bluuebunny/crossref_metadata_2025 huggingface dataset:
Scalability Studies on a cc-NUMA Computer Architecture for Large Automotive Simulations
Authors: Hytopoulos Evangelos , Kremenetsky Mark D. , Andra Ramesh , Sun Richard , Posey Stan
Published: January 2022

The maturity of the Computational Fluid Dynamics methods and the increasing computational power of today’s computers have allowed the automotive industry to incorporate the CFD technology in several stages of the design process. As the application of the CFD technology is moving from the component level analysis to the system level, the complexity and the size of the models increase continuously. Successful simulation requires synergy between CAD, grid generation, and solvers.

The requirement for shorter design cycle has put severe limitations on the turnaround time of the numerical simulations. The time required for a) mesh generation (around bodies of complex geometry, such as the geometry of a complete car), and b) obtaining numerical solutions (for flows with complex physics) has traditionally been the pacing item in CFD applications. Unstructured grid generation techniques and parallel algorithms have been instrumental in making such calculations affordable. Availability of these algorithms in commercial packages has proliferated in the last few years and parallel performance has become a very important factor in the selection of such methods for production work.

Although extensive research has been devoted in determining the optimum parallel paradigm, in practice the best parallel performance can be obtained only when the algorithms and paradigms take into consideration the architectural design of the target computer that they are intended for. The present paper addresses the issues related to the porting and optimization of a commercial code (Fluent/UNS) on a cache-coherent (cc) Non Uniform Memory Architecture (NUMA). Issues related to the Message Passing system and the memory to processor affinity are investigated using both a sample CFD code and Fluent/UNS. The scalability of the code when applied to the problem of the front-end cooling simulation of a development prototype family sedan are presented and discussed. Since speed and accuracy are the ultimate goals for using CAE in the design process a discussion concerning the model preparation time, grid generation process, and solution time will be presented. Comparison with available experimental data will be presented and discussed.
Fluid Transient in a Voided System
Authors: Niyogi Kalyan K. , Burdett Robert R. , Unikewicz Steven
Published: January 2022

The phenomenon of void formation in a piping system due to heat transfer and subsequent collapse due to pump start has been explored. The analysis is based on a computer model developed for the RELAP5 computer program [Ref. 1] and is applied to a cooling water system in a nuclear plant. This evaluation has been performed to respond to a generic concern in the industry. The concern arises from the fact that if the cooling water pump fails and there is significant heat transfer from the process side into the system, there is a potential for void formation in the system. Subsequently, as the pump restarts the void collapses due to pressurization and condensation, and consequently, may result in significant pressure surges.

It has been observed that for a closed system the pressure surges are greatly influenced by the presence of a surge tank connected at the pump suction piping. During the initial period of the restart of the pump the fluid is drawn from the surge tank at a greater proportion until the fluid in the main line is accelerated to a steady state value at which time the flow in the surge line ceases. The relative speeds of the two fluid fronts, one approaching to the void and another departing from the void, at the time of the complete collapse determine the surge pressure.

Factors affecting the surge pressure include the resistance in the surge line, the size of the void and the quality of contained steam, temperature of water surrounding the void, and the amount of non-condensable present in water. The forces calculated for the piping segments could be significant compared to other loads on the supports.

The most effective ways of reducing excessive pressure surges include pressurization and/or increasing the elevation head of the surge tank and increasing the surge line resistance by installing an orifice or throttling of an existing valve.
Column Separation in Inclined Pipes
Authors: Husaini Syed M. , Arastu Asif H.
Published: January 2022

The most commonly used models (based on the Method of Characteristics numerical scheme) for column separation in liquid pipes assume that the vapor pocket occupies the whole cross sectional area of the pipe. Beyond the right and the left boundaries of the vapor pocket the pipe cross sectional area is full of liquid. However, under certain conditions, depending on the pipe gradient, flow rate, etc., the piping downstream of the high elevation point may have flow that only occupies a portion of the pipe cross section. The empty region of the pipe will consist of vapor formed due to the flashing of the liquid. The conventional methodology used for the analysis of column separation cannot be applied under such conditions. A MOC based calculation scheme is developed, which treats the partially filled regions of the piping system as open channel flow. It is generalized to allow for transition from partially full to full flow conditions, and vice-versa. This methodology has been incorporated into the computer program HSTA (Hydraulic Systems Transient Analysis) and the advantages/limitations of the various methodologies are compared.
Numerical Study of Effects of a Bellmouth on the Entrance Flow in a Circular Pipe
Authors: Kanda Hidesada
Published: January 2022

