Flow of a micropolar fluid in a tube with sinusoidal deformation

The flow of a micropolar fluid for sinusoidally deforming boundaries is discussed in detail. The velocity and microrotation fields and the streamfunction are determined and plotted under the assumption of small deformations.

Deformation characterization of superplastic AA7475 alloy

AA7475 alloy was deformed up to 25% elongation in INSTRON at 788K. The grain boundary sliding due to this superplastic deformation was measured by Scanning Electron Microscope. The microstructure and texture development due to this deformation at elevated temperature was analyzed from the Orientation Image Microstructures i.e. the Electron Back Scattered Diffraction Image. The Orientation Image Microstructures revealed that superplastic deformation was associated with recovery and recrystallization in-situ process.

Inelastic Postbuckling of Columns of Variable Flexural Rigidity

Effects of large deformation and inelasticity are considered in formulating the behavior of columns of variable cross section subjected to an axial compressive load. Simple, approximate methods are used to obtain numerical results. The combined effect of the nonlinearities is shown to be of a hardening type for small column deflections

On a finite element model for the analysis of through cracks in laminated anisotropic cylindrical shells

A finite element model for the analysis of laminated composite cylindrical shells with through cracks is presented. The analysis takes into account anisotropic elastic behaviour, bending-extensional coupling and transverse shear deformation effects. The proposed finite element model is based on the approach of dividing a cracked configuration into triangular shaped singular elements around the crack tip with adjoining quadrilateral shaped regular elements. The parabolic isoparametric cylindrical shell elements (both singular and regular) used in this model employ independent displacement and rotation interpolation in the shell middle surface. The numerical comparisons show the evidence to the conclusion that the proposed model will yield accurate stress intensity factors from a relatively coarse mesh. Through the analysis of a pressurised fibre composite cylindrical shell with an axial crack, the effect of material orthotropy on the crack tip stress intensity factors is shown to be quite significant.

Thermal activation parameters for low temperature deformation of alpha-hafnium

Abstract is not available.

A study of the deformation slip lines in quenched and aged Al-2% Ge alloy

Optical microscopy has been employed to observe the slip lines in deformed Al-2% Ge alloy samples. Slip lines have been observed in the as-quenched, partially-aged, fully-aged and over-aged states. The lines tend to traverse fairly straight paths in the case of quenched and partially-aged conditions. Fully-aged samples also reveal such straight running lines when tested at low-temperatures. However, the density of the lines generally decreases as the peak-aged state is approached. These results are in agreement with the idea that thermally activated shearing of the precipitates is occurring in the alloy aged up to peak-hardness. The irregular lines for the over-aged specimens support the view that the moving dislocations by-pass the precipitates during deformation. The influence of test-temperature on the appearance of slip traces has been briefly examined.

Improvement in the voltage grading (axial and radial) of the generator column of a Van de Graaf generator by the use of a resistor chain

It is well known that the use of a series of resistors, connected between the equipotential rings of a Van de Graaff generator, improves the axial voltage grading of the generator. The work reported in this paper shows how the resistor chain also improves the radial voltage gradient. The electrolytic field mapping technique was adopted in the present work.

Deformation and stability regression models for soil nail walls

Lateral displacement and global stability are the two main stability criteria for soil nail walls. Conventional design methods do not adequately address the deformation behaviour of soil nail walls, owing to the complexity involved in handling a large number of influencing factors. Consequently, limited methods of deformation estimates based on empirical relationships and in situ performance monitoring are available in the literature. It is therefore desirable that numerical techniques and statistical methods are used in order to gain a better insight into the deformation behaviour of soil nail walls. In the present study numerical experiments are conducted using a 2 4 factorial design method. Based on analysis of the maximum lateral deformation and factor-of-safety observations from the numerical experiments, regression models for maximum lateral deformation and factor-of-safety prediction are developed and checked for adequacy. Selection of suitable design factors for the 2 4 factorial design of numerical experiments enabled the use of the proposed regression models over a practical range of soil nail wall heights and in situ soil variability. It is evident from the model adequacy analyses and illustrative example that the proposed regression models provided a reasonably good estimate of the lateral deformation and global factor of safety of the soil nail walls.

Role of silicon in resisting subsurface plastic deformation in tribology of aluminium-silicon alloys

Silicon particles standing proud on aluminium-silicon alloy surfaces provide protection in tribology. Permanent sinking of such particles into the matrix under load can be deleterious. The mechanical response of the alloy to nano-indentation of single silicon particles embedded in the matrix is explored. A nominal critical pressure required to plastically deform the matrix to permanently embed the particle is determined experimentally. Within a framework suggested by two-dimensional models of plastic response to indentation, a probable correlation is established between the normal mean pressure required to cause permanent sinking of silicon particles and a factor which relates the relevant particle dimensions.

