bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal Wave Response of an Elastic-Viscoelastic-Elastic Laminate With a Shear Voigt Damping Core
Authors: Douglas B. E.
Published: March 2022

The equations of motion for the longitudinal (i.e. in-plane) wave response of an elastic-viscoelastic-elastic laminated beam containing a generalized shear Voigt viscoelastic core are derived along with closed form expressions for the complex flexural wavenumbers. Comparisons with experiment are made in a mechanical mobility format. The existence of this form of damping is supported through the agreement observed between theory and high resolution sine wave dwell measurements of the driving point mechanical mobility of two damped laminates. The generalized shear Voigt damping core is shown to have a significant effect on the damping performance for anti-resonance modes of the laminate with free-free boundary constraints within the spectral band governed by out-of-phase, in-plane motion between the base and constraining layers. This spectral band for shear Voigt damping is determined from consideration of the limiting case of a lumped parameter mass-spring-mass model. In addition, the resonance modes of the free-free laminate showed a waveguide behavior where the damping is equivalent to the internal damping of the base structure. Finally, this analysis coupled with experimental results show the shear Voigt damping mechanism is dominant in elastic-viscoelastic laminates with relatively soft damping cores and/or stiff constraining layers.
Enhancing the Performance of Constrained Layer Damping by Confining Vibrational Energy
Authors: Allaei Daryoush , Tarnowski David J.
Published: March 2022

A feasibility study was conducted to demonstrate that the combination of Constrained Layer Damping (CLD) and Vibration Control by Confinement (VCC) is an effective and viable approach to today’s noise and vibration problems. The objective of this paper is to report on the degree of improvement of CLD when used in conjunction with VCC. Two panel-type structures, resembling a simplified model of the panel section of a car door, are examined. The entire upper surface of the first panel was covered by CLD. On the other hand, only 63% of the second panel is covered by CLD. A confining rib was added to the second panel to localize the vibrational energy to the remaining 37% of its surface over which no CLD was added. The finite element method was employed to model both structures and generate the numerical results presented in this article. Four equally distributed points were identified to excite and measure the response. The plate was subjected to transient and harmonic excitations. Our preliminary results clearly show that not only VCC can be used as a stand-alone mechanism to suppress or isolate vibrations but also can be combined with CLD to significantly improve performance. Furthermore, additional ramifications of the VCC approach as they apply to passive or active vibration control systems are discussed.
Active Vibration Control Using Modal Techniques
Authors: Hooper Tyler F. , Greif Robert
Published: March 2022

By aligning the coordinates of the control algorithm with the modal coordinates of the flexible structure being controlled, Independent Modal Space Control (IMSC) uses the orthogonality of the mode shapes to minimize the computational requirements of control systems. With an objective of minimizing settling time, a comparison is made of several vibration control algorithms, which use IMSC theory.

For optimal control, this paper presents an incremental search technique to estimate the preferred R values for a given set of initial conditions. Modified Independent Modal Space Control (MISMC) utilizes a time sharing strategy to share a small number of actuators between a greater number of modes. This technique produced discontinuities in the actuator forces which results in spillover and reduces its effectiveness. The Total Independent Modal Space Control (TIMSC) method, introduced in this paper, avoids significant force discontinuities by using all the available modal information.

Additional (non-optimal) comparisons include a method for varying R values during the control process, and also control strategies involving actuator force saturation.
Nonlinear Systems With Multiplicative and Additive Perturbation Under State Space Constraints
Authors: Colonius Fritz , Kliemann Wolfgang
Published: March 2022

Realistic models of mechanical systems often depend on various parameters, such as controlled inputs, material constants, tunable parameters, and uncertainties. Uncertain parameters can be (time varying) deterministic perturbations or stochastic excitations whose influence on the system depends on the perturbation dynamics (multiplicative or additive), the perturbation range, and its statistics in the stochastic case. For a given operating region of the system, i.e. for a set of state space constraints, the behavior of the system within this region depends strongly on the type of perturbation dynamics and on its range. We present some basic theory for additively and multiplicatively perturbed systems, where the uncertainty can be a family of time varying functions, or a Markov diffusion process. The uncertainty range plays the role of a bifurcation parameter and determines concepts like discontinuities of control sets and supports of invariant measures, stability radii, and invariance radii with respect to the constraint set. It turns out that in many instances the stochastic and the deterministic bifurcation scenarios agree, and the cases in which they differ are related to a nonuniform behavior of the stochastically perturbed system. The example of a model of ship roll motion is treated in detail, revealing some of the fundamental agreements and disagreements of the two bifurcation scenarios.
Vibration Absorber for Flexible Structures: Experimental Study Under Random and Sinusoidal Excitations
Authors: Cuvalci O. , Ertas A. , Cicek I. , Ekwaro-Osire S.
Published: March 2022

