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Architected materials present an opportunity to overcome the limited ability of brittle piezoelectric ceramics to strain under electromechanical load. In the absence of a commercially available resin containing piezoelectric nanoparticles, this work seeks to investigate the printability and thermal processability of a prepared piezoelectric particle loaded slurry using laser stereolithography. This was accomplished by comparing the cure depth, in-plane resolution, and the dimensional accuracy achieved with a piezoelectric slurry prepared with barium titanate, to a commercially available silica and alumina-based suspension. The study of thermal processability revealed the dimensional sensitivity of fabricated open architectures to sintering temperature and duration. The prepared piezoceramic slurry, containing barium titanate, was successfully polymerized using laser-stereolithography and its cure depth exhibited a similar response to exposure duration and fluence level as the commercial slurries. The in-plane resolution of the barium titanate-based slurry was unexpectedly high, and may be due to the opacity of the piezoelectric particles. Open architectures with millimeter sized features were successfully fabricated using laser stereolithography. Dimensional accuracy was highest for the alumina-based material system, and the inverse relationship between cured depth and in-plane resolution was reflected in the dimensions of the silica-based parts. Open architected structures further withstood thermal processing. During thermal processing, there was a greater reduction in height for all parts due to higher in-plane concentrations of ceramic particles, relative to the z-direction. Both an increase in sintering temperature and duration resulted in a uniform change of 1%, respectively, in part dimensions. Data collected in this work is to be used as a benchmark to inform formulation requirements, laser stereolithography parameter settings and thermal processing procedures for a custom ceramic slurry containing piezoelectric nanoparticles.

This article analyzes the dynamic stability of pre-warped, rotating circular disks. Simulation is used to determine asymmetric equilibria and corresponding stability maps for varying load and disk rotation. Experimental results corroborated the presence of a rotating, asymmetric equilibrium for low speeds. At higher speeds, aerodynamically excited vibration made it impossible to identify steady equilibria. However, the nature of the aerodynamic excitation and its onset were dramatically affected by the presence of uniform loading on the disk. In addition, at high rotation speeds, the disk appears to have a steady equilibrium rotation at one quarter of the rotation speed of the disk.

The process of adaptive bone remodeling can be simulated with a self-optimizing finite element method. The basic remodeling rules attempt to obtain a constant value for the strain energy per unit bone mass, by adapting density. The precise solution is dependent on the loads, initial conditions, and the parameters of the remodeling rule. While there are several investigations on developing algorithms leading to the bone density distribution in the proximal femur, these algorithms often require a large number of iterations. The aim of this study was to develop a more efficient adaptive bone remodeling algorithm, and to identify how the bone density distribution of the proximal femur was affected by parameters that govern the remodeling process. The forces at different phases of the gait cycle were applied as boundary conditions. The bone density distributions from these forces were averaged to estimate the density distribution in the proximal femur. The effect of varying the initial bone density, spatial influence function, non-linear order of the adaptive algorithm, and the influence range on the converged solution were investigated. The proposed procedure was shown to converge in a fewer number of iterations and requiring less computational time, while still generating a realistic bone density distribution. It was also shown that varying the identified parameters within reasonable upper and lower bounds had very little impact on the qualitative form of the converged solution. In contrast, the convergence rate was affected to a greater degree by variation of these parameters. In all cases, the solutions obtained are comparable with the actual density in the proximal femur, as measured by Dual-energy X-ray absorptiometry (DEXA) scans.

Functionally graded cellular structures such as bio-inspired functionally graded materials for manufacturing implants or bone replacement, are a class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. A gradual increase in cell size distribution, can impart many improved properties which may not be achieved by having a uniform cellular structure. The material properties of functionally graded cellular structures as a function of density gradient have not been previously addressed within the literature. In this study, the finite element method is used to investigate the compressive uniaxial and biaxial behavior of functionally graded Voronoi structures. Furthermore, the effect of missing cell walls on its overall mechanical (elastic, plastic, and creep) properties is investigated. The finite element analysis showed that the overall effective elastic modulus and yield strength of structures increased by increasing the density gradient. However, the overall elastic modulus of functionally graded structures was more sensitive to density gradient than the overall yield strength. The study also showed that the functionally graded structures with different density gradient had similar sensitivity to random missing cell walls. Creep analysis suggested that the structures with higher density gradient had lower steady-state creep rate compared to that of structures with lower density gradient.

Cellular solids such as foams are widely used in engineering applications. In these applications, it is important to know their mechanical properties and the variation of these properties with the presence of defects. Several models have been proposed to obtain the mechanical properties of cellular materials. However, these models are usually based on idealized unit cell structures, and are not suitable for finding the mechanical properties of cellular materials with defects. The objective of this work is to understand the effect of missing walls and filled cells on elastic–plastic behavior of both regular hexagonal and non-periodic Voronoi structures using finite element analysis. The results show that the missing walls have a significant effect on overall elastic properties of the cellular structure. For both regular hexagonal and Voronoi materials, the yield strength of the cellular structure decreases by more than 60% by introducing 10% missing walls. In contrast, the results indicate that filled cells have much less effect on the mechanical properties of both regular hexagonal and Voronoi materials. The effects of material strain hardening on the yield strength of cellular materials are also investigated.

