bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Methods for Performance Evaluation of Actively Controlled Structures
Authors: Akpan Unyime O. , Orisamolu I. R. (Wally)
Published: March 2022

Active Structures have significant practical applications in areas such as vibration, noise and shape control. In recent times, several studies on modeling of the response and control of these structural systems have been undertaken. Most of these studies use deterministic procedures for designing the required active control systems, with the underlying assumption that the design parameters are accurately known. However, for most practical situations, the values of the design parameters are not known exactly and must therefore be treated as random variables. Parametric uncertainties can degrade the performance of an otherwise well designed control system, sometimes leading to instability. In this paper probabilistic models for evaluating the performance of actively controlled structures is presented. A closed loop damping ratio formulation is proposed for the determination of the probability of instability for such structures in the presence of real parameter uncertainties. Furthermore, a probabilistic model for evaluating the performance robustness of actively controlled systems in terms of margin of stability is developed. Advanced probabilistic reliability analysis algorithms namely the first order reliability methods (FORM) and the second order reliability methods (SORM) are used for the estimation of robustness. A comparison of estimates of the probabilistic stability robustness from the proposed closed loop damping ratio formulation and the eigenvalue model which has been employed in recent studies (Field, 1996; Spencer 1992) is undertaken. It is shown that both procedures yield the same result. However, the novel technique has the added advantage of computational efficiency for FORM and SORM applications. Furthermore, it is shown that for the class of controllers considered in this study, robustness estimates from FORM is adequate for meaningful engineering decisions. Sensitivities of the controlled structure stability robustness to uncertainties in model parameters is evaluated using the novel approach.
Single Actuator and Multi-Mode Acceleration Feedback Control
Authors: Bayon de Noyer Maxime P. , Hanagud Sathya V.
Published: March 2022

The objective of the paper is to develop a vibration control design procedure that uses a single actuator to suppress vibrations in many structural modes simultaneously by using acceleration feedback controllers. In this paper, a new technique, based on the cross-over point design, has been developed to compute the compensator parameters to achieve the objective. This new technique has been validated by both experimental studies and simulation studies. The new design procedure has also been compared experimentally and analytically to previous design of acceleration feedback controllers by using the critically damped compensators. Then, experimental and analytical investigations are directed to control more than one mode with a single actuator. This is demonstrated by using piezoceramic wafer actuators and an accelerometer sensor on a beam structure.
Both Fall Direction and Muscle Activation Level Influence Likelihood of Hip Fracture in Falls
Authors: Sabick Michelle B. , Goel Vijay K. , Hay James G. , Banks Scott A.
Published: March 2022

An optimal body position at impact increased the force needed to cause structural yielding in the femur during a fall by up to 280%. Falls which resulted in impact on the posterolateral aspect of the greater trochanter or buttocks were the most likely to result in hip fracture. Decreasing the muscular activation level from tense to relaxed led to a 6% decrease in peak impact force. We recommend that, to be most effective, hip pads be placed on the posterolateral aspect of the greater trochanter. In addition, seniors at risk of hip fracture should be taught to relax their bodies once the onset of a fall is detected, if possible. Both interventions are effective in reducing the peak force experienced at impact.
A Transducer for the Dynamic Measurement of Neural-Space Occlusion in the Spine
Authors: Raynak Geoffrey C. , Nuckley David J. , Ching Randal P. , Tencer Allan F.
Published: March 2022

Spinal injury can be the most devastating of all orthopaedic trauma because of the critical role the spine plays in protecting the neural elements. Geometric changes to the bony foramen designed to accommodate these elements are likely the best predictors of potential neurologic injury [1,2]. Previous experiments have demonstrated poor correlation between post-traumatic and dynamic measurements of spinal canal occlusion taken during impact — with peak transient occlusion levels typically greater than those observed post-injury [3]. Others have hypothesized that mechanical trauma may trigger a cascading sequence of events leading to neurologic damage [4]. Hence, in contrast to post-traumatic measurements, we believe that dynamic measurement of neural-space occlusion during injury may provide better insight into the initiation of these events.
The Influence of Surfactant Physicochemical Properties on Pulmonary Interfacial Flow Analogues
Authors: Gaver Donald P. , Krueger Melissa A. , Ghadiali Samir N.
Published: March 2022

Many of the lung’s mechanical properties are influenced by pulmonary surfactant physicochemical characteristics. Pulmonary surfactant is a complex lipid-protein mixture formed in the type II alveolar cells and secreted into the alveolar subphase [1]. These substances reduce the surface tension at the air-liquid interface of the lining fluid that coats the interior of the lung. At sufficiently high concentrations, pulmonary surfactant reduces the surface tension to near zero and. in the process, stabilizes the alveoli and small airways [2–4].
Effect of Dynamic Glutaraldehyde Crosslinking on the Biomechanics of Pericardium Xenograft Tissue
Authors: Duncan Anthony C. , Boughner Derek
Published: March 2022