The dynamic response of a model that simulates a one-story building with a tip mass attached as a passive vibration absorber subjected to sinusoidal and random excitations has been investigated experimentally. The effect of the forcing frequency, forcing amplitude, mass ratios and frequency ratios on the system response in the neighborhood of the autoparametric region have been studied. The main objective of this study was to conduct a series of experiments for different system parameters to investigate the autoparametric interaction between the two modes of the system.
Mechanism of Paper Feeding on the Roller Overlapped Friction Feeder
Authors: Okayama Masao , Nagasawa Yutaka , Ichikawa Ryoichi , Utsumi Itsunori
Published: March 2022

We study on roller overlapped type friction feeder in which the rotating feed roller and stationary gate roller are overlapped in a direction to the roller’s radius, to increase its rehability. The paper traction forces created by the feeder and the paper double feeding mechanism are also studied.

It is found that the characteristics of the reaction forces between the two rollers and paper which is buckled in three dimensions, and paper traction forces depend upon the position at which a sheet of paper is delivered. It is also found that the paper traction forces increase in proportion to the number of sheets of paper which are fed into the roller overlapped mechanism. The ratio of the overlapped area of the double feeding sheets of paper depends upon the degree of force to deliver the second paper.
A Numerical Solution of the Euler’s Equations With Nonlinear Source Terms in Modeling the Fluid Dynamics of an Air Reverser
Authors: Müftü Sinan , Lewis Timothy S. , Cole Kevin A.
Published: March 2022

A theoretical analysis of the fluid mechanics of the air cushion of the air reversers used in web-handling systems is presented. A two-dimensional model of the air flow obtained by averaging the equations of conservation of mass and momentum over the clearance between the web and the reverser is solved numerically. The effect of the pressure holes in the surface of the air reverser are represented by nonlinear source terms in the modified Euler’s and mass conservation equations. The results of the numerical solution axe compared with a 1D analytical solution of these equations, an empirical formula and the one-dimensional air-jet theory developed for hovercraft. Conditions that maximize the air pressure supporting the web are analyzed and design guidelines are deduced.
Free Vibration of a Rotating Disk/Spindle System With Hydrodynamic Bearings
Authors: Jintanawan Thitima , Shen I. Y.
Published: March 2022

This paper is to study free vibration of a rotating disk/spindle system with hydrodynamic bearings (HDB). The disk/spindle system consists of multiple circular disks clamped on a rigid spindle, which allows infinitesimal rigid-body translation and rotation (rocking). Also, the spindle is mounted on a stationary, flexible, cantilever shaft through two identical radial HDB and a thrust HDB. Equations of motion were first derived in terms of the rigid-body translation and rocking of the spindle, the shaft bending, and the disk vibration. Then an eigenvalue analysis was performed to obtain natural frequencies, modal damping factors, and mode shapes of the rotating disk/spindle system. For a special case of rigid shaft and decoupled translation/rocking spindle, one pair of transverse modes and two pairs of rocking modes were observed. For the transverse modes, the disk/spindle system whirls transversely as a rigid body at half of the rotational speed (i.e., half-speed whirl). In addition, the backward whirl is heavily damped while the forward whirl is lightly damped. The first pair of rocking modes is similar to those found in disk/spindle systems with ball bearings and is lightly damped. The second pair of rocking modes occurs at low frequency. One of these modes is lightly damped and has natural frequency very close to half of the rotational speed. For the general case of a flexible shaft and coupled translation/rocking motion, eight coupled modes were obtained. Three of them occur at the half-speed frequency. Compared with systems with rigid shaft, the other five modes have significantly lower natural frequencies because of the shaft flexibility.
Design of Servo Code and Synchronous Clock Writing Scheme on a High Capacity Disk Drive
Authors: Zhou Jingli , Yu Sheng Sheng , Ma Joseph T.
Published: March 2022

A disk drive servo code and synchronous writing scheme is described in this paper. The encoding and decoding of the servo code; the writing and detecting of the synchronous clock writing can be realized in this system. In this paper, a synchronous clock writing with variable frequency method is discussed. The mathematical analysis of the variable frequency clock writing, the system design, and the writing and detecting of the servo code are presented.
Testing for the Existence of Chaotic Vibration in Truck Hunting Data
Authors: Schroeder Martin P.
Published: March 2022

We discuss the importance of chaotic behavior in truck hunting and apply various methodologies for detecting chaotic motion using test data. Problems associated with such analyses and recommended enhancements to improve analysis reliability are noted.
Examples of Chaotic Motion of Railroad Vehicles in Theory and Experiment
Authors: True Hans
Published: March 2022

The dynamics of moving railroad vehicles is a challenging problem of nonlinear dynamical multibody systems. Already the fundamental guidance system with the flanged steel wheelset on steel rails introduces both kinematic and dynamic nonlinearities in the equations of motion of the vehicle, but there exist also other sources of nonlinearities in moving railroad vehicles. Examples are: Nonlinear responses of suspension elements to actions, play and impacts and hysteresis effects from air springs or dry friction contact.
Stub-Sill Tank Car Damage Tolerance Analysis Full-Scale Validation Test
Authors: Smith Keith B. , Cardinal Joseph W. , McKeighan Peter C.
Published: March 2022

