bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulations of Multi-Mode Combustion Regimes Realizable in a Gasoline Direct Injection Engine
Authors: Kim Sayop , Scarcelli Riccardo , Wu Yunchao , Rohwer Johannes , Shah Ashish , Rockstroh Toby , Lu Tianfeng
Published: March 2021

Lean and dilute gasoline compression ignition (GCI) operation in spark ignition (SI) engines are an attractive strategy to attain high fuel efficiency and low NOx levels. However, this combustion mode is often limited to low-load engine conditions due to the challenges associated with autoignition controllability. In order to overcome this constrain, multi-mode (MM) operating strategies, consisting of advanced compression ignition (ACI) at low load and conventional SI at high load, have been proposed. In this three-dimensional computational fluid dynamics study, the concept of multi-mode combustion using two RON98 gasoline fuel blends (Co-Optima Alkylate and E30) in a gasoline direct injection (GDI) engine were explored. To this end, a new reduced mechanism for simulating the kinetics of E30 fuel blend is introduced in this study. To cover the varying engine load demands for multi-mode engines, primary combustion dynamics observed in ACI and SI combustion modes was characterized and validated against experimental measurements. In order to implement part-load conditions, a strategy of mode transition between SI and ACI combustion (i.e., mixed-mode combustion) was then explored numerically by creating a virtual test condition. The results obtained from the mixed-mode simulations highlight an important feature that deflagrative flame propagation regime coexists with ignition-assisted end-gas autoignition. This study also identifies a role of turbulent flow property adjacent to premixed flame front in characterizing the mixed-mode combustion. The employed hybrid combustion model was verified to perform simulations aiming at suitable range of multi-mode engine operations.
Multidimensional Numerical Modeling of Combustion Dynamics in a Non-Premixed Rotating Detonation Engine With Adaptive Mesh Refinement
Authors: Pal Pinaki , Kumar Gaurav , Drennan Scott A. , Rankin Brent A. , Som Sibendu
Published: March 2021

In the present work, a novel computational fluid dynamics (CFD) methodology was developed to simulate full-scale non-premixed rotating detonation engines (RDEs). A unique feature of the modeling approach was the incorporation of adaptive mesh refinement (AMR) to achieve a good trade-off between model accuracy and computational expense. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations were performed for an Air Force Research Laboratory (AFRL) non-premixed RDE configuration with hydrogen as fuel and air as the oxidizer. The finite-rate chemistry model, along with a ten-species detailed kinetic mechanism, was employed to describe the H2-Air combustion chemistry. Three distinct operating conditions were simulated, corresponding to the same global equivalence ratio of unity but different fuel/air mass flowrates. For all conditions, the capability of the model to capture essential detonation wave dynamics was assessed. An exhaustive verification and validation study was performed against experimental data in terms of a number of waves, wave frequency, wave height, reactant fill height, oblique shock angle, axial pressure distribution in the channel, and fuel/air plenum pressure. The CFD model was demonstrated to accurately predict the sensitivity of these wave characteristics to the operating conditions, both qualitatively and quantitatively. A comprehensive heat release analysis was also conducted to quantify detonative versus deflagrative burning for the three simulated cases. The present CFD model offers a potential capability to perform rapid design space exploration and/or performance optimization studies for realistic full-scale RDE configurations.
An Artificial Intelligence/Machine Learning Based Regression-Clustering-Sensor-Fusion Framework for Predicting Unmeasurable Time-Series Strain From Other Sensor Measurements
Authors: Mohanty Subhasish , Listwan Joseph
Published: March 2021

Typically, in a reactor-coolant fatigue test loop, an autoclave is used for housing the test specimen. For this purpose, a small tubular autoclave is often used. This is for reducing the cost of building the test loop and for avoiding rigorous ASME pressure vessel qualification criterion as required for the qualification of a larger high-pressure-temperature vessel. However, the use of a small autoclave along with high-pressure flow inside the autoclave does not allow to put an extensometer (inside the autoclave) for measuring the strain. The measurement of strain during the fatigue test of a specimen is required to assess the accuracy of the test and for downstream activities such as for stress–strain based material model developments and stress analysis validation. In this paper, we discuss an artificial intelligence and machine learning framework for predicting time-series strain from other sensor measurements such as from load cell, frame pull-rod displacement, and actuator displacement sensors. First the framework was trained and validated against in-air condition fatigue test data (for which the strain was measurable). Then the validated model was used for predicting strain in a reactor-coolant fatigue test loop, in which direct strain was not measurable. The original aim of the research was to improve the mechanical testing and measurements capability for conducting fatigue tests in a high-temperature-pressure reactor-coolant-flow environment. However, a similar approach can be used for predicting strain in an actual reactor component.
An Experimental, Aerodynamic Evaluation of Design Choices for a Low-Pressure Compressor Transition Duct
Authors: Walker A. Duncan , Mariah Ian , Hall Chris
Published: March 2021

