bluuebunny/crossref_metadata_2025 huggingface dataset:
Parallel Computing Issues in a Particle-Continuum Model for Two-Phase Flows
Authors: Sigurgeirsson Hersir
Published: January 2022

We describe a model for two-phase flows where droplets are considered as point particles interacting with the flow, in which they are embedded, and each other. The particles interact with the flow through interchange of mass, momentum, and energy, and with each other through collisions. We investigate algorithms for computer implementation of the model using appropriate data structures to efficiently detect and handle collisions between particles, and to stably and accurately describe the particle-continuum interaction. Parallel implementation of the model poses several challenging problems, such as load balancing the particle portion of the computation and sharing data between the continuum and particle parts. We address these issues through experiments on an SGI Origin2000 and develop some simple models of computational cost.
Parallel Algorithm for the Solution of High Order Discretization of Elliptic PDEs
Authors: Mateescu Gabriel , Ribbens Calvin J.
Published: January 2022

We present a parallel preconditioned-GMRES algorithm for solving second-order elliptic PDEs defined on rectangular domains with Dirichlet and Neumann boundary conditions, and discretized with piecewise Hermite bicubics. The parallel performance of the algorithm is assessed by way of numerical experiments.
An Efficient Finite Element Method for the Representation of Fluid Structure Interaction in Large Structural Transient Dynamic Analyses
Authors: Harkness Alexander W. , Schwirian Richard E.
Published: January 2022

A finite element model method was developed to evaluate fluid structure interaction between core support structures and reactor coolant during rapid Loss Of Coolant Accident (LOCA) conditions in Pressurized Water Reactors (PWR’s). The hydraulic behavior of the reactor coolant was modeled using a series of contained fluid elements linked to the structural elements using linear constraint equations. An advantage of this method is the significant reduction in the number of contained fluid elements required to accurately represent the fluid structure interaction. A large volume of fluid may be modeled by a single contained fluid element without compromising detail in the finite element representation of the structure. This three-dimensional finite element method represents an expansion of the two-dimensional methods presented by Riddell and Schwirian (1983).

To provide verification of the method, finite element analysis results produced for a benchmark analysis were compared directly to a series of hydraulic pressure pulse tests performed previously. The typical hydraulic pulse evaluated had a pressure ranging from 0 to 1200 psig with a duration of less than 40 msec. Good agreement was observed between test and analysis results.
Standardized Geometry Rules for Fluid Flow Analysis Software Applications
Authors: Wilson Roger D.
Published: January 2022

Standardized geometry protocol software is needed for use in conjunction with hydraulic analysis software.

Hydraulic models are used to analyze and solve steady-state and transient problems in many systems.

The owner of such systems often faces the need to utilize less rigorous modeling and problem solving techniques. This is due the high cost of having to repeatedly develop a geometric model of the same system for different hydraulic software applications because of different rules and criteria governing system modeling.

Instead a geometry model of such systems using a standard convention should be developed. All programs would recognize and be compatible with the standard. Such standardization would benefit both the owner and the software manufacturers.

Conceptual ideas about the standardized geometry protocol software are presented.

The protocol software sponsor must be a large organization such as ASME or EPRI to manage the effort through its development.
The Use of Computational Fluid Dynamics (CFD) in Selective Catalytic Reduction System Ductwork Design
Authors: Wilhite David C.
Published: January 2022

A selective catalytic reduction (SCR) system serving a mixture of two different exhaust gas streams is considered. The exhaust gases are petroleum combustion residues and contain high levels of toxic nitrogen oxides (NOx). The SCR system is used to minimize the hazardous content of the two exhaust streams to meet U.S. national standards.

The SCR system injects ammonia into a mixture of the two NOx-laden exhaust streams, which then pass through a catalyst, where a chemical reaction reduces the NOx to harmless water and nitrogen. The system operates most efficiently within specified gas temperature and velocity ranges.

This paper discusses the use of computational fluid dynamics (CFD) to design a ductwork geometry upstream of the SCR system that results in optimum performance. Various geometries are considered based upon physical space restrictions and operating conditions. The improved duct system results in the desired temperature and velocity ranges at the catalyst face while keeping the total application pressure drop below a preset value.
Analysis of Manufacturing Machinery Effectiveness for Surface Mount Lines
Authors: Yang Yung-Chyuan , Ling Frederick F.
Published: January 2022

This research is concerned with the examination of operational and maintenance data of six electronic manufacturing lines; and the evaluation of the overall equipment effectiveness of these lines at an electronic manufacturing company located in Austin, Texas. The underlying purpose was to help plan the adoption of total productive maintenance (TPM) and to help the company gain competitive advantage by optimizing machine effectiveness.

