bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical and Experimental Studies on the Demolding of Injection Molding Parts
Authors: Wang Hao , Kabanemi Kalonji K. , Salloum Georges 
Published: March 2022

Abstract
Numerical and experimental studies are conducted on the demolding stage of injection molding process. Based on an integrated computer-aided-engineering software package, a numerical approach has been proposed to predict the ejection force and to analyze the layout of ejector pins. The predictions are validated in this work by injection molding of polycarbonate boxes. The boxes are molded at given processing condition while ejected with different layouts of ejector pins. The ejection force is measured by load transducers installed behind the ejector pins. The shrinkage of the boxes is also measured by displacement transducers. It is found that the measured total ejection force and its distribution over the pin layouts compare reasonably well with numerical predictions. The validation is also supported by the agreement between the predicted and measured warpage of the boxes. Additional results are provided for a complex molding geometry for which the mold opening and ejection operations need to be considered in studying the demolding.
Smart Processing of Plastics Through Vibration Controlled Shear-Thinning and Orientation
Authors: Ibar J. P. 
Published: March 2022

Abstract
This paper covers the technology of melt vibration during the molding of plastic material (more specifically at low frequency) to reduce the viscosity and ease processability and to produce orientation benefits. The effect of vibration frequency and amplitude on melt viscosity is explained in terms of shear-thinning criteria. The effect of pressure, temperature and cooling rate on shear-thinning is also reviewed to predict how these variables interfere with melt vibration. Applications to injection molding, extrusion and blow molding of uneasily processable plastic melts (such as metallocenes polyolefins) are suggested.
Orientation Formation in Planar Mold Filling: Experimental Results
Authors: Olivero Kristian A. , He Jufang , Altan M. Cengiz 
Published: March 2022

Abstract
The formation of orientation field of short fibers suspended in a highly viscous flow through a planar mold cavity is experimentally analyzed. Such flows are common in injection molding of short-fiber-reinforced composite materials. A suspension of corn syrup and nylon fibers is injected at a constant flow rate through a narrow planar inlet gate into an experimental mold cavity. The flow undergoes a sudden expansion near the inlet gate, followed by a three to one contraction downstream. Photographs of thirteen zones of interest in the vicinity of the sudden contraction are taken through transparent mold walls after the flow achieved steady conditions. Computerized image analysis is performed to obtain orientation data for all the fibers within the zones of interest. This data is used to calculate a through the thickness average of the second-order orientation tensor, which is commonly used to quantify orientation field. The experimental results are qualitatively consistent with numerical predictions based on Jeffery’s theory, but quantitative agreement is not satisfactory. Orientation distribution histograms are generated to provide a more detailed representation of the orientation field. The histograms reveal a bimodal distribution, with an alignment peak along the direction of the theoretically calculated preferred orientation, and a second peak perpendicular to the flow direction. The failure of the second-order orientation tensors to quantitatively describe the experimental data seems to be due to these bimodal distributions. Radial orientation histograms at five zones of interest are presented along with the theoretical predictions at these locations.
Prediction of Race Tracking in Resin Transfer Molding
Authors: Owusu-Ofori Samuel P. , Pai Devdas M. , Sadler Robert L. 
Published: March 2022

Abstract
The resin transfer molding process experiences an unavoidable phenomenon known as race-tracking in which the resin flows along the edges of the mold ahead of the central flow. This phenomena may be severe whereby the resin reaches the top of the mold and exits the mold before it is completely filled. It is of interest to predict this behavior prior to the resin injection. A pre-injection method has been developed to predict whether the flow will be even or skewed and the severity of race tracking. This paper discusses how the method was developed. This method has been successfully used to predict the degree of severity of race tracking in vacuum-assisted resin transfer molding to a high degree of accuracy.
Simulation of Self-Propagating High-Temperature Synthesis Using Finite Element Method
Authors: Swaminathan Vinodh , Koczak Micheal J. , Kalidindi Surya R. 
Published: March 2022

