bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Shot-Peened Surfaces by a Noncontacting Thermoelectric Method
Authors: Carreon Hector , Nagy Peter B.
Published: November 2021

Shot peening is widely used in the aerospace and other industries to increase the damage tolerance of metal parts via producing a thin surface layer of compressive residual stress that prevents crack initiation and retards crack growth during service. Nondestructive evaluation of the prevailing compressive residual stress in the shallow subsurface layer is complicated by the adverse effects of shot peening, such as surface roughness and cold work that manifests itself through increased dislocation density and localized texture. Recent research efforts have revealed that conventional ultrasonic and eddy current NDT methods are simply too sensitive to surface roughness to quantitatively assess the subtle variations in mechanical and electrical properties that are caused by shot peening. On the other hand, noncontacting thermoelectric techniques are very unique among all other methods used in nondestructive materials characterization in that they are solely sensitive to intrinsic material variations regardless of the size, shape, and surface quality of the specimen to be tested. Noncontacting thermoelectric methods, based on magnetic detection of local thermoelectric currents around inhomogeneities in metals when a temperature gradient is established throughout the specimen, are especially well suited for the characterization of shot peened surfaces. Experimental evidence suggests that this method can reliably detect and quantitatively assess otherwise hidden variations in material properties within the shallow surface layer of shot peened specimens. The thermoelectric method is sensitive to all three “material” effects of shot peening, namely residual stress, local texture, and increased dislocation density, but it is entirely insensitive to its “geometrical” by-product, i.e., the rough surface topography. Further development of the thermoelectric method is necessary to study the underlying physical phenomena before it can be successfully adapted to practical inspection problems, but the preliminary results presented in this paper are very promising.
Enhanced Methane-Air Mixing Using Shock and Expansion Waves
Authors: Brasoveanu Dan , Gupta Ashwani K.
Published: November 2021

A unified model of gaseous fuel-air mixing is applied here to study the effect of shock waves on enhanced methane-air mixing. The model uses the fuel mass fraction within infinitesimal fluid elements and the total derivative of this fraction with respect to time to measure the degree and rate of mixing, respectively. The model is strictly accurate only for low-pressure combustors because of the ideal gas law assumption incorporated in the model. The model is also limited to gaseous fuels that contain single chemical specie, or behave like single specie. The model can be applied to any operational conditions or combustor geometry.

Results show that mixing can be completed within the narrow region of the shock wave and therefore in a negligibly short time, if pressure, temperature and velocity distributions within this region are optimized. Furthermore, combining the effects of air preheat and shock waves can enhance both mixing with air penetration into fuel and fuel dispersion into the surrounding air. These results provide important guidelines for the design of supersonic combustors to achieve high efficiency and high intensity, while maintaining a low level of pollutants emission.
Inverse Design of Radial Compressor Components by Modern CFD
Authors: Van den Braembussche R. A. , Antolin J. , Thygesen R.
Published: November 2021

The use of a three-dimensional inverse method for the design of inlet guide vanes, a centrifugal impeller and return channel is demonstrated. The geometry of the different components are iteratively defined until a prescribed velocity distribution is obtained.

The procedure and design criteria for each component are described and the final result is presented. The advantages, disadvantages and problems related to the use of inverse methods are discussed.
The Influence of Inlet Flow Distortion on the Performance of a Centrifugal Compressor and the Development of Improved Inlet Using Numerical Simulations—Part I: Experimental Test Comparison for Compressor Stage Performance
Authors: Kim Yunbae , Engeda Abraham , Aungier Ron , Direnzi Greg
Published: November 2021

The performance of centrifugal compressors can be seriously affected by inlet flow distortion that is by non-uniform inlet flow. The distortion can be in static pressure or stagnation temperature, but the most common distortion is stagnation pressure. Such distortions often occur because of the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure.

In this current work, Part I of two parts, experimental test has been carried out for the comparison of a centrifugal compressor stage efficiency with two different inlet configurations, one of which is straight with constant area and the other is a 90-degree curved pipe with nozzle shape as inlet models. The comparative result from the test showed significant stage efficiency difference between the two different inlet configurations. The result is analyzed and attempt is made to understand the flow structure caused by each type of configuration and the resulting effect on the performance of the stage.
Effects of Scalloped Centrifugal Impellers on Aerodynamic and Rotordynamic Performance Using CFD Techniques
Authors: Moore J. Jeffrey
Published: November 2021

