bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Chaos Control and Tracking to Suppress Alternans in a Cardiac Model
Authors: Christini David J. , Collins James J.
Published: July 2023

Atrioventricular (AV) nodal alternans is a pathological cardiac condition characterized by a beat-to-beat alternation (period-2 rhythm) in AV nodal conduction time. AV nodal conduction time is a vital cardiac-cycle delay which allows ventricular filling and therefore facilitates the efficient pumping of blood. Thus, AV nodal alternans, while electrical in nature, has bio-mechanical repercussions. Here we use chaos control and tracking, respectively, to suppress AV nodal alternans in a cardiac model by stabilizing the model about its unstable period-1 fixed point. We demonstrate that these techniques are robust to imprecise measurements and experimental noise. Importantly, these methods require no knowledge of the underlying system equations. These findings suggest that chaos control and tracking may be useful for biomechanical applications in a clinical environment.
Tracking Controllers for Flexibly Jointed Robotic Manipulators With Extreme Joint Compliance
Authors: Zenieh Salah , Corless Martin
Published: July 2023

We consider the problem of designing robust tracking controllers for uncertain robotic manipulators where the actuators are coupled to the links via flexible joints. We impose no restrictions on the stiffness of the joints; hence robots with very flexible joints can be successfully treated with the proposed controllers. Each proposed controller guarantees exponential convergence of the tracking error for a compact set of initial states: for every compact set C of initial states, there is a controller from a family of nonlinear tracking controllers which guarantees that, provided the initial state is in C, the trajectory of the closed loop system converges exponentially to a small neighborhood of the desired trajectory. Controller design is based on singular perturbation theory and Lyapunov functions.
Nonlinear Modeling and Control of I.C. Engine Idle Speed
Authors: Shah Minesh A. , Franchek Matthew A.
Published: July 2023

Presented in this paper is the nonlinear modeling and control of the idle speed of a Ford 4.6L-2 valve V-8 fuel injected engine. The nonlinear model is of the Hammerstein type model and is identified through input-output data without a priori knowledge of the system dynamics. The nonlinear model is utilized in the development of an H∞ controller with a nonlinear gain that maintains the idle speed within a prespecified output tolerance despite system nonlinearities, an external disturbance, and an actuator saturation constraint. The allowable output tolerance is asymmetric.
Adaptive Robust Motion and Force Tracking Control of Robot Manipulators in Contact With Stiff Surfaces
Authors: Yao Bin , Tomizuka Masayoshi
Published: July 2023

High performance robust motion and force tracking control of robot manipulators in contact with stiff surfaces is considered in this paper. The robot parameters and the stiffness of the contact surface may not be known. The system may also be subjected to uncertain nonlinearities coming from the joint friction of the robot, external disturbances, the contact surface friction model, and the unknown time-varying equilibrium position of the contact surface. An adaptive robust motion and force controller is proposed, which needs measurements of position, velocity and interaction force only. The controller achieves a guaranteed transient performance and final tracking accuracy, a desirable feature for applications and for maintaining contact. In addition, the controller achieves asymptotic motion and force tracking without resorting to high-gain feedback when the system is subjected to parametric uncertainties only.
Deformation and Fracture Response of Steel at High Temperature
Authors: Brust Frederick W. , Zhang Jinmiao
Published: July 2023

To increase energy efficiency, new plants must operate at higher and higher temperatures. Moreover, power generation equipment continues to age and is being used far beyond its intended original design life. Some recent failures which unfortunately occurred with serious consequences have clearly illustrated that current methods for insuring safety and reliability of high temperature equipment is inadequate. Because of these concerns, an understanding of the high-temperature crack growth process is very important and has led to the following studies of the high temperature failure process.

This effort summarizes the results of some recent studies which investigate the phenomenon of high temperature creep fatigue crack growth. Experimental results which detail the process of creep fatigue, analytical studies which investigate why current methods are ineffective, and finally, a new approach which is based on the T*integral and its ability to characterize the creep-fatigue crack growth process are discussed. The potential validity of this new predictive methodology is illustrated.
Dislocation Punching in Functionally-Graded Materials
Authors: Taya M. , Lee J. K. , Mori T.
Published: July 2023

A new dislocation punching model for a functionally graded material (FGM) subjected to a temperature change has been proposed, using Eshelby’s model. FGM, consisting of several layers, is deposited on a ceramic substrate. Two types of microstructures are examined for a layer: one consists of a metal matrix and ceramic particles and the other of a ceramic matrix and metal particles. An elastic energy is evaluated when plastic strain, in addition to thermal mismatch strain, is introduced in the metal phase. The work dissipated by the plastic deformation is also calculated. From the condition that the reduction in the elastic energy is larger than the work dissipated, a critical thermal mismatch strain to induce stress relaxation is determined. The magnitude of the plastic strain is also determined, when the relaxation occurs. The results of the present theory for a special case of FGM, i.e., the case of single interface coincide with those of our earlier work on a thin metal coating on ceramic substrate. The theory is applied to a model FGM consisting of mixtures of Pd and Al2O3 on an Al2O3 substrate.
Fatigue of Ceramic Matrix Composites: Damage Mechanisms and Fatigue Life Diagrams
Authors: Talreja Ramesh
Published: July 2023