The flow characteristics in the bellmouth region of a circular pipe have been numerically studied for Reynolds numbers, Re, ranging from 1000 to 4000. Until now, the axial velocity has been assumed to be uniform at the bell-mouth outlet both experimentally and theoretically. The calculation results, however, reveal that it develops a profile somewhat towards the Poiseuille’s parabolic profile. Next, it was found that the pressure on the wall of the bellmouth is lower than in the central core. This result contradicts both Bernoulli’s law and Prandtl’s boundary-layer assumption. Moreover, a feasible reason for the increase in critical Reynolds number when using bellmouths was identified, i.e., if the bellmouth region is replaced by the pipe one, it was observed that the equivalent Re decreases from the original Re value.
Unsteady Pipe Flows of a Viscoplastic Non-Newtonian Fluid: Effects of Pressure Gradient Waveform
Authors: Hammad Khaled J.
Published: January 2022

Unsteady flows of a Bingham non-Newtonian fluid through a circular pipe have been studied numerically. These flows are impulsively started from rest via imposing a cyclic pressure gradient having a specific waveform. Triangular, sinusoidal, and square waves were considered, each varying around a non-zero mean value corresponding to the steady-state one. The parameters varied in this study are the amplitude of the time varying pressure gradient (8), Strouhal (St), Reynolds (Re), and Yield (Y) numbers within the following range: 1 < ε < 2, 0.1 < St. Re < 100, & 0 < Y < 10. Effects of these parameters on flow transients and asymptotic, i.e. pulsatile, flow field characteristics are demonstrated. Two relevant time scales are introduced, a momentum diffusion time scale, τυ = ρR2/ηp, and a periodic convective time scale, τc = 2π/ω. Time-averaged characteristics of the pulsatile flow field are presented as a function of the ratio τυ/τc. Those characteristics are determined to be quasi-steady-state, and steady-state like within the lowest and highest, respectively, of the studied τυ/τc values. Pulsating the flow of a Bingham fluid, within the low and intermediate τυ/τc ranges leads to substantially higher flow rates than the steady-state ones. This is true for all investigated waveforms with the lowest and highest increases corresponding to the triangular and square waves, respectively.
Experimental Determination of Added Mass in Different Directions of In-Situ Complex Objects With Non-Free Boundary Conditions
Authors: Lynch John
Published: January 2022

Added mass, or virtual mass, is the mass of fluid which moves with a submerged object when the object is accelerating or the fluid is accelerating around it. This concept is of interest many fields. Added mass is normally determined analytically by potential flow theory for relatively simple objects, or by experimental methods for more complicated objects. Even though the objects’ added mass applies to an object with no other objects around it and with uniform boundary conditions, the added mass may be determined experimentally even if the object is mounted rigidly at one end. That is the subject of this paper.
An Analytical Aspect of the Preston Equation
Authors: Hocheng H. , Tsai H. Y.
Published: January 2022

An analytic model of the material removal rate is proposed, and is found equivalent to the empirical Preston Equation reported in 1927 for the glass polishing. The effects of the applied pressure, the polishing velocity between the wafer surface and the pad surface, and the mechanical properties of material are identified. From the viewpoint of microscopic material removal, the material removal rate is proportional to the cubic of the true pressure loaded by a single abrasive, while the relationship is linear when the nominal polishing pressure between pad and wafer is considered.
Dimensional Fault Diagnosis for Compliant Beam Structure Assemblies
Authors: Rong Q. , Ceglarek D. , Shi J.
Published: January 2022

A model-based diagnostic methodology is proposed for the dimensional fault diagnosis of compliant beam-type assemblies in automotive or aerospace assembly processes. This method uses the measurement data to detect and isolate dimensional faults of compliant beam assemblies caused by part fabrication error and part-to-part interferences. The proposed method includes a predetermined fault patterns model and a fault mapping procedure. The fault patterns are modeled by the diagnostic vectors derived from the inversed stiffness matrix of the beam structure. The fault mapping procedure combines Principal Component Analysis (PCA) of measurement data and fault pattern recognition using statistical hypothesis tests. Verification of the proposed method is presented through simulations and one case study.
Fault Diagnosing of Large Rotating Machinery Using Evolutionary Spectrum
Authors: Jia Minping , Du R.
Published: January 2022

Fault diagnosis of large rotating machinery sets is very important for many industry sectors. However, it is also difficult because of its complexity. The conventional fault diagnosis methods are based on FFT spectral analysis. While its effectiveness has been approved by many applications, it also has significant limitations. In fact, it has been found that many faults have similar spectral patterns. In order to pinpoint the cause of the faults, it may be necessary to vary the speed to get additional information. Nevertheless, the speed variation makes the vibration signal non-stationary. This in turn makes the FFT spectral analysis imperative. In this paper, it is proposed to use a new technique, called evolutionary spectrum, to analyze the non-stationary signal and hence diagnose the faults. First, following a brief introduction of wavelet transform, the evolutionary spectrum is described. Next, the implementation procedure of the evolutionary spectrum is given. Then, by means of computer simulation and experiment results analysis, it is shown that the evolutionary spectrum can effective capture the fault patterns and hence, diagnose rotor unbalance and rotor stiffness asymmetric.
Intelligent Diagnosis of the Root Cause for Rejects in the Automatic Transmission Assembly Process
Authors: Chen Yubao
Published: January 2022