Bovine pericardium was fixed under dynamic conditions, low pressures (< 4mmHg) and low vibration rates (1.2 Hz) in a 0.5 % glutaraldehyde solution. After fixation, tensile testing (i.e. relaxation and stress-strain curves) was performed at low (3 mm/s) and high extension rates similar to physiological rates (30 mm/s i.e. 15 000% min−1).
Molecular Mechanisms of Monocyte Adhesion to Cytokine Stimulated Endothelial Cells Under Physiological Flow Conditions
Authors: Kukreti Sharad , McIntire Larry V. , Smith C. Wayne
Published: March 2022

This study investigates the underlying mechansisms of monocyte adhesion to both short term (IL-1β, 4 hr) and long term (IL-4, 24 hr) activated endothelial cells. At a wall shear stress of 2 dynes/cm2, monocytes appear to use multiple pathways for primary and secondary adhesion to IL-1β, 4 hr stimulated endothelial cells. However, on IL-4 24 hr stimulated HUVECs, VLA-4/VCAM-1 was the dominant mechanism for monocyte adhesion. Upon additional histamine exposure of IL-4, 24 hr treated endothelial cells, both P-selectin and VLA-4 were involved and had to blocked simultaneously to abolish monocyte adhesion. A combination of IL-1+IL-4 (24 hr) treatment resulted in a complete loss of the primary adhesive mechanism under flow conditions whereas secondary adhesion remained intact as indicated by static experiments.
Computational Mechanics of Blood Flow and Arterial Wall Interactions: Effect of Wall Mechanical Properties
Authors: Yamaguchi Takami , Kobayashi Takuji
Published: March 2022

The whole atherogenetic process should be considered as a net result of biological, chemical and mechanical interactions between the blood flow and the arterial wall. As common in all three types of interactions, they have several different time scales. Even in the context of wall mechanical responses, we should distinguish very short term, in other words, pure mechanical responses from intermediate and long term responses involving chemical and biological processes, which are results of an accumulation of the former. In our previous reports[1–2], the fluid motion and the wall motion in models of the arterial stenosis and the abdominal aneurysm with thick deformable walls was computed. In the present study, we are interested in some intermediate process in which the arterial wall changes its mechanical properties, and computed the fluid-wall interactions with different stiffness of the lesion.
Experimental Measurement of Cartilage Interstitial Fluid Pressurization Under Confined Compression Stress-Relaxation
Authors: Soltz Michael A. , Ateshian Gerard A.
Published: March 2022

Articular cartilage is an excellent bearing material able to withstand high loading pressures and experience little wear for nearly 70 to 80 years. Many investigators have suggested that these remarkable properties stem partly from the pressurization of cartilage interstitial fluid during joint loading (e.g., [1,8]). Indeed, theoretical analyses of biphasic or poroelastic cartilage contact have demonstrated that upward of 90% of the contact load may be supported by interstitial fluid pressurization (e.g., [1,6,7]). However, direct experimental verification of these theoretical findings has been difficult to achieve and few studies have reported direct measurements of cartilage interstitial fluid pressure [2,3]. Thus, the objectives of this study are to measure both the fluid pressure and total load acting at the cartilage contact interface, to determine the fraction of load supported by interstitial fluid pressurization as a function of time [3], and to compare this result with the biphasic theory for cartilage [9]. These objectives are achieved by testing cartilage cylindrical plugs under confined compression stress-relaxation.
Simulating Soft Tissue With a Tactile Shape Display
Authors: Pawluk Dianne T. V. , Peine William J. , Wellman Parris S. , Howe Robert D.
Published: March 2022

One of a surgeon’s most important tools is a highly developed sense of touch. Surgeons rely on sensations from the fingertips to guide manipulation and to perceive a wide variety of anatomical structures and pathologies. One important property used to assess the health of organs and tissues is compliance, which surgeons normally obtain by squeezing or indenting with their fingers.
Accelerometric/Encoder System and Method to Determine Kinematic Parameters During Stationary Holonomic Exercise
Authors: Figueroa Fernando , Shackelford Linda , Haw Chee Wee
Published: March 2022

A novel method and system to determine angular accelerations, angular velocities, and angular positions of the thigh and calf has been developed. Measurements are taken during stationary bicycle exercise. The approach considers only two dimensional motion (sagital plain). The kinematic parameters are obtained based on acceleration measurements from two two-dimmensional accelerometers fixed to each member (calf and thigh). The method is unique in that it does not perform integration to arrive to angular positions, thus avoiding buildup of errors associated with integration. Tests were performed using simulated data. An error analysis was performed. The system’s expected maximum error is approximately 2° in the calf position for a bicycling speed of one cycle per second.
Friction Properties at Polyethylene-Metal Interface in Total Joint Arthroplasty
Authors: Hashemi A. , Dammak M. , Shirazi-Adl A. , Zukor D. J.
Published: March 2022