Ceramic matrix composites (CMCs) provide higher strength and toughness properties than are possible from monolithic ceramics, in addition to the high temperature resistance. The mechanisms of toughness of these materials have been treated extensively, although some confusion exists in characterizing this property, which has been recently addressed in a systematic manner (Sorensen and Talreja 1995). It is, however, of greater importance in most engineering applications that the long term behavior of CMCs remains in a safe regime. In particular, degradation of stiffness and strength under cyclic loading is a major concern.
Mechanism-Based Design of Composite Structures
Authors: Adjerid Slimane , Beall Mark W. , Dvorak George J. , Fish Jacob , Flaherty Joseph E. , Hudson John , Shek Kam L. , Shephard Mark S. , Wentorf Rolf
Published: July 2023

The paper introduces high temperature composite software developed for mechanism-based design of composite structures. Mechanism-based design is characterized by an understanding of the critical composite behaviors at several physical scales: the fibrous (micro) scale, the ply/weave (meso) scale and the laminated part (macro) scale, and by the specification of the available design parameters to achieve functionality by those behaviors. A software framework is described which integrates material modeling and analysis codes, provides automated assistance, and links to material databases. Elastic and inelastic material modeling codes suitable for high temperature composites with complex reinforcement and weave/lay-up configurations are presented and references to their underlying theories are given. Advanced analysis techniques are outlined for numerically efficient computational plasticity based on mathematical homogenization, idealization error indicators for material scale, three dimensional crack propagation in a fibrous composite, and modeling of reactive vapor infiltration and chemical vapor deposition processes.
Fatigue Damage in Metal Matrix Composites
Authors: Voyiadjis George Z. , Echle Rainer
Published: July 2023

In recent years the design and performance of aerospace vehicles changed due to enhancement and improvement in the design and the materials employed. Special consideration has to be given to the performance of the materials chosen for such vehicles. Titanium matrix composites (TMC) have been identified among the metal matrix composites as candidate materials capable of sustaining the arising loads while maintaining their structural integrity. Material behavior during fatigue loading has to be given special consideration since this loading condition is dominant during the flight regime. Material degradation due to fatigue loading is modeled using a micro-mechanical fatigue damage model for uni-directional metal matrix composites. The evolution of damage is considered at the constituent level by employing a damage criteria for each individual constituent. The overall material damage is obtained by using the Mori-Tanaka averaging scheme. A numerical implementation of the model is used to demonstrate its capabilities by presenting the analytical results for damage evolution in the fibers as well as in the matrix material for isothermal high cycle fatigue loading. Results for varying material and model parameters are also presented.
Effects of Defects in a New Form of Affordable Composite Materials-Rod Reinforcement
Authors: Chan W. S. , Wang J. S.
Published: July 2023

A pultruded rod reinforced composite which can eliminate presence of fiber waviness and reduce cost of laminate manufacturing has become a focus interest to aircraft manufacturers. Due to its characteristics of rod layer, conventional analysis which use the smeared properties across the entire rod layer fails to predict the structural response of this rod reinforced laminates. A closed-form expression was derived and a finite element analysis was conducted for predicting the critical buckling load for this type of laminates with a damage. Damage considered include broken rods, rods split vertically and horizontally, and delamination between the rod layer and angle plies. It is concluded that damages with rods split horizontally and a delamination can reduce the buckling load. For the rods broken, the buckling load will be reduced if a broken space is included. However, the buckling load remains unchanged if rods split vertically.
The Effect of pH on the Mechanism of Corrosion and Stress Corrosion, and Degradation of Mechanical Properties of AA6061 and Nextel 440 Fiber Reinforced AA6061 Composite
Authors: Berkeley D. W. , Sallam H. E. M. , Nayeb-Hashemi H.
Published: July 2023

The breaking load method was used to determine the degradation rate of mechanical properties of wrought T6 aluminum 6061, and Nextel 440 fiber reinforced AA6061 composite, as a function of pH, by measuring their post-exposure residual strength. The materials were exposed to acidic NaCl at two initial pH of 1.5 and 2. Two different exposure techniques were employed; one in which the pH of the solution was kept constant by refreshing the corrosive medium, and a second method in which the solution was not refreshed. The change in pH with exposure time was also investigated to provide a more comprehensive understanding of the role of H+ ions in the corrosion process. At an initial pH of 1.5 the matrix showed a significant strengthening response, after an initial decrease in residual strength with time, if the solution was unrefreshed. However, if the solution was refreshed, the residual strength for both the corrosion and stress corrosion specimens continued to decline at an approximately constant rate. The specimens at an initial pH of 2 show a much more gradual strengthening because of the slower initial reaction rates between the solution and the alloy. The Nextel 440 fiber reinforced AA6061 composite was found to be considerably more susceptible to corrosion than the AA6061 matrix. From the results attained, it was concluded that the pH of the solution played a crucial role in the degradation rate of mechanical properties in the AA6061 matrix, and the Nextel 440 fiber reinforced AA6061 composite.
Thermal Softening of Glassy Particle Modified Tungsten
Authors: LeDuc P. R. , Bao G.
Published: July 2023

