Cagri Ayranci

Effect of Diameter in Predicting the Elastic Properties of 2D Braided Tubular Composites

A thorough understanding of 2D braided composites elastic behavior is necessary for stiffness critical applications. This article outlines the effects of radius of curvature of a unit cell on 2D braided tubular composites’ elastic constants via a sensitivity study. The proposed model is verified using literature and experimental results. The proposed model is first compared to an existing flat unit cell model by setting the radius of curvature to near infinity; elastic constants are in very good agreement. Finally, very good agreement between the experimental and predicted results is observed.

Ply mechanics for braided composite materials

Ply mechanics is an integral part of predicting braided composite material behavior; each braided composite strand is commonly assumed to behave as an off-axis lamina. Herein the development of the fundamental theory is presented for determining elastic constants, as well as stresses and strains. Special cases related to transverse isotropic unidirectional lamina are presented. A number of failure theories are introduced and compared.

Introduction to braided composite material behavior

Braided composites can fulfill the needs of a great number of applications. Yet their use is sparse at best in industrial applications compared to other composite material production methods. Herein we assess the state of braided composites, provide general insight in their history, geometry, behavior, and provide a road map to predicting their behavior.

Characterizing short-fiber-reinforced composites produced using additive manufacturing

Abstract Material extrusion additive manufacturing (MEAM), a sub-branch of three-dimensional (3D) printing is growing in popularity. Test specimens were 3D-printed using commercial polylactic acid (PLA) filament, and PLA filament reinforced with short-carbon fibers (PLA/CF). As-printed specimens and specimens that were annealed at three different temperatures, then subjected to tensile testing. The internal microstructures of the samples were also examined. The effects of the short-carbon fiber fillers on the mechanical properties of 3D-printed PLA were investigated, and the effects of the annealing process on polymer crystallinity and mechanical properties. The annealing process was shown to increase the crystallinity of both sample groups, though no statistically significant effect of annealing on mechanical properties was observed. The tensile properties of the PLA and PLA/CF filaments showed that the addition of carbon fibers to the PLA filament led to a significant increase in elastic modulus of the MEAM samples.

Shape memory composites and braids

Abstract There is a movement in engineering to shift from conventional materials to those that can adapt and morph to their environment as a result of external stimuli. This category of materials is called shape memory materials. Among these, shape memory polymers have great potential due to their light weight and ease of shaping. They can significantly alter the way engineers think of their design approach; however, a number of them have stiffness and strength disadvantages compared to conventional engineering materials. Through composite material-based approaches, shape memory polymers have improved to meet some engineering challenges. Herein, fundamental aspects of shape memory polymers and composites are discussed; furthermore, recent adaptations of shape memory composites to shape memory braided composites are explored.

Additive manufacturing of shape memory polymers: effects of print orientation and infill percentage on mechanical properties

Purpose Material extrusion additive manufacturing, also known as fused deposition modeling, is a manufacturing technique in which objects are built by depositing molten materials layer-by-layer through a nozzle. The use and application of this technique has risen dramatically over the past decade. This paper aims to first, report on the production and characterization of a shape memory polymer material filament that was manufactured to print shape memory polymer objects using material extrusion additive manufacturing. Additionally, it aims to investigate and outline the effects of major printing parameters, such as print orientation and infill percentage, on the elastic and mechanical properties of printed shape memory polymer samples. Design/methodology/approach Infill percentage was tested at three levels, 50, 75 and 100 per cent, while print orientation was tested at four different angles with respect to the longitudinal axis of the specimens at 0°, 30°, 60° and 90°. The properties examined were elastic modulus, ultimate tensile strength and maximum strain. Findings Results showed that print angle and infill percentage do have a significant impact on the manufactured test samples. Originality/value Findings can significantly influence the tailored design and manufacturing of smart structures using shape memory polymer and material extrusion additive manufacturing.

