bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating Center-of-Pressure Based Parameters to Quantify Athlete and Non-Athlete Balance
Authors: Thompson Lara A. , Badache Mehdi 
Published: February 2017

Through ground reaction (foot) forceplate-based, center-of-pressure (COP) parameters, we aimed to investigate differences in standing balance for young, healthy individuals from both athlete (soccer) and non-athlete subject populations. We investigated five, COP displacement and velocity parameters derived from the COP position time series. Soccer athlete and non-athlete subjects performed standing balance for postural tasks of increasing difficulty levels, by varying visual cues (eyes-open/eyes-closed) and base of support (wide/tandem foot placement), leading to four test conditions: 1) wide/eyes-open, 2) wide/eyes-closed, 3) tandem/eyes-open, 4) tandem/eyes-closed.
By investigating position and velocity characteristics of the COP position time series, we observed that the soccer athletes had generally lower COP displacement and velocity parameters (meaning they were more stable and perhaps better able to control their body sway) than the non-athletes. This study lends new insights as to how parameters derived from the COP position can be utilized to determine differences in balance between normal subject populations (e.g., athletes versus non-athletes).
Is the Maturation of Arteriovenous Fistulas a Mechanical or Biological Problem?
Authors: Jodko Daniel , Obidowski Damian , Reorowicz Piotr , Jozwik Krzysztof 
Published: February 2017

During the maturation the high pressure blood from the artery inflows directly to the vein, extends its diameter, and finally the blood flow rate in the vein is even 500-times greater than normal one. The changes of the wall shear stress (WSS) in the vein are thought to play a key role in the remodelling of its wall. However, this process is still not well understood. The aim of this paper is to show an innovative approach for modelling of the vein deformation during the maturation process of a-v fistulas. Dilation of the vein was modelled as two-step complex biomechanical process.
The obtained results concerning final diameter of the vein are compared with average diameter obtained for large group of patients. Moreover, this study shows the changes in the flow rate and the WSS that occur after maturation in the patient-specific fistula.
Development of a Microfabricated Sensor System to Measure Lumbar Spinal Fusion
Authors: Munro Deborah S. , Tsai Eric C. , Lingley Andrew R. , Khbeis Michael T. 
Published: February 2017

Lumbar spinal fusion surgery continues to experience major growth in the United States and worldwide. The surgery is performed by implanting spinal rods and screws within an incision on the lumbar region of the spine. This implanted hardware provides the initial mechanical stiffness until the morselized bone and bone growth factors generate new bone and can provide long term fixation. After surgery, development of the fusion is evaluated with radiographs, but determination of this fusion takes many months as the bone must first mineralize. The early stages are not visible on radiographs; however, this non-mineralized bone does provide substantial mechanical stiffness that could be measured with a sensor. As the spine moves and flexes, it creates a bending moment in the spinal rod, which could be measured as a strain. When initially implanted, this rod would experience its peak strain, but this would decrease as the bone shared some of the load. By periodically sampling the strain with a sensor, a curve could be generated that showed the overall progress of the fusion.
To maximize the output signal, an interdigitated capacitor design was implemented as the most effective way to maximize the capacitance measurement. A design using 51 free-standing, interdigitated fingers resulted in 50 parallel plate capacitors. The interdigitated capacitor was connected to a Low-Z Amplifier circuit and attached to a spinal rod. The rod was then flexed to simulate spinal bending, and the capacitance changed as expected under physiological loads.
Analysis of Preload Loss With Corrosion Protection Layers in the Flow of Force
Authors: Isele D. , Friedrich C. , Isele A. 
Published: February 2017

This contribution investigates the tightening behavior and preload loss of bolted joints with painted coating systems for corrosion protection of components. Friction coefficients are measured with test stand, preload loss is measured by strain gauges. Further evaluation is done with optical roughness measurement to see damage of the painted surfaces in contact areas. Resulting from this hints for applications get obvious. Research progress focuses the quantification of preload loss in different applications. Mechanical loads are neglected at that stage because of minor influence as the temperature.
To sum up, it can be formulated that the tested, robust coating systems can endure yield-point-tightening of high-strength screws and also exist as a complete and coherent layer after the loosening. Therefore corrosion protection could be guaranteed also after a yield-point-tightening, especially underneath the screw head. This is in particular relevant for applications which require repeated tightening of the same screw.
Corrosion protection layers within the flow of force usually change the friction coefficients compared with bare material. This effect influences the assembly of bolted connections dominantly. Controlling the assembly process is getting more difficult because of the increasing scattering from steering parameters, like torque or angle. There might be huge deviations, up to a factor of 6.2, between torque values of a similar assembly process. Therefore process safety cannot be guaranteed, especially if their values miss originally defined tolerances.
To overcome these difficulties it is necessary to use the right assembly method as well as the right coating system. After our opinion the yield-point controlled tightening is the only method which leads to a safe assembly preload, even with coated parts. If the preload loss will be acceptable depends on the coating system and the external conditions.
Design of a Highly Loaded Turbine Exit Case Airfoil With Active Flow Control
Authors: Kurz Julia , Hoeger Martin , Niehuis Reinhard 
Published: February 2017