A micromechanics study is made of the rate-dependent thermal softening behavior of a tungsten matrix composite containing glassy particles. Under adiabatic compression of the composite, the elastic glassy particles thermally soften at relatively high strains, enhancing the thermal softening of the tungsten-based composite, thus reducing the strain rate sensitivity and fostering shear localization. To guide the microstructural design of the particle-modified tungsten-based composite in penetration applications, systematic predictions are made for the stress-strain behavior of the composite under overall adiabatic compression with different temperature-dependent behaviors, sizes, volume fractions of the particle and applied strain rates. It is found that both the onset and the rate of thermal softening of the composite depend critically on the applied strain rate. Owing to thermal softening of the glassy particles, the strain-rate sensitivity of the composite is reduced.
Evaluation of the Multidimensional QR Algorithm for Actuator Placement in Active Control Applications
Authors: Naghshineh Koorosh , Heck Larry P. , Olkin Julia A.
Published: July 2023

In our previous work, we developed a new actuator placement algorithm that is capable of selecting the best actuator placement for active noise control problems over a broadband of frequencies. The actuator selection algorithm is based on a novel extension of the Householder QR subset selection algorithm. In this paper, we improve our algorithm by incorporating seven new measures of actuator performance. The new measures, based on different matrix norms and functions of the actuator frequency responses, yield actuator placements that result in active noise control systems with improved performance and robustness.
Sensitivity of Structural Acoustic Response to Attachment Feature Scales
Authors: Shepard W. Steve , Cunefare Kenneth A.
Published: July 2023

When implementing a discrete computational method to predict the vibro-acoustic behavior of a larger structure one must decide how much effort and refinement to expend on modeling smaller attached structural components. In representing these attachments, or features, it is important to know what scales are important with regard to a valid prediction of the system response. To aid in the study of the impact of feature scales, sensitivity relationships for important system variables are developed in this paper. The sensitivity analysis will, for one, consider the change in the radiated power with respect to changes in the scale of an attached mass. These relations are developed analytically and do not require finite difference methods or eigenvalue derivatives. It is shown that computing the sensitivity of the radiated acoustic power only requires evaluating one additional term as all of the other terms are found during the normal course of modeling the system. Furthermore, the terms that include fluid loading on the structure need only be reevaluated when the excitation frequency is changed. It is also noted that the sensitivity relations developed here can easily be used to investigated the effects of modifying a number of structural parameters.
Feynman Rules for an Elastic Plate With Random Internal Scatterers
Authors: Photiadis Douglas M.
Published: July 2023

The ‘fuzzy structure’ approach proposed by Soize for the analysis of the effects of complex internal structure has been formulated in terms of Feynman diagrams for the case of a large fluid loaded plate. We have derived the Feynman rules both in real space and wavenumber space for the case in which the internals are simple oscillators distributed uniformly and independently in both space and frequency. With the method of calculation established, the mean Green’s function is evaluated to 3rd order in the perturbation expansion to illustrate the ease with which results can be obtained via this technique. The calculation demonstrates that the scattering effects due to the internal structure introduce damping (of a sort) and in addition exposes the parameter which must be quite small in order for low order calculations (e.g. zeroth order) to be meaningful: The ratio of the mass of a single oscillator to the mass which ‘rigidly’ supports the oscillator.
Acoustic Scattering From a Submerged Shell With Many Internal Oscillators
Authors: Bucaro Joseph A. , Photiadis Douglas M. , Houston Brian H.
Published: July 2023

The spectral character (temporal & angular) of the acoustic scatttering from a submerged, framed cylindrical shell in which have been inserted hundreds of dumbbell mechanical oscillators has been measured. The 880 oscillators, which are attached to the frames, are distributed over ten different frequency bands. A comparison of the measured scattering data from the shell — both with and without the attached oscillators — shows marked differences in the features displayed in frequency-angle space. Various mechanisms which might explain the character of these new features are discussed.
Boundary Element Prediction of Sound Propagation in Ducts Containing Bulk Absorbing Materials
Authors: Seybert A. F. , Seman Richard A. , Lattuca Michael D.
Published: July 2023

