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High-Resolution, Real-Time Three-Dimensional Shape Measurement, Song Zhang, Peisen S. Huang
High-Resolution, Real-Time Three-Dimensional Shape Measurement, Song Zhang, Peisen S. Huang
Song Zhang
We describe a high-resolution, real-time 3-D shape measurement system based on a digital fringe projection and phase-shifting technique. It utilizes a single-chip digital light processing projector to project computer-generated fringe patterns onto the object, and a high-speed CCD camera synchronized with the projector to acquire the fringe images at a frame rate of 120frames∕s. A color CCD camera is also used to capture images for texture mapping. Based on a three-step phase-shifting technique, each frame of the 3-D shape is reconstructed using three consecutive fringe images. Therefore the 3-D data acquisition speed of the system is 40frames∕s. With this system, …
Modeling Of The Size Effects On The Behavior Of Metals In Microscale Deformation Processes, Gap-Yong Kim, Jun Ni, Muammer Koc
Modeling Of The Size Effects On The Behavior Of Metals In Microscale Deformation Processes, Gap-Yong Kim, Jun Ni, Muammer Koc
Gap-Yong Kim
For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/mesoscale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the feature/specimen size effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with three separate experiments obtained from previous research: a simple compression with a round specimen, a simple tension with a round specimen, and a simple tension in …
Modeling Of The Semi-Solid Material Behavior And Analysis Of Micro-/Mesoscale Feature Forming, Gap-Yong Kim, Muammer Koc, Rhet Mayor, Jun Ni
Modeling Of The Semi-Solid Material Behavior And Analysis Of Micro-/Mesoscale Feature Forming, Gap-Yong Kim, Muammer Koc, Rhet Mayor, Jun Ni
Gap-Yong Kim
One of the major challenges in simulation of semi-solid forming is characterizing the complex behavior of a material that consists of both solid and liquid phases. In this study, a material model for an A356 alloy in a semi-solid state has been developed for high solid fractions (>0.6) and implemented into a finite element simulation tool to investigate the micro-/mesoscale feature formation during the forming process. Compared to previous stress models, which are limited to expressing the stress dependency on only the strain rate and the temperature (or the solid fraction), the proposed stress model adds the capability of …
An Experimental Investigation On Semi-Solid Forming Of Micro/Meso-Scale Features, Gap-Yong Kim, Jun Ni, Rhett Mayor, Heesool Kim
An Experimental Investigation On Semi-Solid Forming Of Micro/Meso-Scale Features, Gap-Yong Kim, Jun Ni, Rhett Mayor, Heesool Kim
Gap-Yong Kim
The potentials of semi-solid forming technology have generated much interest regarding its application in micromanufacturing. This study investigates the feasibility of using semi-solid forming technology to produce parts with micro/meso features. An experimental setup has been developed to study the effects of die/punch temperature, initial solid fraction, punch speed, and workpiece shape on the semi-solid forming process. A part has been produced for a microreactor application and has been analyzed with an optical measurement system for feature formation. The results indicated complex interaction among the process parameters and the material flow, which affected the final pin formation. The punch temperature …
Phase Field Theory Of Surface- And Size-Induced Microstructures, Valery I. Levitas, D.W. Lee, D. L. Preston
Phase Field Theory Of Surface- And Size-Induced Microstructures, Valery I. Levitas, D.W. Lee, D. L. Preston
Valery I. Levitas
New surface- and size-induced microstructures are found as analytic solutions to a phase field theory of first-order phase transformations. A recently developed exact stability criterion, based on most destabilizing fluctuations, is used to analyze the stability and physical interpretation of each microstructure. Conditions for barrierless surface nucleation, i.e. relationship between surface energy, driving force for the transformation and sample size, are found. If they are met, some of these microstructures are destroyed resulting in the barrierless transformation to alternative phases.