Impeller scallops are intentional cuts in the hub and shroud surfaces at the exit of centrifugal impellers that are intended to prevent high cycle fatigue in these areas. The goal of this analysis is to determine what effect the scallops have on aerodynamic performance, rotordynamic stability, rotating stall criteria, axial thrust, and mechanical shaft power. Furthermore, this study improves the understanding of the interaction with the secondary passage and determines the effect on the flow field entering the diffuser. A 3D viscous CFD model is generated of a single blade passage that couples the primary flow passage with the secondary shroud passage. This approach captures the complex interaction that occurs at the impeller exit due to the presence of the scallops. The predictions show a small penalty in thermodynamic efficiency with the presence of the scallops compared to a baseline case. The results also show a moderate increase in shaft horsepower calculated by integrating static pressure and shear stress acting on the impeller and shroud surfaces. Circumferential swirl in the shroud passage shows only modest increases with the addition of the scallops. Therefore, rotordynamic performance is not significantly affected nor is axial thrust acting on the impeller. The predictions demonstrate the effect the scallops have on the flow field entering the diffuser including variations in flow angle at the impeller exit.
Centrifugal Compressor Design and Testing in Finnish High Speed Technology
Authors: Larjola J. , Backman J. , Esa H. , Pitkänen H. , Sallinen P. , Honkatukia J.
Published: November 2021

This paper reports on the design procedure to produce radial compressors for high speed applications. These compressors are directly connected to a high speed electric motor. Speed control is used instead of IGV and diffuser vane control, and this sets some additional requirements e.g. for the shape of the compressor performance map. It is required that at the design pressure ratio the compressor has a wide operating range in mass flow, when optimal speed control is used. It is also required that the high efficiency range of the compressor is as wide as possible. One-dimensional computation giving the basic geometry and performance map of the compressor is done with a non-commercial program. Then a geometry generation 3D program is used to define the whole compressor wheel geometry. The wheel geometry data is used in the flow and structure analyses. The compressor flow is calculated with a three-dimensional CFD-program, which has specially been modified for centrifugal compressor flow. Particularly in the optimization process of the volute, also time-dependent computation of the complete compressor using the sliding mesh technique is used. The performance of the final compressor geometry is measured in the University test facility and the test results are used to develop the design process. Up to this date, 15 different high speed compressors have been aerodynamically designed and tested in this design loop. The typical pressure ratio of the compressors ranges from 1.6 to 2.5.
Dynamic Mechanical Analysis of Nitinol Beams
Authors: Krishnan Sridhar , Yoon Sung-Ho , White Scott R.
Published: November 2021

The bending behavior of thin nitinol beams under dynamic loading conditions was experimentally characterized using a three-point bending fixture in a Dynamic Mechanical Analyzer (DMA). Differential Scanning Calorimetry (DSC) was also used to measure the transformation temperatures and assess the effects of annealing treatment on the material behavior. The alloy (54.4Ni/45.5Ti wt. %) was chosen so that the austenitic finish temperature was in the range of 50–100°C. Simple beam bending theory was used to calculate the dynamic moduli of the beam and the transformation temperatures were observed in the form of a hysteresis curve of storage modulus. Monotonic three-point bend loading tests were conducted for pure martensite and pure austenite to measure the critical stresses for martensitic (stress-induced) transformation.
Micromechanics of Porous Shape Memory Alloys
Authors: Lagoudas Dimitris C. , Entchev Pavlin B. , Qidwai Muhammad A. , DeGiorgi Virginia G.
Published: November 2021

This work focuses on establishing the properties — both static and dynamic — of porous SMA materials, and their energy absorption capabilities. To accomplish this, micromechanics-based analysis of the overall behavior of SMAs is carried out in the present work. The porous SMA is modeled as a composite with a solid SMA matrix, which is in turn described by a constitutive model available in the literature, and elastic inclusions, which in the limit represent the voids in the porous material. The static macroscopic constitutive behavior of the material is established using both the Mori-Tanaka averaging method and the unit cell finite element method. The dynamic macroscopic constitutive behavior is described using the results obtained by the Mori-Tanaka averaging method.
Compact Drive Electronics for Solid-State Actuators
Authors: Paine Jeffrey S. N. , Bennett David S. , Cuadros Carlos E.
Published: November 2021

As piezoelectric actuators are developed for high strokes and/or high force applications, the amount of piezoelectric material used in the actuator must also increase. Reducing the size of drive electronics becomes difficult using traditional linear power electronics packages when applications require as much as 40 μF of piezoelectric load. In order to efficiently drive piezoelectric actuator systems, bi-directional systems (drivers that recover the energy put into the piezoelectric capacitor) must be used. Since less than 10% of the power going into the piezoelectric actuator is real versus the large reactive load used to power the piezoelectric materials, bidirectional systems have a much higher efficiency. A comparison is made between traditional linear and PWM amplifier systems and tailored piezoelectric bi-directional driver systems. Bi-directional systems have power dissipation levels up to 1/8th those of traditional linear amplifier systems. In the course of the research both linear and PWM concepts were investigated. A rationale for comparing the overall efficiency of drive electronics systems is presented. Some innovative efficient concepts for piezoelectric system drivers are presented and discussed.
Double Adjustable Shock Absorbers Utilizing Electrorheological and Magnetorheological Fluids
Authors: Lindler Jason E. , Wereley Norman M.
Published: November 2021