This paper presents a method for the diagnosis of reject root causes in automatic transmission assembly process based on the fuzzy multiple voting scheme. As the first step, data from all the valid test points were collected and studied based on their statistical characteristics. An information-gain-based procedure was followed to quantitatively evaluate the relevance of each test point to the diagnosis process. Accordingly, an objective rank of all relevant test points was generated for a particularly reject. The root cause of rejects was then identified by a procedure based on a fuzzy multiple voting classification algorithms. This method has been tested with top five rejects in a transmission assembly process and promising results have been obtained.
Thread Formation Mechanism by Planetary Conical Rolling
Authors: Mori Toshihiko , Nakashima Kunihiko , Abraha Petros
Published: January 2022

Planetary conical rolling, PCR, is a large deformation tube forming process that produces high accuracy products. PCR process can therefore be used to produce features on the surface of tubes without an overall distortion. In this research, forming of a thread feature on the surface of thin tubes is experimentally examined. The results show thread forming process is composed of three step by step stages that form a high precision tube surface features.
Thermal Modeling and Control of Material Processing in Scan Welding
Authors: Doumanidis Charalabos , Fourligkas Nikolaos , Korizis George
Published: January 2022

The paper focuses on thermal analysis of scan welding, a new joining technique redesigned to ensure the composite morphologic, material and mechanical integrity of the weld. This is obtained by real-time control of the temperature field by a proper dynamic heat input distribution on the weld surface. This distribution is implemented in scan welding by a single torch, sweeping the joint surface by a controlled reciprocating motion, and power adjusted by feedback of infrared temperature data in-process. A numerical simulation and an analytical multivariable model of the thermal field in scan welding is established, using real-time identification of its parameters. An adaptive thermal control scheme is thus implemented and validated computationally and experimentally on a robotic Gas-Tungsten Arc Welding setup. The resulting thermal features of scan welding are analyzed in terms of material structure and properties of the weldment.
An Analytical, Non-Dimensional Representation of Chip Area for Corner-Radiused Tools Under Depth-of-Cut and Feed Variations
Authors: Ozdoganlar O. Burak , Endres William J.
Published: January 2022

A new, analytical chip-area representation for corner-radiused tools under both depth-of-cut and feed variation is presented. This situation occurs for many tool geometries and under many practical conditions. Results obtained with the new model are compared to an exact area computation algorithm based on geometrical shapes. The new representation and its associated expressions are far more simple than those of the exact area representation. The errors introduced by the new representation are very small, and when a very simple error compensation term derived here is added, almost negligible for most conditions considered.
Environmentally Conscious Disposal Considerations in Cutting Fluid Selection
Authors: Skerlos Steven J. , DeVor Richard E. , Kapoor Shiv G.
Published: January 2022

Traditionally, negative environmental impacts of cutting fluid disposal have not been considered during cutting fluid selection. These impacts may result from hazardous chemicals or chips that might be found in a spent cutting fluid or from excesses in biochemical oxygen demand (BOD), oil content (FOG), nitrates, or phosphates that cutting fluids typically feature. By considering the portion of the cutting fluid life cycle after final use at the machine tool, this work considers simple, quantifiable metrics that might be used to compare fluids based on their impact on industrial wastewater pre-treatments and publicly owned treatment works (POTWs). The discussion begins with definitions of various environmental issues associated with cutting fluid disposal. Subsequently, a three component matrix is developed that can serve as a metric to compare alternative cutting fluids on the basis of the cost of disposal and legally defined hazards due to fluid chemistry and workpiece residuals found in cutting fluid wastes.
Process Design of Resin Transfer Molding With Computer Simulation
Authors: Zhang Chuck , Jiang Shunliang , Wang Ben , Han Kerang
Published: January 2022

Resin transfer molding is one of the most common fabrication methods for composite materials. It is attractive due to its high volume, high performance, and low cost manufacturing of polymer composites. In this process, a dry preform of reinforcing fibers is placed inside a closed mold; then the resin is injected into the mold cavity. The composite part can be removed from the mold after the resin cures. This paper surveys current issues in the resin transfer molding process and focuses on mold filling and simulation. The Control Volume Finite Element Method is applied to simulate the process. The 2-D and 3-D computational methods are presented. The simulation program was developed with C language by the authors. The 2-D and 3-D models were integrated in the program. In real applications, the 2-D elements and 3-D elements can be applied simultaneously according to the specific requirements. MSC/PATRAN 3 software (MacNeal-Schwendler Corporation) was used to generate the finite element mesh and display the results. Some case studies are conducted to demonstrate the application of the computer simulation to RTM process design.
A Constant Engagement Offset for 2-1/2 D Tool Path Generation
Authors: Stori James A. , Wright Paul K.
Published: January 2022

