bluuebunny/crossref_metadata_2025 huggingface dataset:
3-D Variational Analysis of Bonded Composite Plates
Authors: Bogdanovich Alexander , Rastogi Naveen
Published: July 2023

Analysis and design of strong and durable joints of composite structural parts is recognized as primarily important problem. Most common analytical techniques for bonded, bolted, riveted and other typical joints are based on 2-D shell/plate theories which allow one to obtain reasonable results only in the zones away from the sites of high stress/strain gradients. Accordingly, these theories may provide not only quantitatively inaccurate, but even qualitatively wrong results in the zones of sharp stress/strain variation, even in the case of relatively thin adherends. High shear and peel stress concentration (possibly, even singularity) may occur along these lines causing delaminations, subsequent loss of hermeticity and destruction of the joint. Analysis of this problem shows that complete and accurate solution can be only obtained in 3-D elasticity formulation. A general methodology and some preliminary results of solving 3-D problems of bonded plates are presented in this paper. Numerical results reveal high concentration of the in-plane normal stress and transverse normal and shear stresses along the edge lines of the joint.
On the Instability of Ductile Crack Growth
Authors: Kolednik O.
Published: July 2023

The T-theory which is used to assess the possibility of unstable crack growth is critically reviewed. It is found that the theory contains several shortcomings originating from an unsound interpretation of the physical meaning of the (experimental) J-integral for elastic-plastic materials. Unstable crack growth may occur in spite of the fact that the T-theory predicts stability. This is demonstrated by theoretical considerations and by numerical analyses. A physically more reasonable assessment of the onset of unstable crack growth is presented.
A Further Study on the Near Tip Integral Parameter Tε* in Stable Crack Propagation in Thin Ductile Plate
Authors: Okada Hiroshi , Atluri Satya N.
Published: July 2023

In this paper, some basic properties of the near tip integral parameter Tε* (Atluri, Nishioka and Nakagaki (1984)) are presented, for the case of stable crack propagation in thin ductile metal. The authors had carried out an investigation on the physical significances of the Tε* integral for two kinds of integral contour geometries. Brust et al. (1986) used an integral contour geometry, which extends its frontal portion as the crack extends its length. In this paper, such an integral contour is called as “Elongating Contour”. Also, it should be noted that a small contour which surrounds the propagating crack tip and moves along with the tip as the crack propagates, was originally thought (Atluri, Nishioka and Nakagaki (1984)). This one is called as “Moving Contour” in this paper.

Discussions are presented based on simple energy balance statements. It has been found that, the Tε* integral parameters, using the “Elongating” and “Moving” integral contours, measure different physical quantities. The first one measures the energy dissipation inside the small integral contour path Γε, which is some finite value, and the energy release rate at the crack tip. However, the other one with the “Moving Contour” measures the energy release rate the crack tip. This one is nearly zero or very small. As conclusion to this research, the use of “Elongating Contour” is recommended in the case of stable crack propagation in thin ductile plate. Furthermore, the results presented in this paper are generic ones (do not depend on the type of materials). The results presented in this paper, can be applied to fracture problems with any other materials.
T*ε Integral Analysis of Aluminum Specimens
Authors: Omori Yoshika , Kobayashi Albert S. , Okada Hiroshi , Atluri Satya N. , Tan Paul
Published: July 2023

T*ε-integral values associated with stable crack growth in thin 2024-T3 aluminum single edge notched (SEN), central notched (CN) and compact (CT) specimens were evaluated experimentally and numerically along a near-crack contour, Γε, which elongated with crack extension. The surface displacement fields, which were determined by Moiré interferometry and by an elastic-plastic finite element (FE) simulation of the measured stable crack growth, were used to determine the T*ε through an equivalent domain integral method. The experimentally and numerically determined T*ε’s, as well as the crack tip opening displacements (CTOA), were in excellent agreement through a stable crack growth in excess of Δa = 4 mm. T*ε for the SEN and CN specimens coincided while T*ε for the CT specimen was lower. These results, which are similar in trend with the fracture toughness measurements, suggest that T*ε for a given Γε, could be a material property which characterizes stable crack growth.
Small Cracks and High-Cycle Fatigue
Authors: Ritchie R. O.
Published: July 2023

The problem of high-cycle fatigue (HCF) failures that has recently plagued the aircraft jet-engine industry is associated with the rapid growth of small defects under the action of high-frequency vibrational or resonant loading; such defects have been associated with regions of microstructural damage attributed to such processes as foreign object damage, surface fretting and low-cycle fatigue. Since the size of these defects is generally below characteristic inspection limits, traditional design and life-prediction procedures do not specifically address this problem. Moreover, from a fracture-mechanics perspective, small fatigue cracks, of dimensions less than ∼500 μm, often behave in an apparently anomalous fashion, compared to conventional results on through-thickness large cracks, of dimensions greater than ∼5 mm (e.g., in compact-tension specimens). Such “anomalous” small-crack behavior is not limited to metallic alloys but is also seen in ceramics and intermetallics. It is the intent of this paper to briefly review what a small crack is and how its behavior may differ from that of long cracks. Indeed, there are several definitions of small cracks which relate to their size in comparison to the dimensions of the microstructure, the local inelastic zones (e.g., plastic-zone size) ahead of the crack tip, and the zone of crack-tip shielding (e.g., from crack closure) behind the tip. The relevance of this to the HCF problem and more broadly to fatigue life prediction in general will also be discussed.
Force-Deflection Behavior of Individual Unimorph Piezoceramic C-Block Actuators
Authors: Moskalik Andrew J. , Brei Diann
Published: July 2023