Double adjustable shock absorbers allow for independent adjustment of the yield force and post-yield damping in the force versus velocity response. To emulate the performance of a conventional double adjustable shock absorber, an electrorheological (ER) and magnetorheological (MR) automotive shock absorber were designed and fabricated at the University of Maryland. For the ER shock absorber, an applied electric field between two tubular electrodes, located in the piston head, increases the force required for a given piston rod velocity. For the MR shock absorber, an applied magnetic field between the core and flux return increases the force required for a given piston rod velocity. For each shock absorber, two different shaped gaps meet the controllable performance requirements of a double adjustable shock absorber. A uniform gap allows for control of the yield force of the shock absorber, while a non-uniform gap allows for control of the post-yield damping. Force measurements from sinusoidal displacement cycles, recorded on a mechanical damper dynamometer, validate the performance of uniform and non-uniform gaps for adjustment of the yield force and post-yield damping, respectively.
Replication of Sub-Micron Gratings on Plates With Surface Mounted Piezoceramic Patches
Authors: Kurusamy Doraraju G. P. , Joshi S. P.
Published: November 2021

A technique to fabricate gratings on thin PZT (lead zirconate titanate) patches and on the aluminum substrate on which they are mounted has been developed. Due to the fragility and brittleness of thin PZT patches this technique avoids imparting large bending strains on the thin PZT patches. The traditional technique was modified to facilitate application on thin surface mounted PZT patches. The gratings obtained by the technique were of high quality.
Diagnosis of Impact Damage in Composite Structures With Built-In Piezoelectrics Network
Authors: Wang Calvin S. , Chang Fu-Kuo
Published: November 2021

An active diagnostic technique for identifying impact damage in composites is presented. A network of piezoelectric actuators and sensors were built into composites to generate and receive ultrasonic stress waves in the structures. Scattered waves were produced from the damage and were detected by sensors. A signal-processing scheme composed of smoothing filtering and joint time-frequency analysis was applied to minimize noise interference and convert sensor measurements into time-frequency spectrograms for interpretation. An identification method based on time-of-flight information obtained from the spectrograms was developed. Experiments were performed on composites with different configurations. It was demonstrated that the method was able to detect the presence of the damage and characterize the damage to a satisfactory precision. Identification results were verified with X-ray images of the structures.
Active Non-Linear Control of a Buckled Beam
Authors: Pinto Osvaldo C. , Gonçalves Paulo B.
Published: November 2021

Buckled beams have been used in several engineering applications to support lateral loading. These arch-like structures are highly nonlinear and may display several instability phenomena when subjected to dynamic and static loads. In this paper a certain class of optimal non-linear control algorithms is used to control the oscillations of simply supported buckled beams subjected to transversal distributed load. To control the non-linear oscillations of the arch, concentrated moments are applied at suitable points along the beam axis. The results show that the proposed control scheme can not only mitigate the effects of dynamic loading on the vibration amplitudes of the beam but also prevent dangerous instability phenomena. In fact the numerical results indicate that the control algorithm can effectively increase the load-carrying capacity of the beam without demanding large control forces.
Opto-Piezothermoelastic Constitutive Modeling of a New 2-D Photostrictive Composite Plate Actuator
Authors: Shih Hui-Ru , Tzou H. S.
Published: November 2021

Optical actuators can introduce non-contact remote actuation and control effect without any hard-wired connections. In this study, constitutive relations, general opto-piezo(electric)-thermo-elastic equations, and their one-dimensional (1D) form are formulated and applied to a new two-dimensional (2D) planar actuator and composite plates laminated with distributed photostrictive optical actuators. Photodeformation, pyroelectricity, and thermoelasticity are considered in the constitutive relations and coordinate transformations are used to transform the 1D local actuation characteristics to the 2D global actuator coordinate system. Mathematical model and system parameters are then calibrated with experimental data; analytical solution based simulation and experimental results are compared favorably. Thus, the proposed constitutive modeling and governing equations of distributed 2D optical actuators preserve natural photodeformation, pyroelectricity, and thermoelasticity characteristics and applicable to distributed control of 2D continuous systems.
Sound Transmission Loss in Electrorheological Fluids Under DC Voltage
Authors: Szary Marek L. , Noras Maciej
Published: November 2021

Extensive investigations of sound transmission loss (STL) in electrorheological (ER) fluids were conducted in the Acoustics Laboratory in the College of Engineering, Southern Illinois University Carbondale.