This paper describes the Simuloader, a full-scale multiaxial servohydraulic test bed for railcars; Damage Tolerance Analysis, a fracture mechanics based methodology used to establish inspection intervals for fatigue cracked structures; and the use of the former to validate the latter in the Stub-Sill Tank Car Research Program being undertaken by the railroad tank car industry in North America. This paper describes a work in progress; subsequent papers and reports are expected covering the results and conclusions of the program.
A Simple Method for Estimating Railcar Wheel Tread Temperature Rise During Braking
Authors: Moyar G. J. , Carlson F. G.
Published: March 2022

One of the important tools needed to assess the severity of various braking cycles and quantify the capacity of braked wheel treads to resist thermal spalling is a reliable and easy to use computational method for predicting the associated tread temperature rise. Such a simple analytical procedure is developed and satisfactorily correlated with available experimental results in this paper.

It is based on a transient one dimensional thermal solution for surface and near surface temperature histories and takes into account tread heat transfer losses to the rail as well as to the air stream. The procedure is implemented in a spread sheet computer program that accepts any train operation and air brake system input history and computes the resulting train speed and tread temperature histories.

Correlations and comparisons are made to published results as well as some previously unpublished test data obtained by the Association of American Railroads (AAR). The method proposed is well suited to predict the results of stop braking and short time drag braking histories but its analytical assumptions are less satisfactory for long time drag braking simulations.
Capacity Planning & Order Promising in a Remanufacturing Shop
Authors: Shivpuri K.
Published: March 2022

Remanufacturing of Locomotives, Passenger and Freight cars is highly prevalent in the Railroad industry due to the high initial cost associated with these assets. Production scheduling in a remanufacturing shop poses a special challenge as the scope of work involved is not known with great certainty. This uncertainty translates into wide variability in lead times and production inefficiencies. Traditional methods of production planning, more suitable for new manufacture, either fail to give suitable results or are cumbersome to use in the highly dynamic environment. Hence, a novel approach is suggested which gives accurate projections and at the same time is robust enough to cater to the changing ground situation.
Engineering Studies in Support of the Development of High-Speed Track Geometry Specifications
Authors: El-Sibaie Magdy , Jamieson David , Tyrell David C. , Dorsey J. Christopher , Mee Brian , Whitten Brian , Kesler Kevin
Published: March 2022

The Federal Railroad Administration has been directing engineering studies to support the development of high speed track geometry standards. These standards are intended to cover train operating speeds from 110 mph to 200 mph. The studies conducted include evaluation of the use of measuring track geometry with offsets from several chord lengths, computer simulations of vehicle response to track surface and alignment variations, application of the proposed specifications to previously measured track geometry, and comparison of proposed specifications to foreign practice.

The proposed standards use multiple chords to control surface and alignment geometry. Single isolated geometry variations are allowed greater amplitudes than three or more repeated geometry variations. The results of the engineering studies indicate that use of multiple chords is effective in controlling a wide range of geometry variation wavelengths, from less than 30 feet to greater than 250 feet. The computer simulation studies show that at high speed, wheel/rail interaction dominates vehicle response to short wavelength (less than ∼100 feet) alignment variations, while carbody motions dominate vehicle response to long wavelength variations. Derailment and carbody accelerations are the principal concerns in vehicle response to track geometry variations. Application of the proposed specifications to previous measurements of high speed track on the Northeast Corridor indicates a relatively modest number of exception locations (∼1 location every 3 miles). Comparison of the proposed specification with foreign practice indicates that the proposed specification provides a generally similar level of control of track geometry.
Bethsy Test 6.9C Mid-Loop Operation Phenomena Identification Using RELAP5 NPA
Authors: Petelin Stojan , Mavko Borut , Jurkovic Mihael
Published: March 2022

Test 6.9c OECD ISP-38 was performed on “BETHSY” facility, France on April 14. 1992 and simulated loss of RHR system during Mid-Loop operation at 0.5% of nominal value core power. Initial liquid level in RCS was at horizontal axis of the hot legs. Pressurizer and steam generator manways were opened 1 s after the transient was initiated. The paper presents the test observation to the physical phenomena comparing to the experimental data using RELAP5 NPA (Nuclear Plant Analyzer) graphical postprocessor. The most important and interesting turned out to be coolant distribution around the loops.
Study on the Flow Distribution Around a Bathtub Vortex in a Cylindrical Vessel
Authors: Sakai S. , Madarame H. , Okamoto K.
Published: March 2022

