Nitrogen implantation of tool steels and engineering coatings

Ion implantation modifies the surface composition and properties of materials by bombardment with high energy ions. The low temperature of the process ensures the avoidance of distortion and degradation of the surface or bulk mechanical properties of components. In the present work nitrogen ion implantation at 90 keV and doses above 1017 ions/cm2 has been carried out on AISI M2, D2 and 420 steels and engineering coatings such as hard chromium, electroless Ni-P and a brush plated Co-W alloy. Evaluation of wear and frictional properties of these materials was performed with a lubricated Falex wear test at high loads up to 900 N and a dry pin-on-disc apparatus at loads up to 40 N. It was found that nitrogen implantation reduced the wear of AISI 420 stainless steel by a factor of 2.5 under high load lubricated conditions and by a factor of 5.5 in low load dry testing. Lower but significant reductions in wear were achieved for AISI M2 and D2 steels. Wear resistance of coating materials was improved by up to 4 times in lubricated wear of hard Cr coatings implanted at the optimum dose but lower improvements were obtained for the Co-W alloy coating. However, hardened electroless Ni-P coatings showed no enhancement in wear properties. The benefits obtained in wear behaviour for the above materials were generally accompanied by a significant decrease in the running-in friction. Nitrogen implantation hardened the surface of steels and Cr and Co-W coatings. An ultra-microhardness technique showed that the true hardness of implanted layers was greater than the values obtained by conventional micro-hardness methods, which often result in penetration below the implanted depth. Scanning electron microscopy revealed that implantation reduced the ploughing effect during wear and a change in wear mechanism from an abrasive-adhesive type to a mild oxidative mode was evident. Retention of nitrogen after implantation was studied by Nuclear Reaction Analysis and Auger Electron Spectroscopy. It was shown that maximum nitrogen retention occurs in hard Cr coatings and AISI 420 stainless steel, which explains the improvements obtained in wear resistance and hardness. X-ray photoelectron spectroscopy on these materials revealed that nitrogen is almost entirely bound to Cr, forming chromium nitrides. It was concluded that nitrogen implantation at 90 keV and doses above 3x1017 ions/cm2 produced the most significant improvements in mechanical properties in materials containing nitride formers by precipitation strengthening, improving the load bearing capacity of the surface and changing the wear mechanism from adhesive-abrasive to oxidative.

Fibre Bragg grating sensors for distributive tactile sensing

Distributive tactile sensing is a method of tactile sensing in which a small number of sensors monitors the behaviour of a flexible substrate which is in contact with the object being sensed. This paper describes the first use of fibre Bragg grating sensors in such a system. Two systems are presented: the first is a one-dimensional metal strip with an array of four sensors, which is capable of detecting the magnitude and position of a contacting load. This system is favourably compared experimentally with a similar system using resistive strain gauges. The second system is a two-dimensional steel plate with nine sensors which is able to distinguish the position and shape of a contacting load, or the positions of two loads simultaneously. This system is compared with a similar system using 16 infrared displacement sensors. Each system uses neural networks to process the sensor data to give information concerning the type of contact. Issues and limitations of the systems are discussed, along with proposed solutions to some of the difficulties.

Do ‘passive’ medical titanium surfaces deteriorate in service in the absence of wear?

Globally, more than 1000 tonnes of titanium (Ti) is implanted into patients in the form of biomedical devices on an annual basis. Ti is perceived to be ‘biocompatible’ owing to the presence of a robust passive oxide film (approx. 4 nm thick) at the metal surface. However, surface deterioration can lead to the release of Ti ions, and particles can arise as the result of wear and/or corrosion processes. This surface deterioration can result in peri-implant inflammation, leading to the premature loss of the implanted device or the requirement for surgical revision. Soft tissues surrounding commercially pure cranial anchorage devices (bone-anchored hearing aid) were investigated using synchrotron X-ray micro-fluorescence spectroscopy and X-ray absorption near edge structure. Here, we present the first experimental evidence that minimal load-bearing Ti implants, which are not subjected to macroscopic wear processes, can release Ti debris into the surrounding soft tissue. As such debris has been shown to be pro-inflammatory, we propose that such distributions of Ti are likely to effect to the service life of the device.

Distributive tactile sensing using fibre Bragg grating sensors

Two distributive tactile sensing systems are presented, based on fibre Bragg grating sensors. The first is a onedimensional metal strip with an array of 4 sensors, which is capable of detecting the magnitude and position of a contacting load. This system is compared experimentally with a similar system using resistive strain gauges. The second is a two-dimensional steel plate with 9 sensors which is able to distinguish the position and shape of a contacting load. This system is compared with a similar system using 16 infrared displacement sensors. Each system uses neural networks to process the sensor data to give information concerning the type of contact.

