bluuebunny/crossref_metadata_2025 huggingface dataset:
A Synthesis of Design and Lagrangian Bond Graphs
Authors: Redfield Robin C.
Published: July 2023

Standard bond graphs of nonlinear mechanical systems lead to substantial derivative causality which makes equation formulation tough, however, many design variables are easily available in these formulations once the dependencies are sorted though. Lagrangian formulations represent an energetic derivation of the equations of motion with the flexibility and transparency of the bond graph method without derivative causality. Equation derivation is relatively easy. Unfortunately, Lagrangian compositions are minimal in some sense and do not include many of the design variables that may be necessary in real engineering (more than the dynamics). This work integrates the design and Lagrangian bond graph approaches to allow the ease of equation formulation with the benefits of variable availability.
Modeling and Control of a Non-Linear, Flexible, Physical Therapy Dynamometer
Authors: Leonhardt Patrick A. , Zhou Tong
Published: July 2023

This paper investigates the modeling and control of a physical therapy dynamometer with a flexible shaft and a non-linear damping function. Because of the disparate sizes of patients, the system loading varies. Computer models of the system were created by entering bond graphs into the Computer Aided Modeling Program - Graphical (CAMPG). These models were modified to include the non-linear element and were simulated numerically using the Advanced Continuous Simulation Language (ACSL).

Two families of controllers using the feedback linearization technique were formulated, one that treats the system as completely rigid, and a second that accounts for, and attempts to control the system flexibility. It was found that the second family of controllers had a performance advantage, because they can be made less sensitive to parametric variation by increasing the flexibility of the system. Increasing the system flexibility also has a cost advantage, because less sophisticated components can be used.
Hardware Method for Accurate Measurements in a Transmit-Receive Ultrasonic Ranging System
Authors: Tong Chia-Chang , Figueroa J. Fernando , Barbieri Enrique
Published: July 2023

This paper describes a method to accurately determine the distance between a transmitter and receiver in an Ultrasonic Ranging System. The method has an accuracy associated with phase measurement systems, which are more accurate than typical ranging systems that use magnitude thresholding to measure time-of-flight (TOF). The significance of the method described is that the maximum measurement range is not limited to one wavelength (or one period) of the acoustic wave used. This limitation is typical of phase-based ranging systems. The maximum range is limited only by the method used to measure TOF, which in our case was the maximum count of a 16-bit counter at 1 MHz clock rate. The acoustic ranging system described uses simple circuitry to extract a digital pulse with a duration equivalent to the TOF. The prototype system developed is very stable and robust, and it exhibits an accuracy of ±0.295 mm at a range of 0.5842 m. This accuracy could be further improved by compensating for variations in the speed of sound caused by temperature variations.
Force Analysis of a Stewart Platform-Based Force/Torque Sensor Using a Linearization Technique
Authors: Kang Chul-Goo , Han Jeong-Hoon
Published: July 2023

A Stewart platform-based force/torque sensor with 6 instrumented elastic legs needs the solution of forward kinematics of the Stewart platform in order to obtain the force and torque acting on the upper plate from given 6 leg forces. However, the solution of the forward kinematics is not known in a closed-form.

In this paper, a solution of the forward kinematics is derived by means of the linearization of the solution of inverse kinematics, and this solution of the forward kinematics is used for the calculation of the force and the torque of the force/torque sensor. In order to investigate the validity of the proposed method, the Stewart platform-based force/torque sensor is designed in view of the isotropy of the measurable forces and torques, and error analyses are conducted for the forces and the torques of the sensor.
Development and Uncertainty Assessment for a Novel Laser-Based, Optical Position Sensor
Authors: Beck B. Terry , White Warren N. , Garimella Vijay
Published: July 2023

This paper examines the feasibility of a novel laser-based optical position sensing technique. The method utilizes a laser light sheet to sense spatial position in one dimension, which could be applied to a machining head assembly or a robot arm link. The image of the light sheet is viewed on a flat diffusely reflective screen and is detected by a high resolution video camera and associated image acquiring hardware/software. Position information is obtained by processing the video image. The basic principles of the technique are demonstrated with a simplified experimental test setup for a single (position) degree of freedom. The method offers the advantages of being very simple, extremely inexpensive and highly accurate. The investigation involved a detailed experimental and theoretical evaluation of the potential of the measuring technique. The basic application of the necessary line sensing hardware/software, and a theoretical and experimental evaluation of the repeatability and potential overall accuracy of the method are discussed in this paper.
Preliminary Experiments on Using Direct Calibration for Determining Part-in-Hand Location
Authors: Murray William R. , Pohlhammer Christopher M.
Published: July 2023

The sensor system for a new vision-guided automated cell that fills part trays with parts that were shipped in bulk is described. In this automated cell, bulk parts first are singulated and presented by a vision-based, flexible parts feeder. Subsequently, the robot picks a part from the feeder output station, presents the part to a second sensor system where the part-in-hand location is sensed. Finally, correcting for measured errors in how the part was grasped, the robot places the part in the output part tray. The principal feature of this technical approach is the two stages of sensing: initial crude, fast sensing to determine part location with sufficient accuracy to allow the robot to grasp the part; and final sensing with the part in hand to allow for accurate placement in an output tray. Final sensing is necessary to accommodate errors in initial sensing as well as errors in grasping, which are significant with a gripper capable of handling multiple part styles.

