bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Penetrating Head Injury
Authors: Zhang Jiangyue , Yoganandan Narayan , Pintar Frank A. , Gennarelli Thomas A.
Published: May 2008

The objective of this study is to biomechanical quantify the intracranial displacement and pressure distributions associated with civilian projectiles to advance clinical understanding of the pathophysiological consequences of penetrating head injuries. A finite element head model was developed in an attempt to investigate the penetrating processes and brain injury mechanisms. Two geometrical shapes of projectiles (flat and pinpoint headed) were considered for penetration. They were modeled as rigid bodies (6.5 and 9 g) impacting at an initial velocity of 300 m/s. The head was modeled as a spherical skull with left and right hemispheres. Material properties and damage criteria for the skull and brain were based on literature. The penetration process was modeled with eroding contact surface method with LS-DYNA. Elements considered damaged were removed from further computation when the stress or strain reached their thresholds. Temporal displacement and pressure distributions are described. The effects of projectile type on the wounding pattern are discussed. The entry location responded with higher magnitudes of displacement than other locations (e.g., exit, mid brain). The flat head projectile penetration resulted in higher magnitudes of pressure and displacement than the pinpoint projectile in the entire skull-brain system. The finite element analysis provides a quantitative understanding of the localized intrinsic responses secondary to projectile penetration.
Optimization of Industrial Processes Involving Radiant Heating, Through Non-Linear Programming
Authors: Daun K. J. , Howell J. R. , Morton D. P.
Published: May 2008

Radiant enclosures are often used in manufacturing processes; examples include the rapid thermal processing of semiconductor wafers, automotive paint curing, and baking food products. In these processes, infrared radiant heaters are used to impose a specified temperature history on the product. In order to ensure the homogeneity of the final product and to avoid deformation due to thermal stresses, a uniform temperature must also be maintained over the entire product throughout the process. This paper presents an optimization methodology that determines the optimal transient heater settings by minimizing an objective function defined as the sum of the variance of the temperature from the desired temperature evaluated at discrete locations on the product surface, integrated throughout the duration of the process. The radiation heat transfer analysis is first carried out using an infinitesimal-area technique. The objective function is then minimized using a quasi-Newton method incorporating an active set method in order to enforce design constraints derived from the heater characteristics. This design methodology is demonstrated by solving two industrially-relevant design problems.
Residual Stresses in Self-Curing Bone Cement During Hip Arthroplasty
Authors: Li Chaodi , Wang Ying , Mason James J.
Published: May 2008

Bone cements are widely used to fix prostheses into bones for joint arthroplasty. During cement curing in total hip arthroplasty, residual stresses are introduced in the cement mantle. A finite element method was developed to predict such residual stress built-up. The effects of curing history on the residual stress distribution were investigated. Results showed that the predictions of the residual stresses agreed with the experimental tests very well. The residual stress build-up was shown to depend on the curing history. By preheating the prosthesis stem prior to implantation, a desired low level residual stress at the critical interface was obtained.
Enhancement of Air Cooling Limits for Telecom Heat Sink Applications Using Impinging Air Jets
Authors: Sansoucy Eric , Oosthuizen Patrick H. , Refai-Ahmed Gamal
Published: May 2008

A numerical study was carried out to investigate the heat transfer rate from a parallel flat plate heat sink under a turbulent impinging air jet. The target surface was confined by a horizontal nozzle plate. The jet was discharged from a sharpedged nozzle in the nozzle plate. The numerical model included the standard k-ε turbulence model. Average Nusselt numbers are reported for Pr = 0.7, 5000 ≤ Re ≤ 30000, L/d = 2.5 and 0.833 at H/d = 3 where L, H and d define the length of the square heat source, nozzle-to-target spacing and nozzle diameter, respectively. Enhancements of heat transfer rates, relative to the bare heat source, were found to vary from 1.9 to 3.5 and 4.1 to 12.0 in the presence of a base and a heat sink, respectively. The coefficient of enhancement was strongly dependent on the Re. The spacing H/d was also altered for L/d = 2.5 at Re = 30000. The enhancement in heat transfer due to the heat sink was shown to increase slightly with nozzle-to-target spacing. The Nusselt number was correlated in terms of Re, fluid properties and geometric parameters of the configuration.
“Reversible Macromolecules” as Scaffolds for Adaptive Structures
Authors: Long Timothy E. , Elkins Casey L. , Kilian Lars , Park Taigyoo , Trenor Scott R. , Yamauchi Koji , Colby Ralph H. , Leo Donald J. , Love Brian J.
Published: May 2008