Fibre Bragg grating sensors for distributive tactile sensing

Distributive tactile sensing is a method of tactile sensing in which a small number of sensors monitors the behaviour of a flexible substrate which is in contact with the object being sensed. This paper describes the first use of fibre Bragg grating sensors in such a system. Two systems are presented: the first is a one-dimensional metal strip with an array of four sensors, which is capable of detecting the magnitude and position of a contacting load. This system is favourably compared experimentally with a similar system using resistive strain gauges. The second system is a two-dimensional steel plate with nine sensors which is able to distinguish the position and shape of a contacting load, or the positions of two loads simultaneously. This system is compared with a similar system using 16 infrared displacement sensors. Each system uses neural networks to process the sensor data to give information concerning the type of contact. Issues and limitations of the systems are discussed, along with proposed solutions to some of the difficulties. © 2007 IOP Publishing Ltd.

Injectable hydrogels with high fixed charge density and swelling pressure for nucleus pulposus repair:biomimetic glycosaminoglycan analogues

The load-bearing biomechanical role of the intervertebral disc is governed by the composition and organization of its major macromolecular components, collagen and aggrecan. The major function of aggrecan is to maintain tissue hydration, and hence disc height, under the high loads imposed by muscle activity and body weight. Key to this role is the high negative fixed charge of its glycosaminoglycan side chains, which impart a high osmotic pressure to the tissue, thus regulating and maintaining tissue hydration and hence disc height under load. In degenerate discs, aggrecan degrades and is lost from the disc, particularly centrally from the nucleus pulposus. This loss of fixed charge results in reduced hydration and loss of disc height; such changes are closely associated with low back pain. The present authors developed biomimetic glycosaminoglycan analogues based on sulphonate-containing polymers. These biomimetics are deliverable via injection into the disc where they polymerize in situ, forming a non-degradable, nuclear "implant" aimed at restoring disc height to degenerate discs, thereby relieving back pain. In vitro, these glycosaminoglycan analogues possess appropriate fixed charge density, hydration and osmotic responsiveness, thereby displaying the capacity to restore disc height and function. Preliminary biomechanical tests using a degenerate explant model showed that the implant adapts to the space into which it is injected and restores stiffness. These hydrogels mimic the role taken by glycosaminoglycans in vivo and, unlike other hydrogels, provide an intrinsic swelling pressure, which can maintain disc hydration and height under the high and variable compressive loads encountered in vivo. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Failure in composite materials

The economic and efficient exploitation of composite materials in critical load bearing applications relies on the ability to predict safe operational lives without excessive conservatism. Developing life prediction and monitoring techniques in these complex, inhomogeneous materials requires an understanding of the various failure mechanisms which can take place. This article describes a range of damage mechanisms which are observed in polymer, metal and ceramic matrix composites.

Distributive tactile sensing using fibre bragg grating sensors

Two distributive tactile sensing systems are presented, based on fibre Bragg grating sensors. The first is a one-dimensional metal strip with an array of 4 sensors, which is capable of detecting the magnitude and position of a contacting load. This system is compared experimentally with a similar system using resistive strain gauges. The second is a two-dimensional steel plate with 9 sensors which is able to distinguish the position and shape of a contacting load. This system is compared with a similar system using 16 infrared displacement sensors. Each system uses neural networks to process the sensor data to give information concerning the type of contact.

Characterization of engineered human lung tissue

Characterizing engineered human lung tissue is an important step in developing a functional tissue replacement for lung tissue repair and in vitro analysis. Small tissue constructs were grown by seeding IMR-90 fetal lung fibroblasts and adult microvascular endothelial cells onto a Polyglycolic acid (PGA) polymer template. Introducing the constructs to dynamic culture conditions inside a bioreactor facilitated three-dimensional growth seen in scanning electron microscopy images (SEM). Characterization of the resultant tissue samples was done using SEM imagery, tensile tests, and biochemical assays to quantify extra-cellular matrix (ECM) composition. Tensile tests of the engineered samples indicated an increase in the mechanical properties when compared with blank constructs. Elastin and collagen content was found to average 3.19% and 15.49% respectively in relation to total mass of the tissue samples. The presence of elastin and collagen within the constructs most likely explains the mechanical differences that we noted. These findings suggest that the necessary ECM can be established in engineered tissue constructs and that optimization of this procedure has the capacity to generate the load bearing elements required for construction of a functional lung tissue equivalent.