The enabling technology for this approach is direct calibration, which is used in final sensing. In direct calibration, the entire manipulation system — the robot, the sensors, and the parts to be handled — is calibrated for the required task in a single procedure to directly determine the relationship between the part feature information in sensor coordinates and the part location (position and orientation) in robot coordinates. This calibration procedure is accomplished in two steps: calibration data are generated by using the robot to move the part(s) under the view of the sensors; and the best-fit mapping representing this process is determined.

As a proof-of-concept experiment, a prototype of this tray-loader system was run with six types of complex, injection-molded plastic parts from a desktop printer. Preliminary results from this experiment are presented. These results indicate that final sensing, based on direct calibration, is sufficiently accurate in determining part-in-hand location for use in flexible automatic tray loading.
Neural Network Control of Nonminimum Phase Systems Based on a Noncausal Inverse
Authors: Register Andrew H. , Book Wayne J. , Alford Cecil O.
Published: July 2023

A new approach for feedforward ANN control of nonminimum phase mechanical systems is proposed. A standard backpropagation-of-errors ANN is used to form an inverse model controller which is applied to simulated nonminimum phase systems. Learning in the new approach is based on the convolution between a noncausal impulse response and a desired tip trajectory. Selection of the proper input set, input scaling and the ANN structure are investigated. Once the input and structure are specified, the ANN is trained over a single trajectory. After training, the ANN is used to drive the system in an open-loop configuration. Plots of the system states resulting from the ideal excitation and from ANN excitation are compared. The results obtained by varying both the number of units and the input set are presented. The results demonstrate the effectiveness of the proposed ANN inverse model approach.
Sensor Technology Integration and Intelligent Decision Making in an Industrial Prototype for Herring Roe Grading
Authors: Croft Elizabeth A. , de Silva Clarence W. , Kurnianto Setiawan
Published: July 2023

The automated grading of non-uniform products, such as fruit, cuts of meat, and other discrepant goods is an ongoing problem. In some areas technical advances in have permitted the on-line, single-criteria sorting of millions of items per minute. However, for many non-uniform products, especially those for which a multi-factor decision about overall quality is required, grading is still done substantially by hand.

Herein, we describe the development and integration of sensor technology for Herring Roe Grading. Size, shape, firmness/texture and weight all play key roles in determining the grade of each roe skein. These variables are subjective both in the way they are determined by humans, and in the way they affect the grade of a skein. Thus, an “intelligent” decision-making system was used to determine the final grade of the product. The system uses a fuzzy-logic knowledge base developed through acquisition of knowledge from grading experts and off-line experiments.
Fuzzy-Based Energy Managment System for Large Buildings
Authors: Shoureshi R. , Brackney L. , DeRoo B.
Published: July 2023

A hierarchical fuzzy logic controller composed of supervisor, coordinator, and local levels is applied to the problem of building temperature and lighting control. The intelligent control structure is designed to take advantage of variable occupancy, utility cost, and building dynamics are used as inputs to an adaptive fuzzy relation which generates local controller setpoints based on accumulated knowledge of past building usage and behavior. The supervisor is autonomously optimized with respect to a performance index penalizing energy consumption, occupant discomfort, and fuzzy model error Implementation of the controller in an office building is discussed.
Recognition of Multiple Objects Using Geometric Hashing Techniques
Authors: Edwards Jeff , Shoureshi Rahmat
Published: July 2023

This paper discusses the technique of geometric hashing applied to the recognition of multiple, possibly occluded, objects in the presence of a typical industrial lighting environment. This approach is based on local features and accepts image interest point as input in its current form. The algorithm can also be expanded to accept more robust features such as line segments and curves as inputs. The implementation described in this paper is designed to recognize primarily flat objects from a camera perspective perpendicular to the surface of a worktable. However, the algorithm can be generalized into 3D vision system by incorporating the affine approximation to the perspective viewing transformation. Much of the computational load is performed off-line and stored in a hash table for rapid access times during actual object recognition. Because of these characteristics, the geometric hashing technique is highly suitable for flexible assembly cell applications as discussed herein.
Robust Fault Detection and Isolation for Linear Input Time-Delay Systems
Authors: Yao Y. X. , Kovacevic R. , Zhang Y. M.
Published: July 2023

