Caroline Howell

Aluminum is a desired commodity for building vehicles, electronics, or other miscellaneous things. However, pure aluminum is soft and not as durable as needed for certain objects such as ships. Therefore, Aluminum-Magnesium alloys were introduced as a solution. These alloys help keep the lightweight features of aluminum while increasing strength, formability, and weldability. Yet, the magnesium segregation can lead to localized corrosion and stress corrosion cracking. This research is primarily focused on applications of Al-Mg alloys in saltwater environments, such as Navy ships, which are built using Al 5xxx alloys. This project investigated 20 samples of Aluminum 5456 that were broken into four subgroups which underwent different conditions to simulate the everyday stress and strain of a ship. The different conditions tested include sensitization, salt corrosion, and sensitization-salt corrosion. After enduring these conditions, the samples underwent a slow strain tensile test to further simulate the rough life of a ship. These tensile tests used a slow strain rate to ensure the observance of hydrogen embrittlement and stress corrosion cracking during the failure of the alloy. After failure, the samples’ fracture surface was observed under the scanning electron microscope (SEM) to examine the strain effects on the metal. Aluminum alloys seem to experience brittle failure more often than ductile failure after exposure to nautical conditions, which is more catastrophic. Understanding the different fractures and cracks of the grain boundaries can help lead to the design of better materials that are more resistant to brittle failure and reduce the precipitation of magnesium.

The intensity of a sound wave emitted from a point source in an isotropic and reflectionless region of space will decrease by the square of the distance from the source. However, if boundaries are introduced, then the reflected waves can interfere with each other and with the incident wave. Therefore, sound waves emitted from a source in an enclosed room will have an intensity which follows the inverse square law for short propagation distances, but deviates as incident and reflected waves of comparable amplitudes interfere with each other. This project makes use of the MATLAB clone GNU OCTAVE to calculate the intensity of a sound wave as a function of distance from a source which is placed in an enclosed room. This calculation considers multiple possible paths along which a wavelet can propagate along to reach the detector: a direct path, 6 paths containing one reflection each, and 30 paths containing two reflections each. It then determines the relative amplitude and phase for each of these paths in order to create a superposition of these 37 wavelets at the position of the detector. Squaring this superposition wave’s amplitude yields the sound intensity at the location of the detector.

The intensity of scattered light from water droplets in steam changes when viewed from different angles. In this project, a laser is incident upon steam produced by boiling water, and it is scattered at different angles. The scattered light is then captured by a camera and analyzed in a computer program, OCTAVE. The intensity of the scattered light is dependent on the scattering angle, with the intensity decreasing as the angle approaches 90 degrees from above or below. This effect can be explained by Mie Scattering. Mie Scattering is the scattering of electromagnetic waves by uniform isotropic particles. The water droplets in the steam absorbs and scatters the laser and transforms its energy into different forms accounting for the low intensity at 90 degrees. This project maps the intensity of the light in OCTAVE by analyzing the pictures from different radial and polar angles.