Mechanical behaviour of irregular fibre materials

This work investigates the effect of fibre irregularities on the mechanical behaviour of the irregular fibres using the finite element method (FEM). The first part of this work examines that the effect of fibre dimensional irregularities on the linear and non-linear tensile behaviour of the fibres, using a two-dimensional (2D) finite element models. In the linear simulation, a concept of method Young’s modulus is introduced. The method Young’s modulus, breaking load and breaking extension are affected by the magnitude and frequency of diameter variation in the fibre specimen. Fibre dimensional variation and the gauge length effect are also simulated. In the non-linear analysis, some additional information is obtained on changes in the yield and post-yield regions, which are clearly shown in the load-extension curves. Further investigation is focused on the flexural buckling behaviour of fibres with dimensional irregularities. A three-dimensional (3D) finite element model is used to simulate the buckling deformation of dimensionally irregular fibres, and the critical buckling load of the simulated fibre is calculated. Two parameters, the effective length and the average diameter within the effective length of an irregular fibre, are considered to be the key factors that influence the buckling behaviour of the fibre. An important aspect of this work is the calculation of the effective length of an irregular fibre specimen during buckling. This method has not been reported before. The third part of this work is on the combined tensile and torsional behaviour of fibres with dimensional irregularities, using a three-dimensional (3D) finite element model. Two types of fibres, polyester and wool, are simulated with sine waves of different level (magnitude) and frequency at different twist levels. For the polyester fibre, experiment verification of the simulation results has been carried out, and the results indicate the FE model is well acceptable for the simulation. The final part of this work examines the combined effect of dimensional and structural irregularities on the fibre tensile behaviour. Three-dimensional (3D) finite element models are used to simulate the cracks (transverse, longitudinal, combined transverse and longitudinal cracks) and cavities distributed in uniform fibres and fibres with 30% level of diameter variation, respectively. One of important conclusions is that under the simulated conditions, the dimensional irregularity of fibre influences the tensile behaviour of fibres more than the fibre structural irregularity. The fibre dimensional irregularity affects not only the values of the breaking load and breaking extension, but also the shape of load-extension curves. However, the fibre structural irregularity simulated in the study appears to have little effect on the shape of the load-extension curves. In addition, the effect of crack or cavity size, type and distribution on fibre tensile properties is also investigated.

The effect of humidity and temperature on Wool Comfort Meter assessment of single jersey wool fabrics

The Wool ComfortMeter provides an objective measurement of the fabric-evoked prickle discomfort rating provided by wearers. This work aimed to quantify the sensitivity of the Wool ComfortMeter over a range of different temperature and humidity conditions to determine the recommended test conditions for its operation. The design was: three temperatures (notionally 20, 25 and 30°C) at three relative humidities (RHs, notionally 50, 65 and 80%) each with two replicates, using six different wool single jersey knits (mean fibre diameter 19.5–27.0 µm). As it was difficult to achieve exactly some of the extreme combinations of temperature and RH, some combinations were repeated, providing a total of 23 different assessment conditions. Data were analysed using restricted maximum likelihood mixed model analysis. The best fixed model included RH, RH2, temperature and the interaction of temperature and RH, accounting for 95% of the variation in Wool ComfortMeter readings. Wool ComfortMeter values were almost constant at 55–60% RH. Generally, the Wool ComfortMeter value reduced with increasing RH > 60% at temperatures of 25°C and 28.5°C as the regain of the fabric increased. However, at 20°C little change was detected as RH was increased from 50 to 80% as there were only small changes in fabric regain. The observed effects were in a good agreement with existing knowledge on the effect of regain on the mechanical properties of wool fibre. Wool ComfortMeter is best operated under standard conditions for textile testing of 65% RH and 20°C.

An experimental investigation of edge strain and bow in roll forming a V-section

V-sections were roll formed from two grades of steel, and the strain on the top and bottom of the strip near the edge was measured using electrical resistance strain gauges. The channels were bent to a radius of 2 and 15 mm along the centerline. The steel strips were of mild and dual phase steel of yield strength 367 MPa and 597 MPa respectively. The longitudinal bow was measured using a 3-dimensional scanning system. The strain measurements were analysed to determine bending and mid-surface strains at the edge during forming. The peak longitudinal edge strain increased with material yield strength for both profile radii. For the 15 mm radius, the bow was larger in the dual phase steel than in the mild steel. For the 2 mm profile radius, the bow was smaller compared with the 15 mm profile radius and it was similar for both steels. It was observed that the difference between the peak longitudinal edge strain and yield strength to Youngs modulus ratio of the material is an important factor in determining longitudinal bow.

Elastic modulus and hardness of cortical and trabecular bovine bone measured by nanoindentation

The elastic modulus and hardness of several microstructure components of dry bovine vertebrae and tibia have been investigated in the longitude and transverse directions using nanoindentation. The elastic modulus for the osteons and the interstitial lamellae in the longitude direction were found to be (24.7±2.5) GPa and (30.1±2.4) GPa. As it's difficult to distinguish osteons from interstitial lamellae in the transverse direction, the average elastic modulus for cortical bovine bone in the transverse direction was (19.8±1.6) GPa. The elastic modulus for trabecular bone in the longitude and transverse direction were (20±2) GPa and (14.7±1.9) GPa respectively. The hardness also varied among the microstructure components in the range of 0.41–0.89 GPa. Analyses of variance show that the values are significantly different.