Most piezoelectric actuators used in smart structure applications are either stiff stacks which produce high forces and small deflections, or compliant benders which produce large deflections and small forces. This leaves a mid-range gap in actuator performance in which many applications operate. A new class of solid state piezoceramic actuators, known as C-blocks, has been developed as a mid-range actuator. A C-block is a semicircular composite bender. It can be combined in series and/or parallel to increase actuator deflection and/or force. A simple analytical model for the steady-state force-deflection behavior of an individual unimorph piezoceramic C-block was derived and experimentally verified with two case studies. The results demonstrate that the stiffness of an individual C-block is six times more than that of a comparable straight bender.
Nonlinear Analysis of Piezothermoelastic Laminated Composite Beams
Authors: Bao Y. , Tzou H. S.
Published: July 2023

Conventional analyses of piezoelectric laminated structures are based on the linear theories. Investigations of nonlinear characteristics are still relatively scarce in recent years. In this paper, static, dynamic, and control effects of a piezothermoelastic laminated beam with an initial nonlinear large static deflection (the von Karman type geometric nonlinear deformation) and temperature and electric inputs are studied. It is assumed that the piezoelectric layers are uniformly distributed on the top and bottom surfaces of the beam. Beam equations incorporating the nonlinear deflections, piezoelectric layers, temperature and electric effects are simplified from the generic piezothermoelastic shell equations. Analytical solutions of nonlinear static deflection and eigenvalue problems of the nonlinearly deformed beam including temperature and electric effects are derived. Active control effects on nonlinear static deflections and natural frequencies imposed by the piezoelectric actuators via high control voltages are investigated. A numerical example is provided and response behavior discussed.
A Theoretical Modeling of Wave Localization due to Material Damping: Results
Authors: Esteban Jaime , Lalande Frederic , Rogers Craig A.
Published: July 2023

In the first part of this paper (Esteban, et al., 1996a), a methodology to study the effects of material damping in the phenomena of sensing localization, as well as a quantification of the damping in a structure, were derived. The results obtained using this analytical procedure supported with experiments will be here presented. Since damping in structures cannot be predicted, but experimentally measured, numerical and experimental analysis are carried out jointly in order to obtain the damping in the structure and the energy losses that occur. A long beam structure, butt bolted at the middle, is analytically and experimentally investigated: The beam is longitudinally and transversely excited, and the response is measured before the mid-span connection, calculating the phase speed of the wave and reconstructing the dispersion curve relation for the system. A measurement of the viscoelastic material properties of the beam structure is obtained with the use of this procedure. These values are inserted into the equations describing the dynamics of the system to further investigate its damping, through measurements of the specific damping capacity of the structure. The effect on the localization of the energy of vibration to a region close to the wave generating source is observed by comparing the energy dissipation due to material damping to that due to structural joints.
On-Board Truck Computers and Accident Risk
Authors: Ayres T. J. , Donelson A. , Brown S. , Bjelajac V. M. , Van Selow W.
Published: July 2023

On-board trip computers facilitate record-keeping in trucks, but some models permit drivers to enter data manually while driving. Three approaches were taken to investigate the potential risk associated with such devices. A review of studies involving other in-vehicle devices revealed that drivers can safely time-share visual attention between the road and a display. An experiment conducted in a controlled driving environment found that head and eye movements while using an on-board truck computer were similar to those for common devices and activities such as operating a radio or checking the odometer. Analysis of accident reports from North Carolina and the Fatal Accident Reporting System showed that in-vehicle devices were only rarely cited as distracters in accidents. Based on these findings and on the safety benefits provided by truck computers, it is expected that these will have a net positive impact on truck fleet safety.
Psychophysical Validation of Photographic Representations
Authors: Ayres T. J.
Published: July 2023

In order to represent how a scene would appear to a typical observer, a photographic print can be calibrated based on careful observation. A psychophysical validation procedure is described, involving the use of visual stimulus charts. The scientific rationale and basis for this procedure is reviewed, and additional applications are discussed.
Predicted Thermally Induced Stresses in an Epoxy Molding Compound at the Chip Corner
Authors: Uschitsky M. , Suhir E.
Published: July 2023