In this paper, we propose a robust fault detection and isolation method for linear input time-delay systems under unknown disturbances. The factorization approach in the frequency domain is used to obtain results. A parameterization for all residual generators for fault detection is proposed. Based on the results of parameterizations, the robust residual generator design is studied. A performance index that contains a measure of the effects of disturbances and faults is introduced. It is shown that the residual is robust against the disturbance and sensitive to the fault. The application of residual evaluation for such systems is also discussed.
Decentralized Stabilization
Authors: Shahin Ali , Perez Ronald
Published: July 2023

This paper gives an existence condition for decentralized stability which not only includes all known previous results as special cases but also yields a criterion for the solution of the input-output pairing problem. General existence conditions under which the stability of the individual loops of a square multivariable system imply the global asymptotic stability of the multivariable system itself are very useful in practice. They indicate when in principle it is possible to obtain stable closed loop performance of a multivariable system by tuning every loop separately. Such conditions are particularly pertinent in the design of fault tolerant control systems. Of major interest in such design situations is the improved input-output control structure assignment which enhances the desired decentralized stability and control.
A Higher-Order Method for Dynamic Optimization of a Class of Linear Systems
Authors: Agrawal S. K. , Veeraklaew T.
Published: July 2023

This paper deals with optimization of a class of linear dynamic systems with n states and m control inputs, commanded to move between two fixed states in a prescribed final time. This problem is solved conventionally using Lagrange’s multipliers and it is well known that the optimal solution satisfies 2n first-order linear differential equations in the state and Lagrange multiplier variables.

In this paper, a new procedure for dynamic optimization is presented that does not use Lagrange multipliers. In this new procedure applied to a class of linear systems with controllability index p=nm, optimal solution satisfies m differential equations of order 2p. The boundary conditions on these m variables are computed in terms of higher derivatives (up to p – 1) at the initial and final time. These higher-order differential equations are solved using classical weighted residual methods, methods relatively unknown to controls community but extremely popular with researchers in mechanics. This new procedure for dynamic optimization, higher order necessary condition solved by weighted residual method, is computationally more efficient compared to other conventional procedures, offering benefits for real-time applications.
Perturbation Analysis of Global Bifurcations in Parametrically Excited Systems With Zero-to-One Internal Resonance
Authors: Feng Z. C.
Published: July 2023

In this work we study the existence of Silnikov homo-clinic orbits in the averaged equations representing the modal interactions between two modes with zero-to-one internal resonance. The fast mode is parametrically excited near its resonance frequency by a periodic forcing. The slow mode is coupled to the fast mode when the amplitude of the fast mode reaches a critical value so that the equilibrium of the slow mode loses stability. Using the analytical solutions of the unperturbed integrable Hamiltonian system, we evaluate a generalized Melnikov function which measures the separation of the stable and the unstable manifolds of an annulus containing the resonance band of the fast mode. This Melnikov function is used together with the information of the resonances of the fast mode to predict the region of physical parameters for the existence of Silnikov homoclinic orbits.
On an Improved Simple Cell Mapping Unravelling Algorithm
Authors: Guttalu Ramesh S.
Published: July 2023

The cell mapping method has attractive features for studying global behavior of nonlinear dynamical systems, especially for locating stable periodic solutions and their domains of attractions. A major hurdle in practical implementation of the method for analyzing higher order system is due to its computational memory requirements. The storage of the cell map itself forms a significant portion of the overall memory requirement for cell mapping analysis. In this paper, we outline a procedure for eliminating the storage requirement for the cell map by modifying the existing simple cell mapping unraveling algorithm. The key factor in the modification comes from the analysis of an individual cell sequence originating from a given cell and how its ultimate mapping sequence is determined before a new sequence is generated. Since such a sequence must terminate in either a sink cell or a periodic motion, we propose a modified algorithm which combines this feature effectively with the existing algorithm. The utility of the proposed unraveling algorithm is demonstrated by computing bifurcation of periodic solutions of a strongly nonlinear mechanical system. Some features of the dynamic behavior are analyzed to show the existence of periodic solutions and chaotic behavior.
Friction and Impact Induced Vibrations in Machines
Authors: Pfeiffer Friedrich
Published: July 2023

Paper considers friction and impacts as contact events with unilateral character. Many interconnections in machines show this behavior. Problems of modeling and practical examples are discussed.
Analysis of a Coulomb Friction Damper for Suppressing Oscillations of Drive Shafts of Vehicles
Authors: Wang Xinchao , Noah Sherif , Vahabzadeh Hamid
Published: July 2023

To improve fuel efficiency of automatic transmissions, their torque converters are typically locked up at about 40 mph after which 100% of the torque is transmitted from the engine to the transmission. One cause of fuel inefficiency is the viscous losses in the torque converter at lower vehicle speeds due to slippage between the pump and turbine of the transmission’s torque converter. Consequently, the automotive industry has been experimenting with imposing an early lock-up of the torque converter to enhance fuel efficiency. However, damping in the driveline would drastically be reduced. A sudden excitation could then lead to oscillation of the drive shafts which is transmitted to the occupants of the vehicle. This could cause an unpleasant driving experience.

