bluuebunny/crossref_metadata_2025 huggingface dataset:
Adhesions of the Patellar and Quadriceps Tendons: Mathematical Model Simulations
Authors: Roglic H. , Kwak S. D. , Henry J. H. , Ateshian G. A. , Rodkey W. G. , Steadman J. R. , Mow V. C.
Published: March 2022

Following knee surgery, especially after anterior cruciate ligament (ACL) reconstruction, a small percentage of patients complain about significantly decreased patellar mobility accompanied by anterior knee pain, sometimes severe. The limited mobility and knee pain usually do not disappear even with aggressive physical therapy. Arthroscopic exploration of these knees reveals a closure of the patellar tendon-tibial (PTT) interval, i.e., severe fibrous adhesion of the patellar tendon to the anterior aspect of the tibia, the formation of fibrous tissue between the quadriceps tendon and the femur, and a ‘closed-off’ suprapatellar pouch. Other investigators have also noted such adhesion (Paulos et al., 1987 & 1994; Jacobson et al., 1989), and Hughston (1985) attributed the tendon adhesion to the scarring of infrapatellar and suprapatellar fat pad caused by the surgery. While the adhesions are important clinical problems associated with knee surgery, no study to date, other than our experimental study on patellar tendon contracture, has quantitatively investigated the effect of these adhesions on knee kinematics and contact forces (Ahmad et al., 1997). In this study, we use a 3-D mathematical model of the knee joint to analyze the effects of the patellar tendon adhesion (PA) to the anterior tibia, and the quadriceps tendon adhesion (QA) to the anterior femur. Our objective, therefore, is to demonstrate the effects of these types of post-operative adhesions on patellofemoral joint mechanics.
Replacement of Biological Parts Using Solid Freeform Fabrication Technologies
Authors: Crawford R. H. , Barlow J. W. , Beaman J. J. , Bourell D. L.
Published: March 2022

The use of Solid Freeform Fabrication (SFF) for creating models and visual prototypes of products is gaining rapid acceptance in industry as an aid to decreasing time-to-market while increasing product quality. The strengths of these processes include rapid turnaround time and the ability to create parts of almost unlimited shape complexity. Research in these technologies has now turned to searching for new processes and material systems that will allow the creation of functional parts. One promising area of application is fabrication of replacement biological parts. SFF technologies are particularly suited to these applications because of the complex shapes involved. Research at The University of Texas at Austin is focused on the Selective Laser Sintering (SLS) process and the development of biocompatible material systems that can be processed with SLS. In this paper we describe the status of SLS processing of calcium powders to form artificial bones. We also present the results of animal implantation tests to prove biocompatibility of the materials.
Similarities Between Gait Adaptations in Preoperative and Postoperative Total Hip Replacement Patients
Authors: Hurwitz D. E. , Foucher K. C. , Andriacchi T. P. , Rosenberg A. G. , Galante J. O.
Published: March 2022

Gait adaptations among postoperative total hip replacement (THR) patients may be a response to the prosthesis and changes in the reconstructed joint mechanics or may be a learned response from an adaptation that was present preoperatively. Similarities have been reported between gait adaptations in preoperative and postoperative patients for THRs (1), but this was demonstrated in cross-sectional data and not longitudinal data. These gait adaptations may have implications on hip joint loading, rehabilitation protocols and can result in additional compensations at other joints. This longitudinal study tested the hypothesis that gait adaptations present preoperatively persist postoperatively.
Microdevices Made by the LIGA Technique for Applications in Minimally Invasive Therapy
Authors: Wallrabe Ulrike , Mohr Jürgen , Ruther Patrick , Ruzzu Antonio
Published: March 2022

For modern diagnostic and therapeutic methods new miniaturized analytical components and surgical tools are needed. This becomes obvious in the fields of endoscopic treatments or catheter based interventions. Since cleaning and sterilization of miniaturized devices is difficult or even impossible many of these tools are expected to be disposable. Therefore, they should be available at reasonable prices which can be achieved by batch fabrication of the devices. Using the LIGA technique diverse polymers and metals can be patterned which enables numerous applications. Turbines, pumps, valves, lenses, and spectrometers are developed for the use in minimally invasive therapy.
Analysis for Design of a Composite Hip Prosthesis
Authors: Joshi Makarand G. , Santare Michael H. , Advani Suresh G. , Miller Freeman
Published: March 2022

Total hip arthroplasty (THA) using metallic hip prostheses has been successfully performed since the early 1960’s and is now a routine procedure. The use of cement to fill the space between the bone and the prosthesis, and bony ingrowth, where the bone grows into a porous prosthesis, have been the two primary methods of fixation used. For the structure of the femur before THA, the load distribution can be essentially resolved into an axial component, two bending moments and a torsional moment which depend upon the leg stance. The distribution of these load components is changed after THA. The current methods of fixation allow for transfer of axial loads to the bone mainly through shear stresses at the bone-implant interface (The muscles attached to the femur transfer load and moments as before THA). The bending moment is effectively transferred to the bone, however, the great disparity in the stiffness of a metallic prosthesis and the surrounding bone reduces bending displacements changing the bending moment distribution in the surrounding bone. The current procedure although very successful in the older population has a relatively lower rate of success in the younger population.
Design and Evaluation of a Programmable Triaxial Joint Simulator
Authors: O’Connell Mary K. , James Susan P.
Published: March 2022