Mechanical reliability of epoxy molding compounds in plastic packages depends on the stress level at the chip corners. In this analysis we evaluate the effect of radii of curvature at the corners and the interfacial delamination on the thermally induced stresses caused by the thermal contraction mismatch of the epoxy and silicon. We found that, in the case of perfect adhesion, the calculated stresses are in the range of 5,000–10,000 psi, depending on the fillet radius. The role of the delamination at the chip/epoxy interface was assessed using Fracture Mechanics approach. We showed that delamination leads to a substantial increase in the stress level at the delamination tip. The predicted stresses are in the range of 20,000–100,000 psi, depending on the delamination length and the fillet radius. We showed also that the stress intensity factor KI for the local stresses is proportional to the stress level at the chip corner and the square root of the delamination length. The combined action of the thermally and delamination induced stresses can lead to crack (delamination) propagation. The initiated crack can be stopped (“arrested”) if this stress reaches a “critical” level. We conclude that the propensity of the molding compound to a thermo-mechanical failure can be reduced by employing compounds with high adhesion strength, and that increased radii of curvature at the chip corners might result in appreciable reduction of the induced stresses. The obtained results can be helpful in reliability analyses and physical design of plastic packages.
“Thick” Plastic Packages With “Small” Chips vs “Thin” Packages With “Large” Chips: How Different Is Their Propensity to Moisture-Induced Failures?
Authors: Suhir E. , Ilyas Q. S. M.
Published: July 2023

We suggest a simple geometrical parameter reflecting the combined effect of the chip width, the pad width, and the underchip thickness of the molding compound on the propensity of a plastic electronic package to a moisture-induced failure. We use this parameter to analyze the experimental data for the moisture level leading to such a failure. We show that “thick” packages (such as PLCC, MQFP, etc) with “small” (4–5mm wide) chips are less prone to moisture induced failures, than “thin” packages (such as TQFP) with “large” (8–10mm wide) chips. “Thick” packages are also less sensitive to the change in the moisture content. We show also that, from the standpoint of structural analysis, the distinction between “thick” and “thin” packages is due primarily to the level of the in-plane (“membrane”) stresses in the underchip portion of the molding compound: in “thick” packages bending stresses only should be considered, while in “thin” packages both the bending and the in-plane (“membrane”) stresses should be accounted for. The obtained results are intended to be used in the development of guidelines (“figures of merit”) that would enable one to separate packages that need to be “baked” and “bagged” (or “rebaked” and “rebagged”) from those that supposedly do not.
Impact of Polymerization on Warpage Prediction of Molded Plastic Packages
Authors: Teng Sue Y. , Sarihan Vijay , Thomas Ron , Adhihetty Indira
Published: July 2023

Warpage determination and minimization in molded plastic packages is critical to package reliability, especially for large plastic packages. Power modules with exposed heat sinks fall in this category. Seamless contact of these power modules with the external heat sink, or cold plate, is also required for effective thermal dissipation. Hence, accurate prediction of warpage is very important for reducing the design cycle time for this class of packages.

Conventional modeling methodologies maintain the assumption that the package is stress-free and undeformed at the molding temperature. Warpage prediction is typically based solely on the differential thermal expansion of the package materials during cool down from the mold temperature. These assumptions, however, result in a large discrepancy between the predicted warpage and the actual measured warpage. This study resolves this disparity by proposing a methodology which accounts for the impact of polymerization of the mold compound on package warpage after the package is removed from the mold.

A hybrid FEM and experimental methodology has been developed which determines the impact on package warpage prediction due to polymerization, in addition to the differential thermal contractions of the various materials in the package during the cool down process after mold release.
A Comparison of Viscoplastic and Plastic Constitutive Models for Pb/Sn Solder Alloys
Authors: Basaran Cemal
Published: July 2023

In the literature there has been a number of constitutive models proposed for modeling thermomechanical behavior of Pb/Sn solder alloys. Some of these models are based on the plasticity (using time independent irreversible deformations), and some are based on the viscoplasticity (using time dependent irreversible deformations). In this paper it is demonstrated that Pb/Sn solder alloys are highly viscous materials, and that their behavior cannot accurately be modeled with a plasticity based model.
Evaluation of Minimum Zone Straightness by Nonlinear Optimization Method
Authors: Orady Elsayed A. , Li Songnian , Chen Yubao
Published: July 2023

Fitting algorithm is considered one of the significant uncertainty factors to the measurement results using CMM. In this paper, a new algorithm, named Nonlinear Optimization Method (NOM) has been developed for the evaluation of straightness error. To improve the accuracy, efficiency and robustness of NOM, data filtering and rebuilding are incorporated in the method. The algorithm, Least Squares Method (LSM) and Convex Hull Method (CVH) are applied to data sets obtained with CMM measurements on the surfaces machined with different processes such as milling, planning, grinding and hand-finishing. Practically valuable results have been obtained and the algorithm has proven to guarantee Minimum Zone Evaluation (MZE) of straightness.
Point-to-Point Probe Performance Test of Kinematic Touch Trigger Probes on Coordinate Measuring Machines
Authors: Shen Yin-Lin , Moon Sung-Ho
Published: July 2023