The S-shaped duct which transfers flow from the low-pressure fan to the engine core in large civil turbofans presents a challenging problem. Aerodynamically it has a spatially and temporarily varying inlet flow combined with a complex flow field which develops under the combined influence of pressure gradients and streamline curvature. It must also accommodate the transfer of structural loads and services across the main gas path. This necessitates the use of structural vanes which can compromise aerodynamics, introduce unwanted component interactions, and erode performance. This must all be achieved with minimum length/weight and without flow separation. This paper presents a comprehensive aerodynamic evaluation of three design options for a transition duct containing (i) a long-chord, structural compressor outlet guide vane (OGV), (ii) a aerodynamically optimal but non-structural OGV in conjunction with a small number of load bearing struts, and (iii) a fully integrated OGV and strut design. Evaluation was performed using a low-speed test facility incorporating a 1½ stage axial compressor and engine representative transition duct. Measured data suggest that all the options were viable. However, the aerodynamic vane and discrete struts produced the lowest system loss with the other two options being comparable. The performance of the structural vane was sensitive to off-design conditions producing a notable increase in loss at a low flow coefficient. The optimized aerodynamic vanes were much less sensitive to off-design conditions while the fully integrated design showed only very small changes in loss.
The Finite Element Analysis of Dynamic Interaction of High-Speed Shinkansen, the Rail, and Bridge
Authors: Tanabe Makoto , Wakui Hajime , Matsumoto Nobuyuki
Published: March 2021

A finite element formulation to solve the dynamic behavior of high-speed Shinkansen cars, rail, and bridge is given. A mechanical model to express the interaction between wheel and rail is described, in which the impact of the rail on the flange of wheel is also considered. The bridge is modeled by using various finite elements such as shell, beam, solid, spring, and mass. The equations of motions of bridge and Shinkansen cars are solved under the constitutive and constraint equations to express the interaction between rail and wheel. Numerical method based on a modal transformation to get the dynamic response effectively is discussed.

A finite element program for the dynamic response analysis of Shinkansen cars, rail, and bridge at the high-speed running has been developed. Numerical examples are also demonstrated.
Considerations in Positive to Negative Conversion for Machining Features Using Convex Decomposition
Authors: Waco Douglas L. , Kim Yong Se
Published: March 2021

Form features intrinsic to the product shape can be recognized using a convex decomposition called Alternating Sum of Volumes with Partitioning (ASVP). Since the form feature decomposition is compact and faithful to the product shape, it includes both positive and negative components. For machining applications, the positive components are converted into corresponding negative components to represent the removal volume. The positive to negative conversion is done in top-down manner by abstracting the positive components using halfspaces determined by the original faces and combining with the parent negative component. In this paper, we describe the considerations in handling interacting sibling positive components which have a common parent component.
Development of Machining Alternatives, Based on MRSEVs
Authors: Nau Dana S. , Gupta Satyandra K. , Kramer Thomas R. , Regli William C. , Zhang Guangming
Published: March 2021

One missing link between CAD and CAM is the lack of a systematic methodology for generating and evaluating alternative ways to manufacture a proposed design. To address this problem, we are developing a systematic approach for generating and evaluating alternative ways to manufacture machined parts, in order to provide information to the designer about the manufacturability of the proposed design, and information to the process engineer about how best to machine the part. This paper describes our overall approach, and how MRSEVs (Material Removal Shape Element Volumes, a STEP library of machining features) can be used to support it.
Semi-Symbolical Equations of Motion for Flexible Multibody Systems
Authors: Melzer Frank
Published: March 2021

The need for computer aided engineering in the analysis of machines and mechanisms led to a wide variety of general purpose programs for the dynamical analysis of multibody systems. In the past few years the incorporation of flexible bodies in this methodology has evolved to one of the major research topics in the field of multibody dynamics, due to the use of more lightweight structures and an increasing demand for high-precision mechanisms such as robots. This paper presents a formalism for flexible multibody systems based on a minimum set of generalized coordinates and symbolic computation. A standardized object-oriented data model is used for the system matrices, describing the elastodynamic behaviour of the flexible body. Consequently, the equations of motion are derived in a form independent of the chosen modelling technique for the elastic bodies.
Time Step Criteria for Solving Unsteady Engineering Field Problems
Authors: Mohtar Rabi , Segerlina Larry
Published: March 2021

Parabolic equations govern a variety of time-dependent problems in science and engineering. Applying numerical methods such as the finite element or the finite difference method in the space domain changes the partial differential equation to a system ordinary differential equations (ODE’s). Another numerical method is needed to solve the ODE’s in the time domain. The following paper presents time step estimates to solve the system of ODE’s that satisfy both stability and accuracy criteria. These time steps are related to the Froude and Courant Numbers. Suggestions as to which time scheme is the best to use is also presented.
Feature-Based Design: 4 Hypotheses for Future CAD Systems
Authors: Rosen David W.
Published: March 2021