The STL was investigated for different kinds of ER suspensions in frequency ranges from 100 Hz to 2kHz. Applied DC voltage to the different electrodes allowed normal and shear stress to develop in the ER fluid respectively. The electric field density was variable. Sound transmission loss was obtained by measurement of the sound pressure level in front of and behind the sample. Under both normal and shear stress in ER fluid, STL decreases with increasing stress. Those properties of ER fluids can be useful in noise and vibration control applications.
Internal Resonance of a Beam/Traveling-Mass System
Authors: Siddiqui S. , Golnaraghi F. , Heppler G. R.
Published: November 2021

The dynamics of a cantilever beam undergoing large amplitude oscillations while experiencing a nonlinear interaction with an attached lumped spring/mass system are investigated. The resulting partial differential equations contain trigonometric non-linearities that are treated using methods of weighted residuals and do not require series expansions about the equilibrium positions. The resulting nonlinear ordinary differential equations are solved using a formulation of the average acceleration method.
Approaches to Reducing Silent Chain Noise of Cab Motorcycles
Authors: Pan M. , Shieh Eddy T.
Published: November 2021

Silent chains have extensively replaced roller chains in drive systems owing to annoying noise problems. But, for some types of cab-motorcycles, especially sheet-frame cabs, the annoying noise originated from silent chains can still not been accepted. In this study, silent chain noise of cab motorcycles has been well investigated by firstly the order analysis and time-frequency analysis of measured noise, and secondly the analysis of origination and transmission of noise. Therefore, noise mechanism can be precisely uncovered and understood. Some experiments were conducted to discover three primary issues of a noise problem, i.e., noise source, transmission path, and response. In addition, to explain a noise component resulting from structure resonance, the mode shape at 1640 Hz was constructed based on the running mode principle. Different engineering modifications have been validated to reduce this transmission-part noise. Useful proposals can be concluded as design guidelines.
Statistical Investigation of Resistance Spot Welding Quality Using a Two-Stage, Sliding-Level Experiment
Authors: Li Wei , Cheng Shaowei , Hu S. Jack , Shriver Justin
Published: November 2021

Quality variation in resistance spot welding is a major concern in the automotive industry. This paper investigates the weld quality using a newly developed two-sage, sliding-level experiment. Welding current is treated as a “slid factor” and is determined based on the settings of other process variables. Engineering knowledge is applied in statistical model selection. From the analysis, it is found that abnormal process conditions, including axial misalignment, angular misalignment, poor fitup, edge weld, and electrode wear, significantly affect the size of the welds, and thus cause large variations on the weld quality. Although they may help increase the weld size, these abnormal process conditions generally lead to a less robust welding process. Developed initially for this study, the new experimental design and analysis procedures are believed to be generic and can be applied to other processes.
Excimer Laser Micromachining of Silicon and On-Line Machining Depth Discovery Using Laser Interferometry
Authors: Theppakuttai Senthil , Chen Shaochen
Published: November 2021

In this paper a parametric study on the excimer laser micromachining of silicon (Si) is conducted and a Michelson interferometer is used for the in-situ diagnostics of the machining depth on the sub-micron and micron scales. An excimer laser of wave length 308 nm is used for the micromachining process. A He-Ne laser of 632.8 nm wavelength is used as the light source for the interferometer and the setup consists of a beam splitter, beam expander and other optics. The interference patterns caused due to the change in the path length between the two interferometer arms gives the machined depth information. These interference patterns are captured by using a photodiode and an oscilloscope. Results from the interferometer are compared with the actual depth measurements obtained by using a surface profilometer in combination with an optical microscope. It is observed that the depths of machining obtained by the surface profile measurement are in accordance with the interferometer measurements with a very high accuracy. The experimental results demonstrate the feasibility of applying this system for the in-situ monitoring of the micromachining process.
Robust Control of Piezo Actuator for Active Error Compensation in Diamond Turning
Authors: Yu Jianming , Li C. James
Published: November 2021

This paper describes a new control strategy for the micro positioning system used in a diamond turning process to improve workpiece geometry in spite of hysteresis nonlinearity and guideway/spindle errors. The control strategy consists of two nested loops. The inner loop is a model-based robust controller, which compensates for the hysteresis nonlinearity associated with piezo actuators, and the outer loop is a P-integrator learning controller which eliminates the unmodeled error sources such as guideway and spindle errors. This control strategy was applied to the error compensation in a diamond turning process. Cutting tests were conducted and showed an order of magnitude improvement in the workpiece form accuracy from 10 μm to 1μm on an aluminum alloy disk.
Suppressing Cracking in Resistance Welding AA5754 by Mechanical Means
Authors: Zhang Hongyan , Senkara Jacek , Wu Xin
Published: November 2021

In this paper mechanical aspects of cracking during single- and multi-spot welding of AA5754 was investigated by both experimental and analytical approaches. The impact of mechanical loading on crack initiation and propagation was studied with the consideration of various process parameters including the loading imposed by electrodes, the formation of liquid nugget, and constraining factors during and after welding. Tensile properties of AA5754 and their dependence on the temperature were tested at room and up to solidus temperatures, in order to provide a reference of cracking stress. Thermal-mechanical analysis was conducted based on the temperature field around the nugget and the state of stress encountered during welding. This analysis revealed that tensile stress might build up in the vicinity of the nugget during cooling, thus explained the experimental observation. General guidelines for suppressing cracking were proposed, i.e. to provide sufficient constraint around the weld spot during and after welding.
Swept Volume Study and Its Application to Real-Time Simulation of Enhanced Machine Controllers (EMC)
Authors: Wang Karen L.
Published: November 2021