Contour-parallel and direction-parallel machining strategies typically result in widely varying cutter engagements, excessive plunging and slotting, and sharp velocity discontinuities. In this paper, a new offset is introduced which maintains a constant cutter engagement throughout. By incorporating such an offset into spiraling tool paths, constant chip geometry can be achieved for the majority of the material removal operation. An algorithm for constant engagement tool path generation for convex geometries is developed, and experimental results are presented which demonstrate greatly reduced force variations while cornering.
Nonlinear System Identification Using Lumped Parameter Models With Embedded Feedforward Neural Networks
Authors: Fan Yimin , Li C. James
Published: January 2022

This paper describes a new methodology to identify multi-degree-of-freedom nonlinear systems from the system’s operating data. The methodology includes a new nonlinear model architecture which embeds feedforward neural networks to represent unknown nonlinearities in a lumped parameter model, and a learning algorithm to train the embedded neural networks as well as the other model parameters to obtain model fidelity. Three simulated and experimental examples are used to validate the proposed methodology.
New Concepts on Multi-Sensor Monitoring for Reconfigurable Machining Systems
Authors: Kannatey-Asibu Elijah
Published: January 2022

Effective monitoring of a manufacturing process is essential for ensuring product quality. This paper outlines some basic concepts that will form the fundamental building blocks for selecting an appropriate monitoring system for any given machining system. Presented are the concepts of Fault, Sensor, Signal Processing, and Computing Spaces, and their generic characteristics. A mapping theory that should enable suitable sensors, signal processing algorithms, and computer hardware and software to be selected for a given machining system is discussed. Such a fundamental theory should facilitate development of monitoring systems for reconfigurable machining systems.
Detection, Modelling, and Compensation of Geometric Errors in Coordinate Measuring Machines
Authors: Barakat Nael A. , Elbestawi Mohamed A.
Published: January 2022

A rapid and inexpensive approach is proposed for identifying the existence of geometric and kinematic errors in a Coordinate Measuring Machine (CMM) by means of a circular profile measurement. The proposed approach is applied to an existing CMM where test results are compared to simulation results and errors are identified. Further, a method to improve the CMM performance by error compensation is explained. This method consists of the general and systematic kinematic and geometric error modelling of a CMM for a reference temperature, in addition to the development of a compensation strategy to correct these errors. To verify the rapid error identification approach proposed above and to calculate the error model coefficients for the CMM under investigation, individual errors of the CMM are measured by laser interferometry. The resulting error model is employed directly in the compensation for the CMM errors. Performance improvement of this CMM is presented through measurement of its work tolerance before and after compensation, in accordance with the ASME standards for CMM performance evaluation.
Analysis of the Runout Effect on Hole Quality in Drilling
Authors: Chiou Richard Y. , Wu Kun
Published: January 2022

This paper describes an experimental study of the mechanism of drilling runout and its influence on hole quality. This approach considered the effects of the drilling runout on the hole quality features under various cutting conditions. The drilling runout model was developed as a flexible cantilever beam with a tilt offset. A series of drilling experiments was performed to investigate the drilling runout effect on the hole quality. Standard twist drills were used to drill aluminum workpieces. The drilled hole quality was measured by a Coordinate Measuring Machine (CMM). It showed that the drilling runout has a significant effect on hole quality.
Kinematics Performance Analysis of a Parallell-Chain Hexapod Machine
Authors: Song Jing , Mou Jong-I , King Calvin
Published: January 2022

Inverse and forward kinematic models were derived to analyze the performance of a parallel-chain hexapod machine in this paper. Analytical models were constructed for both ideal and real structures. Performance assessment and enhancement algorithms were developed to determine the strut lengths for both ideal and real structures. The strut lengths determined from both cases can be used to analyze the effect of structural imperfections on machine performance. In an open-architecture control environment, strut length errors can be fed back to the controller to compensate for the displacement errors and thus improve the machine’s accuracy in production.
Comparison of First-Order Shear and Plane Strain Assumptions in Warpage of Simply Supported Printed Wiring Boards
Authors: Polsky Yarom , Ume I. Charles
Published: January 2022

