From dry yarns to complex 3D woven fabrics: a unified simulation methodology for deformation mechanics of textiles in tension, shear and draping

Common methods of modelling the behaviour of fibrous materials, such as yarns and (woven) fabrics, is to treat them as continuous solids. The fibrous behaviour is then taken into account by appropriate constitutive laws. However, the development of such constitutive laws is very complex and requires several specificities (large deformations, orthotropic material behaviour, local crushing, …). Furthermore, by treating the material as a solid material important information about the micromechanics is “lost”. This presentation will show a more viable modelling methodology to simulate the deformation mechanics of fibrous materials and it is based on the use of virtual fibres. This recently developed method effectively takes the fibrous behaviour into account by modelling a yarn as a bundle of virtual fibres, see Figure 1. Each virtual fibre is modelled as a chain of truss elements in Abaqus\Explicit. The virtual fibres can realign themselves and slide relative to each other resembling the mechanics in a real yarn. The advantages of this method will be illustrated by applying it to some very complex problems such as the mechanical behaviour of 3D woven fabrics, draping behaviour of fabrics and stitching of sandwich panels

Fluid-structure interaction of a wind turbine blade employing a refined finite element model coupled with a blade-element momentum method

Typically the aero-elastic simulation tools that are used in industry employ simple beam models to represent the blades of a wind turbine. The aerodynamic loads are usually calculated using a fast blade-element momentum (BEM) method. These models allow relatively fast calculation of the aero-elastic behavior of the blade which is required in order to allow the simulation of a large number of load cases as required by the IEC 61400 [1] and GL [2] standards in a feasible amount of time. Such beam models do however not incorporate the level of detail required to provide the complete stress and strain distribution in the blade, nor are they able to take into account nonlinear effects such as the change in cross-section of the blade due to the brazier effect [3]. Alternatively, highly detailed 3d computational fluid dynamics (CFD) simulations can be coupled with refined finite element (FE) models to obtain highly accurate results both regarding the flow around the blade as regarding the stress and strain distribution within the structure. However, the computational cost of such a simulation is enormous. In this work a coupling has been developed between the BEM code HAWC2-aero, which was developed by DTU [4] and the Abaqus FE solver. This allows a fluid-structure interaction (FSI) simulation by means of a so-called “weak” coupling, meaning that the two different solvers are run sequentially in iterations until convergence is achieved. In this way, a refined structural model is coupled with a fast aerodynamics tool, allowing steady-state fluid-structure interaction (FSI) simulations at an acceptable computational cost. The more advanced structural model allows the investigation of the influence of structural properties such as individual composite plies as well as their positioning, orientation and materials on the aero-elastic behavior of the blade. The influence of non-linear effects on the blade’s aero-elastic behavior can also be analyzed. The finite element model is used to locate stress hot-spots or buckling effects. Loads were applied using two different methods. One method uses distributing couplings to spread the load of a spanwise cross-section over all the nodes on that section. The other method uses concentrated forces at specific nodes to introduce the loads

Regularized Newton-Raphson method for small strain calculation

Digital Image Correlation (DIC) has been proven to be a highly reliable framework for the full-field displacement and strain measurement of materials that undergo deformation when subjected to physical stresses. This paper presents a new method that extends the popular Newton-Raphson algorithm through the inclusion of spatial regularization in the minimization process used to obtain the motion data. The basic principle is that the motion data is calculated between corresponding blocks in the reference and deformed images using adaptively previously obtained motion estimates in the immediate vicinity of the respective location along with the local block-based image information. The results indicate significant accuracy improvements over the classic approach especially when the block sizes and strain calculation windows used for motion and strain estimation decrease in size

Dynamic mode-I delamination of composite laminates using a drop-weight tower and optical data-acquisition

Impact events can hardly be called quasi-static. To test for relevant properties with quasi-static test methods thus seems to make little sense, especially when materials with a rate-sensitivity are the subject of testing. Therefore, a test setup is developed to obtain the trac-tion-separation behaviour and fracture toughness of composites in mode I delamination at impact rates of deformation. An optical technique is applied to obtain the load-deflection curve, allowing for contactless measurements

Characterization of the modal parameters of composite laminates using innovative ultrathin polymer waveguide sensor foils

The use of composite materials, like glass- and carbon- fiber reinforced polymers, is expected to increase exponentially in the coming years. Consequently, in order to monitor the structural health of these materials, the development of new sensing devices is rapidly accelerating. For this purpose, our research groups have recently developed new ultra-thin polymer waveguide sensors which can be exploited to measure both uniaxial and multiaxial strains occurring in composite components. These sensing foils are manufactured by creating Bragg gratings in waveguides realized in flat polymeric substrates, which makes their placement and alignment easier compared to traditional fiber optic sensors. Moreover, using a non-straight waveguide it is possible to spatially multiplex the sensing gratings in such a way that an optical strain rosette can be created. This paper investigates the suitability of the proposed polymer waveguide sensors for the estimation of the modal parameters of composite components

Dense and accurate motion and strain estimation in high resolution speckle images using an image-adaptive approach

Digital image processing methods represent a viable and well acknowledged alternative to strain gauges and interferometric techniques for determining full-field displacements and strains in materials under stress. This paper presents an image adaptive technique for dense motion and strain estimation using high-resolution speckle images that show the analyzed material in its original and deformed states. The algorithm starts by dividing the speckle image showing the original state into irregular cells taking into consideration both spatial and gradient image information present. Subsequently the Newton-Raphson digital image correlation technique is applied to calculate the corresponding motion for each cell. Adaptive spatial regularization in the form of the Geman-McClure robust spatial estimator is employed to increase the spatial consistency of the motion components of a cell with respect to the components of neighbouring cells. To obtain the final strain information, local least-squares fitting using a linear displacement model is performed on the horizontal and vertical displacement fields. To evaluate the presented image partitioning and strain estimation techniques two numerical and two real experiments are employed. The numerical experiments simulate the deformation of a specimen with constant strain across the surface as well as small rigid-body rotations present while real experiments consist specimens that undergo uniaxial stress. The results indicate very good accuracy of the recovered strains as well as better rotation insensitivity compared to classical techniques

Influence of specimen geometry on the fatigue behavior of a carbon fabric reinforced pps

This manuscript studies the tension-tension fatigue behavior of a carbon fabric reinforced PPS and the influence of the specimen geometry on the obtained results. First, the fatigue experiments are preformed according to the ASTM D3479/D3479M standard using the rectangular shaped specimen, but virtually all specimens fail in the tabbed section. This, however, means that fatigue lifetime may be underestimated. Therefore, a new dumbbell-like shape was assessed. Based on the occurring stress concentrations in the tabbed section, the dog bone-like shape was first optimised numerically using FEM, and then, the optimised specimen was tested in tension-tension fatigue. It can be concluded that this dumbbell shape yields better results in terms of acceptable failure and that the used shape has a significant influence on the fatigue lifetime