The overall equipment effectiveness of these six lines, consisting of one line with machines made by Manufacturer A, one line with machines made by Manufacturer B, and four lines with mixtures of machines made by both of the manufacturers, are all below fifty percent. The result reveals the need to reexamine the traditional maintenance strategies. This research also investigates possible causes for the aforementioned level of overall equipment effectiveness.
Application of Shannon’s Communication Theory to Degradation Assessment of Systems
Authors: Bryant Michael David
Published: January 2022

An analogy is made between a machine component (or system) and a communications channel. During operation, information is sent as a signal over a communications channel from transmitter to receiver. The signal over the channel is altered by limited dynamic bandwidth, nonlinearities and noise. The goal is for the receiver to extract and reproduce the message, despite distortions and noise. Design of communications systems is aided by powerful theorems of Shannon (1949), which establish minimum signal to noise ratios for error free transmission.

A machine component (or system) accepts a “signal” from an upstream component, by its function alters that signal, and then passes the “signal” on to the next downstream component. In the analogy of this article, a machine is a communications channel. When operating properly, the “signal” from an upstream component is “received” by a downstream component. Faults in the machine which disrupt functionality alter the “signal”. Faults will be viewed as agents that alter system parameters or contaminate the signal with “noise”. Unless the signal to noise ratio is kept sufficiently high, downstream components cannot “resolve” the “signal message” error free, and the machine malfunctions.

In this article, Shannon’s theorem’s will be applied to machinery to establish performance limits, and develop a failure criteria to assess functionality of new or degraded machinery. With these, operational condition of machinery and maintenance needs can be predicted.
Locator and Sensor Placement for Automated Coordinate Checking Fixtures
Authors: Wang Yu (Michael) , Nagarkar Sanjeev R.
Published: January 2022

This article proposes a systematic method for the optimal design of sensor locations for an automated Coordinate Checking Fixture (CCF). The fixture can be employed for making at-machine assessments of the dimensional accuracy of manufactured components. Coordinate measurements obtained by the sensors built into the fixture can be utilized in estimating geometric parameters of a manufactured part. Two important issues that arise in the design of a CCF are the optimal number of sensors to be used and the best locations for each sensor. The proposed method uses statistical analyses of the Fisher information matrix and the prediction matrix to obtain an optimal set of sensors from an initial candidate set. Sensors are placed at locations that maximize the determinant of the Fisher information matrix for best parameter estimation, while the sensor of the least contribution to the measurement objective is iteratively eliminated. With the benefit of physical insight, the design procedure results in a balanced decision for the optimal placement of sensors. The developed method also addresses the problem of selection of part locators for part localization in the CCF. An example is provided for illustration of the developed procedure.
A Control System for Microwave Processing of Materials
Authors: Groombridge Paul , Siores Elias , Oloyede Adekunle
Published: January 2022

This paper discusses a control system for microwave processing of materials. Microwave joining of ceramics and drying of timber are currently industry practices whilst microwave joining of engineering plastics and curing of epoxy adhesives are still being researched. In this study, all materials are processed in rectangular sections of waveguide fed by a magnetron with a maximum output power of 2 kW operating at 2.45 GHz. The most significant problems encountered when processing these materials are: (i) maintaining proper tuning to ensure maximum power transfer, (ii) thermal runaway, where the heating rate proceeds so rapidly that the material burns within a few seconds, and (iii) hot spot development, where localised regions heat up at a faster rate than adjacent regions. A computerised automated control system has been developed to alleviate these processing problems and has been successfully employed in joining a range of ceramics and engineering plastics, curing epoxy adhesives and drying wood. Results of preliminary tests obtained using the developed prototype are presented.
A Total Cost Comparison of Alternative Tolerancing Formulae
Authors: Graves Spencer B.
Published: January 2022

An important part of many engineering design projects is to specify the amount of variability permitted in critical characteristics of materials, components, and assembly. Different formulae have been suggested for relating input and output specifications. This article reviews the four basic tolerancing formulae that have appeared in the literature and shows that each solves a slightly different problem. In particular, optimal tolerances are based on costs and the probability distributions of input characteristics. Examples of alternative cost-distribution models are provided that (a) make each of the four basic formulae optimal, and (b) make optimal a solution not related to any of these formulae. This establishes that optimal tolerancing is influenced by issues not explicitly considered in the traditional debate over worst-case vs. statistical tolerancing.
Geometrical and Thermal Modeling for Design and Control of Material Deposition Processes
Authors: Kwak Yong-Min , Doumanidis Charalabos
Published: January 2022