Status on pre-surgical deformation apparatus for fracture fixation plates

Purpose: This paper reviews the apparatus used for deformation of bone fracture fixation plates during orthopaedic surgeries including surgical irons, pliers and bending press tools. This paper extends the review to various machineries in non-medical industries and adopts their suitability to clinics-related applications and also covers the evolution of orthopaedic bone plates. This review confirms that none of the studied machineries can be implemented for the deformation of bone fracture fixation plates during orthopaedic surgeries. In addition, this paper also presents the novel apparatus that are designed from scratch for this specific purpose. Several conceptual designs have been proposed and evaluated recently. It has been found that Computer Numerical Control (CNC) systems are not the golden solution to this problem and one needs to attempt to design the robotic arm system. A new design of robotic arm that can be used for facilitating orthopaedic surgeries is being completed.

Mechanics of Deformation under Traction and Friction of a Micrometric Monolithic MoS2 Particle in Comparison with those of an Agglomerate of Nanometric MoS2 Particles

Tribology of small inorganic nanoparticles in suspension in a liquid lubricant is often impaired because these particles agglomerate even when organic dispersants are used. In this paper we use lateral force microscopy to study the deformation mechanism and dissipation under traction of two extreme configurations (1) a large MoS2 particle (similar to 20 mu m width) of about 1 mu m height and (2) an agglomerate (similar to 20 mu m width), constituting 50 nm MoS2 crystallites, of about 1 mu m height. The agglomerate records a friction coefficient which is about 5-7 times that of monolithic particle. The paper examines the mechanisms of material removal for both the particles using continuum modeling and microscopy and infers that while the agglomerate response to traction can be accounted for by the bulk mechanical properties of the material, intralayer and interlayer basal planar slips determine the friction and wear of monolithic particles. The results provide a rationale for selection of layered particles, for suspension in liquid lubricants.

Elimination of axial venous reflux

Chronic venous disease (CVD), including uncomplicated varicose veins and chronic venous insufficiency, is one of the most common medical conditions in the Western world. The central feature of CVD is venous reflux, which may be primary, congenital, or result from an antecedent event, usually an acute deep venous thrombosis (DVT). When the history of DVT is clear, the clinical manifestations of secondary CVD are commonly referred to as the post-thrombotic syndrome. Regardless of the underlying etiology, the final pathway leading to symptoms is ambulatory venous hypertension. The spectrum of symptoms and signs of CVD ranges from minor cosmetic problems to venous ulceration, which results in considerable morbidity and increased medical costs. Aims of this study were to evaluate the outcome of superficial venous surgery performed with or without preoperative duplex evaluation and venous marking with hand-held doppler, to assess short-term outcome of ultrasound-guided foam sclerotherapy in patients with axial superficial venous incompetence, as well as to compare reflux patterns after catheter-directed and systemic thrombolysis of deep ileofemoral venous thrombosis, and to evaluate the long-term outcome of deep venous reconstructions for severe chronic venous insufficiency. The study consists of five separate retrospective projects and includes 315 patients. Of this, 133 patients had undergone superficial venous surgery 2 to 5 years earlier according to preoperative duplex examination and venous marking, or according to clinical evaluation alone, or to a written plan without venous marking. A total of 112 patients had undergone ultrasound-guided foam sclerotherapy 5.5 to 16.5 months before. In addition, 32 patients had received either catheter-directed or systemic thrombolysis for DVT 2 to 3 years earlier, and 38 patients had undergone deep venous reconstructions 2 to 7 years earlier. In the present studies, some venous reflux was present postoperatively irrespective of the method of evaluation or ablation of the reflux. It seemed, however, that preoperative examination with duplex ultrasound and marking of reflux sites before the operation by the operating surgeon improves the outcome of superficial venous surgery. Ultrasound-guided foam sclerotherapy is effective in elimination of venous reflux in selected cases in short-term follow-up. Catheter-directed thrombolysis for deep iliofemoral venous thrombosis reduces later reflux and most probably the development of post-thrombotic syndrome as well. The outcome of deep venous reconstructions, especially for post-thrombotic deep venous incompetence, is poor. Thus, prevention of valvular damage by active treatment of deep venous thrombosis is important.