Features are meaningful abstractions of geometry that engineers use to reason about components, products, and processes. For design activity, features are design primitives, serve as the basis for product representations, and can incorporate information relevant to life-cycle activities such as manufacturing. Research on feature-based design has matured to the point that results are being incorporated into commercial CAD systems. The intent here is to classify feature-based design literature to provide a solid historical basis for present research and to identify promising research directions that will affect computer-based design tools within the next few years. Applications of feature-based design and technologies of feature representations are reviewed. Open research issues are identified and put in the context of past and current work. Four hypotheses are proposed as challenges for future research: two on the existence of fundamental sub-feature elements and relationships for features, one that presents a new definition of design features, and one that argues for the successful development of concurrent engineering languages. Evidence for these hypotheses is provided from recent research results and from speculation about the future of feature-based design.
Towards a Consistency Management in a Feature-Based Design
Authors: Ovtcharova Jivka , Jasnoch Uwe
Published: March 2021

It is a common goal in the development of feature-based design systems to support users with extended facilities, such as comprehensive semantically correct feature-based models, conformability of tools to user requirements and to different applications, and communication via standardized interfaces. However, the current state of the art in feature-based design does not meet the most of these requirements, particularly the integration of design, reliability and maintainability of constraints.

This paper presents recent research on design by features using the constraint satisfaction approach. We determine the basic requirements for defining and administering constraints in feature-based models and propose an architecture for consistency management in feature-based design systems. The two main modules of interest are Feature Frame and Consistency Manager. The Feature Frame intends to enclose different feature data into one information set, called Feature Resources and to create and manipulate such resources using Feature Mechanisms. The Consistency Manager provides functionality for definition, evaluation and satisfaction of constraints in feature-based models.

Furthermore, in this paper the relation between feature-based design, consistency management and object-oriented paradigm is clarified. In contrast to previous publications where features and constraints are associated with objects in a programming language sense, our starting point is the ontological view to the object concept. We advocate that features and constraints are not objects themselves, but attributes and laws assigned by us to objects to describe properties of them. Thus, feature-based design can be characterized as the art of defining and manipulating properties of design objects.
Simultaneous Computer-Aided Design of Rotational Plastic Parts
Authors: Chong Colin , Sogabe Kiyoshi , Ishii Kosuke
Published: March 2021

This paper addresses the problem of balancing rotational plastic parts during the early stages of design. The study develops an interactive methodology that uses a solid modeling CAD system and considers injection molding concerns simultaneously with static and dynamic balance. The Transfer Matrix Method evaluates the dynamic characteristics by predicting the approximate critical speed of the part. Design Compatibility Analysis (DCA) checks for injection molding guidelines. Using these evaluation modules interactively, designers can develop a functional and manufacturable part quickly.
NERO: A Teleoperated Wall Climbing Vehicle for Assisting Inspection of a Nuclear Reactor Pressure Vessel
Authors: Luk B. L. , Collie A. A. , White T.
Published: March 2021

NERO is a series of teleoperated wall climbing vehicles. Each vehicle carries a specific tool for assisting inspection of a nuclear reactor pressure vessel in the U.K. They adopted a simple sliding frame walking mechanism to cope with 250mm head room and 25mm obstacles on the surface. Vacuum suckers are used by the vehicle for climbing vertical surface. The NERO vehicle is driven remotely by an operator via a control console. The status of the vehicle and the control console is displayed on the console’s computer monitor. These vehicles completed their tasks successfully by September 1992.
Computer-Aided Coordinate Metrology
Authors: Yau Hong-Tzong , Menq Chia-Hsiang
Published: March 2021

Three-dimensional coordinate metrology has gained much attention in recent years. On one hand, the accuracy and repeatability of a coordinate measuring machine (CMM) are approaching the sub-micron level. On the other hand, there is hardly any part that exists of which the dimensions cannot be measured with a CMM. This paper presents the recent development and applications in three-dimensional coordinate metrology. The emphasis has been placed in the utilization of computers and integration with CAD/CAM systems. Three important technologies, namely, CAD-directed inspection, three-dimensional optimal match, and reverse engineering are presented and discussed. With computers and CAD/CAM support, three-dimensional coordinate metrology has become an active part of the computer-integrated manufacturing (CIM). Its versatility and high degree of automation have made the CMM a universal inspection machine for quality control of manufactured parts in computer integrated manufacturing.
A Computational Approach to Solve Interactive Engineering Design Problems Comprising Fuzzy Design Variables
Authors: Iqbal Numan , Kinzel Gary L.
Published: March 2021