In this paper the sound propagation in a rectangular duct containing a bulk absorbing foam liner is investigated. The foam is characterized by the complex characteristic impedance which is measured using an improved two-cavity method. The complex characteristic impedance is used to predict the normal incidence impedance and absorption coefficient of the foam which is compared to measured data obtained using the ASTM E-1050 test method. The complex characteristic impedance is also used to predict the attenuation through a layer of foam in a plane wave tube for which measured results are also available. Finally, the boundary element method is used to predict the attenuation of sound in a rectangular duct where one surface is covered with foam. Comparison with experiment is shown for several frequencies.
The Design of a Robust Controller for Hydrostatic Transmissions
Authors: Hampson S. P. , Chawdhry P. K. , Burrows C. R.
Published: July 2023

Hydrostatic transmissions are often used for speed control in applications where large load-torque fluctuations may cause unacceptable changes in the output speed. The traditional approach is to use a closed-loop configuration and a classical control algorithm, but this often leads to unsatisfactory performance requiring on-line tuning. Modern robust controllers offer an alternative approach since they are able to explicitly take process uncertainties into account. One possibility is to use an H∞ controller for which the weights need to be selected to achieve the required disturbance rejection properties. This paper describes a case study which shows that an H∞ controller is capable of rejecting periodic torque disturbances generated by a mechanical mechanism while providing good tracking of the reference speed.
Acceleration Characteristics of Servo-Controlled Pneumatic Cylinder
Authors: Pu J. , Wong C. B. , Moore P. R.
Published: July 2023

Knowledge concerning the acceleration characteristics of pneumatic drives is useful in the design, control, and tuning of servo-pneumatic systems. In this paper the force/speed characteristics of an asymmetric actuator are outlined and verified. The paper then considers the rate at which a pressure differential can be established. This then leads to the concept of meter-in and meter-out control zones. The results reported in this paper should promote interests in pneumatic servos for certain profile following applications.
Analysis and Testing of Inelastic Buckling of a Ring Stiffened Cylinder
Authors: Ryan John D.
Published: July 2023

Naval vessels fabricated from high strength steels (HY-100) traditionally require higher yield strength weld metal to protect the weld from high strains. However, these high strength welds are costly due to strict fabrication requirements. Alternatively, reduced fabrication costs can be achieved by using slightly lower strength welds designed for use with lower strength HY-80 steel. To verify the validity of this approach, the U.S. Navy is supporting the optimized weldment properties project to evaluate the effect of lower strength welds on the performance of welded structures and institute applicable design changes.

One phase of this program included numerical and experimental evaluation of ring-stiffened cylinder structures under hydrostatic pressure loading. The objective was to modify the existing design criteria to account for the use of undermatched welds. Finite element analyses were developed using the ABAQUS and STAGS analysis codes. These analyses modeled the nonlinear, inelastic response of the structure and were used to predict buckling pressures for the structures. Experimental models were fabricated and tested to validate the numerical analyses. The experiments and analyses have resulted in design criteria modifications associated with the use of undermatched welds in hydrostatically loaded, ring-stiffened cylinder structures.
Structural Analysis of a Composite Nuclear Fuel Waste Disposal Container
Authors: Garroni James D. , Crosthwaite J. Les
Published: July 2023

A composite container for the retention and disposal of used CANDU™ nuclear fuel was structurally analyzed. The design employs an inner steel vessel for support against external pressure and a close-fitting outer copper vessel for corrosion resistance. The container is deposited in an underground disposal vault in granitic rock and is surrounded by a clay-based buffer that swells when contacted by groundwater. It must withstand the swelling pressure of the buffer plus the hydrostatic pressure of the groundwater at a minimum 500-m depth. The case was analyzed in which a small manufacturing defect penetrates the copper shell, allowing groundwater to seep between the vessels and gradually convert the steel of the inner vessel to magnetite. Because the specific volume of magnetite is approximately twice that of steel, the outer surface of the steel vessel progressively swells while the remaining (uncorroded) shell thins. Outward deformation of the copper vessel is resisted by the buffer and surrounding rock, therefore pressure on the steel vessel gradually increases as it corrodes.

The finite element code, ANSYS, was used to predict the minimum corrosion that would produce plastic collapse of the steel vessel. Knowledge of the rate of conversion of steel to magnetite under disposal-vault conditions could then allow an estimate of the time-to-collapse following the initial ingress of groundwater.
Finite Element Analysis (FEA) of Motor Operated Valves (MOV) Disc Tabs Subjected to Valve Opening Loads
Authors: Rao K. R. , Chism J. Wesley
Published: July 2023

Nuclear power plants valve testing programs require determination of opening loads for certain motor operated valves (MOV). The opening loads must be evaluated to determine if the valve components are within acceptable stress limits. These loads may cause the valve internals to appear overstressed when conventional linear hand calculations are used to determine valve component stresses. Finite element analyses (FEA) methods have been developed to permit more accurate determination of component stresses. This paper describes the FEA methods used to analyze valve components. Acceptance criteria using FEA methods which are not explicitly addressed in the ASME Code are explained in this paper. Using a Case Study Example of a Disc Tab of a motor operated valve (MOV), it is demonstrated how the stated acceptance criteria can be satisfied.
Approximate Evaluation Method for Crack Growth Rates Under Repeated Large Plastic Deformation
Authors: Igi Satoshi , Hidaka Kentaro , Kawahara Masanori
Published: July 2023