Self-healing macromolecular structures, submicron capsules and fibers with molecular recognition, stimuliresponsive molecules, solvent-free rheological reversibility, multivalency in rational drug design, and the emergence of new fields of adaptive and evolutive chemistry will require a predictive synergy of tailored non-covalent and covalent bonding in molecular design. Supramolecular chemistry has emerged as a stimulating focal point that will enable these scientific and technological discoveries, and biorecognition and biomolecular organization often serve as the inspiration for the future design of supramolecular assemblies. Linear and branched macromolecules are conventionally prepared using unique combinations of step-growth and chain polymerization strategies wherein the repeating units are irreversibly connected using stable covalent bonds. Moreover, optimum physical properties and commercial success of macromolecules are derived from our ability to prepare exceptionally high molecular weights in a controlled fashion. Although high molecular weight linear macromolecules are desirable for the optimization of physical performance and commercial impact, high molecular weights often compromise future solvent-free manufacturing, melt processability, thermal stability, and recyclability of the final products. Our recent efforts have demonstrated the utility of living anionic polymerization techniques to place functionality at desired positions on the polymer backbone. This control allowed investigation of the relationship between topology and tailored functionality, a fundamental investigation that may lead to interesting adaptive and smart applications. Specifically, the synthesis of polyisoprene homopolymers in a variety of topologies was performed, as well as the introduction of complementary hydrogen bonding to diverse families of hydroxyl containing polymeric and monomeric precursors.
Effect of Anterior Cruciate Ligament Reconstruction With an Autologous Semitendinosus-Gracilis Graft on Neuromuscular Function
Authors: Williams Glenn N. , Barrance Peter J. , Snyder-Mackler Lynn , Buchanan Thomas S.
Published: May 2008

The quadrupled semitendinosus-gracilis (ST-G) graft is rapidly becoming the graft of choice for orthopaedic surgeons when reconstructing the anterior cruciate ligament (ACL). During this procedure orthopaedic surgeons harvest the distal semitendinosus and gracilis tendons and use them to replace the ruptured ACL. Although people who undergo this procedure have good functional outcomes over the short-term, we do not know the effect that harvesting these two tendons has on neuromuscular function. The purpose of this study was to examine the effect that ACL reconstruction with an autologous ST-G had on musculotendinous morphology. The methods used in the study included digital reconstruction of knee musculature from magnetic resonance images (MRI). Marked reductions in muscle volume, cross-sectional area, and length were observed in the semitendinosus and gracilis when reassessed approximately 6 months following surgery (after the subjects had returned to sports participation). The subjects appeared to compensate for the diminished medial knee flexor function with the biceps femoris (a lateral muscle) and semimembranosus muscles. These findings may have important implications for joint loading, the long term health of the knee, and surgical decision-making.
Adaptations for Controlled Hand Movements in Duchenne’s Muscular Dystrophy
Authors: Bowen Roscoe C. , Seliktar Rami , Rahman Tariq , Alexander Michael , Scavina Mena
Published: May 2008

A number of neuropathologies such as Duchenne’s muscular dystrophy (DMD), cause disability in the upper extremity due to the loss of muscle strength. This will eventually prevent the individual from moving their arms in three-dimensional space so it has been proposed that a robotic orthosis could support and augment movement. This orthosis would need to accommodate the movement capabilities of the user. To accomplish this, knowledge of how movements are formed and controlled in the presence of neuromuscular disease needs to be determined. While the arm was supported in a floatation device, DMD subjects were asked to make pointing movements to several targets in the transverse plane. This was done from two start positions while torso movement was constrained and unconstrained. The hand trajectories formed while the torso was constrained were essentially straight but at a cost to the uni-modality of the hand velocity profile. In this configuration the velocity profile contains several phases of acceleration and deceleration producing a multi-modal profile. However, the additional degrees of freedom introduced in the unconstrained torso configuration were employed is such a manner as to produce a smooth uni-modal hand velocity profile.
Glass Formation During Room Temperature, Isothermal Drying
Authors: Aksan Alptekin , Toner Mehmet
Published: May 2008

Isothermal drying and glass transition of solutions and films have drawn considerable attention from many industries. We here explore the feasibility of modifying the isothermal drying and vitrification kinetics of carbohydrate solutions in order to ensure the stability and quality of their ingredients. Modulated Differential Scanning Calorimetry experiments with isothermally dried trehalose and trehalose/dextran solutions were performed and the glass transition kinetics have been determined. Three distinct drying regimes were observed. With isothermal, isobaric drying at 0%RH, it was indeed possible to reach the glassy state for a trehalose and a trehalosedextran system. With the addition of high molecular weight sugars, the glass transitions of isothermally dried carbohydrate solutions can be accelerated as a function of dextran mass ratio in the sample.
The Effect of Position and Path Repeatability on Biomechanical Testing of Diarthrodial Joints
Authors: Darcy Shon P. , Gil Jorge E. , Woo Savio L.-Y. , Debski Richard E.
Published: May 2008

To improve surgical procedures and rehabilitation protocols for injuries to the anterior cruciate ligament (ACL), the function of the ACL and ACL graft during in vivo activities must be understood. Robotic manipulators with a payload less than 500 N (low-payload) have been used to study joint and ligament function during application of external loading conditions (Fujie, 1993; Fujie, 2000). Robotic manipulators with a payload capacity of at least 1500 N (high-payload) will be needed to simulate high joint contact forces that have been estimated to be between 2 to 5 times body weight (Morrison, 1970; Escamilla, 1998). However, there is a trade-off between payload capacity and position and path repeatability. The objective of this study was to determine the effect of position and path repeatability of two high-payload robotic manipulators, (KUKA™ KR210 and FANUC™ S900W) used to apply external loads to diarthrodial joints and determine the corresponding joint kinematics and forces in the soft tissue structures.
Strain Is the Major Factor for Chondrocyte Death in Articular Cartilage Under Static Load
Authors: Shah Amit K. , Yuan Li-Jen , Torzilli Peter A. , Chen C. T. Christopher
Published: May 2008