Ultra high molecular weight polyethylene (UHMWPE) is currently used in artificial joints as the best polymer for bearing against metallic counterparts. It has a low coefficient of friction, a good resistance against wear, and a high toughness. In recent years however, the suitability of this material has been questioned due to the association between implant loosening by osteolysis in the joint vicinity and polyethylene debris. Friction characteristics at polyethylene-prosthesis articular interface influence the state of stress at and around articular regions and consequently the extent of surface damage and wear of both materials in contact. In this investigation, following our earlier bone-implant friction studies [1–3], uni- and bi-directional friction properties of polyethylene-metal interface are measured under different contact pressures and two conditions of wet and dry.
A Relationship Between Frontal Plane Geometry and Contact Stress Distribution in a UHMWPE of a TKR Component
Authors: Natarajan R. N. , Beard B. J. , Andriacchi T. P.
Published: March 2022

Permanent deformation in the Ultra High Molecular Weight Polyethylene tibial component has been reported in more than 60% of retrieved components (T.Wright 1968). Under conditions of elastic and plastic deformation, the femoral condyle can penetrate into the polyethylene component such that the smaller contact radii existing at the edges of the primary contact radii in the frontal plane can come into contact with the polyethylene surface (Figure 1). Under these conditions Hertzian contact theory or finite element models that do not include both elastic and plastic deformation would not apply. The aim of this study was (1) to calculate the penetration of the femoral condyle into the polyethylene component as a function of the frontal plane radii, and (2) to predict the altered contact stress distribution in the polyethylene component under conditions where penetration exceeds the primary bearing surface.
Touch Feedback Using Binary Tactor Displays: Unexpected Results and Insights
Authors: Murray Anne M. , Klatzky Roberta L. , Shimoga Karun B. , Khosla Pradeep K.
Published: March 2022

Most researchers support the idea that touch feedback should enhance a human operator’s ability to manipulate remote or virtual objects. In this paper, we discuss an experiment we conducted to demonstrate quantitatively the usefulness of touch feedback for a pick-and-place manipulation task in a dexterous telemanipulation environment. We also examine how the actuation threshold for our binary, low-frequency vibrotactile touch feedback system affects an operator’s performance.

The results are not what we originally expected. When direct visual feedback was provided, there was no marked improvement in task performance as measured by task completion time, number of errors committed, mean grip force, and maximum grip force when using binary touch feedback. Analysis suggests that when a human operator had good visual confirmation of the grasp, as the subjects did in this experiment, the visual feedback dominated the binary touch feedback. We believe this dominance was due, in part, to the characteristics of the touch feedback: it was binary, providing less information than the visual feedback, and there were longer delays in receiving the touch stimuli than the visual information.
Designing Haptic Interfaces for Teleoperational and Virtual Environments: Should Spatially Distributed Forces Be Displayed to the Fingertip?
Authors: Lederman Susan J. , Klatzky Roberta L.
Published: March 2022

The current study evaluated the role of spatially distributed fingertip forces in the performance of a set of sensory (force detection, spatial acuity, vibrotactile detection) and perceptual (roughness perception, 2D edge orientation, and 3D lump detection via fingertip palpation) tasks. Vision was not permitted. Each task was performed with and without spatially distributed, fingertip-force information. The elimination of such spatial cues substantially impaired performance of all but the vibrotactile-detection and roughness-perception tasks. Despite some decline in roughness perception, subjects were still able to perform related tasks reasonably well. The results offer scientific support for incorporating spatially distributed, fingertip force information in the design of dextrous haptic interfaces.
The Programming of a Telemanipulator With the Force-Cube
Authors: Schaude Horst F. , Dillmann Rüdiger
Published: March 2022

While programming a telemanipulator the operator often uses special input devices to generate trajectories, which are to difficult for automatic planers. Though the trajectories are evaluated by a simulation and shown on a graphical animation, it is much faster to give the operator direct haptic feedback if a collision will occur while executing the trajectory. To combine the haptic feedback with an intuitive input device, we have developed the ForceCube. The input parameters are separated in three translational and three rotational values. They are matched on three orthogonal sides of a cube in such way, that their axes correspond to their counterparts in the real word. Each of the axes can be blocked in one direction. With this feature it is possible to move the manipulator with contact in one direction and without any constraints in the other directions. The ForceCube is integrated in the teleoperation system TelOS developed at the Institute for Real-Time Computing and Robotics.
Vibrotactile Feedback for Industrial Telemanipulators
Authors: Dennerlein Jack Tigh , Millman Paul A. , Howe Robert D.
Published: March 2022

Industrial applications of haptic feedback systems that add dexterity to telemanipulators have been limited due to their complexity, low reliability, and high cost. A promising and attractive alternative technology for industry is vibrotactile feedback. These systems are simple and can be added at low cost to existing telerobotic systems to provide robust contact information. We have developed a single channel prototype vibrotactile sensor and display system for a high capacity deep sea remote manipulator, the Schilling Robotic Systems TITAN-II. The vibration sensor consists of a pair of steel plates machined to fit inside the gripper jaws. Embedded between the plates are piezoelectric film strips molded into a rugged silicone rubber layer. Impact and frequency response tests indicate the sensor is durable to the extreme loading and sensitive to a large range of vibration frequencies of the industrial setting. Tests of the prototype system on the TITAN-II again proved the sensor to be rugged and durable while also being sensitive. In informal tests, operators found the system enhanced operation of the robot.
A Holonomic Omnidirectional Wheelchair With Augmented Stability Using a Reconfigurable Footprint Mechanism
Authors: Wada Masayoshi , Asada Haruhiko H.
Published: March 2022