The goal of a joint simulator is to replicate the conditions experienced by an implanted prosthesis. The accuracy of in vivo joint modeling has become increasingly important as new materials, surface treatments, coatings, and implant designs are created. Force, motion, and environmental conditions are critical for modeling in vivo joints. True physiological joint articulations consist of three orthogonal force components coupled with triaxial motion.
Liner/Shell Load Transfer Mechanisms in a Modular Acetabular Component for Total Hip Replacement
Authors: Kurtz Steven M. , Ochoa Jorge A. , White Christopher V.
Published: March 2022

Modular acetabular components have seen widespread clinical use since the 1980’s (Collier et al., 1992). However, nonconformity between the polyethylene liner and the metal shell may exist in modular acetabular components by design, due to limitations on polyethylene liner manufacturing tolerances, or from the incorporation of locking mechanisms to attach the liner to the shell. Previous research has demonstrated that the stresses at the articulating surface are sensitive to nonconformity between the liner and the metal shell (Kurtz et al., 1994). Deleterious rim loading may also occur in a rimmed polyethylene liner with radial interference between the liner and the metal shell (Kurtz et al., 1993).
Osseocompatibility Tests: Do Biomechanical Factors Influence the Results?
Authors: Gharpuray Vasanti M. , Kerns Laura E. , Zyblewski Sean , Hiatt Mark J. , Zhuang Ming , Powers Dennis L.
Published: March 2022

The transcortical “plug” model has been used by numerous investigators for the evaluation of the response of bone to implanted biomaterials. It is generally assumed that this model represents a loaded or functional situation and thus is suitable for evaluation of bone ingrowth into porous surfaces. However, other investigators have suggested that this is an essentially unloaded situation. Further, different researchers have reported a wide range of results from experiments designed to measure the response to apparently similar implant materials (Black, 1989).
Improved Mechanical Properties of Bone Cement by Ultrasonic Vibration
Authors: Saha Subrata
Published: March 2022

Self-curing polymethylmethacrylate (PMMA) or acrylic bone cement is used extensively in total joint arthroplasty and in the repair of bone defects [1]–[3]. However, the hand mixing of the methylmethacrylate polymer and the liquid monomer entraps air bubbles making the cement porous. This adversely affects the mechanical properties of the bone cement [4]. This has prompted several investigators to improve the mechanical properties of bone cement by reducing the porosity due to air bubbles by the use of centrifugation or by vacuum mixing [5]–[8]. In this study we investigated if ultrasonic vibration during cement mixing could reduce the porosity and improve the mechanical properties of surgical grade polymethylmethacrylate.
A Dynamic Computed Tomography Technique for In Vitro Measurements of Local Aortic Elastic Modulus
Authors: Lee Mark , Drangova Maria , Holdsworth David
Published: March 2022

The ability to quantify the mechanical/material properties of the arterial system has been a highly sought after asset in the study of arterial atherosclerosis; however, conventional methods that take into account the dynamic viscoelastic nature of the artery are either destructive or lack high local spatial resolution[ 1,2]. A novel computed tomographic (CT) technique has been utilized to obtain the instantaneous measurement of the dynamic elastic modulus of intact excised porcine aortic vessels undergoing physiological pressure waveforms.
A Procedure to Determine Equilibrium Postural Configurations for Arbitrary Locations of the Feet
Authors: Gonzalez L. Javier , Sreenivasan S. V.
Published: March 2022

Existing rehabilitation devices for patients with balance problems are passive, and they do not distinguish between different levels of imbalance a patient might possess. The ideal rehabilitation machine would be a robotic device that would provide ‘barely adequate’ support to the patient without compromising its ability to prevent falls. It would also allow the patient to perform normal postural motions including nominal sway and typical responses to external disturbances.
Force Reflection for WIMPs: A Button Acquisition Experiment
Authors: Eberhardt Silvio , Neverov Misha , West Todd , Sanders Carl
Published: March 2022

The purpose of this study was to evaluate whether the common computer-interface task of button acquisition is performed more rapidly when buttons are surrounded by force attraction basins. Button acquisition time measures were obtained from five participants for each of five different pointer device configurations. A normal mouse served as control, and the remaining four configurations used a normal mouse mechanically linked to the end-effector of a PHANToM force-reflection mechanism (SensAble Devices, Cambridge, MA). Two configurations applied forces on the mouse in the direction of a (graphical) button whenever the cursor was in the vicinity of the button. Anchoring the PHANToM to the mouse also allowed comparing relative and absolute pointer positioning. Over all participants, mean button acquisition time improvements of at least 10% were obtained when using force reflection. Individual means were in every case better when force-reflection was used. Across participants, there was no difference between absolute and relative positioning, whether or not force-reflection was enabled.
Design and Analysis of Tunable Springs in Haptic Interface of Endoscopic Graspers
Authors: Faraz Ali , Payandeh Shahram
Published: March 2022