In thermal solid freeform fabrication of layered products, simultaneous quality assurance of the part geometry and material structure requires concurrent design of the process conditions with the product features. For a heat transfer analysis yielding the material structure, an analytical, distributed-parameter quasi-linear thermal model is developed and tested in scan welding. This is based on Green’s field, identified in-process by infrared temperature sensing to reflect thermal nonlinearities. Similarly, a mass transfer model of the layer surface geometry is established on an analogous concept of the material deposition field, approximated by an ellipsoidal shape and identified in-process by Laser 3D scanning of the part topology in fused deposition modeling tests. The invertibility and computational efficiency of both models provide a basis for design of adaptive feedback control strategies for the thermogeometrical characteristics of rapid prototypes.
What Layered Manufacturing Can and Cannot Do for Rapid Production Tooling
Authors: Feng Chang-Xue (Jack)
Published: January 2022

Although the initial and primary use of layered manufacturing is rapid prototyping, demands of applying it to rapid tooling is growing dramatically in recent years, and using it to rapid tooling is making more and more sense in terms of saving more time and more money. There are different ways of applying layered manufacturing technology to rapid tooling, such as direct and indirect tooling, hard and soft tooling, using machines from different vendors, and applying to sand casting, investment casting, die casting, injection molding, etc. Furthermore, what accuracy and surface roughness can be provided to production tooling is another major consideration in rapid tooling. As a result, there are many challenges and research opportunities, in addition to many successful cases. Consequently, what layered manufacturing can and cannot do for rapid production tooling will be the focus of this paper.
A Framework on Design for Machining Operations
Authors: Xu Xun W. , Kong Helen
Published: January 2022

Given the fact that current technology has created islands of automation, lack of integration is a major obstacle in the widespread use of CAD/CAM in routine engineering work. This paper presents a case study of design for manufacturing. Design features in a CAD/CAM package have been investigated. Machining features as well as the cutting tools which can be used to produce the machining features are discussed and categorised. Feature mapping is then performed which establishes the links between design features and machining features, and between machining features and cutting tools. As a result, manufacturing information can be readily available at the design stage.
Machine Fault Diagnosis Through a Recursive Optimal Pairwise Linear Discriminant Function Method
Authors: Gu Shuxin , Ni Jun , Yuan Jingxia , Lee Jay
Published: January 2022

A Recursive Optimal Pairwise Linear Discriminant Function (ROPLDF) method based on pattern recognition theory is developed for multiple class fault diagnosis. This approach does not need a priori failure probabilistic knowledge. Optimal pairwise linear discriminant function (OPLDF) is implemented to enhance the performance of the classification, and a recursive method is developed to allow the on-line updating of the coefficients of the OPLDF. Comparison results show that the proposed approach has better performance than other conventional approaches, such as the multiple linear discriminant function method and the feedforward neural network method. A tapping experimental result indicates that the proposed multiple class classification method is effective for practical use. The success rate of this approach for the tapping process condition diagnosis could be 100% with a trained diagnostic model.
Intelligent Decision Making Based on On-Line Non Contact Measurement During Machining Process
Authors: Campana Claudio , Shetty Devdas
Published: January 2022

This paper presents an experimental approach for intelligent monitoring of a Computer Controlled Machining Process. The article reviews the ongoing development in the area of open architecture control for machine tools. This is followed by presentation of the hardware and software scheme adopted to implement on-line inspection procedures. Force overload and vibration in a machining operation can affect dimensional accuracy and surface finish of the workpiece. As such, it is essential to inspect such parameters as surface roughness and geometrical data in an on-line fashion. The surface roughness data is obtained using a new laser based procedure where as geometrical data is obtained using a specially designed optical digitizer. Information from these sensors are used in a rule-based algorithm that provide the appropriate adaptive control of feed rate and spindle speed applied to the machining operation. The supervisory decision making strategy ensures the application of the correct process adjustment so as to optimize the entire machining process.
Force Modeling for Cup Wheel Surface Grinding
Authors: Hekman Keith A. , Liang Steven Y.
Published: January 2022

This paper describes the development of a model for the forces in surface grinding with a cup wheel. The model incorporates the considerations of material removal from the front end of the wheel, the velocity differential between the wheel and part, the material removal from the bottom contact surface of the wheel, to deflection of wheel, and the wheel loading due to buildup. A series of grinding tests were performed with square workpiece and circular workpiece containing a center hole to provide a variety of depths of cut hence a distinct force profile. Experimental measurement of forces is presented in comparison to the model prediction. Statistical significance on the variations with model parameters has been presented on the basis of modeling error analysis.
Some Approaches for Modeling and Analysis of a Parallel Mechanism With Stewart Platform Architecture
Authors: De Sapio Vincent
Published: January 2022