The default 49-point sampling plan specified in the ANSI B89 standard when applied to kinematic touch trigger probes is investigated in this paper. The default sampling plan was tested by using experimental data and research findings indicate that a systematic bias in the Z coordinate of the best-fit center of the reference ball exists when testing performances of kinematic touch trigger probes. A two-latitude sampling plan synthesis method based on a pretravel model for touch trigger probes is proposed in this paper. It is shown that the proposed method can be used to synthesize sampling plans resulting in a near-unbiased reference ball center in probing tests even when noise is included in the probing data. The proposed method is not to replace the three-dimensional (3D) probe testing procedure, but to be used together with the 3D probe testing method, to reveal the actual probe performance or roundness of the measurements.
Thermal Management in Direct Chip Attach Assemblies
Authors: Baldwin Daniel F. , Beerensson James T. , Sitaraman Suresh K.
Published: July 2023

Direct chip attach packaging technologies are finding increasing application in electronics manufacturing particularly in telecommunications and consumer electronics. In these systems, bare die with bumped interconnect bond pads are assembled in a flip chip configuration (i.e., active face down) directly to low-cost organic substrates. In this work, the thermal management of three direct chip attach technologies is investigated. Experimental measurements are conducted exploring the junction-to-ambient thermal resistance and thermal dissipation path for the three interconnect technologies which include solder attach, anisotropic adhesive attach, and isotropic adhesive attach. A first order chip-scale thermal design model is developed for flip chip assemblies exhibiting good agreement with the experimental measurements.
Anisothermal Fatigue Analysis of Solder Joints in a Convective CBGA Package Under Power Cycling
Authors: Hong Bor Zen , Yuan Tsorng-Dih , Burrell Lloyd G.
Published: July 2023

This paper presents the use of an integrated flow-thermo-mechanical analysis method and tools for numerically studying the effect of local heat transfer coefficient on anisothermal cyclic fatigue behavior of solder joints in a CBGA (ceramic ball grid array) package under power cycling. A cyclic chip power load of 1 watt to 10 watts at a frequency of 5 cph (cycles per hour) with an air flow speed of 0.5 m/s was used to simulate a typical field condition for a 32mm CBGA air cooled package. Temperature dependent viscoplastic properties of Pb-Sn (lead-tin) alloys were used to model the solder joint behavior in the package. An approach using the Δϵeqin-modified Coffin-Manson Law was applied to estimate the fatigue life of the solder joint. The Δϵeqin represents a saturated equivalent inelastic strain range as determined by the finite element model. The results of anisothermal deformation and fatigue response of solder joint are compared to that of a condition of constant temperature cycling.
A Multi-Axial Thermo-Mechanical Fatigue Tester for Electronic Packaging Materials
Authors: Lu Minfu , Liu Sheng
Published: July 2023

A multi-axial thermo-mechanical mini-fatigue tester has been developed at Wayne State University for investigating the behaviors of small specimens, particularly in the field of electronic packaging materials and structures. The testing and calibration of machine is described in this paper. Materials tested include a copper wire, two kinds of polyimide films, a lead-free solder alloy.
Fluid Compressibility Effects in Semiactive Vibration Absorbers (SAVA)
Authors: Mo C. , Lee J. , Khaw C. , Kuehn J. , Patten W. N.
Published: July 2023

Recent past work by this research team has demonstrated that semiactive hydraulic vibration absorbers hold the promise of providing an ideal means of mitigating structural vibration. This paper examines an issue that must be treated when designing a semiactive vibration absorbers (SAVA) system for application to a full scale structure; fluid compressibility. An expanded and consistent dynamic model of the flow process is first established. A laboratory experiment is then presented to identify pertinent parameters. A simple feedback control is then tested on a single degree of freedom laboratory structure to verify the findings.
Development of a Neural Network Flush Airdata Sensing System
Authors: Rohloff Thomas J. , Catton Ivan
Published: July 2023

Neural network techniques have been successfully applied in the development of flush airdata aviation instrumentation. Current flush airdata sensing (FADS) systems use a matrix of pressure measurements from the vehicle nose to infer airdata states. The objective of this investigation was to use flight data available from the NASA Dreyden Flight Research Center to train a multi-layered, feed-forward neural network to solve the FADS airdata estimation problem. Using a modified back propagation training algorithm, a neural network was developed to represent the mapping between the pressure-matrix-input and the airdata-output vector spaces. The resulting FADS neural network allows for accurate airdata estimation over the range of flight conditions considered. The results of this investigation demonstrate that neural networks can be applied to flush airdata systems, and can be as robust as the existing semi-empirical model.
Servo Performance of Actuator Bearing Greases
Authors: Prater Walter L. , Stone Garvin J. , Tierney Kevin W. , Karis Tom E.
Published: July 2023

The hysteresis properties of a magnetic recording disk drive rotary actuator servo were measured for bearings lubricated with three different types of grease. The three types of grease tested were: 1) mineral oil with a polyurea thickener, 2) polyol ester oil with a polyurea thickener, and 3) perfluorinated polyether (PFPE) oil with a polytetrafluoroethelyne (PTFE) particle thickener.

The grease dynamic viscosity and yield stress were measured to characterize the grease flow properties.