In endoscopy, tissue manipulation is performed by long graspers which do not reflect the grasping force to the surgeon hand properly, due to their mechanical limitations. In this study, other electro-mechanical designs are considered to enhance the force reflection. The type synthesis of such a haptic interface leads to the application of tunable springs. The design of tunable spring is optimized based on the haptic and surgical requirements. Moreover, by using suitable control laws, it was shown that the primary requirements can be met according to the simulation results. The limited bandwidth of such a system, along with possible improvements, and future works are also discussed.
Haptic Display for Replication of Rheological Behaviour of Surgical Tissues: Modelling, Control, and Experiments
Authors: Scilingo Enzo Pasquale , De Rossi Danilo , Bicchi Antonio , Iacconi Pietro
Published: March 2022

Current technology of minimally invasive surgery deprives the surgeon almost completely of the perception of rheological properties of manipulated tissues. As a first attempt to solve this problem, we realized a sensorized surgical tool, whose visual display was however not completely satisfactory. We present a preliminary realization of a tactile display returning the kinesthetic tactile sensation of the stiffness and damping of manipulated tissues. We also discuss identification algorithms of the model of the manipulated materials for detecting their properties and for replicating their dynamic behavior through the tactile display.
Intelligent Control for Electrical Power Generation Systems
Authors: Shoureshi Rahmat , Li Hanchu , Kramer Robert , Klaiman Henry
Published: March 2022

Deregulation of electric power, introduction of independent power producers and increase competition have introduce new challengers to the utility industry. The ability to project short term demands and be able to respond to highly varying loads with high power quality are essential elements of a reliable and secure power system. This paper presents a new approach to the automatic generation control that combines advanced in neural networks, control theory, and electric power systems.
Design of a Self-Organizing Fuzzy Logic Controller for Two Dimensional End Milling Operations
Authors: Chang Hsin-Chi , Gau Jenn-Terng , Lu Wen F.
Published: March 2022

In this study, a Self-Organizing Fuzzy Logic Controller (SOFLC) is designed for the control of two dimensional end milling operations. In order to achieve high quality product and high production rate in 2-D end milling operations, it is important to minimize the tracking error, and regulate the cutting force at (or below) a certain level with possible maximum cutting feedrate. SOFLC avoids the need of the prior knowledge of the system, and is able to generate and modify the control rules by learning based on a given performance criterion. With the learning capability, SOFLC is used to limit the tracking error, and to regulate the cutting force in 2-D end milling operations. Simulation results show that the SOFLC is able to minimize the tracking error through its learning and keep the cutting force at or below a reference level.
A Fuzzy Logic Controller for Orbital Rendezvous
Authors: Luo Jia , Kluever Craig A.
Published: March 2022

A new application of fuzzy logic is investigated. A control scheme based on fuzzy logic techniques is developed for the orbital rendezvous phase of a low-thrust spacecraft. The minimum-fuel trajectory between specified energy levels is utilized as a reference trajectory. The fuzzy logic controller responds effectively to a range of initial state perturbations and results in very precise terminal orbit conditions with good tracking performance. The fuzzy logic controller exhibits better tracking performance and in some cases substantial fuel savings compared to a Linear perturbation control method. Numerical results are presented for a range of rendezvous maneuvers.
Analysis, Design and Experimental Verification of Active Vibro-Acoustic Control
Authors: Shoureshi Rahmat A. , Vance James , Eberhard Günter , Karkosch Hans-Jürgen
Published: March 2022

Sound and vibration quality have become a major differentiating factor for general machinery and specifically the automotive vehicles and aircraft. This paper provides an overview of research and development results interms of analysis and design tools, as well as, a unique control approach to the problem of low frequency active vibration and undesirable noise. Implementation results on different vehicles and an aircraft are presented.
A Hybrid Bed/Chair System for Bedridden Patients: Elimination of Transfer Between a Bed and Wheelchair
Authors: Mascaro Stephen , Asada Haruhiko H.
Published: March 2022