Many countries have suffered from large earthquakes in the past few decades. Extensive efforts are required to estimate the fracture behavior under cyclic plastic strains in steel components so as to prevent or minimize fatal accidents. Crack growth rates under cyclic loads have been generally analyzed by Paris’ law by using a linear elastic fracture mechanics concept, “ΔK”, stress intensity factor range. But, this approach cannot be valid in the domain of large plastic deformation. An alternative approach could be developed by substituting J-integral or crack tip opening displacement for stress intensity factor. However, this is yet not very easy to apply in real complicated structural components, as it takes much excessive computational time for the calculation of the governing fracture parameters.

The present paper proposes an approximate method to evaluate crack growth rates under repeated large plastic deformation by using an easier formulation based on an approximate analysis of fracture parameters. Crack growth experiments have been conducted under cyclic axial plastic loadings in order to verify the validity of the proposed formula. Experimental results showed fairly good agreement to the proposed formula. Discussion is as well directed to the change in the feature of fracture surfaces during growth.
An Analysis of the Two Bar Ratcheting Behavior Using the Viscoplasticity Theory Based on Overstress (VBO)
Authors: Nakamura Toshiya , Krempl Erhard
Published: July 2023

The ratcheting behavior of the “unsymmetric two bar system” was investigated by numerical experiments. The two bars are restrained to the same length and are subjected to a constant load. One bar sees cyclic temperature variations while the other bar is kept at constant temperature. The material models employed are rate-independent plasticity (kinematic hardening) and the Viscoplasticity Theory based on Overstress (VBO) matched to represent the cyclic neutral 6061 T6 Aluminum alloy elastic and inelastic deformation behavior. For simplicity temperature independent material properties were assumed. Numerical analyses were performed to investigate the effects of rate of thermal loading and temperature range.

Elastic-inelastic shakedown is ultimately achieved due to work hardening There is a strain range increase until it reaches a steady value. Kinematic hardening and VBO predict almost the same strain range which for the case of VBO is nearly rate independent. The behavior for both material models is very different for the mean strain. For VBO, the number of cycles to shakedown is rate-dependent and is considerably larger than for kinematic hardening. Finally, the steady state mean strain and strain range are computed directly for VBO.
A Computational Engine for the Nonlinear, Transient Response of Preloaded Structures
Authors: Kulak R. F. , Pfeiffer P. A.
Published: July 2023

The transient loading of mechanical components and structures is usually performed with the assumption that there are no preloads applied to them since preloads are usually small and can be neglected. However, for certain structures used in the nuclear power industry, the preloads are significant and must be considered in the transient analysis. Two examples of these types of structures are prestressed concrete containments and inter-compartment locks, which respond with both geometric and material nonlinearities during transient loadings. An efficient computational engine is presented in this paper for the solution of these types of problems. An example is presented to illustrate the algorithm. A preloaded platen, which is part of an inter-compartment lock, is subjected to an impulsive load. The resulting transient response of the system is presented.
Demonstration of the Electric Controlled Pneumatic Brakes on the Union Pacific Railroad
Authors: Cartwright Robert A. , McConnell David S.
Published: July 2023

The purpose of the demonstration was to evaluate what degree Union Pacific Railroad should support further development of Electronic Controlled Pneumatic (ECP) brakes, by investigating:

Crew Acceptance

Equipment Reliability

Train Performance

Possibility of “wire line” Distributed Power.

The results obtained concerning these issues are discussed along with Union Pacific’s philosophy concerning this technology.
Curved Plate Wheel Design for a Commuter Railroad’s Reverse Dish 32″ Car Wheel
Authors: Rusin Thomas M. , Coughlin John M. , Damergis George
Published: July 2023

An improved curve plate wheel is presented for the 32″ reverse dish wheel which will reduce the incidences of thermally cracked wheels. The finite element method (FEM) design process, for the first time, employed elastic-plastic methodology and incorporated the residual stress from the manufacturing process. Dynamometer measurements of the thermal and mechanical stresses of the straight plate version of the wheel are compared to FEM thermal and thermal elastic-plastic predictions, for high speed stops. Finite element predictions of the thermal and mechanical stresses for the curve plate wheel are compared to those of the straight plate wheel.
Failure Mechanisms in 3-D Braided Composite Beams Under Pure Bending
Authors: Wang A. S. D. , Kumar Amrita
Published: July 2023

In this paper, we discuss some results obtained from an on-going experimental study on failure and failure mechanisms in three-dimensionally braided composite beams subjected to pure bending.
Three-Dimensional Penetration Modelling of Composite Plates
Authors: Chen J. K. , Beraun J. E.
Published: July 2023

