MULTIMODAL PERFORMANCE AND RELIABILITY ANALYSIS OF THE PIERRE AUGER OBSERVATORY NORTH SITE

The Pierre Auger Cosmic Ray Observatory North site employs a large array of surface detector stations (tanks) to detect the secondary particle showers generated by ultra-high energy cosmic rays. Due to the rare nature of ultra-high energy cosmic rays, it is important to have a high reliability on tank communications, ensuring no valuable data is lost. The Auger North site employs a peer-to-peer paradigm, the Wireless Architecture for Hard Real-Time Embedded Networks (WAHREN), designed specifically for highly reliable message delivery over fixed networks, under hard real-time deadlines. The WAHREN design included two retransmission protocols, Micro- and Macro- retransmission. To fully understand how each retransmission protocol increased the reliability of communications, this analysis evaluated the system without using either retransmission protocol (Case-0), both Micro- and Macro-retransmission individually (Micro and Macro), and Micro- and Macro-retransmission combined. This thesis used a multimodal modeling methodology to prove that a performance and reliability analysis of WAHREN was possible, and provided the results of the analysis. A multimodal approach was necessary because these processes were driven by different mathematical models. The results from this analysis can be used as a framework for making design decisions for the Auger North communication system.

IMPROVED SENSITIVITY OF RESONANT MASS SENSOR BASED ON MICRO TILTING PLATE AND MICRO CANTILEVER

Vapor sensors have been used for many years. Their applications range from detection of toxic gases and dangerous chemicals in industrial environments, the monitoring of landmines and other explosives, to the monitoring of atmospheric conditions. Microelectrical mechanical systems (MEMS) fabrication technologies provide a way to fabricate sensitive devices. One type of MEMS vapor sensors is based on mass changing detection and the sensors have a functional chemical coating for absorbing the chemical vapor of interest. The principle of the resonant mass sensor is that the resonant frequency will experience a large change due to a small mass of gas vapor change. This thesis is trying to build analytical micro-cantilever and micro-tilting plate models, which can make optimization more efficient. Several objectives need to be accomplished: (1) Build an analytical model of MEMS resonant mass sensor based on micro-tilting plate with the effects of air damping. (2) Perform design optimization of micro-tilting plate with a hole in the center. (3) Build an analytical model of MEMS resonant mass sensor based on micro-cantilever with the effects of air damping. (4) Perform design optimization of micro-cantilever by COMSOL. Analytical models of micro-tilting plate with a hole in the center are compared with a COMSOL simulation model and show good agreement. The analytical models have been used to do design optimization that maximizes sensitivity. The micro-cantilever analytical model does not show good agreement with a COMSOL simulation model. To further investigate, the air damping pressures at several points on the micro-cantilever have been compared between analytical model and COMSOL model. The analytical model is inadequate for two reasons. First, the model’s boundary condition assumption is not realistic. Second, the deflection shape of the cantilever changes with the hole size, and the model does not account for this. Design optimization of micro-cantilever is done by COMSOL.

Nanomechanics of cellulose crystals and cellulose-based polymer composites

Cellulose-polymer composites have potential applications in aerospace and transportation areas where lightweight materials with high mechanical properties are needed. In addition, these economical and biodegradable composites have been shown to be useful as polymer electrolytes, packaging structures, optoelectronic devices, and medical implants such as wound dressing and bone scaffolds. In spite of the above mentioned advantages and potential applications, due to the difficulties associated with synthesis and processing techniques, application of cellulose crystals (micro and nano sized) for preparation of new composite systems is limited. Cellulose is hydrophilic and polar as opposed to most of common thermoplastics, which are non-polar. This results in complications in addition of cellulose crystals to polymer matrices, and as a result in achieving sufficient dispersion levels, which directly affects the mechanical properties of the composites. As in other composite materials, the properties of cellulose-polymer composites depend on the volume fraction and the properties of individual phases (the reinforcement and the polymer matrix), the dispersion quality of the reinforcement through the matrix and the interaction between CNCs themselves and CNC and the matrix (interphase). In order to develop economical cellulose-polymer composites with superior qualities, the properties of individual cellulose crystals, as well as the effect of dispersion of reinforcements and the interphase on the properties of the final composites should be understood. In this research, the mechanical properties of CNC polymer composites were characterized at the macro and nano scales. A direct correlation was made between: Dispersion quality and macro-mechanical properties Nanomechanical properties at the surface and tensile properties CNC diameter and interphase thickness Lastly, individual CNCs from different sources were characterized and for the first time size-scale effect on their nanomechanical properties were reported. Then the effect of CNC surface modification on the mechanical properties was studied and correlated to the crystalline structure of these materials.