A hybrid wheelchair/bed system for eliminating transfer between the bed and chair is developed and tested. A powered wheelchair can be docked to a bed portion and reconfigured to a flat stationary bed so that the bedridden person does not have to change seating when transferring between the chair and bed. Moreover the powered wheelchair can be docked to a toilet directly and automatically so that the bedridden can use the toilet without changing seating. A holonomic omnidirectional vehicle with a ball wheel mechanism is used for the wheelchair. The high maneuverability and holonomic nature of the vehicle allow the chair to be docked easily and precisely against a fixture. First, this paper describes the basic concept of the reconfigurable holonomic omnidirectional mobile bed with unified seating, or RHOMBUS for short. Issues on the mechanical design of the vehicle, chair, and bed are addressed, followed by control issues. A compliant bumper mechanism is used to assist in both bed and toilet docking control as well as to ensure rider comfort. A hybrid stiffness control docking method using force sensors embedded at optimal locations within the bumper is developed. A prototype system was designed and tested. The vehicle was successfully docked to the bed despite a small clearance ratio as well as large lateral and angular initial errors.
Control and Calibration of a 6-Axis Ultrasound Scanner for In Situ Measurement of Articular Cartilage Geometry and Thickness
Authors: O’Bryan J. , Murphy M. C. , Ito K. , Mann R. W.
Published: March 2022

The development of improved orthopedic implants, diagnostic tools and surgical procedures for clinicians requires a better understanding of the human musculoskeletal system and joint kinematics. Mathematical models continue to play an important role in advancing the understanding of musculoskeletal system performance. At the core of any useful mathematical model is a sound representation of the fundamental mechanics of the system and reliable, repeatable measurements of the necessary physical parameters. For joint models, essential data include the three dimensional geometry of the articulating surfaces and ligament insertion sites, the articulating cartilage thickness, and material properties of the different tissues.
Generating Pathological Gait Patterns via the Use of Robotic Locomotion Models
Authors: Ephanov Anton , Hurmuzlu Yildirim
Published: March 2022

In this article we explore a feasibility of modeling normal and pathological human gait using a relatively simple five-element model. We use a robust, nonlinear control scheme to regulate the gait pattern of the model. Simulated gait patterns are generated through the use of five constraint relationships that depend on four gait parameters. Two pathological conditions due to muscle weaknesses were simulated by modifying the control torques at the joints. We demonstrate that the model successfully approximates the qualitative and quantitative dynamic trends that were observed in normal and pathological human locomotion.
Motion Control of a Mobile Manipulator by Input-Output Linearization
Authors: Chung Jae H. , Velinsky Steven A. , Hess Ronald A.
Published: March 2022

This paper discusses the modeling and control of a spatial mobile manipulator which consists of a robotic manipulator mounted upon a wheeled mobile platform. By neglecting slip of the wheeled platform’s tires, nonholonomic constraints are introduced into the equations of motion which complicates the control problem. The dynamic equations of the mobile manipulator are derived using the Lagrange-d’Alembert formulation. In this formulation, the equations of motion are projected onto the subspace of allowable motions. Then, the solvability of tracking problems for the mobile manipulator is investigated by using input-output feedback linearization. The feasibility of the control approach is demonstrated through computer simulation.
Integrator Backstepping Control of a Pneumatic Actuator-Based Robot Manipulator
Authors: Rifal Osamah M. El , Bridges Michael M.
Published: March 2022

The tracking performance of a single link pneumatically actuated robot arm has been investigated. The actuator pressure dynamics were considered, and an exact model knowledge integrator backstepping-based, IB, controller was designed with flow rates as the system’s control inputs. A more realistic valve flow model was then developed with valve control currents as the system inputs. Exact model knowledge based plant inversion techniques were used to compute the required control current given the desired flow rate and chamber pressure. In order to avoid reverse flow in the valves and singularities in the flow function, the controller gains were adjusted to ensure that the chamber pressures were maintained above and below the exhaust and supply pressures, respectively, throughout the experiments. Furthermore, flow choking, i.e. valve saturation, imposed further limitation on the system’s bandwidth. The tracking performance of the IB controller, when compared to linear PD control, was found to provide superior tracking performance. Finally, it is hypothesized that the tracking speed for IB control can be increased, by varying the value of the computed (i.e. desired) control based on the desired direction of motion.
Multibody Dynamic Formulation Using Modified Velocity Transformation for Real-Time Simulation
Authors: Lee Kwang-Pyo , Choi Gyoo-Jae , Yoon Yong-San
Published: March 2022

It is known that the multibody dynamic formulations based on the velocity transformations are suited for the real-time dynamic simulation. However the conventional velocity transformations have many trivial calculations due to sparsity resulting in less efficient formulation. To avoid that inefficiency we are suggesting the modified velocity transformations that become more compact by bookkeeping which joint coordinates relate to which specific kinematical quantity. The modified velocity transformations and their related terms are calculated efficiently using the recursive algorithms. For the unconstrained open-chain multibody systems we improve the efficiency further by applying the Cholesky decomposition algorithm modified for the doubly bordered block diagonal matrices in solving the linear equations after making the mass matrices doubly bordered block diagonal with numbering the coordinates in proper order.
Robust Adaptive Compensation for a Class of Nonlinear Systems
Authors: Du Hongliu , Nair Satish S.
Published: March 2022

