Robust ODF smoothing for accurate estimation of fiber orientation

Q-ball imaging was presented as a model free, linear and multimodal diffusion sensitive approach to reconstruct diffusion orientation distribution function (ODF) using diffusion weighted MRI data. The ODFs are widely used to estimate the fiber orientations. However, the smoothness constraint was proposed to achieve a balance between the angular resolution and noise stability for ODF constructs. Different regularization methods were proposed for this purpose. However, these methods are not robust and quite sensitive to the global regularization parameter. Although, numerical methods such as L-curve test are used to define a globally appropriate regularization parameter, it cannot serve as a universal value suitable for all regions of interest. This may result in over smoothing and potentially end up in neglecting an existing fiber population. In this paper, we propose to include an interpolation step prior to the spherical harmonic decomposition. This interpolation based approach is based on Delaunay triangulation provides a reliable, robust and accurate smoothing approach. This method is easy to implement and does not require other numerical methods to define the required parameters. Also, the fiber orientations estimated using this approach are more accurate compared to other common approaches.

Natural fiber reinforced composites for femoral component of total hip arthroplasty

This paper describes a theoretical approach to compare two types of fiber reinforced composite materials for femoral component of hip implants. The natural fiber reinforced composite implant is compared with carbon fiber reinforced composite and the results are evaluated against the control solution of a metallic implant made of titanium alloy. With identical geometry and loading condition, the composite implants assumed lower stresses, thus induced more loads to the bone and consequently reduced the risk of stress shielding, whilst the natural fiber reinforced composite showed promising result compared with carbon fibers. However, natural fibers, as well as carbon fibers, lack the power to improve interface debonding due to excessive loads in interface. Nevertheless, natural fiber reinforced composite could be an appropriate alternative given its capability of tailoring and achieving the optimal fiber orientation and robust design.

Rapid composite tube manufacture utilizing the quickstep™ process

In this study, a novel method for manufacturing composite tubes utilizing the Quickstep^TM process has been developed. Tubes manufactured from `quick-cure' Toray G83C prepreg have demonstrated highly repeatable axial crush behavior with an average specific energy absorption (SEA) of 86 kJ/kg. The cure cycle is optimized by comparing the results from compression, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and porosity testing. The tube lay-up is optimized using compression and porosity test results. The effect of changes in fiber-orientation on SEA is also investigated. Process development has resulted in a robust manufacturing method capable of producing fully cured, high performance composite tubes with a cure cycle of 7 min. This corresponds to a 95% reduction in time compared to an equivalent autoclave cycle.

Orientation relationship, texture and microstructure in electromagnetic processed materials (EPM)

In this work, some of our recent results in microstructure, texture and orientation relationship resulting from the application of an external high magnetic field during diffusional and non-diffusional phase transformation in both steel and functional metallic materials have been summarized. A 12-T magnetic field was applied to the diffusional decomposition of austenite in 0.81C-Fe alloy and martensitic transformation of a Ni-Mn-Ga magnetic shape memory alloy. For the 0.81C-Fe alloy, it was found that the magnetic field induces the formation of proeutectoid ferrite and slightly enhances the <001> fiber component in ferrite in the transverse field direction. The magnetic dipolar interaction between Fe atoms in the transverse field direction accounts for this phenomenon. The magnetic field favors the formation of pearlite with Pitsch-Petch 2 (P-P 2) and Isaichev (IS) orientation relationships (OR) between the lamellar ferrite and cementite. For the Ni-Mn-Ga magnetic shape memory alloy, the magnetic field makes the martensite lamellas to grow in some specific directions with their c-axes [001] orientated to the field direction and transverse field direction.

A theoretical analysis for fiber contacts in multilayer nanofibrous assemblies

A theoretical analysis is presented for the estimation of the number of contacts between fibers in random multilayer nanofibrous assemblies with arbitrary fiber diameter and orientation. The statistics of fiber contacts for single-layer nanofiber mats were considered first, and the equations were developed for three-dimensional multilayer nanofibrous assemblies by considering the superposition of the single-layer assemblies. Based on the theoretical approach presented here for multilayer nanofibrous networks, the network porosity, mean fiber diameter and a function of fiber aspect ratio contribute to a model to determine the average number of fiber contacts per unit fiber length in multilayer nanofibrous mats. The theory is studied parametrically and results compared with the work of a model presented by Samson. It is shown that the presented model compared to the existing models is more sensitive with the fiber diameter in the nano-scale. It is also believed that the presented theory for fiber-to-fiber contacts is more realistic and useful for further studies of multilayer nanofibrous assemblies.

Improvement of coating durability, interfacial adhesion and compressive strength of UHMWPE fiber/epoxy composites through plasma pre-treatment and polypyrrole coating

Ultra-high-molecular-weight polyethylene (UHMWPE) fibers have exceptionally higher specific strength and stiffness compared with other high-performance fibers. However, the interfacial adhesion and compressive performance of UHMWPE fiber-reinforced polymer composites (FPCs) are extremely low. The challenges are to achieve load transfer at the interface between the fiber and matrix at a molecular level. Here, we show that plasma pre-treatment of UHMWPE fibers followed by coating with polypyrrole (PPy) results in an 848% improvement in the interfacial adhesion and 54% enhancement in compressive performance. This method takes advantage of a toughening mechanism observed in spider silk and collagen, which the hydrogen bond power the load transfer. The results showed that these improvements of interfacial adhesion and compressive strength were attributed to hydrogen-bonding interactions between the plasma pre-treated UHMWPE and PPy, which improves the fiber-matrix-fiber load transfer process. In addition, the hydrogen-bonded PPy coatings also endowed durability electrical conductivity properties of the UHMWPE fiber.