Parallel mechanisms represent a family of devices based on a closed kinematic architecture. This is in contrast to serial mechanisms, which are comprised of a chain-like series of joints and links in an open kinematic architecture. The closed architecture of parallel mechanisms offers certain benefits and disadvantages (stiffness versus dexterity, etc.). A particular subset of parallel mechanisms is known as Stewart platforms (or hexapods). The classic Stewart platform is based on a set of six independently actuated struts. The struts translate through sphere joints which reside on a stationary platform. Each strut terminates at a ball joint residing on a mobile tool platform. All joints allow passive rotation. The effect of this kinematic architecture is that the tool platform can be controlled to move in six axes. This report addresses some analytic approaches for modeling and characterizing these devices. These approaches cover inverse and forward kinematics, Jacobian evaluation, path execution, workspace envelope modeling, tool velocity characterization, and structural stiffness. A characterization is also made of a hybrid parallel-serial architecture consisting of a Stewart platform and a two-axis serial tool head. Numerical algorithms are also provided.
Determination of Number of Independent Parameters for the Self-Calibration of Parallel-Link Mechanisms
Authors: Zhuang Hanqi , Liu Lixin
Published: January 2022

Self-calibration can be a desirable feature for an intelligent machine such as a computer controlled numerical machine tool that must function outside of controlled laboratory conditions. This is because it is inevitable that variations in the kinematic model arise from imperfections in the manufacturing process and changes of environment conditions. Self-calibration facilitates online compensation of errors induced by loading, thermal and other nongeometric errors.

This paper focuses the determination of the maximum number of independent kinematic parameters of a parallel-link mechanism for system self-calibration. Under the assumption of ideal joints and links, a method for obtaining this number is given. A number of examples is given to illustrate the applicability of the proposed method. The result can also be extended to tackle conventional calibration tasks.
Effect of Layering of Joint and Beam on Damping Capacity in Machine Tool Structure
Authors: Purohit Kamlesh , Sharma C. S.
Published: January 2022

In this paper a comparative study of damping capacity offered by individual and combination of three methods i.e. (i) Unconstrained (free) layering (ii) Constrained (sandwich) layering and (iii) Joint interface layering has been presented. The joint interface layering has been found to be the most effective way of applied damping treatment, which not only provides reasonable high loss factor but is also simple and easy to incorporate in any existing machine tool structure.
Some Aspects of the Thermal Performance of a Tape Ball Grid Array (TBGA) Package
Authors: Sathe Sanjeev B. , Sammakia Bahgat G.
Published: January 2022

This paper deals with the thermal management of a TBGA chip carrier package. In TBGA packages the back side of the chip is available for heat sink or heat spreader (cover plate) attach. By attaching a heat sink directly to the chip and using a thin layer of high thermal conductivity adhesive, a very low internal thermal resistance can be achieved. The package is attached to an organic card and placed vertically in a channel. A three dimensional conjugate heat transfer model is used, accounting for conduction and radiation in the package and card and convection in the surrounding air. A simplified turbulence model is developed to predict temperatures in the low Re turbulence regime. A parametric study is performed to evaluate the effects of card design, air velocities, interconnect thermal conductivities and thermal radiation on the chip junction temperatures. An experimental study was also conducted to verify the model. Even though the geometry is highly complex due to the multi-layer construction of the module and the card, agreement between the model and the experimental measurements is excellent. It was shown that radiation heat transfer can be an equally significant mode as convection in the natural convection regime.
Three-Dimensional Simulation of Microchip Encapsulation Processes
Authors: Han Ruihua , Gupta Mahesh
Published: January 2022

A three-dimensional simulation of moving boundaries in an inertia-free, incompressible flow is presented. A control volume approach with a fixed finite element mesh is used to predict the fluid front advancement. Predicted fluid front advancement and pressure variation in a flow domain similar to the mold used for microchip encapsulation are compared with the corresponding experimental results.
Three-Dimensional Finite Element Modeling of Flip Chip Packages Under Thermal Loading
Authors: Yao Qizhou , Qu Jianmin
Published: January 2022

In this study, both two-dimensional and three-dimensional finite element analyses were used to study the stress distribution in and deflection of the flip chip assembly under thermal loading. It is found that the three-dimensional results compared favorably with experimental measurements, while the two-dimensional results consistently overestimate both stresses and deflection. Among the two-dimensional models, plane stress assumption seems to yield results closer to the full three-dimensional predictions. Furthermore, three-dimensional models were used to investigate the effect of printed wiring board size on the overall deflection of the flip-chip assembly. This size effect of the printed wiring board has significant implications on the design of multi-chip modules. The results indicate that a square array placement pattern is preferable to a staggered array for multiple chip modules in order to reduce mechanical interaction between chips. For square arrays, such mechanical interaction between chips can be neglected when the minimum distance between adjacent chips is more than 2 times the chip size.
Thermo-Solutal Issues in Very Large Diameter Silicon Crystal Growth
Authors: Zhang T. , Wang G.-X. , Ladeinde F. , Prasad V.
Published: January 2022