This paper proposes design details pertaining to a robust adaptive method for the compensation of uncertainties, for a class of nonlinear systems. The adaptive part of the control law uses a Gaussian network and robustness is provided by a sliding mode term. In the design, learning and control bounds are guaranteed by properly constructing the control architecture for which some methods are proposed. The robust adaptive control strategy, with the proposed design guidelines, has been validated using a hardware example case of a nonlinear electromechanical system. Experiments have shown that the inclusion of the proposed stable learning and robust terms into the control design, using the proposed constructive methods, results in improved system performance.
Comparison of Two Finite-Element Schemes for Feedback Control of a Timoshenko Beam
Authors: Tadi M.
Published: March 2022

This note is concerned with the application of two finite element schemes for use in designing feedback control laws for a Timoshenko slewing beam. The equations are presented in an abstract first order form. Feedback laws are obtained in the context of LQR theory. The effectiveness of two different finite element schemes in obtaining convergent functional gains are compared.
Robust Performance Analysis of Vibration Isolation Tables Using Tree-Structured Transfer Functions
Authors: Wilson Bruce H. , Erin Cem
Published: March 2022

The coefficients of physically-based models are often only known within certain bounds. Such parameter uncertainty complicates the control design problem. As eliminating all uncertainty is not a realistic option, formulating the model so that its behavior over the entire uncertainty space is easily determined can facilitate design and analysis. The model form suggested in this paper is a tree-structured transfer function. Bond graph theory provides the means to synthesize a transfer function with this structure. Both tree-structured and conventional transfer functions of a vibration isolation table, with five uncertain parameters, have been synthesized, and the former simplified the robust analysis problem more than the latter. The tree-structured transfer functions allowed the response envelope to be easily determined over key frequency ranges. The advantages of tree-structured over conventional transfer functions demonstrated in this paper suggest that this alternate form may be better suited for both nominal and robust analysis.
Performance Maximization of Internal Combustion Engine Idle Speed Control via Actuator Saturation
Authors: Herman Paul , Franchek Matthew A.
Published: March 2022

Presented in this paper is the design and implementation of a saturating idle speed controller for a Ford V-8 fuel injected engine subjected to a torque load disturbance. The performance specification for the controller design is |Δrpm| ≤ 140 rpm where the controlled input is the by-pass air valve (BPAV). The controller design is realized using a frequency domain approach developed in Herman and Franchek (1997). An experimental verification of the controller is presented. The performance objective is satisfied using saturation control during the engine speed transients.
Lateral Control of Vehicles Using Non-Linear Sliding Surfaces
Authors: Saraf Sujit , Tomizuka Masayoshi
Published: March 2022

Lateral controllers for vehicles on automated highways are required to ensure small tracking errors even while providing a comfortable ride. In addition, they must be robust to changes in operating conditions and road-vehicle parameters. Sliding mode control has been successfully used to provide robust lateral control. However, such control usually has a high gain nature, often resulting in poor ride quality. The problems of tire and actuator saturation are also not addressed explicitly. This paper proposes the use of non-linear sliding surfaces for lateral control of road vehicles, to take advantage of the robustness of sliding mode control while avoiding the possible problems of ride discomfort and tire or actuator saturation. Simulation results are presented.
A Complete Fault Diagnostic System for Longitudinal Control of Automated Vehicles
Authors: Rajamani Rajesh , Hedrick J. Karl , Howell Adam
Published: March 2022

A complete system for fault diagnostics of the longitudinal controllers in a platoon of automated vehicles is developed. The diagnostic system is designed to provide automated monitoring and fault identification of all the sensors and actuators used in the longitudinal control system, including radar sensors and inter-vehicle communication. The system uses several reduced-order nonlinear observers constructed from a longitudinal dynamic model of the vehicle. Multiple estimates of signals are obtained by designing each observer to utilize a different sensor measurement. Different combinations of all the available sensor signals and the observer estimates are then processed to construct a bank of 10 different residues. We show analytically that a fault in any of the sensors or actuators creates a unique subset of these residues to grow so as to enable exact identification of the faulty component.

Simulation results are presented to demonstrate the working of the fault diagnostic system in the presence of various faults.
On the Development of Boundary Layers in Non-Newtonian Fluids
Authors: Rajagopal K. R.
Published: March 2022

Boundary layers, regions of concentration of vorticity, appear adjacent to boundaries in the flow of a linearly viscous fluid at high Reynolds numbers. When the equations governing the flow of the linearly viscous fluid are appropriately non-dimensionalized, we find that the inertial term is multiplied by the Reynolds number, and this term while it is the only non-linear term in the equation is of lower order than the highest order term in the equation usually leading to a singular perturbation problem at high Reynolds numbers. The study of boundary layers in such fluids has led to significant developments in singular perturbation theory.
Viscoelastic Free Surface Jets and Filaments
Authors: Bechtel S. E. , Cao J. G. , Forest M. G.
Published: March 2022

