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

Near-microscale modelling of dry woven fabrics under in-plane shear loading

This article proposes a near micro-scale modelling technique to predict nonlinear shear behaviour of dry woven fabrics in a picture frame test using the digital element method. In the proposed model, the fabric yarns are modelled as bundles of virtual fibres that are then modelled by the truss elements in finite element code. Additionally, our finite element analysis was performed in a repeated unit cell and the contact friction among the fibres is explicitly considered. Especially, we proposed so-called enhanced periodic boundary conditions to capture the mechanical behaviour of fabrics both in the small and large shear angle regimes

Delamination resistant composites by interleaving bio-based long-chain polyamide nanofibers through optimal control of fiber diameter and fiber morphology

In this work an innovative electrospinning system is proposed that simultaneously has an adequate temperature resistance, a high increase in mode I (þ51%) and mode II (þ96%) delamination performance and can be commercially produced. Interleaving nanofibrous veils can potentially solve the issue of the limited delamination resistance encountered in composite laminates, but industrial upscaling has always been impeded by one or more critical factors. These constraining factors include a limited temperature stability of the nanofibers, a lack in simultaneous mode I and II delamination performance increase and the complexity of the electrospinning system because non-commercial polymers or specialty nanofibers (e.g. coaxial) are required. In this paper, a robust electrospinning system is proposed that is the first to overcome all major hurdles to make nanofiber toughening industrially viable. A new class of nanofibers based on biosourced polyamide 11 and its poly(ether-block-amide) co-polymers is used to deal with those shortcomings. The nanofibers have tuneable diameters down to 50 nm and cross-section morphologies ranging from circular to ribbon-shaped. The key to this work is the fundamental underpinning of the toughening effect using a broad range of interleaves with different mechanical and thermal properties, fiber diameters and fiber morphologies, all produced from the same bio-based base polymer. Generally, round and thin nanofibers performed better than larger and ribbon-like fibers. The relationship between the fiber morphology and the delamination performance is further underpinned using detailed analysis of the fracture surface. Ultimately, this results in a range of optimized nanofibrous veils capable of improving the delamination resistance considerably without suffering from the aforementioned drawbacks

Finite element simulations to evaluate deformation of polyester tubular braided structures

The use of narrow tubular braided structures for biological tissue support has made it possible to produce highly flexible and robust soft tissue reinforcement structures. These attributes make the braids ideal in supporting ruptured and broken tissues during healing and regeneration. There have been continued efforts to improve the design in order to reinforce tissues while still maintaining their flexibility; this has been undertaken by exploring the deformation behavior of these structures. Mechanical modeling, which provides an in-depth understanding of the deformation mechanism of structures, plays an important role in designing structural changes in tubular braids. This paper reports the results of numerical and experimental investigations into the radial contraction and deformation mode of two types of tubular braided fabricssingle and double braidedsubjected to uniaxial tensile loading under quasi-static conditions. Realistic geometrical structures were developed for mechanical modeling of tubular braids in terms of tensile loads, elongation, radial contraction and braid angle. The results indicated that there was a good match between experimental and simulated tensile behavior of the braided structures. It was established that the amount of braided yarns within the structure had the likelihood of influencing the radial contraction and braid angle in the braided structure under uniaxial tensile deformation. The results portrayed that braided structures would undergo large deformations at low loads. It was also established that there would be more structural stability as the yarns increased, evidenced by more loads in the double-braided structure as compared to the single-braided tubular structure

Improving mechanical properties for extrusion-based additive manufacturing of poly(lactic acid) by annealing and blending with poly(3-hydroxybutyrate)

Based on differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, polarizing microscope (POM), and scanning electron microscopy (SEM) analysis, strategies to close the gap on applying conventional processing optimizations for the field of 3D printing and to specifically increase the mechanical performance of extrusion-based additive manufacturing of poly(lactic acid) (PLA) filaments by annealing and/or blending with poly(3-hydroxybutyrate) (PHB) were reported. For filament printing at 210 °C, the PLA crystallinity increased significantly upon annealing. Specifically, for 2 h of annealing at 100 °C, the fracture surface became sufficiently coarse such that the PLA notched impact strength increased significantly (15 kJ m−2). The Vicat softening temperature (VST) increased to 160 °C, starting from an annealing time of 0.5 h. Similar increases in VST were obtained by blending with PHB (20 wt.%) at a lower printing temperature of 190 °C due to crystallization control. For the blend, the strain at break increased due to the presence of a second phase, with annealing only relevant for enhancing the modulus.</jats:p