Embedded wireless sensor networks are part of a strategy for implementing improved structural health and usage monitoring in rotorcraft. In order to realize this goal, methods of powering the embedded sensors have to be identified. One approach is to make the power supply become an integral part of the sensor. This integrated monitoring system will then be less intrusive and, therefore, easier to integrate into existing systems. Piezoelectric materials can be an important part of this strategy. One method to harness power is to use piezoelectric materials to recover energy lost due to vibration and rotation of the equipment. This recovered energy can then be used to provide energy to power sensors directly or to extend the lifespan of batteries which power the sensors. This paper investigates the potential of using strains on a rotating blade to power sensors during flight. The preliminary numerical investigation indicates that this may be a promising approach.Copyright © 2008 by ASME

Three-dimensional structure of trabecular bone can be modeled by 2D or 3D Voronoi structure. The effect of missing cell walls on the mechanical properties of 2D honeycombs is a first step towards understanding the effect of local bone resorption due to osteoporosis. In patients with osteoporosis, bone mass is lost first by thinning and then by resorption of the trabeculae [1]. Furthermore, creep response is important to analyze in cellular solids when the temperature is high relative to the melting temperature. For trabecular bone, as body temperature (38 °C) is close to the denaturation temperature of collagen (52 °C), trabecular bone creeps [1]. Over the half of the osteoporotic vertebral fractures that occur in the elderly, are the result of the creep and fatigue loading associated with the activities of daily living [2]. The objective of this work is to understand the effect of missing walls and filled cells on elastic-plastic behavior of both regular hexagonal and non-periodic Voronoi structures using finite element analysis. The results show that the missing walls have a significant effect on overall elastic properties of the cellular structure. For both regular hexagonal and Voronoi materials, the yield strength of the structure decreased by more than 60% by introducing 10% missing walls. In contrast, the results indicate that filled cells have much less effect on the mechanical properties of both regular hexagonal and Voronoi materials.

The vibration characteristics of a circumferentially cracked rotating disk are investigated. The disk is assumed to be axisymmetric, flexible and clamped at the center. The crack increases the local flexibility of the disk at the crack location and is modeled as linear and torsional springs, connecting the two segments of the disk. The spring constants are evaluated by considering crack opening displacements due to bending moment and shear force at the crack location. The equations of motion of two segments of the disk, for disk operating in vacuum as well as subjected to shear fluid flow are developed. Using the Finite Difference Technique, the coupled systems of equations are solved and the natural frequencies and mode shapes are obtained. The mode shapes are seen to be comparatively flattened in the inner region of the disk separated by the crack and heightened towards the periphery of the disk. Shear fluid loading reduces the critical speeds and results in a quicker onset of instability. The degree of instability caused by the crack is a function of crack depth and location. Critical speeds increase with increasing crack distance from the central clamp and decrease with increasing crack depth.Copyright © 2007 by ASME

The vibration characteristics of a circumferentially cracked rotating disk are investigated. The disk is assumed to be axisymmetric, flexible and clamped at the center. The crack increases the local flexibility of the disk at the crack location and is modeled as linear and torsional springs, connecting the two segments of the disk. The spring constants are evaluated by considering crack opening displacements due to bending moment and shear force at the crack location. The equations of motion of two segments of the disk, for disk operating in vacuum as well as subjected to shear fluid flow are developed. Using the Finite Difference Technique, the coupled systems of equations are solved and the natural frequencies and mode shapes are obtained. The mode shapes are seen to be comparatively flattened in the inner region of the crack and heightened towards the periphery of the disk. Shear fluid loading reduces the natural frequencies and results in a quicker onset of instability. It is observed that the effect of the crack on the vibration characteristics of the disk is mainly a function of the crack location.Copyright © 2007 by ASME

Introduction: Meniscal tears are a common occurrence in the human knee joint. Orthopaedic surgeons routinely perform surgery to remove a portion of the torn meniscus. This surgery is referred to as a partial meniscectomy. It has been shown that individuals who have decreased amount of meniscus are likely to develop knee osteoarthritis. This research presents the analysis of the stresses in the knee joint upon various amounts of partial meniscectomy. Methods: To analyse the stresses in the knee joint using finite element method an axisymmetric model was developed. Articular cartilage was considered as three layers, which were modelled as a poroelastic transversely isotropic superficial layer, a poroelastic isotropic middle and deep layers and an elastic isotropic calcified cartilage layer. Eight cases were modelled including a knee joint with an intact meniscus, 10%, 20%, 30%, 40%, 50%, 60% and 65% medial meniscotomy. Findings: Under the axial load of human weight on the femoral articular cartilage with 40% removal of meniscus high contact stresses took place on cartilage surface. Further, with 30%, 40%, 50% of meniscectomy significant amount of contact area noticed between femoral and tibial articular cartilage. After 65% of meniscectomy the maximal shear stress in the cartilage increased up to 225% compared to knee with intact meniscus. It appears that meniscectomies greater than 20% drastically increases the stresses in the knee joint. I. BACKGROUND