Several studies have shown that stress, strain, and stress/strain rate at certain levels can kill chondrocytes, but the major factor is unclear. The objective of this study was to determine the effects of strain and stress on chondrocyte death. Bovine cartilage explants (5 mm) at the age of 2 and 24 month were indented (3 mm) at 3.12, 6.25 and 12.5 MPa to reach a final strain of 15, 30, 45, 60 and 75%. Cell death in the center and on the edges of the indented region was assessed at 0, 3 and 7 days post-loading, and quantified using commercially available software. Our results showed cell death in the center region increased with strain (p<0.001) but decreased with age (p<0.001). Cell death at the edges of the indented region was greater than that of the center (p<0.001), and increased with strain (p<0.001). With post-load incubation, a decrease of cell death was found in the explant loaded with 60 and 75%. Cells with positive TUNEL-staining and positive M30-staining were consistently seen in the middle and deep zones in the center region 3 days after load removal. This suggests that two types of cell injury/death (necrosis and apoptosis) occur simultaneously. Linear regression and ANOVA suggest that strain is the major factor for chondrocyte death under static load.
Biomechanical Study of Rear Child Chest Injury Measures Related to Collapsing Front Seats in Rear Impacts
Authors: Saczalski Kenneth J. , Sances Anthony , Kumaresan Srirangam , Meyer Steve , Burton Joseph Lawson , Lewis Paul R.
Published: May 2008

Government recommendations have been made to place children into the rear seating areas of motor vehicles in order to alleviate airbag hazards in frontal impact. In most moderate to severe rear impacts, however, the adult occupied front seats will “yield” or “collapse” into the rear seat area and thus pose another potential head and chest injury hazard to the rear seated children. Numerous factors or variables, each with a wide parameter range, influence whether or not an occupied collapsing front seat will result in engagement with the rear occupant, and whether that engagement is likely to cause injury to the rear-seated occupant. A combined experimental and analytical method, employing instrumented surrogates in a sled-buck test set-up, has been utilized to study the multivariable potential injury problem of the rear-seated child in rear impact. A 3 year-old H-III surrogate, seated in the built-in booster seat of a minivan, was used as the rear seat passenger in this study. Five tests were utilized. The experimental surrogate data from the test method is combined into a “polynomial response function” that expresses “injury levels” (i.e. HIC and chest G) as a function of the many variables, and allows for analytical “interpolation and extrapolation” at variable combinations and ranges not tested. Actual accident cases were compared with the biomechanical injury measures. The present study presents a methodology to delineate the biomechanics of injuries using multivariate analysis.
Reproducing the Motion of a Diarthrodial Joint During a Clinical Examination Using Robotic Technology
Authors: Moore Susan M. , Thomas Maribeth , Gabriel Mary T. , Zeminski Jennifer , Woo Savio L.-Y. , Debski Richard E.
Published: May 2008

Six-degree-of-freedom (DOF) robotic/universal force-moment sensor (UFS) testing systems have become very useful tools in the study of biomechanics of joints. (DeFrate 2001, Fujie 2000, Rudy 1996) Researchers have successfully utilized these systems to determine joint kinematics using force control algorithms. Recent interest in using these robotic systems to reproduce previously recorded motions of a diarthrodial joint during a clinical examination has emerged. However, reproducing these previously recorded kinematics using a robotic/UFS testing system poses several problems.
An Experimental and Analytical Evaluation of the Nonlinear Viscoelastic Properties of the Healing Medial Collateral Ligament in a Goat Model
Authors: Abramowitch S. D. , Clineff T. D. , Debski R. E. , Woo S. L.-Y.
Published: May 2008

The medial collateral ligament (MCL) is one of the most frequently injured ligaments in the knee. Although it can heal spontaneously after rupture, laboratory studies have shown that the mechanical properties of the healing MCL remain inferior to normal for up to two years after injury (1). Additionally, the healing MCL has been shown to display increased amounts of stress relaxation and creep (2). In order to more completely describe the viscoelastic properties of healing ligaments, we propose to use the Quasi-Linear Viscoelastic (QLV) theory formulated by Fung (1972). This theory has been used to successfully describe the viscoelastic properties of many soft-tissues (3). Recently, our research center has developed an improved approach to determine the constants describing the QLV theory based on data collected from a stress relaxation experiment that utilizes a slow strain rate during loading. This approach allows for experimental errors that commonly result from fast strain rates to be avoided (ex. overshoot) (4). Therefore, the objective of this study were to use this new approach to determine the constants describing the quasi-linear viscoelastic behavior of the healing goat MCL at 12 weeks after injury.
In Vivo Bone Motion From High Frame Rate Stereo Radiography
Authors: Anderst William J. , Tashman Scott
Published: May 2008

