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Aerospace and Mechanical Engineering (252)

Graduate College (252)AuthorsFasel, Hermann F. (13)Heinrich, Juan C. (12)Madenci, Erdogan (12)Arabyan, Ara (11)Balsa, Thomas F. (11)Kececioglu, Dimitri B. (11)Nikravesh, Parviz E. (10)Pearlstein, Arne J. (10)Wirsching, Paul H. (10)Chen, Chuan F. (9)View MoreTypes
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A combined experimental and analytical approach for interface fracture parameters between dissimilar materials in electronic packages

Kay, Norman R. (The University of Arizona., 2003)

Failure of materials and interfaces are commonly linked to the fracture parameters such as the stress intensity factors and the energy release rate. However, there exists no experimental procedure for the direct measurement of these fracture parameters. This dissertation reports on the development of a new technique to obtain these parameters by testing specimens created from post-production electronic packages. The results from the experimental testing are then used as the input for an analytical model which computes the desired parameters. The specimens are thin strips of post production electronic packages. A crack is introduced along the interface in the specimen. Loading is applied to the specimen using the bend fixture inside the chamber of a scanning electron microscope, and images are captured following each load step. Digital image analysis on these images provides the displacement field around the crack tip to be used as boundary conditions in the analytical model. A hybrid formulation is developed utilizing the exact solution for the stress and displacement fields based on the eigenfunction expansion method under general loading. The region has two dissimilar elastic or viscoelastic material wedges with perfect bonding, and is not limited to a particular geometric configuration. The solution method is based on the principle of virtual work in conjunction with the use of Laplace transformation to eliminate time dependency. The strength of the singularity is obtained in the time space without resorting to approximate Laplace inversion techniques. However, the intensification of the stress components is obtained by employing an approximate inversion technique. One of the main contributions of this dissertation is the development of multiple techniques for the creation of test specimens from electronic packages. These methods involve different procedures of encapsulation for sectioning and techniques for the introduction of the crack to the interface. A second development is the technique of testing using image capture in conjunction with digital image correlation to find localized displacements. The third contribution from this work is the development of an analytical model to accurately model the region near the junction of two dissimilar viscoelastic materials.

A closed loop technique for aircraft performance optimization

Berry, Robert L. (The University of Arizona., 1970)

COMPREHENSIVE APPROACH FOR EVALUATION AND CONSTRUCTION OF ACCEPTANCE SAMPLING PROCEDURES.

ZONNENSHAIN, AVIGDOR. (The University of Arizona., 1983)

Acceptance sampling procedures are widely used in industry as part of the total quality control activities. The acceptance procedure is usually constructed based on a set of statistical and/or economic requirements specified by the producer and/or the consumer. After the acceptance procedure is determined, the users are interested in evaluating its statistical and economic characteristics. This dissertation presents a comprehensive approach for constructing and evaluating acceptance sampling procedures. A large variety of statistical and economic characteristics is studied, from both the producer's and consumer's viewpoints. A part of the acceptance procedure is the sampling plan. Various statistical characteristics of the sampling plan are studied. The statistical evaluation of the acceptance procedure consists of analyzing these characteristics. The economic analysis includes identification of the possible actions during the acceptance procedure and evaluation of the producer's profit and the consumer's cost functions associated with each action. Guidelines for applying the statistical and economic characteristics in the evaluation process are presented. In a real situation, sampling may be subjected to inspection errors, which can affect the statistical and economic characteristics of the acceptance procedure; so all the characteristics were restudied for an error-prone sampling inspection. The statistical and economic characteristics are used to specify sets of requirements for constructing acceptance procedures. Selection of an appropriate set is based on the needs of the user, the available data, and the conditions under which the procedure is to be applied. The concluding step is to combine the construction and evaluation methods into an overall analysis cycle of "construct-evaluate-reconstruct." Computer programs are given to facilitate application of the evaluation and construction processes. This study deals explicitly with single sampling plans for attributes. The analysis is based on the Bayesian approach in which the prior distribution is a mixed binomial with a beta weight function. However, the presented approach can be applied to any type of sampling and prior distribution. The results of the study can be used by decision makers as a tool to improve the use of acceptance procedures in a large variety of scenarios.