Swept volume study plays an important role in manufacturing. As an application, a collaborative effort has been made to construct an integrated simulation system to validate the enhanced machine controllers (EMC) developed at the National Institute of Standards and Technology. Commercial NC simulation packages available assume ideal controller behavior, i.e., a linear cut is exactly linear, a circular cut is exactly circulate, and all axes are linear and orthogonal. But for the EMC problem it is an opposite situation: it is assumed that the controller inputs (i.e., numerical control programs) are correct, and the controller itself needs to be proven. In this paper, commercial CAD/CAM packages and research on swept volume are integrated to develop an EMC simulation system in which tool configurations, swept volumes and final machined parts are displayed in a superior 3D graphics environment. Unlike the commercial NC simulation packages, the developed EMC simulation system includes all the effects of the controller and machine tool, so that errors in the trajectory-blending algorithm appear on the stock, improperly tuned servos would show oscillation, and nonlinear axes would show tolerance violation.
New Frontiers in Mold Construction: High Conductivity Materials and Conformal Cooling Channels
Authors: Jacobs Paul F.
Published: November 2021

Why are almost all production plastic injection molding core and cavity inserts made from steel? Steel is certainly NOT the hardest material. Steel is also definitely NOT the most corrosion resistant material. Finally, steel most assuredly is NOT the best conductor of heat. So why are production tools made from steel? The real answer is probably because that’s the way they have been made for many years. People are used to working with steel molds. The results are predictable. However, as two mold case studies, in addition to Finite Element Analysis (FEA) results presented in this paper will show, there are now commercially available inserts that achieve: (1) shorter lead times, (2) faster cycle times, (3) enhanced productivity, (4) lower unit part cost, and (5) reduced part distortion.
Transient Thermal Analysis of an Anisotropic Conductive Film Package Assembly Process
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom
Published: November 2021

Transient thermal simulation was performed to analyze thermal response of the assembly process for a package using Anisotropic Conductive Film (ACF). Two assembly processes were modeled: a simplified process where the package was fixed at two different temperatures during assembly, and a detailed process where the package experienced a ramping heating process, followed by a constant temperature curing process. A 3D conjugate Computational Fluid Dynamics (CFD) study was first conducted, followed by a 3D conduction-only analysis due to the minimal effect of convection and radiation.

Results from the detailed process modeling indicated that during the initial ramping, within 0.02 second, the die and nozzle head experienced a small temperature drop due to the cooling effect of the ACF material and substrate. The ACF material also displayed a steep increase in temperature after contacting the die, followed by a short decay, then ramped up again. At the end of the 10-second ramping process, the ACF reached a temperature of almost 203°C, while the die was at 206°C. During the 5 seconds of curing, all parts reached steady state in less than 2 seconds.
Thermal Contact Resistance of Phase Change and Grease Type Polymeric Materials
Authors: Prasher Ravi S. , Simmons Craig , Solbrekken Gary
Published: November 2021

Thermal interface material (TIM) between the die and the heat spreader or between the heat spreader and the heat sink in any electronic package plays a very important role in the thermal management of electronic cooling. Due to increased power and power density high-performance TIMs are sought every day. Phase change materials (PCM) seem to be very good alternative to traditionally used thermal greases because of various reasons. These phase change materials also have the advantage of being reworked easily without damaging the die.

Typically these phase change materials are polymer based and are particle laden to enhance their thermal conductivity. The thermal conductivity of these materials is relatively well understood than their contact resistance. Current work focuses on explicitly measuring the contact resistance and the thermal conductivity of a particular phase change TIM and some silicon-based greases. Effect of various parameters, which can affect the contact resistance of theses TIMs and Greases, are also captured. The steady state measurements of the thermal conductivity and the contact resistance was done on an interface tester.

In general the work on the contact resistance of fluid-like polymer based TIM, such as thermal grease or phase change polymer has been experimental in the past. A semi-analytical model, which captures the various parameters affecting the contact resistance of two class of materials; the phase change and the thermal grease is also developed in this paper. This model fits very well with the experimental data.
Incremental Single Point Forming
Authors: Jeswiet J. , Ali A.
Published: November 2021

The process of single point incremental micro-plastic forming is presented. This process is used to form sheet metal into complicated shapes without the use of either a male or female die. The process uses a single point tool which plastically deforms sheet metal to give a local micro-deformation. By doing this incrementally, and controlling the tool path with a CNC mill, the plastically deformed points are, in effect, added as the tool moves to give a final shape. The sheet metal is held in place by a blank-holder which moves in a vertical plane on four posts. Deformation of the strip can be achieved in one of two ways: either with a supporting, fixed tool about which the single point forming tool moves or by inversion of the process in which the supporting, fixed tool is not used. The paper describes experiments with both techniques.
Tractive Kinematic Regression: A Computer Assisted Deep Drawing Method
Authors: Ulintz Peter J.
Published: November 2021

