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Package strength becomes challenging and issue for thin package used in mobile application. Package with low strength may result in package failure such as inside die cracking or package cracking through epoxy mold compound (EMC) when package is subjected to external loading from assembly process or field application. Package design and strength assessment methodology are essential for robust package used in mobile application. In this study, uMCP package is selected to demonstrate package strength investigation and improvement. Three-point bend (3PB) testing approach and finite element analysis (FEA) method are adopted for package strength study. A strain-controlled methodology is developed for package strength assessment. FEA simulation results show that mold cap thickness and mold clearance are 2 key factors for package strength. Die strength is another key factor for robust package strength design. In addition, effect of EMC material on package strength is also investigated.

The air conditioning (A/C) system is the largest auxiliary load in electric urban buses that operate in tropical climates. Reducing the energy consumption of the A/C system is therefore vital in reducing the energy demand from the traction battery hence improving vehicle range and in reducing the operational costs. This paper focuses on improving the refrigerant side performance by investigating a multi-stage vapour injection cycle. System modelling of the cycles was done in GT-Suite to investigate the improvement in the energy efficiency of the A/C system with multiple vapour injections in comparison to the conventional vapour compression system. The results showed an improvement in coefficient of performance (COP) enhancement of 23 %. Additional challenges of the proposed cycle are discussed to address the feasibility of implementing a multi-stage vapour injection system in urban electric buses.

This study investigates the learning approach of the designed Flipped Reading Platform (FRP) and its effects on primary school students' general Chinese reading and comprehension capabilities. This study was undertaken as part of the Quality Education Fund project in Hong Kong, titled "Flipped Reading: Enhancing the Learning and Teaching of Reading Strategies and Comprehension in Chinese via an Interactive Cloud Platform." This paper presents the design of the Interactive Cloud Platform FRP, which incorporates elements of both reading strategies and learning activities, and investigates the changes in students' reading performance, applied strategies, and active learning level with the application of FRP. The results show the experimental students using the FRP in the pilot scheme generally gained more in three stages of reading comprehension, and that low-achieving students learned reading strategies better. Analysis of FRP log activities shows students' active engagement in reading and perceived competence. Different learning outcomes were also found within the experimental group, categorized by BYOD and non-BYOD classes. Implications of the study show the effectiveness of FRP, and the design demonstrates how the reading measures integrated the assessment indicators of both international and local standards in the domain of Chinese Language reading. Further research can be developed to examine individual online reading performance and learning behaviour on FRP.

Due to the high pressure inside compressed natural gas (CNG) containers, its safety is the first important factor to be considered. Leak-before-break (LBB) is an important methodology of maintaining the integrity of pressure vessels. However, the Joule-Thomson (JT) cooling effect occurred during a leak may impact the validity of the LBB approach. In this paper, a looping model based on MATLAB software is developed starting with the gas at room temperature and 250 bar at the entrance of the crack. From this, the pressure and JT temperature drop is calculated initially, which in turn affects the gas properties, such as viscosity, density, thermal conductivity and heat transfer coefficients. Heat transfer and FEA analysis using a 3D model of the plate with a central through-thickness crack are carried out. Under the internal pressure of 250 bar, the temperature drop and the stress intensity factor in the vicinity of the crack is 59.7 ° C and 120 MPa m 1/2 , respectively. The stress intensify factor obtained is higher than the fracture toughness of the material at the same low temperature. However, the structure may not experience a catastrophic failure. The reasons for this phenomenon are discussed in the paper.

This paper proposes a method for simulating the heat transfer process of high pressure argon gas leaking through a narrow crack which causes the Joule-Thomson cooling effect (JT cooling effect). A once-through (decoupled) model was developed to firstly calculate the gas pressure drop at different crack depth, followed by the temperature drop. A MATLAB code was also developed to iteratively calculate the properties of leaking gas in a crack which was fitted as formula as boundary conditions in heat transfer simulation in COMSOL program. The simulated lowest temperature of the test plate in the vicinity of the crack is 13.8 °C after decreasing from the temperature of 30 °C with initial argon gas pressure of 91 bar. An experiment test rig designed and tested under the same conditions showed a good agreement between the simulation and experiment at the obtained lowest temperature in the test plate. The method is useful for predicting the lowest temperature in the vicinity of the crack caused by the JT cooling effect.

The investigations on optimization of composite composition of nickel–zirconia for the functionally graded layered thermal barrier coating for the lowest but uniform stress field under thermal loading is presented. The procedure for obtaining temperature- and composition-dependent thermal and mechanical properties of various coating compositions is discussed. These material parameters were used in thermo-mechanical finite element stress analyses of a nickel substrate with the coating. The results showed that the Von-Mises stresses in the substrate and the interfaces were the lowest with the coating profile that followed a concave power law relationship with the index n ≈ 2.65. Accepted version

Introduction Reconstruction of the weight bearing, thick and durable heel, in soft tissue injuries of the foot remains a difficult and challenging problem. The thick glabrous epidermis and dermis, and the fibrous septae of the subcutaneous layer provide unique properties for withstanding pressure and shock associated with gait.

