Fabrication and Strength-Based Design of a Meso Forceps

2009 ◽  
Author(s):  
M. E. Aguirre ◽  
G. Hayes ◽  
C. Yuangyai ◽  
M. Frecker ◽  
J. Adair ◽  
...  
Keyword(s):  
Ultimate Strength ◽  
Research Effort ◽  
Optimization Method ◽  
Surgical Instruments ◽  
Full Density ◽  
Stress Constraint ◽  
Material Strength ◽  
Aspect Ratios ◽  
Length Width ◽  
Dimensional Parameters

A novel fabrication process and design optimization method for a mesoscale forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments using an iterative fabrication-design technique. The current paper focuses on the fabrication of thick (∼hundreds of microns) two dimensional parts with large aspect ratios (length/width > 20). The paper also describes an optimization method that accounts for manufacturing requirements and material strength. The process begins with the fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol bath. Finally, the photoresist molds are removed via pyrolysis, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with large aspect ratios, sharp edges (∼ 1 μm), and a resolution of 2 μm. An optimization algorithm, using ANSYS optimization module, is formulated to determine the effect of dimensional parameters and material strength on the optimal design and predicted performance of the compliant meso forceps. Three ultimate strength values are separately implemented as a stress constraint in our optimization problem. Results conclude that our manufacturing process is capable of producing meso scale forceps considering the anticipated ultimate strength at this scale.

Fabrication and Design of a Nanoparticulate Enabled Micro Forceps

2008 ◽  
Author(s):  
M. E. Aguirre ◽  
G. Hayes ◽  
M. Frecker ◽  
J. Adair ◽  
N. Antolino
Keyword(s):  
Optimization Problems ◽  
Compliant Mechanism ◽  
Research Effort ◽  
Optimization Method ◽  
Fabrication Process ◽  
Surgical Instruments ◽  
Full Density ◽  
Material Strength ◽  
Aspect Ratios ◽  
Dimensional Parameters

A novel fabrication process and design optimization method for a micro forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments. The micro forceps is a monolithic compliant mechanism that due to its two-dimensional design can be manufactured using the new fabrication process. The process begins with fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol wipe. Finally, the photoresist molds are removed with a reactive ion etch (RIE) step, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with a large aspect ratio (≥40:1), sharp edges (∼ 1 μm), and a resolution of 2 μm. Two optimization problems are formulated to determine the effect of dimensional parameters and material strength on the performance of the compliant micro forceps. First, performance is sensitive to small changes in the geometry, indicating that dimensions and shrinkage rates must be carefully controlled during processing. Second, performance can also be improved by using very large aspect ratios and/or improvements in material strength. A sample part manufactured using the new process is presented.

Failure Strain Criterion Accounting for the Effect of Material Strength

2021 ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Failure Criterion ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength Steels ◽  
Local Failure ◽  
Material Strength ◽  
Lode Parameter ◽  
Steel Grades

Abstract The objective of this study is to investigate the effect of the Lode parameter on different material strengths. Recent work has shown that ductile failure highly depends on the stress state characterized by both the stress triaxiality T and the Lode parameter L, which is related to the third deviatoric stress invariant. Thus, for six different steel grades, two different specimen geometries were manufactured to account for two different Lode parameters (L = −1 and L = 0), whereas T is controlled by introducing different sized notches at the center of the specimens. By performing tensile experiments and running finite element simulations, the ductile failure loci of the six materials showed variations between the two specimen geometries, indicating that the failure highly depends on the stress state characterized by both T and L. This indicates the need to reassess the ductile local failure criterion in the ASME codes that only accounts for T as a stress state measure. A Lode sensitivity parameter LS is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels.

Topology Optimization of Compliant Mechanisms Using Hybrid Discretization Model

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Hong Zhou
Keyword(s):  
Topology Optimization ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Diagonal Element ◽  
Initial Guess ◽  
Stress Constraint ◽  
Design Variables ◽  
Hybrid Discretization

The hybrid discretization model for topology optimization of compliant mechanisms is introduced in this paper. The design domain is discretized into quadrilateral design cells. Each design cell is further subdivided into triangular analysis cells. This hybrid discretization model allows any two contiguous design cells to be connected by four triangular analysis cells whether they are in the horizontal, vertical, or diagonal direction. Topological anomalies such as checkerboard patterns, diagonal element chains, and de facto hinges are completely eliminated. In the proposed topology optimization method, design variables are all binary, and every analysis cell is either solid or void to prevent the gray cell problem that is usually caused by intermediate material states. Stress constraint is directly imposed on each analysis cell to make the synthesized compliant mechanism safe. Genetic algorithm is used to search the optimum and to avoid the need to choose the initial guess solution and conduct sensitivity analysis. The obtained topology solutions have no point connection, unsmooth boundary, and zigzag member. No post-processing is needed for topology uncertainty caused by point connection or a gray cell. The introduced hybrid discretization model and the proposed topology optimization procedure are illustrated by two classical synthesis examples of compliant mechanisms.