Abstract
Self-Propagating High-Temperature Synthesis (SHS) is an energy efficient process for the synthesis of refractory ceramics and intermetallic compounds, and composites of these materials including functionally gradient materials (FGMs). The process utilizes the large exothermic heat of reaction between two or more elements (or compounds) in order to convert the reactants into one or more useful products. The products of SHS, in general, have been observed to possess significant amounts of residual porosity. It has been reported that a certain amount of liquid phase during the reaction aids in the consolidation process. In order to control the amount of liquid formed during SHS, it is necessary to develop a good understanding of the parametric influence of the various process parameters such as pre-heat, dilution, heat losses, etc. on the SHS reaction. In this study, a commercial finite element program, ABAQUS (1996), has been used to simulate SHS and to study the effects of process parameters that influence and help control the reaction. Processing maps have been developed for Ni-Al system based on the FEA results that can aid in syntheses of nickel aluminides and FGMs using these compounds with low residual porosities.
Effects of Stress Concentrations at the Slipping Fiber/Matrix Interface on Tensile Strength of Ceramic Matrix Composites
Authors: Ahn B. K. , Curtin W. A. 
Published: March 2022

Abstract
Ceramic matrix composites can exhibit a transition from strong, tough behavior to brittle behavior as the interfacial sliding resistance τ between the fibers and the matrix increases. The detailed micromechanical reasons for this dangerous transition are not well understood, but are clearly important for optimizing performance in such composite systems. One mechanism of weakening involves a transition, with increasing τ, from “global” to “local” load transfer from broken to unbroken fibers near the slipping interface. These stress concentrations have been nicely investigated previously by Steif and coworkers (1991) for 2d geometries and by Weitsman and coworkers (1993) using shear-lag for an axisymmetric problem, but the precise implications of these stress concentrations on actual tensile composite failure have not been fully investigated. Here, the problem of stress concentrations in the fiber is revised using the very accurate yet efficient Axisymmetric Damage Model of Pagano (1993) to calculate the axial fiber stresses. The geometry is axisymmetric with a transverse matrix crack and a debond crack along the fiber/matrix interface having a constant sliding resistance τ. The stress concentrations obtained are compared to previous results, and generally increase with increasing τ. More importantly, the fiber surface stresses are then used to determine the probability of fiber fails by surface flaws having a Weibull probability distribution, and the overall composite strength is calculated in a manner similar to that originally suggested by Thouless and Evans for a single matrix crack. The results show a decrease in strength with increasing τ, relative to the common approximation of assuming uniform stresses across the fiber cross-section. The nature of the tough to brittle transition will be discussed in light of these results.
Effect of Creep Feed Grinding Parameters on Strength and Finish of Alumina
Authors: Sathyanarayanan G. , Plebani Louis J. , Wang Hsueh-Ming S. 
Published: March 2022

Abstract
The reliability of ground ceramics is affected by the subsurface cracks. Alumina was creep feed ground by utilizing a 25-1 fractional factorial design to vary the bond type, mesh size and concentration, feed rate, and depth of cut. The unit load, i.e., the normal force transmitted by each grit, was obtained from the normal grinding force and utilized to analyze the material removal mechanism and the observed roughness. The flexural strength is obtained from four point bending tests and correlated with unit load and surface finish. The study shows that creep feed grinding is best suited for alumina. Also the present study shows that fine mesh size and fast feed rate are recommended to grind alumina in order to obtain higher flexural strength.
High Strain Rate Normal Indentation of Ceramics: Implications for Material Removal Mechanisms
Authors: Subhash Ghatu , Koeppel Brian J. , Anton Richard J. , Huang Yonggang Y. , Chandra Abhijit 
Published: March 2022