Flow field around a bathtub vortex in a cylindrical vessel was measured. A gas core of the bathtub vortex was stationarily formed at the center of the vessel. An inlet open channel and an outlet pipe were equipped at the top tangentially and at the bottom center, respectively. Flow field was visualized using ink tracer or particle tracers, resulting in the velocity distribution measured. The downward velocity in the central region was found to be proportional to the distance from the original surface without the gas core except in the neighborhood of the outlet. Using the Laser Doppler Velocimeter, radial distribution of the downward velocity in the vessel was measured. The velocity distribution in the central region was found to be very complex. In the lower flow rate condition, the highest velocity position was the center. However, with increasing the flow rate, the highest position moved to outside. The inside of the central region was almost stagnant. The flow rate through the central region was 10 ∼ 50 % of the total flow rate. Formation of the stagnant region was related to the determination of the downward velocity gradient.
Heat Transfer Modeling of the LSTF Passive Residual Heat Removal System
Authors: McCreery Glenn E. , Kullberg Craig M. , Schultz Richard R. , Yonomoto T. , Anoda Y.
Published: March 2022

Data from a model Passive Residual Heat Removal (PRHR) system operated in the ROSA facility during simulated loss-of-coolant accidents were compared with heat transfer calculations using a one-dimensional steady-state computer model. The calculations agree reasonably well with the data. The PRHR consists of a “C” shaped tube bundle submerged in a large tank filled with water. The calculations show that subcooled nucleate boiling occurred near the heat exchanger inlet. The boiling region was followed by turbulent and then laminar natural convection regions for horizontal and vertical the tubes. Transition boiling, with intermittently occuring patches of steam attached to the tubes, may have occurred near the inlet for the higher heat transfer tests, but did not significantly affect the overall heat transfer process.
Integrated Simulations of Structural Performance, Molding Process and Warpage for Gas-Assisted Injection Molded Parts
Authors: Chen Shia-Chung , Cheng Nien-Tien , Hu Sheng-Yan
Published: March 2022

Integrated simulations of part structural performance, processing characteristics and warpage for the gas-assisted injection molded parts were carried out using a unified CAE model. An analysis algorithm based on DKT/VRT elements superimposed with beam elements representing gas channels of various section geometry was first developed to evaluate part structural performance. During melt/gas filling stage, a mixed control-volume/finite-element/finite-difference method combined with dual-filling-parameter technique was implemented to trace the advancements of melt and gas fronts. For the prediction of secondary gas penetration, flow model of isotropic-shrinkage origin was introduced. Cooling analysis was executed utilizing cycle-averaged boundary element approach considering hollowed core geometry within gas channels. Thermal-induced residual stress was then calculated to predict part warpage. The analysis accuracy from this unified model of 2 1/2-D characteristics show reasonable accuracy when compared with molding experiment and part bending tests. The only difference between process simulation and structure/warpage analyses is that different values of equivalent diameters assigned to beam element representing gas channel should be used, respectively.
Rotational Molding of Low-Density LLDPE Foams
Authors: Liu Guobin , Park Chul B. , Lefas John A.
Published: March 2022

This paper presents plastic foam processing for the manufacture of LLDPE foams in rotomolding. In order to better understand the mechanisms of foaming, a fundamental study on the foaming process in rotomolding has been conducted. First, the decomposition behavior of the chemical blowing agents was studied by a thermogravimetric analyzer (TGA). The rheological properties of zero-shear viscosity and melt elasticity for LLDPEs were measured using a rotational stress rheometer. Also, an optical microscope with a hot stage was effectively used to study the cell nucleation, growth, coalescence and coarsening in LLDPE melts which provide an improved understanding of the foaming dynamics with a chemical blowing agent in rotational molding. Finally, the actual foaming behavior in rotomolding has also been studied. The experimental results indicate that the amount of blowing agent, the heating time, and the processing temperature play an important role in determining the cell morphology in rotational foam molding.
Semi-Empirical Process Modeling: Model and Database Integration
Authors: Wang H. P. , Perry Erin M. , Lee Martin K.
Published: March 2022

Process modeling has been successfully used in the plastics injection molding industry over the past decade. However, mathematical descriptions in certain areas of plastics processing are either not very well understood or are too complicated to be formulated. An alternative method, such as the semi-empirical approach which integrates models with data bases, has been found to be very effective in helping the tooling engineer with the following problems: understanding the interactions between product design, process conditions, and materials; identifying the process windows; and shortening the tooling design cycle time. Two semi-empirical process models, for the polyurethane foaming and profile extrusion processes, are discussed here to illustrate this useful methodology.
Numerical Simulation of Heat Transfer During Thermoforming
Authors: Wang C. H. , Nied H. F.
Published: March 2022

