Mechanical Engineering Commons^™

Generation And Analysis Of Fcg Data Using A Single Specimen And Kmax - ∆K Testing Matrix, Sree Phani Chandar Reddy

Masters Theses

A custom method to generate fatigue crack growth (FCG) data requires testing of multiple specimens at different load ratios. In addition, it includes the application of a load shedding procedure from pre-cracking level to threshold.

In this thesis, a novel method of testing has been investigated that utilizes a single specimen and a testing matrix in terms of K_maxand ∆K values corresponding to predetermined R-ratios for which FCG data, da/dN, are recorded. Automatic K-controlled tests on 2324-T39 Al alloy were conducted using the ∆K increasing and ∆K decreasing procedures while K_maxwas kept constant. Results show that …

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 …

Ductile-Regime Machining Of Silicon Carbide And Quartz, Deepak Ravindra

Masters Theses

Silicon carbide (SiC) and quartz are one of the advanced engineered ceramic materials designed to operate in extreme environments. One of the main reasons for the choice of these materials is due to its excellent electrical, mechanical and optical properties that benefit the semiconductor, MEMS and optoelectronic industry respectively. Manufacturing these materials is extremely challenging due to its high hardness, brittle characteristics and poor machinability. Severe fracture can result when trying to machine SiC and quartz due to its low fracture toughness. However, from past and current research efforts, it has been proven that ductile regime machining of brittle materials …

Prediction Of Fatigue Crack Growth Retardation Due To A Tensile Overload Using Two-Parameter (∆K, Kmax) Approach, Wataru Tsutsui

Masters Theses

A theoretical crack growth study on powder metallurgy aluminum alloys AA5091 and AA8022 was conducted. Specifically, the research focused on the crack growth retardation due to the application of a tensile overload. The tensile overload creates a plastic zone ahead of the propagating crack tip that induces the compressive residual stress after unloading. Such compressive residual stress pushes the crack tip faces against each other, which results in crack growth retardation.

In the study, simulation started from the calculation of the compressive residual stress. The details of the calculation steps are explained in the thesis. Eventually, the stress intensity factor …

Investigative Study On An Energy Theorem For Developing Testing Functions For Numerical Simulations Of Multibody Dynamic Systems, Kulasegaram Gugaratshan

Masters Theses

Multibody dynamic systems designers utilize computer software extensively to simulate the motion of mechanical systems. The governing differential equations of motion are formulated and solved numerically. The accuracy of the numerical solutions is always a concern to the analyst. There have been many investigations done around the world to check the accuracy of these simulations, and based on these investigations, many methods have been developed. These methods are usually based on energy balance equations and can be used to test the validity or the correctness of the numerical solutions. This thesis analyzes and compares these methods based on their formulation …

Iterative Design Of The Aeroship Through Flight Testing, Michael R. Schulte

Masters Theses

This research covers the design, construction, and testing of a hybrid flight platform called the Aeroship. The Aeroship is a combination of current aerodyne and aerostat technology that have been merged at an optimal ratio. In order to create an efficient design, flight testing was employed as a catalyst for design changes. The final design was then flight tested for performance validation using videogrammetry.