One proposed solution concerns an inline friction damper to be integrated with the drive shafts of the vehicle in such a way that friction damping only occurs when oscillations of the shafts occur. The study reported here deals with a comprehensive nonlinear transient analysis of the proposed Coulomb friction damper which was performed to assess the effectiveness of the damper.

Two cases involving a sudden loading of the drive shafts at two levels of disturbance (at second and third gear) are studied. One case considers the response of the driveline to a sudden application of torque when the torque converter is already locked. The second case examines the consequences of a sudden lock-up of the converter clutch.

The study shows that the second case will create more severe oscillatory response of the drive shaft. The results of the parametric study for the effects of the friction damper on the oscillations of the drive shafts reveal varied levels of generated damping and overshoot. For some parameters, the amount of damping and/or reduction of overshoot is not significantly improved. This has been found to result from a non-slip condition which occurs at the friction damper surfaces. To remedy this situation, a passive slip control mechanism is used to vary the normal force on the surfaces of the friction pads with the angle of shaft twist. Another approach was to use a preloading arrangement with the friction damper. A discussion is included to provide physical insight into the performance of the friction damper in controlling the transient response of the drive shafts.
Lyapunov Feedback Design for Stabilization of Stall and Surge in Axial Compressors
Authors: Krstić Miroslav
Published: July 2023

We design a feedback controller that globally stabilizes stall and surge instabilities in a nonlinear compressor model. This is achieved with a backstepping design which avoids cancellation of the system’s useful nonlinearities — the nonlinearities that would otherwise be cancelled in a feedback linearizing design. The resulting control law is extremely simple and optimal with respect to a non-quadratic cost functional that is meaningful for the compressor model. As in a previous bifurcation-theoretic design, we change the character of the bifurcation at the stall inception point from subcritical to supercritical, however, since we use Lyapunov tools, our controller also achieves global stability.
Global Chaos Control in a Periodically Forced Oscillator
Authors: Lenci S. , Rega G.
Published: July 2023

The problem of controlling the chaotic response of a simple mechanical system — an inverted pendulum subjected to an external periodic base excitation — has been analyzed.

The controlling procedure consists in inhibiting the transverse homoclinic intersection by acting on the shape of the excitation. The optimal solution of the global control problem, i.e., the excitation which simultaneously breaks the right and left intersections and thus reduces the chaos region as much as possible, has been obtained.

A preliminary numerical analysis has been carried out in order to test the theoretical predictions of the global problem as well as of the one side problem previously analysed by the same and by other authors.
Feedback Control of Chaos via Liapunov-Floquet Transformation
Authors: Ravindra B. , Boghiu Dan , Sinha S. C.
Published: July 2023

A general framework for local control of chaos in non-autonomous systems using feedback strategies is considered in this work. The present approach falls under the attempts to use conventional Lyapunov type methods to control chaos in nonlinear systems. It is important to note that in the past, some studies related to control of chaos in non-autonomous systems were incorrect because the authors ignored time varying nature of the problem. In the present work, due consideration is given to the non-autonomous nature of the problem in choosing the control law. The general approach presented is specialised to the case of a sinusoidally driven Duffing’s oscillator to illustrate the control scheme.
Stability of Multi-Degree of Freedom Stochastic Nonlinear Systems
Authors: Whalen Timothy M.
Published: July 2023

Melnikov’s method for finding necessary conditions for homoclinic chaos is extended to a class of stochastically forced multi-degree of freedom nonlinear systems. The stochastic forcing induces a stochastic Melnikov process, and simple zeros of this process imply transversal intersection of appropriate stable and unstable manifolds. This process can also provide information on probabilities of escape and mean exit rates from regions of phase space. In generalizing results from single degree of freedom stochastic systems, however, some new concepts (and reinterpretations of old concepts) are addressed.