Novel Method For Structured Light System Calibration, Song Zhang, Peisen S. Huang
Novel Method For Structured Light System Calibration, Song Zhang, Peisen S. Huang
Song Zhang
System calibration, which usually involves complicated and time-consuming procedures, is crucial for any 3-D shape measurement system. In this work, a novel systematic method is proposed for accurate and quick calibration of a 3-D shape measurement system we developed based on a structured light technique. The key concept is to enable the projector to “capture” images like a camera, thus making the calibration of a projector the same as that of a camera. With this new concept, the calibration of structured light systems becomes essentially the same as the calibration of traditional stereovision systems, which is well established. The calibration …
Generic Nonsinusoidal Phase Error Correction For 3d Shape Measurement Using A Digital Video Projector, Song Zhang, Shing-Tung Yau
Generic Nonsinusoidal Phase Error Correction For 3d Shape Measurement Using A Digital Video Projector, Song Zhang, Shing-Tung Yau
Song Zhang
Structured light system using a digital video projector is increasingly used for a 3-D shape measurement because of its digital nature. However, the nonlinear gamma of the projector causes the projected fringe patterns to be non-sinusoidal, which results in phase error therefore shape measurement error. Previous work showed that, by using a small look-up-table (LUT), this type of phase error can be reduced significantly for a three-step phase-shifting algorithm. In this research, we prove that this type of phase error compensation method is not limited to a three-step phase-shifting algorithm. It is generic for any phase-shifting algorithm. The phase error …
High-Resolution Real-Time 3d Absolute Coordinates Measurement Using A Fast Three-Step Phase-Shifting Algorithm, Song Zhang, Dale Royer, Shing-Tung Yau
High-Resolution Real-Time 3d Absolute Coordinates Measurement Using A Fast Three-Step Phase-Shifting Algorithm, Song Zhang, Dale Royer, Shing-Tung Yau
Song Zhang
High-resolution, real-time 3-D absolute coordinate measurement is highly important in many fields. This paper presents such a system that measures 3-D absolute geometric shapes and positions at 30 frames per second (fps), with an image resolution of 532 × 500. The system is based on a digital fringe projection and fast three-step phase-shifting method. It utilizes a digital-light-processing (DLP) projector to project color encoded computer generated phase-shifted fringe patterns in grayscale, a high-speed CCD camera synchronized with the projector to capture fringe images at 90 fps. Based on the three-step phase-shifting algorithm, any successive three fringe images can be used …
Ginzburg-Landau Theory Of Microstructures: Stability, Transient Dynamics, And Functionally Graded Nanophases, Valery I. Levitas, D. L. Preston, Dong Wook Lee
Ginzburg-Landau Theory Of Microstructures: Stability, Transient Dynamics, And Functionally Graded Nanophases, Valery I. Levitas, D. L. Preston, Dong Wook Lee
Valery I. Levitas
The stability, transient dynamics, and physical interpretation of microstructures obtained from a Ginzburg-Landau theory of first-order phase transformations are studied. The Jacobi condition for stability fails numerically, thus an alternative exact stability criterion, based on critical (most destabilizing) fluctuations, is developed. The degree-of-stability parameter is introduced to quantify the physical stability of long-lived unstable microstructures. For nanofilms, the existence of functionally graded nanophases is demonstrated. Numerical simulations indicate that graded nanophases can be produced by dissolving material from both surfaces of a nanofilm. Stability under finite fluctuations and post-bifurcation microstructure evolution are investigated numerically.