Actuator bias current was measured on files to quantify changes in the hysteresis and linearity. Head settle times were measured following a random seek pattern.

Actuators made with the mineral oil and polyol ester oil polyurea thickened greases had acceptable actuator bias current and head settle times. Actuators made with the PFPE grease exhibited large bias hysteresis, significant non-linearity, and the head settle time was significantly longer than for those actuators made with mineral oil grease.

The reasons for the increased hysteresis and settle time observed with the PFPE grease were investigated. It was found that the PTFE grease particles get shredded and deposited in the raceway and they also form large agglomerates that impede the smooth rolling of the bearing.
Shear Mechanical Behavior of the Human Lumbar Anulus Fibrosus and the Effects of Degeneration
Authors: Iatridis James C. , Kumar Sanjay , Krishnan Leena , Rawlins Bernard A. , Weidenbaum Mark , Mow Van C.
Published: July 2023

Clinically, it is observed that a correlation may exist between low back pain and activities associated with torsional loading of the lumbar intervertebral discs (IVD). Analysis of the localized mechanical response of the IVD under different loading conditions is necessary for evaluation of internal stresses and strains within the disc which are responsible for successful performance or failure of the IVD. An understanding of the localized shear mechanical properties of the IVD is an important step toward the development of a precise mathematical model of the entire IVD and motion segments. While some information is available on the shear mechanical behavior of the nucleus pulposus [2] and anulus fibrosus (AF) [3], more information is required to completely characterize their material behaviors. The objective of this study was to investigate the shear mechanical behavior of the AF with attention to frequency of loading, axial compressive stress, and degree of degeneration.
Local Gas Transport Rate in Oscillatory Flow in a Model Human Central Airways
Authors: Tanaka Gaku , Ito Jin , Oka Kotaro , Tanishita Kazuo
Published: July 2023

The rate of local axial gas transport in oscillatory flow through a model human central airways was measured to evaluate the gas exchange during high-frequency oscillation. A rigid model of human airways consists of asymmetrical bifurcations up to third generation, of which geometries were determined by the study of Horsfield et al. (1971). A bolus of CO2 tracer was injected into the trachea, and effective diffusivities as a function of location in the airways were obtained by CO2 washout profiles. The rate of increase of effective diffusivity depends on the local flow conditions and differs with branches. The effective diffusivity in the left main bronchus becomes 3 times greater than that in the straight tube, whereas no significant effect is observed in the right main bronchus.
Sinusoidal Oscillating Flow Through Asymmetrical Bifurcation
Authors: Yamaguchi Ryuhei , Okada Kazuki , Ikeda Tomohiko
Published: July 2023

The respiratory system is characterized by many bifurcations. The bronchi are composed of symmetrical and asymmetrical bifurcations. It is generally considered that the gas mixing during the respiration are induced by the flow through the bronchi.

In the present study, the axial and the transverse velocity components have been measured in the asymmetrical bifurcation by LDV. Consequently, the asymmetry of axial flow and the secondary flow around the flow divider have been clarified experimentally.
The Zero-Tension Hypothesis for the Mechanism of Atherogenesis and the Wall Shear Stress Gradient (WSSG) Predictor Equation
Authors: Lei Ming , Kleinstreuer Clement , Truskey George A. , Archie Joseph P.
Published: July 2023

Non-uniform hemodynamic factors are believed to play important roles in the onset and development of atherosclerotic lesions in branching blood vessels and intimal hyperplasia at graft-artery bypass junctions. At present, a variety of theories regarding the hemodynamic aspects of atherogenesis have been proposed, which include almost all hemodynamic factors, such as high and low shear stresses, oscillatory shear index (OSI), temporal and spatial variations of wall shear stresses, flow separation, long particle residence time, and secondary flow, etc.[1–4] However, the underlying mechanism of endothelial cell (EC) response to hemodynamic forces leading to atherosclerosis is still not well understood.
Arterial Wall Transport Simulation: Porohyperelastic/Transport Finite Element Models
Authors: Kaufmann M. V. , Simon B. R. , Baldwin A. L.
Published: July 2023

Porohyperelastic transport-swelling (PHETS) models (Kaufmann [1996], Simon et al [1995]) for soft tissues have been developed and applied to problems of transport within the walls of large arteries. The general theory developed in [Kaufmann, 1996] includes mass transport by diffusion and convection, the influence of electrical and chemical potentials, and osmotic swelling, as well as the characteristic nonlinear finite deformation of the tissue. The models couple the behavior of the porous solid skeleton, mobile tissue fluid and concentrations of charged species. This abstract presents a finite element model (FEM) of the convection-diffusion of an uncharged single species through a rabbit aorta under various intraluminal pressures. The results of these models show good qualitative agreement with experimental results. The general PHETS theory coupled with the FEM implementation of the theory could provide insight into the transport associated with causal factors of atherosclerosis. The models can be used to study the effectiveness of various drug delivery systems.
A Finite Element Investigation of Solid Phase Transverse Isotropy in Contacting Biphasic Cartilage Layers
Authors: Donzelli Peter S. , Spilker Robert L.
Published: July 2023