Although 200 mm diameter wafers presently dominate the semiconductor market, 300 mm wafers are expected to be commonly used at the turn of the century. Larger wafer diameter is needed in order to increase the chip yield due to increase in chip size due to higher integration and performance of both memory (DRAM) and microprocessor (MPU) devices. mm diameter single crystals. As the crystal diameter is increased from 200 mm to 300 mm or larger, the size of the melt increases significantly leading to much more complex melt dynamics. Turbulent melt flow phenomena make the predictions and control of growth conditions very difficult. Understanding of the heat and mass transport in large melt systems is therefore critical to the growth and control of high-quality, large-diameter silicon single crystals. This paper examines various thermal-solutal issues related to Czochralski growth of 300 mm silicon crystals such as turbulence in the melt, heat transfer, oxygen transport and control, and the recent progress is reviewed.
Development of a Knowledge-Based 3D CAD System for Plastic Injection Mold Design
Authors: Lee K. S. , Zhang Y. F. , Fuh J. Y. H. , Ye X. G. , Li Z. , Nee A. Y. C.
Published: January 2022

This paper discusses the methodology in developing a 3D CAD system for injection mold. There are hundreds of parts in a set of mold, these parts can be classified and managed by an assembly method. The assembly tree structure can be looked upon as a reverse tree, each branch represents a sub-assembly tree structure, and leaves are part files. The parts are created by parametric geometrical model, parameters are used to control part size. A linkage between geometrical model and part database was built up to load the standard parts automatically. Associations are created among these parts by referring parameters with each other. A version management method is discussed to keep design status and restore to previous design as necessary. Mold design specification functions such as parting, cooling, mold base, insert creation are also provided to designers. A knowledge-based 3D CAD system is currently being used in the local mold design and manufacturing companies.
An Integrated Computer-Aided Modular Fixture Design System for Interference Free Design
Authors: Kow T. S. , Kumar A. Senthil , Fuh J. Y. H.
Published: January 2022

In the development of an automated fixture design system, issues such as automated points and elements generation, and interference free design are of great concern to achieve a quality design in a shorter time. The automation of the fixture design process is of great importance in view of the current trend towards an automated manufacturing environment. This paper describes a CAD-based methodology in developing a modular fixture design system using Unigraphics (UG) solid modeler, integrated with a modular fixture element database based on a hole-based IMAO modular fixturing system. Parametric modeling technique has been applied to construct the database. An integrated methodology is introduced to the system where the functions of interactive, semi-automated and automated fixture design system are combined collaboratively in single environment. This provides the flexibility and functionalities in making the design process more efficient. The interactive fixture design module facilitates the designer to select the fixturing faces, points and elements in building a fixture. Semi-automated and automated fixture design modules are built by transforming the designers’ experience and knowledge into rules and algorithms so as to automate the selection of fixturing points and elements. More importantly, the system aims at producing a tool collision-free fixture design using its machining interference detection module based on cutter swept volume approach.
A Data and Knowledge Management System for Hydraulic Fixtures
Authors: Trappey Amy J. C. , Hou Jiang-Liang
Published: January 2022

In order to achieve an efficient integration of product information, the product data for design, manufacturing, untill logistic supports should be incorporated into a product data management (PDM) system. Specifically, large amount of manufacturing information, e.g., tooling, machining, and fixturing specifications, are determined at the production planning stage. These information need to be properly documented and managed for better production planning and control. Due to the increasing demand of modern fixture and tooling applications, this paper focuses on the construction of information system for hydraulic, automatic fixtures. Using the characteristic features of hydraulic fixtures, a data library (database) including the geometric and non-geometric information is built. By linking the database management system (DBMS) and the CAD system, information on the CAD system can be easily accessed by fixture planners. The knowledge library (knowledge base) is developed incorporating the expertise of experienced tool engineers for fixture selection. After integrating the data and knowledge libraries, the system can automatically select the suitable fixture elements according to the workpart features and machining conditions. Finally, this paper also demonstrates the system using an aerospace part as the example. The main objective of the system implementation is to reduce the fixture planning time and cost, particularly for hydraulic fixturing.
A Unified Approach to Mechanical Adhesion by Finite Element Analysis of Straight Sections
Authors: Sancaktar Erol , Narayan Kiran
Published: January 2022