This paper presents a method to calculate functional joint space during dynamic movement. This method combines high-speed biplane radiographic image data and three-dimensional (3D) bone surface data obtained from computed tomography (CT). Subjects were patients undergoing anterior cruciate ligament (ACL) reconstructive surgery. Three tantalum beads were implanted bilaterally into both the femur and tibia during surgery. CT scans were performed after bead implantation, and the CT slices were reconstructed into 3D solid figures, with the implanted beads identifiable within the stack of CT slices. Subjects were tested 6,12 and 24 months post surgery. Testing activities included downhill running on a treadmill and one-legged hopping onto a force plate. During testing, the stereo-radiographic imaging system collected images at 250 frames per second. Later, the implanted beads were identified in the x-ray images and tracked in 3D with an accuracy of 0.10 mm. The 3D bead location data were used to position the reconstructed solid bone figures in 3D space. In this way, the location of each bone surface was determined each instant. This method can be used to identify the regions of close contact between bones during dynamic motion, to calculate the surface area of subchondral bone within close contact, and to determine the changing position of the close contact area during dynamic activities. Using these techniques, comparisons can be made between subchondral bone motion in healthy and reconstructed joints and changes in dynamic joint space can be measured over time.
The Role of Blood Impulse in Cerebral Aneurysm Coil Compaction: Effect of Aneurysm Neck Size
Authors: Lieber Baruch B. , Sadasivan Chander , Gounis Matthew J. , Wakhloo Ajay K.
Published: May 2008

Endovascular occlusion of cerebral aneurysms with bare platinum detachable coils is now recognized as preferable to surgical clipping (ISUIA Group, 2003, ISAT Group, 2002, Bavinzski et al, 1995, Thornton et al, 2002). Dependent on coil packing density (the ratio of the coil volume deposited in an aneurysm to that of the aneurysm volume), aneurysm location, size and neck width, coil compaction with recanalization of the aneurysm remains in the long-term a major concern. The aneurysm neck size is reported to be the main predictor for aneurysm recanalization (Fernandez-Zubillaga et al, 1994). The forces exerted on the coil mass at the aneurysm neck due to blood pulsatility are larger for wide neck aneurysms as compared to small neck aneurysms (Bavinzski et al, 1995). However, impingement forces have not been evaluated. We evaluated the force impinging on the aneurysm neck in a simplified aneurysm (basilar top) geometry utilizing the impulse-momentum equation and Womersley’s flow. Maximum impingement force as a function of aneurysm neck to parent lumen diameter ratio varies as a sigmoid curve. Analysis of the hemodynamic forces affecting coil compaction in cerebral aneurysms shows that the coil mass at the aneurysm neck may be subjected to cyclic impulse impingement due to redirection of blood momentum. Orientation of the aneurysm neck and the main axis of the aneurysm in relation to the oncoming parent vessel flow may help clinicians predict the risk of coil compaction and the location of subsequent aneurysm recanalization.
Design and Evaluation of a System for Testing and Analysis of Rollovers With Narrow Objects
Authors: Meyer Steven E. , Herbst Brian , Forrest Stephen , Sances Anthony , Kumaresan Srirangam
Published: May 2008

Recent statistics highlight the significant risk of serious and fatal injuries to occupants involved in rollover collisions due to excessive roof crush. The government has reported that in 2002, Sports Utility Vehicle rollover related fatalities increased by 14% to more than 2400 annually. 61% of all SUV fatalities included rollovers. [1] Rollover crashes rely primarily upon the roof structures to maintain occupant survival space. Frequently these crashes occur off the travel lanes of the roadway and, therefore, can include impacts with various types of narrow objects such as light poles, utility poles and/or trees. A test device and methodology is presented which allows for dynamic, repeatable rollover impact evaluation of complete vehicle roof structures with such narrow objects. These tests allow for the incorporation of Anthropomorphic Test Dummies (ATDs) which can be instrumented to measure accelerations, forces and moments to evaluate injury potential. High-speed video allows for detailed analysis of occupant kinematics and evaluation of injury causation. Criteria such as restraint performance, injury potential, survival space and the effect of roof crush associated with various types of design alternatives, countermeasures and impact circumstances can also be evaluated. In addition to presentation of the methodology, two representative vehicle crash tests are also reported. Results indicated that the reinforced roof structure significantly reduced the roof deformation compared to the production roof structure.
Forces Induced by Peak Systolic Flows in Asymmetric Endovascular Grafts
Authors: Finol Ender A. , Amon Cristina H.
Published: May 2008