Heat transfer during thermoforming can be conceptually modeled in three distinct stages. In the first stage, the polymer sheet is heated to a temperature above its glass transition temperature in preparation for forming. Heating during this stage is usually accomplished using radiant heaters and causes sagging of the plastic sheet. Once the sheet has attained the necessary forming temperature, the second stage of heat transfer occurs when the polymer sheet is subjected to large stretching during rapid inflation. Heat transfer during this inflation stage is strongly influenced by the large increase in surface area that accompanies stretching of the plastic. Finally, in the third conceptual heat transfer stage, the plastic contacts the metal mold surface and heat is conducted from the hot plastic to the cooler metal surface. Of particular interest in this paper, is the calculation of the cooling that occurs during the rapid inflation phase of polymer processing. Sample calculations are presented for various thermoforming scenarios that illustrate the nature of this cooling mechanism.
Numerical Simulation of Injection/Compression Molding
Authors: Wang T. James
Published: March 2022

Injection/compression molding (ICM) is often referred to as coining, stamping, compressive-fill, or hybrid molding. It can produce parts with more homogeneous properties and less molded-in stresses, and this may not be possible with conventional injection molding. It can also produce extremely thin or large parts which may require larger machine if conventional injection molding were used.

A CAE software has been developed to simulate the ICM process. Two areas will be emphasized to show the advantage of the ICM process over the conventional injection molding process. One is the opening of the mold halves during the molding process allows resin flow to proceed to the extremities of the cavity more easily and consequently reduces the injection pressure and clamping force. Process window design will be discussed. The other is the packing due to the compression motion requires less pressure gradient, i.e., more effective packing. It results in more uniform and smaller pressure throughout the entire cavity. This is essential to produce parts with low residual stress such as compact disk and lens.
Mode Coupling Theory for Evanescent Wave Optical Fiber Sensors
Authors: Parnas Richard S. , Woerdeman Dara L.
Published: March 2022

Optical fiber based sensors have potential in the composites processing industry as well as many other industries, but cost and robustness often mitigate the advantages of optical fiber sensors. The least expensive type of optical fiber sensor is a length of fiber either embedded in the part or in distal contact with the part surface. In the case of embedded evanescent mode sensors, important issues hinge on interpreting the evanescent signal obtained during processing or in service inspection. An optical model based on mode coupling theory is presented below to provide a description of the sensing volume around the fiber from which signal is collected during evanescent measurements. The model is developed for a fluorescence sensor but the optical theory could be equally applied for infrared or other types of optical fiber sensors.
A Novel Process Control for Injection Molding Based Upon On-Line CAE Systems
Authors: Wang Pei-Jen , Lin Jin-Yow
Published: March 2022

A novel process control system for injection molding based on the integration of Computer Aided Engineering systems (CAE) and process control models has been studied and verified. The objective is to develop a scientific approach for on-line process control by making use of the results from the CAE systems. Initially, the design of injection molded products should be finished with the help of the CAE systems after the dimensions of the products have been determined. From a set of process conditions given by the CAE results, an automatic design of experimentation procedure was conducted for locating the processing window. The processing window was then employed as the CAE inputs for establishing a process model by employing adaptive fuzzy-neural networks. In addition, a set of quasi-optimal process condition was achieved if an optimization objective had been determined based on production requirement. Finally, appropriate cycle-to-cycle control actions on tuning process conditions were taken while the pertinent feedback signals from the process were stored. This process control methodology has been demonstrated with test cases showing promising results.
Orientation Formation in Planar Mold Filling: Theory and Numerical Predictions
Authors: He Jufang , Olivero Kristian A. , Altan M. Cengiz
Published: March 2022

Orientation formation in a steady, Newtonian, Hele-Shaw flow containing rigid, neutrally buoyant, slender fibers is numerically analyzed. The Hele-Shaw model is used to simulate flows through mold cavities consisting of thin planar sections. In this study, orientation results are calculated for a mold cavity containing a three to one sudden contraction. The suspension is injected from a single inlet gate at constant volume flow rate. Initially, the planar stream function is numerically solved by an Eulerian finite difference method to obtain the flow field. Subsequently, a Lagrangian particle tracking method is used to calculate the orientation field from the flow kinematics. The three-dimensional orientation formation throughout the mold cavity is obtained by a new method which calculates the second-order orientation tensors directly from flow kinematics and particle aspect ratio. With this new method, time-consuming integrals and inaccurate closure approximations commonly used in orientation calculations are avoided. The rotational dynamics of each particle are described by Jeffery’s theory. The numerical results are valid for multi-particle, dilute suspensions in which the orientation field can be fully described by the second-order moment of the orientation probability density function (OPDF). The orientation results are presented at different layers through the thickness of the mold cavity, ranging from the midplane to the top wall. In addition, the second-order orientation tensor is averaged through the mold thickness at a number of points in the vicinity of sudden contraction. These averaged orientation tensors are compared with the experimental data obtained from the same flow configuration by Olivero et al. (1997).
Calculation and Optimisation of the Feeding System in Thermoplastics Injection
Authors: Van Rutten N. , Dupret F.
Published: March 2022