The smoothed particle hydrodynamics (SPH) technique in conjunction with the macro-mechanics approach for fiber composites was developed to predict impact damage of composite structures. For investigating the detailed perforation process and damage progression, 3-D simulations of a graphite/epoxy composite laminate struck by a steel projectile were performed. The predicted damage in the composite target agrees well qualitatively with the experimental results. This study has demonstrated that SPH can be a robust and viable analytical tool for predicting the accurate response of fiber-reinforced composite structures subjected to high-velocity impact.
Damage Growth in Stitched Graphite/Epoxy Laminates Under Mode I Fracture and Compression Loading
Authors: Sharma Suresh K. , Sankar Bhavani V.
Published: July 2023

Published studies have reported outstanding improvements in Mode I fracture toughness and compression after impact (CAI) strength of fibrous composites due to through-the-thickness (z-fiber) reinforcement. One of the methods of through-the-thickness reinforcement successfully experimented by the authors is stitching of textile composites. Our results have shown improvements of about 30 times higher Mode I fracture toughness as characterized by critical strain energy release rate (GIc) and up to 400% increase in the CAI strength over the unstitched textile composites. In this paper we illustrate the damage growth and its underlying mechanisms in the case of stitched composites as observed in our studies. The role and interplay of starter crack, first line of stitches, needle and bobbin yarns, type of stitch lock, stitch density and other processing parameters are discussed. Double Cantilever Beam (DCB) tests were conducted on 24 ply graphite/epoxy (AS4/3501-6) uniweave textile laminates stitched with different yarns and densities to measure Mode I fracture toughness. 48 ply AS4/3501-6 uniweave textile laminates with different simulated impact damage were tested in compression to measure CAI strength. In addition, the effect of stitching on thinner 16 ply AS4/3501-6 plain weave textile laminates was studied where the gains in CAI strength, though noticeable, are much less than for the thicker laminates.
Matrix Cracking With Irregular Fracture Fronts as Observed in Fiber Reinforced Ceramic Composites
Authors: Hu Kai X. , Yen Chao-pin , Wyatt Karl W.
Published: July 2023

As a result of matrix cracking in fiber reinforced composites, fracture planforms assume a wide variation of profiles due to the fact that fiber bridging strongly affects the behavior of local crack fronts. This observation raises the question on the legitimacy of commonly used penny-shaped crack solutions when applied to fiber reinforced composites. Accordingly, investigation of the effects of fracture front profiles on mechanical responses is the thrust of this paper. We start with the solution of a penny-shaped crack in a unidirectional, fiber reinforced composite, which demonstrates necessarity of considering wavy fracture fronts in fiber reinforced composites. A theoretical framework for fiber reinforced composites with irregular fracture fronts due to matrix cracking is then established via a micromechanics model. The difference between small crack-size matrix cracking and large crack-size matrix cracking is investigated in detail. It is shown that the bridging effect is insignificant when matrix crack size is small and solution of effective property are obtained using Mori-Tanaka’s method by treating cracks and reinforcing fibers as distinct, but interacting phases. When the crack size becomes large, the bridging effects has to be taken into consideration. With bridging tractions obtained in consistency with the micromechanics solution, and corresponding crack energy backed out, the effective properties are obtained through a modification of standard Mori-Tanaka’s treatment of multi-phase composites. Analytical solutions show that the generalization of a crack density of a penny-shaped planform is insufficient in describing the effective responses of fiber-reinforced composites with matrix cracking. Approximate solutions that account for the effects of the irregularity of crack planforms are given in closed forms for several cases, including rectangle, polygon, rhombus, cross and the wavy fracture front.
Plane Stress Dynamic Crack Growth Along a Ductile/Rigid Interface
Authors: Deng Xiaomin
Published: July 2023

Dynamic crack growth along elastic bimaterial interfaces have been studied extensively in the past decade by many researchers. In contrast, studies of dynamic interfacial fracture under elastic-plastic conditions are still very limited. In this presentation, the results of an analytic investigation of the asymptotic stress and deformation fields at the tip of a dynamically growing interface crack between a ductile material and a rigid substrate under plane stress conditions will be reported. The ductile material is taken to be ideally plastic and obey the J2 flow theory of plasticity. Under steady-state conditions, the asymptotic structure of the crack-tip stress, velocity and strain fields has been obtained. The study reveals that two types of crack-tip sectors exist, namely uniform and nonuniform plastic sectors and that the stress, strain and velocity fields are bounded in all sectors. In a uniform sector, the rectangular Cartesian components of the stress, strain and velocity fields are constant, and there is no plastic strain accumulation. In a nonuniform sector, the stress, strain and velocity components at a point depend on the angular position of the point in the crack-tip polar coordinate system and are governed by a system of simultaneous ordinary differential equations. This is a sector where plastic strains can accumulate. A general crack-tip sector assembly has been obtained for a practical range of crack growth speeds. Several nontrivial families of admissible solutions of the crack-tip fields based on this general assembly of uniform and nonuniform crack-tip sectors will be presented and discussed. Finally, comparisons with corresponding plane strain solutions (Deng, 1993 a) will be made.
Comparison of Physical Aging Effects on the Tension and Compression Creep of the IM7/K3B Composite
Authors: Gates Thomas S. , Veazie David R. , Brinson L. Catherine
Published: July 2023