Other Than a Citizen: Vernacular Poetics in Postwar America

Few symbols of 1950s-1960s America remain as central to our contemporary conception of Cold War culture as the iconic ranch-style suburban home. While the house took center stage in the Nixon/Khrushchev kitchen debates as a symbol of modern efficiency and capitalist values, its popularity depended largely upon its obvious appropriation of vernacular architecture from the 19th century, those California haciendas and Texas dogtrots that dotted the American west. Contractors like William Levitt modernized the historical common houses, hermetically sealing their porous construction, all while using the ranch-style roots of the dwelling to galvanize a myth of an indigenous American culture. At a moment of intense occupational bureaucracy, political uncertainty and atomized social life, the rancher gave a self-identifying white consumer base reason to believe they could master their own plot in the expansive frontier. Only one example of America’s mid-century love affair with commodified vernacular forms, the ranch-style home represents a broad effort on the part of corporate and governmental interest groups to transform the vernacular into a style that expresses a distinctly homogenous vision of American culture. “Other than a Citizen” begins with an anatomy of that transformation, and then turns to the work of four poets who sought to reclaim the vernacular from that process of standardization and use it to countermand the containment-era strategies of Cold War America.

In four chapters, I trace references to common speech and verbal expressivity in the poetry and poetic theory of Charles Olson, Robert Duncan, LeRoi Jones/Amiri Baraka and Gwendolyn Brooks, against the historical backdrop of the Free-Speech Movement and the rise of mass-culture. When poets frame nonliterary speech within the literary page, they encounter the inability of writing to capture the vital ephemerality of verbal expression. Rather than treat this limitation as an impediment, the writers in my study use the poem to dramatize the fugitivity of speech, emphasizing it as a disruptive counterpoint to the technologies of capture. Where critics such as Houston Baker interpret the vernacular strictly in terms of resistance, I take a cue from the poets and argue that the vernacular, rooted etymologically at the intersection of domestic security and enslaved margin, represents a gestalt form, capable at once of establishing centralized power and sparking minor protest. My argument also expands upon Michael North’s exploration of the influence of minstrelsy and regionalism on the development of modernist literary technique in The Dialect of Modernism. As he focuses on writers from the early 20th century, I account for the next generation, whose America was not a culturally inferior collection of immigrants but an imperial power, replete with economic, political and artistic dominance. Instead of settling for an essentially American idiom, the poets in my study saw in the vernacular not phonetic misspellings, slang terminology and fragmented syntax, but the potential to provoke and thereby frame a more ethical mode of social life, straining against the regimentation of citizenship.

My attention to the vernacular argues for an alignment among writers who have been segregated by the assumption that race and aesthetics are mutually exclusive categories. In reading these writers alongside one another, “Other than a Citizen” shows how the avant-garde concepts of projective poetics and composition by field develop out of an interest in black expressivity. Conversely, I trace black radicalism and its emphasis on sociality back to the communalism practiced at the experimental arts college in Black Mountain, North Carolina, where Olson and Duncan taught. In pressing for this connection, my work reveals the racial politics embedded within the speech-based aesthetics of the postwar era, while foregrounding the aesthetic dimension of militant protest.

Not unlike today, the popular rhetoric of the Cold War insists that to be a citizen involves defending one’s status as a rightful member of an exclusionary nation. To be other than a citizen, as the poets in my study make clear, begins with eschewing the false certainty that accompanies categorical nominalization. In promoting a model of mutually dependent participation, these poets lay the groundwork for an alternative model of civic belonging, where volition and reciprocity replace compliance and self-sufficiency. In reading their lines, we become all the more aware of the cracks that run the length of our load-bearing walls.

Synergy between Piezo1 and Piezo2 channels confers high-strain mechanosensitivity to articular cartilage.

Diarthrodial joints are essential for load bearing and locomotion. Physiologically, articular cartilage sustains millions of cycles of mechanical loading. Chondrocytes, the cells in cartilage, regulate their metabolic activities in response to mechanical loading. Pathological mechanical stress can lead to maladaptive cellular responses and subsequent cartilage degeneration. We sought to deconstruct chondrocyte mechanotransduction by identifying mechanosensitive ion channels functioning at injurious levels of strain. We detected robust expression of the recently identified mechanosensitive channels, PIEZO1 and PIEZO2. Combined directed expression of Piezo1 and -2 sustained potentiated mechanically induced Ca(2+) signals and electrical currents compared with single-Piezo expression. In primary articular chondrocytes, mechanically evoked Ca(2+) transients produced by atomic force microscopy were inhibited by GsMTx4, a PIEZO-blocking peptide, and by Piezo1- or Piezo2-specific siRNA. We complemented the cellular approach with an explant-cartilage injury model. GsMTx4 reduced chondrocyte death after mechanical injury, suggesting a possible therapy for reducing cartilage injury and posttraumatic osteoarthritis by attenuating Piezo-mediated cartilage mechanotransduction of injurious strains.

