Afzali, Amir (M.S. Mechanical Engineering)

Contamination Induced Failures in Microelectronic Packages

This thesis lays the foundation for a deterministic approach to corrosion failure modeling in microelectronic packages. The sources and mechanisms of contaminant ingress, and the mechanisms of corrosion are presented. A deterministic failure model is then proposed and discussed.

Hoffman, Harry Joseph (M.S. Mechanical Engineering)

Application of the Hopkinson Split Bar to Gun Propellant Testing

A Hopkinson Split Pressure Bar apparatus was used to test JA2, M30 and HELOVA gun propellants at strain rates of 600-2000/s. The split bar apparatus, a widely used device to measure the dynamic mechanical properties of materials, consists of two elastic bars with a specimen sandwiched between them and a means of generating an elastic stress pulse in the bars. The specimen is loaded beyond the esastic range. Instrumentation of the bars allows the recording of the strain historyin the bars during the test event. The strain history on the input bar gives a record of the strain rate history in the sample. The output bar strain history is proportional to the stress history in the sample.

Khan, Sohail Ahmad (M.S. Mechanical Engineering)

A Constitutive Stress-Strain Model for Linerboard Under Various Constant Moisture and Temperature States

Presented is the experimental study and constitutive model development for the sorption parameters and non-linear uniaxial tensile stress-strain behavior of Virginia Fiber 33 pound paper. Moisture dependent coefficients for the constitutive equation have been related to the relative humidity and temperature by means of adsorption isotherms at 10, 20, and 30oC temperatures. Uniaxial tensile stress-strain tests were conducted at five constant moisture contents associated with relative humidities of 30, 45, 60, 75, and 90% and three constant temperatures of 10, 20, and 30oC. The constitutive model consists of two parameters; the elastic modulus and a stress-strain parameter A. The modulus is modeled using Nissan's constitutive equation. The parameter A is modeled using a three parameter polynomial function of moisture content and a linear function of temperature.

Rao, Prathviraj (M.S. Mechanical Engineering)

Application of Infrared Thermography for Quantitative Detection of Surface Flaws

Transient infrared thermography methods have been developed which when coupled to a simulation model of heat transfer, can be used for the quantitative detection of surface cavities. The experimental approach consists of infrared scanning of the top surface of a plane slab with a surface flaw, which has been heated on the bottom surface. The time taken for the specimen to reach "critical" temperature states are recorded and used as a parameter in the solution of the inverse problem of a one-dimensional heat conduction model, in order to predict the flaw depth. For the specimen tested, this methodology is capable of predicting the depth of surface cavities within a range of 6% overprediction for the cases examined here.

Syed, Ahmer (M.S. Mechanical Engineering)

Vibration Analysis of Printed Wiring Boards

Traditionally, a printed wiring board is analyzed for its natural frequency by assuming edge guides and connectors as providing classical type of supports (free, simple, or clamped) and components as acting distributed mass over its entire surface. In reality, edge guides and connectors are of spring construction and provide elastic support to the edge of the PWB. In addition, the components not only add mass to the PWB, but also increase its stiffness depending upon their location and orientation on the board. These factors strongly affect the natural frequency of the wiring board and their ignorance leads to a false assessment of vibratory behavior of the wiring board and, thus, an unreliable design.

This thesis focuses on how real boundary conditions and components mounted on the PWB affect the natural frequencies of printed wiring boards. Experimental analysis were performed and the results were compared with analytical and finite element analyses. A fully automated finite element analysis program was developed for the natural frequency analysis of printed wiring boards in an overall Computer Aided Life Cycle Engineering (CALCE) environment. This research is important because the natural frequency information of a PWB is useful in prediction the dynamic behavior under vibration and shock loadings, as well as in estimating the fatigue lives of components' leads and solder joints.