Applications are presented to the dynamics of a feedback controlled buckled column subject to stochastic forcing. The stochastic Melnikov process is calculated, and illustrations of the effect of system parameters on system dynamics and chaos are given. The use of the Melnikov process as an estimator of mean exit rates from preferred regions of phase space is investigated.
Nonlinear Control of Flexible Structures
Authors: Oueini Shafic S. , Nayfeh Ali H. , Pratt Jon R.
Published: July 2023

An approach for implementing an active nonlinear vibration absorber for distributed-parameter systems is presented. The technique is based on exploiting the saturation phenomenon exhibited by multidegree-of-freedom systems with quadratic nonlinearities possessing a two-to-one autoparametric resonance. The strategy consists of introducing a second-order controller and coupling it with the plant through a sensor and an actuator, where both the feedback and control signals are quadratic. Once the plant is forced near resonance, its response saturates to a small value, and the remaining oscillatory energy is channeled into the controller. We present theoretical and experimental results of the application of the proposed saturation controller. The plant under consideration consists of a flexible beam. The feedback signal is generated by a strain gage, and the actuation is achieved through piezoceramic patches attached to the beam. The equations of motion are developed and analyzed through perturbation techniques. Then, the controller is built in electronic components, and the strategy is tested by regulating the response of a steel cantilevered beam.
Modal Coupling of a Cantilever Beam Attached to a Rotating Body
Authors: Lee Christopher L. , Murphy Kevin D.
Published: July 2023

This is an investigation into the nonlinear dynamics of a cantilever beam attached to a rotating body; specifically, the near resonant response of one in-plane mode and one out-of-plane mode of the beam (with respect to the horizontal plane of rotation) driven by a periodic out-of-plane excitation. The modes are coupled through quadratic and cubic nonlinear terms arising from nonlinear axial stretching and large amplitude displacements. The natural frequencies of the modes are commensurate in a near one-to-one ratio.

The existence and stability of periodic solutions are examined using a second-order perturbation analysis. Regions for system parameters are identified where single or multi-mode responses occur.

The effects of beam foreshortening and centrifugal stiffening as well as gyroscopic effects are included which capture the dominant characteristics of rotating systems such as helicopter blades, robot arms, flexible machinery, and satellite bodies with flexible appendages.
Instabilities in a Two Degree of Freedom Torsional System Driven by a Hooke’s Joint
Authors: Asokanthan Samuel F. , Meehan Paul A.
Published: July 2023

Torsional instabilities in a drive-line which incorporates a Hooke’s joint due to fluctuating angular velocity ratio across the joint are examined. Numerical simulations and bifurcation analysis performed on the full nonlinear equations further demonstrate the existence of parametric, quasi-periodic and chaotic instabilities. Onset of chaotic motion was shown to be characterised by a quasi-periodic route. Predicted instabilities indicate the range of drive shaft speeds to be avoided during the design of a drive-line which employs a Hooke’s joint.
Prediction and Control of Dynamics for a Class of Oscillators With Nonlinear Restoring Force
Authors: Natsiavas S. , Mitsi S. , Tsiafis I.
Published: July 2023

An analysis is presented for two degree of freedom weakly nonlinear oscillators, with symmetric restoring force. Conditions of 1:3 internal resonance and subharmonic resonance of the lower linear natural mode are assumed to be satisfied simultaneously. Initially, a set of slow-flow equations is derived, governing the amplitudes and phases of approximate response, by applying an asymptotic analytical method. Determination of approximate periodic steady-state motions of the system is then reduced to solution of sets of polynomial equations which is performed analytically. Then, a systematic search is performed based on this analysis, revealing effects of the system parameters on the existence and stability properties of periodic steady-state motions for an example mechanical system. The results are first presented in the form of frequency-response diagrams and attention is focused on understanding the evolution and interaction of the various solution branches as the internal resonance detuning parameter is varied. In addition, numerical integration of the slow-flow equations reveals that for some parameter combinations they accept periodic solutions, corresponding to quasiperiodic motions of the mechanical system.
Nonlinear Dynamics of a Fluid-Conveying Cantilevered Pipe With a Small Mass Attached at the Free End
Authors: Païdoussis Michael P. , Semler Christian
Published: July 2023

In this paper, the planar dynamics of a fluid-conveying cantilevered pipe with a small mass attached at the free end (’end-mass’, for short) is examined theoretically and experimentally. An experimental study is undertaken with elastomer pipes conveying water, with metal or plastic end-masses. The main purpose is to extend the work of Copeland and Moon on a modified configuration: the motion is constrained to be planar instead of three-dimensional, and the pipe is modelled as a beam having a non-negligible flexural rigidity instead of a string hanging under gravity. As in previous studies, it is demonstrated that for the system with no end-mass, only one stable periodic solution exists, at least for the parameters considered. On the other hand, in the presence of a small end-mass, the dynamics is much richer and different types of periodic solutions are found to exist. Jump phenomena as well as chaotic oscillations are observed both in the experiments and numerically, revealing the importance of even a small mass on the dynamics. Qualitative and quantitative agreement between theory and experiments is rather good.
Modeling of Porosity Effects in Gas-Filled Composites Using Biot’s Parameter
Authors: Salamon N. J. , Ganesan R.
Published: July 2023

