Knitted Metal Research Articles

Influence of Wire Geometry on the Mechanical Behavior of the TiNi Design

The present article is aimed at studying the deformation behavior of TiNi wire and knitted metal TiNi mesh under uniaxial tension and revealing the role of wire geometry on their main mechanical characteristics and mechanisms of deformation behavior. The temperature dependence curve of the electrical resistance indicates that a two-stage martensitic transformation of B2→R→B19′ is occurring, and is responsible for the superelasticity effect. The TEM results showed that at room temperature, the TiNi wire has a nanocrystalline structure composed of B2 austenite grains. A change in the deformation mechanism was established under the uniaxial tension, where the TiNi wire exhibits the effect of superelasticity, while the knitted metal TiNi mesh made from this wire is characterized by hyperelastic behavior. Fracturing of the knitted metal TiNi mesh requires significant loads of up to 3500 MPa compared to the fracture load of the TiNi wire. With the uniaxial tension of the wire, which maximally repeats the geometry of the wire in knitted metal mesh, an increase in mechanical characteristics was observed.

Contact management in knitted metal mesh through an adaptive node placing

The structural analysis of metal knitted meshes needs important computational resources due to non-linear behavior. The structures made of several filiform elements interlaced together often show large displacements and several contacts among yarns, so that they require advanced methods to predict their response. In this work, a contact-search algorithm between thin curved beams is presented. The contact recognition is based on the intersections between single elements to evaluate possible contact and its location. The method allows simplifying the 3D problem of contacts among wires into a 2D structure, easy to manage and model with a reduced computational cost. The filiform elements are modeled through a Wire Element, whose characteristic is to decouple its structural behavior – based on ending nodes – to its geometrical internal shape that is used for contact management. The Wire Element considers thin wires with circular sections. Its shape is entrusted to intrinsic geometry using a cubic polynomial function whose independent variable is the angle of the tangent to the curve. This approach is useful when analyzing complex structures such as meshes in which several loops are intertwined and subjected to contact activation during loading. Some examples to explain the method and its potential are shown.

FeCrAl as a Catalyst Support.

The iron-chromium-aluminum alloy (FeCrAl) is an exceptional support for highly exothermic and endothermic reactions that operate above 700 °C in chemically aggressive environments, where low heat and mass transfer rates limit reaction yield. FeCrAl two- and three-dimensional structured networks-monoliths, foams, and fibers-maximize mass transfer rates, while their remarkable thermal conductivity minimizes hot spots and thermal gradients. Another advantage of the open FeCrAl structure is the low pressure drop due to the high void fraction and regularity of the internal path. The surface Al2O3 layer, formed after an initial thermal oxidation, supports a wide range of metal and metal oxide active phases. The aluminum oxide that adheres to the metal surface protects it from corrosive atmospheres and carbon (carburization), thus allowing FeCrAl to operate at a higher temperature. The top applications are industrial burners, in which compact knitted metal fibers distribute heat over large surface areas, and automotive tail gas converters. Future applications include producing H2 and syngas from remote natural gas in modular units. This Review summarizes the specific preparation techniques, details process operating conditions and catalyst performance of several classes of reactions, and highlights positive and challenging aspects of FeCrAl.

Knitted Wire Mesh Reinforced Powder Composite Materials Produced by Rolling*

The rolling of porous knitted wire mesh reinforced powder composite tapes is discussed. Data are reported on the effect of the architecture and structural and deformation features of knitted metal wire meshes on the processing parameters of reinforced composite tapes. It is established that using knitted wire as reinforcement for powder composites can help rolling difficult-to-form powder compositions. Despite their porosity, the resultant tapes have sufficient load-carrying capcaity and service properties required for some applications (electrode tapes, reinforced graphite seals).