Mechanical properties and cellular response of novel electrospun nanofibers for ligament tissue engineering: Effects of orientation and geometry

Electrospun nanofibers are a promising material for ligamentous tissue engineering, however weak mechanical properties of fibers to date have limited their clinical usage. The goal of this work was to modify electrospun nanofibers to create a robust structure that mimics the complex hierarchy of native tendons and ligaments. The scaffolds that were fabricated in this study consisted of either random or aligned nanofibers in flat sheets or rolled nanofiber bundles that mimic the size scale of fascicle units in primarily tensile load bearing soft musculoskeletal tissues. Altering nanofiber orientation and geometry significantly affected mechanical properties; most notably aligned nanofiber sheets had the greatest modulus; 125% higher than that of random nanofiber sheets; and 45% higher than aligned nanofiber bundles. Modifying aligned nanofiber sheets to form aligned nanofiber bundles also resulted in approximately 107% higher yield stresses and 140% higher yield strains. The mechanical properties of aligned nanofiber bundles were in the range of the mechanical properties of the native ACL: modulus=158±32MPa, yield stress=57±23MPa and yield strain=0.38±0.08. Adipose derived stem cells cultured on all surfaces remained viable and proliferated extensively over a 7 day culture period and cells elongated on nanofiber bundles. The results of the study suggest that aligned nanofiber bundles may be useful for ligament and tendon tissue engineering based on their mechanical properties and ability to support cell adhesion, proliferation, and elongation.

Progetto e sviluppo di un banco di prova per sistemi di determinazione e controllo d'assetto di CubeSat

Progettazione di dettaglio di un banco di prova per testare sistemi ADCS per CubeSat: Alma Test-Bed. Ci si è concentrati sul progetto di un primo nucleo di AlmaTB in grado di testare il controllo di tipo magnetico. Fanno parte di AlmaTB una gabbia di Helmholtz, un air-bearing system, un CubeSat di test, un metrology system. La gabbia di Helmholtz è un apparato costituito da tre coppie di bobine, una per ogni asse spaziale, che serve ad annullare il campo magnetico locale e simulare quello che si troverà in orbita attorno alla Terra. Un software ricava i dati del campo magnetico terrestre da modello IGRF a determinate coordinate e quota e fornisce agli alimentatori del set di bobine l'indicazione della corrente da distribuire. L'air-bearing system è un cuscinetto d'aria generato da un compressore che serve a ricreare le caratteristiche condizioni dell'ambiente spaziale di microgravità e attrito quasi-zero. Il CubeSat di test sarà montato su questo sistema. Il CubeSat di test, nella prima versione di AlmaTB, contiene i sensori e gli attuatori di tipo magnetico per determinare e controllare l'assetto di un nanosatellite. Il magnetometro presente all'interno è utilizzato anche come controllo del funzionamento della gabbia di Helmholtz. Il metrology system traccia i movimenti e l'inclinazione del CubeSat. Questo fornisce il riferimento di assetto vero, in modo da capire se il sistema ADCS lavora correttamente. Una volta che il banco di prova sarà completato e operativo sarà possibile testare algoritmi di determinazione e controllo di assetto che utilizzano diversi dispositivi tra sensori e attuatori disponibili nel mock-up. Su una workstation sono installati i software di controllo ed elaborazione dati. Si è scelto di procedere con un approccio di tipo "chiavi in mano", cioè scegliendo, quando disponibile, sistemi già completi e disponibili sul mercato. La prima versione di AlmaTB nasce dall'importante, vasto lavoro di matching tra i diversi apparati.

Plásticos reforçados a base de tecidos híbridos: efeitos da anisotropia e geometria normativa na caracterização mecânica e da fratura

As most current studies, reinforced plastics have been, in recent years, a viable alternative in building structural elements of medium and large, since the lightness accompanied by high performance possible. The design of hybrid polymer composites (combination of different types of reinforcements) may enable structural applications thereof, facing the most severe service conditions. Within this class of composite materials, reinforced the underlying tissues hybrid high performance are taking space when your application requires high load bearing and high rigidity. The objective of this research work is to study the challenges in designing these fabrics bring these materials as to its mechanical characterization and fracture mechanisms involved. Some parameters associated with the process and / or form of hybridization stand out as influential factors in the final performance of the material such as the presence of anisotropy, so the fabric weave, the process of making the same, normative geometry of the specimens, among others. This sense, four laminates were developed based hybrid reinforcement fabrics involving AS4 carbon fiber, kevlar and glass 49-E as the matrix epoxy vinyl ester resin (DERAKANE 411-350). All laminates were formed each with four layers of reinforcements. Depending on the hybrid fabric, all the influencing factors mentioned above have been studied for laminates. All laminates were manufactured industrially used being the lamination process manual (hand-lay-up). All mechanical characterization and study of the mechanism of fracture (fracture mechanics) was developed for laminates subjected to uniaxial tensile test, bending in three and uniaxial compression. The analysis of fracture mechanisms were held involving the macroscopic, optical microscopy and scanning electron microscopy