Abstract
The static indentation fracture mechanics approach does not fully capture the rate sensitive nature of failure behavior in ceramics. Accordingly, a dynamic indentation technique was developed to investigate material removal mechanisms at strain rates similar to those encountered in realistic grinding situations. The technique is designed to deliver a single indentation load of duration 100 microseconds. Compared to static loading, it is observed that lateral cracking is promoted under dynamic loading rates. The implications of dynamic loading on the material removal mechanisms are discussed.
Orthotropic Column Buckling: The Euler and Engesser/Haringx/Timoshenko Formulas Versus an Elasticity Solution
Authors: Kardomateas George A. 
Published: March 2022

Abstract
The well known column buckling formulas of Euler and these of Engesser / Haringx / Timoshenko (which correct for transverse shear) were derived for isotropic materials, and are routinely used in composite structural applications. The accuracy of these formulas, when orthotropic composite material and moderate thickness are involved, is investigated in the present study by comparing the critical loads from these formulas with the predictions of a three-dimensional orthotropic elasticity solution. The column is assumed to be in the form of a hollow circular cylinder and the Euler or Timoshenko loads are based on the axial modulus. As an example, the cases of an orthotropic material with stiffness constants typical of glass/epoxy or graphite/epoxy and the reinforcing direction along the periphery or along the cylinder axis are considered. First, it is found that the elasticity approach predicts in all cases a lower than the Euler value critical load. Moreover, the degree of non-conservatism of the Euler formula is strongly dependent on the reinforcing direction; the axially reinforced columns show the highest deviation from the elasticity value. Second, the Engesser or first Timoshenko shear correction formula is conservative in all cases examined, i.e. it predicts a lower critical load than the elasticity solution. The Haringx or second Timoshenko shear correction formula is in most cases (but not always) conservative. However, in all cases considered, the second estimate is always closer to the elasticity solution than the first one. For the isotropic case both Timoshenko formulas are conservative estimates.
Stacking Sequence Effects on the Process-Induced Free-Edge Stresses in Thermoplastic Composite Laminates
Authors: Domb Moshe M. , Hansen Jorn S. 
Published: March 2022

Abstract
A numerical model is developed for prediction of the process-induced thermal residual stresses in thermoplastic composite laminates. The model addresses the development of the residual stress state in fracture-critical free-edge regions as well as through-thickness stress variations. The current approach provides a unique capability for the investigation of the influence of thermal processing and structural parameters on the resulting buildup of residual stresses during manufacturing. Therefore, it can assist in the design and analysis of thermoplastic composites to tailor mechanical and strength characteristics. Thermal processing considered here includes solidification from the molten state at a specific surface cooling rate, and application of a posterior annealing cycle. A significant reduction in the free-edge stresses is obtained via a quench/anneal cycle in comparison to the recommended nominal cooling from the melt. Alteration of the stacking sequence of the plies in the laminate can further reduce the magnitude of the interlaminar stresses. Results are shown for the case of a quasi-isotropic APC-2 (graphite/PEEK) laminate configuration.
Free Vibration Analysis of Composite Plates With Tailored Thermal Residual-Stresses
Authors: de Almeida Sérgio Frascino Müller , Hansen Jorn S. 
Published: March 2022

Abstract
Thermal residual-stresses introduced during manufacture and their effect on the free vibration of stringer stiffened composite plates is investigated. The principal idea in the work is to include stiffeners on the perimeter of a composite plate in which the laminate for the stiffeners and the plate are different. Such an arrangement yields manufacturing induced thermal residual-stresses which result from the difference in manufacturing and operating temperatures as well as the difference in thermal expansion coefficients and elastic properties of the plate and the stiffeners. The analysis is based on an enhanced Reissner-Mindlin plate theory and involves two separate calculations. In the first, the thermal residual-stress state is determined for an unconstrained plate. In the second, the free vibration problem is solved; thermal effects from the first calculation are included by way of nonlinear membrane-bending coupling which in turn defines the free vibration reference state. The problem is solved using a finite element formulation to determine the natural frequencies and vibration modes of the plates. Two different plate-stiffener geometries are used to illustrate the effects of stringer size, stringer placement and temperature difference. Two principal results are obtained: first, it is shown that thermal residual-stresses can have a significant effect on the natural frequencies; secondly, thermal residual-stresses can be tailored to increase natural frequencies.
On the Optimization of Composite Cylindrical Sandwich Shells Subjected to Beam Type Bending
Authors: Vinson Jack R. 
Published: March 2022