In this paper a design process of a highly loaded profile for a turbine exit case (TEC) application is described. The profile has an increased pitch to chord ratio which is approximately 50% higher compared to conventional airfoils. For the design of the airfoil a two-dimensional (2D) computational fluid dynamics (CFD) prediction method was used in addition to in-house design rules and low Reynolds number experience from previous experiments. Furthermore, common knowledge from turbine and compressor design as well as turbine exit guide vane studies was evaluated and taken as basis for the new design.
To verify the highly loaded design, the profile was tested over a wide Reynolds number range in the high speed cascade wind tunnel of the Institute of Jet Propulsion (ISA) at the University of the German armed forces in Munich.
The experiments showed a very good agreement between the CFD predictions and the measurements for high Reynolds numbers. In the low Reynolds number regime the tendency to massive flow separation was slightly underestimated by the CFD predictions. It is particularly challenging as the CFD predictions still have problems to calculate open separation bubbles. Active flow control (AFC) by fluidic oscillators was also part of the design process and successfully applied on the profile.
Gait-Monitoring Wearable Technology for Transtibial Prosthetics
Authors: Hebert Kolby V. , Keen Rachel S. , King Derek R. , Shady Sally F. 
Published: February 2017

Approximately 40,000 transtibial amputations occur each year in the United States. Current lower leg prosthetic options range from passive artificial limbs to computerized electronic models [1]. Because of insurance limitations, most patients use less sophisticated prosthetics. The average cost of lower leg prosthetics and corresponding medical care for single-leg veterans is at least $1.4 million due to increased rehabilitation times [1]. Gait training methods for transtibial amputees include extended rehabilitation processes lasting up to 9 months. These exercises provide no empirical data to analyze patient gait progress.
The device design is a wearable technology that acquires gait information that is evidentiary for physicians when deciding to continue or dismiss further rehabilitation and follow up medical appointments. The technology includes a gyroscope, accelerometer, microprocessor, and electronic components housed in a 3D printed casing that is attachable to any prosthetic, or a biological leg. Pressure sensors are embedded into a sock-like foot covering that is used in tandem with the other electronics.
Gait data collection was validated by comparing gait parameter values with literature values. A series of control tests on non-amputees was conducted in order to gather standard data and develop consistent testing practices for the prototype design. These findings are used as a reference when evaluating amputee gait data against non-amputee gait data.
As the microprocessor collects data, information is stored onto a memory card used to relay data to the developed program for data analysis. Data analysis is supported by a graphical user interface via LabView which provides valuable gait data to physicians and physical therapists. Gait data analysis is expected to result in asymmetrical patterns for below-the-knee amputees compared to non-amputees as well as abnormal pressure loads throughout the foot [1].
Experimental Investigation on Liquid Infiltration Speed in Liquid Nanofoam
Authors: Li Mingzhe , Lu Weiyi 
Published: February 2017

Liquid nanofoam (LN) as a novel material for energy absorption applications exhibits superior properties, including high energy absorption efficiency, ultra-fast energy dissipation, light weight and small size, over existing options. It is a liquid suspension of nanoporous particles, whose nanopore surface is non-wettable to the liquid molecules. Past studies on LN have focused on quasi-static responses, and the actual system performance under dynamic loadings has remained unclear. In this study, the mechanical behavior of two types of LN samples at various strain rates and the liquid flow speed in the nanopores have been experimentally investigated.
The quasi-static behavior of LN is rigorously characterized by an Instron 5982 universal tester, from which we find that large amount of energy is dissipated into heat due to the effective excess solid-liquid interfacial tension, and confirm that the energy absorption efficiency of the LN is determined by the liquid infiltration pressure and the total deformability.
The dynamic behavior of the LN is investigated by impacting it with a lab-customized drop tower apparatus at intermediate strain rates (around 102 s−1), from which the measured strain-stress curves are highly hysteretic. By comparing with the quasi-static sorption isotherm curve, we show that the liquid infiltration pressure as well as the total deformability of the LN sample in liquid marble form is not affected by the increased strain rate. This suggests that the dynamic behavior of LN can be characterized by quasi-static compressive tests.
In the dynamic tests, the ultra-fast energy dissipation rate of LN indicates that the real liquid flow speed in nanopores is much higher than that predicted by the continuum theory. The flow speed can be directly measured from the strain rate by considering the total surface area of the nanoporous particles exposed to the liquid phase. The flow speed is related to the external remote pressure and the 3D porous structure of nanoporous particles.
We have examined for the first time the dynamic behaviors of LN, and demonstrated the energy absorption capacity of LN can be activated at desired pressure range by virtue of the strain rate-independent liquid infiltration behavior. This is the first experimental approach to characterize the liquid flow speed in nano-environment. These findings provide strong evidence supporting the potential application of LNs to mitigate energy in blunt impact scenarios such as head to head and head to shoulder collisions in sports, traffic accidents and ballistic impact.
Characterization of Lumbar-Level Spinal Fusion on the Whole Human Spine Under Vibrations
Authors: Lipscomb Kristen , Sarigul-Klijn Nesrin , Klineberg Eric O. 
Published: February 2017