A three-dimensional numerical model is developed using computational fluid dynamics software FLUENT v6.3.26 to investigate the influence of curved substrate on the plasma flow fields and subsequent in-flight particle behavior. The curved substrates have two different dimensional shapes and are positioned in two orientations (convex or concave). It is found that inclusion of the substrates with different shapes in different directions significantly affects the plasma flow fields at the vicinity of the substrate, although the most upstream region of the plasma field remains unaffected. Plasma temperature and velocity contours and flow vectors in the computational domain, especially at regions near substrates are presented. Investigations on the size effect on the in-flight particle parameters are carried out, which show that smaller particles tend to acquire higher velocities and temperatures. Moreover, smaller particles are more susceptible to the flow change by the substrate inclusion. However, for the size range of the zirconia feedstock we used later, there is no obvious effect of the substrate inclusion on the particle distribution on the substrate surface.

PurposeIn‐flight refueling is one of the most important technologies developed in military aviation. The purpose of this paper is to analyze the dynamic behaviour of fuel during a refuel process by means of an internal flow analysis software program.Design/methodology/approachThe dynamic behaviour of fuel during a refuel process is analyzed by means of an internal flow analysis software program called Flowmaster. The refueling system is analyzed by representing physical components as flow resistances and control volumes and calculating the flow rates and pressures along the system. Both steady and transient state analyses are performed to identify the locations where high‐pressure surges are likely. The peak pressures are compared to allowable proof pressures of system components to ensure that they are not exceeded.FindingsIt was found that a transient analysis of the fuel behaviour in the refuel pod system for a complete refueling process can be completed successfully with Flowmaster software.Originality/valueThe paper models a complete refueling process with the sequence of trail, fuel transfer and rewind phase in order to analyse the fuel‐transient behaviour, in particular near to the times where the valves are activated.

The use of phase-Doppler anemometry (PDA) to characterize the detail in-flight plasma sprayed particle behavior has been demonstrated previously [Ma et al. Plasma Chem Plasma Process 24(1):85; 25(1):56] The present articles shows further that a direct relationship may exist between the PDA measured particle volume flux and the coating microstructure and deposition efficiency (DE). In the situation when the precise particle temperature information is not available, the PDA measured particle volume flux may provide an alternative to predict quantitatively the variation of the coating microstructure and the DE. By monitoring the in-flight particle volume flux variations, instead of the particle velocity, size and temperature individually and simultaneously, the optimal settings of the plasma spraying parameters may also be determined conveniently. However, it is noted that the effective applications of such approach depend largely on the particle surface morphology and the pre-determination of the particle size range.

In the plasma spray coating process, the coating’s profile and overall thickness are dependent on the number of overlapping traverses of the torch, the shape of the particle spray plume, the spatial distribution of the in-flight parameters of the particles within, and the orientation of the substrate. In this paper, a semi-empirical methodology for predicting three-dimensional deposits by the plasma spray process is developed. It comprises of three stages: first, spatial distributions of the in-flight parameters of multi-sized particles within the spray plume are determined by Computational Fluid Dynamics simulations. The size and shape parameters of the splats formed when individual droplets impact and spread out are obtained by experiments. Finally, a computer program is developed to integrate the particle parameters distribution and the empirical splat geometric data to generate a three-dimensional profile representing the deposit. The procedures predict the deposition volumes and thicknesses for different substrate inclinations with good agreement to experimentally sprayed deposits.

Upcoming stringent regulations on emissions and fuel efficiency are driving the automotive industry towards lightweight vehicle design. Thus, a higher share of carbon fiber composite materials in vehicle structures is expected. Current literature addresses development processes of composite components under a limited scope, however the considerations of design parameters used in these studies are inadequate for the realistic development of a full vehicle structure, especially in a resource-constrained development project. In addition, existing vehicle structure design philosophies applied for metal structures cannot be directly ported over for composite design due to differences in material properties, failure modes and design for manufacturing limitations. Thus, an approach to develop a fully functional composite vehicle body with reference to realistic functional and roadworthiness requirements along with process considerations of interlinked relationship between design, simulation, manufacturing and final assembly of the prototype's vehicle structure is introduced. This methodology was applied to develop EVA, a prototype electric taxi concept for tropical megacities. EVA was presented at the Tokyo Motor Show 2013 boasting a body-in-white (BIW) weight reduction of more than 100 kg compared to a series production steel BIW. This paper presents the development process of a fully functional prototype vehicle body taking into account the production process and therefore, provides a versatile guideline for future projects.