The influence of transverse shear strain in the lamination theory modeling of Printed Wiring Board (PWB) deflection due to support conditions was examined. The in-plane mechanical properties of the core materials of a commercial PWB were measured as a function of temperature. Classical laminated plate theory and first-order shear deformation theory solutions for the out-of-plane deflection of a bare board configuration with two opposite edges simply supported and the remaining edges free were obtained. The weight of the board was approximated as a distributed transverse load. The effect of material property decrease with temperature and FR-4 layer thickness were examined to compare first-order shear and plane strain assumptions for the predicted warpage.
Challenges in Slicing Large Diameter Silicon Wafers Using Slurry Wiresaw
Authors: Chandra Mohan , Leyvraz Philippe , Talbott Jon A. , Gupta Kedar P. , Kao Imin , Prasad Vish
Published: January 2022

This paper describes the challenges present in slicing large diameter silicon ingots using the multiple slurry wiresaw or commonly known as the wiresaw. The wiresaw uses a web of wires moving at a fast speed with a suitable abrasive suspended in a media dropped over the wires. The silicon ingot is lowered on to the web from top down and the cutting action is achieved by the abrasive particles rolling and indenting on the ingot thus removing material. While the cutting mechanism itself is fairly well understood, to achieve the similar surface finish and quality compared to smaller diameter ingots, the cutting parameters of large diameter ingots is not so straightforward. There are many parameters which have to be taken into account which normally would have been neglected or thought insignificant in the case of smaller ingots. We will discuss the various parameters that are affected while slicing small diameter ingots (typically 100 mm) as well as larger diameters (typically 300 mm). Results of experimental tests using commercial wiresaws for slicing these ingots are given to show the effect of wire speed, table speed, the nature of the slurry and other parameters. We also will show how such effects can be described in an analytical fashion by models that have been developed to demonstrate such cutting mechanism.
Current Status of 300 mm Silicon Wafer Characterization
Authors: Messina Troy , Au Chi , Shih Steven , Yang Zach , Goodall Randy , Huff Howard
Published: January 2022

Characterization data for polished 300mm silicon wafers has been obtained, including wafer supplier process and reclaim capability, flatness, particles, interstitial oxygen, metrology tool availability, and tool contamination. Silicon supplier-I300I correlation studies are also detailed.
Technology and System Challenges for 300 mm Metal and Polysilicon Plasma Etch
Authors: Papanu James , Loewenhardt Peter , Olson Dale , Kholodenko Arnold
Published: January 2022

The development of 300mm metal and polysilicon plasma etch systems presents numerous technical challenges. The main efforts can be delineated as mainframe and integration, chamber development, and process characterization and development. With respect to system mainframe and integration, we discuss wafer handling in detail. Discussion of the chamber design effort includes decoupled plasma source development, the electrostatic wafer chuck, and gas feed and distribution as guided by the use of fluid flow simulation. Process and hardware performance data are presented as they illustrate design success.
Performance Prediction of Elastomeric Gasket Materials by Compression Stress Relaxation
Authors: Pannikottu Abraham , Samples Robert , Sadon Stanley J.
Published: January 2022

In the automotive industry, the most widely used technique to predict the sealing capacity of an elastomeric gasket material is based on compression set data which is obtained after short term aging in air or reference fluids. Compression set measures the percentage of permanent deformation after the removal of the applied strain. This is an indirect measure of the sealing capacity and it can easily be misleading as a predictor of the sealing performance of gasket materials. Recent increases in service temperature requirements along with use of “SG” grade motor oils have created the need for a better means of assessing the high temperature, long term performance of elastomeric materials used in automobile engine gaskets. This paper reports Compression Stress Relaxation measurements on a variety of gasket materials using the Wykeham-Farrance Compression Stress Relaxation tester. This study also examines the effect of cycling heating and cooling on the retention of sealing force of gasket materials and includes the cumulative effect of exposure of the gasket material to motor oils and ASTM #2 oil at 125°C up to 1008 hours.
Stress Analysis of Bolted Joints With Plain Washers
Authors: Sawa Toshiyuki , Yasui Hajime
Published: January 2022

Bolted joints have been widely used in many kind of industries, being used commonly. Recently, the bolt strength has been improved and high strength bolts are usually used. As the bolt strength increases, bolt preload increases. In reliable design standpoint of bolted joints, the contact stress at the bearing surfaces between a bolt head and a clamped part must be examined in order to prevent the permanent set due to over stress at the bearing surfaces. Thus, flat washers have been used in bolted joints in order to enlarge the bearing area. In this paper, the contact stress at the bearing surfaces between a plain washer and a clamped part is analyzed using the axisymmetric theory of elasticity as a contact problem, where clamped parts are finite hollow cylinders. In the analysis, a bolt head and bolt shaft are replaced by finite solid cylinders and a plain washer and the clamped parts by finite hollow cylinders. In the numerical calculations, the effects of the stiffness, the thickness and the outer diameter of plain washers on the contact stress distribution are examined. Furthermore, it is important to know the mechanical behaviors of bolted joints with plain washers subjected to external loads. When, an external load W is applied to a bolted joint with a plain washer, an increment of axial bolt force Ft occurs in the bolt and the contact stress between the clamped parts is decreased. The ratio Ft/W is known as the load factor and it is necessary to know the load factor in designing bolted joints with plain washers. The analysis of the load factor is also done. In addition, the effects of plain washers on the load factor are examined in the numerical calculations. The experiments to measure the load factor of bolted joints with plain washers are carried out. The results of the analysis are compared with the experimental results.
Effect of Interface Configuration on the Mechanical Behaviors of Bolted Joints
Authors: Kudo Atsushi , Sawa Toshiyuki
Published: January 2022