In the United States alone, 12–15% of the population will visit their physician for back pain problems each year, creating a direct annual cost of nearly $40 billion. Pain in the spine may be associated with spinal instability and intervertebral disc (IVD) degeneration. The causes of disc degeneration are not completely understood, but have been thought to be linked to excessive loading conditions and whole body vibrations. Patients not responding to non-operative treatment may be considered for surgical fusion.
Vibrations of the spine near its resonant frequency are more likely to lead to spinal injury and subsequent pain. These vibrations may result from prolonged exposure to mechanical vibrations, for example from riding in vehicles. Little is understood about the effect of spine pathologies or treatment techniques on this frequency. While fusion procedure may aid in stabilizing the spine, it may also lead to changes in spine biomechanics. A high fidelity anatomically accurate whole spine finite element model was developed and utilized to examine vibration in the spine using modal analysis. Vibration modes and resonant frequencies were obtained in the healthy spine along with cases of lumbar spine disc degeneration and fusion at several levels, including L4-L5, L3-L5, L5-S, L4-S, and L3-S.
The Effect of Padding Layers Arrangement on Mitigating Head Impacts
Authors: Mansoor-Baghaei Shahab , Sadegh Ali M. 
Published: February 2017

In this study the effect of the stiffness sequence of the padding materials of sports equipment, and in particular helmets, on absorbing the impact to the head has been investigated. Specifically, for each arrangement of the padding materials, the strain in the brain has been calculated. In addition, for each impact, the acceleration of the centroid of the head and the Head Injury Criterion (HIC) has also been obtained. As the first preliminary study a simple spherical model of head/brain, including the skull and the brain and three layers of the padding have been generated. The materials of the three layers of padding vary from viscoelastic, soft elastic to a hard elastic material. Then the head was impacted to the padding with the speed of 2 m/s. Finally the sequence of the padding layers was rearranged and the head was impacted to the padding with the same speed. For each case, the HIC value of the impact was determined.
The results revealed that when the viscoelastic materials was in the middle (the first case) the HIC was 143.5 and the strain in the brain at the center corresponding to corpus callosum was 0.192%. Also for, the second case, where the viscoelastic materials was directly the contacting layer with the head, the HIC value was 46.8 and the brain strain was 0.15%. The reason that the strain in corpus callosum has been determined in this analysis is due to the fact that the literature reflects that the strain in corpus callosum is a good predictor for the onset of concussion due to an impact.
It was concluded that when the viscoelastic padding is located on the outer surface of the protective padding device, the HIC value and the strain in the brain are lower, i.e. it is safer. This study can be employed to analyze head impacts with different layered barriers, i.e., composite materials, sandwich panels, glass, and also the interior trim of a car and as well as many other protective paddings.
Experimental Investigations of a High Frequency Master-Slave Fluidic Oscillator to Achieve Independent Frequency and Mass Flow Characteristics
Authors: Bettrich Valentin , Niehuis Reinhard 
Published: February 2017

High frequency fluidic oscillators have been of scientific interest for many decades. Especially over the last couple of years fluidic oscillators became more important for active flow control applications. At the Institute of Jet Propulsion of the University of the German Federal Armed Forces Munich studies on different kinds of flow control methods were carried out on aerodynamically highly loaded low pressure turbine blades. On the basis of these studies, the most efficient way to trigger transition at low Reynolds numbers was found to be with fluidic oscillators at frequencies up to 10 kHz.
Still, it is an open issue whether it is most efficient to trigger Tollmien-Schlichting waves, stimulate Kelvin-Helmholtz instabilities or simply induce a frequency independent disturbance in form of a periodic impulse for boundary layer control on aero-dynamically highly loaded low pressure turbine blades. To find an answer to these questions, a high frequency master-slave fluidic oscillator is introduced with an independent frequency and mass flow characteristic. Any frequency from the master oscillator’s characteristic can be chosen and the mass flow rate can be controlled with the slave oscillator. Contrary to concepts with fast switching valves or piezo actuators, this actuator is based on a working principle without the necessity of any moving and life limited parts.
Based on experimental results, the characteristics of the master as well as the coupled oscillator are shown. The predictable operation of the coupled device is demonstrated in detail for a constant overall mass flow rate at discrete frequencies of 5 and 6 kHz. In addition, it is also shown that the mass flow can be varied with one master-slave arrangement by a factor of six while keeping the frequency constant at 5 or 6 kHz, respectively.
Besides proof of concept these investigations focus on relevant parameters for active boundary layer and transition control. The frequency and velocity spectra of the coupled device are presented for constant frequency and constant mass flow operating points. Based on these results the improvement potential of the coupled oscillator for fundamental research on this topic is discussed.
Effects of Defects on the Performance of Hierarchical Honeycomb Metamaterials Realized Through Additive Manufacturing
Authors: Rahman Kazi Moshiur , Letcher Todd , Hu Zhong 
Published: February 2017