During the filling stage of injection molding, important thermal phenomena take place in the mold feeding system. We present a non-isothermal model for the flow through the runners and the gates that permits us to accurately simulate the filling of thermoplastics parts. Comparison with experiments demonstrates the validity of our approach.
Learning About Design Concepts From Natural Functionally Graded Materials
Authors: Nogata Fumio
Published: March 2022

The goal of this report is to provide a new insight into nature as a source of inspiration for optimizing mechanical properties of structural components through functionally graded and/or multi-phased microstructures. It is shown that biological structure is designed to have uniform strength at all positions in both radial and axial directions. Design principles and processes in plants show that plants have a cell-based sensing system for external mechanical stimuli that plays a similar role as the piezoelectric effect in bones, i.e., mechanical stress/strain changes the stationary electric potential of plants, theryby influencing the growth activity of their load carrying members. The ingenious construction of some selected biomaterials demonstrates clearly that it would be better to spend more time and money on developing functionally graded materials governed by uniform strength; for example, structure using the optimal placement of fibers, various microstructures, porous or cellular structures, etc., rather than developing new materials with high-stiffness.
Reduction of Residual Stresses in a Two Dissimilar Materials Joint by Using a Functionally Graded Material
Authors: Yang Ying Yuan , Munz Dietrich
Published: March 2022

To reduce the residual stresses in a joint, especially those near the free edge of the interface, different approaches are possible. The best one is the introduction of a functionally graded material (FGM). In this paper the effect of the profile function in FGM on the residual stresses near the free edge of the interface and in the center of the joint will be discussed. It is shown that the residual stress in the joint can be reduced significantly by introducing a favorable FGM interlayer and that the stresses in the joint can be minimized by varying the profile function of the FGM. Finally, the effect of the stress jump at the interface on the failure behavior will be presented and the advantages of a joint with a graded material will be shown.
Crack Initiation in Notched Unidirectional Graphite/Epoxy Composites
Authors: Chow C. L. , Yang Fan , Fang H. Eliot
Published: March 2022

The paper describes an investigation examining damage responses and failure characteristics of unidirectional graphite/epoxy composites containing a central circular hole subjected to off-axis uniaxial tension. A recently developed damage mechanics model is extended to determine the progressive damage process around the hole and the effect of such damage on the in-plane behaviors and final failure of the notched composites. The generalized stress and strain constitutive equations and the relationship between the damage variable and material properties are briefly outlined first. The anisotropic mechanical behavior of the composites is investigated by using a nonlinear finite element procedure incorporated with the damage-coupled constitutive equations. As the failure of fiber reinforced composite materials may basically be either fiber dominated or matrix dominated, separate damage criteria are proposed to capture fiber failure and matrix or fiber/matrix interaction failure in unidirectional composites. The damage model is validated by comparing the numerical prediction and experimental data obtained from a Moiré interferometry technique. Preliminary results indicate that the proposed damage model provides an effective alternative method to study progressive failure behavior in unidirectional composites.
Effects of Out-of-Plane Deformation on Stress Rupture of Unidirectional Polymer Matrix Composites
Authors: Mahieux Céline A. , Reifsnider Kenneth L.
Published: March 2022

The use of composite materials instead of conventional engineering materials is more frequently considered, especially for applications with dominant weight constraints. Polymer matrix composites offer advantages such as relative ductility or lower cost of manufacturing compared to other composites. The different cases of loading for these materials need to be explored. Out-of-plane loading is an important case, and the literature is sparse when it comes to large displacements for these materials. Such large displacements can occur for a variety of applications. Some unidirectional fiber reinforced polymer matrix composites are, for example, stocked in rolled tapes. Even at room temperature, this large deflection of the material could result in the degradation of its properties over a long period of storage. In service, the bending load can be combined with thermal or chemical loads. Intuitively, the combination of the mechanical load and elevated temperature could accelerate the degradation process. The practical case that lead to this research was the study of polymer matrix composites for replacement of one layer of the steel armor in flexible pipes used by the oil industry in ocean water. The temperature of the oil circulating inside the pipe creates an elevated temperature. The effects of the combination of the quasi-static bending load intrinsic to the pipe geometry and aggressive environments are unknown and need to be investigated.