Experimental and analytical methods were used to investigate the similarities and differences of the effects of physical aging on creep compliance of IM7/K3B composite loaded in tension and compression. Two matrix dominated loading modes, shear and transverse, were investigated for two load cases, tension and compression. The tests, run over a range of sub-glass transition temperatures, provided material constants, material master curves and aging related parameters. Comparing results from the short-term data indicated that although trends in the data with respect to aging time and aging temperature are similar, differences exist due to load direction and mode. An analytical model was used for predicting long-term behavior using short-term data as input. This model worked equally as well for the tension or compression loaded cases and provided more accurate long term predictions for the shear mode as compared to the transverse mode.
Comparison of Effectiveness of Shape Memory Alloy and Composite Stiffeners in Stability Problems of Composite Shells and Plates
Authors: Birman Victor
Published: July 2023

The effects of composite and shape memory alloy stiffeners on stability of composite cylindrical shells and rectangular plates subjected to a compressive load are compared. The governing equations for reinforced cylindrical shells are developed based on the Love first approximation theory and smeared stiffeners technique. It is shown that composite stiffeners are more efficient in cylindrical shells, while shape memory alloy stiffeners may be preferable in flat plates or in long shallow shells. It is also proven that shape memory alloy stiffeners increase the upper and lower buckling loads of cylindrical shells modeled as single-degree-of-freedom systems by the same amount.
Photodeformation and Light-Temperature-Piezoelectric Coupling of Optical Actuators: Part 2 — Vibration Control
Authors: Liu B. , Tzou H. S.
Published: July 2023

Non-contact optical actuators driven by high-energy lights are investigated and applications to active vibration control of plates are demonstrated in this study. An optical servo control system coupled with a rectangular plate is proposed. Active vibration control and modal control effectiveness of the rectangular plate are evaluated. The proportional velocity feedback is compared with the Lyapunov control. Experimentally calibrated simulation results show that the optical actuators are effective in vibration control and the highest frequency of controllable vibration can achieve several hundred Hertz. The time histories also indicate that the Lyapunov control is more effective as compared with the proportional feedback control.
Cracking in Ferroelectric and Antiferroelectric Ceramic Multilayer Actuators
Authors: Gong Xiaoyan , Yu Honghui , Suo Zhigang , McMeeking Robert M.
Published: July 2023

This paper models cracking in the poling process of a ferroelectric actuator and the operation of an antiferroelectric actuator. In each case, domain switching or phase transition produces large electric displacement and strain. Around an internal electrode edge, such strain causes cracking, which, in turn, is a precursor to electrical breakdown. We model domain switching or phase transition by large increases of both the electric displacement and field induced strain under a small change in the electric field near the coercive field. Ignoring the stress contribution to the electric field, we solve the electric field around the internal electrode edge for nonlinear electric field and electric displacement relations. We then solve a standard elastic residual strain problem to determine the stresses in the structure. Fracture mechanics is then used to determine the cracking conditions in actuators. We find that a critical thickness exists, below which cracking will not occur. This agrees with the prediction of Hao et al (1996), and Gong and Suo (1996).
Combustors for Micro-Gas Turbine Engines
Authors: Waitz Ian A. , Gauba Gautam , Tzeng Yang-Sheng
Published: July 2023

The development of a hydrogen-air microcombustor is described. The combustor is intended for use in a 1 mm2 inlet area, micro-gas turbine engine. While the size of the device poses several difficulties, it also provides new and unique opportunities. The combustion concept investigated is based upon introducing hydrogen and premixing it with air upstream of the combustor. The wide flammability limits of hydrogen-air mixtures and the use of refractory ceramics enable combustion at lean conditions, obviating the need for both a combustor dilution zone and combustor wall cooling. The entire combustion process is carried out at temperatures below the limitations set by material properties, resulting in a significant reduction of complexity when compared to larger-scale gas turbine combustors. A feasibility study with initial design analyses is presented, followed by preliminary experimental results from a 1:1 scale silicon carbide microcombustor. Issues of flame stability, heat transfer, ignition and mixing are addressed. A discussion of requirements for catalytic processes for hydrocarbon fuels is also presented.
Control of Roll Moment by MEMS
Authors: Lee Gwo-Bin , Ho Chin-Ming , Jiang Fukang , Liu Chang , Tsao Tom , Tai Yu-Chong , Scheuer Fabien
Published: July 2023

In this paper, we will illustrate that the motion of a delta wing can be controlled by actuators fabricated by micromachining technology, if the size of the micro-actuator matches the thickness of the thin boundary layer at the leading edge of the delta wing. This match provides a coupling between the micro actuator and the flow instability which serves as an effective amplifier of the artificial disturbances. The distributed micro-actuators perturb the flow and break the symmetry of the two leading edge separation vortices such that a torque is obtained.
Vehicle Rollover: Assessing the Relative Importance of Risk Factors With Crash Scenario Analysis
Authors: Donelson Alan C. , Ramachandran Karuna , Davis Martin S.
Published: July 2023

