In the present study, two surface engineering technologies have been used for distinctively different purposes. Whilst nickel/aluminium has been deposited using unbalanced magnetron sputtering for thermal barrier applications, a separate investigation was carried out involving the deposition and characterisation of diamond like carbon (DLC) coating using plasma enhanced chemical vapour deposition (PECVD). Unbalanced magnetron sputter ion plating at various flow rates, magnetron power and substrates has been used to deposit novel intermetalic NiAI and nitrogen doped NiAI thin films. These have been characterised using surface stylus profilometry, energy dispersive spectroscopy (EDAX), X-Ray diffraction (XRD) and atomic force microscopy (AFM). Scratch tester (CSM) combined with acoustic emission during loading have been utilised in order to compare the coating adhesion. Acoustic emission was used during the indentation process to determine the critical load under which the film begins to crack and/ or break off the substrate. The average thickness of the films was found to be approximately 1 pm. EDAX data revealed that all of the NiAl and nitrogen doped NiAI thin films exhibited near equiatomic NiAI composition with the best results being achieved using 300 Watt DC power for Ni, and 400 Watt DC power for Al targets respectively. X-Ray diffraction spectra revealed the presence of the 3 NiAI phase. AFM results films on glass samples exhibited a surface roughness of :5 100 nm. The nanoindentor results for coatings on glass substrates displayed hardness and elastic modulus of 7.7 GPa and 100 CPa respectively. The hardest coatings were obtained with 10% of nitrogen. Scratch test results indicated that the best adhesion was achieved at 300 W for Ni, and 400 W for Al targets compared to that of samples with other power values. DLC and Ti doped DLC films using Titanium Isopropoxide (TIPOT) were deposited at various flow rates, bias voltages and substrates using PECVD. The as-grown film thicknesses were in the thickness range of 90-1 00 nm and were dependent on the TIPOT flow rate. As the flow rate of TIPOT was increased the average roughness was found to decrease in conjunction with the film thickness. The 10/10 ratio obtained from Raman spectra decreased when the bias voltage on the stainless steel substrates was increased. This indicates an increase in the graphitic nature of the film deposited. In addition, SIMS analysis showed that the Ti peak became much more pronounced at TIPOT flow rates above 25 sccm. On the glass substrates the ID/to ratio increased when the bias voltage was increased indicating a greater degree of diamond like character. For a different set of experimental conditions, the as-grown films were of the order 200-400nm. When the bias voltage was altered from 100 to 400V the thickness decreased and Raman 'D'1G ratio increased with increasing bias voltage on the glass substrates. However, in contrast, on the stainless steel substrates the 1D110 ratio decreased with bias voltage. For both of the coatings, the contact angle of the films decreased with increasing bias voltages.

The present study investigates the reliability approach to the design of a critical mechanical component and applies this approach to several design problems. For the design of a critical component the combination of maximum loads and minimum material strength is selected for the design. Under the probabilistic approach, maximum load and minimum material strength values are considered as random variables having Extreme Value density functions of Type I (maximum) and Type III (minimum), respectively. With this combination of probability density functions for the material strength and the load, a closed form solution does not seem to be feasible for either the probability density function of the safety factor or for the probability of failure of the design. Consequently, numerical evaluations are made for the probability density function of the safety factor Ʋ the probability of failure Pf and the mean value of the safety factor, ῡ , for a set of parameter values of the density functions for the maximum load and the minimum strength. The effect of changing these parameter values on the probability of failure is studied. An important feature of the design of a critical component from the reliability approach, in general, is that the reliability statement implies a specific "mission" time of operation for the component. This is due to the dependence of the value of certain parameters of E.V. models on the length of time over which the extreme value measurements are taken. Three design models are considered under the reliability approach for a given load and material strength, and reliability specification. The parameters defining the extreme value density functions of load and material strength are assumed to be given. In model 1, the problem of designing a single critical mechanical component subjected to purely axial loads is considered for a given single material. The failure criterion in such a case is assumed to be separation and the output of the design process is a cross section area A of the component with a specified reliability over a corresponding period of operating time. This cross section area is considered as a statistical constant in order to avoid additional mathematical complexity. In model 2, the design problem of the first model is extended by considering more than one material available for the design. The design problem thus considered is one of selecting one among various alternative materials on the basis of some design criterion such as minimum weight, etc. The method consists of calculating the design cross section area for each material available and then calculating the value of the design criterion for each design. The material which optimizes the value of the design criterion becomes the choice for that design. It is observed that for a given load distribution and various available materials, the design cross section area is a function of