Fuzzy set theory has been found to be useful in representing inherent imprecision when a component or system is analyzed. The concepts of fuzzy set theory were earlier incorporated by the authors in an existing constraint manager developed at The Ohio State University. This paper describes a simplified computational approach to solve engineering design problems with fuzzy design variables in an interactive fashion. In an attempt to reduce the time and computational effort involved in fuzzy calculations, a modification in the Vertex Method is used. A comparison of computational time and effort for both the original method and the modified method is presented.
A Numerical Study of Non Uniform Multiple Site Cracks Emanating From a Two Dimensional Rivet Hole Array
Authors: Gioioso Paul M. , Rodriguez Jorge
Published: March 2021

A study was performed to assess the effect of multiple site damage (MSD), which has been observed in a number of aging aircraft, on the fatigue life of lap splice joints in fuselage structures. Numerical modeling was used to simulate various MSD occurrences in models similar to riveted aircraft structures (e.g. rows of 5/32″ diameter holes separated by a finite distance, for a T2024-T3 aluminum material) under simulated fatigue loading. Several geometric factors were examined, and their effect on MSD propagation investigated. Nonuniform MSD was also modeled, and all effects were compared on a global scale. Results indicate that a tighter array configuration allowed for a shorter fatigue life, as did the introduction of the nonuniform crack. However, the effect of the staggered offset was negligible in comparison to the effect of the rivet spacing and the location of the nonuniform crack. The size and initial location of the nonuniform crack had the greatest influence on the stress distribution and the fatigue life.
Knowledge-Based Parametric Modeling for Nozzles
Authors: Saxena Mukui , Irani Rohinton K.
Published: March 2021

This paper describes a new, and unique, system for design and analysis of a family of parts with a specific focus on gas turbine nozzles. The system, built on the tenets of knowledge-based engineering (KBE) within an object-oriented framework, supports the notion of scalable products that can be resized through reparametrization. The KBE system for the parametric design of nozzles has been integrated with a Topology and Geometry Utility System (TAGUS) and geometry-based mesh generators (QUADTREE and EXTREME) to develop a turnkey system. The resulting system is shown to help reduce the design cycle time and to increase engineering productivity by representing design and manufacturing information as part of the complete product definition.
Computer Aided Analysis of Nonlinear Consolidation
Authors: Bhat Dinesh , Zaman Musharraf , Laguros Joakim
Published: March 2021

Consolidation is one of the major problems in clayey foundation settlements. This paper presents a user-friendly software developed by the authors, based on finite element (FE) method including the concept of infinite elements. The software is found to be very efficient tool for the analysis of consolidation settlement potentials of bridge approaches founded on clayey soils.
An Interactive Fluid Mechanics Tutorial Using Authorware
Authors: Toogood R. W. , Wong D.
Published: March 2021

Computer-based instructional technology has developed significantly in recent years. Rapid developments in hardware are now being paced by significant advances in courseware authoring tools. This paper presents a brief overview of one such software tool, Authorware Professional for Windows1. This package allows easy development of highly interactive computer-based learning modules. Authorware was used to develop a number of instructional modules for use in an introductory course in fluid mechanics. Some examples of the courseware are given to show the flexibility and power of this software tool.
Use of Statistical Modelling Techniques for Simulation
Authors: Mazharsolook Ebrahim , Robinson David C. , Casey Jonathan D.
Published: March 2021

Statistical methods are explored for the use in modelling of discrete manufacturing. The developed methodologies based on Design of Experiments (DOE) and stepwise regression to obtain the product model are described. This model is then embedded within a software system which is used for simulation of design changes, process changes and disturbances. The software is used to predict final test results in respect of up-stream parameter changes.

A case study is presented o show the implementation of this method of modelling in Quality Control of manufacture. This case study has successfully been implemented. The system is currently assisting the company in design of similar product.

Feasibility of applying Artificial Intelligen (AI) techniques to Model-Based Quality Control (MBQC) is investigated. An outline of the future development of Hybrid MBQC is then presented.
A Fast Sequential Hidden-Line Removal Algorithm
Authors: Pao Y. C. , Qin P. Y. , Yuan Q. S.
Published: March 2021

A fast hidden-line removal algorithm for single convex or concave object, and multiple objects has been developed. It is applicable to both solid objects constructed with planar faces, and with curved surfaces which are represented by meshes. The invisible lines are removed in phases and the computing time in all phases is minimized. Line edges and plane elements involved in the solid object are sorted in the order of their coordinate values. Bounding rectangular boxes are used to determine the overlaps. In place of the trigonometric functions, a simplified linear function is adopted for reducing the computing time. Illustrative examples are presented to demonstrate the practical applications of the developed algorithm.
Application of Semantic Data Modeling to Science and Engineering
Authors: Rishe Naphtali , Li Qiang
Published: March 2021

This paper describes the application of semantic modeling using the Semantic Binary Database Model, SBM, to the design of databases having embedded measurement and scientific data, as well as complex interrelations between various objects. A case study of an environmental engineering database is considered.
Computer-Assisted Catalog Selection With Multiple Objectives
Authors: Bradley S. R. , Agogino A. M.
Published: March 2021