A novel wheelchair moving platform with varying wheelbase and tread is designed and built. The width of wheelchairs for residential use is limited to the width of standard doorways which the wheelchair must go through. Yet the wheelchair must have an enough stability margin although the patient’s mass centroid may significantly change. In this paper, a new mechanism for varying the footprint of a four-wheeled omnidirectional wheelchair is presented. The chair is mounted on a moving platform with four ball wheels allowing for holonomic, omnidirectional motion. Two pairs of ball wheels at the diagonal positions of the chassis are fixed, respectively, to two beams that intersect at the pivotal point in the middle. The angle between the two beams crossing at the pivotal point is varied actively so that the ratio of the wheelbase to the tread can be varied. Four independent servomotors driving the four ball wheels allow the wheelchair to move along three axes, i.e. x, y, and ϕ, and change the footprint at the same time. The footprint configuration is controlled based on the measurement of the mass centroid position in such a way that the mass centroid can be kept within the footprint at all times. First the concept of the reconfigurable footprint mechanism is described, and its kinematic and static behavior is analyzed, followed by the control design for augmenting the vehicle stability. A prototype wheelchair platform is designed, built, and tested.
A Two Dimensional Dynamic Model Simulation of Human Knee Joint
Authors: Türkay O. S. , Küçük H. , Akgün I. , Aydingöz Ö. , Aşkar G. Altay , Dökmeci M. C.
Published: March 2022

A two dimensional dynamic model of the human knee joint is improved by employing more realistic bone profiles and ligament models. The knee model consists of a fixed rigid femur and a moving rigid tibia connected by the fiber tissues. The two articulating surfaces are represented by polynomial equations. The knee joint ligaments are modeled as nonlinear springs with a linear-parabolic operating region which is considered to be a more representative model. The nonlinear differential equations of motion constrained by geometrical nonlinear algebraic equations are solved numerically to simulate the knee dynamics under external pulse forcing. The flexion and extension motions, and the effects of pulse direction and ligaments insertion coordinates on the ligaments tension and point contact forces are discussed.
Robust Control of a Differentially Steered Wheeled Mobile Robot
Authors: Zhang Yulin , Hong Daehie , Velinsky Steven A.
Published: March 2022

This paper presents a robust control algorithm for exponentially stable tracking control of a differentially steered Wheeled Mobile Robot (WMR). The exponential tracking property is guaranteed with kinematic uncertainties, such as wheel slippage and radius errors. The control algorithm has been designed for use in a WMR which is being specifically developed for applications in highway maintenance and construction. For such applications, the uncertainties arise due to the road surface conditions and the high loads encountered (both inertial and tool forces). However, the system under development is equipped with a two dimensional cable extension transducer which has been proven to be a rugged and accurate position measurement system (Hong, et al., 1995), so that the robust control algorithm developed is suitable and ensures good tracking performance. The algorithm is applicable to any differentially steered WMRs provided that accurate position measurement is available. The efficiency of the robust control algorithm is illustrated with numerical simulations.
Modeling and Control of a 2-Dimensional Overhead Crane
Authors: Lee Ho-Hoon
Published: March 2022

In this paper, a trolley-axis-based swing angle description is proposed for a 2-dimensional overhead crane, and then a new nonlinear dynamic model for the crane is derived based on the proposed swing angle description. The dynamic model is equivalent to that for 3-link flexible robots having only the first flexible mode. Furthermore, when the model is linearized around the vertical stable equilibrium, it becomes decoupled and symmetric with respect to the travel and traverse axes of the crane. From this result, a decoupled feedback control method is proposed based on the linearized model via the loop shaping and the root locus methods. Theoretical and experimental results show that the proposed control method guarantees not only fast damping of load swing but also accurate control of trolley position with sufficient damping for the 2-dimensional motion of the crane.
A Simulation Study of the Workspace and Dexterity of a Stewart Platform Based Machine Tool
Authors: Saxena Vivek , Liu Dongming , Daniel Cecil M. , Sutherland John W.
Published: March 2022

A machine tool based on a Stewart platform structure has many inherent advantages. These include: six degree of freedom, low mass and high structural rigidity. However, a good understanding of the kinematics of the structure is required for successful implementation of such a machine tool. Two attributes of a Stewart platform based machine tool — the workspace and dexterity are investigated in this work. The workspace is analyzed using a point discretization method in which discrete points are checked by the inverse kinematic solution of the Stewart Platform. The workspace thus obtained is presented graphically for various positions and orientations of the end effector. The dexterity of the workspace is studied by calculating the condition number for each discrete point. The results of the workspace and dexterity study are explained. The plots of workspace and dexterity may be used in the design stage for efficient utilization of the available workspace for a given machining operation.
Modeling of a 5-Speed Automatic Transmission for Shift-Quality Control
Authors: Lee Je-Kee , Peng Huei , Park Yeong-Il
Published: March 2022