In this paper we examine the necessary versus self-consistent consequences of a slender aspect ratio on viscoelastic free surface jet flows. As in Schultz & Davis (1982), the equations of the 3-D free surface jet problem are nondimensionalized with presumed disparate length scales in the transverse and axial directions, and a perturbation theory for the slender jet is obtained by positing an expansion in the slenderness parameter (i.e. the ratio ε of these scales). A different perturbation problem ensues for each regime of free jet behavior. We exhibit three regimes, one in which the slenderness scaling of the 3-D free surface jet problem forces a separation-of-variables (s-o-v) structure of the solution (that is, the radial coordinate explicitly factors out at each order in ε), another in which the s-o-v structure is not forced but is a solution, and a third in which the s-o-v structure is not a solution. These three regimes are prototypes for general filament behavior: of the many possible regimes, many are of the first type (the separation of variables structure is unique), many more are of the second type (the separation of variables solution exists but cannot be shown to be unique), and the rest are of the third type (if a slender solution exists it does not have a s-o-v structure).
A Heuristic Approach to Model Viscosity in the Momentum Equations
Authors: Gingold Harry , Gera Dinesh
Published: March 2022

A new approach to model viscosity in the conservation of momentum equations is presented and discussed. Coefficient of viscosity is modeled in such a way that it reaches asymptotically to infinity at the solid boundary but still yields a finite value for the shear stress at the solid wall. Basic objective of this research is to show that certain combinations of higher order normal velocity gradients become zero at the solid boundary. Modified solutions for the couette flow and poiseuille flow between parallel plates are obtained by modeling the coefficient of viscosity in a novel way. Also, viscous drag computed by our model is expected to yield higher values than the values predicted by the existing models, which matches closely to the experimental data.
Pulsatile Blood Flow in a Stenosed Artery
Authors: Pontrelli Giuseppe , Pedrizzetti Gianni
Published: March 2022

Unsteady axisymmetric flow in a constricted tube is studied. A shear-thinning model for viscosity of the blood is proposed. The motion equation is written in vorticity-streamfunction formulation and is integrated numerically by a finite difference scheme. The dependence of the flow on the dimensionless parameters has been investigated and differences with the newtonian case are discussed.
Flow of Yield-Stress Fluids in Complex Geometries
Authors: Vradis George C.
Published: March 2022

Experimental and computational results related to the flow of purely viscous non-Newtonian fluids exhibiting a yield stress are presented and discussed. A number of geometries and flow conditions have been analyzed representing both attached and separated flows of Bingham and Herschel-Bulkley fluids. The presence of a yield-stress is shown to significantly impact the flow characteristics, as compared to those in the case of a Newtonian fluid, in particular in the cases where separation of the flow would be expected.
Pulsating Viscoelastic Flow in Tubes of Arbitrary Cross-Section Shapes
Authors: Letelier Mario F. , Siginer Dennis A.
Published: March 2022

The axial velocity field in a tube of arbitrary cross-section geometry is determined for the case in which a viscoelastic fluid obeys a constitutive law of the multiple-integral type.

The flow is linearized by means of a perturbation scheme for small amplirud oscillations of the pressure gradient. At the first order for the velocity, a solution is found for cross-section contours of a wide variaty of shapes. In this method the no-slip boundary condition is imposed in contours whose shape depends on an infinite set of arbitrary functions that can be selected according to some guiding rules. In this manner, the resulting cross-sections approach ellipses, triangles, squares and many other regular and non-regular shapes. The analysis shows that very complex flow patterns, as depicted by isovel curves, develop according to the values of the fluid parameters and the solid boundary shapes. These results are necessary for further developments leading to the study of secondary flows.

The paper presents the analytical formulations and the flow fields associated to several tube geometries and different values of the fluid parameters.
A New Approach for Thermal Fatigue Testing of the Underfill/Passivation Interface
Authors: Gurumurthy Charan K. , Jiao Jinbao , Norris Larry G. , Hui Chung-Yuen , Kramer Edward J.
Published: March 2022

Delamination of the underfill/passivation interface due to thermal fatigue is a major cause for failure of DCA assemblies. Hence, we have developed a new technique based on a non-contact fiber optic displacement sensor to investigate the crack growth rate per cycle da/dN of an interfacial crack under thermal fatigue conditions. The sample is prepared as a multilayered cantilever beam by capillary flow of the underfill over a polyimide coated metallic beam. During thermal cycling the crack growth along the interface from the free end changes the displacement of this end of the beam and we measure this displacement at the lowest temperature in each thermal cycle. The change in beam displacement is converted into crack growth knowing the geometry of the specimen. The crack growth rate depends on the maximum difference in the strain energy release rate of the crack in each cycle. This paper outlines the theoretical basis of the technique and provides initial results obtained for a commercial underfill dispensed over a commercial (PMDA/ODA) polyimide. The technique was validated by comparing the crack growth measured by displacement changes with direct optical microscopy measurements of the crack length.
Potential Failure Sites in a Flip-Chip Package With and Without Underfill
Authors: Madenci E. , Shkarayev S. , Mahajan R.
Published: March 2022