The primary objective of this study was to optimize the geometry and volume of the substrate in lap, butt and scarf adhesive joints under various loading and boundary conditions by finite element analysis. The finite element models are validated by evaluating for convergence and by calculating theoretical values using strength of materials and applied elasticity. The results of this study are significant in optimizing mechanical adhesion because any real joint surface may contain a combination of the above model joints on a smaller scale. Studying the behavior of these basic models will help in optimizing topography of surfaces to be bonded. As a novel approach for design purposes new parameters involving stress times joint volume and stress divided by joint volume as well as stress gradients are considered. Finite element meshes of the basic lap, butt and four scarf joints (30°, 45°, 60°, 75°) having 25.4 mm adhesive length are completed. Upon validation of these models, they are subjected to various loading and boundary conditions and results obtained. Several models are created to evaluate the effect of the volume of substrate in the lap and butt joints. Considering the fact that large strain gradients result in failure, this study focuses not only on the magnitudes, but also on the gradients of stresses and strains in optimizing the joint strength. This study has concluded that there exist significant differences in the interfacial stresses with respect to the scarf angle, considering lap and butt to be special cases of scarf with 0° and 90° angles, as well as with respect to the adhesive material properties.
The Damping Characteristics of Machine Structures Assembled by Bonding: A Beam in Which Two Steel Strips Are Partially Joined by an Adhesive
Authors: Kobayashi Takashi , Nakano Yuichi
Published: January 2022

The purpose of this paper is to clarify the damping characteristics of adhesively bonded structures and to establish a method to estimate the damping capacity. As a fundamental study, the damping characteristics of a beam in which two steel strips are partially joined by an adhesive are investigated. Analytically, strain energy distributions are analyzed by a finite element analysis. Then, the damping capacity of the adhesively bonded beam is estimated using the strain energies and damping ratios of the two materials which are obtained independently by experiment. The validity of the proposed estimation method of the damping capacity is confirmed by experiment. The analytical results are in fairly good agreement with the experimental ones. Furthermore, the temperature dependency of the damping capacity is examined.
Stress Analysis of Bolted Circular Flanged Joints With Tap Bolts
Authors: Kobayashi Takashi , Morohoshi Tsuneshi , Sawa Toshiyuki
Published: January 2022

The purpose of this paper is to examine a contact stress distribution at the interface of a cylindrical clamped part fastened with a tap bolt to a body which is sufficiently larger than the clamped part. The contact stress distribution is analyzed as a contact problem of two bodies by using the axisymmetric theory of elasticity. The effect of positions of screw thread on the contact stress distribution is clarified in the numerical calculations. The load factor and the ratio of additional axial bolt force to a load are also analyzed. It is found that the contact stress becomes greater near the bolt hole when the position of screw thread is the upper. Experiments to measure the contact stress and the load factor are carried out. The analytical results show a fairly good agreement with the experimental ones. In addition, the contact stress distribution, the load factor and the maximum bolt stress of bolted circular flanged joints with multiple tap bolts are analyzed by using axisymmmetric theory of elasticity. The experiments to measure the load factor and the maximum bolt stress are carried out. A fairly good agreement is seen between the analytical and the experimental results. It is found that the value of the load factor is small and it is less than 0.1.
Low-Cycle Fatigue in Aluminum Microbeams
Authors: Vinci Richard P.
Published: January 2022

Cyclic plasticity and fatigue failure have long been recognized as two of the most important areas of study in bulk materials. Just like large-scale mechanical components, small-scale structures found in microelectromechanical systems are often subjected to cyclic loading. It is known that the tensile strength of thin film media on substrates can differ significantly from that of bulk materials, so it is expected that cyclic behavior will differ as well. However, the mechanisms that separate bulk from small-scale behavior are still not well understood. Only preliminary work has been performed in the area of cyclic loading of thin films [1,2].
Fatigue and Fracture Testing of Microelectromechanical Systems
Authors: Ballarini Roberto , Mullen Robert L. , Kahn Harold , Heuer Arthur H.
Published: January 2022

Polysilicon fracture mechanics specimens have been fabricated using standard MEMS (microelectromechanical systems) processing techniques, and as a result, have characteristic dimensions comparable to typical MEMS devices. These specimens are fully integrated with simultaneously fabricated electrostatic actuators which are capable of providing sufficient force to ensure catastrophic crack propagation from notches produced using micromachining. Thus, the entire fracture experiment takes place on-chip, without any possible influences from external sources. Fracture has been initiated using both monotonic and cyclic resonance loading. A typical device is shown in the figure below.

This talk will review the (1) design of the experiment, (2) fabrication procedure, (3) measurements of bending strength, critical energy release rate, and fatigue life under cyclic loading, and (4) changes being incorporated in the structural design to make the testing procedure more robust.
Cycle Based Modeling of Composite Fatigue
Authors: Dzenis Yuris A.
Published: January 2022