The shift quality control of a 5-speed automatic transmission (A/T) is studied in this paper. The major technical challenge arises from the fact that the gear ratios of both gearsets may have to change simultaneously, which requires precise coordination. For the particular A/T studied in this paper, this “swap shift” occurs during second to third gear upshift. The dynamic equations during this 2-to-3 upshift are derived using the lever analogy technique. A nonlinear programming problem is then formulated to compute the optimal shift control algorithm, which strikes a balance between smoothness and shift time.
Vehicle Lateral Control on Automated Highways: A Backstepping Approach
Authors: Chen Chieh , Tomizuka Masayoshi
Published: March 2022

A backstepping controller is designed for lateral guidance of the passenger car in automated highway systems. In this design, the vehicle lateral tracking error is viewed as the output regulated by the relative yaw angle of the car with respect to the road centerline, and the relative yaw angle is controlled by the vehicle’s front wheel steering angle. The closed loop performance of lateral and yaw dynamics can be specified and guaranteed simultaneously in this approach. A smooth road model is used in calculating the feedforward part of the steering command. Nonlinear position feedback, which acts as low gain control at small tracking errors and high gain control at larger tracking errors, is introduced to compromise between passenger ride comfort and tracking accuracy. Simulation results conducted on the complex vehicle model show the effectiveness of the backstepping design approach.
Robust and Gain Scheduled H∞ Controllers for Lateral Guidance of Passenger Vehicles in AHS
Authors: Hingwe Pushkar , Tomizuka Masayoshi
Published: March 2022

This paper presents two lateral control designs for passenger vehicles in the Automated Highway System (AHS). The control designs are a natural combination of input-output linearization technique and the H∞ control design techniques. Input-output linearization in the context of steering angle as the input and lateral error at a certain point on the vehicle as the output is the first design step. Even though this form is amenable to robust control techniques such as the Sliding Mode Control, there is insufficient, damping of the yaw dynamics, especially at high longitudinal velocities. The damping of the yaw dynamics is improved by adding an outer feed back loop based on the H∞ control techniques.
A Hybrid Semiactive Control for Secondary Suspension Applications
Authors: Ahmadian Mehdi
Published: March 2022

The performance of semiactive “skyhook” dampers for secondary suspensions is compared with passive dampers, using a single suspension model. The simulation results indicate that, compared to passive suspensions, semiactive skyhook dampers provide a more favorable control of the dynamic resonance without decreasing the isolation effectiveness of the suspension. Further, it is shown that skyhook dampers provide a better control of one body at the expense of less control of the other body. An alternative semiactive control policy, called “hybrid control,” is introduced to provide a better control of both the bodies that the suspension connects together. The hybrid control can be implemented using the same hardware commonly used for the existing semiactive dampers.
On Ultrasound High Frequency Linear Viscoelasticity
Authors: Giordano Michele , Astarita Gianni
Published: March 2022

An elementary analysis of wave propagation in viscoelastic materials is presented. Data on linear viscoelasticity obtained with ultrasound high frequency wave excitation are reviewed in this light. It is concluded that such data seem to indicate that a), propagation of very high frequency waves is dominated by a viscous mechanism; and b), values of the complex propagation modulus M* do not lie on any reasonable extrapolation of the mechanical G* data. Possible interpretations of these results are discussed.
Boundary Conditions for Electro-Magneto-Hydrodynamics
Authors: Dulikravich George S. , Jing Youhao
Published: March 2022

A general mathematical model of characteristic and non-reflecting boundary conditions for a system of partial differential equations governing unified Electro-Magneto-Hydrodynamic (EMHD) flows is developed. The novelty of this work is that it includes effects of linear polarization and magnetization of the media. A formulation using characteristic wave relations at the boundaries is derived for the extended Maxwell’s equations and the extended Navier-Stokes equations so that it can be used to specify inflow and outflow free boundary conditions. The emphasis is on using recent theoretical results on well-posedness of boundary conditions for standard Navier-Stokes and Maxwell’s equations to construct a systematic method for specifying the physical and numerical boundary conditions for electro-magneto-hydrodynamics. The formulation is fully three-dimensional and suitable for direct numerical implementation. The results show strong influence of electric and magnetic fields on fluid flow characteristics.
Vibration-Assisted Liquid Composite Molding: Practical and Numerical Simulation
Authors: Ayorinde Emmanuel O. , Gibson Ronald F. , Deng Feihua , Baig Bakhtiar
Published: March 2022

Vibration assistance in the process of liquid composite molding (LCM), a relatively new concept, is investigated in this paper. A non-Newtonian resin simulator fluid (1% polyacrylamide/water solution) is injected with vibration assistance into a simulator mold, with pre-placed actual (industrial) pre-form. Mold filling under various conditions is investigated.