THE TRANSLATION OF A SPHERE AT LOW REYNOLDS NUMBER IN THE VICINITY OF A FREE SURFACE

Ruetmann, Mihkel, 1940- (The University of Arizona., 1970)

THE EFFECT OF UNIFORMLY SPACED ELASTIC SUPPORTS ON THE MODAL PATTERNS ANDNATURAL FREQUENCIES OF A UNIFORM CIRCULAR RING

McKinley, Joseph William, 1937- (The University of Arizona., 1970)

Adaptive model-following control for hyperthermia treatment systems.

Kress, Reid Leonard. (The University of Arizona., 1988)

The purpose of this research was to develop three real-time adaptive temperature controllers for hyperthermia heating systems. Each scheme is made adaptive by using a transient Gaussian estimation routine to estimate the tissue blood perfusion and by then using these estimated values either in an optimizing routine, or in an observer, or in both. The optimizing routine uses a steady-state Gaussian estimation technique to optimize the power distribution until the best possible match is obtained between the steady-state temperatures predicted by a treatment model and a prespecified ideal temperature distribution. The observer uses a treatment model to control unmeasured locations. The first adaptive control scheme uses the optimizing routine alone, the second uses the observer alone and the third uses both the optimzing routine and observer. The performance of each of the adaptive control schemes is compared to a standard proportional-integral-derivative (PID) control scheme for one-dimensional simulations of typical treatments. Results comparing the deviation of the controlled temperature distribution to the ideal desired temperature distribution for all locations and all times indicate that the adaptive schemes perform better than the PID scheme. It can be concluded that adaptive control yields improved performance if good a priori knowledge of the treated region tissue and perfusion region boundaries is available. While these control schemes were designed for eventual implementation on a scanned focused ultrasound hyperthermia treatment system, the techniques are applicable to any system with the capability to vary specific power with respect to location and with an unknown distributed energy sink proportional to the temperature elevation.

Analysis and fabrication of paraboloidal CFRP sandwich mirrors.

Hong, Tayo Steve. (The University of Arizona., 1991)

The low areal weight requirements of telescopes in aerospace applications has driven the study on composite mirrors for several years. For example, the primary parabolic mirror in a balloon-borne, Cassegrain telescope required an optical quality better than 30 microns in figure RMS error. A parametric study on composite sandwich mirrors was conducted by using finite element analysis as well as optical analysis. The factors covered the cell sizes, core materials, core thicknesses, face layups, and support configurations. Based on theoretical calculations, many high quality spherical composite sandwich mirrors were generated by using a non-heat curing process. The CFRP faces and Nomex core were chosen as the baseline materials for mirror fabrication due to their high strength and low weight. The proposed replication method applied an interface layer between face and surface coat to eliminate print-through problems. Many important goals have been realized in those mirror samples with optical laser interferometer testing. These include the figure RMS error less than 2 microns and the surface RMS error less than 0.05 micron. The areal weights of the mirror samples are less than 7 kg/m². The thermal stability of these mirrors was observed from the optical results with thermal cycling tests. The proposed 2-meter parabolic composite sandwich mirror, with an areal weight of less than 10 kg/m², would consist of either [0/90/45/-45](s) layup faces with an optimal 3'' core or (QC) layup faces with a total core thickness of 5 inches. Both a ring support around the equator and the 18-point Hindle-type support would lead to the best optical quality under both self weight and thermal loading.

