M. Tech. (Mechanical Engineering) Vaal University of Technology / Monitoring the condition of equipment in industry is very important to prevent unplanned breakdowns and to prolong their life. This is necessary, since it is not always economically viable to stop equipment at regular intervals to do maintenance. Failure on machines can lead to high repair costs and production losses. It is thus of paramount importance that early failure symptoms be identified by means of condition monitoring. This study in the field of condition monitoring is performed to determine if the mechanical shock values induced in defect bearings could be used to measure the condition of a bearing while operating under variable speed and variable load. Variable speed and variable load is becoming more popular in industry because variable speed drives applications ensure effective process control. Variable speed application, cause fault frequencies to fluctuate and therefore vibration applications for constant speed applications, which are speed-dependent, can no longer apply. Vibration-monitoring techniques that have applied for many years have now become obsolete in these variable speed applications. Methods such as Short Time Fourier Transformation (STFT), time scale like wavelet transform, and Order tracking has been applied in variable speed applications with some success. These methods analyses the vibration phases on the signal buy compensating for the speed changes. In this thesis, the Shock pulse method is selected as the analyses tool to measure the mechanical shock. Shock pulse monitoring does not focus on the vibration phases but measures in a small-time window when mechanical shocks are induced in the bearing material before the vibration phase. There is very little documented research in the field of mechanical shock pulse monitoring for conditions of variable speed and variable loads, and therefore this research focuses on recording these mechanical shock values by empirical tests. The tests were performed on a bearing with an induced defect on the outer race. The rolling element of the bearing strikes the defect and the mechanical shock value (dBsv) is measured. The mechanical shock is measured with the Shock pulse method in a small-time window before vibration occurs. In this time window, the dBsv is recorded over time to provide diagnostic information of the bearing during acceleration, deceleration and various loading conditions. These mechanical shocks are elastic waves that mirror the impact-contact-force's time function and the Shock pulse monitoring accelerometer, which is tuned to 32 kHz, will respond to the elastic wave fronts with transient amplitudes proportional to the square of the impact velocities. The mechanical shock values were analysed and reoccurring fault levels were identified on each empirical test. These recurring events from the empirical tests were used as primary data for analysis in this research. These tests were performed on a bearing with an induced failure and it was found that the dBsv measured over time could not be used to monitor the condition of the bearing under variable speed applications. This was because the dBsv changed as the speed increased. To overcome this problem Sohoel’s theory was applied and the initial mechanical shock value (dBi) was calculated for the bearing. The dbi value was subtracted from the dBsv and a value called the maximum mechanical shock value (dBm) was obtained. The dBm values stayed constant for the duration of the test and this allowed the condition of the bearing to be measured under variable speed and variable load conditions with some exception. The exception to the findings was that the dBm values stayed constant during acceleration phases, but during the deceleration phases the values were erratic and scattered. At speed below 200rpm the dBm values did not stay constant and therefore it was concluded that the dBm value recorded the best results only when thrust on the bearing was maximum. The other exception was under no-load conditions. The values were erratic and scattered, and therefore the results were not a true reflection of the bearing condition. The third exception was that the results on bearings with various loads remained constant during increased load changes unless the loading was erratic. During erratic load changes, the results were affected. The results also indicated that the larger the defect on the bearing raceway, the higher the dBm values were. Multipil defects on the bearing race ways were not part of this thesis and this gives an opertunity for futher research. The Shock pulse monitoring technique was 100% successful in monitoring the bearing condition only while the speed of the bearing was increasing. The results obtained in this work demonstrated that the condition of bearings can be monitored in applications of variable speed and variable load if the exception are eliminated and to obtain conclusive results the mechanical shock pulses should be measured over time and not be used as once-off value.

abstract: With increasing concerns of the intrinsic toxicity of lead (Pb) in electronics, a series of tin (Sn) based alloys involving silver (Ag) and copper (Cu) have been proposed as replacements for Pb-Sn solder and widely accepted by industry. However, they have a higher melting point and often exhibit poorer damage tolerance than Pb-Sn alloys. Recently, a new class of alloys with trace amount of rare-earth (RE) elements has been discovered and investigated. In previous work from Prof. Chawla's group, it has been shown that cerium (Ce)-based Pb-free solder are less prone to oxidation and Sn whiskering, and exhibit desirable attributes of microstructural refinement and enhanced ductility relative to lanthanum (La)-based Sn-3.9Ag-0.7Cu (SAC) alloy. Although the formation of RESn3 was believed to be directly responsible for the enhanced ductility in RE-containing SAC solder by allowing microscopic voids to nucleate throughout the solder volume, this cavitation-based mechanism needs to be validated experimentally and numerically. Additionally, since the previous study has exhibited the realistic feasibility of Ce-based SAC lead-free solder alloy as a replacement to conventional SAC alloys, in this study, the proposed objective focuses on the in in-depth understanding of mechanism of enhanced ductility in Ce-based SAC alloy and possible issues associated with integration of this new class of solder into electronic industry, including: (a) study of long-term thermal and mechanical stability on industrial metallization, (b) examine the role of solder volume and wetting behavior of the new solder, relative to Sn-3.9Ag-0.7Cu alloys, (c) conduct experiments of new solder alloys in the form of mechanical shock and electromigration. The research of this new class alloys will be conducted in industrially relevant conditions, and the results would serve as the first step toward integration of these new, next generation solders into the industry. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