The thermal integrity of an electronic package depends on the strength of the interface between dissimilar materials. Due to high thermo-mechanical stress concentrations arising from large temperature excursions, electronic packages become prone to cracking at regions with geometric and/or material discontinuities. Thus, the accurate calculation of the thermo-mechanical stresses in regions of high stress concentrations is critical to achieving a reliable design. These high-stress-concentration regions pose a major concern, especially in the design of flip-chip packages. Understanding the mechanisms for relaxing the high stress concentrations through the use of appropriate material properties, bump and adhesive joint geometry, and filler size in a flip-chip package will aid in design improvements for ensuring the thermo-mechanical reliability of electronic packages.

In this study, the effect of underfill on the level of stress concentrations is investigated and possible failure sites are identified by using a global/local finite element approach. The global elements capture the exact singular behavior of the stresses near the geometric and material discontinuities. Potential failure sites are established by applying concepts from fracture mechanics.
A New Approach to Calculate Atomic Flux Divergence by Electromigration
Authors: Sasagawa Kazuhiko , Nakamura Naoaki , Saka Masumi , Abé Hiroyuki
Published: March 2022

The atomic flux divergence obtained from current density and temperature in metal lines undamaged by electromigration is useful to predict the formation of initial void. In this study, a new method to calculate the atomic flux divergence used for predicting the formation of initial void is proposed considering two-dimensional distributions of current density and temperature and also simply considering the line structure not only of polycrystalline line but also of bamboo line. The flux divergence is formulated based on the Huntington-Grone’s equation and modeling of line structure. For the verification, electromigration phenomenon near the corner of an angled polycrystalline line, which results in two-dimensional distributions of current density and temperature, is treated as an example. The usefulness of the proposed method is discussed by comparison of the prediction of void formation near the corner with the experimental result.
Toughening of High Performance Epoxy Adhesives Using Core-Shell Particles
Authors: Sue Hung-Jue , Puckett P. Mac , Wang Yee Y.
Published: March 2022

Epoxy adhesives are commonly toughened by carboxylic terminated butadiene nitrile (CTBN) rubber to improve the T-peel and Lap-shear strength of adhesives. Unfortunately, many key material properties, such as glass-transition temperature (Tg), Young’s modulus, thermal expansion coefficient, and processability, will be compromised if CTBN rubber is utilized for toughening. Furthermore, CTBN rubber has been shown to be ineffective in toughening high performance, highly crosslinked thermosets. Novel rubber toughening approaches have to be sought to overcome the above-mentioned problems.

The present work focuses on the use of a core-shell particle (CSP) technology, which is comprised of either a rubber core or a rigid plastic core and a shell that stabilizes the dispersion of particles in thermosets. The results indicate that the toughness can be greatly improved by introducing the CSP for toughening. No reduction in Tg is observed. The modulus of elasticity of the CSP-toughened epoxy systems can be maintained if the core of CSP being utilized is rigid. Furthermore, since the viscosity of the toughened epoxy only increases slightly, no compromise in processability is made. These CSP may be suitable for toughening highly filled thermosets for electronic applications.
Opportunities and Needs for Interfacial Fracture Mechanics in Microelectronic Packaging Industry
Authors: Chen William T. , Questad David , Read David , Sammakia Bahgat
Published: March 2022

This paper will review the trends for semiconductors, the impact on electronic products, and the requirements on electronic packaging materials, design, reliability and manufacturing. There is an increasing realization that materials and mechanics principles can be utilized to great advantage in electronic packaging industry. New electronic packages such as ball grid array modules (BGA), chip scale packages (CSP), MicroVia substrates, and low temperature solder bump assemblies, present interesting opportunities for the utilization of fracture mechanics principles in the analysis and modeling of those packages. This paper will present, from a packaging engineer’s perspective, the utilization of interfaial fracture mechanics in the packaging community. Particular emphasis will be on fracture mechanics applied to interfaces in an assembled packaging structure.
An Experimental and Numerical Analysis of Near Tip Behavior in a Multi-Phase Material
Authors: Liu C. T. , Ravichandran G.
Published: March 2022

In this paper, the local strain fields near the crack tip in a multi-phase material subjected to two different strain rates (0.05 min−1 and 0.25 min−1) at room temperature were analyzed, experiment-ally and numerically. Precracked specimens made from polybutadiene rubber embedded with hard particles were used in the crack propaga-tion tests. A grid method was used to obtain the strain fields near the crack tip and a nonlinear finite element computer code was used to determine the near tip strain fields. The results of analyses show that a good correlation exists between the experimental and the numerical results.
The Mechanics of Hydride Formation and Embrittlement
Authors: Lufrano J. , Sofronis P. , Birnbaum H. K.
Published: March 2022