Adaptive blind source separation using constant modulus criterion and signal mutual information

We address the problem of adaptive blind source separation (BSS) from instantaneous multi-input multi-output (MIMO) channels. It is known that the constant modulus (CM) criterion can be used to extract unknown source signals. However, the existing CM based algorithms normally extract the source signals in a serial manner. Consequently, the accuracy in extracting each source signal, except for the first one, depends on the accuracy of previous source extraction. This estimation error propagation (accumulation) causes severe performance degradation. In this paper, we propose a new adaptive separation algorithm that can separate all source signals simultaneously by directly updating the separation matrix. The superior performance of the new algorithm is demonstrated by simulation examples

Blind equalization of non-irreducible and non-column-reduced channels driven by constant modulus signals

We address the blind equalization of finite-impulse-response (FIR), multiple-input multiple-output (MIMO) channels excited by constant modulus (CM) signals. It is known that the algorithms based on the constant modulus (CM) criterion can equalize an FIR MIMO channel that is irreducible and column-reduced. We show in this paper that the CM property of signals can be exploited to construct a zero-forcing equalizer for a non-irreducible and non-column-reduced channel. We also give a lower bound for the order of the equalizer. Simulation examples demonstrate the proposed result.

New blind source estimation methods based on constant modulus criterion

This thesis presents two novel algorithms for blind chancel equalization (BCE) and blind source separation (BSS). Beside these, a general framework for global convergent analysis is proposed. Finally, the open problem of equalising a non-irreducible system is answered by the algorithm proposed in this thesis.

The effect of microstructure on the decrease of the apparent Young's Modulus in DP 780 steel

Currently, there is a significant effort into developing novel multiphase microstructures to further improve the strength/ductility combination of advanced high-strength steels. To achieve this, the effect of the microstructure on sheet formability needs to be further understood. In this study, the effect of the microstructure on the variation of the elastic modulus in loading and unloading of DP 780 steel has been investigated. Five microstructures with varying volume fractions of ferrite and martensite were generated using different heat treatment cycles. Tension tests were performed to different strain values and the Young’s Modulus during loading and unloading was determined. The test results show that the reduction in unloading modulus with prestrain depends on the volume fraction and hardness of the martensitic phase.

Effect of elastic modulus and poisson's ratio on guided wave dispersion using transversely isotropic material modelling

Timber poles are commonly used for telecommunication and power distribution networks, wharves or jetties, piling or as a substructure of short span bridges. Most of the available techniques currently used for non-destructive testing (NDT) of timber structures are based on one-dimensional wave theory. If it is essential to detect small sized damage, it becomes necessary to consider guided wave (GW) propagation as the behaviour of different propagating modes cannot be represented by one-dimensional approximations. However, due to the orthotropic material properties of timber, the modelling of guided waves can be complex. No analytical solution can be found for plotting dispersion curves for orthotropic thick cylindrical waveguides even though very few literatures can be found on the theory of GW for anisotropic cylindrical waveguide. In addition, purely numerical approaches are available for solving these curves. In this paper, dispersion curves for orthotropic cylinders are computed using the scaled boundary finite element method (SBFEM) and compared with an isotropic material model to indicate the importance of considering timber as an anisotropic material. Moreover, some simplification is made on orthotropic behaviour of timber to make it transversely isotropic due to the fact that, analytical approaches for transversely isotropic cylinder are widely available in the literature. Also, the applicability of considering timber as a transversely isotropic material is discussed. As an orthotropic material, most material testing results of timber found in the literature include 9 elastic constants (three elastic moduli and six Poisson's ratios), hence it is essential to select the appropriate material properties for transversely isotropic material which includes only 5 elastic constants. Therefore, comparison between orthotropic and transversely isotropic material model is also presented in this article to reveal the effect of elastic moduli and Poisson's ratios on dispersion curves. Based on this study, some suggestions are proposed on selecting the parameters from an orthotropic model to transversely isotropic condition.

Highly conductive and thermally stable ion gels with tunable anisotropy and modulus

A new liquid-crystalline ion gel exhibits unprecedented properties: conductivity up to 8 mS cm(-1) , thermal stability to 300 °C, and electrochemical window to 6.1 V, as well as adjustable transport anisotropy (up to 3.5×) and elastic modulus (0.03-3 GPa). The combination of ionic liquid and magnetically oriented rigid-rod polyanion provides widely tunable properties for use in diverse electrochemical devices.

Evolution of elastic modulus in roll forming

Roll forming is a continuous process in which a flat strip is incrementally bent to a desired profile. This process is increasingly used in automotive industry to form High Strength Steel (HSS) and Advanced High Strength Steel (AHSS) for structural components. Because of the large variety of applications of roll forming in the industry, Finite Element Analysis (FEA) is increasingly employed for roll forming process design. Formability and springback are two major concerns in the roll forming AHSS materials. Previous studies have shown that the elastic modulus (Young’s modulus) of AHSS materials can change when the material undergoes plastic deformation and the main goal of this study is to investigate the effect of a change in elastic modulus during forming on springback in roll forming. FEA has been applied for the roll forming simulation of a V-section using material data determined by experimental loading-unloading tests performed on mild, XF400, and DP780 steel. The results show that the reduction of the elastic modulus with pre-strain significantly influences springback in the roll forming of high strength steel while its effect is less when a softer steel is formed.