Modeling of porosity effects on the thermal-chemical decomposition of porous, polymer composites at high temperature is treated analytically for no gas flow and compared with finite element results which permit gas flow. A function is proposed for the variation of Biot’s pressure-stress coupling factor in terms of porosity and a constant which can be determined from experiments. The results show this function adequately describes the coupling factor and that the inclusion of gas flow (permeability) is essential to accurate results.
A Micromechanical Model for Layered Porous Materials
Authors: Wu Yinan , Katsube Noriko
Published: July 2023

A micromechanical model for porous layered materials has been developed. The micromechanical approach for layered materials is combined with a poroelastic constitutive model. Explicit expressions for effective elastic moduli, thermal expansion coefficients, and poroelastic moduli are obtained. The effect of pore pressure on the overall deformation of the composites is described by the effective poroelastic constants. The obtained results reduce to those of layered materials when there are no pores. Applications of the obtained model to thermochemically decomposing composites are discussed.
Microscopic Examination of Titanium Matrix Composites Subjected to Testing Designed to Cause Varying Dominant Damage Mechanisms
Authors: Calcaterra J. R. , Johnson W. S.
Published: July 2023

Titanium Matrix Composites (TMC’s) like SCS-6/Timetal 21S are envisioned for use as a structural material for advanced aircraft and in the next generation of turbine engine. In general, damage in representative temperature and load regimes can be dominated by either mechanical, environmental or time dependent deformation and damage mechanisms. Mechanical deformation, present under all load conditions, includes mechanisms such as matrix yielding and fiber/matrix debonding. Time dependent deformation refers to either the creep or relaxation of the matrix and will typically occur at moderately high elevated temperatures. Environmental damage is also time dependent but is distinguished by the fact that it describes the chemical interaction of the composite and the environment. Environmental damage in SCS-6/Timetal 21S composites is commonly thought to be caused by the oxygen embrittlement of the matrix. This damage type becomes prevalent at high elevated temperatures which are near the operational limit of the material. Testing has been completed at Georgia Tech to separate the three damage types listed above. This test matrix involved isothermal constant amplitude fatigue tests at temperatures of 400, 500 and 650°C with hold times at the maximum stress varying from 1 to 100 seconds. Testing was conducted on laminates with stacking sequences of both [0/±45/90]s and [90/±45/0]s. The changes in stacking sequence yielded significant differences in cyclic lives for identical test conditions. Fractographic examination of the specimens indicate that the true cause for environmental attack is not the formation of brittle oxides, but the coarsening of the alpha grains in the microstructure. This form of damage is shown to affect the fracture morphology of specimens at all temperatures, but proper selection of the stacking sequence can reduce the importance of this effect and increase cyclic lives.
Edge Stresses in a Laminated Composite Strip Subjected to Axial Temperature Gradients
Authors: Swett Dwight W. , Shiflett Geoffrey R.
Published: July 2023

One of the most severe problems associated with the use of laminated composite structures in thermal environments is the susceptibility to delamination due to the edge effect stresses arising from the thermal expansion mismatch between the constituent laminae. In addition, the problem may be compounded by the introduction of extreme thermal gradient effects as well. Trade studies to develop a satisfactory design for these types of thermal environments have heretofore been rather limited due to the lack of accurate analytical assessments for the edge effects that arise from these thermal loads. The predominant amount of investigation for these types of thermal gradient problems has been restricted to detailed numerical finite element analyses that do not lend to rapid concurrent engineering design processes. No analytical solution has been available to address the thermoelastic edge effects in composite laminates resulting from thermal gradients.

In this paper, a combination of Airy stress functions and direct displacement functions is utilized to obtain the plane elasticity solution for the stresses and displacements in a multilayer laminated anisotropic strip subjected to a temperature gradient that is arbitrarily symmetric in the longitudinal direction. The solution cannot be guaranteed to satisfy the free edge normal traction requirement since only resultant force is enforced to zero; however, convergence for enforced zero transverse slope at the strip ends can be established, as the eigenfunctions are orthogonal. Thus the solution is exact for these edge conditions. Numerical results are presented for several examples and compared to those obtained from our own MSC/NASTRAN finite element analyses. The correlation with the finite element numerical results was determined to verify the solution and indicated application of the solution as an approximation to free edge engineering problems is very reasonable for a broad range of practical cases involving temperature gradient effects.
Structural Response of Oxidation Resistant Carbon-Carbon Composites
Authors: Ashley T. H. , Ochoa O. O.
Published: July 2023

The experimental assessment as well computational simulation of time, temperature, and oxidation dependent material properties of carbon-carbon composites with inhibited matrix is undertaken. The material system examined is HITCO 2D CC137EH, highly inhibited (boron carbide particulates), eight harness satin weave, RT42 CVD SiC coated carbon-carbon composite laminate.

