Engineering Commons^™

Optimum Failure Truncated Testing Strategies, Erik Kostandyan

Dissertations

Accumulated fatigue damage on mechanical components due to random stress loads eventually causes failure. Therefore products with lower failure rates are more desirable. Testing mechanical components for their intended purpose under predetermined working conditions is a common practice used by industries to prevent failures. Fatigue tests are categorized as Time Truncated or Failure Truncated, known in the literature as Type I and Type II tests, respectively. In failure truncated tests, the mechanical components are tested until the desired number of results is obtained. The parameters of a typical failure truncated test include the capacity of the test facility, the actual …

Simulation, Synthesis, And Characterization Of Hydrogels And Nanocomposite Gels., Kamleshkumar J. Suthar

Dissertations

Stimuli-responsive gels are three-dimensional, cross-linked polymeric materials that undergo large physical change in response to the environmental stimuli, like temperature, pH, electrical potential, and irradiation. Ferrogels are colloidaldispersion of magnetic nanoparticles in the hydrogel network. The magnetic nanoparticles are attached to the polymeric network by different adhesive forces; as a result, it becomes sensitive to the applied magnetic field.

The main objective of this research is the simulation, synthesis, and characterization of the hydrogel and ferrogel. Simulation of the hydrogel response was performed for various environmental stimuli using a multiphysics finite element analysis software, COMSOL. The pH and electrical response …

Analytical, Computational And Experimental Studies Of Capillary Flow In Complex Geometries, Yongqing Peng

Dissertations

The dynamic processes of capillary flow in complex geometries have been studied analytically, computationally and experimentally in this research. A general approach for modeling the capillary flow in arbitrary irregular geometries with straight axis of symmetry is proposed. Using this approach, the governing equation to describe the dynamic capillary rising motion in capillaries with nonuniform elliptical cross-section is first derived under the assumptions of parabolic distribution of the axial velocity and constant contact angle. The calculation results for the capillary flow in different tubes with irregular wall show that, in comparison with existing models that have been tested, the present …

Atomistic-Based Finite Element Simulation Of Carbon Nanotubes, Yang Yang

Dissertations

Since first found in the form of multi-walled carbon nanotubes (MWNTs) by Iijima(1991), carbon nanotube (CNT) for its outstanding and unique properties have gained overwhelming attentions from across the spectrum of the science and engineering fields. CNTs are structurally perfect, small size, low density, high stiffness, high strength (Qian et al., 2002), and their electronic properties depend on the particular distortion as well as the initial tube diameter and chirality, ranging from narrow-gap or moderate-gap semiconducting to metallic (Pantano et al., 2004b), which can be utilized in nanoscale sensors and devices. These appealing characteristics provide strong drives for the possible …

Load Interaction Effects On Fatigue Crack Growth, Stoyan Ivanov Stoychev

Dissertations

Load excursions, in the form of tensile and compressive overloads are known to produce interaction effects during subsequent constant amplitude loading. In this work, the fatigue crack growth and crack closure levels, under both constant amplitude and variable amplitude loading, are investigated in the aluminium-lithium alloy 2090-T84, and the aluminium alloys 2024-T351 and 7150-T651. The crack closure measurements were obtained using both a crack tip opening displacement (CTOD) gauge and a crack mouth opening displacement (CMOD) gauge.

Fatigue crack growth tests were performed on specimens of thickness 1.6mm, 3mm, 6mm and 14mm. Tests were performed at load ratios of 0.1 …

Investigation Of The Iced Flowfield Characteristics Related To The Stall Margin Instrumentation Used In Icing Conditions, Erik Pederson

Dissertations

The purpose of this dissertation is to investigate the relationship between the flowfield surrounding an iced airfoil and the stall margin instrumentation developed for use in icing conditions. The stall margin system indicates to the pilot the change in available lift due to ice accretions on the leading edge of an airfoil. This system displays the change in the form of a normalized lift coefficient. Four pressure ports are chosen to specifically maintain a constant calibration curve, for pressure versus normalized lift coefficient, regardless of ice shape. This allows these pressures to be used to determine the change in maximum …

Study Of Automotive Hydromount Mechanism, Min Lu

Dissertations

The hydromount mechanism is studied. It was determined that the dynamic characteristics of the hydromounts are related to the rubber static stiffness, rubber damping coefficient, volumetric stiffness, and effectiveness of the oscillating fluid in the inertia track. At high frequencies the motion of the fluid in the inertia track diminishes so that its effect is negligible and may be ignored. It is also concluded that the rubber damping has a minimal effect on the hydromount dynamic properties and may be neglected. The maximum loss angle, which corresponds to the maximum damping coefficient of the hydromount, occurs near the inertia track …

Active Local Volume Displacement Cancellation Of A Vibrating Baffled Beam, Marcellin Zahui

Dissertations

An active noise control apparatus is developed. The device reduces the sound radiated from a vibrating clamped beam. The attenuation of the sound field is obtained through minimization of local volume displacements of the vibrating beam. Two single-input/single-output cancellation devices are used. Each device employs a motion sensor and an acoustic actuator. The actuator is a loudspeaker equipped with a pressure sensor to detect its volume displacement. The motion sensor signal is related to the local volume displacement of the structure which is then reduced by a loudspeaker driven with an equal but opposing volume displacement. The volume displacement sensors …