Analysis of a Non-Traditional Micro Tube Hydroforming Process

As the demand for miniature products and components continues to increase, the need for manufacturing processes to provide these products and components has also increased. To meet this need, successful macroscale processes are being scaled down and applied at the microscale. Unfortunately, many challenges have been experienced when directly scaling down macro processes. Initially, frictional effects were believed to be the largest challenge encountered. However, in recent studies it has been found that the greatest challenge encountered has been with size effects. Size effect is a broad term that largely refers to the thickness of the material being formed and how this thickness directly affects the product dimensions and manufacturability. At the microscale, the thickness becomes critical due to the reduced number of grains. When surface contact between the forming tools and the material blanks occur at the macroscale, there is enough material (hundreds of layers of material grains) across the blank thickness to compensate for material flow and the effect of grain orientation. At the microscale, there may be under 10 grains across the blank thickness. With a decreased amount of grains across the thickness, the influence of the grain size, shape and orientation is significant. Any material defects (either natural occurring or ones that occur as a result of the material preparation) have a significant role in altering the forming potential. To date, various micro metal forming and micro materials testing equipment setups have been constructed at the Michigan Tech lab. Initially, the research focus was to create a micro deep drawing setup to potentially build micro sensor encapsulation housings. The research focus shifted to micro metal materials testing equipment setups. These include the construction and testing of the following setups: a micro mechanical bulge test, a micro sheet tension test (testing micro tensile bars), a micro strain analysis (with the use of optical lithography and chemical etching) and a micro sheet hydroforming bulge test. Recently, the focus has shifted to study a micro tube hydroforming process. The intent is to target fuel cells, medical, and sensor encapsulation applications. While the tube hydroforming process is widely understood at the macroscale, the microscale process also offers some significant challenges in terms of size effects. Current work is being conducted in applying direct current to enhance micro tube hydroforming formability. Initially, adding direct current to various metal forming operations has shown some phenomenal results. The focus of current research is to determine the validity of this process.

PERFORMANCE EVALUATION OF LLDPE/CaCO3 MODIFIERS WITH AND WITHOUT TITANATE COUPLING AGENT ON ASPHALT BINDER AND MIXTURE

The complexity and challenge created by asphalt material motivates researchers and engineers to investigate the behavior of this material to develop a better understanding, and improve the performance of asphalt pavement. Over decades, a wide range of modification at macro, meso, micro and nano scales have been conducted to improve the performance of asphalt pavement. This study was initiated to utilize the newly developed asphalt modifier pellets. These pellets consisted of different combinations of calcium carbonate (CaCO3), linear low-density polyethylene (LLDPE) and titanate coupling agent (CA) to improve the asphalt binder as well as pavement performance across a wide range of temperature and loading pace. These materials were used due to their unique characteristics and promising findings from various industries, especially as modifiers in pavement material. The challenge is to make sure the CaCO3 disperses very well in the mixture. The rheological properties of neat asphalt binder PG58-28 and modified asphalt binder (PG58-28/LLDPE, PG58-28/CaCO3, PG58-28/CaCO3/LLDPE, and PG58-28/CaCO3/LLDPE/CA), were determined using rotational viscometer (RV) test, dynamic shear rheometer (DSR) test and bending beam rheometer test. In the DSR test, the specimens were evaluated using frequency sweep and multiple shear creep recovery (MSCR). The asphalt mixtures (aggregate/PG58-28, aggregate/ PG58-28/LLDPE, aggregate/PG58-28/CaCO3, aggregate/PG58-28/LLDPE/CaCO3 and aggregate/PG58-28/LLDPE/CaCO3/CA) were evaluated using the four point beam fatigue test, the dynamic modulus (E*) test, and tensile strength test (to determines tensile strength ratio, TSR). The RV test results show that all modified asphalt binders have a higher viscosity compared to the neat asphalt binder (PG58-28). Based on the Jnr results (using MSCR test), all the modified asphalt binders have a better resistance to rutting compared to the neat asphalt binder. A higher modifier contents have resulted in a better recovery percentage of asphalt binder (higher resistance to rutting), except the specimens prepared using PECC’s modified asphalt binder (PG58-28/CaCO3/LLDPE). The BBR test results show that all the modified asphalt binders have shown comparable performance in term of resistance to low temperature cracking, except the specimen prepared using the LLDPE modifier. Overall, 5 wt% LLDPE modified asphalt binder was found to be the best asphalt binder in terms of resistance to rutting. Meanwhile, 3 wt% PECC-1CA’s modified asphalt binder can be considered as the best (in terms of resistance to thermal cracking) with the lowest mean critical cracking temperature. The appearance of CaCO3 was found useful merely in improving the resistance to fatigue cracking of asphalt mixture. However, application of LLDPE has undermined the fatigue life of asphalt mixtures. Adding LLDPE and coupling agent throughout this study does not sufficiently help in terms of elastic behavior which essential to enhance the resistance to fatigue cracking. In contrast, application of LLDPE has increased the indirect tensile strength values and TSR of asphalt mixtures, indicates a better resistance to moisture damage. The usage of the coupling agent does not change the behavior of the asphalt mixture, which could be due to imbalance effects resulted by combination of LLDPE and CaCO3 in asphalt binder. Further investigations without incorporating CaCO3 should be conducted further. To investigate the feasibility of using LLDPE and coupling agent as modifiers in asphalt pavements, more research should be conducted on different percentages of LLDPE (less than 3 wt%), and at the higher and w wider range of coupling agent content, from 3 wt% to 7 wt% based on the polymer mass.