Cellular metamaterials are of immense interest for many current engineering applications. Tailoring the structural organization of cellular structures leads to new metamaterials with superior properties leading to low weight and very strong/stiff materials. Incorporation of hierarchy to regular cellular structures enhances the properties and introduces novel tailorable metamaterials.
For many complex cellular metamaterials, the only realistic manufacturing process is additive manufacturing (AM). The use of AM to manufacture large structures may lead to several types of defects during the manufacturing process, such as missing/broken cell walls, irregular thickness, flawed joints, missing (partial) layers, and irregular elastic plastic behavior due to toolpath. For large structures, it would be beneficial to understand the effect of defects on the overall performance of the structure to determine if the manufacturing defect(s) are significant enough to abort and restart or whether the material can still be used.
Honeycomb structures are used for the high strength to weight ratio applications. These metamaterials have been studied and several models have been developed based on idealized cell structures to explain their elastic plastic behavior. However, these models do not capture real-world manufacturing defects resulting from AM. The variation of elastic plastic behavior of regular honeycomb structures with defects has been studied, but the performance of hierarchical honeycomb structures with defects is still unknown. In this study, the effects of missing cell walls are investigated to understand the elastic behavior of hierarchical honeycomb structures through simulations using finite element analysis. Regular (zero order), first order and second order hierarchical honeycombs have been investigated in this study. The first level of hierarchy has been implemented by changing each three edge vertex of a regular hexagonal honeycomb lattice by adding another smaller hexagon. The second level of hierarchy is created by adding another smaller hexagon at each three edge vertex of the hexagons added for the first order hierarchy. For the hierarchical cases, the overall density of the honeycomb is held constant to the parent structure (zero order or regular) by reducing the thickness of the cell wall in the first and second order structures. ANSYS® was used to develop finite element models to analyze the performance of both perfect and defected regular, first order and second order hierarchical honeycombs. Defects were added to the model by randomly removing cell walls. Hierarchical honeycombs demonstrated more sensitivity to missing cell walls than regular honeycombs. On average, the elastic modulus decreased by 45% with 5.5% missing cell walls for regular honeycombs, 60% with 4% missing cell walls for first order hierarchical honeycomb and 95% with 4% missing cell walls for second order hierarchical honeycombs.
Understanding the Differences in Hemispherical Dome and Biaxial Test During Equi-Biaxial Tension on Cruciform
Authors: Nikhare Chetan P. , Vorisek Emmett , Nolan John , Roth John T. 
Published: February 2017

One metal manufacturing process which uses thousands of processes to trim, stretch, draw, bend etc. under a big umbrella is sheet metal forming. Using heavy equipment, the sheet metal parts are deformed into complex geometries. The complexity in these parts produces multi-axial stress and strain, a state for which it is critical to analyze using conventional tools. Traditionally, the mechanical properties of materials have been characterized using the uniaxial tension test. This test is considered adequate for simple forming operations where single axis loading is dominant. Previous studies, however, have noted that the data acquired from this type of testing is not enough and additional details in other axes under simultaneous deformation conditions are important. To analyze the biaxial strain, some studies have suggested using the limiting dome height test and bulge test. However, these tests limit the extent of using multi-axial loading and the resulting stress pattern due to contact surfaces. Therefore, researchers devised the biaxial machine which is designed specifically to provide biaxial stress components using multiple and varying loading conditions.
The idea of this work is to evaluate the relationship between the dome test data and the biaxial test data. For this comparison, cruciform specimens with a diamond shaped thinner gage in the center were deformed with biaxial stretching on the biaxial testing machine. In addition, the cruciform specimens were bi-axially stretched with a hemispherical punch in a conventional die-punch setting. Furthermore, in each case, the process was simulated using a 3D model generated on ABAQUS. These models were then compared with the experimental results. The forces on each arm, strain path, forming and formability was analyzed. The differences between the processes were detailed. It was found that biaxial tests eliminated the pressurization effect which could be found in hemispherical dome tests.