Two representative cells; namely in-plane and through-the-thickness of this architecture, are developed to interpret the material properties and mechanical response of the laminate with two dimensional finite elements. The mechanical loading is treated as both monotonic and cyclic. Effective properties and the thermo-mechanical response of the laminate simulated by the models follow closely the experimental data.
Interphase Shear Strength of Titanium Metal Matrix Composites at Elevated Temperatures
Authors: Tamin M. N. , Osborne D. J. , Ghonem H.
Published: July 2023

A series of fiber pushout tests on thin-slice samples of a SCS-6/Timetal-21S composite were carried out to determine the load values at which partial and full debonding occurs. Finite element calculations of the stress field in the specimen were employed to assess the interphase strength of the composite as function of temperature. In these calculations, the semi-infinite thickness and the traction-free surface effects of the thin-slice samples on the corresponding stress field are considered. For each of these specimens, the distribution of shear stress along the fiber/matrix interface is determined in order to identify a region of stress localization which is taken in this study to be a measure of the interphase shear strength. This strength is then identified as the balance of forces at this localized field due to the traction-free surface of the composite section. Both contributions from process-induced residual stress and geometry-induced constraint of the traction-free surface to the strength are considered. The results of this study showed that the interphase shear strength decreases with an increase in temperature and processing-related residual stress contributes about 35 % to the interphase shear strength at room temperature. Furthermore, the interphase shear strength as calculated in this paper was found to be larger than that determined by considering uniformly distributed shear stress along a pushout fiber.
A Systematic Shear-Lag Approach for Analyzing the Failure Mechanisms in Ceramic Matrix Composites
Authors: Robertson David D. , Solti James P. , Mall Shankar
Published: July 2023

The present study examines various damage progression criteria to provide input to a shear-lag analysis of ceramic matrix composites (CMCs). The shear-lag as well as other analysis methods require matrix and fiber crack densities in addition to interfacial debond lengths as input to the analysis before the composite behavior can be approximated. The present approach examines criteria for damage progression consisting of a critical matrix strain energy to control matrix crack density, a Weibull-type damage progression scheme for fiber cracks, and ultimate interfacial shear stress to provide debond lengths. Fatigue modeling is also accomplished through an effective fiber pullout where the eventual failure in fatigue is modeled by the available elastic energy exceeding the work to fiber pullout.
Modeling of Inelastic Metal Matrix Composite Response Under Multiaxial Loading
Authors: Ahmad Jalees , Nicholas Theodore
Published: July 2023

A mechanistic framework is proposed which may facilitate establishment of inelastic deformation surfaces (analogous to yield surface for metals) and flow-rules for some composites. The motivation is to develop a method for three dimensional stress analysis of composites in the nonlinear regime.
Failure Analysis of Fiber Composites at Phase Interface
Authors: Edmiston Harry D. , Nomura Seiichi
Published: July 2023

Failure criteria of fiber reinforced composites expressed in terms of externally applied stresses are derived based on the interface stress distribution. The composite is modeled by a single inclusion surrounded by a matrix which possesses the properties of the composite. Using the Eshelby’s method and the self-consistent approximation, the interface stress can be derived analytically as a function of fiber and matrix properties and the fiber volume fraction. Using the proposed method, failure envelopes can be drawn that can properly reflect the effect of fiber shapes and anisotropy.
Fatigue Damage Evolution in a Short Fiber Reinforced Metal Matrix Composite
Authors: Canumalla Sridhar , Pangborn Robert N.
Published: July 2023

The micromechanisms of fatigue failure of a short, alumina-silicate fiber reinforced cast aluminum alloy (A356) are investigated in this study. The nature of damage evolution is studied by three complementary perspectives — i) monitoring of the mechanical response, ii) microscopy on the gage length and fracture surface, and iii) probing of the microstructural changes in the bulk nondestructively using acoustic emission. The damage evolution in the composite is driven by strain or fatigue cycles imposed on the specimen and is manifested as three distinct mechanisms: a) cracking at hollow shot particles early in the life, b) microcracking in the form of fracture of fibers oriented in the direction of the loading and splitting or decohesion at fiber/matrix interface of transversely oriented fibers, and c) void formation at fiber ends and other stress concentrations. The interaction among the different modes, which defines the evolution of microstructural damage, is described. A flow chart for the progression of damage is presented and the most important steps in the damage evolution are identified. Suggestions are made for improving fatigue performance by tailoring the microstructure of the composite.
Bridging Fiber Stress in Metal Matrix Composites: An Analytical Model
Authors: Ghonem H.
Published: July 2023

A modified shear-lag model suitable for describing bridging fiber stress in metal matrix composites subjected to fatigue loadings has been developed. The model considers the influence of the stress field in the fiber/matrix bonded zone as well as the ratio of the reversed to non-reversed sliding length within the interface debonding region of the fiber. Parameters representing the post-processing residual stress field and the load ratio of the applied loading cycle are also considered.
Electromagnetic Moving Armature Actuators for Active Vibration Control
Authors: Murray Bruce S. , Madden Richard , Berkman E. Frank
Published: July 2023