Transient hydrogen diffusion and hydride formation coupled with material deformation are studied in a hydride forming system. The concept of terminal solid solubility of hydrogen as affected by stress is described and the mode of hydrogen diffusion through the two-phase material (matrix+hydride) is discussed. Probabilistic precipitation of hydride is modeled in the neighborhood of a crack tip under mode I plane strain loading and a uniform initial hydrogen concentration below the stress free terminal solid solubility. A full transient finite element analysis allows for numerical monitoring of the development and expansion of the hydride zone. Information about the shape, size, and density of the hydride in the hydride zone is obtained. The mechanistic effects of the solute hydrogen and hydride formation on the stresses at the crack tip are analyzed and their consequence on the fracture toughness resistance of the material is calculated.
Yield Strength of Nitrogen Alloyed Duplex Steels: Hall-Petch Analysis and Micromechanical Predictions
Authors: Werner E. A. , Horvath W. , Prantl W.
Published: March 2022

For the prediction of the yield strength of nitrogen alloyed ferritic-austenitic duplex steels, accurate knowledge on the single phases’ yield strength and their geometrical arrangement within the duplex microstructure is required. Since the matrix-inclusion character of the phases markedly influences the yield strength σyd of duplex steels, linear models for σyd (Voigt-model) cannot serve for an accurate prediction of σyd. A non-linear rule of mixture, however, is a more sophisticated approach to calculate σyd. Micromechanical models combined with finite element computations are efficient tools to accurately predict the influence of the topology of the microstructure on σyd only if the yield strengths of the single phases are distinctly different, i.e. the yield strength ratio of ferrite to austenite ψ is larger than 2. Experiments on duplex steels show, however, a marked influence of the phase arrangement on σyd even for ψ ∼ 1. To explain this behavior a modified non-linear rule of mixture is proposed, which incorporates the in-situ yield strengths of the phases as upper and lower bounds for σyd. The discrepancy between the experiments (and their analysis) and the predictions from the micromechanical approach convincingly demonstrates the necessity to include crystallographic details such as dislocation-interface boundary interactions and misorientation and crystal structures of adjacent grains in improved micromechanical models for the yield strength of duplex steel microstructures.
Measurement and Quantification of Surface Roughness
Authors: Dewhurst Timothy B. , Mason Scott D.
Published: March 2022

The development of surface roughness during underlying bulk deformation is of critical importance to some metalforming industries such as beverage can and automobile manufacturers. This work is investigating the correlation between surface roughness and texture evolution within the material. The first phase of this work has concentrated on the measurement of surface roughness in compression specimens; various approaches to identifying meaningful metrics to quantify this roughness; and the documentation of the deformation path and texture evolution during the process. In identifying an appropriate metric for surface roughness, the work has focused on the use of fractals, standard statistical measures, and power spectrums. Each of these is evaluated for use in this type of study as it will be necessary in the near future to have a reliable method of comparing the experimental results to computer modeling for surface roughness. In the second phase of this work, polycrystal plasticity models will be used to track both texture evolution and the development of surface roughness during the deformation process. The computational results will be closely compared to the experimental results presented here.
Sustained-Load Cracking in Mill Annealed Ti-6Al-4V at Room Temperature
Authors: Lenets Youri , Thomas James P. , Nicholas Theodore
Published: March 2022

Sustained-load crack growth in the near threshold regime was studied at room temperature in a mill-annealed Ti-6Al-4V titanium alloy forging using mini-C(T) specimens in the C-L orientation. The observed sustained-load cracking behavior exhibited an apparent crack length dependence beyond that accounted for by the fracture mechanics parameter K. In addition, the initial value of K, applied after crack extension by fatigue, influenced the subsequent crack growth rates. The influence of the far-field specimen stresses on the hydrogen diffusion process at the crack tip and transient crack growth rate effects appear to be responsible for the observed behavior.
Predicting the Precipitation Hardening Response of Particle Strengthened Alloys Hardened by Ordered Precipitates
Authors: Fragomeni James M. , Hillberry Ben M.
Published: March 2022

A model/method was developed for predicting the precipitation hardening response of particle strengthened alloys hardened by ordered precipitates based on the microstructure, composition, and heat treatment, and utilizing a minimum number of experimental tests. The overall approach was based on the dislocation particle interaction mechanics, particle growth and coarsening, thermodynamics, and particle strengthening mechanisms applicable to precipitation hardened alloys. The model/method evaluates, from a minimum number of experimental tensile tests, several of the microstructural constants necessary in determining the precipitation strengthening response of a particle strengthened alloy. The materials that were used as vehicles to demonstrate the model were precipitation hardenable aluminum-lithium-zirconium and nickel-aluminum alloys. Utilizing these demonstration alloys, the method used a minimum number of four tensile tests to predict the variation in strength with aging time, aging temperature, and composition, for the underaged, the peak-aged, and the overaged conditions. Predictions of the precipitation strengthening response were made using the Wagner particle distribution model and the predicted results using this distribution model compared well with the experimental yield strength results.