy.

Enhancing delamination resistance with intralaminar stiffness tailoring: A numerical study of variable stiffness composites

In general, strategies and techniques involving intralaminar stiffness tailoring are primarily used to improve compressive capacity (buckling and post-buckling) or tensile properties rather than interlaminate toughness for composites. However, in this work, we show the potential of utilizing intralaminar stiffness tailoring to enhance delamination resistance by specifically investigating the perforated variable stiffness composite plate with a different layout of curvilinear fibers. Firstly, a standard finite element model with the typical cohesive interface to evaluate the delamination performance of different composites is established and is verified against the averrable experimental data of intact constant stiffness composites. Then, two kinds of curvilinear fibers for the perforated composite plates under the Mode I and Mode II delamination test are investigated considering the different fiber layouts and the size of the central cutout. The reaction force–displacement curve and the R-curve of the composites with the curvilinear fibers are obtained to show the enhancement effect of the intralaminar stiffness tailoring on the delamination resistance. The interlaminate toughness of the curvilinear fibers laminate can overperform the straight fibers laminate up to 71% and 63% in the mode Ⅰ and mode Ⅱ cases (r = 8). The underlying mechanism is discussed in detail to inspire new ideas for intra-laminar stiffness tailoring to improve interlaminar toughness.

Validation of a shape-optimized 2-unit cantilevered inlay-retained fiber-reinforced resin-bonded dental prosthesis

Statement of problemCurrent designs of fiber-reinforced composite (FRC) resin-bonded fixed dental prostheses (RBFDPs) have a limited lifespan, failing mainly through veneer-fiber delamination, debonding, and fracture. PurposeThe purpose of this in vitro study was to validate a new inlay-retained 2-unit cantilevered RBFDP with an optimized cavity and fiber layout proposed in a previous study by using simulated occlusal loading. Material and methodsTwo groups of specimens (n=20), 1 with and 1 without glass fibers, were used to test the influence of the cavity design and that of the fiber layout on their load capacity, respectively. The specimens without fibers were directly cut from a resin-ceramic block by using a computer-aided manufacturing system, while those with fibers were manually fabricated with unidirectional glass fibers and composite resin in a silicone mold. The specimens with and without fibers were attached to abutments made of the same resin-ceramic with a cyanoacrylate-based adhesive and a resin-based dental cement, respectively. An increasing compressive load was applied on the mesial fossa of the premolar pontic until failure. Cracking in the specimens during loading was monitored with a 2-channel acoustic emission (AE) system. ResultsAll the specimens without fiber reinforcement debonded from the abutments. Those using the optimized shovel-shaped cavity design had a mean ±standard deviation failure load (50.0 ±17.3 N) that was 193% higher than that of those with the conventional step-box design (17.1 ±6.2 N; P<.001). No significant difference was found between the groups for the mean number of AE events per specimen (step-box: 49 ±34 versus shovel-shaped: 63 ±34; P=.427), the mean amplitude of each event (58.4 ±1.3 dB versus 59.5 ±2.4 dB; P=.299), or the mean time to failure (283.2 ±122.3 seconds versus 297.5 ±66.7 seconds; P=.798). Between the groups of specimens with reinforcing fibers, the mean failure load of the conventional design was approximately half that of the optimized one. Again, no significant difference was found for the mean number of AE events per specimen (conventional: 28 ±18 versus optimized: 52 ±53; P=.248) or the mean amplitude for each AE event (64.9 ±4.2 dB versus 61.7 ±5.2 dB; P=.187). The connectors of 8 fiber-reinforced specimens with the conventional design fractured; the other 2 debonded from the abutments. Half of the shape-optimized fiber-reinforced specimens had fractured abutments, but the cantilevers remained intact, 4 specimens fractured at the connector, and only 1 debonded from its abutment. ConclusionsThe shape-optimized 2-unit cantilevered FRC RBFDP had a higher load capacity than the conventional design.

A Bioinspired Orthopedic Biomaterial with Tunable Mechanical Properties Based on Sintered Titanium Fibers.

Inadequate mechanical compliance of orthopedic implants can result in excessive strain of the bone interface, and ultimately, aseptic loosening. It is hypothesized that a fiber-based biometal with adjustable anisotropic mechanical properties can reduce interface strain, facilitatecontinuous remodeling, and improve implant survival under complex loads. The biometal is based on strategically layered sintered titanium fibers. Six different topologies are manufactured. Specimens are tested under compression in three orthogonal axes under 3-point bending and torsion until failure. Biocompatibility testing involves murine osteoblasts. Osseointegration is investigated by micro-computed tomography and histomorphometry after implantation in a metaphyseal trepanation model in sheep. The material demonstrates compressive yield strengths of up to 50MPa and anisotropy correlating closely with fiber layout. Samples with 75% porosity are both stronger and stiffer than those with 85% porosity. The highest bending modulus is found in samples with parallel fiber orientation, while the highest shear modulus is found in cross-ply layouts. Cell metabolism and morphology indicate uncompromised biocompatibility. Implants demonstrate robust circumferential osseointegration in vivo after 8 weeks. The biometal introduced in this study demonstrates anisotropic mechanical properties similar to bone, and excellent osteoconductivity and feasibility as an orthopedic implant material.

