INFLUENCE OF GNP ON THE TENSILE RESPONSE OF STITCHED COMPOSITES

Through-the-thickness stitching of layered composites provides through-the- thickness reinforcement to enhance the interlaminar tensile and shear strengths while maintaining structural continuity. However, under planar mechanical loads, stitched composites develop strain concentrations in the resin rich areas around the stitch seam causing a local reduction in mechanical properties. In this study, nanographene toughened epoxy is used to reduce strain concentrations around stitch seams and increase the global tensile performance in stitched composites. Stitched carbon fiber preforms ([+45/-45] ), infused with an unmodified epoxy resin were used as baseline laminates and compared to specimens infused with an epoxy resin containing a dispersion of 9 nm nanographene platelets. Specimens with two different periodic stitching patterns (0o and 90o) were fabricated and tested under uniaxial loading. The surface strain fields were obtained using digital image correlation (DIC). Noticeable differences were seen in the strain distributions and tensile properties of these test articles. Specimens with the nanographene-modified matrix showed reductions in the strain concentrations around the stitch seams, thereby increasing the local modulus of elasticity. This study presents the influence of nanographene-modified matrix on the tensile response of stitched composites

Measuring fibre orientation and predicting elastic properties of discontinuous long fibre thermoplastic composites

Elastic properties in critical areas of 3 D shells made from discontinuous long fibre (DLF) composites are difficult to determine via traditional methods, due to the heterogeneity of the material and the geometry of the part. In this paper, a method is proposed to predict the local modulus of DLF composites based on a micrograph of the polished edge of a specimen. The position and orientation of each fibre are extracted from the micrograph and used in conjunction with classical lamination theory to predict the elastic modulus. Fibre discontinuity is accounted for by including a correction factor based on the Cox formula for averaged elastic constants. Model predictions successfully matched the experimental tests results. In a previous study, material flow during compression moulding of recycled DLF panels led to anisotropic behaviour, which was hypothesized to be caused by chip alignment in the flow direction. By using the proposed method, chip alignment due to flow was confirmed and the anisotropy in the elastic modulus was accurately predicted.

On the Planarization Mechanism and Pad Aging Effects of Soft Pad Polishing: A Perspective From the Micro-Mechanical Properties of Soft Pads

The local viscoelastic properties of soft polishing pads with different usage durations are measured by a micro-scale mechanical analysis testing platform. The testing reveals stimulus-adaptive local viscoelasticity of soft pads under the activation of asperity contact. This phenomenon suggests asperity-dependent local modulus. Such an increase of local modulus induced by higher asperity provides a further enhancement effect to the planarization of surface asperity. Furthermore, the measurement outcomes suggest that the reaction of local micro-scale viscoelastic properties of the soft pad surface to the workpiece asperity will decay with usage time. The current study provides a detailed understanding of the aging effects for the soft pad and explains the performance decay during soft pad polishing from a local micro-scale interfacial perspective.

Mappings of Lp-integrable distortion: regularity of the inverse

Let be an open set in ℝn and suppose that is a Sobolev homeomorphism. We study the regularity of f–1 under the Lp-integrability assumption on the distortion function Kf. First, if is the unit ball and p > n – 1, then the optimal local modulus of continuity of f–1 is attained by a radially symmetric mapping. We show that this is not the case when p ⩽ n – 1 and n ⩾ 3, and answer a question raised by S. Hencl and P. Koskela. Second, we obtain the optimal integrability results for ∣Df–1∣ in terms of the Lp-integrability assumptions of Kf.

Evaluating Fouled Ballast Using Seismic Surface Waves

This paper presents the equipment and Spectral Analysis of Surface Wave (SASW) approach for non-invasively characterizing railroad track ballast and foundation layers. Surface wave testing on a railroad track is more complicated than that on soil sites or pavements because of the presence of ballast, crossties, and rails as well as the complexity of ballast-soil foundation structure in terms of the variation of shear-wave velocity with depth. Using portable SASW equipment, the Young’s Modulus of the ballast was calculated for both clean and fouled ballast in wet and dry conditions. In addition, the local modulus is determined at different locations under the tie, e.g. tie center or edge, to investigate modulus variation and tie support under a single tie. Expansion of the system to measure the modulus under two adjacent ties is also discussed and may be suitable for evaluating ballast performance under §213.103, which requires ballast to perform the following serviceability functions: (1) transmit and distribute the load of the track and railroad rolling equipment to the subgrade; (2) restrain the track laterally, longitudinally, and vertically under dynamic loads imposed by railroad rolling equipment and thermal stresses exerted by the rail; (3) provide adequate drainage for the track; and (4) maintain proper track crosslevel, surface, and alignment”.

The Improved Method for Image Edge Detection Based on Wavelet Transform with Modulus Maxima

The improved method for image edge detection based on wavelet transform modulus maxima included following steps: wavelet transform was adopted to compute local modulus maximum of edge and noise. Based on the differences between wavelet transforms of edge and noise, the separation of noise and edge was achieved by detecting local modulus maximum with quadratic discriminate method. Simulation results indicate that the inconsistency between high precision localization and high denoising ability existing in traditional edge detection algorithm could be resolved by means of the algorithm.