In this paper, strategies appropriate for the computer support of engineering catalog selection are presented for selection problems involving multiple objectives. Problems with and without random and uncertain parameters are considered, and appropriate computer-assisted methods for their solution developed. Special attention is paid to the question of when the generation of a utility function using the methods of multi-attribute utility analysis is a useful part of the selection method. Motor catalog selection examples are used to clarify the concepts.
Structuring Information and Coordinating Teams in Product Development
Authors: Kannapan Srikanth M. , Bell David G. , Taylor Dean L.
Published: March 2021

This paper analyzes the information environment of a product development program in a manufacturing enterprise as a domain in which intelligent agents can facilitate coordination. The information environment refers to information accessed, shared and generated in a product development program. The analysis suggests a structure for defining agents and agent interactions, and clarifies coordination needs in the context of the product development process. An architecture of intelligent agents embedded in a coordination environment is proposed as a means of providing infrastructure and process support to product development. The process of extension of requirements, and the selection and parametric refinement of handbook design solutions of a relief valve is used to illustrate the analysis and architecture for coordination in product development. The functional requirements identified for product development coordination are: (a) explicit representation of development team perspective and product model aspect definitions and mappings among them, (b) encapsulation of views and changes of the product models by intelligent agents, and (c) management of scenarios of interaction between perspectives through their agents. Representation of the dynamics and hierarchy in product development environments is outlined.
Experimental Investigation of Isolated and Simultaneous Internal Resonances in Suspended Cables
Authors: Lee Christopher L. , Perkins Noel C.
Published: March 2021

The near resonant response of suspended elastic cables driven by harmonic, planar excitation is investigated experimentally. Measurements of large amplitude cable motions confirm previous theoretical predictions of fundamental classes of internally-resonant responses. For particular magnitudes of equilibrium curvature, strong modal interactions arise through isolated (two-mode) or simultaneous (three-mode) internal resonances. Four qualitatively different periodic responses are observed: 1) pure planar response, 2) 2:1 internally resonant non-planar response 3) 1:1 internally resonant non-planar response, and 4) simultaneous, 2:2:1 internally resonant non-planar response. Quasi-periodic responses are also observed.
Nonlinear Normal Modes in a Class of Nonlinear Continuous Systems
Authors: King Melvin E. , Vakakis Alexander F.
Published: March 2021

A general methodology is developed for computing the nonlinear normal modes of a class of undamped vibratory systems governed by nonlinear partial differential equations of motion. A nonlinear normal mode is defined as free motion during which all points of the system vibrate equiperiodically, reaching their extremum positions at the same instants of time. The analytical methodology is based on a previous work by Shaw and Pierre (1992b), where the displacements and velocities at any point of a structure were expressed as functions of the displacement and velocity of a single reference point. The dynamics of the continuous system were then restricted to invariant manifolds of the phase space.

Motivated by the methodology presented by Shaw and Pierre, we express the displacement of an arbitrary point of the structure as a function of the displacement of a single reference point. Assuming undamped oscillations (and thus conservation of energy), a singular partial differential equation for the function relating the displacements is derived, and is subsequently solved using an asymptotic, power series methodology. Applications of the general theory are then given by computing the nonlinear normal modes of a simply supported beam resting on a nonlinear elastic foundation, and of a cantilever beam having geometric nonlinearities. The stability of the detected modes is then investigated by a linearized stability analysis.
Nonlinear Coupled Response of Serpentine Belt Drive Systems
Authors: Beikmann R. S. , Perkins Noel C. , Ulsoy A. G.
Published: March 2021

This theoretical and experimental study identifies a key nonlinear mechanism that promotes strongly coupled dynamics of serpentine belt drive systems. Attention is focused on a prototype three-pulley system that contains the essential features of automotive serpentine drives having automatic (spring-loaded) tensioners. A theoretical model is presented that describes pulley and tensioner arm rotations, and longitudinal and transverse belt response. A recent investigation demonstrates that infinitesimal belt stretching creates a linear mechanism that couples transverse belt response to tensioner arm rotation. Here, it is further demonstrated that finite belt stretching creates a nonlinear mechanism that may lead to strongly coupled response in the presence of an internal resonance. Theoretical and experimental results confirm the existence of this nonlinear coupling mechanism. In particular, it is shown that very large transverse belt vibrations can result from small resonant torque pulses applied to the crankshaft or accessory pulleys.
Theoretical and Experimental Study of the Nonlinearly Coupled Heave, Pitch, and Roll Motions of a Ship in Longitudinal Waves
Authors: Oh I. G. , Nayfeh A. H. , Mook D. T.
Published: March 2021