Fundamental relation between overall damage and failure process in laminates under cyclic loading and damage development within cycles is addressed. A general model for damage evolution and failure analysis of laminates under cyclic loading was developed based on the stochastic mesomechanics approach. The model combines lamination theory and a theory of excursions of random processes beyond the bounds. Randomness of elastic and strength properties of plies, laminate microstructure, and cyclic loading are taken into account. Capabilities of the model were illustrated by examples. The model was found capable of predicting three stages in the overall damage accumulation process, i.e. initial damage, gradual damage development, and final failure. Relative durations of these stages depended on load cycle parameters. Theoretical predictions were compared with acoustic emission observations of damage development in an unnotched graphite-epoxy laminate under low-cycle fatigue. Overall time history of acoustic emission was separated into emission during loading and unloading portions of the loading cycles. Histories of the locations of the AE sources and distributions of the acoustic events over the stress range were analyzed. It was concluded that most of the new damage was developed during the loading portions of the loading cycles. The emission during unloading was attributed to friction between crack faces. The time history of the new damage exhibited initial, steady, and final damage development stages. The new damage was developed over the entire stress range with higher damage rates at higher stress. Experimental observation corroborated with the results of theoretical analysis.
The Fracture Mechanics of Microelectromechanical Systems
Authors: Ballarini Roberto
Published: January 2022

A review of the state-of-the-art fracture mechanics of microelectromechanical systems (MEMS) is presented. Experimental data for fracture toughness, fatigue crack growth, and stress corrosion is critically reviewed, and recommendations are made for future research. A similar discussion is provided for theoretical fracture mechanics models.
Selected Elements of Thermomechanics for Constitutive Equations
Authors: Hall Richard B.
Published: January 2022

Elements of constitutive model formulation for simple materials within a thermodynamic, finite deformation framework are reviewed, especially as related to the rational mechanics approach. Selected applications to anisothermal viscoelasticity, viscoplasticity, elasticity and damage mechanics are described.
Dimensional Stability of Composite in a Space Thermal Environment
Authors: Kim Ran Y. , Crasto Allan S. , Schoeppner Gregory A.
Published: January 2022

Composites are steadily replacing metals in weight-critical space structures primarily because of their high specific moduli. Many space structures require not only high stiffness but precision alignment and dimensional stability as well. These parameters are sensitive to thermal strains caused by the mismatch in coefficients of thermal expansion (CTE) of the constituents, anisotropy in ply CTE, and variations in service temperature. The CTE of a laminate can change in service as a result of mechanically or thermally induced microcracking and this may result in undesirable distortion of the composite structure.

In this work, changes in the CTE of a representative space structural material-XN-70/RS3 graphite/cyanate-ester were studied using strain gages. The longitudinal and transverse CTEs of unidirectional and crossply ([0/90]2s) laminates were initially determined over the temperature range of −157°C to 121°C. Specimens were then subjected to thermal cycles from −150°F to 250°F to induce microcracking. The specimen CTE was again measured in the same location after 25, 50, 100, 200, 500 and 1000 cycles, and the corresponding crack density (in the vicinity of the strain gage) was determined by microscopic examination of a polished specimen edge. Predictions of CTE variation with crack density were made using the axisymmetric formulation of a large-radius, hollow, layered-cylinder model, which is equivalent to the flat laminate formulation. The experimental results compared fairly well with the predictions for a [0/90]2s cross-ply laminate. This paper also includes a discussion of the statistical variation of the measured CTEs.
Analysis and Characterization of Interfacial Fracture Toughness in Model Composite
Authors: Tandon G. P. , Kim R. Y.
Published: January 2022

The aim of the present study is to evaluate interfacial fracture toughness in model polyester/epoxy composite. This composite system was recently studied by Tandon and Pagano [1] in a push-out test. The progressive debonding portion of the load-displacement response including initiation of debonding, propagation and eventually catastrophic debonding of the remainder of the bonded interface were predicted using a single parameter characterized as the critical shear energy release rate of the interface. The model [1] predicted the apparent toughness of the interface to increase with the length of the debond while the numerical contribution of shear stresses to the potential energy release rate was found to be nearly constant.

In this work, we have used the end-notch flexure specimen (0.5 inch thick) consisting of polyester and epoxy rectangular beams with a non-adhesive insert on the interface (mid plane) as a starter crack, to evaluate the Mode II fracture toughness. A three point bending fixture with a total span of 4 inches is installed in a load frame and tested in a displacement control mode. The Mode II fracture energy is calculated from the load-deflection curve and crack extension data using compliance calibration method. The end-notch flexure specimen is also analyzed using the large radius axisymmetric damage model by Schoeppner and Pagano [2]. It has been shown that in the limit as the ratio of average cylinder radius R to laminate thickness T approaches infinity, the stress components and the governing equations of the large radius model are analytically equivalent to the flat laminate formulation. The crack-closure method is then used to calculate the potential energy release rate and the analytical predictions are compared with the experimental data.
Micromechanical Modeling of Fiber Fragmentation in Single Fiber Composite Specimens
Authors: Davis Jean E. , Qu Jianmin
Published: January 2022

In this paper, a micromechanics model is developed to model the fiber fragmentation test using single fiber composite specimens (SFC). The SFC specimen considered here consists of a single brittle (SiC) fiber embedded in a ductile (Al) matrix. The goal is to predict the longitudinal constitutive behavior of the composite as damage occurs and to determine if the interfacial strength can be estimated from the fiber fragment length at a given effective strain.