In designing a bolted joint, it is important to examine the sealing performance and to estimate the load factor, that is the ratio of an additional axial bolt force to a load. In order to improve the sealing performance raised faces of the interface have been used. But these interfaces in bolted joints have been designed empirically and the theoretical grounds are not made clear. In the present paper, in the case of T-shaped flanges with raised faces the sealing performance (clamping effect) is analyzed by a two-dimensional theory of elasticity and the point matching method. Then, the load factor is analyzed. Moreover, with the application of the load a bending moment is created in bolts and the stress is added due to this bending moment. The bending moment in the bolt is also analyzed. In order to verify these analysis experiments were carried out to measure the load factor and the maximum bolt stress. The analytical results are in a fairly good agreement with the experimental ones.
A Three Dimensional Finite Volume Method in Curvilinear Coordinates for Complex Geometries: Formulation and Analysis
Authors: Banerjee Sibashis S. , Hassan Y. A.
Published: January 2022

A strongly conservative finite volume formulation for complex geometries in three-dimensions using a complete transformation of the governing equations on a nonstaggered grid is presented. This method retains its conservative character at the scalar discretization level. The use of physical contravariant components as dependent variables eliminates the need for any transformation to calculate the cell face mass fluxes. A partially implicit treatment of the nonorthogonal diffusion terms is used to enhance the diagonal dominance of the scheme. This is an extension of the method proposed by Sharatchandra (1994). The method is then tested for two test problems for which analytical solutions are available and an error analysis is performed.
Reliability HCF Design of Gas Turbine Blades Using Probabilistic Goodman Diagram
Authors: Shen M.-H. Herman
Published: January 2022

A probability-based procedure has been developed to predict reliability of gas turbine engine blades subjected to high cycle fatigue. The procedures provides a systemic approach for predicting and designing turbomachinery blading reliability against various potential fatigue problems for all relevant vibratory modes and taking into account variability in geometry (e.g. dimensional variation, mistuning, etc.), unsteady aerodynamics, structural damping, and thermal loading. The variability in materials (e.g. damage, cracks, degradation, etc.) can be also considered in this approach. A reliability prediction was performed on gas turbine blades at high frequency modes (e.g. third strip modes) using a probabilistic vibratory stress distribution in conjunction with the Haigh or modified Goodman Diagrams. The cumulative reliability and risk assessment are then calculated using the fast probability integration (FPI) technique to construct a novel probabilistic Goodman (or Haigh) diagram which provides blade’s lifetime design guide line and an optimal maintenance strategy in management in decisionmaking relating to the PM/inspection scheduling, replacement, spare parts requirements.
Adhesion, Adhesion Hysteresis and Friction in MEMS Under Controlled Humidity Ambients
Authors: de Boer M. P. , Knapp J. A. , Redmond J. M. , Michalske T. A. , Maboudian R.
Published: January 2022

In surface micromachining, compliant structures and high surface to volume ratios render surface properties such as adhesion and friction critical parameters in system reliability. The adhesion and friction of polycrystalline silicon (polysilicon) MEMS structures depends strongly on the ambient to which they are subjected. This dependence is reduced, but not eliminated, when molecular coatings are applied to their surfaces. From measured adhesion energy (Γ, J/m2) for uncoated beams, we demonstrate that capillary condensation produces an exponential dependence of adhesion on relative humidity (RH). For coated beams, we demonstrate that after substantial exposure to high RH ambients, adhesion begins to vary along the length of the beam. This implies a localized breakdown mechanism of the molecular coating. Finally, we present data on a new structure to measure friction in MEMS. With this structure, we can infer slip on a nanometer length scale.
Load Transfer Characteristics in the Vicinity of Fiber Breakage
Authors: Tandon G. P. , Pagano N. J. , McCartney L. N.
Published: January 2022