The loss of dynamic stability and the resulting large-amplitude roll of a vessel in a head or following sea were studied theoretically and experimentally. A ship model with three degrees of freedom (roll, pitch, heave) was considered. The governing equations for the heave and pitch modes were linearized and their harmonic solutions were coupled with the nonlinear equation governing roll. The resulting equation, which has time-varying coefficients, was used to predict the response in roll. The principal parametric resonance was considered in which the excitation frequency is twice the natural frequency in roll. Force-response curves were obtained. The existence of jump phenomena and multiple stable solutions for the case of subcritical instability was observed in the experiments and found to be in good qualitative agreement with the results predicted by the theory. The experiments also revealed that the large-amplitude roll is dependent on the location of the model in the standing waves.
Chaotic Vibrations of Rotor/Bearing/Stator Systems With Looseness or Rubs
Authors: Muszynska Agnes , Goldman Paul
Published: March 2021

This paper presents results of numerical simulation of the dynamic behavior of a one-lateral-mode unbalanced and radially side-loaded rotor with either loose pedestal (looseness in a stationary joint), or with one oversize bearing (looseness between a rotating and stationary joint), or with occasional rotor/stator rubbing.

The nonlinearities of these systems (variable stiffness, impacting, and friction) are associated with intermittent contacts with the stationary element. The results, based on a local impact model, developed in the author’s previous publications, exhibit regular periodic, as well as chaotic vibration patterns of the rotor.
Forced Vibrations of an Elastic Plate Interacting With a Layer of Granular Material
Authors: Obodan Y.
Published: March 2021

A variable-structure system, consisting of a thin horizontal elastic plate, loaded by a heavy layer of granular material is considered. The system is excited by prescribed vertical vibrations of the plate boundaries. An essentially nonlinear vibrational rheological model with unilateral constraints is proposed for simulation of the layer behavior. During the coupled motion stages the layer dynamic response on the interface between plate and granular layer is described by the Volterra integro-operator relationship with nonlinear isochronic force-displacement characteristic. The governing set of equations includes the plate dynamics differential equation, an integro-differential equation of the layer dynamics, and also appropriate boundary and initial conditions. Due to utilization of the Galerkin method and Kroosh approximation, the initial set is reduced to the set of nonlinear differential equations. The latter is integrated numerically. Model identification is carried out by the computer processing of the experimental bending strain histories. Influence of the excitation parameters, height of the layer, and damping on the bending strains is analyzed. Adequate simulation of the layer behavior for one-period modes is achieved with regard to the motion periodicity, the values of the strain peaks, the critical time points and the duration of the main time stages. Analysis of numerical phase trajectories and Poincaré sections predicts transition to stochastic vibration modes and the existence of stable two-period limit cycles, when the maximum forcing acceleration is increased above 3g.
Splitting of Separatrices in the Rapidly Forced Duffing Oscillator
Authors: Vakakis Alexander F.
Published: March 2021

The splitting of the stable and unstable manifolds of the rapidly forced Duffing oscillator with negative stiffness is investigated. The method used relies on the computation of analytic approximations for the orbits on the perturbed manifolds, and the asymptotic approximation of these orbits by successive integrations by parts. It is shown, that the splitting of the manifolds becomes exponentially small as the perturbation parameter tends to zero, and that the estimate for the splitting distance given by the Melnikov Integral dominates over high order corrections.
On Minimizing Thermal Deflections of Laminated Plates
Authors: Abrate S.
Published: March 2021

Thermal deflections of symmetrically laminated plates that are continuous over many line supports are determined using the Rayleigh-Ritz method. The constitutive equations and the thermal loads are expressed in terms of four non-dimensional lamination parameters. Layups that minimize thermal deflections are determined for several types of composite plates subjected to temperature increases that vary linearly through the thickness.
Quantification Versus Go/No-Go Criteria
Authors: Brickman Dennis B. , Barnett Ralph L.
Published: March 2021

Compliance or non-compliance with a sound safety code or standard is currently the most rational way of judging whether a product or system is sufficiently safe. Many such codes and standards specify minimum numerical criteria such as loading, tilt angle, and duration time by which compliance may be judged. Usually it is more valuable to make judgements based on quantitative test data as opposed to meeting minimum criteria. For example, a lawn and garden tractor will remain stable when tilted laterally to 28.7° compared with the go/no-go minimum specification of 20°. This paper illustrates the richness of quantification for a number of different products including hook-on high chairs, grinding wheels, structural members, and smoke detectors.
Design Variation Simulation of Thick-Walled Cylinders
Authors: Eggert Rudolph J.
Published: March 2021

Thick-walled cylinders exposed to high, static internal pressures may experience both elastic and plastic deformation. Primary design considerations include loads, geometry and material properties. However, variations in geometry and material properties due to conventional manufacturing processes, and variations of internal pressure due to actual usage patterns, propagate through the system resulting in off-design stresses and strains which may cause failure. These variations can be evaluated using probabilistic methods which are discussed in this paper. Von Mises-distortion energy yield theory is presented to predict elastic, plastic and residual stresses in thick-walled cylinders. The design variation simulation method using Monte Carlo simulation and available statistical information is used to design a pressure vessel for servo-hydraulic experiments. The use of autofrettage to induce favorable compressive stresses at the inner bore, thereby improving the margin of safety and overall reliability, is also presented.
Failure Prediction Using the Ring-on-Ring Test and the CARES/LIFE Integrated Design Program
Authors: Powers Lynn M. , Salem Jonathan A. , Choi Sung R.
Published: March 2021