CubeSats, specially the 6U standard, is nowadays the tendency where many developers point towards. The upscaling size of the standard and payloads entail the increase of the satellite overall mass. Composite materials have demonstrated the ability to fulfill expectations like reducing structural masses, having been applied to different types of spacecraft, including small satellites. This Thesis is focused on designing, manufacturing, and dynamic testing of a 6U CubeSat made of carbon fiber, fiberglass, and aluminum. The main objective of this study was obtaining a mass reduction of a 6U CubeSat structure, maintaining the stiffness and strength. Considering the thermal effects of the used materials an outgassing test of the used materials was performed and the experimental results are presented. The CubeSat structure was entirely manufactured and tested at Cal Poly Aerospace Engineering Department facilities. A mechanical shock test and random vibration test were performed using a shock table and a shake table respectively. Results of both tests are presented. A correlation between the Experimental data and the Finite Element Model of the satellite was carried out. Finally, a comparison between 6U structure studied and aluminum 6U structures available in the market is presented.

abstract: With the increasing focus on developing environmentally benign electronic packages, lead-free solder alloys have received a great deal of attention. Mishandling of packages, during manufacture, assembly, or by the user may cause failure of solder joint. A fundamental understanding of the behavior of lead-free solders under mechanical shock conditions is lacking. Reliable experimental and numerical analysis of lead-free solder joints in the intermediate strain rate regime need to be investigated. This dissertation mainly focuses on exploring the mechanical shock behavior of lead-free tin-rich solder alloys via multiscale modeling and numerical simulations. First, the macroscopic stress/strain behaviors of three bulk lead-free tin-rich solders were tested over a range of strain rates from 0.001/s to 30/s. Finite element analysis was conducted to determine appropriate specimen geometry that could reach a homogeneous stress/strain field and a relatively high strain rate. A novel self-consistent true stress correction method is developed to compensate the inaccuracy caused by the triaxial stress state at the post-necking stage. Then the material property of micron-scale intermetallic was examined by micro-compression test. The accuracy of this measure is systematically validated by finite element analysis, and empirical adjustments are provided. Moreover, the interfacial property of the solder/intermetallic interface is investigated, and a continuum traction-separation law of this interface is developed from an atomistic-based cohesive element method. The macroscopic stress/strain relation and microstructural properties are combined together to form a multiscale material behavior via a stochastic approach for both solder and intermetallic. As a result, solder is modeled by porous plasticity with random voids, and intermetallic is characterized as brittle material with random vulnerable region. Thereafter, the porous plasticity fracture of the solders and the brittle fracture of the intermetallics are coupled together in one finite element model. Finally, this study yields a multiscale model to understand and predict the mechanical shock behavior of lead-free tin-rich solder joints. Different fracture patterns are observed for various strain rates and/or intermetallic thicknesses. The predictions have a good agreement with the theory and experiments. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2011

In this thesis, different optomechanical design and adhesive configurations for mounting mirrors and prisms used in a laser system are investigated. Maintaining stability and strength of optical components of a laser device is difficult especially if the system is to be used in military environment. In order to determine the strength of prism mounts to high acceleration levels, mathematical correlations derived by Yoder are used. By use of these mathematical correlations, safety factor of different prism mounts and adhesive configurations are calculated for an acceleration level of 40g. So as to decide most stable mirror mount and adhesive configuration, several experiments are conducted. For the experiments, 5 different optomechanical mounts are designed. Then, 25 mirrors are bonded to the designed mounts with 5 different adhesives. These experiments are done to simulate harsh military environmental conditions such as thermal shock, mechanical vibration and mechanical shock. In the experiments, angular movement of mirrors due to adhesive cure, thermal shock, mechanical vibration and mechanical shock are monitored. Thermal shock is applied between -40&ordm / C and 70&ordm / C with a temperature change of 22&ordm / C/min. On the v other hand, mechanical vibration of 14 grms and mechanical shock of 40g for 6 ms is applied in the experiments. Shortly, this study is done for determination of the most stable mirror and prism mount design and adhesive combination of a laser system subjected to extremely harsh environments.