The single fiber, axisymmetric concentric cylinder model is widely used for analyzing the thermo-elastic stress field in a composite representative volume element. In this study, the concentric cylinder model has been utilized to evaluate the load transfer characteristics in the immediate vicinity of a broken fiber in a unidirectional composite. A number of researchers have studied the stress distributions around discontinuous fibers. The so-called shear lag analysis is frequently used for analysis of stress transfer between fiber and the matrix. However, this simplified approach leads to inaccurate predictions of shear stresses and energy release rates [1]. By developing sets of recurrence relations, McCartney [2] has extended the two cylinder stress transfer model to multiple cylinders and used the technique to study the stress transfer behavior when fiber fracture occurs. Using Reissner’s variational principle, Pagano [3] has developed the axisymmetric damage model to approximate the elastic stress field and energy release rates of bodies composed of concentric cylinders containing damaged regions either as annular or penny-shaped cracks in the constituents and/or debonds between them. This variational model of a concentric cylinder [3] can be easily employed to simulate fiber breakage.

The prediction of micro-mechanical damage initiation and growth in composite materials requires accurate stress and deformation analyses. For the fiber fracture stress transfer problem, singularities are encountered for the axial stress in the matrix in the plane of fiber fracture. In this work, the detailed stress and displacement fields in the neighborhood of fiber break are analyzed using the recursive [2] and variational [3] methods, and compared with the asymptotic stresses around the crack tip [4] and with other numerical methods such as FEM using mesh refinement in the regions of singularity. In this study a comparison of the different solutions is presented highlighting the distance at which leading terms of asymptotic analysis are dominant and the ability of the approximate elasticity solutions to capture the local radial and angular distributions near the crack tip. Also, the assumptions of the more commonly used shear-lag analyses will be critically assessed.
A Novel Eigenfunction Expansion Solution for a Three-Dimensional Crack Problem
Authors: Chaudhuri Reaz A. , Xie Minsheng
Published: January 2022

A new eigenfunction expansion method is developed to obtain hitherto unavailable explicit expressions for three-dimensional asymptotic singular stress fields in the vicinity of (a) an interior point (edge), (b) the surface corner point (vertex) and (c) the transition region located at the front of a a semi-infinite crack. In comparison with the existing asymptotic methods valid for the interior region, the present method is considerably easier to implement, and is also computationally more efficient in the sense that it does not need to resort to iterative schemes to solve the system of three coupled partial differential equations of three-dimensional elasticity theory.

At the crack front, the edge or the interior solution is valid at all points except the two vertices or the surface corner points, which Me in the closure of the edge. The edge or interior point singularity Si is understood in the context of a dihedron emerging radially (in the sense of the cylindrical polar coordinate system) from the edge and distributed over the crack front except the vertex. The vertex or the surface corner point singularity is, on the contrary, to be understood in the context of a cone emerging radially (in the sense of the spherical coordinate system) from the vertex. For the surface corner point, the present asymptotic analysis yields that the singular stresses are proportional to ρ−ss fij(q, f) as ρ → 0, ρ, θ, ϕ being the spherical coordinate system, where σs is the surface corner point singularity. For this special case of a crack, both si and ss are found to be equal to 0.5, although for other problems, e. g., a re-entrant corner of arbitrary interior angle, these are not equal. In the transition region, where both the edge and vertex solutions are superposed, a renormalization type approach is used to keep the crack front displacement finite, which, in turn, satisfies the locally finite strain energy condition for uniqueness.

Finally, the relationship between the strain energy release rate and the stress intensity factor is also investigated from a three-dimensional standpoint. Furthermore, numerical results pertaining to development of plastic yield zone ahead of the front of a semi-infinite crack are also obtained. The latter results are consistent with experimentally observed yield zones.
Interaction of Two Circular Cylindrical Inhomogeneities Under Antiplane Shear
Authors: Linzhi Wu
Published: January 2022

For the inhomogeneous medium with inclusions or inhomogeneities including fibers, whiskers, particles, cracks, etc. (see Mura, 1987), the interaction between inclusions or inhomogeneities is very important in analyzing and investigating the following problems: the stress concentration near inclusions or inhomogeneities, the effective properties, the damage mechanism and failure mode, etc. For this purpose, the elastic field of the infinite homogeneous isotropic medium with two circular cylindrical inhomogeneities under the antiplane shear stress is investigated. The corresponding analytical solution is obtained by using the conformal mapping and the theorem of analytic continuation. Here, two circular cylindrical inhomogeneities are parallel to each other, infinitely long along the direction perpendicular to xy-plane and have the radii rl and r2, respectively. When the matrix, assumed to be infinite in all directions, is subjected to the uniform antiplane shear stress, the present problem is the antiplane one.