Endovascular repair (EVAR) has emerged as an alternative, less-invasive surgical technique for the treatment of patients diagnosed with abdominal aortic aneurysms (AAAs). The anatomical pathway of blood flow in the abdominal aorta is restored by the implantation of an endovascular graft (EVG), effectively depressurizing the aneurysm and initiating a remodeling process of the diseased aorta. The short-term results of endovascular grafting are promising, but its long-term success has been compromised by the occurrence of graft migration and detachment, which induce endoleaks or incomplete occlusion of the aneurysm from the blood circulation. The forces induced by the blood as it flows through the graft are believed to be a factor of probable cause in the partial detachment from its proximal and distal anchoring points and the migration of the graft downstream. The purpose of this study is to utilize analytical tools to provide an estimation of the forces required to secure the graft proximally when relying only on stresses induced by the flow.
Controlled Drug Releasing Intravitreal Implant Using Biodegradable PLGA
Authors: Park Juyoung , Melhem Murad , Pankaj Desai , Millard Ronald W. , Banerjee Rupak K.
Published: May 2008

The goal of this work is to compare the in vitro drug (Nimodipine) release rate from three different types (matrix, reservoir, and combination types) of intravitreal implants using a biodegradable polymer (PLGA). The matrix implants were prepared by a solvent cast method and the reservoir implants were fabricated by using a pellet press. The combination implants were a mixed type of matrix and reservoir implants. Each implant was placed in a vial with 7mL of Phosphate Buffered Saline (PBS) containing 0.4 g/L of Bovine Serum Albumin (BSA) and 0.5 mL aliquots were removed for the drug assay for 25 days. The sample was analyzed to determine the concentration using High Performance Liquid Chromatography (HPLC). Over 20 days, the average steady state release rate in vitro is 13.05±6.17, 2.66±1.98, 8.85±6.36 μg/day for matrix, reservoir, and combination implants, respectively.
Development of a Finite Element Model of the Inferior Glenohumeral Ligament of the Glenohumeral Joint
Authors: Newman William J. , Debski Richard E. , Moore Susan M. , Weiss Jeffrey A.
Published: May 2008

The shoulder is one of the most complex and often injured joints in the human body. The inferior glenohumeral ligament (IGHL), composed of the anterior band (AB), posterior band (PB) and the axillary pouch, has been shown to be an important contributor to anterior shoulder stability (Turkel, 1981). Injuries to the IGHL of the glenohumeral capsule are especially difficult to diagnose and treat effectively. The objective of this research was to develop a methodology for subject-specific finite element (FE) modeling of the ligamentous structures of the glenohumeral joint, specifically the IGHL, and to determine how changes in material properties affect predicted strains in the IGHL at 60° of external rotation. Using the techniques developed in this research, an improved understanding of the contribution of the IGHL to shoulder stability can be acquired.
Active Biaxial Mechanical Properties of Bladder Wall Tissue
Authors: Nagatomi Jiro , Chancellor Michael B. , Sacks Michael S.
Published: May 2008

The urinary bladder is a smooth muscle organ whose main functions are to store and to void urine. Since the most important aspect of the storage function of the bladder is to maintain low intravesical pressure in order to protect the upper urinary tract from backflow of urine, the compliance of the bladder wall is one of the key functional paramters to assess the health of this organ. Previously, our laboratory reported, for the first time, the biaxial mechanical properties of bladder wall tissue in the inactive state (in the absence of calcium in the testing bath solution and thus smooth muscle contraction was abolished) (Gloeckner et al. 2002). The bladder in vivo, however, normaly exhibits passive smooth muscle tone during filling and active contraction during voiding. Therefore, in order to completely characterize the bladder tissue mechanical behaviors, it is necessary to examine the load-deformation relationship of the bladder under the passive and active states. In the present study, a novel experimental model was designed to allow collection of biaxial stress-strain data from urinary bladder wall tissue under passive, active and inactive states.
Design of Gravity Balancing Leg Orthosis Using Non-Zero Free Length Springs
Authors: Agrawal Abhishek , Agrawal Sunil K.
Published: May 2008

For retraining stroke victims, there is a need for rehabilitation devices, which can support the weight of leg during walking. Machines that gravity balance the leg are potentially very useful. This paper presents gravity balancing designs using non-zero free length springs. These designs are further optimized for spring connection points and parameters of the spring such as free length and stiffness.
Natural Convection From a Pipe Buried in a Porous Medium With Variable Permeability
Authors: Ngo C. C. , Lai F. C.
Published: May 2008

Natural convection from a buried pipe with a layer of backfill is numerically examined in this study. The objective of the present study is to investigate how a change in the permeability of the backfill would affect the flow patterns and heat transfer results. Numerical calculations have covered a wide range of the governing parameters (i.e., 10 ≤ Ra1 ≤ 500 and 0.1 ≤ K1/K2 ≤ 10) for various backfill thicknesses (0.5 ≤ t/ri ≤ 2). The results suggest that a more permeable backfill can minimize the heat loss and confine the flow to a region close to the pipe.
Dynamic Postural Stability Testing During Standup Forklift (Lift Truck) Operation
Authors: Harris Gerald F. , DeRosia John
Published: May 2008

