Characterizing the deformation response of a unidirectional non-crimp fabric for the development of computational draping simulation models

In several countries around the world, including Canada, government incentives have been put in place to improve the fuel efficiency of vehicles and reduce CO2 emissions. Improvements in composites manufacturing technology, such as high-pressure resin transfer molding and quick curing resins, makes it practical to lightweight through the incorporation of carbon fiber reinforced polymer (CFRP) parts into the body-in-white structure of vehicles. However, the technology has only been realized for small production rates and is currently in the developmental phase towards full automation for high-volume production. Hence, there is a need to developed and calibrate fabric draping simulations models to support this effort and enable the design of CFRP production processes that incorporate cost-effective fabric reinforcement material, such as heavy tow unidirectional non-crimp fabric (UD-NCF). This work aimed to expand the understanding of the forming behaviour of UD-NCFs, within the context of the development of automation capabilities for fabric preforming. The investigation focused on the characterization of the macroscale response of a UD-NCF, including an investigating of associated local deformation mechanisms, to calibrate a macroscale constitutive model and support the development of a computational fabric draping simulation model. The fabric characterization consisted of a series of experimental tests that measured the fabric in-plane and out-of-plane deformation responses reminiscent of draping operations. The tests were conducted with respect to the carbon fiber (CF) tow longitudinal and transverse directions. The experimental tests conducted were the longitudinal, transverse, and off-axis extension tests; the picture frame test (PFT); the cantilever; and friction sliding test in both material directions. The longitudinal extension and bending stiffness were found to be significantly higher than the respective transverse extension and bending stiffnesses. Also, at low strains, the fabric transverse extension stiffness was found to be negligible until crimping in the transverse glass fibers was removed. Regarding the fabric friction response, the coefficients of friction were higher on the stitching fabric side and when sliding occurred in the longitudinal fabric direction. Also, an investigation of the fabric mesoscale deformation mechanisms revealed the generation of CF tow undulations and intertow gapping, mainly generated by deformation of the stitching, when the fabric was subjected to transverse extension and shear deformations. To address difficulties associated with sliding of the glass fibers at the clamps during extension and PFT testing a clamping design was proposed that fully restrained the glass fibers, while at the same time preventing specimen damage at the grips. 2D DIC was used to study the development of strains in the fabric during all in-plane experimental tests. Challenges associated with fabric surface texturization and strain measurements through digital image correlation were investigated and addressed to improve the optical strain analysis. A surface texturization technique with an oil-based paint was implemented in all tests as it created high contrast speckle patterns on the fabric surface and the least amount of fabric deformation interference when compared with two other surface texturization techniques. Using the experimental results, a macroscale material model, chosen from the existing material model library available in the commercial finite element software LS-DYNA® was calibrated to simulate forming operations. The material model was calibrated for in-plane and out-of-plane deformation modes in accordance with the experimental tests conducted. The material model parameters were identified by simulating the experimental tests conducted during the fabric characterization process and an iterative inverse parameter identification approach until a good correlation was obtained between the numerical simulations and the corresponding physical tests. In most cases, piecewise linear functions were used to approximate the experimental test data before entering into the material model. Finally, to validate the calibration of the material model, a single-layer 100-mm diameter hemispherical test with a displacement controlled punch was performed and simulated using the calibrated material model. In addition to the calibrated material model, results from the friction tests were used to define contact boundary conditions in the draping simulation model. A good agreement was obtained between the simulation predictions of macroscopic deformations observed in the fabric, including contour shape and wrinkling, and the experimental results

3DBodyNet: Fast Reconstruction of 3D Animatable Human Body Shape from a Single Commodity Depth Camera

Knowledge about individual body shape has numerous applications in various domains such as healthcare, fashion and personalized entertainment. Most of the depth based whole body scanners need multiple cameras surrounding the user and requiring the user to keep a canonical pose strictly during capturing depth images. These scanning devices are expensive and need professional knowledge for operation. In order to make 3D scanning as easy-to-use and fast as possible, there is a great demand to simplify the process and to reduce the hardware requirements. In this paper, we propose a deep learning algorithm, dubbed 3DBodyNet, to rapidly reconstruct the 3D shape of human bodies using a single commodity depth camera. As easy-to-use as taking a photo using a mobile phone, our algorithm only needs two depth images of the front-facing and back-facing bodies. The proposed algorithm has strong operability since it is insensitive to the pose and the pose variations between the two depth images. It can also reconstruct an accurate body shape for users under tight/loose clothing. Another advantage of our method is the ability to generate an animatable human body model. Extensive experimental results show that the proposed method enables robust and easy-to-use animatable human body reconstruction, and outperforms the state-of-the-art methods with respect to running time and accuracy