Combining today’s computer technology with new generation, multiple-action, hydraulic press equipment, has created a new process opportunity in deep drawing. Integrating these modern machine and computer controls with innovative programming and tool designs, has led to the development of a production process that produces a double reverse-drawn, cylindrical shell that significantly exceeds traditional Limiting Drawing Ratios (LDR). The method used to produce these shells employs a recently developed technique, herein referred to as Tractive Kinematic Regression, or more simply, the TKR process.

The TKR process promotes material flow by “feeding” material into the die cavity, as opposed to the punch having to “draw” or “pull” in the flange. This is accomplished through the use of concurrent - but unequal - force and motion curves of a forward moving punch and a regressing (reverse moving) die ring. The computer controlled kinematics, forces and motion curves resulted in less material straining and thereby, provided increased formability and improved LDR.
Stress and Strain Histories of Multiple Bending-Unbending Springback Process
Authors: Huang H.-M. , Liu S.-D. , Jiang S.
Published: November 2021

A drawbead model with sheet metal passing through multiple bending-unbending processes was employed in this study to understand the springback phenomenon and to develop a numerical simulation technique for more accurate prediction of the springback process. The deformation process is simulated using an implicit Finite Element Modeling code. The predicted results were compared with the physically measured ones, including clamping and restraining forces, thickness strains and the curvatures of the deformed sheets. Consideration of the Bauschinger effect and employment of a combined isotropic and kinematic hardening models greatly improve the prediction accuracy. Stress and strain histories under various conditions during the drawing process are studied in detail in an attempt to provide a better basis for comparison for dynamic explicit solutions.
Three-Dimensional Tube Geometry Control for Rotary Draw Tube Bending: Part 1—Bend Angle and Overall Tube Geometry Control
Authors: Lou Huazhou , Stelson Kim A.
Published: November 2021

Traditional trial-and-error springback compensation methods have the problems of high scrap rate, low efficiency, high cost of fixtures and operator experience dependency. The method presented in this paper uses on-line measured springback data from the same batch to predict and compensate for springback. Because there are no springback data for the first bend, bend-rebend control is used to make the first bend to eliminate trial tubes. In addition to springback, relaxation and radial growth are also estimated and compensated for to make a bend more accurate. A process control method is developed to optimize the overall control strategy such that the overall tube error is minimized without increasing the required hardware accuracy. The optimal process control strategy has significantly higher accuracy than the traditional trial-and-error method. The details of statistical analysis of tube tolerance and adaptive bend correction algorithm are presented in part 2 of the paper.
Measurement of the Material State Including the Effects of Recovery and Recrystallization
Authors: Bange M. E. , Beaudoin A. J. , Stout M. G. , MacEwen S. R.
Published: November 2021

Deformation at elevated temperatures in combination with high strain rates leads to recovery and recrystallization in aluminum alloys. Previous work in recrystallization has emphasized the detailing of microstructural trend in progression from the deformed to the annealed state. In the following, we examine the effect of rate dependence on deformation on AA 5182 and AA 6061. It is demonstrated that identification of underlying microstructural mechanisms is critical. An experimental program is then outlined for characterization of recovery and recrystallization of AA 5182. Instantaneous hardening rate and flow stress are developed from interrupted compression tests. These data are used to establish a quantitative measure of recovery through evaluation of a state variable for work hardening, the mechanical threshold. It is intended that the results serve as a foundation for development of relations for evolution of a mechanical state variable in the presence of recrystallization. Such a framework is necessary for the practical prediction of interstand recrystallization in hot rolling operations.
Modeling of Plastic Behavior of Anisotropic Sheet Metals With Voids
Authors: Chien W. Y. , Pan J. , Tang S. C.
Published: November 2021

The influence of plastic anisotropy on the plastic behavior of porous ductile materials is investigated by a three-dimensional finite element analysis. A unit cell of cube containing a spherical void is modeled. The Hill quadratic anisotropic yield criterion is used to describe the matrix normal anisotropy and planar isotropy. The matrix material is assumed to be elastic perfectly plastic. Macroscopically uniform displacements are applied to the faces of the cube. The finite element computational results are compared with those based on the closed-form anisotropic Gurson yield criterion suggested in Liao et al. (Mechanics of Materials, 1997, pp. 213-226). Three fitting parameters are suggested in the closed-form yield criterion to fit the results based on the modified yield criterion to those of finite element computations.
Discussion of the Worst Case Scenario of FLD0
Authors: Arwashan Naji
Published: November 2021