In this paper, ps laser is employed to fabricate surface textures on Ni substrate. A regular 2D array of micro-bumps-based texture which is superimposed with nano-ripples has been demonstrated on Ni, which displays superhydrophobic surface property with a WCA > 150 degree. Also, 3 major types of surface textures have been fabricated on Ni mold including periodic ripples, micro-bumps array and micro-pits array pattern. Hot embossing on PMMA substrate with laser textured Ni mold has been conducted. The surface wettability of embossed polymer has been converted from original hydrophilic to highly hydrophobic with a WCA of up to 128 degree. The developed process has a potential application in the fabrication of microfluidic devices.In this paper, ps laser is employed to fabricate surface textures on Ni substrate. A regular 2D array of micro-bumps-based texture which is superimposed with nano-ripples has been demonstrated on Ni, which displays superhydrophobic surface property with a WCA > 150 degree. Also, 3 major types of surface textures have been fabricated on Ni mold including periodic ripples, micro-bumps array and micro-pits array pattern. Hot embossing on PMMA substrate with laser textured Ni mold has been conducted. The surface wettability of embossed polymer has been converted from original hydrophilic to highly hydrophobic with a WCA of up to 128 degree. The developed process has a potential application in the fabrication of microfluidic devices.

Spacecraft thermal control materials (TCMs) play a vital role in the entire service life of a spacecraft [NASA Preferred Reliability Practices: Spacecraft Thermal Control Coatings Design and Application (Practice No. PD-ED-1239), 1995, pp. 1–6] . Most of the conventional TCMs degrade in the harmful space environment [R.D. Karam, Satellite Thermal Control for Systems Engineers, AIAA, Virginia, USA, 1998, pp. 147–163] . In the previous study, plasma sprayed alumina (PSA) coating was established as a new and better TCM for spacecrafts, in view of its stability and reliability compared to the traditional TCMs [R.M. Li, S.C. Joshi, H.W. Ng, Presented in 2nd International Conference on Materials for Advanced Technologies & IUMRS, Singapore, 2003, pp. 1–4] . During the investigation, the surface roughness of PSA was found important, because the roughness affects the radiative heat exchange between the surface and its surroundings. Parameters such as root-mean-square roughness cannot properly evaluate surface roughness effects on radiative properties of opaque surfaces [M.F. Modest, Radiative Heat Transfer, 2nd ed., Academic Press/Elsevier Science, USA, 2003, pp. 90–92] . Some models have been developed earlier to predict the effects, such as Davies’ model [H. Davies, Proceedings of IEEE vol. 101, part IV, 1954, pp. 209–214] , Tang and Buckius's statistical geometric optics model [K. Tang, R.O. Buckius, Int. J. Heat Mass Transfer 44 (2001) 4059–4073] . However, they are valid only in their own specific situations. In this paper, an energy absorption geometry model was developed and applied to investigate the roughness effects with the help of 2D surface profile of PSA coated substrate scanned at micron level. This model predicts effective normal solar absorptance ( α ne ) and effective hemispherical infrared emittance ( ɛ he ) of a rough PSA surface. These values, if used in the heat transfer analysis of an equivalent, smooth and optically flat surface, lead to the prediction of the same rate of heat exchange and temperature as that of for the rough PSA surface. The model was validated through comparison between a smooth and a rough PSA coated surfaces. Even though not tested for other types of materials, the model formulation is generic and can be used to incorporate the rough surface effects for other types of thermal coatings, provided the baseline values of normal solar absorptance ( α n ) and hemispherical infrared emittance ( ɛ h ) are available for a generic surface of the same material.

Splats are obtained by atmospheric plasma spraying of yttria-partially-stabilized (8%) zirconia and captured by fast traversing flat and inclined substrates in front of plasma torch. The angles of inclination of the substrates enable the particles to impact on the substrate at different angles of incidence. The effects of the angle of impact on the splat final morphology and spreading behavior have been examined by Scanning Electron Microscopy (SEM) and a Coordinate Measurement Machine (CMM) surface profiler. From SEM, oblique impact produces features such as fingering, ridging, splashing, overlapping and elliptical shaped splats. To quantify spreading behavior, two geometric characteristics, namely, spread factor (ξ) and aspect ratio (ψ) are measured by CMM. The spread factor (ξ) is the ratio of the splat circular equivalent diameter to the droplet diameter, for which the splat equivalent diameter is assumed by considering the elliptical shape to occupy the same area as a circular shape. The aspect ratio (ψ) is the ratio of the major to minor diameters of the ellipse, it being assumed that the elliptical shape of the splat is geometrically perfect. This paper presents the spread factors and aspect ratios of individual splats at different substrate inclinations and their comparison to available literature. Curved fitted quadratic equations for spread factor and aspect ratio are proposed. In addition, the Madejski's Reynolds number based spread factor model is modified to fit the authors' experimental data. These equations are necessary for future work on numerical simulation of deposit profiles on realistic engineering parts having complex curved surfaces.