Characterization of hot deformation behavior of Zr-1Nb-1Sn alloy

The hot deformation behavior of beta-quenched Zr-1 Nb-1Sn was studied in the temperature range 650-1050 degrees C and strain rate range 0.001-100 s(-1) using processing maps. These maps revealed three different domains: a domain of dynamic recovery at temperatures <700 degrees C and at strain rates <3 x 10(-3) s(-1), a domain of dynamic recrystallization in the temperature range 750-950 C-degrees and at strain rates <10(-2) S-1 with a peak at 910 degrees C and 10(-3) S-1 (in alpha + beta phase field), and a domain of large-grain superplasticity in the beta phase field at strain rates <10(-2) s(-1). In order to identify the rate controlling mechanisms involved in these domains, kinetic analysis was carried out to determine the various activation parameters. In addition, the processing maps showed a regime of flow instability spanning both alpha + beta and beta phase fields. The hot deformation behavior of Zr 1Nb-1Sn was compared with that of Zr, Zr-2.5Nb and Zircaloy-2 to bring out the effects of alloy additions. (C) 2006 Elsevier BN. All rights reserved.

Hot deformation behaviour of Mg–3Al alloy—A study using processing map

The hot deformation behaviour of Mg–3Al alloy has been studied using the processing-map technique. Compression tests were conducted in the temperature range 250–550 °C and strain rate range 3 × 10−4 to 102 s−1 and the flow stress data obtained from the tests were used to develop the processing map. The various domains in the map corresponding to different dissipative characteristics have been identified as follows: (i) grain boundary sliding (GBS) domain accommodated by slip controlled by grain boundary diffusion at slow strain-rates (<10−3 s−1) in the temperature range from 350 to 450 °C, (ii) two different dynamic recrystallization (DRX) domains with a peak efficiency of 42% at 550 °C/10−1 s−1 and 425 °C/102 s−1 governed by stress-assisted cross-slip and thermally activated climb as the respective rate controlling mechanisms and (iii) dynamic recovery (DRV) domain below 300 °C in the intermediate strain rate range from 3 × 10−2 to 3 × 10−1 s−1. The regimes of flow instability have also been delineated in the processing map using an instability criterion. Adiabatic shear banding at higher strain rates (>101 s−1) and solute drag by substitutional Al atoms at intermediate strain rates (3 × 10−2 to 3 × 10−1 s−1) in the temperature range (350–450 °C) are responsible for flow instability. The relevance of these mechanisms with reference to hot working practice of the material has been indicated. The processing maps of Mg–3Al alloy and as-cast Mg have been compared qualitatively to elucidate the effect of alloying with aluminum on the deformation behaviour of magnesium.

On the mechanical behavior of compacted pack ice : A theoretical and numerical investigation

Pack ice is an aggregate of ice floes drifting on the sea surface. The forces controlling the motion and deformation of pack ice are air and water drag forces, sea surface tilt, Coriolis force and the internal force due to the interaction between ice floes. In this thesis, the mechanical behavior of compacted pack ice is investigated using theoretical and numerical methods, focusing on the three basic material properties: compressive strength, yield curve and flow rule. A high-resolution three-category sea ice model is applied to investigate the sea ice dynamics in two small basins, the whole Gulf Riga and the inside Pärnu Bay, focusing on the calibration of the compressive strength for thin ice. These two basins are on the scales of 100 km and 20 km, respectively, with typical ice thickness of 10-30 cm. The model is found capable of capturing the main characteristics of the ice dynamics. The compressive strength is calibrated to be about 30 kPa, consistent with the values from most large-scale sea ice dynamic studies. In addition, the numerical study in Pärnu Bay suggests that the shear strength drops significantly when the ice-floe size markedly decreases. A characteristic inversion method is developed to probe the yield curve of compacted pack ice. The basis of this method is the relationship between the intersection angle of linear kinematic features (LKFs) in sea ice and the slope of the yield curve. A summary of the observed LKFs shows that they can be basically divided into three groups: intersecting leads, uniaxial opening leads and uniaxial pressure ridges. Based on the available observed angles, the yield curve is determined to be a curved diamond. Comparisons of this yield curve with those from other methods show that it possesses almost all the advantages identified by the other methods. A new constitutive law is proposed, where the yield curve is a diamond and the flow rule is a combination of the normal and co-axial flow rule. The non-normal co-axial flow rule is necessary for the Coulombic yield constraint. This constitutive law not only captures the main features of forming LKFs but also takes the advantage of avoiding overestimating divergence during shear deformation. Moreover, this study provides a method for observing the flow rule for pack ice during deformation.