Most biological materials are anisotropic and inhomogeneous. Experimental studies of cartilage, meniscus, bone, ligament and tendon all point to orthotropic and nonlinear material response to applied load. In studying joint articulation these nonlinearities, along with complex, curved geometries and the nonlinearity implicit in contact, must be modeled, making analytic investigations of joint contact biomechanics intractable. Since articular contact plays the primary role in load transfer in joints, we will explore the effect of tissue anisotropy using a canonical joint contact problem. A biphasic contact finite element model (1, 2) will be employed for this investigation so the important fluid flow and stress-shielding effects (3, 4) can be understood.
Coupled Fluid-Structure Analysis of Bi-Leaflet Mitral Mechanical Heart Valve Dynamics
Authors: Makhijani Vinod B. , Siegel John M. , Singhal Ashok K.
Published: July 2023

Several important design problems with contemporary mechanical heart valve (MHV) prostheses such as thrombus formation and hemolytic trauma can be attributed to the valve fluid dynamics. Blood flow in the vicinity of the valve is influenced by valve motion which, in turn, is influenced by time-varying fluid-imposed lift and drag forces on the occluder. Thus, the valve fluid and structure dynamics are linked through complex fluid-structure interactions. In order to develop design criteria for MHVs with improved valve closure efficiency and minimized flow resistance and fluid shear stresses, both valve occluder and blood flow dynamics need to be simultaneously considered.
Virtual Reality Training Simulation With Force Feedback: Palpation of Lesions
Authors: Langrana Noshir , Burdea Grigore , Dinsmore Michael , Gomez Daniel , Harper Eric , Silver Deborah , Mezrich Reuben
Published: July 2023

Our current goal is to combine the advantages of medical imaging with force feedback technology to develop a virtual simulation where the user can touch soft tissue looking for a tumor beneath the surface. When it is touched, the tumor gives a different force profile, making it feel as though something is actually beneath the surface. If this capability was combined with medical imaging, the physician would be able to touch and examine organs that were not previously palpable without surgery.
Hybrid Approach to the Biomechanical Design of a Dummy Human Neck
Authors: Yoganandan Narayan , Cheng Joseph , Pintar Frank A. , Shams T. , Rangarajan Nagarajan
Published: July 2023

A hybrid approach combining the efforts of computer modeling and experimental testing was used to advance the design of a new dummy neck with improved biofidelity. A lumped spring-mass-dashpot model was exercised including the appropriate anthropomorphic, kinematic, and dynamic performance requirements. The prototype consisted of five layers of aluminum and butyl rubber discs. A pair of cables were inferiorly attached with springs connecting the head to the base of the neck in the anterior and posterior regions. Flexion, extension, and lateral bending tests were conducted at velocities ranging from five to ten mph. Dynamic biomechanical and high-speed photography data were analyzed. Increasing velocities produced increasing magnitudes of forces, moments, accelerations and angular velocities. The experimental response from the prototype dummy neck closely matched with computer simulations. The head-neck rotation angle, head-lag angle, and the head center of gravity displacement correlated with computer simulations. Principles of computer modeling combined with the dynamic experimental techniques are a valuable tool to advance the design of a new anthropomorphic neck.
Thermal Analysis of Two-Phase Microchannel Cooling
Authors: Chen N. C. J. , Felde D. K. , Yoder G. L.
Published: July 2023

A design calculation has been performed to determine thermal limits in support of an experiment in two-phase microchannel water cooling. Under the operating conditions (one atmosphere pressure and 23°C inlet temperature), the calculation predicts that the experimental channel can withstand a maximum surface temperature of 115°C and a heat flux up to 975 W/cm2 without exceeding the critical heat flux limit. The predicted results also indicate that a uniform heat flux along the channel in the two-phase domain can be achieved so that the heat losses from the experimental test section can be calculated in a straightforward manner.
Liquid Flow Characteristics in a Diamond-Pattern Micro-Heat-Exchanger
Authors: Ravigururajan T. S. , Drost M. K.
Published: July 2023

The paper outlines the single-phase flow characteristics of a diamond-pattern micro-heat-exchanger. An experimental setup was built to study the characteristics of micro-channel heat exchangers. The experimental study was conducted for the following parameters: working fluid - Refrigerant-124; mass flow rate - 35 ml/min to 260 ml/min; and heat flux - 10 W/cm2 to 100 W/cm2. The heat transfer enhancement is less than that obtained in a parallel-channel micro-heat-exchanger. The enhancement is also independent of the mass flow rate. The pressure drop increased at a rate faster than that experienced in a parallel-channel flow.
Development of a Micropump for Microelectronic Cooling
Authors: Wong C. Channy , Adkins Douglas R. , Chu Dahwey
Published: July 2023

To demonstrate a system integration process for Micro-Electro-Mechanical Systems (MEMS), we are building an active cooling MEMS unit for microelectronics applications. This integrated unit will incorporate a micropump, temperature sensors, microchannels, and heat exchange devices into a single unit. The first phase of this research project is to develop and test a micropump capable of moving the working fluid within the integrated device. This paper will discuss the design, development, testing, and evaluation of a micropump concept.