This paper investigates the threshold of dynamic postural stability during standup forklift (lift truck) operation. Through a series of controlled tests, live subject data is gathered to determine the effect of upper extremity support during acceleration perturbation of the forklift (standing platform). The level of perturbation causing loss of balance is in close agreement with earlier studies and supports the use of a door in a standup forklift to arrest loss of balance, falling and injury during routine standup forklift (lift truck) operation.
Optimization of Electrical Output in Response to Mechanical Input in Piezoceramic Laminated Shells
Authors: Danak Amita D. , Yoon Hwan-Sik , Washington Gregory N.
Published: May 2008

The piezoelectric ceramic, Lead Zirconate Titanate (PZT), is capable of producing large voltages in response to an applied mechanical stress when employed in a laminate manufactured using the THUNDER process. This study addresses the issue of optimizing mechanical parameters in a PZT unimorph to maximize charge generated due to mechanical strain. The PZT unimorph structure is initially curved and generates a surface charge when vertically loaded. In the analysis, the principles of shallow shell and linear piezoelectric laminate theories are employed to obtain an expression for charge in terms of geometry, material properties and loading. Analytical relationships are then derived that can be used to optimize the charge produced from these generators. Numerical parametric studies are then conducted to maximize the charge generation by manipulating dimensions of the components. Experimental results show a “convergence” to a theoretically predicted ‘applied force vs. deformation’ relationship when the PZT unimorph is subjected to a pressure load. Finally, a charge collecting circuitry for harvesting the charge produced is designed and presented.
Failure Prediction of Tubular Hydroforming Process Following Pre-Bending
Authors: Xia Z. C.
Published: May 2008

Tubular hydroforming process for a majority of automotive parts is a complex process where the initially straight tube undergoes a series of pre-bending, pre-forming, die closure and then the final pressurization. The pre-bending process is usually carried out by a rotary bending machine and utilizes an inside mandrel to prevent the tube from collapsing during bending. Because of the high pressure exerted by the mandrel in the normal direction of the tube sheet, the failure mechanism for the tube in the subsequent hydroforming process will differ significantly from that experienced in sheet metal stamping process, which can be well characterized by the Forming Limit Diagram (FLD). The presentation begins with experimental evidence of material failure during hydroforming following pre-bending, and continues with two predictive models for analysis. One is a Gurson-type void growth model, and the other a damage based model which takes into account the effect of hydrostatic pressure in damage growth. Numerical examples are given to illustrate the effectiveness of both models and are compared to experimental data. Their applicability in an industrial production environment is discussed.
Uncertainty Quantification in Models of Microfluid Systems
Authors: Najm Habib N. , Debusschere Bert J. , Knio Omar M. , Ghanem Roger R. , Matta Alain , Le Maiˆtre Olivier P.
Published: May 2008

Uncertainty quantification (UQ) in models of physical systems is a necessary tool for both model validation and engineering design optimization. We have applied UQ tools using stochastic spectral polynomial chaos techniques to the modeling of fluid flow in an electrokinetically driven microchannel, allowing for detailed buffer electrochemistry and finite rate analyte reactions. The model includes full coupling of wall electric double layer potential with variations in PH and local electric field. Allowing for uncertainties in species mobilities, buffer equilibrium constants, and wall properties, we have computed the resulting uncertainty in predicted model outputs, illustrating the impact of growth of uncertainty on confidence in model predictions. We present details of the computational UQ techniques with specific focus on their application in the electrochemical micro fluidic context. We also present UQ results pertaining to model protein labeling in an electokinetically-pumped microchannel flow.
Effect of Coupled Rotations on Knee Joint Ligament Forces Under Drawer Loads in Flexion
Authors: Moglo K. E. , Shirazi-Adl A.
Published: May 2008

A validated non-linear 3-D finite element model of human tibiofemoral joint was utilized to investigate the effect of constraint on tibial coupled internal-external and varus-valgus rotations on the passive joint response and force in ligaments under 100N drawer loads at different flexion angles. The model consisted of two bony structures and their articular cartilage layers, menisci and four principal ligaments. For the cruciate ligaments, the results showed that, in the fully unconstrained joint, ACL force decreased with flexion but remained as the primary ligament to resist the posterior femoral load throughout the range of flexion considered. A further significant decrease in ACL force with flexion angle was computed as the joint coupled rotations were constrained. As for PCL ligament, a minor contribution was at full extension under 100N anterior femoral load which further decreased as the coupled rotations were constrained. With joint flexion up to 90°, PCL force, however in contrast to ACL force, substantially increased in both constrained and unconstrained joints. Collateral ligaments, in the unconstrained joint at full extension, were the primary structures to resist the anterior femoral load but had negligible role in posterior-directed load. With joint flexion up to 90°, however, forces in collateral ligaments diminished. Similar trends were computed after fixing coupled tibial rotations with the exception of much greater LCL force and smaller MCL force at full extension under femoral anterior load and larger MCL force in flexion.
Current Challenges in the Control of Haptic Interfaces and Bilateral Teleoperation Systems
Authors: Speich John E. , O’Malley Marcia K.
Published: May 2008