Effects of interfacial interactions and interpenetrating brushes on the electrospinning of cellulose nanocrystals-polystyrene fibers

This study investigated the electrospinning of polystyrene solutions using added unmodified and modified (with grafted nitrobenzene and trifluoromethyl benzene functionalities and polystyrene brushes) cellulose nanocrystals (CNCs). A strong correlation existed between the formation of beads on the fibers and the degree of dispersion of CNC particles in the electrospinning mixtures. Agglomerates of CNC particles always concentrated in the form of beads. The best dispersion in N,N dimethylformamide (DMF) mixtures was obtained using CNC-2 surfaces that were modified using trifluoromethyl benzene functional groups. Using CNC-2 also resulted in both uniform and bead-free electrospun fibers. Despite good dispersion in DMF, the use of grafted polystyrene (PS) chains with CNC-g resulted in beads above a 1.0% concentration level. This result is attributed to more favorable interactions between the CNC-g brushes during the DMF solvent evaporation stage of electrospinning. The electrospinning of CNC/PS nanocomposites at very low CNC concentrations (<1.0%) showed strong adhesion bonds at the polymer-CNC interfaces. Excellent mechanical properties were also produced by using interpenetrating networks of surface brushes.

Is suture comparable to wire for cerclage fixation? A biomechanical analysis

Background Cerclage wire is the current standard for circumferential bone fixation. Advances in technology have improved modern sutures, allowing for expanded utility and broader application. The present study compared the strength and durability of cerclage fixation between modern suture materials and monofilament wire. Methods The Surgeon’s Knot, the Nice Knot and the Modified Nice Knot, were each tied using three separate suture materials: no. 2 FiberWire (Arthrex, Naples, FL, USA), no. 2 Ultrabraid (Smith & Nephew, Andover, MA, USA) and no. 5 Ethibond (Johnson & Johnson, Somerville, NJ, USA). These sutures were compared with monofilament wire. Sutures were secured around a fixed diameter using three additional half hitches, whereas a 1.2-mm (18 gauge) stainless steel monofilament wire was used for comparison. One fellow and one orthopaedic surgery resident each tied five trials with every knot/material combination. Samples were subjected to cyclic loading and quasi-static load testing. Respectively, cyclic displacement over time and load to failure were analyzed. Clinical failure (3 mm of cyclic displacement) and absolute failure (opening of the knot or material failure) were the outcomes of interest. Results During cyclic loading, Ethibond displaced significantly less over time compared to monofilament wire (p < 0.003), whereas FiberWire showed no significant difference. Ultrabraid also behaved similar to wire, except displacing significantly more than wire only with the Surgeon’s Knot (p = 0.02). During load to failure, Ethibond and FiberWire failed at significantly greater loads than monofilament wire (p < 0.001), whereas Ultrabraid performed similar to wire. Knot types did not appear to impact the results. Conclusions High-performance sutures achieve superior results in biomechanical testing under cyclic and quasi-static load compared to monofilament wire, suggesting that they provide an alternative to wire for cerclage fixation with select clinical application. Biomechanical security of suture cerclage is dependent on suture material, although it is not altered significantly by choice of knot. An ex-vivo study with clinical application would further reinforce whether suture cerclage offers a valid alternative to wire cerclage.

Utilization of finite element analysis for rapid curing of fiber-reinforced polymers in a novel two-phase curing technique for braided rebars

This study focused on determining the capability of a proposed two-step curing process for composite rebars production. A finite element analysis is carried out on rapid curing of fiber-reinforced polymer rebars during a continuous braid trusion manufacturing process. This process combines pultrusion and braiding techniques to produce fiber-reinforced polymer rebars. The system uses a novel two-step curing technique to obtain a uniform cure profile. This is achieved by embedding small diameter steel wires within the core of the rebar. In the first step, as the rebar passes through an induction coil, a curing radially in the outward direction is initiated due to the induction coil. In the second step, the induction-initiated curing rebar enters a series of ovens, initiating radially inward curing. The resulting fiber-reinforced polymer rebars can be used as alternative to steel reinforcement in applications where steel cannot be utilized due to its corrosive or metallic nature. The result of this study showcased the importance of induction unit in obtaining a uniform cure profile.