Vectorial distributed acoustic sensing based on a multicore fiber and phase-sensitive optical time-domain reflectometry.

A vectorial distributed acoustic sensing (vDAS) system is proposed and demonstrated for distributed two-dimensional vector vibration measurements based on phase-sensitive optical time-domain reflectometry (ΦOTDR). An optical pulse compression (OPC) algorithm was used to achieve high spatial resolution and suppress fading noise, and a Rayleigh-enhanced seven-core fiber (eSCF) was used to magnify the differentials of Rayleigh backscattering (RBS) in various cores undergoing vibrations. A combination of OPC and eSCF allows the system to fully quantify perturbations with a spatial resolution of 1.1 m and a strain resolution of 1.1 pε/√Hz, achieving a maximum acceleration sensitivity of 1.04 mrad/g at 60 Hz and an orientation reconstruction error of 1.92°. The proposed vDAS system can achieve vectorial distributed vibration sensing without the need for specific fiber layouts or complex reconstruction algorithms, increasing its potential for applications in vertical seismic profiles or pipeline inspection.

A full-scale topology optimization method for surface fiber reinforced additive manufacturing parts

Additive manufacturing provides new design space for fiber-reinforced composite structures given the flexibility in fiber layout and substrate material distribution. Hence, the present research develops a topology optimization method dedicated for surface fiber reinforcement design. The targeting part is composed of fiber contents reinforcing the boundary contour and isotropic substrate materials infilling the structural interior. The idea of full-scale modeling of the fiber contents and the approach of addressing the bi-modulus reinforcement effect are highlighted. Specifically, under the SIMP framework, the fiber contents (including the fiber materials and the wrapping matrix materials) are identified through boundary layer extraction with double layers of density smoothing and projection, and the reinforcement fiber materials are recognized through analytical skeleton extraction from the boundary layer. In this manner, constant-thickness fiber contents are modeled and more importantly, stringently incorporated into the topology optimization problem formulation. Both the boundary layer thickness and the fiber reinforcement thickness can be explicitly controlled by modifying the projection threshold parameters. Compliance minimization problems are considered in the current study. Sensitivities of the objective and constraint functions are derived to guide the design update. Several numerical and experimental examples are provided to demonstrate the validity and effectiveness of the proposed method, especially disclosing the impact on the derived topological structures by incorporating boundary layer fibers.

Performance-Based Fibre Design for Ultra-High Performance Concrete (UHPC)

The paper presents a method to establish a performance-based fibre design of high-strength micro steel fibres for ultra-high-performance concrete (UHPC). The performance-based fibre design considers effects of fibre layout, fibre orientation, and type of loading (quasi-static and cyclic) and expands the current approach using experiences and suitability testing results. The performance-based fibre design is based on a so-called utilization rate, which is determined via pullout tests of high-strength micro steel fibres in UHPC under quasi-static as well as high cyclic loading with varying orientations and embedment depths. The utilization rate for a straight fibre pullout is 0.27 on average considering the measured tensile strength of the fibre and 0.50 considering the manufacturers specifications. For inclined fibres, additional bending stresses occur at the exit point of the fibre channels, leading to a significant increase in local tensile stress. Therefore, the utilization rate of inclined fibres under quasi-static loading is approximately 60–70% higher than in the case of straight embedded fibres (comparing it to the measured tensile strength). Comparing the utilization rate to the manufacturer’s specification, it increases to approximately 1.00. Under cyclic loading, the additional bending stresses in inclined fibres result in a local increase of the load amplitude, leading to a reduced fatigue resistance and premature fibre rupture, underlining the feasibility of a performance-based fibre design.

Finite element modelling of 3D printed continuous carbon fiber composites: Embedded elements technique and experimental validation

A finite element approach for the simulation of composite parts with complex geometry realized by continuous fiber reinforced additive manufacturing is described. The embedded elements technique was adopted to accurately represent the layout of matrix and fibers while retaining an effortless finite element model setup. A simple specimen geometry with three different fiber layouts was chosen for experimental testing to allow the comparison of the embedded elements approach with conventional analytical or numerical methods for stiffness assessment. A complex specimen geometry with multiple notches was also printed, with three different fiber layouts, to further validate the use of the embedded elements technique in presence of 3D printed fiber deposition patterns for which conventional methods could not be applied. This study showed that the embedded elements approach, compared to more traditional techniques based on homogenization, may allow an accurate prediction of stiffness with the additional ability to model complex fiber deposition patterns, a simpler finite element analysis setup and a potentially richer output.