The integrated design program CARES/LIFE calculates the fast-fracture and time-dependent reliability of monolithic ceramic components subjected to thermomechanical loading. A summary of the program capability is included in the paper. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. The results from finite element analysis are used to evaluate component reliability due to inherent surface and/or volume flaws. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The fast-fracture strength of sintered alpha silicon carbide tested in three- and four-point bend was used to predict the failure strength distribution of ring-on-ring tests. The specimens were tested in the annealed conditions. CARES/LIFE predicted the biaxial failure accurately when the noncoplanar strain energy release rate criterion was applied. For time-dependent life prediction, dynamic fatigue ring-on-ring test data on soda-lime glass is used to demonstrate the fatigue parameter estimation capability of CARES/LIFE.
Thermal Shock and Fatigue Behavior of Ceramic Tubes
Authors: Segall A. E. , Hellmann J. R. , Tressler R. E.
Published: March 2021

A narrow circumferential helium quench was used to thermally shock and fatigue internally heated alumina, reaction bonded, and sintered alpha silicon carbide tubes at 500°C and 1000°C. During these tests, transient temperature measurements required for thermal and stress-profile calculations were obtained through the use of micro-thermocouples positioned along the internal surface of the tubes. Acoustic emissions were also employed for in situ monitoring of crack initiation and propagation of the resident flaw populations during the single and repeated (up to 5) thermal shocks. Post-quench inspections and destructive burst tests were used to correlate the existence, extent, and statistical (Weibull) nature of the damage induced by the cycling. Results indicated progressive strength degradation in alumina tubes with repeated thermal cycles. In contrast, the thermally-cycled silicon carbide samples either showed no damage at all, or suffered minimal progressive strength degradation after the first cycle. In any case, the complex stress distributions computed from an FEA-based inverse heat transfer analysis were required to understand the observed damage (crack paths) and apparent fatigue behavior.
Fatigue Evaluation in Ceramic Materials by Acoustic Emission
Authors: Jadaan Osama M. , Liu K. C. , Pih H.
Published: March 2021

Progressive damage due to tension-tension cyclic fatigue loading for three distinct ceramic materials was evaluated using the acoustic emission (AE) technique. The objective of this study was to determine the capabilities of the AE method to detect the imminence of failure and to locate potential fracture sites. Results indicated that the AE technique was capable of predicting failure by showing an increase in energy/count rate prior to failure. Although potential fracture sites can be identified, exact location of the final fracture site can be known only when catastrophic failure takes place.
Fatigue Behavior of Adhesive Joints Under Biaxial Loading Conditions
Authors: Sancaktar Erol
Published: March 2021

Fatigue data obtained under biaxial loading conditions for adhesively bonded joints are used to plot S-N type diagrams to assess the effects of biaxiality in loading. Independently Loaded Mixed-Mode Specimens (ILM MS) are used for data collection purposes. These specimens are basically two (steel) beams bonded to be fatigue loaded under cantilever (opening) mode while a simultaneous but physically separate in-plane (static) shear load is also induced with the aid of a small hydraulic piston embedded in the specimen. Application of such static shear loads results in different S-N behavior for the bonded joint. The model adhesives used are Metlbond 1113-2 and Metlbond 1113 solid film thermosetting adhesives similar to those commonly used in aircraft and aerospace industries. The former is an elastomer-modified epoxy adhesive and the latter is identical except that it containes a synthetic earner cloth. Thus, the effects of carrier cloth in adhesive’s S-N behavior is also assessed. Analytically, the classical linear log-log representation of the adhesive S-N data is explored and modifications necessary to reflect the effects of biaxiality in loading and also the presence of a carrier cloth are assessed. The fatigue failure results are also compared with results obtained under monotonic biaxial loading conditions.
Approximate Residual Interface Compression in a Laminated Magnet
Authors: Jahanian Shahriar , McPhate A. J.
Published: March 2021

Present design of large laminated magnets are based on effective modulus of elasticity for the plate stack that is invariant with interplate compression. Experimental results indicates this is not a valid assumption. This analysis considers the specific design used for compact electron storage ring dipole magnet at the Center for Advanced Micro Devices (CAMD) at Louisiana State University. An iterative technique, using FEM is developed to approximate the effective modulus throughout the magnet structure. This particular magnet is constructed from 1424 steel plates (1.5mm × 610mm × 780mm) by first compressing a 45° 2.93m raduis curvilinear stack to a specified preload and then welding straight and curved straps to the exterior of the stack. Release of the preload allowsexpansion of the stack and forces stretch of the straps, the resultant interplate compression is considerably different from the initial preload and varies throughout the magnet.