Nonterrestrial utilization of materials: Automated space manufacturing facility

Four areas related to the nonterrestrial use of materials are included: (1) material resources needed for feedstock in an orbital manufacturing facility, (2) required initial components of a nonterrestrial manufacturing facility, (3) growth and productive capability of such a facility, and (4) automation and robotics requirements of the facility

Wafer-level processing of ultralow-loss Si3N4

Photonic integrated circuits (PICs) are devices fabricated on a planar wafer that allow light generation, processing, and detection. Photonic integration brings important advantages for scaling up the complexity and functionality of photonic systems and facilitates their mass deployment in areas where large volumes and compact solutions are needed, e.g., optical interconnects. Among the material platforms available, silicon nitride (Si3N4) displays excellent optical properties such as broadband transparency, moderately high refractive index, and relatively strong nonlinearities. Indeed, Si3N4 integrated waveguides display ultralow-loss (few decibels per meter), which enables efficient light processing and nonlinear optics. Moreover, Si3N4 is compatible with standard complementary metal oxide semiconductor (CMOS) processing techniques,which facilitates the manufacture scalability required by mass deployment of PICs. However, the selection of a single photonic platform sets limitations to the device functionalities due to the intrinsic properties of the material and the fundamental limitation of optical waveguiding. Multilayer integration of different platforms can overcome the limitations encountered in a singleplatform PIC.This thesis presents the development of advanced techniques for the waferlevel manufacturing of ultralow-loss Si3N4 devices and approaches to enable their interface with active components like modulators and chip-scale comb sources (microcombs). The investigation covers the tailoring of a waveguide to the functionality required, the wafer-scale manufacturing of Si3N4, and how to overcome the limitations of a single platform on a wafer. These studies enable high-yield fabrication of microcombs, the integration of two Si3N4 platforms on the same wafer, and a strategy to efficiently couple to an integrated LiNbO3 layer to expand the chip functionality and scale up the complexity of the PIC

Wrinkling behaviour of biaxial non-crimp fabrics during preforming

The necessary lightweighting of the transport sector to meet emission reduction targets can be helped through the expanded use of composites. However, for the high volume production of composites to be cost-effective, it is needed that they can be manufactured through automated liquid composite moulding (LCM). Furthermore, the defects that occur during the initial preforming stage of LCM, notably wrinkles, are a key obstacle preventing automation and adoption of LCM, because wrinkles significantly compromise the component performance, and because there is currently no reliable method for mitigating them. To pave the way towards wrinkling mitigation during preforming, this thesis aims to characterise the wrinkling behaviour of non-crimp fabrics (NCFs) as well as to investigate how the wrinkling severity is affected by the tool geometry. These aims are achieved through both experimental and numerical approaches. Firstly, experimental forming tests are conducted to characterise the mechanisms, severity and variability of wrinkling for a ±45° biaxial NCF during preforming, considering four contrasting benchmark geometries. Secondly, a large dataset of forming simulations for various tool geometries is generated and used to investigate the effect of geometry on wrinkling severity, and to develop a deep learning based surrogate model for rapidly predicting the fabric wrinkling over a given tool geometry. The results demonstrate that two macroscale wrinkling mechanisms exist for this NCF and that the most severe wrinkles occur consistently via lateral fabric compression during material draw-in rather than tow compression at shear-lockup. Furthermore, they show that the wrinkling variability is significant and is especially apparent for multi-layer forming. Additionally, the tool geometry is shown to have a substantial effect on wrinkling with more tapered geometries leading to less severe wrinkling. Lastly, the surrogate model is demonstrated to achieve similar predictions to the finite element simulations but at a much lower computational cost, thus enabling the optimisation of component geometry for minimal wrinkling

The prediction of wrinkle formation in non-crimp fabrics during double diaphragm forming