The Forming Limit Diagram is used in circle grid analysis to check the safety of a formed panel. The shape of the Forming Limit Diagram for steel is always the same, it is only the vertical position of the diagram that varies depending on the value of FLD0. For steel, FLD0 is widely accepted to be dependent on the thickness and n value which are both inherently indeterministic, and can exhibit variations, small or large, depending on the manufacturing process. To account for this variability in determining the safety of a formed panel, the engineering practice in many companies is to use a minimum value for FLD0 called Worst Case Scenario, because it is calculated using minimum values for both t and n. This paper presents a different and better approach to calculate the minimum value of FLD0. The approach is based on probabilistic concepts, and allows the calculation of a minimum value for FLD0 that is related to a certain probability of occurrence. The derivation technique used in the paper is borrowed from Reliability Analysis and tailored to solve our problem. The derivation leads to a simple formula that can be easily used. The minimum value of FLD0 calculated according to the paper is more accurate than the Worst Case Scenario, and provides better cost saving since it is always greater than the Worst Case Scenario value.
Improving Formability in Sheet Metal Stamping With Active Drawbead Technology
Authors: Bohn M. L. , Xu S. G. , Weinmann K. J. , Chen C. C. , Chandra A.
Published: November 2021

Aluminum is expected to gain popularity as material for the bodies of the next generation of lighter and more fuel-efficient vehicles. However, its lower formability compared with that of steel tends to create considerable problems. A controllable restraining force caused by adjusting the penetration of drawbeads can improve the formability. This paper describes the effects of temporal variations in drawbead penetration on the strain distribution in a symmetric stamped part. Comparison of the results of numerical simulations with the corresponding experimental results shows that the predictions of strain distribution on the panel are in very good agreement. Furthermore, forming limit diagram analysis indicates that the active drawbead concept is beneficial to the formability of AA 6111-T4.
In Process Control of Strain in a Stretch Forming Process
Authors: Hardt D. E. , Norfleet W. A. , Valentin V. M. , Parris A.
Published: November 2021

The process of stretch forming is used extensively in the aerospace industry to form large sheet panels of mild curvature. This has traditionally been a low precision process requiring considerable hand-working at assembly. However, recent demands for faster, less wasteful production have placed new demands on the accuracy and consistency (quality) of this process. In this paper the various modes of control for this process are examined, from both an analytical and experimental point of view. It is shown clearly that the process is least sensitive to material and machine property variations if controlled to a target level of strain in specific areas of the sheet. This method is compared with the conventional methods of controlling either the force applied to the sheet during stretching or the displacement of the stretch jaws.

A series of both lab scale and full production experiments concur with the analytical findings, demonstrating reduced process variation if strain feedback is used. Lab experiments and analysis indicate that far greater reductions are possible if a more precise form of strain control is used. In production trials forming wing leading edges, a manually implemented strain control showed a shape variation reduction of 50% over normal factory practice using force control.
Environmentally Conscious Investigation of Cutting Fluid Mist Behavior via Particle Image Velocimetry in Turning
Authors: Chiou Richard Y. , Chen Jim S.-J. , Cooper Derrek , Ciuciu Cristian
Published: November 2021

In this paper, Particle Image Velocimetry (PIV) monitoring approach for cutting fluid mist behavior in machining is proposed. Particle Image Velocimetry is a technique that uses a combination of lasers and a CCD camera to analyze the fluid flow field. Experiments were performed to investigate the transient mist patterns due to the impinging cutting fluid on a rotational workpiece in a turning operation. The measurements displayed the velocity profiles and sizes of the generated fluid mist both in the near-field and far-field. This paper contains the results of a preliminary experiment to measure and analyze mist generation mechanism on a lathe. The experimental investigation concerning the mist behavior in a turning operation can be used as basis for human exposure and health hazard analysis. Some preliminary results were obtained and recommendations were made for future research.
Theory of Torsional Chatter in Twist Drills: Model, Stability Analysis and Comparison to Test
Authors: Bayly Philip V. , Metzler Sandra A. , Schaut Adam J. , Young Keith A.
Published: November 2021

The mechanism of torsional chatter in drilling differs qualitatively and quantitatively from other types of chatter. In this paper we show that torsional chatter can be explained by the torsional-axial coupling inherent in a twisted beam; the beam “untwists” and extends in response to an increase in cutting torque. Based on a model of this mechanism, predictions of stability boundaries and chatter frequencies are derived by frequency domain analysis, and confirmed by numerical simulation and experimental tests. The effect of the torsional-axial coupling is opposite that of traditional cutting in that an increase in cutting forces leads to axial extension and greater chip load. Because of this sign difference, the limiting depth of cut is governed by the positive real part of the frequency response function, which explains the unexpected fact that torsional chatter occurs below the natural frequency of the tool.
The Effect of Dynamic Consistency in Spindles on Cutting Performance
Authors: Smith Scott , Winfough W. R. , Young Keith , Halley Jeremiah
Published: November 2021