Before the fiber fractures, the fiber-matrix interface is assumed perfect. During fiber fracture, the interface is damaged. An imperfect interface model is then employed. When the fiber fractures, the fragments are assumed to be uniformly distributed such that the fragment lengths are equal at each given load level. The Weibull strength distribution was used to relate the fiber fragment length to the tensile strength of the brittle fiber. An increase in the applied effective strain causes successive fractures in the fiber, in that the fragments become increasingly shorter. The length of the fiber fragments at a given level of effective strain is dependent upon the interfacial shear strength.

The finite element method was used to provide numerical solutions for the state of stress and fiber length at a given applied effective strain for each SFC, and to allow a better understanding of the interaction of each component. The numerical solutions were used to construct effective stress-strain curves showing the constitutive behavior and effective strain-fiber fragment length plots of each SFC modeled. Classical elasticity and mechanics of materials modeling techniques were also used to derive analytical solutions for the state of stress in each SFC. Approximate longitudinal stress-strain relationships were developed from these analytical solutions.
Guided Waves in a Fiber-Reinforced Composite Material With Interface Layers
Authors: Datta S. K. , Zhung W. , Shah A. H.
Published: January 2022

The mechanical response and failure of high-temperature fiber-reinforced materials are critically dependent on the mechanical properties of the interface (interphase) layers between the fibers and the matrix. Even though considerable amount of work has recently been done on the fracture of these materials, characterization of interface properties and their influence on deformation and failure is found to be a challenging problem. Guided ultrasonic waves provide a powerful tool to obtain the mechanical properties of the interface layers and the quality of the bond between the fiber and the matrix. In this paper, we present a model study of dispersion characteristics of both axisymmetric (n = 0) and nonaxisymmetric (n = 1) guided waves in a SiC fiber reinforced glass matrix. Here n stands for the circumferential wavenumber. It is assumed that the fiber has two surrounding layers separating it from the matrix: a thin layer of carbon and then a thin layer of TiB2. Surrounding matrix is a glass cylinder. Comparison of dispersion characteristics with and without the interface layers shows mode dispersion curves come very close at certain frequency-wavenumber values as if they cross. This phenomenon is often characterized as “pinching” and is found to be very sensitive to the interface (interphase) properties. Examination of the mode shapes at these points reveals mode interchanges. It is argued that careful study of the pinch effect can be used to obtain mechanical properties of the interface (interphase).
Sine Convolution Solution of the Integral Equation Form of Lamé’s Equations
Authors: Stenger Frank
Published: January 2022

We present here two integral equation formulations to the homogeneous Lamé equations(1.1)μ Δu+(λ+μ)∇ div u=0, as described in detail in [3]. In the final expanded paper of this abstract, we also shall present a detailed procedure for the approximate solution of these equations via Sinc convolution for the case of a region V that is a half space, as well as when V consists of two composite slabs in R3.
Effect of Deformation-Induced Change of Fiber Orientation on Nonlinear Behavior of Polymeric Composite Laminates
Authors: Sun C. T. , Zhu C.
Published: January 2022

Deformation can cause some change in fiber orientation in composite laminates. The purpose of this paper was to investigate the effect of such fiber orientation on the nonlinear behavior of polymeric composite laminates. Overstress viscoplasticity model was used to describe the rate-dependent nonlinear behavior of the composite lamina, and the laminate was modeled with the classical laminated plate theory. To verify the model, experiments were conducted on various laminate specimens of IM7/5260 and AS4/PEEK composites at different loading rates. The thermal residual stresses induced during curing were included using a simple thermoelasticity method. It was found that when curing stresses were not taken into consideration, the laminated plate theory would predict stiffer nonlinear responses than the data from the experimental results. For such laminates, the predictions with curing stresses are softer than without thermal stress, and usually good agreement between predictions and experiments can be reached. However, for some other laminates such as [±30°]ns, the predictions without curing stresses are too soft compared with the experimental data at relatively high strain level, and the consideration of curing stresses may make the predictions even worse. Moreover, such deviation between predictions and experiments cannot be remedied by considering possible damage or delamination in the laminates, since these factors will reduce the stiffness of the material. As a result, the theory will predict an even softer response if these factors are taken into account. It is clear that some other factors might be responsible for the deviation.

In this study, we found that the change of fiber orientation induced by deformation could play an important role in nonlinear stress-strain behavior. For angle ply laminates with θ greater than 45°, curing stresses are dominant in the behavior, and the change of fiber orientation has no effect. For θ lying between 20° and 40°, the curing stresses have a significant effect at low strain levels, while fiber orientation change has a greater effect at high strain levels.