Numerical models have been developed using computational fluid dynamics (CFD) analysis program FLUENT V6.02© to investigate the effect of the substrate on the behavior of the plasma flow fields and in-flight particles. Simulations are performed for cases where flat substrates are either present or absent, for the former, the substrate is oriented perpendicularly or inclined to the torch axis. It is shown that although the presence of perpendicular or inclined substrate significantly influences the plasma flow fields at the vicinity of the substrate, the particle behavior remain relatively unaffected. The insignificant effect of the substrate on particle behavior is qualitatively verified by experimental observation using SprayWatch© imaging diagnostics equipment. Images captured by the equipment confirm that the particles travel through the plasma plume with high momentum and show no sudden change in theirtrajectories right before impacting the substrate. Both the numerical and experimental findings show that the freestream model is sufficiently detailed for future work of this nature.

Real time close-up images of in-flight particles plasma sprayed onto a substrate and in freestream condition (without substrate present) are captured. Besides the images, particle behavior in terms of temperature, velocity, and heading are measured by the Spray Watch particle imaging diagnostics system. The monitoring and measurement of particle behavior have been performed for substrates inclined at various angles to investigate the effect of the substrate on particle behavior. The close-up images show that particles propelled from the torch travel with high momentum and are not affected by the substrate and inclination angle. Quantitative analyses of the particle average velocity and heading data with and without the different inclined substrates also lead to similar conclusions. The particle velocity is resolved into tangential and normal velocity components parallel and perdendicular to the substrate, respectively. The tangential velocity component controls the degree of splat elongation into elliptical shape from the circular shape seen in perpendicular impact. This is of practical importance in industrial spraying of engineering components of complex curvatures. A higher tangential velocity component also implies that more powders are lost through rebounding and overspraying and thus reducing the deposition efficiency. The normal velocity component decreases when substrate inclination increases, which tends to weaken the coating adherence.

A comprehensive, geometrically accurate, nonlinear C0-C7 FE model of head and cervical spine based on the actual geometry of a human cadaver specimen was developed. The motions of each cervical vertebral level under pure moment loading of 1.0 Nm applied incrementally on the skull to simulate the movements of the head and cervical spine under flexion, tension, axial rotation and lateral bending with the inferior surface of the C7 vertebral body fully constrained were analysed. The predicted range of motion (ROM) for each motion segment were computed and compared with published experimental data. The model predicted the nonlinear moment-rotation relationship of human cervical spine. Under the same loading magnitude, the model predicted the largest rotation in extension, followed by flexion and axial rotation, and least ROM in lateral bending. The upper cervical spines are more flexible than the lower cervical levels. The motions of the two uppermost motion segments account for half (or even higher) of the whole cervical spine motion under rotational loadings. The differences in the ROMs among the lower cervical spines (C3-C7) were relatively small. The FE predicted segmental motions effectively reflect the behavior of human cervical spine and were in agreement with the experimental data. The C0-C7 FE model offers potentials for biomedical and injury studies.

The feasibility of forming porous metallic materials by the plasma spraying process was studied. The process involved the co-spraying of two materials: aluminum (Al) and calcium oxide (CaO), the former being the metallic phase that eventually was retained as the porous structure, while the latter being the sacrificial phase was removed giving rise to pores in the Al matrix. For this the Al and the CaO powders of four different compositions were blended and plasma sprayed on a mold cavity. The CaO was dissolved from the sprayed structure by treating in either water or glycerol. The surface and cross sectional microstructure of the specimens after treatment in water and glycerol showed a more or less uniform pore distribution. The dissolution of CaO, leading to the porous microstructure was confirmed by the X-ray diffractometry. In the XRD spectra, the specimens in the as-sprayed untreated condition exhibited peaks corresponding to both CaO and Al, while, the peaks corresponding to CaO were absent in specimens after water and glycerol treatments confirming CaO dissolution. The study clearly showed that porous aluminum material could be manufactured by plasma spraying.

It is essential to analyze the residual stresses during the deposition of plasma sprayed coatings since they adversely affect the coatings' performance during their service. In this article, finite element coupled heat transfer and elastic-plastic thermal stress analysis using a general purpose commercial FEM software ANSYS (ANSYS Inc., Southpointe, PA, USA) are presented to simulate the in situ residual stress generation during plasma spraying of duplex thermal barrier coatings (TBCs). The complicated physical spray process was idealized and a multiple layer-by-layer coating structure was assumed. In the simulation, the geometry was updated layer by layer and results from the previous layer analysis, including temperature and displacement, were used as loads for the current layer analysis. The predicted specimen temperature and curvature agreed well with those experimentally measured by thermocouples and a specially designed laser-displacement-measurement system, respectively. A simple method by post-deposition treatment was also proposed to effectively reduce the residual stress level in the coated specimen, with the possibility of eliminating the residual stress.