Abstract
Sandwich construction offers several advantages over monocoque and various discretely stiffened structures. These include greater load carrying ability, reduced weight, higher buckling loads and higher fundamental natural frequencies. The equations for the analysis and design of sandwich cylindrical shells subjected to beam type bending are presented herein. These equations are then manipulated to provide the face thickness, core depth, and core shear modulus to produce a minimum weight structure for a given load index and face material system. A factor of merit to select the best face material is also presented. As examples, Carbon/epoxy and E-glass/epoxy cross-ply composite faced sandwich shells are compared, as well as comparison with a monocoque cross-ply laminated shell.
Experimental Study of Wavy-Stratified and Countercurrent Annular Flow Using Photochromic Dye Activation Technique
Authors: Kawaji Masahiro , Karimi Gholamreza , Nasr-Esfahany Mohsen 
Published: March 2022

Abstract
A non-intrusive flow visualization method called photochromic dye activation (PDA) technique has been used to investigate flow structures and mechanisms in wavy-stratified and annular flows in a horizontal channel and wavy falling films in countercurrent annular flow in a vertical tube. This non-intrusive flow visualization technique utilizes light activation of a photochromic dye material dissolved in a clear liquid and is a molecular tagging technique, requiring no seed particles. It has been used to yield both quantitative and qualitative flow data in the liquid phase in wavy-stratified, annular and countercurrent annular flows.
On Incompressible Turbulent Flow
Authors: Gao Ge , Yong Yan 
Published: March 2022

Abstract
A new unilateral average scheme is proposed in this paper for the purpose of retaining the first-order statistical information of turbulence fluctuations. In this approach, the fluctuations are divided into two groups according to their projections onto the mean flow. A forward (backward) fluctuation has a positive (negative) projection, and the corresponding ensemble average is called forward (backward) drift velocity. The momentum equations of these drift flows are derived within the framework of the Navier-Stokes equations. With the aid of the concept of modified eddy viscosity, these momentum equations join the conventional Reynolds-averaged Navier-Stokes equation constituting rational equations of incompressible turbulent flow. The rational equations contain no empirical coefficients, and their very same form is valid for all flow regions. The merit of the present approach is demonstrated by a numerical example of transition simulation of a flat-plate boundary layer without using the wall functions. Details of the transition, including change in velocity profiles from laminar to turbulent and change in thickness and length of the boundary layer in the transition zone, are in good agreement with existing experimental results.
Performance of the Triple-Concentric Air-Assist Atomizer
Authors: Mansour Adel , Humphrey William , Chigier Norman 
Published: March 2022

Abstract
The spray characteristics of the triple-concentric air assist atomizer have been explored using a Greenfield Digital Spray Analyzer and a Malvern Particle Sizer. The improved performance of the atomizer, as measured by the total amount of air required to generate a particular average droplet size, was demonstrated. A nearly ten-fold reduction in the total air quantity required for atomization is achieved.
Does a Strange Attractor Exist in Two-Phase Vertical Upflow?
Authors: Langford Heather M. , Beasley Donald E. 
Published: March 2022