An analytical model based on the control volume finite element representation is constructed for the process. A comparison of the experimental and computational results showed good agreement. Effects of the presence of the preform, the damping of the input vibration in the mold space, and how it is affected by various parameters are investigated.
Nondestructive Elastic Property Characterization of IC Encapsulants
Authors: Canumalla Sridhar , Oravecz Michael G.
Published: March 2022

The elastic properties of IC packaging materials (molding compounds and underfills) are measured nondestructively, over a microscopic area, in this study. The first application involves determining the engineering moduli of molding compounds (MP8000CH, MP190ML, 6300HA and 7320) from a nondestructive measurement of ultrasonic velocities. The second application involves the characterization of processing flaws in flip-chip packages to a) unambiguously identify delaminations (or voids) from resin rich areas, and b) quantitatively estimate the relative change in filler content. Concomitant changes in elastic properties of the underfill are also determined. Regions of filler segregation, exhibiting a lower impedance of about 3.9 MRayl (26% lower) are estimated to have a Young’s modulus of 7 GPa (50% lower) and a CTE of 41 x 10-6/°C (57% higher than the base material). Techniques presented in this paper have potential application in advanced process control, yield management and in analysis of package reliability.
Adhesion and Reliability of Polymer/Inorganic Interfaces in Microelectronic Applications
Authors: Snodgrass J. M. , Kook S.-Y. , Kirtikar A. , Dauskardt R. H.
Published: March 2022

The reliability of microelectronic components is profoundly influenced by the interfacial fracture resistance (adhesion) and resistance to progressive debonding of interfaces. In this study we examine the interfacial fracture properties of representative polymer interfaces commonly found in microelectronic applications. Specifically, interface fracture mechanics techniques are described to characterize adhesion and progressive debonding behavior of a polymer/metal interface under cyclic fatigue loading. Cyclic fatigue debond-growth rates were measured from ∼10−10 to 10−6 m/cycle and found to display a power-law dependence on the applied strain energy release rate range, ΔG. Fracture toughness test results show that the interfaces typically exhibit resistance-curve behavior, with a plateau interface fracture resistance, Gss, strongly dependent on the interface morphology and the thickness of the polymer layer. The effect of a chemical adhesion promoter on the fracture energy of a polymer/silicon interface was also characterized. Micromechanisms controlling interfacial adhesion and progressive debonding are discussed in terms of the prevailing deformation mechanisms and related to interface structure and morphology.
Die Strength Evaluation in the Presence of Edge Cracks
Authors: Leung Betty , Guo Yifan , Sarihan Vijay
Published: March 2022

Achieving a reliable package requires ensuring the reliability of each of its components and their interconnections. In practice, die strength is adversely affected when dies undergo various manufacturing processes. High stresses are also induced when dies are subject to conditions such as testing, handling, and operation. Die reliability depends on processed die strength under possible stress conditions. Existing information on the die strength is limited to what is known about perfect, unprocessed silicon. The accurate measure of the strength of processed dies is achieved through evaluation of the real component. This work focuses on the comparative analysis of test methodologies and the effects of processing. Characterization of actual die defects dies, primarily due to processing, is followed by experimentation utilizing a system designed at Motorola’s AISL specifically for the testing of small dies. Failure analysis of fractured dies reveals the effects of different test methods and the roots of die fracture. Coupling the experimental data from this work with predicted stress results produced through finite element analysis, a measure of the adequacy of a die’s strength for a given package can be made, providing valuable information for purposes of package reliability and enhancement.
Strain Localization in Single Crystals: Thermodynamic Consideration
Authors: Le Khanh Chau
Published: March 2022

This paper presents a model describing strain localization in single crystals. Constitutive relations for slip systems axe proposed within the framework of thermodynamics. A generalized Schmid law is formulated in terms of the Eshelby stress tensor. The strain localization is found to be possible when the hardening rate for active slip systems has fallen to a certain critical positive value hcr. The latter is determined for double active slip systems. A comparison with corresponding results available in the literature is provided.
Nondestructive Evaluation of Fiberglass Reinforced Plastic Subjected to Localized Heat Damage, Using Acoustic Emission
Authors: Nayeb-Hashemi H. , Kisnomo P. , Saniei N.
Published: March 2022

Fiberglass reinforced composites are extensively used in electronic and aerospace applications due to their high specific strength. In these applications, they are often subjected to localized heat damage due to various sources such as electronic over heating, electric arching, and laser beams. In order to ensure their reliability, it is important to predict their residual properties using nondestructive evaluation techniques.

Unidirectional fiberglass composite specimens were manufactured using three layers of a fiber glass prepreg. Some of the specimens were subjected to a localized heat damage using a heated copper tip with a diameter of 12.5 mm at 360° C and other specimens were subjected to a laser beam operated at 0.64 Watts/mm2 for various exposure time. In addition, the number of laser damaged spots varied among similar specimens. The specimens were then subjected to tension tests while acoustic emission activities of specimens were collected.