High-Aspect-Ratio Electroplated Structures With 2μm Beamwidth

1999 ◽  
Author(s):  
Xiaobin Li ◽  
Siddharth Kiyawat ◽  
Hector J. De Los Santos ◽  
Chang-Jin “CJ” Kim
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Stress Gradient ◽  
Optimization Method ◽  
Nickel Layer ◽  
Driving Voltage ◽  
Aspect Ratios ◽  
Nickel Electroplating ◽  
Electroplating Process ◽  
Micro Structures

Abstract Narrow beamwidth is highly desirable for many micromechanical elements moving parallel to the substrate. A good example is the electrostatically driven flexure structure, whose driving voltage is determined by the width of the beam. This paper presents the process flow and the result of a high-aspect-ratio electroplating process using photoresist (PR) molds. Following a systematic optimization method, PR molds with aspect ratios up to 4.0 were fabricated with a beamwidth of only 2.1μm. Higher aspect ratios, up to 6.8, were achieved using PR double coating technique, with a beamwidth of 2.6μm. Using a Cr/Cu seed layer, nickel electroplating was successfully carried out to translate the PR molds into nickel micro-structures. We observed bend-down of the fully released nickel cantilevers that are over 8μm thick. Further investigation suggested a combined effect of residual stress gradient in the electroplated nickel layer and in-use stiction of the cantilever beams.

Strength of Minimum Structure Platforms Under Ship Impact

2004 ◽  
Vol 126 (4) ◽  
pp. 368-375 ◽  
Author(s):  
Gage S. Grewal ◽  
Marcus M. K. Lee
Keyword(s):  
Numerical Investigation ◽  
Ultimate Strength ◽  
Energy Absorption ◽  
Structural Integrity ◽  
Research Effort ◽  
Design Guidelines ◽  
Design Issues ◽  
Plastic Energy ◽  
Ship Collision ◽  
Important Design

This paper presents the findings of a numerical investigation into the strength of minimum structure platforms subject to a ship impact. The study has identified important design issues that should be addressed in order to improve the survivability and continued serviceability of minimum structures after a ship impact. It was found that, due to a lack of research effort, design guidelines governing ship impact on minimum structures are lacking in comparison with conventional jacket platforms. In particular, requirements governing the minimum amount of plastic energy absorption in minimum structures are not clearly defined. Ship impact analyses were therefore carried out in order to compare their structural integrity with that for a jacket under ship collision conditions and to evaluate the effects on their ultimate strength. The study not only established any degradation of system strength, but has also determined the amount of plastic energy absorption under various impact scenarios.

Stability and resonant wave interactions of confined two-layer Rayleigh–Bénard systems

2014 ◽  
Vol 754 ◽  
pp. 415-455 ◽  
Author(s):  
S. V. Diwakar ◽  
Shaligram Tiwari ◽  
Sarit K. Das ◽  
T. Sundararajan
Keyword(s):  
Travelling Waves ◽  
Current Work ◽  
Wave Interactions ◽  
Resonant Wave ◽  
Aspect Ratios ◽  
Fluid Systems ◽  
Dimensional Parameters ◽  
The Individual ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

AbstractThe current work analyses the onset characteristics of Rayleigh–Bénard convection in confined two-dimensional two-layer systems. Owing to the interfacial interactions and the possibilities of convection onset in the individual layers, the two-layer systems typically exhibit diverse excitation modes. While the attributes of these modes range from the non-oscillatory mechanical/thermal couplings to the oscillatory standing/travelling waves, their regimes of occurrence are determined by the numerous system parameters and property ratios. In this regard, the current work aims at characterising their respective influence via methodical linear and fully nonlinear analyses, carried out on fluid systems that have been selected using the concept of balanced contrasts. Consequently, the occurrence of oscillatory modes is found to be associated with certain favourable fluid combinations and interfacial heights. The further branching of oscillatory modes into standing and travelling waves seems to additionally rely on the aspect ratio of the confined cavity. Specifically, the modulated travelling waves have been observed to occur (amidst standing wave modes) at discrete aspect ratios for which the onset of oscillatory convection happens at unequal fluid heights. This behaviour corresponds to the typical $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}m$:$n$ resonance where the critical wavenumbers of convection onset in the layers are dissimilar. Based on all of these observations, an attempt has been made in the present work to identify the oscillatory excitation modes with a reduced number of non-dimensional parameters.

scholarly journals Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1528
Author(s):  
Wenlong Li ◽  
Zhihui Xie ◽  
Kun Xi ◽  
Shaojun Xia ◽  
Yanlin Ge
Keyword(s):  
Heat Flux ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Width Ratio ◽  
Microchannel Heat Sink ◽  
Rectangular Microchannel ◽  
Entropy Generation Minimization ◽  
Aspect Ratios ◽  
Length Width

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.