Most problems that would benefit from motor vehicle risk analysis involve questions about the importance of design features or other characteristics of vehicles relative to factors related to drivers, driving environments, and types of collisions. Outcomes of motor vehicle accidents result from interactions among several or more pre-crash and at-crash factors. The inherent complexity of motor vehicle accidents often defeats traditional approaches to multivariate regression analysis. This paper introduces a new technique called crash scenario analysis. Rather than treating many causal factors as discrete variables, combinations of factors define crash scenarios. A single variable (scenario risk) measures the likelihood of crash outcomes for vehicles involved in each unique scenario. The authors applied crash scenario analysis to vehicle rollover and used logistic regression to estimate the importance of vehicular factors relative to scenario risk. Findings indicated that scenario risk was a much stronger predictor of rollover in fatal crashes than vehicle static stability factor (T/2H).
The Nuisance Fire Problem With Acetylene B Cylinders
Authors: Tudor Andrew H. , Mniszewski Kim R.
Published: July 2023

On November 19, 1992, a three-story, twenty-two unit condominium project in the Los Angeles area was consumed by fire. The structure, in the framing stages of construction, burnt to the ground. Several adjoining structures sustained varying degrees of fire damage. The fire was caused by a golf ball-sized fire emanating from the threaded connection in a plumber’s air/acetylene piping system, caused by a leak at the threaded connection between the acetylene B tank and the regulator. Unfortunately, a small nuisance fire in this area can quickly become a dangerous and unmanageable fire upon operation of the (safety) fusible plug, which is proximate to this connection.

Results of literature searches and reviews of appropriate industry standards indicate that this valve site is prone to these “nuisance” fires. Analysis of other sizes of acetylene tanks indicate a design philosophy significantly different from that used for the subject B tank. These design differences have profound safety implications. Results of analysis and testing of conventional acetylene B tanks have demonstrated inherent defects and have identified existing designs that eliminate these defects. A complete analysis addressing human factors, standards, mechanical, and thermal design issues is presented. Testing further supported and validated the analytical models where necessary.

The ultimate objective is to design an acetylene tank which can sustain human error, allow for a means to eliminate or control the nuisance fire and can demonstrate superior fire performance. An alternative design was identified that achieves this. Changes to DOT and CGA standards regarding such tanks are recommended.
IEEE Human Factors Standards Program
Authors: Voss T. J.
Published: July 2023

Within the Institute of Electrical and Electronics Engineers (IEEE), Subcommittee 7 (SC-7), Human Factors and Control Facilities, of the Nuclear Power Engineering Committee (NPEC) develops and maintains human factors standards. SC-7 members have extensive expertise in the human factors of nuclear generating facilities. NPEC provides funding for standards development or revision, oversees the activities of SC-7, and has power of approval for standards produced by NPEC subcommittees.

IEEE Std 1023-1988 is the upper tier document which defines the human factors tasks required to support the integration of human performance into the design process. The standard was reaffirmed in January 1995 and is to be revised within the next two years. Presently, three lower tier documents, in various stages of development, expand upon the upper tier standard. IEEE Std 845-1988 (in revision) presents methods for measurement of human performance. IEEE Std 1082 (final draft in ballot) deals with the human reliability analysis aspects of probabilistic risk assessment. IEEE Std 1289 presents human factors guidance for design of computer-based display systems.

In addition to producing and maintaining human factors standards, SC-7 has sponsored a series of conferences on human factors in power plants. The next one, “Human Factors in Power Generation: A Global Perspective,” will take place in Orlando, Florida, from June 7–12, 1997.
Characterization and Modeling of the Creep Behavior of Xydar G930 Liquid Crystalline Polymer
Authors: DiFilippo Vincent , Saigal Anil , Zimmerman Michael A.
Published: July 2023

Liquid crystalline polymers (LCPs) are a relatively new class of polymers with excellent high temperature properties. They are being considered for electronic packaging applications, such as molded multichip modules, where high dimensional tolerances are critical for component operation. High stresses and temperatures can be generated in molded leadframes during surface mount soldering operations and component service. Under these conditions, time dependent deformation or creep could result in warpage and failure of molded leadframes. In order to aid designers in estimating component lifetimes, the creep properties of Xydar G930 were investigated. Xydar G930 is a LCP with 30 wt.% glass filler. A series of short term (24 h) uniaxial creep tests were conducted at several temperatures and stress levels ranging from room temperature to 350°F, and 0.3 UTS to 0.8 UTS, respectively. Values of steady state creep rate were calculated from the creep curves and fit to an Arrhenius analog as a function of temperature and a power law relation as a function of stress. Results showed linear viscoelastic behavior at low stresses and significant dependence of creep on temperature and stress.