The analysis technique introduced in this paper is a simplified approach to the interplate compression modeling and consists of the supeposition of two simple analysis; one with straps attached, one without straps attached. An iterative approach is used to incorporate the dependence of effective compressive modulus on the interplate compression. An estimate of the average modulus is assumed for the entire stack and residual compression is calculated. From this residual compression and from experimental data, a distribution of compressive modulus throughout the magnet is computed. From this computed distribution, a new estimate for the compressive modulus is made for each element of the model and the analysis iterated. The net results are the compressive modulus distribution throughout the magnet ia a form suitable in subsequent dynamic analysis.
An Overview of Elevated Temperature Damage Mechanisms and Fatigue Behavior of a Unidirectional SCS-6/Ti-15-3 Composite
Authors: Castelli Michael G. , Gayda John
Published: March 2021

The fatigue behavior of a unidireclionally reinforced titanium matrix composite (TMC), SiC/Ti-15-3, was thoroughly characterized to support life prediction modeling of advanced TMC disks designed for gas turbine engine rotor applications. The results of this coupon-level experimental investigation are reviewed in this paper. On a stress basis, the isothermal fatigue behavior of the [0°] TMC revealed significant improvements over the unreinforced matrix. In contrast, the [90°] TMC exhibited degraded properties and lives for similar comparisons. This was attributed to the weak fiber/matrix interfacial bond. Encasing the [0°] TMC with a Ti-15-3 case did not affect isothermal fatigue lives at higher strain levels. However, at lower strain levels, relatively rapid initiation and propagation of large fatigue cracks in the case degraded the fatigue lives. Thermomechanical fatigue (TMF) lives were significantly reduced for the [0°] TMC when compared to isothermal lives. At high strains, in-phase TMF produced extremely short lives. This degradation was attributed to fiber overload failures bought about by stress relaxation in the matrix. At low strains, out-of-phase TMF conditions became life-limiting. Environment-assisted surface cracking was found to accelerate fatigue failure. This produced extensive matrix damage with minimal fiber damage. For the [90°] TMC, TMF conditions did not promote an additional degradation in cyclic life beyond that observed under isothermal conditions.
A Deformation and Life Prediction of a Circumferentially Reinforced SiC/Ti 15-3 Ring
Authors: Arnold S. M. , Wilt T. E.
Published: March 2021

A computational methodology has been developed to predict the fatigue life of typical aerospace components, here the specific example is a circumferentially reinforced SiC/Ti-15-3 compressor ring designed for applications at 800° F. The analysis encompasses both a static burst pressure prediction and a life assessment of the cladded ring. A three dimensional stress analysis was performed using MARC, a nonlinear finite element code, wherein both the matrix cladding and the composite core were assumed to behave elastic-plastic. The composite core behaviour was represented using Hill’s anisotropic continuum based plasticity model with bilinear hardening. Similarity, the matrix cladding was represented by an isotropic perfectly plastic model. The load-displacement (i.e., internal pressure versus radial deflection) response of the ring was used to determine the static burst pressure.

The life assessment was conducted using the stress analysis results, in conjunction with a recently developed multiaxial, isothermal, continuum damage mechanics model for the fatigue of unidirectional metal matrix composites. This model is phenomenological, stress based, and assumes a single scalar internal damage variable, the evolution of which is anisotropic. The accumulation of damage is included in the stress analysis by employing the concept of effective stress. In the current application, however, the damage model is computationally-decoupled from the finite element solution. The specific methodology for this computationally-decoupled fatigue damage simulation is outlined and results are given in terms of the evolution of damage and design life curves.
NDE of Titanium Alloy MMC Rings for Gas Turbine Engines
Authors: Baaklini George Y. , Percival Larry D. , Yancey Robert N. , Kautz Harold E.
Published: March 2021

Progress in the processing and fabrication of metal matrix composites (MMC’s) requires appropriate mechanical and non-destructive testing methods. These methods are needed to characterize properties, assess integrity, and predict the life of engine components such as compressor rotors, blades, and vanes. For this paper, we investigated the capabilities and limitations of several state-of-the-art nondestructive evaluation (NDE) technologies in characterizing titanium MMC rings for gas turbine engines. We examined the use of NDE technologies such as x-ray computed tomography, radiography, and ultrasonics in identifying fabrication-related problems that cause defects in components. Acousto-ultrasonics was explored to assess degradation of material mechanical properties by using stress wave factor and ultrasonic velocity measurements before and after the burst testing of the rings.

We concluded that radiography and pulse-echo ultrasonics are viable imaging techniques for fast and complementary evaluation of the rings. Furthermore, acousto-ultrasonics can be useful in a comparative analysis with a standard ring and for intermittent evaluation during the life of the rings. X-ray computed tomography can identify the manufacturing steps resulting in poor quality components, guide machining of components to final dimensions, and lead structural and design engineers to realistic component life-prediction models.