Development of a Hybrid Catalytic Gas Burner

A prototype hybrid catalytic radiant gas burner suitable for EU condensing boilers (4–25 kW) was developed based on the novel concept of a rich catalytic/homogeneous combustion with interstage heat removal. An extensive experimental campaign was carried out to validate the hybrid catalytic combustion technology through the detailed characterization of the operating features of the prototype burner with special focus on the catalytic partial oxidation reactor, which simultaneously acts as a radiant element. Methane combustion tests were conducted also in direct comparison with two low-NOx forced air commercial systems: a fully premixed gas burner stabilized with a knitted metal wire cover and a blue–flame turbulent diffusive burner with multiple swirled fuel nozzles and high-speed air injection. The novel burner shows the potential for improved performance with regard to heat transfer efficiency, pollutants emissions, stability, rangeability, and safety of operation.

Multifunctional and dimensionally stable flexible fibre composites for space applications

Large deployable reflectors typically use knitted metal mesh reflecting surfaces. Knitted metal meshes are characterized by excellent stowability properties. For the operation, meshes have to be tensioned, which leads to much lower accuracy. In order to keep the stowability advantages of knitted meshes but enhancing shape accuracy, a flexible reflecting surface material composed of carbon fibre reinforced silicone (CFRS) has been developed and investigated. Due to its low bending stiffness determined by the silicone matrix, the composite material can be manufactured easily with double curvature and nearly ideal parabolic shape. Compared to the conventional stiff matrix composites, which give high accurate double curved reflecting surfaces, an additional functionality is acquired by using a flexible silicone matrix. The use of this material allows for easy stowing and deployment. Because of the carbon fibres, the CFRS is characterized with a very low thermal expansion coefficient (measured and calculated about −0.36e–6/°C) with no moisture absorption or micro-cracking effects even under strong environmental cycles. These points indicate a high dimensional stability of the material. Results obtained from different thermo-mechanical and radio-frequency (RF) characterization tests for such CFRS surfaces confirm the expected behaviour. The measured RF properties, such as insertion loss, cross-polarization, reflectivity, and passive inter-modulation (PIM), show that the created material can be used even up to 15 GHz of RF. Higher frequencies can be achieved in different cases. Several application examples are addressed further in the paper.

Knitted nitinol stent insertion for various intestinal stenoses with a modified delivery system

Background: Insertion of metallic stents for esophageal stenoses is well established, but these stents are technically difficult to place elsewhere in the GI tract. Moreover, major complications have occurred when metal stents with sharp ends have been placed in these locations. The currently available flexible, blunt-ended, knitted nitinol stent is intended for use only in the esophagus. Because its short delivery system cannot reach segments of the gut distal to the esophagus, the delivery device was modified to facilitate intestinal access, and its performance was evaluated in the treatment of malignant intestinal obstructions. Methods: The Ultraflex delivery system was modified by connecting an additional plastic tube and a suture cord; the length was increased from 95 cm to 150 cm or more. Stents used were 18 to 23 mm in diameter, and 10 to 15 cm in length. A knitted metal stent was inserted by using the modified delivery system in 10 patients (7 men, 3 women, mean age 68 years); 8 with gastric outlet, 1 with jejunal, and 1 with proximal colonic obstruction. Results: Metal stent insertion was successful in all patients with significant relief of symptoms and restoration of the ability to eat. The patient with a jejunal stent required placement of a second stent because of bending of the initial stent. No major complications (migration or perforation) occurred. Conclusion: This technique appears to facilitate placement of a metal stent with blunt ends in the duodenum, small intestine, and proximal colon. Manufacturers should offer blunt-ended stents with long delivery devices.

Tribological properties of thermally expanded graphite reinforced with knitted metal nets

Production of thermally expanded graphite composites reinforced with knitted copper net is developed and their tribological properties are determined. Wear resistance under reciprocating and rotary movement can be improved by the reinforcement. Reinforced thermally expanded graphite seals may be a substitute for asbestos-containing materials.

Flame arresters based on materials of knitted metal grids

Flame arresters based on materials of knitted metal grids

Noise‐reducing fluid‐flow devices

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