In this study, the digitized geometrical data of the embalmed skull and vertebrae (C0–C7) of a 68-year old male cadaver were processed to develop a comprehensive, geometrically accurate, nonlinear C0–C7 FE model. The biomechanical response of human neck under physiological static loadings, near vertex drop impact and rear-end impact (whiplash) conditions were investigated and compared with published experimental results. Under static loading conditions, the predicted moment-rotation relationships of each motion segment under moments in midsagittal plane and horizontal plane agreed well with experimental data. In addition, the respective predicted head impact force history and the S-shaped kinematics responses of head-neck complex under near-vertex drop impact and rear-end conditions were close to those observed in reported experiments. Although the predicted responses of the head-neck complex under any specific condition cannot perfectly match the experimental observations, the model reasonably reflected the rotation distributions among the motion segments under static moments and basic responses of head and neck under dynamic loadings. The current model may offer potentials to effectively reflect the behavior of human cervical spine suitable for further biomechanics and traumatic studies.

Conventional thermal control materials (TCMs) used in satellites tend to deteriorate in the severe space environment, many times leading to unanticipated mission problems. New and better TCMs are constantly sought to reduce difficulties in satellite thermal design. In this paper, the possibility of using plasma-sprayed alumina (PSA) coating for thermal control of a satellite is examined. Such PSA coatings have proved to be a good thermal barrier coating material for hot section components in aircraft engines. Panels of aluminum alloys such as 2024-T3, 6061-T6, 7075, and so on which are commonly used for satellite applications, form a very compatible substrate for PSA coatings. Various physical and processing parameters and simulated in-service behaviour for PSA were studied analytically and experimentally. Preliminary investigations reveal that the PSA coatings have good potential as a substitute to conventional TCMs for micro-satellite panels, including solar arrays.

A detailed three-dimensional head-neck (C0–C7) finite element (FE) model developed previously based on the actual geometry of a cadaveric specimen was used to characterize the whiplash phenomenon of the head-neck region during rear-end collision. A maximum rear impact pulse of 8.5 G of acceleration was applied to C7. The effects of a headrest on the responses of head-neck complex were also discussed. The study demonstrates the effectiveness of the current C0–C7 FE model in characterizing the gross responses of human cervical spine under whiplash. The results showed that during whiplash, the lower cervical levels, especially the C6–C7, experience hyperextension in the early phase of acceleration. The whole cervical spine is at risk of extension injuries rather than flexion injuries in whiplash. The use of a proper headrest can effectively reduce the cervical spine from extension injury during the acceleration phase of cervical spine in whiplash.

Detailed measurements of particle in-flight characteristics have been carried out using a PDA system for benchmarking as well as to provide further information to aid the development of simulation models. The parameters studied included four conditions of primary gas flow rate and carrier gas flow rate. The particle velocities, diameters, and the corresponding volume flux at different locations were obtained. Due to the one port particle injection arrangement, it was noted that particles in general sprayed with an angle η deviated from the nozzle axis Z n , to the opposite side of the powder feeder port. The particles would also deviate from the spraying cone axis with a divergence angle (φ). The deviation and divergence angles were examined under different plasma spraying conditions. The measurement data rates at different cross-sectional planes were also obtained so as to compare the results derived from the volume flux measurement and the actual coating on a substrate at the equivalent standoff distance. It was found that the spraying area obtained from the measurement-data-rate increased with downstream distance and a linear relationship between spraying area and distance was also established. Comparing the integrated results, it was noted that the spraying areas derived from the measurement data rate were close to the actual spraying areas obtained from the coordinate measurement machine (CMM) results.

Objective: Although a number of in vivo, in vitro, and finite element studies have attempted to delineate the natural biomechanics, injury mechanisms, and surgical techniques of the cervical spine, none has explored the influence of various preload magnitudes and orientations on the biomechanical responses. Methods: A nonlinear three-dimensional finite element model of the lower cervical spine (C5-C6) was used for this study. The model was tested under four preload magnitudes and three orientations. For every preload, magnitude, and orientation, pure moments of 1.8 Nm were applied to the superior surface of the moving vertebra (C5) in flexion, extension, lateral bending, and torsion. The resulting rotational motions were obtained and compared against literature data Results: The predicted biomechanical responses under the same loading directions varied, depending on the preload magnitudes and orientations. With flexion and extension, increasing the preload magnitudes and varying the C5-C6 orientation in the sagittal plane changed the rotational motions by 1% and 18%, respectively. Under normal orientation and with increasing preload magnitudes, flexion and extension increased, whereas lateral bending and torsion decreased. These changes were found to be influenced by several spinal components: posterior facets, passive ligaments, and stiffening ofthe intervertebral disc. The predicted responses under the direction of loading varied significantly, depending on the preload magnitudes and orientations. Under fixed preload magnitudes and varying the three types of orientations, rotational motions were not affected under flexion but changed under extension, lateral bending, and axial rotations. Under normal orientation and increasing preload magnitudes, biomechanical responses under flexion and extension increased, whereas lateral bending and torsion decreased. Changes in the predicted responses were found to be influenced by several spinal components: posterior facets, passive ligaments, and stiffening of the intervertebral disc. Conclusion: The findings of the current study were important for the further understanding of the cervical biomechanics during in vitro testing.