This paper presents a survey of current research focused on the control of haptic interfaces and bilateral teleoperation sys tems. Time delay is a significant control issue, along with the closely related topic of control via the Internet. Ok key concern is the assurance of stability in the presence of constant or vari able time delay. The transparency of bilateral systems, or the extent to which they accurately represent the feel of the envi ronment to operator, is another important control concern. The stability and transparency of haptic interface systems is also a significant research area. This paper presents a survey of the current state-of-the-art with regard to control in haptics and bilateral teleoperation.
Influence of Geometry and Deformation on the Performance of Profiled Hydrosatic Thrust Bearings
Authors: Feng Jianpeng , Cherukuri Harish , Johnson Robert E. , Manring Noah
Published: May 2008

In a previous study, the authors investigated the effect of various thrust bearing profiles on the bearing performance and concluded that bearing performance is significantly influenced by the deformations resulting from lubrication film pressure. In the present work, results from a recent study on the effect of the interaction between the ball-joint and bearing on bearing deforma tion and hence, on bearing performance are reported. The motivation behind the study is to investigate the impact of raising or lowering the contact area between the ball-joint and bearing surface on bearing performance as this has the effect of influenceing the bearing deformation. Several designs involving various geometries of the bearing that affect the contact area are considered. The coupled fluid-solids problem is solved by using an iterative technique where the fluid problem is solved using the lubrication theory and the bearing deformation is analyzed by using the commercial FEA software ABAQUS standard. Results from the numerical simulations are compared with experimental results for the standard design of the bearing. The effect of varying the pocket width on the load carrying capacity of the bearing is also investigated.
Processing-Microstructure-Strength Predictions for Short Fiber Reinforced Composite Structures Based on a Spray Deposition Process
Authors: Siegmund Thomas , Wang Bo , Cipra Raymond , Liakus James
Published: May 2008

An approach to the prediction of strength of spray deposited composite structures is described. The work documented links manufacturing simulations, providing the fiber microstructure information, to a strength prediction formulation that can finally be incorporated into structural stress analysis.
Magnetorheological Hydraulic Actuator Driven by a Piezopump
Authors: Yoo Jin-Hyeong , Sirohi Jayant , Wereley Norman M. , Chopra Inderjit
Published: May 2008

Magnetorheological (MR) fluids can be used in a variety of smart semi-active systems. The MR damper shows an especially great potential to mitigate environmentally induced vibration and shocks. Another aspect of MR fluids is the construction of MR valve network in conjunction with a hydraulic pump resulting in a fully active actuator. These devices are simple, have few moving parts and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezopump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electromechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the actuator to achieve controllable damping. The design, construction and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, biviscous and Bingham-plastic representations of MR fluid behavior, and is evaluated with experimental measurements. This will provide a design tool to develop an actuator for a specific application.
Boron Carbide-Silicon Carbide Laminated Ceramics for Ballistic Protection
Authors: Orlovskaya N. , Adams J. , Chheda M. , Shih J. , Yarmolenko S. , Sankar J. , Lugovy M. , Subbotin V.
Published: May 2008

The paper describes the development of tough boron carbide-silicon carbide ceramic laminates with enhanced ballistic performance for armor application. Laminates with strong interfaces can provide high fracture toughness and damage tolerance along with improved ballistic protection. The enhancement of the mechanical/ballistic performance of laminates is obtained through design of controlled residual stresses in separate layers. The research produced a fundamental knowledge of the interrelationships between processing, residual stresses, and mechanical behavior of boron carbide based multilayered ceramic composites with an enhanced understanding of laminate’s fracture toughness, strength, and Young’s modulus. It was expected that the newly developed laminates would have necessary mechanical properties to increase maximum critical velocity of dwell/penetration transition during impact experiments.
Elevated Temperature Tensile Behavior of Nextel™ 720 Fibers
Authors: Pai D. M. , Yarmolenko S. N. , Freeman E. , Zawada L. P.
Published: May 2008

The tensile behavior of Nextel 720 fibers at elevated temperature was compared with room temperature results for both bare and monazite-coated fibers. While coated and uncoated fibers have nearly identical tensile strengths and Weibull moduli at room temperature, differences in response were seen at elevated temperature. Coated fibers tested at 1200°C were found to have a 40% drop in strength. Uncoated fibers at high temperature exhibited 55% less strength than at room temperature. However, the tensile strength distribution for uncoated fibers tested at high temperature exhibited two distinct populations, indicating two different failure mechanisms. One population showed a 50% drop while the other showed a 64% drop. The coating was thus found to have a protective effect in terms of short-duration high-temperature exposure. Further, the effect of soaking on strength was investigated by thermally soaking coated and uncoated fibers in air at 1200°C for 100 hours prior to tensile testing at elevated temperature. In this case, the long duration of thermal exposure appeared to eliminate the beneficial effects of the coating. Soaked fibers, both coated and uncoated, were found to have nearly identical strengths at 1200°C—a reduction of about 60%.
Mechanical Characterization of a Nanotube-Polyethylene Composite Material
Authors: Santare Michael H. , Tang Wenzhong , Novotny John E. , Advani Suresh G.
Published: May 2008