Corrugation And Buckling Defects In Wound Rolls, Jonathan A. Wickert, P.M. Lin
Corrugation And Buckling Defects In Wound Rolls, Jonathan A. Wickert, P.M. Lin
Jonathan A. Wickert
Sheet metal, paper, and polymer webs are often stored and processed as large rolls comprising thousands of layers. Depending on the elastic properties of the web material, the roll's dimensions, the type of core, and the winding tension, the stresses that develop within the roll can be sufficiently high to cause local or gross buckling defects to form. For instance, the cylindrical core onto which the web is wound can collapse, a failure mode that is termed "v-buckling." In other cases, while the core might remain intact, a group of layers interior to the roll can wrinkle into a near-sinusoidal …
Trapezoidal Phase-Shifting Method For Three-Dimensional Shape Measurement, Peisen S. Huang, Song Zhang, Fu-Pen Chiang
Trapezoidal Phase-Shifting Method For Three-Dimensional Shape Measurement, Peisen S. Huang, Song Zhang, Fu-Pen Chiang
Song Zhang
We propose a novel structured light method, namely a trapezoidal phase-shifting method, for 3-D shape measurement. This method uses three patterns coded with phase-shifted, trapezoidal-shaped gray levels. The 3-D information of the object is extracted by direct calculation of an intensity ratio. Compared to traditional intensity-ratio-based methods, the vertical or depth resolution is six times better. Also, this new method is significantly less sensitive to the defocusing effect of the captured images, which makes large-depth 3-D shape measurement possible. If compared to sinusoidal phase-shifting methods, the resolution is similar, but the data processing speed is at least 4.5 times faster. …
Fast Three-Step Phase-Shifting Algorithm, Song Zhang, Peisen S. Huang
Fast Three-Step Phase-Shifting Algorithm, Song Zhang, Peisen S. Huang
Song Zhang
We propose a new three-step phase-shifting algorithm, which is much faster than the traditional three-step algorithm. We achieve the speed advantage by using a simple intensity ratio function to replace the arctangent function in the traditional algorithm. The phase error caused by this new algorithm is compensated for by use of a lookup table. Our experimental results show that both the new algorithm and the traditional algorithm generate similar results, but the new algorithm is 3.4 times faster. By implementing this new algorithm in a high-resolution, real-time three-dimensional shape measurement system, we were able to achieve a measurement speed of …
High-Resolution, Real-Time 3d Absolute Coordinate Measurement Based On A Phase-Shifting Method, Song Zhang, Shing-Tung Yau
High-Resolution, Real-Time 3d Absolute Coordinate Measurement Based On A Phase-Shifting Method, Song Zhang, Shing-Tung Yau
Song Zhang
We describe a high-resolution, real-time 3D absolute coordinate measurement system based on a phase-shifting method. It acquires 3D shape at 30 frames per second (fps), with 266K points per frame. A tiny marker is encoded in the projected fringe pattern, and detected by software from the texture image and the gamma map. Absolute 3D coordinates are obtained from the detected marker position and the calibrated system parameters. To demonstrate the performance of the system, we measure a hand moving over a depth distance of approximately 700 mm, and human faces with expressions. Applications of such a system include manufacturing, inspection, …
Kinetics Of Strain-Induced Structural Changes Under High Pressure, Valery I. Levitas, Oleg M. Zarechnyy
Kinetics Of Strain-Induced Structural Changes Under High Pressure, Valery I. Levitas, Oleg M. Zarechnyy
Valery I. Levitas
A mechanism-based microscale kinetic theory for strain-induced structural changes (SCs) (that includes phase transformations (PTs) and chemical reactions (CRs)) is developed. Time is not an independent parameter in this theory; instead, plastic strain is a time-like parameter. Kinetics depends essentially on the ratio of the yield strengths of phases. Stationary and nonstationary solutions of the kinetic equations are analyzed for various cases, including SCs between two phases in an inert matrix and between three phases in silicon and germanium. A number of experimental phenomena are explained, and material parameters controlling the kinetics of strain-induced SCs are determined. This includes the …
Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven
Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven
Valery I. Levitas
Plastic shear significantly reduces the phase transformation (PT) pressure when compared to hydrostatic conditions. Here, a paradoxical result was obtained: PT of graphitelike hexagonal boron nitride (hBN) to superhard wurtzitic boron nitride under pressure and shear started at about the same pressure(∼10GPa) as under hydrostatic conditions. In situ x-ray diffraction measurement and modeling of the turbostratic stacking fault concentration (degree of disorder) and PT in hBN were performed. Under hydrostaticpressure, changes in the disorder were negligible. Under a complex compression and shear loading program, a strain-induced disorder was observed and quantitatively characterized. It is found that the strain-induced disorder suppresses …
Nucleation Mechanism For Reconstructive Solid-Solid Phase Transitions Via Melt Mediated Nanocluster Transformation, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Nucleation Mechanism For Reconstructive Solid-Solid Phase Transitions Via Melt Mediated Nanocluster Transformation, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
A general nucleation mechanism is proposed and justified thermodynamically and kinetically. The authors apply it to the β-δphase transformation (PT) in the HMX crystal. It explains the observation of a reconstructive PT very close (0.6K) to the phase equilibrium temperature, despite the large volume change and interface energy. Nanosize clusters of β phase dissolve in a liquid and transform into δ phase clusters. The liquid completely removes the elasticenergy generated by a large volume change. Cluster to cluster PT also drastically reduces the change in interfacial energy. Suggested kinetics for the β-δ PT is in good agreement with experiments..