Nonlinear Dynamic Analysis of Micro Cantilever Beam Under Electrostatic Loading

2012 ◽  
Vol 28 (1) ◽  
pp. 63-70 ◽  
Author(s):  
C.-C. Liu ◽  
S.-C. Yang ◽  
C.-K. Chen
Keyword(s):  
Cantilever Beam ◽  
Nonlinear Dynamic Analysis ◽  
Nonlinear Behavior ◽  
Computationally Efficient ◽  
Hybrid Scheme ◽  
Electrostatically Actuated ◽  
Aspect Ratios ◽  
Beam System ◽  
Length Width ◽  
Micro Cantilever

ABSTRACTA hybrid differential transformation / finite difference scheme is used to analyze the complex nonlinear behavior of an electrostatically-actuated micro cantilever beam which high aspect ratios (length/width). The validity of the proposed method is confirmed by comparing the numerical results obtained for the tip displacement and pull-in voltage of the cantilever beam with the analytical and experimental results presented in the literature. The hybrid scheme is then applied to analyze both the steady-state and the dynamic deflection behavior of the cantilever beam as a function of the applied voltage. Overall, the results confirm that the hybrid method provides an accurate and computationally-efficient means of analyzing the complex nonlinear behavior of both the current micro cantilever beam system and other micro-scale electrostatically-actuated structures.

Supersonic jet control with shifted tabs

2016 ◽  
Vol 232 (3) ◽  
pp. 433-447 ◽  
Author(s):  
K Maruthupandiyan ◽  
E Rathakrishnan
Keyword(s):  
Pressure Gradient ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Pressure Oscillation ◽  
Adverse Pressure Gradient ◽  
Mixing Enhancement ◽  
Aspect Ratios ◽  
Core Length ◽  
Expansion Level ◽  
Length Width

Mixing characteristics of a Mach 2 jet controlled by shifted tabs have been studied at different levels of expansion at the nozzle exit. Two identical rectangular flat tabs of aspect ratios (length/width) 3, 4, 5 and 6, offering 2.5% blockage each, located diametrically opposite, found that the mixing promotion caused by the shifted tab increases with increase of adverse pressure gradient (that is, below NPR 5). On the contrary, the mixing enhancement caused by tab placed at the nozzle exit decreases with increase of adverse pressure gradient. At higher NPRs from 5 to 8 for shifted tab configuration, the amplitude of centerline pitot pressure oscillation is considerably smaller than the uncontrolled jet. At lower NPRs, corresponding to expansion level pe /pa, from 0.383 to 0.511, shifted tab is found to be a better mixing promoter than the tab at the nozzle exit. But for expansion levels from 0.511 to 1.022, mixing promoted by tab at nozzle exit is better than the shifted tabs. Shifted tab at 0.5D results in about 55% reduction in core length, at NPR 3, and the corresponding core length reduction by tabs at 0.25D, 0.5D, and 0D is 25.93%, 22.2%, and 14.81%, respectively.

Autonomous propulsion of nanorods trapped in an acoustic field

2017 ◽  
Vol 825 ◽  
pp. 29-48 ◽  
Author(s):  
Jesse F. Collis ◽  
Debadi Chakraborty ◽  
John E. Sader
Keyword(s):  
Density Distribution ◽  
Stokes Equations ◽  
A Priori ◽  
Model Systems ◽  
Small Scale ◽  
Mathematical Framework ◽  
Dimensionless Frequency ◽  
Physical Mechanisms ◽  
Aspect Ratios ◽  
Length Width

Acoustic fields in a liquid medium can trap and suspend small particles at their pressure nodes. Recent measurements demonstrate that nanorods immersed in these fields generate autonomous propulsion, with their direction and speed controlled by both the particle’s shape and density distribution. Specifically, slender nanorods with an asymmetric density distribution about their geometric centre are observed to move steadily with their low density end leading the motion; particle geometry exerts an equally significant and potentially opposing effect. In this article, we investigate the physical mechanisms underlying this combined density/shape induced phenomenon by developing a simple yet rigorous mathematical framework for axisymmetric particles. This only requires solution of the (linear) unsteady Stokes equations, which can be performed numerically or analytically. The theory holds for all particle shapes, particle aspect ratios (length/width) and acoustic frequencies. It is applied to slender dumbbell-shaped particles and asymmetric nanorods – these provide model systems to investigate the competing effects governing propulsion. This shows that geometric and density asymmetries in the particle generate axial jets that can produce motion in either direction, depending on the relative strengths of these asymmetries and the acoustic Reynolds number (dimensionless frequency). Strikingly, the propulsion direction is found to reverse with increasing frequency, an effect that is yet to be reported experimentally. The general theory and mechanism described here enable the a priori design and fabrication of nano-motors in fluid for transport of small-scale payloads and robotic applications.

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