Terms Of Orientation Distribution Function Research Articles

Mechanical analysis of bi-component-fibre nonwovens: Finite-element strategy

In thermally bonded bi-component fibre nonwovens, a significant contribution is made by bond points in defining their mechanical behaviour formed as a result of their manufacture. Bond points are composite regions with a sheath material reinforced by a network of fibres’ cores. These composite regions are connected by bi-component fibres — a discontinuous domain of the material. Microstructural and mechanical characterization of this material was carried out with experimental and numerical modelling techniques. Two numerical modelling strategies were implemented: (i) traditional finite element (FE) and (ii) a new parametric discrete phase FE model to elucidate the mechanical behaviour and underlying mechanisms involved in deformation of these materials. In FE models the studied nonwoven material was treated as an assembly of two regions having distinct microstructure and mechanical properties: fibre matrix and bond points. The former is composed of randomly oriented core/sheath fibres acting as load-transfer link between composite bond points. Randomness of material’s microstructure was introduced in terms of orientation distribution function (ODF). The ODF was obtained by analysing the data acquired with scanning electron microscopy (SEM) and X-ray micro computed tomography (CT). Bond points were treated as a deformable two-phase composite. An in-house algorithm was used to calculate anisotropic material properties of composite bond points based on properties of constituent fibres and manufacturing parameters such as the planar density, core/sheath ratio and fibre diameter. Individual fibres connecting the composite bond points were modelled in the discrete phase model directly according to their orientation distribution. The developed models were validated by comparing numerical results with experimental tensile test data, demonstrating that the proposed approach is highly suitable for prediction of complex deformation mechanisms, mechanical performance and structure-properties relationships of composites.

Numerical modelling of damage initiation in low-density thermally bonded nonwovens

Due to random orientation of fibres and presence of voids in their microstructure, low-density thermally bonded polymer-based nonwovens demonstrate complex processes of deformation and damage initiation and evolution. This paper aims to introduce a micro-scale discontinuous finite element model to simulate an onset of damage in low-density nonwovens. In the model, structural randomness of a nonwoven fabric was introduced in terms of orientation distribution function (ODF) obtained by an algorithm based on the Hough Transform. Fibres were represented in the model with truss elements with orientations defined according to the computed ODF. Another structural element of nonwovens – bond points – were modelled with shell elements having isotropic mechanical properties. The numerical scheme employed direct modelling of fibres at micro level, naturally introducing the presence of voids into the model and thus making it suitable for simulations of low-density nonwovens. The obtained results of FE simulations were compared with our data of tensile tests performed in principal directions until the onset of damage in the specimens.

Orientation Behavior of Carbon Fiber Axes in Polymer Solutions under Magnetic Field Estimated in Terms of Orientation Distribution Function

Orientation behavior of carbon fibers (CFs) in polymer solution/gel under magnetic field was estimated in terms of the orientation distribution function. The estimation was done by a series of spherical harmonics of the orientation distribution function of the reciprocal lattice vector of the (002) plane measured for the composite films. Despite a number of papers concerning the orientation of CFs and carbon nanotubes under magnetic field, all estimations have been done in terms of the second-order orientation factor of the (002) plane. The work described in this paper was first successful for the direct estimation of orientation of CF axes within the dried film in terms of orientation function by considering a random orientation of the CF axes around the magnetic field direction. In this experiment, poly(vinyl alcohol) (PVA) was adopted as the solution to disperse CFs and to prepare the composite films by evaporating solvent. The normalized function obtained experimentally was analyzed in comparison with...

Improvement of Drawability of Titanium-Stabilized Interstitial-Free Steel by Optimization of Process Parameters and Texture

A detailed study on the effect of cold rolling and annealing temperature on the texture and drawability of Ti-stabilized interstitial-free (IF) steels have been made with a view to achieving high drawability. The presence of shear type and cold-deformation type of textures in the hot bands of 3.8-, 4.3- and 4.5-mm thickness has been attributed to finish rolling below the Ar3 temperature. The 4.5-mm hot band was selected for further studies as it showed a strong γ fiber. Cold rolling of the hot band was done in the range of 60 to 90 pct, followed by batch annealing in the range of 660 °C to 750 °C. For a particular annealing temperature, a maximum in the intensity of \( {\left\{ {{\text{111}}} \right\}}{\left\langle {{\text{110}}} \right\rangle } \) component, and in average normal anisotropy, an rm value was observed with the increase in cold reduction, followed by a drop with further cold reduction. The results are discussed in terms of orientation distribution function (ODF), recrystallization behavior, and precipitation of FeTiP, (Ti, Mn) S, and TiC particles. Fine FeTiP-type precipitates in the grains and at the grain boundaries in samples annealed at 660 °C, as well as samples associated with (Ti, Mn)S in samples annealed at 750 °C, were found to be detrimental for the development of beneficial γ fiber and improved drawability, while coarse FeTiP-type precipitates in 80 pct cold-reduced samples annealed at 680 °C and 710 °C resulted in maximum rm values of 2.29 and 2.25, respectively. The dissolution of TiC at an annealing temperature of 750 °C adversely affected drawability due to the solute drag effect of solute carbon. An optimized combination of cold reduction and annealing temperature has been established for achieving a uniform γ fiber along with high rm values.

Deformation mechanism of nylon 6 gel and melt films estimated in terms of orientation distribution function of crystallites

Abstract Nylon 6 films were prepared by gelation/crystallization from solutions. The solvents used were a formic acid-chloroform mixture, trifluoroethanol and benzyl alcohol. Maximum values for Young's modulus and the orientational degree of the b-axes (the crystal fibre axes), were obtained for the drawn films prepared from formic acid-chloroform solution. These values, however, were lower than those of melt films. To study the reason for this, the deformation mechanism of gel films prepared from the formic acid-chloroform cosolvent was investigated and compared with the deformation mechanism of melt film using the orientation distribution function of crystallites. The distribution functions of both films exhibited similar profiles, indicating the preferential orientation of the b-axis with respect to the stretching direction by the rotation of crystallites around the c-axis, leading to taut tie molecules. This mechanism was found to be quite different from the molecular orientation of ultradrawn polyethylene gel films associated with significant crystal transformation from a folded to a fibrous type.