Caroline Howell

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.

Internship with Georgia Institute of Technology, Atlanta, GA; Research Advisors: Dr. Josh Kacher and Jordan Key; SUIN REU sponsored by NSF grant EEC-1757579 and NNCI; Abstract: 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.

Polyethylene (PE) and Polypropylene (PP) are two of the most widely used plastics today, accounting for over 40% of global plastic consumption. During the recycling process, PE and PP often fail to be adequately separated due to their similar structures and densities. Recycling these plastics together leads to significant degradation and phase separation because the polymers themselves are inherently immiscible. In addition, recycled polymers have typically undergone considerable thermo-mechanical degradation during their lifetime by the combined effect of humidity, UV light, chemical oxidation, and other environmental factors. Therefore, when it comes to recycling PE/PP blends, there is a major challenge of the quality deficiency leading to a significant amount of plastic ending up in landfills and the environment. RockyTech has developed a reactive compatibilizer known as REVLINK to tackle the challenges of recycling PE/PP blends. The key strategy involves incorporating reversible covalent bonds into polyolefin linear chains to enable their crosslinking at the particle interface to achieve polymer fusion. This innovative process enables upcycling of mixed polyolefins with enhanced properties, allowing for multiple recycling cycles without property degradation. With the addition of only 1 wt.% REVLINK into a PE/PP blend, it can significantly improve the performance, including 18% increase in flexural modulus, 200% increase in elongation at break, and possible reduction in melt flow index (MFI). Not only can REVLINK improve the recycling quality of mixed plastics, but it can also tune the properties of PE itself. Compared to pure PE, a blend of PE with 10% PP and REVLINK exhibits improved performance, including a 10% increase in flexural modulus, a 40% increase in elongation at break, and a 23% increase in tensile strength. REVLINK is a novel innovation with the goal of creating a more circular economy by turning plastic waste into a sustainable product.