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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #2)

Study of Structural Morphology of Hemp Fiber from the Micro to the Nanoscale by Bei Wang; Mohini Sain; Kristiina Oksman (pp. 89-103).

The focus of this work has been to study how high pressure defibrillation and chemical purification affect the hemp fiber morphology from micro to nanoscale. Microscopy techniques, chemical analysis and X-ray diffraction were used to study the structure and properties of the prepared micro and nanofibers. Microscopy studies showed that the used individualization processes lead to a unique morphology of interconnected web-like structure of hemp fibers. The nanofibers are bundles of cellulose fibers of widths ranging between 30 and 100 nm and estimated lengths of several micrometers. The chemical analysis showed that selective chemical treatments increased the α-cellulose content of hemp nanofibers from 75 to 94%. Fourier transform infrared spectroscopy (FTIR) study showed that the pectins were partially removed during the individualization treatments. X-ray analysis showed that the relative crystallinity of the studied fibers increased after each stage of chemical and mechanical treatments. It was also observed that the hemp nanofibers had an increased crystallinity of 71 from 57% of untreated hemp fibers.

Keywords: cellulose nanofibers; hemp; microfibrils; nanostructures; characterization

Tribological Evaluations of Polyester Composites Considering Three Orientations of CSM Glass Fibres Using BOR Machine by B. F. Yousif; N. S. M. El-Tayeb (pp. 105-116).

In the current work, the effects of chopped strand mat (CSM) glass fibre 450 g/m² on tribo-properties of unsaturated polyester are evaluated. Experimental tests were performed by using Block on Ring (BOR) machine against polished stainless steel under dry contact condition. Three principle orientations of CSM glass fibre in the matrix were considered, i.e. namely Parallel (P-O), Anti-Parallel (AP-O) and Normal (N-O). Specific wear rate, friction coefficient and interface temperature were determined and presented as a function of applied load (30–100 N), and sliding distance (0–14 km) at two different sliding velocities (2.8 and 3.9 m/s). Scanning electron microscopy (SEM) was used to observe the damages features on the worn surfaces. The results showed that the orientations of CSM glass fibre significantly influenced the tribological performance of polyester composite. Better tribo performance were achieved when the polyester was reinforced with CSM glass fibre and tested at Parallel orientation. Moreover, specific wear rate and friction coefficient of polyester was reduced by 75%, and 55% at P-O of CGRP composite. The damage features were predominated by debonding of fibers, matrix deformation and polyester debris transfer.

Keywords: CSM glass fibre; Orientations; Neat polyester; Wear and friction

Experimental Determination of the Transversal and Longitudinal Fibre Bundle Permeability by J. S. U. Schell; M. Siegrist; P. Ermanni (pp. 117-128).

In the resin transfer moulding process, fabrics are very often used as reinforcement. These fabrics consist of fibre bundles. In this context, both the permeability of the macroscopic fabric and the permeability of the fibre bundle are the key parameters to accurately predict the impregnation of the fabrics, the impregnation time and resulting void content. The fibre bundle permeability can be either predicted theoretically or experimentally. Whereas the theoretical determination lacks on accuracy as the realistic packing of the fibres in the bundles is not integrated in the models. In this work, we present an experimental setup to measure the longitudinal and transversal permeability of fibre bundles. The results are compared to model predictions.

Keywords: Fibre bundle; Permeability measurement

The Dry Sliding Wear Behavior of Interpenetrating Titanium Trialuminide/Aluminium Composites by Shouren Wang; Yong Wang; Changchun Li; Qing Chi; Zhenyi Fei (pp. 129-144).

Owing to the brittle reinforced phase are introduced into ductile matrix phase, metal–intermetallic interpenetrating composites exhibit various types of wear mechanism such as adhesive, abrasive, and fatigue wear. In present work, the wear model has been proposed according to the mixing rule. Many factors such as special topology structure characteristic of reinforcement and elastic module were discussed in this model. The model based on the maximal and minimal hypothesis posts the mathematic relation among volume content of reinforcement, elastic module and wear rate. Increase in the volume fraction of reinforcement leads to improvement in the wear resistance. Unlike the Khruschov model and Zum-Gahr model, the proposed model was no longer follow linear rule. One kind of Al₃Ti/Al composite with different volume content was fabricated and many wear test data were obtained to validate the correctness and universality of the model.

Keywords: Interpenetrating composites; Dry sliding wear; Wear model; Wear mechanism

Numerical Analysis of Stiffener Runout Sections by Andrea Faggiani; Brian G. Falzon (pp. 145-158).

The recent trend of incorporating more composite material in primary aircraft structures has highlighted the vulnerability of stiffened aerostructures to through-thickness stresses, which may lead to delamination and debonding at the skin–stiffener interface, leading to collapse. Stiffener runout regions are particularly susceptible to this problem and cannot be avoided due to the necessity to terminate stiffeners at rib intersections or at cutouts, interrupting the stiffener load path. In this paper, experimental tests relating to two different stiffener runout specimens are presented and the failure modes of both specimens are discussed in detail. A thinner-skinned specimen showed sudden and unstable crack propagation, while a thicker-skinned specimen showed initially unstable but subsequent stable crack growth. Detailed finite element models of the two specimens are developed, and it is shown how such models can explain and predict the behaviour and failure mode of stiffener runouts. The models contain continuum shell elements to model the skin and stiffener, while cohesive elements using a traction-separation law are placed at the skin–stiffener interface to effectively model the debonding which promotes structural failure.

Keywords: Composites; Delamination; Debonding; Stiffener runout; Finite elements

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.14, #2)