High-density polyethylene (HDPE) was used as the matrix material for a carbon nanotube (CNT) polymer composites. Multi-wall carbon nanotube composite films were fabricated using the melt processing method. Composite samples with 0%, 1%, 3% and 5% nanotube content by weight were tested. The mechanical properties of the films were measured by the small punch test and wear resistance was measured with a block-on-ring wear tester. Results show increases in the stiffness, peak load, work-to-failure and wear resistance with increasing nanotube content.
The Application of Computational Fluid Dynamics to Define a Relationship Between Wall Shear Stress and Pseudointima Formation Within a Porous ePTFE Graft Implanted Within a Baboon
Authors: Costello James R. , Chen Changyi , Giddens Don P. , Hanson Stephen R.
Published: May 2008

Local hemodynamics and wall shear stress (WSS) impact healing of implanted expanded polytetrafluoroethylene (ePTFE) vascular grafts. Since adverse outcomes occur shortly after implantation, we documented the effect of local hemodynamics on short-term healing. We implanted a control or a stenotic ePTFE graft with a 60 μm internodal porosity into the abdominal aorta of 15–20 kg juvenile male baboons. At one month we harvested all grafts using in situ pressure perfusion. We interrogated the local hemodynamics with aid of computational fluid dynamics. We constructed three different geometric grids of the vascular grafts. We defined the first grid based on the material specifications of the graft material. We constructed the second grid by outlining the contours of the graft from the sectioned and stained histologic slides. Lastly, we created the third grid by capturing the graft contours from axial sections of the in vivo grafts acquired with a 1.5 T Phillips® MRI. Using volumetric flow rate and PC-MRI data, we performed steady state and pulsatile simulations. We then correlated the calculated wall shear stress and the measured pseudointima formation. The results demonstrated that high wall shear stress fails to inhibit intimal thickening during short term graft healing.
High Authority Morphing Structures
Authors: Bart-Smith Hilary , Risseeuw Philip E.
Published: May 2008

Recent advances in actuation technology and multifunctional materials have presented a unique opportunity to develop structures that have the ability to morph to a variety of shapes while under significant load constraints. One of the many applications of these “high-authority” systems is for morphing air wings for control and drag reduction. The exciting solution to this is the creation of a statically determinate structure that incorporates linear actuators to produce morphing capabilities. Statically determinate structures satisfy Maxwell’s necessary condition that the number of member forces equal the number of joint equilibrium equations. By imposing this condition on the structure it is possible to actively change the shape of the overall structure without resulting in failure. In a morphing foil, the only induced strain within passive members will be due to the hydrodynamic forces present. Deformation of the truss members is stretch-dominated—they do not experience bending—and thus improve the load carrying capacity of the structure. Of primary interest are Shape Memory Alloy (SMAs) actuators. SMAs are useful for shape morphing concepts where large forces are needed. A prototypical foil has been built around a statically determinate structure that incorporates linear actuators to produce morphing capabilities. These “smart” foils have been tested in a wind tunnel to examine their drag reduction capabilities.
An Intelligent Numerical Simulation Environment on Component-Based Models: Part I
Authors: Deng Weiwen , Gu Edward Y. L.
Published: May 2008

This paper mainly discusses numerical simulation on a component-based model, in which a large complex dynamic system is presumably partitioned into and modeled by a number of interconnected components, which often corresponds to the physical nature in the real world. An independent component computation (ICC) method is proposed to deal numerically with component-based models. With ICC method, each component model is numerically solved independently of, and concurrently with others. This method, combined with the object-oriented methodology and expert system technology, leads to an intelligent numerical simulation environment, which is presented in detail in Part II.
A Mass Transport Model for CVD Coating of Optical Fibers
Authors: Huang Wei , Chiu Wilson K. S.
Published: May 2008

Carbon coated optical fibers are produced by the chemical vapor deposition process which includes multi-species mass transport with chemical reactions. A proper numerical model of this process will help elucidate the basic mechanisms and optimize the process to improve coating quality. A heat transfer model has been developed in our research group. We are now developing an applicable chemical kinetics model to include mass transport with gas phase and surface reactions. Several different chemical reactor models have been tried, including a continuous-stirred tank reactor (CSTR) model, a plug flow reactor (PFR) model and a multi-component diffusion model with the Maxwell-Stefan approximations. We found that in reactor conditions with well-mixed or large mass Peclet number, the CSTR and PFR models validate well with experimental results. But a multi-component gas diffusion model is needed for low mass Peclet number conditions. The model has been extended to a wider range of temperatures necessary for this optical fiber coating process.
Opportunities and Challenges in Mesoforming
Authors: Cao Jian , Wang Zhong , Krishnan Neil , Swanson Anthony Michael
Published: May 2008

In the last ten years, miniaturization technologies have revolutionized product design and have lead to many innovative applications in the automotive industry, healthcare, environmental monitoring, industrial processing, energy consumption, defense, etc. Here, the current state-of-the-art in mesoforming (forming of metals in the scale of 0.1 mm to several millimeters) is reviewed, followed by our preliminary investigation of one mesoforming example.