Liquid composite moulding (LCM) processes are an economical alternative to autoclave-cured prepreg, as intermediate material forms are less expensive, capital equipment costs are lower and cycle times are shorter. LCM is suitable for producing aerospace quality components, but the process chain is dependent on a separate preforming process to convert 2D fibre formats into complex 3D shapes prior to moulding. Preforming is difficult to automate to ensure defect-free architectures, as multiple plies are often formed at the same time according to predefined forming loads and constraints. Corrections to the draping direction, force and sequence can be easily refined during manual hand layup, as the laminator works on one ply at a time. Corrections to the forming sequence cannot be easily made during automated forming, therefore numerical models are required during the design phase to refine process parameters to ensure that defects do not evolve. This thesis seeks to develop a robust simulation methodology for modelling the forming behaviour of biaxial fabrics, in order to enable effective identification of forming related defects and assist in process design for improving the quality of preforms. Research has been conducted in three main areas: (I) Material characterisation and model development. A macroscale constitutive model has been developed to simulate the forming behaviour of biaxial fabrics, based on an explicit finite element scheme, incorporating the effects of bending stiffness to predict wrinkling. Cantilever tests were employed to characterise the bending behaviours of a twill-weave woven fabric and a non-crimp fabric (NCF) with pillar stitches, providing linear (a constant rigidity) and nonlinear bending stiffness models to represent the fabric materials. Experimental and numerical studies have shown that the bending behaviour of the fabrics is nonlinear, which is dependent on the fibre curvature along the bending direction. Forming simulations using a constant bending stiffness from the standard cantilever test (BS EN ISO 9073-7; 1998) produced unrealistic predictions for fabric bending and wrinkling behaviours, while the nonlinear model produced more accurate forming induced wrinkle patterns compared to the experimental data. The nodal distance between the deformed fabric mesh and the tool surface was identified to be a suitable method to locate areas containing out-of-plane defects, using the principal curvature to further isolate wrinkles from areas of fabric bridging (poor conformity). (II) Multi-resolution modelling approach for defect identification. A multi-resolution modelling strategy was developed for determining forming induced defects in large-scale DDF components, using a macroscopic global-to-local sub-modelling technique. The fabric constitutive model developed in Stage (I) above was used for predicting macro-scale defects (i.e. wrinkling and bridging defects at the ply level) during double diaphragm forming (DDF) of a generic geometry comprising local changes in cross-sectional shape. Comparisons between simulations and experimental results confirmed the accuracy of the forming model, but the runtime of the full-scale shell-element model was found to be impractical. Therefore, a multi-resolution modelling strategy was developed to improve the overall computational efficiency. Areas containing potential defects were initially determined by a full-scale global simulation using a coarse membrane-element mesh (element edge length of ~5mm). Results with higher resolution (wrinkle amplitude of ~1mm) and more realistic shapes were subsequently obtained by local sub modelling, using higher order shell-element meshes, based on boundary conditions derived from the global simulation. The applied methodology enabled an 87% saving in the runtime compared to the high fidelity full-scale shell-element model for the same geometry, with the length of wrinkles and area of fabric bridging predicted within 10% compared to experimental data. These reductions will become more significant as the overall length scale is increased for components produced by DDF, as defects will tend to be within more localised regions. (III) Defect formation and mitigation during multi-ply NCF forming. Forming experiments and simulations were performed to investigate the mechanism of wrinkling in multi-layered NCF plies during DDF. Simulation results indicate that in-plane fibre compression, caused by dissimilar shear deformation between adjacent plies, can lead to out-of-plane wrinkles, where the wrinkle length is a function of the relative fibre angle at the ply-ply contact interface. The most severe wrinkles occurred when the inter-ply angle was 45° for a multi-ply biaxial NCF preform. Numerical and experimental studies have shown that out-of-plane wrinkles are sensitive to the friction resistance between NCF plies and therefore lubricating the fibres can minimise wrinkling defects caused by dissimilar inter-ply deformation. In summary, results from the first part of the thesis (Chapter 3 and Chapter 4) demonstrate the importance of incorporating a curvature-dependent bending behaviour into fabric constitutive modelling for correctly predicting forming behaviour of bi-axial fabrics. The multi-resolution forming simulation strategy (Chapter 5) extends the capability of the proposed fabric model to predict macroscale defects in large structures more efficiently. The study on multi-ply fabric forming (Chapter 6) provides further understanding about the effect of inter-ply sliding on ply wrinkling, enabling a feasible solution for wrinkle mitigation. The results from this work can be directly extended for industrial application to improve the performance of composite structures made via fabric preforms