Unsteady viscous flow past a lifting plate

Schmall, Robert Anthony, 1932- (The University of Arizona., 1974)

Wavetrains in diverging mixing layers

Yapo, Sylvain Achy (The University of Arizona., 1991)

It is generally accepted that a linear stability theory, together with a slowly diverging base flow, can describe many of the characteristics of coherent structures in free shears flow. In this dissertation we model these two-dimensional instability waves as they travel in a slightly inhomogeneous steady and viscous unstable base flow. These unstable and inviscid wave packets are analysed using linear stability theory. The analysis is performed by separating the physical flow in two parts. In the first part, the instability waves are evolving in a parallel mixing layer and their solution serves of initial conditions for the second part of the flow. The parallel flow analysis leads to the receptivity of the flow to both pulse-type and periodic excitations. This part of the study is done by solving the initial-value problem completely and studying its long-time behaviour, which is a wave packet. We then repeat the same analysis with some modifications and arrive at the receptivity of the flow for sinusoidal excitations. We find that a shear layer is very receptive to high-frequency disturbances that are generated near the center line of the layer. The second part of the solution is concerned with the evolution of the wave packets on longer space-time scales which are associated with non-parallel effects arising from the spreading of the mixing layer. The solution in this part of the physical flow is handled by extending Whitham's kinematic wave theory, and the ray equations for instability waves are derived for physical and propagation spaces using a WKB J expansion. Our high-frequency ansatz also leads us to the derivation of a very simple complex amplitude equation. While the rays obtained represent characteristics in the complex plane along which the complex frequency of our disturbances is conserved (steady base flow), the amplitude equation expresses the conservation of the volume integrals of a complex wave action density subject to a certain flux and a source term. The amplitude equation was rendered easily tractable due to a transformation of our dependent variables and their practical projections on the cross and propagation spaces. Different methods, (steepest descent, ray-tracing, and fully numerical solution) are used to solve the ray equations, and comparisons are made among them. The results presented are obtained for the piecewise linear profile of Rayleigh and the general tanh profile. The very good agreement among all the methods of solution reveals the validity of the method of characteristics in the complex plane, (ie complex rays). Finally we perform some calculations for spatially varying shear layers and and study their implications in the development of spatial instability modes. We discover that when starting with a convectively unstable base velocity profile it is possilble to interrupt the development of spatial instability modes by allowing the base velocity profile to vary slowly and become absolutely unstable. However the reverse is not true. That is to say that in a base flow that is initially absolutely unstable, one does not observe spatial modes, even after the base flow is permitted to assume slowly a convectively unstable profile.

Parameter estimation in reconstructing temperature fields during hyperthermia.

Liauh, Chihng-Tsung. (The University of Arizona., 1991)

In this dissertation, a state and parameter estimation algorithm is implemented and modified to predict the blood perfusions and thus the complete steady-state temperature fields based on input from a limited number of temperature measurements taken during simulated hyperthermia treatments. Several fundamental phenomena related to this inverse problem are investigated from simple direct models. The general conditions under which these multiple minima occur are shown to be solely due to the existence of symmetries in the inverse problem formulation. Both an adjoint formulation and a sensitivity equation method are derived and used to determine the elements in the Jacobian matrix associated with the inverse problem of estimating the blood perfusion and temperature fields during hyperthermia cancer treatments. These methods and a previously developed influence coefficient method for obtaining that matrix are comparatively evaluated by solving a set of numerically simulated inverse hyperthermia problems. An improved state and parameter estimation algorithm has been developed to reduce the total computational time required. If the change of the unknown perfusion parameters is small a linear approximation scheme is implemented in which the old Jacobian matrix (or sensitivity matrix) is used, instead of recalculating the new Jacobian matrix for the next iteration. Results show that if the temperature is approximated as a linear (or quasi-linear) function of the blood perfusion, the linearizing approach considerably reduces the CPU time required to accurately reconstruct the temperature field. One of the model mismatch problems between the actual tumor and the simulated models is selected and investigated for the one-dimensional case. The model mismatch present in this dissertation is caused by the discretization of a perfusion field into several discrete zones. It is our attempt to understand the effects of the model mismatch problems from a simple model, and then generalize to more complicated three-dimensional cases which could occur during hyperthermia treatments. To simulate the ultrasound hyperthermia treatments, a scanned focussed ultrasound power field is generated and then used to create the transient power-on data and the steady-state temperature field. The feasibility of using the transient power-on data to estimate the attenuation coefficient and the blood perfusion and thus reconstruct the steady-state temperature field is presented.

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