The AE activity of all specimens showed three distinct regions. An early activity, followed by a relatively dormant activity period and a high exponential activity before final failure. The period of the dormant activity was independent of the contact heat duration of less than 15 minutes. However, the dormant period for the laser damaged specimens was a function of the number of laser damaged spots. The majority of the early activities for all specimens were related to mechanisms other than fiber fracture. The activity in the dormant period for contact heat damage was mainly controlled by the fiber fracture, while for the undamaged and laser damaged specimens was by the interfacial failure. This could be justified since laser damaged specimens contained numerous damaged fibers leading to a significant interfacial shear stress. The failure modes of specimens further supported this conclusion.

The state of the damage in the composite was predicted using the AE-stress delay concept.
On Dynamic Modeling of Multi-Link Spatial Manipulators With Flexible Links and Joints
Authors: Farid Mehrdad , Lukasiewicz Stanislaw A.
Published: March 2022

A redundant Lagrangian/finite element approach is proposed to model the dynamics of lightweight spatial manipulators with both flexible links and joints. The links are assumed to be deformable due to bending and torsion. The elastic deformations of each link are expressed in its tangential (clamped free) local floating frame. The constraint equations due to the connectivity of the links are added to the equations of motion of the system by using Lagrange multipliers. The resulting mixed set of nonlinear differential equations and algebraic equations (DAEs) is solved numerically to predict the dynamic behavior of the system. The dynamic model derived here is free from the assumption of a nominal motion and takes into account not only the coupling effects between the rigid body motion and the elastic deformations of the links, but also the interaction between flexible links and actuated flexible joints.
Coupled Oscillations of Spherical Gas Bubbles
Authors: Jang Young J. , King Melvin E.
Published: March 2022

The dynamics of several (two, three and four) interacting spherical gas bubbles are investigated using the method of multiple scale. Numerical solutions for the steady-state amplitudes and phases of systems of two and four bubbles are presented. An interesting phenomenon observed is that of nonlinear localization, wherein vibrational energy becomes spatially localized to a single bubble (strong localization) or to a subset of bubbles (weak localization). Moreover, it is shown that the spatially extended motion (wherein all bubbles oscillate with identical amplitudes and phases, which one would obtain based upon a linearized analysis) is unstable, and thus not physically realizable, for certain separation distances.
A Nonlinear Wear Model
Authors: Nielsen Jakob Birkedal
Published: March 2022

A nonlinear wear model for a cylinder rolling over a periodically varying surface is derived from the theory of half spaces. The model describes how some irregularities on the surface are amplified whereas others are levelled out as the number of cylinder passages increases. This is a pure nonlinear contact mechanical effect independent of the dynamic response of the cylinder and the support. The aim of the present work is to demonstrate, that these nonlinearities, which often are neglected in models for wheel/rail interaction, play an important role in the evolution of corrugation of rails.
A NUCARS Investigation of the Effect of Pedestal Liner Compliance on Rail Vehicle Hunting
Authors: Ahmadian Mehdi
Published: March 2022

The effect of pedestal liner compliance on rail vehicle hunting is investigated using a NUCARS simulation model of a heavy freight locomotive. The need for the pedestal liners, as well as some of the existing designs, is discussed. A new design for pedestal liners is recommended to improve the critical hunting speed of the railway vehicles. Different possible arrangements for the recommended design are also presented. Further, a NUCARS simulation model of a three-axle locomotive is used to show that the new design can significantly increase the critical hunting speed, without adversely affecting the curving performance of the vehicle.
On the Virtues of Steerable Locomotive Bogies
Authors: Ahmadian Mehdi
Published: March 2022

An overview of steerable bogies (or trucks) for railway vehicles is provided, along with their potential benefits to railroad operations. Some of the common designs for steerable bogies are reviewed. A NUCARS simulation model is used to compare a three-axle steerable and straight bogie in terms of their curving dynamics in 7.5- and 10-degree curves. The simulation results show that steerable bogies have a substantially lower axle angle of attack and wheel/rail lateral force. Further, the benefits of steerable bogies in terms of increased operational efficiency to the railroads are discussed.
Evaluation of Process Control During On-Line Consolidation of Thermoplastic Composites
Authors: Pistor Christoph M. , Yardımcı M. Atıf , Castro Raoul , Güçeri Selçuk I.
Published: March 2022

Laser assisted tape winding is a manufacturing technique to produce thermoplastic composite parts of high quality. It is an additive semi-freeform fabrication process that utilizes thermoplastic composite prepreg tape as the base material. The tape is fused by the heat delivered from a laser beam, while it is wound onto a cylindrical mandrel. To ensure proper consolidation to the substrate, a roller applies the necessary compaction pressure.