This paper presents the results of three measurements of dynamic consistency in machine tool spindles. First the effect of reclamping and of the rotational orientation of a tool in a single spindle (40,000 rpm 40 kW) was evaluated. Then 5 different spindles of the same model (20,000 rpm 75 kW) were compared, first with a flexible tool and then with a stiff tool. It was seen that in all the tests the natural frequencies did not vary greatly, but that in some situations the damping showed significant variability. The effect of this damping variation on stability and cutting performance is evaluated for both conventional and for high speed machining.
Computational Biomechanics of Human Spine Under Wrapping Compression Loading
Authors: Shirazi-Adl A. , Parnianpour M.
Published: November 2021

Computational biomechanics of the human spine under a novel compression loading that follows the curvature of the spine is performed by evaluation and comparison of the detailed response of the spine under various types of compression loading at different postures. The nonlinear finite element formulation of wrapping elements sliding without friction over solid body edges is developed and used to study the load-bearing capacity of thoracolumbar (T1-S1) and lumbosacral (L1-S1) spines under one or several wrapping compression forces. Follower load at the L1, axially-fixed compression at the L1, and combined axially-fixed compression plus constrained rotations are also considered for comparison. Moreover, for the detailed lumbosacral model, the effect of changes in the position of wrapping elements and in the lumbar curvature on results are considered. The idealized wrapping loading substantially stiffens the spine allowing it to carry very large compression loads without hypermobility. It diminishes local segmental shear forces and moments as well as tissue stresses. In comparison to fixed axial compression, therefore, the compression loading by wrapping elements that follow the spinal curvatures increases the load-bearing capacity in compression and provides a greater margin of safety against both instability and tissue injury. These findings suggest a plausible mechanism in which postural changes and muscle activation patterns could be exploited to yield a loading configuration similar to that of the wrapping loading. To alleviate hypermobility in compression, the wrapping loading could also allow for the application of meaningful compression loads in experimental as well as model studies of the multi-segmental spinal biomechanics.
Use of Finite Elasticity in Abdominal Aortic Aneurysm Research
Authors: Vorp David A. , Wang David H.-J.
Published: November 2021

Abdominal aortic aneurysm (AAA) is a condition whereby the terminal aorta permanently dilates to dangerous proportions, risking rupture. Rupture of AAA is a significant cause of death in this country that is generally avoided by surgical repair. In order to improve our understanding and diagnosis of this disease, we call upon first principles of finite elasticity. We use such principles to estimate the AAA wall strength and acting wall stress, which in turn allow evaluation of an individual aneurysm’s risk of rupture. In this paper, we summarize the work that has been performed to date in applying finite elasticity to abdominal aortic aneurysm research.
Effects of Inhomogeneous Fixed Charge Density on the Electrical Signals for Chondrocytes in Cartilage
Authors: Lai W. M. , Sun D. D. , Ateshian G. A. , Guo X. E. , Mow V. C.
Published: November 2021

An important step toward understanding the signal transduction mechanisms that modulate cellular activities is the accurate prediction of the mechanical and electro-chemical environment of the cells in well-defined experimental configurations. One such configuration is the steady permeation experiment (e.g., bioreactors) in the open circuit condition. Using our triphasic theory, we have calculated the strain, velocity and the electric potential fields inside a layer of charged articular cartilage, through which a uni-univalent salt (e.g., NaCl) solution permeates under a constant pressure difference across the layer. The fluid flow through the tissue gives rise to an electrical potential difference across the tissue. This potential difference is the well-known “streaming potential” that is measured by Ag/AgCl electrodes placed across the tissue on the outside. Our results show that inside the tissue, in addition to the streaming potential caused by fluid convection, there is also a “diffusion potential” caused by cation and anion concentration gradients that are induced by the gradient of fixed charge density (FCD) inside the tissue. The gradient of FCD may be intrinsic, i.e., the tissue has an inhomogeneous FCD distribution, or it may also be caused by a non-uniform compaction of the solid matrix as is the case in steady permeation where the drag force exerted by the permeating fluid onto the solid matrix causes a compressive strain field inside the tissue. In this experimental configuration, the diffusion potential would compete against the streaming potential. The magnitude and the polarity of the electric field depend, amongst other material parameters, on the compressive stiffness of the tissue. For softer tissue (e.g., aggregate modulus <0.54 MPa for a set of realistic material and testing parameters), the diffusion potential dominates over the streaming potential and vice versa for stiffer tissue. For articular cartilage what the cells see in situ is the combined electrical effect of intrinsic and deformation induced inhomogeneity of FCD. The present results provide not only quantitative information, but also new insight into an important problem in biotechnology. These results also demonstrate that for proper interpretation of the mechano-electrochemical signal transduction mechanisms that is needed for modulating cellular biosynthetic activities, one must not ignore the important effects of diffusion potential.