Coupled heat transfer and elastic–plastic finite element analyses were conducted to study thermal stress generation and development during deposition of a nickel–cobalt (NiCoCrAlY) alloy on an aluminum disc (AA1100) substrate. A general purpose commercial finite element method (FEM) software ANSYS was used for the simulation of the temperature as well as stress and strain histories during the deposition process. A FEM special software feature called the element birth and death was used. The stress built-up during spraying was experimentally obtained by means of deflection measurement. A close agreement between the numerically predicted deflected shapes of the specimen and the experimental results indicated that the stress–strain distributions from the numerical elastic–plastic model could be applied with reasonable accuracy.

A two-port powder injection scheme applied to atmospheric plasma spray (APS) was investigated using a 2-D Phase Doppler Anemometer (PDA). The 8 wt.% yttria partially stabilized zirconia (YSZ) powders were sprayed from a Miller SG-100 arc plasma torch. Radial distributions of mean particle velocities, diameter and volume flux were measured and evaluated under different combinations of plasma and carrier gas flow rates. It was found that as a result of the interaction between the powder–gas flows from the two opposite injectors, both the mean particle velocity and mean diameter distribution were more symmetrical about the centerline of the plasma torch. The volume flux distributions evaluated using PDA measurements were also compared with the actual sprayed stationary deposit. Although there existed some obvious difference between the two cases, measurements using a PDA were able to approximately predict the variation of actual deposits under different conditions.

Posterior decompressive techniques including one- and two-level laminotomies and laminectomies are often used in treating cervical stenosis. Previously, several in vitro studies were conducted to help us understand the biomechanical changes occurring in the cervical spine after these surgical techniques. However, changes in the intersegmental flexibility under combined flexion-extension remain unclear. In this study, a 3-D nonlinear intact model of the C2–C7 was developed to evaluate the influence of one- and two-level laminotomies and laminectomies on the intersegmental moment rotational responses and internal stresses. The intact model was validated by comparing the predicted responses against experimental data. The validated model was then modified to simulate various surgical techniques for finite element analysis. Results showed that one- and two-level laminectomies increase the C2–C7 rotation motions by about 15% and 20%, respectively. The predicted increase in rotational motions also correlated well with the published data. Furthermore, results indicated that laminectomies would influence the biomechanical responses on both the affected and adjacent motion segments. In contrast, laminotomies have no significant effects on cervical biomechanics. To conduct a one-level laminectomy study, current findings indicate that it takes at least five motion segments to capture the immediate postsurgical biomechanical changes accurately and realistically. Minimally invasive cervical spine surgeries with one- or two-level laminotomies are preferred over one- and two-level laminectomies. Also, there is no consideration as to the efficacy of the two techniques in decompressing the spinal cord or nerve roots, which is the goal of the surgery, but is not examined in this study.

Methods: The study was designed to analyze the load distribution of the cancellous core after implantation of vertical ring cages made of titanium, cortical bone, and tantalum using the finite element (FE) method. The intact FE model of C5-C6 motion segment was validated with experimental results. Results: The percentage of load distribution in cancellous core dropped by about one-third of the level for the intact model after the cage implantation. The difference among cages made of different materials (or different stiffnesses) was not very obvious. Conclusions: These results implied that the influence of the cage on the load transfer in the cancellous core is greatly related to the cage's dimensions and position within the intervertebral space. The dimension and position of the cage that least disturb the load distribution in cancellous core could be criteria in cage development.

The objective of this study was to determine the intersegment stability, disc degeneration, and osteophytes formation on the multisegment cervical spine (C2-C7) after unilateral and bilateral facetectomy. A geometrically accurate non-linear three-dimensional model of the intact human cervical spine was created from the digitized coordinates of the dry vertebrae. The intact model was validated against the published results under physiological loading conditions. Eight surgically altered models were created from the intact model. The intact and surgical altered models were subjected to physiological loading. The inclusion of five levels in the present model allowed accurate determination of the intersegment responses and internal cortical bone and disc annulus stress in the adjacent spinal components. Results indicated that facetectomy performed on C5-C6 significantly affects the corresponding stress and intersegment motions at the corresponding C5-C6 levels. The maximum increases were 18 per cent for bilateral facetectomy and 7 per cent for unilateral facetectomy under lateral bending. Combined flexion-extension and axial rotation caused an approximately similar amount of increases after total facetectomy. In addition, adjacent segments (C4-C5 and C6-7) also experience a slight increase in the intersegment responses and internal stress after facetectomy. It has been shown that facetectomy of greater than 50 per cent resulted in segment hypermobility and substantial increase in the disc annulus and cortical bone stress. Increase in the stress may lead to osteophytes formation. This study revealed important information that will help clinicians identify the critical intersegment stability and to decide on the amount of facets resection.

