Mechanical Engineering
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Browsing Mechanical Engineering by Author "Barber, Gary"
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Item DEVELOPMENT OF DIGITAL SHEAROGRAPHY FOR COMPLEX DEFECTS INSPECTION(2021-11-09) Zhang, Boyang; Yang, Lianxiang; Barber, Gary; Qu, Hongwei; Narainen, RoderigueDigital shearography measures the first derivative of the object surface deformation, which has the advantages of high sensitivity, full field, non-contact, realtime and anti-disturbance. It is widely used in materials inspection in industry. The information acquisition methods of the first derivative distribution are mainly divided into the intensity method and the phase shift method. The intensity method is to directly obtain the first derivative phase distribution by subtracting the light intensity map. The phase shift method to obtain phase information can be divided into temporal phase shift and spatial phase shift. Most digital shearography systems are single camera based and can only capture one image every shoot. However, unpredictable defects like the narrow crack and minor flaws could induce incomplete detection due to some limitations. There are two major issues on the measurement, one is the defect with the irregular shape which is not sensitive to the digital shearography, another is the deformation made of defects that is much smaller than the resolution of cameras. Digital Shearography measures the first derivative of deformation on the object surface because the shearing direction determines the derivative direction being measured, tests using multiple shearing directions are sometimes required to detect all kinds of defects. When the deformation is long and narrow as a crack while the shearing direction is perpendicular to the crack growing direction, digital shearography has the best sensitivity. In opposite, if the crack growing direction is parallel to the shearing direction, digital shearography is not able to find it out. Irregular shape defects detection is a tough challenge for digital shearography. Another challenge is the defects that are too small for the field of view. The limited pixels can miss the defects due to the low signal to noise ratio. To increase the sensitivity of detecting minor defects, a small field of view measurement is needed but it is time consuming in a large surface area inspection. The new development can be divided into three categories: 1) Modified Michelson interferometer based dual shearing digital shearography. 2) Spatial light modulator based dual shearing direction shearography. 3) Polarized digital shearography for simultaneous dual sensitive measurement. The basic theory, optical path analysis, preliminary studies, results analysis and research plan are shown in detail in this dissertation.Item Molecular Dynamics Simulation Of The Effect Of Particle Hardness On Tribological Properties Of Nanofluids(2022-07-20) Xu, Cang; Barber, Gary; Schall, James; Yang, Ankun; Qau, Hongwei; Zhao, PengThe determination of physical properties of nanofluids is mature, but the knowledge of tribological properties of nanofluids is limited. In this paper, the effects of surface roughness, fluid thickness, nanoparticle hardness, and number of nanoparticles on friction are explored systematical using a 2D Lennard-Jones molecular dynamics model. LJ parameters were chosen such that the ratio of stiffness of the nanoparticles to the opposing surfaces was approximately equal to ratio of stiffness of either aluminum oxide or zinc oxide to steel. A total of two hundred and twenty configurations were investigated. The results show that the benefits or drawbacks of nanofluid lubricants are sensitive to the friction regime (boundary, mixed, or hydrodynamic). When nanoparticles are present in lubricant-starved boundary conditions (fluid thickness less than the surface roughness amplitude), nanoparticles offer support that keeps the opposing surfaces separated. This separation results in reduced contact between the opposing surfaces and provides surface smoothing, which in turn lowers friction relative to the base fluid. At intermediate levels of fluid thickness where the fluid thickness and roughness are approximately equal, the presence of nanoparticles has a detrimental effect on friction. Nanoparticles jam and lock surfaces together and increase friction relative to the base fluid. As fluid thickness increases, the friction of the nanofluid generally remains higher than the base fluid likely due to the increased viscosity of fluid due to the presence of the nanoparticles. This work suggests nanofluids may offer limited benefits under specific lubrication conditions, but are detrimental under most conditions.Item Self-Crack Healing of Engineering Ceramics(2022-03-21) Hammood, Israa Arif; Barber, Gary; Adams, Robert; Schall, J Dave; Debnath, Debatosh; Yang, Ankun; Zaidan, ShihabThe purpose in its simplicity is to heal the damage in a sample composed of ceramic particles through the heat treatment or through applying another source to heal the damage might be through using a laser source at room temperature to reduce the cost of wasting efforts and materials. The system can be designed to include a sensor to sense the damage in the component and a healing agent like loose particles or a specific source that provides an immediate treatment through the heating in order to create or generate the glassy phase. Self-crack-healing materials are able to sense the crack and heal it. The notion of not giving up on things can be considered as the motive for such type of research. Most ceramics are brittle and hence they are sensitive to flaws and cracks. Ceramics are subjected to thermal and mechanical stresses during service. Residual stresses may eventually cause microcracks (internal and surface cracks) and the failure of the component in use. This limits their use as structural engineering materials, and thus applying or inducing a self-crack healing ability would be a solution to overcome this problem. Great benefits can be expected from the components in use while applying the self-healing ability, such as reducing maintenance, inspection, and the cost of machining and polishing as well, which enhances the reliability of the component in use, and hence achieving a higher structural integrity*. Developing new materials with increasing resistance to wear and corrosion is the goal for many researchers and manufacturers as well. Consequently, an attempt to imitate the mechanisms employed by nature through the biological systems have been made to design self-healing materials and coatings for corrosion protection which can result in complete recovery*. Ceramics can be used in many applications including aeroengine turbine blades, gas turbine blades, high performance bearings and many other applications that require high temperature service *. However, these ceramics have low fracture toughness, which means that they are brittle and sensitive to flaws such as micro and macro cracks, which limit their applications as structural components. The present research is focused on the self-crack healing ability of Spinel nanocomposites and SiC bonded Kaolinite. The self-crack healing behavior was investigated as a function of the healing conditions (time, temperature, and chemical composition) as well as the mechanism responsible for healing the cracks.