The fabrication of high quality rings with circular (Beyeler, 1988 and Irwin, 1994) and non-circular (Pistor et al. 1995) shape using quarter inch wide prepreg tape (PPS/Carbon, PEEK/Carbon) has been successfully demonstrated. The shape of the beam utilized in these investigations was determined by a series of lenses that formed the circular beam of the CO2 laser into a vertical narrow ellipse approximately 6.4 mm high and 2 mm wide (Pistor et al., 1995). The area illuminated by the infrared laser was therefore preset and not adjustable, limiting the set-up to the processing of quarter inch wide tape.

One of the advantages of using a laser beam for the consolidation of thermoplastic resins is the that extremely high heat trnsfer rates to the resin are possible. This can be exploited not only for laser power adjustments in response to variations in tape laying velocity (Pistor et al., 1995), but also for scanning of a circular beam spot over the desired consolidation area. For the described set-up, a vertical slit of adjustable height was realized by scanning the laser beam vertically with a frequency of 100–500 Hz. Scanning height and frequency as well as motion and laser power are computer controllable.
Characterizing the Microstructure of Fused Deposition Polymer Components
Authors: Rodríguez José F. , Thomas James P. , Renaud John E.
Published: March 2022

The speed and accuracy with which Fused Deposition (FD) ABS plastic components can be made gives this rapid-prototyping technology unique potential as a new method for manufacturing complex structural components. Quantitative relationships between the FD process variables and the resulting mechanical properties are needed for intelligent manufacture of polymer components with tailored strength properties. This work examined the influence of the process variables on the resulting microstructure (void and interface bond length densities) of two configurations with uniaxial fiber orientation. The results showed the void and interface densities to be strongly dependent on the fiber-to-fiber gap and extrusion flow rate settings; the influence of extrusion and envelope temperatures is much smaller. The skewed fiber configuration exhibited the lowest void density but also the lowest interface density values. However, the difference observed in the values for the interface density were not as big as for the case of the void density. An investigation of the influence of the process variables on the interface bond strengths and the tensile behavior of pre- and post-extruded fibers as a function of loading rate and test temperature is in progress.
Densification in Heterogeneous Powder Mixtures by Creep
Authors: Zavaliangos Antonios
Published: March 2022

Successful preparation of functionally gradient materials by powder metallurgy requires usually the application of external pressure. Therefore the densification of two component mixtures under pressure needs to be understood. In this paper we study the densification of a two phase powder mixture with the two constituents deforming by power law creep. A theoretical framework is presented and various aspects of the model are discussed.
Observation and Prediction of Damage Evolution in Continuous Fiber Titanium Matrix Composites
Authors: Allen David H. , Foulk James W. , Helms Kayleen L. E.
Published: March 2022

Titanium matrix composites (TMC’s) are known to undergo significant environmental degradation at elevated temperatures. As a part of this research effort the TMC SCS-6/Ti-ß21S [0]4 has been fatigue tested at 482°C and 650°C. Additional specimens have been oxidized at 700°C and then fatigued at 482°C to failure. The life limiting physical mechanisms identified from the experiments are material inelasticity, surface embrittlement and subsequent surface cracking, fiber/matrix debonding, fiber-bridging, and eventual fiber failure.

A model incorporating all of these physical phenomena has been developed in an ongoing effort by the authors. This model will be briefly presented herein. The model utilizes the finite element method coupled with models for material inelasticity, surface embrittlement. and crack propagation. Material inelasticity is predicted using Bodner’s unified viscoplastic model. Crack propagation is modeled via the inclusion of cohesive zone elements. Surface embrittlement is accounted for through the degradation of material properties. Both monotonic and fatigue loadings have been modeled at 482°C and 650°C for oxidized and unoxidized specimens. Results indicate that surface crack propagation rates are significantly slower when matrix viscoplasticity is included in the model instead of elasticity. Furthermore, surface cracking in degraded specimens enhances fiber stresses compared to undegraded specimens. This difference apparently causes premature failure of the degraded composite.
Material Modeling for Cross-Ply Ceramic Matrix Laminates With Progressive Damages and Environmental Degradation
Authors: Yen Chian-Fong , Jones Mark L.
Published: March 2022

A physically-based damage model has been developed to predict the nonlinear behavior of cross-ply ceramic matrix laminates due to progressive failures. It has been shown to model the nonlinear stress-strain response of chemical vapor infiltrated (CVI) SiC/SiC composites under tension loading accurately. This model utilizes a consistent set of measurable material parameters as inputs and shows good agreement with measured tensile stress-strain curves for a variety of ply thickness ratios. The material model is also utilized to characterize the environmentally induced property degradation in CMC’s.
Failure Mechanisms in Off-Axis and Angle-Ply Fiber Reinforced Ceramic Composites
Authors: Selvarathinam A. S. , Weitsman Y. J.
Published: March 2022

Continuous fiber reinforced ceramic composites (CFCC) consist of brittle ceramic matrix (ϵum ≈ 0.15%) reinforced by relatively ductile ceramic fibers (ϵuf ≈ 1.1%), with intentionally weak interfaces. This combination of material properties enhances the ductility of the CFCC in the fiber direction.