Gpu-Assisted High-Resolution, Real-Time 3-D Shape Measurement, Song Zhang, Dale Royer, Shing-Tung Yau
Gpu-Assisted High-Resolution, Real-Time 3-D Shape Measurement, Song Zhang, Dale Royer, Shing-Tung Yau
Song Zhang
This paper describes a Graphics Processing Unit (GPU)-assisted real-time three-dimensional shape measurement system. Our experiments demonstrated that the absolute coordinates calculation and rendering speed of a GPU is more than four times faster than that of a dual CPU workstation with the same graphics card. By implementing the GPU into our system, we realized simultaneous absolute coordinate acquisition, reconstruction and display at 30 frames per second with a resolution of approximately 266K points per frame. Moreover, a 2+1 phase-shifting algorithm was employed to alleviate the measurement error caused by motion. Applications of the system include medical imaging, manufacturing, entertainment, and …
Interfacial And Volumetric Kinetics Of The Β→Δ Phase Transition In The Energetic Nitramine Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine Based On The Virtual Melting Mechanism, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Interfacial And Volumetric Kinetics Of The Β→Δ Phase Transition In The Energetic Nitramine Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine Based On The Virtual Melting Mechanism, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
In the recent papers, 1,2 we presented a thermodynamic and kinetic model of the β→δ phase transformation (PT) in the organic energetic crystal octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). It was based on the hypothesis that the kinetics of the β→δ PT is governed by the thermodynamics of melting of the δ phase. In particular, the activation energy for growth was found to be equal to the heat of fusion Δhδ→m . Nucleation was modeled empirically by the reversible first-order kinetics. The proposed kinetics described the experimental data quite well, however, a number of questions still remain.
Melt Dispersion Mechanism For Fast Reaction Of Nanothermites, Valery I. Levitas, Blaine W. Asay, Steven F. Son, Michelle Pantoya
Melt Dispersion Mechanism For Fast Reaction Of Nanothermites, Valery I. Levitas, Blaine W. Asay, Steven F. Son, Michelle Pantoya
Valery I. Levitas
An unexpected mechanism for fast oxidation of Alnanoparticles covered by a thin oxide shell (OS) is proposed. The volume change due to melting of Al induces pressures of 0.1–4GPa and causes spallation of the OS. A subsequent unloading wave creates high tensile pressures resulting in dispersion of liquid Al clusters, oxidation of which is not limited by diffusion (in contrast to traditional mechanisms). Physical parameters controlling this process are determined. Methods to promote this melt dispersion mechanism, and consequently, improve efficiency of energetic nanothermites are discussed.
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting, Significantly Below The Melting Temperature. Application To Hmx Energetic Crystal, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, Blaine W. Asay
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting, Significantly Below The Melting Temperature. Application To Hmx Energetic Crystal, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, Blaine W. Asay
Valery I. Levitas
We theoretically predict a new phenomenon, namely, that a solid−solid phase transformation (PT) with a large transformation strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100 K) below the melting temperature. We show that the energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, stresses relax and the unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking which does not affect the thermodynamics or kinetics of the solid−solid transformation. Thus, virtual melting represents a new …