Recent research has demonstrated that natural frequencies associated with some circumferential modes inn fluid filled tanks may be close to the frequency of earthquake excitation. This can lead to a resonance phenomenon, and consequently failure of the tanks. In this paper, we perform natural frequency analysis of fluid-filled tanks, using finite element analysis. The problem is solved for different geometries and water levels of tanks. Results are provided for circular, cylindrical tanks and cylindrical tanks with coaxial walls and a fluid annulus. Combinations of parameters most likely to cause resonance are presented.Copyright © 2006 by ASME

In this paper, a hydrodynamically coupled flexible disk rotating in a thin housing is mathematically modeled and an attempt is made to explain the jump instability phenomenon that occurs when the disk rotation speed is varied slightly. The disk is assumed to have an initial warped profile due to slight imperfections in the manufacturing process. After non-dimensionalization of the participating variables, a hybrid formulation is carried out. Radial flows above and below the disk are taken into consideration. The deflection and pressure equations form a coupled system, and a solution is attempted using the shooting method. The deflections obtained are plotted to obtain the deflected disk profile and appropriate conclusions are drawn.Copyright © 2006 by ASME

This paper presents an efficient method for simulating the bone remodeling procedure. This method is based on the trajectorial architecture theory of optimization and employs a truss-like model for bone. The truss was subjected to external loads including 5 point loads simulating the hip joint contact forces and 3 muscular forces at the attachment sites of the muscles to the bone. The strain in the links was calculated and the links with high strains were identified. The initial truss is modified by introducing new links wherever the strain exceeds a prescribed value; each link undergoing a high strain is replaced by several new links by adding new nodes around it using the Delaunay method. Introduction of these new links to the truss, which is conducted according to a weighted arithmetic mean formula, strengthens the structure and reduces the strain within the respective zone. This procedure was repeated for several steps. Convergence was achieved when there were no critical links remaining. This method was used to study the 2D shape of proximal femur in the frontal plane and provided results that are consistent with CT data. The proposed method exhibited capability similar to more complicated conventional nonlinear algorithms, however, with a much higher convergence rate and lower computation costs.

Conventional method of measuring the mechanical properties of rotating machinery is to couple sensors on the machine through a slip ring, which is a non-trivial, expensive, lengthy and manpower intensive process. An alternative to this is to use a contactless RF slip ring which has no physical wear and hence no maintenance. But application of contactless RF slip ring is possible only if these services are low powered and sensor signals can be multiplexed. With the advance in low powered MEMS sensors, contactless slip ring system can be used. But providing power to these sensors is an issue. One approach would be to harness power from the untapped surrounding energy which could be used to recharge and/or replace battery powered connections. One method to accomplish this is to use piezoelectric materials (PZT) to capture energy lost due to vibration and rotation of the test equipment. This captured energy can then be used to provide uninterrupted power to the appropriate sensors. Focusing our attention on blades, rotating structures will be modeled as cantilever beam. Piezoelectric bimorph attached to the rotating cantilever beam will provide an estimate for the available power that can be used for harvesting.Copyright © 2006 by ASME

A system of parallel disks may be cooled by passing a fluid between these disks. Depending on the disk geometries, their distance, mechanical properties and fluid velocity, the disks may be subjected to transverse vibration which may be damped or become unstable. There are number of papers on the flow induced vibration in pipes with various boundary conditions addressing their transverse vibration characteristics. However, there is very little information on the vibration characteristics of disks with axisymmetric fluid flow in between. The equation of motion of two parallel disks with an axisymmetric flow in between is developed using Hamiltonian principle. In the initial phase of this study, it was assumed that two plates move in the same direction, thus maintaining their initial gap. The governing equations are non-dimensionalized and the effects of plates moment of inertia, density, geometry and fluid velocity on the dynamic response of the plates are obtained.Copyright © 2005 by ASME

Traditionally, the cantilever modal shape of liquid-filled tanks has been considered as the most critical mode. However, recent research has demonstrated that natural frequencies associated with some circumferential modes might be close to the frequency of earthquake excitation. This can lead to a resonance phenomenon, and consequently failure of the tanks. In this paper, we perform Natural Frequency Analysis of fluid-filled tanks, using finite element analysis. Modeling and solution employ ADINA potential-based flow elements, which require the assumption of inviscid, irrotational and incompressible flow. The problem is solved for different geometries and water levels of tanks; the results are compared with the current results in the literature and the difference is demonstrated.Copyright © 2005 by ASME

Thickness profiles for rotating disks that maximize critical speed are determined for use by designers of industrial circular saws. The disk thickness is permitted to vary between fixed lower and upper bounds, the lower bound corresponding to the minimum thickness saw capable of supporting the in-plane stresses associated with cutting forces and rotation, the upper bound corresponding to the thickness of the saw teeth. The optimal thickness profile consists of two annuli, the inner one with thickness equal to the upper bound, the outer one with thickness equal to the lower bound. With the optimal thickness profile, the critical speed can be raised up to 24%, depending on the clamping ratio of the disk and the lower bound. Optimal thickness profiles and increases in critical speeds are described and compared to existing saw designs.