The micropump which was developed is an electrohydrodynamic (EHD) injection pump. Fabrication of the pump was accomplished using laser micromachining technology, and two initial designs were examined for full fabrication. The first design has two silicon parts stacked vertically on top of each other. Gold is deposited on one side of each stacked plate to serve as electrodes for the electrohydrodynamic pump. A Nd:YAG laser is used to drill an array of circular holes in the “well” region of both silicon parts, leaving an open pathway for fluid movement. Next the silicon parts are aligned and bonded together, thus becoming a EHD pump. Fluid flow has been observed when an electric voltage is applied across the electrodes. The second design has the silicon parts which contain the flow grid oriented “back-to-back” and bonded together. This “back-to-back” design has a shorter grid distance between the anode and cathode plates so that a smaller voltage is required for pumping. Preliminary results from laboratory experiments have demonstrated that this EHD micropump design can achieve a pressure head of about 287 Pa with an applied voltage of 120 V.
A Coupled Numerical Technique for Self-Consistent Analysis of Micro-Electro-Mechanical-Systems
Authors: Aluru N. R. , White J.
Published: July 2023

An efficient algorithm for self-consistent analysis of 3-D micro-electro-mechanical-systems (MEMS) is described. The algorithm employs a hybrid finite-element/boundary-element technique for coupled mechanical and electrical analysis. The coupled algorithm is shown to converge rapidly and is much faster than relaxation for tightly coupled problems.
Towards a Functional MEMS Neurowell by Physiological Experimentation
Authors: Wright John A. , Tatic-Lucic Svetlana , Tai Yu-Chong , Maher Michael P. , Dvorak Hannah , Pine Jerome
Published: July 2023

Specificity in neuron targeting during stimulation and recording is essential in executing complex neuronal network studies. Physiological experiments have shown that young (less than one week old) cultured neurons can escape through a 0.5 μm-square hole. Through iterative physiological experimentation, a functional MEMS structure we call a canopy neurowell has been developed. Essentially a micromechanical cage, the structure consists of a well, an electrode bottom, and a nitride canopy cover with integrated micro-tunnels. It is able to physically confine, and make electrical contact with, a neuron. Potentially, neurowells are capable of multi-site studying of long-term, in vitro and in vivo neural systems. Experiments show that the canopy neurowell is mechanically functional and biologically compatible.
Design Techniques for Minimizing Manufacturing Variations in Surface Micromachined Accelerometers
Authors: Bart Stephen F. , Samuels Howard R.
Published: July 2023

In an effort to improve performance and reduce die area and cost, we have developed an open-loop surface-micromachined accelerometer, the ADXL76. The deposition and etching processes which define the dimensions of the sensing structure can have a wide variation in their characteristics, which can lead to large variations in output sensitivity. This paper describes techniques which were used to design an accelerometer structure that is significantly less sensitive to these dimensional variations.

Symmetry was used throughout the structure. In addition to the global four-fold symmetry of the overall structure, local symmetry in the series capacitor unit cells and tether environments was used. This included adding extra etch uniformity structures which make the etch environment around the tethers equivalent to the etch environment around capacitor gaps. The use of these etch uniformity structures increased the correlation between the tether width and the capacitor gap by almost a factor of 4. In addition, the sensors nominal geometry was optimized to minimize the variation of the output sensitivity due to etch and warpage variations. Using these techniques, the ADXL76 accelerometer demonstrated a factor of 2 reduction in the standard deviation of pre-trim sensitivity as compared to an equivalent design that did not use these techniques. This improved sensitivity distribution allows for a smaller trim range, which results in the use of less die area and a faster trim. In addition, the improved correlation between the as-fabricated tether width and capacitor gap allows for more accurate trimming. Thus the overall post-trim sensitivity distribution is much improved as compared to previous closed-loop accelerometer designs.
Pressure-Shear Impact Investigation of the Dynamic Response of Ceramics
Authors: Sundaram Sairam , Clifton Rodney J.
Published: July 2023

Results of pressure-shear plate impact experiments on an alumina ceramic (AD85) containing a significant amount of glassy phase are presented. The ceramic shows a weak, strain softening behavior; this has been attributed to the intergranular glassy phase. The ceramic is modeled by using an atomistic constitutive model for the response of the glass. This model utilizes the concept of free volume. Computations performed using this constitutive model show that the increase in free volume that occurs during the deformation is responsible for the observed softening response.
Statistical Aspects of Toughness in Brittle Fracture
Authors: Chudnovsky Alexander I. , Gorelik Michael L.
Published: July 2023