From the results obtained, it can be found that the elastic field depends on the shear moduli of individual phases, the geometric parameters of the system and the applied shear stresses at infinity. When one of two circular cylindrical inhomogeneities has the same shear moduli with matrix, the present expressions can degenerate into the results of Gong and Meguid (1992). In addition, numerical results show that the shear moduli of two circular cylindrical inhomogeneities and the geometric parameters of the system have the important effect on the shear stress distribution. The presence of two circular cylindrical inhomogeneities makes the stress field between these two inhomogeneities to have sharper changing tendencies. When two circular cylindrical inhomogeneities approach each other, the interaction between these two inhomogeneities is more prominent.
Transient Elastic Wave Propagation and Local Dynamic Stress Concentration in Woven Fabric Composites
Authors: Chou Tsu-Wei , Chen Baoxing
Published: January 2022

Investigations of the response of composites to time-dependent loadings are of considerable importance in structural analysis of many engineering fields, including aerospace, aeronautic, naval and automotive applications. Wave propagation in woven fabric composites poses major theoretical and experimental challenges. The mathematical modeling of dynamic stress concentrations in woven fabric composites is a fairly difficult task due to the great number of wave interactions between the fiber and the matrix. When composite structures composed of woven fabric preforms are loaded impulsively, stress waves propagate in different constituent phases at different speeds, which results in dynamic normal and shearing stresses at the interfacial bond region as well as at the yarn cross-over points. The concentration of these stresses may initiate unstable delamination and eventually failure of the laminated structure. This paper presents a theoretical study on the elastic wave propagation and local dynamic stress concentration in woven fabric composites. The analysis focuses on the unit cell of an orthogonal woven fabric composite, which is composed of two sets of mutually orthogonal yarns of either the same fiber (non-hybrid fabric) or different fibers (hybrid fabric) in a matrix material. Using the mosaic model for simplifying woven fabric composites and a shear lag approach to take into account the inter-yarn deformation, a one-dimensional analysis has been developed to predict the local elastodynamic and elastostatic behavior. The initial and boundary value problems are formulated and then solved using Laplace transforms. Closed form solutions of the dynamic displacements and stresses in each yarn, and the bond shearing stresses at the interfaces between adjacent yarns, are obtained in the time domain for in-plane, as well as out-of-plane impact loadings. When time tends to infinity, the dynamic solutions approach to their corresponding static solutions, which are also developed in this article. Solutions of certain special cases are identical to those reported in the literature. Lastly, the dynamic stresses and bond shearing stresses of plain weave composites subjected to step uniform impacts are presented and discussed as an example of the general analytical model.
Comparison of Elastic Properties for Unidirectional and Woven Laminates
Authors: Schoeppner G. A. , Roy A. K.
Published: January 2022

An experimental program to examine the relationship between the material constants of laminates made of unidirectional pües and laminates made of woven fabric composites including plain weave (PW) and eight harness satin (8HS) weave has been conducted. All of the unidirectional and woven composite tension, compression and shear test coupons were fabricated with the same carbon fiber and toughened epoxy resin system. The test specimens were instrumented with back-to-back rosette strain gages and monitored throughout the test. The PW and 8HS woven fabric specimens were tested in both the warp and fill directions. The stress-strain curves of the woven fabric specimens reveal a knee (change in slope) at about 70 ksi, indicating the failure initiation process. The stress field of the weave geometry will be analyzed to understand the failure initiation process.
Interlaminar Phenomenon in Composite Materials: 1969–1999
Authors: Pipes R. Byron
Published: January 2022

The development of multiaxial laminates consisting of layers of collimated, high performance fibers in a polymer matrix provided the opportunity to design material properties for each application. The earliest analytical methods for determining stresses in the individual laminae assumed linear strain variation through the laminate thickness (Kirchhoff assumption). For much of the design work with composite laminates this simplification was both appropriate and convenient. Yet in 1969 it was postulated by the leading engineers and scientists (such as Dr. N.J. Pagano and Dr. J. E. Ashton) that a planar state of stress within each laminae could not exist near a laminate free-edge. The argument rested on the fact that inplane shearing stresses, induced in the angle-ply laminae of a laminate under normal external loads, could not exist at the free-edge.

Numerous investigators began analyses of the three-dimensional stress state in finite-width laminates including Pagano, Pipes, Puppo and Evenson. Several important developments came for this early work. First, the interlaminar load transfer mechanism between laminae in finite-width laminates was fully articulated as a boundary-layer phenomenon and the influence of stacking sequence on the sign of the interlaminar normal stress for bidirectional laminates was discovered. The roles of laminate material anisotropy and geometric variables such as laminae-to-laminate thickness and laminae-to-laminate width were clarified. A singularity in the interlaminar normal stress at the free-edge was postulated in this early work.

The development of three-dimensional and anisotropic finite-element methods and increases in computation power lead to the further investigation of the afore mentioned phenomenon and to the ability to analyse the three-dimensional state of stress occurring at numerous geometric discountinuities typically found in composite structure. These analyses have confirmed many of the findings of the earlier work and provide powerful tools for investigations required in the future.