Abstract
Instantaneous pressure measurements in air-water vertical upward flow in a circular pipe were analyzed to determine if the signals are consistent with deterministic chaotic behavior. Analysis of conventional Fourier power spectra characteristics yielded evidence consistent with a chaotic signal. Chaos measures were employed to provide both qualitative and quantitative evidence of the nature of the dynamics in bubbly flow (hemispherical cap), slug flow, and churn flow. A qualitative study of the system trajectory in phase space revealed dynamics consistent with a nonlinear system. The positive definite values of Kolmogorov entropy for all pressure signals quantitatively indicated that the system may be governed by chaotic dynamics. Therefore, the flow regimes studied in this investigation indicate the presence of a strange attractor.
Some Investigations on Flow Through Chevrons of Moisture Separator and Reheater Used in Nuclear Power Plants
Authors: Iyer V. Keshava , Dasgupta A. , Rao B. Venkat , Srivastava R. 
Published: March 2022

Abstract
An innovative working model of a Moisture separator reheater (MSR) used in nuclear power plants was fabricated using transparent acrylic sheets. All the internal flow passages including drain water siphoning arrangement was modelled. The sinusoidal vanes (chevrons) of the MSR were made out of galvanised iron sheets. The model was tested in an air flow test rig fitted with water spray nozzles, mounted in counter flow direction. Effect of inlet flow velocity on the performance of the MSR was studid over range of air flow velocities between 4.50 to 6.75 m/s. The pressure drop occurring in the fine separator of MSR was determined from the probe traverse data at the fine separators. The critical velocity of the flow through the chevron packs was determined from the probe traverse data. Using the overall separation efficiency, the average droplet size used in the air-water droplets was calculated. The pressure drop data can be used to detect fouling of the chevrons. The operating flow velocities at inlet to chevrons are known for the present experimental results.
Propagation of Thermal and Evaporation Waves Through Water-Wet Porous Media During Through-Flow Air Drying
Authors: Stacey Devin A. , Udell Kent S. 
Published: March 2022

Abstract
The simultaneous propagation of thermal and evaporation waves through a one-dimensional, water-wet porous media subjected to through-flow air drying is investigated through a set of theoretical, numerical, and experimental studies. The injection of dry air at a constant temperature, equal to the uniform initial temperature of the medium, is considered. Theory is developed for the limiting cases of i) a fast evaporation wave velocity relative to the characteristic thermal wave velocity, and ii) a fast thermal wave velocity relative to evaporation wave velocity. Mass and energy conservation equations are transformed to coordinates moving with the waves and the general energy transfer and drying behavior is described. Numerical simulations and experiments were performed for the two limiting cases plus one in which the evaporation wave velocity was approximately equal to the speed of the thermal wave. The numerical simulations and experimental data verified the basic features of the theoretical description. Theoretical, numerical and experimental results show that dryout times and temperature distributions in the one-dimensional porous medium were strongly dependent on the relative speeds of the thermal and evaporation waves. Contrary to conventional thought, the temperatures found in the porous matrix are not directly related to wet-bulb values. Under the condition where the evaporation wave velocity is equal to the speed of the thermal wave, a theoretical singularity suggests a very large temperature drop at the front; simulations and data for velocities approximately equal show the temperature at the front continuing to decrease with time to an extrapolated limit of freezing water.
Modeling of Growing Billet Shape in Spray Forming Process Using Scanning Gas Atomizer
Authors: Kang Shinill , Chang Dong-Hoon , Lee Eon-Sik 
Published: March 2022

Abstract
A numerical method is presented to predict and analyze the shape of a growing billet produced from the “spray forming” which is a fairly new near-net shape manufacturing process. It is important to understand the mechanism of billet growing because one can obtain a billet with the desired final shape without secondary operations by accurate control of the process, and it can also serve as a base for heat transfer and deformation analyses. The shape of a growing billet is determined by the flow rate of the alloy melt, the mode of nozzle scanning which is due to cam profile, the initial position of the spray nozzle, scanning angle, and the withdrawal speed of the substrate. In the present study, a theoretical model is first established to predict the shape of the billet and next the effects of the most dominant processing conditions, such as withdrawal speed of the substrate and the cam profile, on the shape of the growing billet are studied. Process conditions are obtained to produce a billet with uniform diameter and flat top surface, and an ASP30 high speed steel billet is manufactured using the same process conditions established from the simulation.