Applications of Phase-Doppler anemometry to the measurements of metal (nickel) particle size and velocity in the plasma spray process have been studied and analyzed with the aid of Mie scattering theory. The optimum optical settings used in two PDA systems were determined and tested experimentally. Measurements at cross-sectional planes 5 and 10 cm below the SG-100 (Miller) plasma gun were obtained and discussed. In this study, only one particle injection port was used. It is noticed that the variation of the percentage of the diameter validation rate would affect the volume flux results considerably. If the diameter validation rate can be maintained above 65%, the integrated volume flux would be close to the results obtained from the total volume deposited on a substrate or from the estimation based on the mass balance in the powder feeder (measured before and after spraying). The PDA measurement may also provide some predictions on the deposition area and the corresponding maximum height of the coating at a specific stand-off distance from the nozzle.

The objective of this study was to investigate the effect of the thoracic posterior vertebral elements on the kinematics of T10–T11 motion segment in sagittal plane by assessing the locations and loci of the instantaneous axes of rotation (IARs) under flexion and extension pure moments using finite element (FE) method. The IAR has proven to be a useful parameter of vertebral motion and it is an indicator of spinal instability. An anatomically accurate FE model of thoracic T10–T11 functional spinal unit (FSU) was used to characterize the loci of centers of rotation for the intact T10–T11 FSU and disc body unit (without posterior vertebral elements) under flexion and extension pure moments. The centers of rotation predicted by the intact model and disc body unit of thoracic T10–T11 for both flexion and extension were directly below the geometrical center of the moving vertebra. However, the loci of the IARs were significantly affected by the posterior vertebral elements. The loci of instantaneous axes of rotation for the intact model were tracked superoanteriorly and inferoposteriorly for flexion and extension with rotation, respectively. While, for the disc body unit, the loci were detected to diverge lateroinferiorly from the mid-height of the intervertebral disc, they converge medio-inferiorly toward the superior endplate of the inferior vertebra T11 with increased moment. These findings may offer an insight to better understanding the kinematics of the human thoracic spine and provide clinically relevant information for the evaluation of spinal stability and implant devices functionality.

This paper presents an investigation of the influence of plasma spray process conditions on the in-flight particle behavior and their cumulative deposition to form a coating on the substrate. Three-dimensional computational fluid dynamics (CFD) analyses were performed to model the in-flight particle behavior in the plasma-spray process and their deposition on the substrate. The plasma spray was modeled as a jet issuing from the torch nozzle through the electrical heating of the arc gas. In the model, particles were injected into the plasma jet where they acquired heat and momentum from the plasma, some got melted and droplets were formed. By means of a droplet splatting model, the particle in-flight data generated by the CFD analyses were further processed to build up an imaginary three-dimensional deposition profile on a flat stationary substrate. It is found that the powder carrier gas flow rate influences the particle distribution on the substrate by imparting an injection momentum to the particles that were directed radially into the plasma jet in a direction perpendicular to the plasma jet. The larger sized particles will acquire higher injection momentum compared with the smaller sized particles. This causes particle distribution at the substrate surface that is elliptical in shape with the major axis of ellipse parallel to the particle injection port axis as illustrated in Fig. 1. Larger particles tend to congregate at the lower part of the ellipse, due to their greater momentum. The distribution of particle size, temperature, velocity, and count distribution at the substrate was analyzed. Further, based on the size and the computed particle temperature, velocity histories, and the impact sites on the substrate, the data were processed to build up a deposition profile with the Pasandideh-Fard model. The shapes of deposition profiles were found to be strongly driven by the segregation effect.

In the human spine, it is well known that facet joints play a significant role in load transmission and providing stability. It has also been hypothesized to be one of most probable sources of low back pain. Experimental determination of the load-bearing role of lumbar intervertebral joints, such as the facets joints, under axial compression has not been a straightforward task. In this study, the role of the facets in load transmission through a L2–L3 motion segment under axial compression is investigated using a L2–L3 finite element (FE) model, incorporated with an accurate three-dimensional geometry of facet joints with the inclusion of surface-to-surface continuum contact representation. The effects of osteoarthritis on facet force and biomechanical behaviors are also investigated by assuming friction at the facet joints. The study shows that the facet joints resisted 8% more in load for joints with osteoarthritics as compared with the normal joints. High percentage increase in contact facet force was also predicted for joint with osteoarthritics deformity. The use of the analytical FE model provided yet another efficient alternative for predicting the load transmission and contact force for degenerative joints, so as to provide a better understanding of the biomechanics of the spine as well as the pathophysiology of the various spinal disorders and degenerative conditions.