Statistical features of brittle fracture such as tortuousity of crack path, scale effect and scatter of toughness parameters are well documented. The apparent randomness of the process is closely associated with the distribution of defects on various scales within a solid. The phenomenological description of microdefects is represented by a random field of specific fracture energy γ following the framework of Statistical Fracture Mechanics (SFM). A brief review of SFM is presented. SFM is a first theory that proposed a way to relate the fracture toughness and roughness of crack path using continuum mechanics formalism. At the same time, the engineering application of the model was limited due to its mathematical complexity. We employ the Monte Carlo method to overcome the analytical difficulties of SFM. Fracture toughness dependency on the tortuousity of crack trajectories, loading conditions and material microstructure are illustrated by computer simulation of tests for common specimen geometries. The ambiguity of the concept of conventional toughness is addressed.
Localization in Disordered Brittle Media: Lattice Models
Authors: Mastilovic Sreten , Vujosevic Milena , Krajcinovic Dusan
Published: July 2023

The transition from a statistically homogeneous to a heterogeneous strain field is one of the frequently considered and often poorly understood intrinsic failure modes in damage tolerant materials with a disordered microstructure and inferior cohesive (fracture) strength. This type of transition occurs in brittle materials, such as rocks and concrete, primarily but not exclusively in the absence of long range tensile principal stresses. Numerous analytical and experimental studies were focused on the purely phenomenological, deterministic and continuum aspects of the deformation of a laterally confined cylindrical specimen subjected to the axial compression. At the same time the stochastic aspects of the problem and the effect that the disordered micro-structure of the material has on the localization have been only occasionally subjected to scrutiny. Similar failure modes may also take place in brittle materials subjected to high velocity impacts or random fluctuations of temperature. The focus of this short study is to highlight the non-deterministic aspects of the localization phenomenon using the methods of the statistical physics. At the current stage of this research program only the two-dimensional models were considered. Hence, the derived conclusions are largely of a qualitative nature.
Damage Evolution of Particulate Reinforced Titanium Composites
Authors: Tong Wei , Huang Shan , Li Xianghong
Published: July 2023

Particulate reinforced titanium matrix composites are relatively a new class of metal matrix composites, which are superior to aluminum matrix composites in high temperature (up to 650°C) and corrosive conditions (Abkowitz et al. 1995, Tong et al. 1995, Tong, 1996). Particulate-reinforced titanium composites are shown to have increased stiffness and strength; but their tensile ductility is strongly affected by the degree of metal-ceramic interfacial reaction during the consolidation and post-consolidation annealing processes (Tong et al. 1994). Formability and related damage evolution of such materials under dynamic loading are regarded to be vital to their secondary rapid forming, machining, cutting, and to the understanding of their wear and erosion properties. Some reinforcement particle damages have been observed during the processing of titanium composites, which can be related to the rapid build-up of very large local high stresses (Tong and Ravichandran 1994, Benson et al. 1995). The initiation and growth of damages at macro to micro scales in titanium composites are the focus of this investigation. The outcome of the investigation provides valuable guidance for optimizing materials processing for improved performance of particulate reinforced titanium composites and for their potential engineering applications.
The Effect of Cell Size on the Tensile Behavior of Microcellular Polycarbonate
Authors: Kumar Vipin , Weller John E.
Published: July 2023

Previously, processing conditions were presented that produce polycarbonate (PC) foams with the same density and significantly different average cell size (Kumar and Weller, 1994a). It was shown that the average cell size could be varied by an order of magnitude in different foams while maintaining the same foam density. The ability to produce foams with controlled density and cell size opened the possibility for a systematic evaluation of the effect of cell size on the mechanical properties of cellular materials.

A set of experiments was performed to determine if cell size (or equivalently processing conditions) had an affects the tensile behavior of microcellular polycarbonate. A series of tensile tests was performed on polycarbonate foams where the cell size was varied from approximately 2 μm to 37 μm, while the relative density was held nearly constant at 0.56. It was determined that the tensile behavior of microcellular PC is not affected by the average cell size for the range of microstructures produced in this study. The stiffness, strength and toughness showed no definitive trends with cell size. Consequently, the only microstructural variable that determines the tensile properties is the bulk foam density.
Study of Foam Sheet Formation: Part III — Effects of Foam Thickness and Cell Density
Authors: Lee S. T. , Ramesh N. S.
Published: July 2023

The existing cell growth model in the literature has been modified to include the gas loss effects due to surface evaporation experienced in a high surface to volume ratio of this foam sheet formation. As it exits from the high pressure die, nucleation occurs due to sudden pressure drop and then the sheet experiences natural cooling, expansion due to gas diffusion and gas loss from its surface. Rheological experiments were performed to supply simulation parameters for the modeling using the Haake rheometer. Both HCFC-22 and -142b were studied with low density polyethylene (LDPE) in generating the rheological data. They were also used to make foams to generate experimental data discussed in this paper using a 70 mm counter-rotating twin screw extruder. The theoretical and experimental results are compared in terms of foam density and foaming efficiency. Foaming efficiency is defined as the actual expansion over maximum possible theoretical expansion dictated by the ideal gas law for a particular blowing agent. The agreement is good when the foam expansion is under ten times and the deviation increases when the foam expands further, in which bubble-bubble interaction effects become significant.