The present paper relates the recent advances in characterizing stress rupture for unidirectional carbon fiber reinforced polymer matrix composites in end-loaded bending and extends our earlier modeling efforts (Russell et al., 1997, Mahieux et al., 1997). Experimental observations are presented, and three life-prediction models are discussed in the following sections.
An Investigation of Crack/Microstructure Interaction in a Layered Intermetallic Composite
Authors: Wang Rong , Ye Fan , Katsube Noriko , Soboyejo Wole
Published: March 2022

The results of a recent study of the crack/microstructure interactions in layered MoSi2/Nb composites are presented. Toughening by crack bridging and blunting mechanisms will be modeled in using micromechanics concepts. Finite element models for the prediction of interfacial debonding and mixed mode crack growth are also presented. The paper will highlight use of combined mechanics and materials approaches in the engineering of damage tolerant intermetallic matrix composites.
Thermal Residual Stress Analyses of Nextel 440/Aluminum Composite
Authors: Nayeb-Hashemi Hamid , Yang Yimin
Published: March 2022

Finite element analyses were performed in order to evaluate the residual stresses developed during fabrication process of the Nextel 440/Al-6061 composite. The Nextel 440 fiber has a square section with two half circle attached to the opposite sides geometry. The purpose of the analyses was to find out the effect of fiber orientation and fiber spacing on the thermal residual stresses in the composite after the composite was cooled down to room temperature. It was found that high compressive stresses developed between two fibers and the absolute value of the compressive stresses increased as the two fibers approached each other. However, significant tensile stresses developed between fibers once the two fibers touched each other. The transition from compression to tension could be explained by considering the force balance between contacting fibers. It seems that the residual stresses around fibers are not significantly affected by the boundary conditions of the unit cell models. But the effect of the fibers on the thermal residual stresses of the matrix is seen all over the matrix material. The normal stresses on the fiber/matrix interface is higher when the two fibers are orientated at 45 degrees to each other, than those when the two fibers are orientated at zero degree to each other. The normal stress at the fiber/matrix interface for this fiber geometry was higher compared to that would have developed if round fibers were used.
Transport in Fibrous Battery Electrode Substrates
Authors: Sastry A. M. , Cheng X. , Choi S. B.
Published: March 2022

Advanced fibrous electrode substrates for use as substrates for the nickel electrodes in NiMH automotive cells are being studied analytically and experimentally. The electrodes must resist local failures under hundreds of charge/discharge cycles, during which these fibrous networks (impregnated with active material) are subjected to swelling loads induced by the cell electrochemical reaction. These fibrous materials can be effectively used as substrates for chemical reactions because of their combinations of high surface area and high conductivity. It is shown here these materials’ conductivity can be characterized using a statistical technique in conjunction with an adaptation of a classic continuum model. These approaches are presented here, and compared with experimental data on conduction in fibrous media. The new approach provides an efficient way of predicting the gradual loss in performance observed in battery materials.
Novel Processes for Fabricating Ceramic Composites and Future Outlook for Markets and Applications
Authors: Sheppard Laurel M.
Published: March 2022

Ceramic matrix composites (CMCs) can be broken down into two major classes: discontinuously reinforced and continuously reinforced. Discontinuously reinforced CMCs consist of a matrix phase (typically alumina or silicon nitride) to which a reinforcing phase (such as silicon carbide particles, platelets or whiskers) is added. This type of CMC is in the early stage of commercialization in applications where wear is a major issue such as cutting tools and extrusion dies.

Continuous fiber reinforced CMCs consist of an array of continuous ceramic fibers, either uniaxially arrayed, multi-axially arrayed, or woven as a cloth, that are embedded in a ceramic or glass matrix. This type of CMC is currently at the pre-commercial development/application demonstration stage for applications where high temperatures and high stresses occur. Such applications include gas turbine components and heat exchangers.
Statistics of Strength of Elastic-Brittle Composite Materials
Authors: Ostoja-Starzewski M. , Alzebdeh K. , Jasiuk I.
Published: March 2022

We study crack patterns and effective stress-strain response in unidirectional fiber-matrix composites subjected to out-of-plane and in-plane loading. The fibers are aligned in the longitudinal direction and arranged randomly, with no overlap, in the transverse plane. The fibers and the matrix are isotropic and elastic-brittle, which allows a parametrization of a wide range of composites in terms of a stiffness ratio and a strain-to-failure ratio. The analysis is carried out numerically using very fine two-dimensional spring networks permitting simulation of the crack initiation and propagation by sequentially removing bonds which exceed a local fracture criterion. Particular attention is given to the effects of scale and geometric randomness in these composites. We consider several “windows of observation” (scales) and study crack patterns, types of constitutive responses, and statistics of the corresponding scale dependent effective elastic stiffness and strength of such composites.
Effect of Holding Time on Damage State in a Thermal Barrier Coating
Authors: Nusier S. Q. , Newaz G. M. , Chaudhury Z. A. , Ahmed T.
Published: March 2022

Spallation is a major failure condition experienced by thermal barrier coatings (TBCs) subjected to thermal and mechanical loads. Although evidence of spallation is substantiated and mechanistic models to describe the failure condition is prevalent in literature, the progressive nature of damage evolution leading to spallation has not been addressed adequately. In this study, the effect of holding time on damage evolution in partially stabilized zirconia TBC on Nickel-based single crystal superalloy, Rene N5, was studied. Button specimens with Electron Beam - Physical Vapor Deposition (EB-PVD) TBC coating were thermally cycled. The bond coat was PtAl. Two different thermal cycle profiles were used to assess damage development. Damage state was tracked using microscopy and thermal wave imaging technique on samples subjected to a series of thermal cycles. It was found that if the sum of hold times at the same peak temperature are kept constant for two different thermal cycles profiles, similar damage states can be obtained.
Similitude of Failure and Size Effect in Fiber Composites
Authors: Bažant Zdeněk P.
Published: March 2022