The definition of cervical spinal instability has been a subject of considerable debate and has not been clearly established. Stability of the motion segment is provided by ligaments, facet joints, and disc, which restrict range of movement. Moreover, permanent damage to one of the stabilizing structures alters the roles of the other two. Although many studies have been conducted to investigate cervical injuries, to date there are only limited finite element investigations reported in the literature on the biomechanical response of the cervical spine in these respects. A comprehensive, geometric, nonlinear finite element model of the lower cervical spine has been successfully developed and validated under compression, anterior-posterior shear, and sagittal moments. Injury studies were done by varying each spinal component independently from the validated model. Seven analyses were conducted for each injury simulation (model without ligaments, model without facets, model without facets and ligaments, and model without disc nucleus). Results indicate that the role of the ligaments in resisting anterior and posterior shear and flexion and axial rotation moments is important. Under other physiologic loading (anterior-posterior shear, flexion-extension, lateral bending, and axial rotation), the disc nucleus is responsible for the initial stiffness of the cervical spine. The results also highlight the importance of facets in resisting compression at higher loads, anterior shear, extension, lateral bending, and torsion. The results provide new insight through injury simulation into the role of the various spinal components in providing cervical spinal stability. These findings seem to correlate well with experimental results as well as with common clinical experience.

The capability of plasma spraying for producing near net shape, free-standing components of metallic, ceramic and layered composites with alternate ceramic and metallic layer systems was studied. A simple and efficient mold mandrel with attachments to release the sprayed component was designed and machined. The plasma spraying was carried out, with powders of nickel and zirconia–8 wt.% yttria to form shapes such as nozzles, cones and cylinders. The plasma spray parameters and the mold mandrel operation were standardized by trial and error to produce the near net shapes. The microstructure, fracture morphology and microhardness of the sprayed components were studied. The study showed that the shapes constituting metallic, ceramic and layered composites with alternate layers of ceramic and metallic materials could be successfully formed by plasma spraying.

This study was conducted to develop a detailed, nonlinear three-dimensional geometrically and mechanically accurate finite-element model of the human lower cervical spine using a high-definition digitizer. This direct digitizing process also offers an additional method in the development of the finite-element model for the human cervical spine. The biomechanical response of the finite-element model was validated and corresponded closely with the published experimental data and existing finite-element models under axial compressive loading. Furthermore, the results indicated that the cervical spine segment response is nonlinear with increasing stiffness at higher loads. As a logical step, a parametric study was conducted by evaluating the biomechanical response related to the changes in the modeling techniques of the finite-element model and the mechanical properties of the disk annulus. Variations of the predicted horizontal disk bulge were investigated under axial compressive displacements for the normal model, the model without facet articulations, and the model without nucleus. Removal of nucleus fluids causes an inward bulge of the inner annulus layers, with the displacement magnitude dependent on external loads. The result indicates that the nucleus fluid plays an important role in cervical spine mechanics. Simulated facetectomy indicates a decrease in the stiffness of the cervical spine. The study shows that, in reality, the stiffness of the lower cervical spine depends closely on factors such as the spinal geometry and physical properties, thereby resulting in various force and displacement responses.

The role of particle injection velocity and size on the microstructure of plasma sprayed alumina coating was studied with reference to the process chart formulated by the computational fluid dynamics (CFD) study reported earlier. For this, three grades of alumina powder with mean sizes of 25, 40 and 76 μm were utilized and sprayed under different injection velocities. The coating was characterized using scanning electron microscopy (SEM) for surface structure, X-ray diffractometry (XRD) for phase changes and Micro-Vickers hardness test measurements. The particle states were found to change depending on the injection velocity and size in correlation with the process chart, as revealed in the form of unmelted particles or well spread splats in the coating surface microstructure. This was further confirmed by the XRD results which showed a steady decrease in α-alumina content with increase in the injection velocity indicating a rise in the extent of complete melting of alumina particles in the case of 25 μm mean size powder. The micro-hardness also varied considerably depending on the injection velocity, due to the changes in the extent of the melting of alumina particles. A close correlation between the particle states depicted in the process chart and the coating microstructure was observed indicating the validity of the process chart and its suitability to put into actual coating applications.

The role of particle injection velocity in influencing the nature of alumina coatings obtained by plasma spraying was studied. Previously reported process chart obtained by computational fluid dynamics (CFD) study on the particle states of alumina with respect to particle injection velocity and size was verified experimentally. For this purpose, alumina particles of three different size ranges with a mean size of 25, 40, and 76 μm were subjected to different injection velocities. The coating obtained was analyzed for cross-sectional microstructure and thickness by optical microscopy. In addition, the role of particle injection velocity and size in influencing the coating-deposition efficiency was studied. The experimental results agreed well with the CFD results, which had indicated the dependence of particle trajectory in the plasma plume on the particle injection velocity and size leading to the changes in the extent of melting. While a higher coating thickness and deposition efficiency was obtained with 25-μm particles, with further increase in particle size, a reverse trend was observed. This was attributed to the changes in heat-transfer characteristics of the particles with size, which governed the coating buildup and deposition efficiency.