Shakers or vibration generators for the purpose of active vibration control should be extremely linear (i.e., low distortion), have small time lag, be capable of extended continuous reliable operation. Other attributes such as high force to weight ratio, compactness, ruggedness, ease of mounting, efficiency, and no special cooling are also desirable. Conventional shakers developed for laboratory or less demanding applications typically do not have all these attributes. We find that electromagnetic moving armature transducers can be designed to meet many of the above attributes better than other approaches. A 225 N (50 lbf) actuator example is used to present mechanical and electrical features that satisfy requirements of linearity, stability, size and force outputs. A larger 9 kN (2000 lbf) shaker example is used to illustrate the use of feedback control in the actuator to improve linearity even further and flatten frequency response.
Sound Scattering by a Submerged Shell Near the Sea Surface: Source and Receiver Close to the Shell
Authors: Huang H. , Gaunaurd G. C.
Published: July 2023

In previous work we studied the scattering of incident plane sound waves by a spherical elastic shell submerged in water which was arbitrarily near its free surface (H. Huang and G. C. Gaunaurd, Proceedings, 1995a). That study presented an exact solution of the problem valid for any shell depth beneath the free surface, and it used the method of images and the addition theorem for the spherical wave functions. We study the problem again, here, for cases in which the incident waves are now emitted from point sources anywhere in space beneath the free surface (i.e., close to the shell or to the free surface), and the receiver can pick up the scattered returns from arbitrary space positions. Among the many detailed results of the present study, it was found that for a point source near the shell, the scattered field is significantly different from that produced by a plane incident wave. [That field, in turn, is different from that returned in the elementary case of a shell in “free space”, i.e., away from any boundary.] A number of comparisons are shown as the shell and point-source take on positions that are: (1) at different depths beneath the free surface, and (2) at different distances from each other. For point sources more than twenty shell radii away from the shell, the far-field backscattered echo is not much different from that produced by a plane incident wave incident on the shell at the same depth. Our earlier solution can then be used in such cases. For point sources any closer to the shell, the present solution must be used. In such cases, as the shell and point source move further away from the free surface, together, a pattern of rapid oscillations is developed in the resulting form function which is the precise generator of the Lloyd’s mirror effect of elementary acoustics. The scattered field generated by an array of such point sources insonifying the shell, can also be obtained by a linear superposition of the exact solution given here.
Sound Radiation From a Finite Cylinder
Authors: Hu Qiang , Wu Sean F.
Published: July 2023

A formulation is derived which expresses the radiated acoustic pressure in terms of the tangential and normal components of the particle velocity at the surface of a vibrating object. The boundary condition at an impermeable surface requires that the normal component of the particle velocity be equal to that of the surface velocity, which is usually specified for acoustic radiation problem. The tangential component of the particle velocity is different from that of the surface velocity, but can be determined by using an intensity probe. In this paper, both the tangential and normal components of the particle velocity at the surface of a vibrating object are assumed specified. Hence the radiated acoustic pressure can be obtained by direct integrations of these known quantities over the surface. The formulation thus derived is validated on sound radiation from a right cylinder of finite length.
A New Methodology of Applying Measured Acceleration and Forces as Excitation on Powertrain Models for Noise Prediction
Authors: Vlahopoulos Nickolas , Stark Richard D. , Kargus Walter
Published: July 2023

Numerical methods can be used to compute the vibration of powertrain systems or components and the corresponding radiated noise. Specifically, the finite element method can be utilized in computing the structural vibration1, 2, 3. The structural response will constitute the boundary conditions for the boundary element method in computing the radiated noise4, 5, 6. In order to achieve reliable noise predictions it is important to have accurate information for the structural vibration since it is the source of the noise. In this work a new methodology for applying the loads on the structure is presented. It allows to exert as excitation a combination of measured accelerations, and forces or pressures. The innovative elements of this work are: (i) the methodology utilized in prescribing the acceleration at certain parts of the structure, (ii) integrating the vibration analysis within the acoustics software and creating a single process for computing the noise.
Effect of Expansion Chamber on the Resonance Frequency of Side Branches and Herschel-Quincke Tubes
Authors: Selamet Ahmet , Radavich Paul M.
Published: July 2023

Side branches connected to main ducts are known to create conditions susceptible to flow-acoustic coupling. A closed-end side branch resonator and a Herschel-Quincke tube, both coupled with an expansion chamber, are considered in the present study. The resonance frequency for these configurations is investigated as a function of the geometrical variations. The implications of the changes in resonance frequency are then discussed in relation to the flow-acoustic coupling.