The present brief paper reviews recent test resuts at Northwestern University and to briefly outlines some new theoretical, experimentally yet unconfirmed, deductions for the law governing the size effect in failures with an asymptotic residual stress in the crack, which may be either tensile, due to unbroken crack-bridging fibers, or compressive, due to buckling of fibers in a kink band treated apporoximately as a compression crack. This law is of approximate nature and ensues as a simple asymptotic matching of the size effects for small and large structural sizes.
Analytical Simulation of Strength Size Effect in Composite Materials
Authors: Tabiei Ala , Sun Jianmin
Published: March 2022

This paper presents a theoretical analysis of strength size effect associated with the length, width, and thickness of laminated composites. The presented expressions for prediction of the reliability use the Equal Load Sharing Rule (ELS Rule) which are determined by sequential multi-step failure of single lamina or sublaminate. The developed equations are validated using two sets of experimental data obtained from published data. The influence of the length, width, and thickness on the ultimate strength of laminated composites is demonstrated. Strength size effect is analyzed for the inplane strength parameters. The developed size effect equations are implemented in a user defined subroutine UMAT in the finite element code ABAQUS to demonstrate their applicability in numerical analysis.
Nonlinear Analysis of Curved Composite Panels Subjected to Combined Temperature Gradient and Mechanical Loads
Authors: Noor Ahmed K. , Peters Jeanne M.
Published: March 2022

The results of a detailed study of the effect of cutout on the nonlinear response of curved unstiffened panels are presented. The panels are subjected to combined temperature gradient through-the-thickness combined with pressure loading and edge shortening or edge shear. The analysis is based on a first-order shear-deformation Sanders-Budiansky type shell theory with the effects of large displacements, moderate rotations, transverse shear deformation and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, principal strains, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the nonlinear response to variations in the panel parameters, as well as in the material properties of the individual layers. Numerical results are presented for cylindrical panels and show the effects of variations in the loading and the size of the cutout on the global and local response quantities and their sensitivity to changes in the various panel, layer and micromechanical parameters.
Minimization of the Periodic Thermoelastic Deformation in Space Structures by Active Loads
Authors: Rand Omri , Givoli Dan
Published: March 2022

The paper presents a numerical scheme for the open-loop optimal control of the thermoelastic deformation of space structures. The space structure response and the control loads are assumed to be periodic in time, with a given period. The numerical methodology is based on a finite element-harmonic balance procedure which is tailored with an adequate optimization scheme. Various cost functionals are considered, which involve the elastic deformation of the structure and include penalties on the control magnitudes. The performance of the thermoelastic and control schemes are demonstrated via numerical examples.
Thermoelastic Analysis of Laminated Composite Plates and Shells Based on High-Order Theory
Authors: Verijenko Viktor E. , Tauchert Theodore R. , Adali Sarp , Scott Murray L. , Shaikh Chippy S.
Published: March 2022

Due to increased use of laminated composite plates and shells as a primary structural elements the requirements of their analysis and design are constantly moving to a significantly higher level. The understanding of behaviour of these structures under different loading conditions including such as thermal, static, dynamic and their combinations becomes of paramount importance for the safe design. In the present paper a derivation of a new higher-order theory for the analysis of thermoelastic composite plates and shells is presented. The theory based on kinematic hypothesis which were derived on the basis of iterative technique, and it takes into account transverse shear deformations. It is shown that the results obtained on the basis of this theory are accurate and that the theory allows to improve understanding of the response of laminated composites under thermal and static loading.
Thermal Shape Control of Active and Sensory Piezoelectric Composite Plates
Authors: Lee Ho-Jun , Saravanos Dimitris A.
Published: March 2022

Previously developed mechanics for piezoelectric composite materials are extended to account for thermal effects. The updated mechanics accounts for thermal effects which arise due to: (1) coefficient of thermal expansion mismatch between the various composite and piezoelectric layers, (2) pyroelectric effects on the piezoelectric plies, and (3) the temperature dependence of the composite and piezoelectric properties. The coupled mechanical, electrical, and thermal response of piezoelectric composite materials is captured at the material level. A layerwise laminate theory is formulated with the inherent capability to model both the active and sensory response of piezoelectric composite materials. Finite element equations are developed and implemented for a bilinear plate element. Numerical studies are conducted on a simply supported graphite/epoxy plate with attached piezoceramic patches to investigate thermal shape control applications and to study the resultant stress state.