the ratio of the mean strength to its standard deviation and not a function of the mean value of strength alone. It is, therefore, considered logical to take this ratio of the mean strength to the standard deviation as the measure of the quality of the material and express the cost of material (dollars per lb.) as a function of this ratio. This is in contrast with the conventional design approach where the cost of material is considered as a function of a single value of strength of material only. Model 3 considers the design problem of making a choice from among several materials on the basis of the economic criterion of minimum cost. The cost of material is considered as a function of the ratio of mean strength to standard deviation, as mentioned earlier. In the absence of data required to assess this functional relationship, a linear relationship is assumed. Another cost factor, the cost of safety factor values, is introduced. This cost is a measure of the margin of safety provided in the design for each component. As the safety factor is a random variable in the probabilistic approach, tools such as statistical decision theory and utility theory are used to obtain the cost of design for each material. These cost values are then weighted with respect to the probability density function of the safety factor. The expected overall cost of the design is then evaluated for each material and the given load distribution, such that the desired reliability value is attained. The material corresponding to the minimum value of the expected overall cost is selected as the optimal choice of the designer. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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<p dir="ltr">This study explores how undergraduate engineering students interacted with users, user proxies, and user information during engineering design curricular experiences at a Large Midwestern University. Such practices are essential to human-centered design, a prominent framework within engineering design curriculums. While human-centered design can help students develop more sustainable, responsive, and desirable products for those who use them, engineering design educators need a better understanding of how and why engineering students engage in human-centered design. Such an understanding can enable us to learn how best to support students’ human-centered design learning.</p><p dir="ltr">The first phase of this study examined how undergraduate engineering students experienced human-centered design according to Zoltowski et al.’s (2012) <i>Ways of Experiencing Human-Centered Design</i> framework. I developed a survey instrument with open-ended reflections and used an a priori coding approach to identify how a large sample of undergraduate engineering students (n = 135) experienced <i>human-</i>centered design (as opposed to technology-centered or service-oriented design). Over half of the students demonstrated ways of experiencing design that incorporated human-centric design practices (51%), but a critical mass (31%) emphasized technology-centered or service-oriented views in their survey reflections. This finding suggests that human-centered design is more common compared to these other forms of design among students who were enrolled in the engineering design curriculums from which I sampled. This finding is promising in light of other studies showing students’ difficulty with making human-centric engineering considerations.</p><p dir="ltr">Next, I interviewed a subset of survey respondents (n = 21) whose reflections evidenced human-centered design experiences. Through interviews, I sought to develop a better understanding of the nature of their user interactions, including what aspects of the curriculum encouraged them to interact with users. I used critical incident technique to identify critical incidents that contributed to students’ deeper understanding of user experiences as they relate to their design project. I identified 81 critical incidents that I grouped into 12 unique user interaction types, which I then grouped into five design activities (Information Gathering, Idea Generation, Feedback, Iteration, and Evaluation). Each of these user interaction types afforded students the opportunity to integrate user information into their design process or prompt a change in their valuation or appreciation of user information during their design process, which ultimately contributes to a more comprehensive design experience. Instructors can use these user interaction types to guide their development of human-centered design experiences that promote students’ deeper understanding of and application of human-centered design.</p><p dir="ltr">Finally, I created a narrative depiction of two students’ design journeys by weaving the critical incidents I extracted from their interviews into a story. These two students were selected as they demonstrated variation in user interaction types, with one student’s story focused on immersion in a community context and the other focused on how multiple different user interaction types bolstered their confidence in their design decisions throughout their design journey. Thus, the stories depict how these two students’ design journeys supported their achievement of learning outcomes pertinent to human-centered design learning. Moreover, these stories provide guidance for instructors seeking to promote their students’ personal motivations and design confidence related to design projects in engineering design curriculums that value human-centered considerations.</p><p dir="ltr">Taken together, by understanding what leads students to engage with users throughout the design process and the nature of these engagements, the findings from this study position engineering educators to develop curricula and pedagogy that theoretically promote engineering students’ holistic applications of human-centered design.</p>

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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