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Single Point Incremental Forming (SPIF) is a die-less sheet metal forming method. Because SPIF does not use custom tooling, this process allows for parts to be made at low cost and short lead times. In this thesis electric current is applied through the tool to alter the formability of samples formed with SPIF. The research goal of this work is to determine if formability is effected by resistive heating alone or if there is some formability change due to the current interacting with the material. An apparatus that allows electrical current to be applied through the tool during forming is designed and implemented. A method is also developed to allow the contact area between the tool and sheet to be estimated, with particular focus on developing a method that allows for experimental measurement. The effect of applied current on formability is estimated by evaluating the maximum wall angle that can be formed in a single pass, using a variety of tool sizes and current settings. Using the contact area model to estimate current density, a signicant increase in formability is found at a current density range that agrees with previously published literature on electrically assisted forming of the same material. The results show that across multiple tool sizes, a significant increase in formability is observed when applying a current density (A/mm2) larger than the current threshold density published in the literature. A study is also performed to test the performance of a set of novel tool shapes. By using parabolic tools, it was found that formability can be improved while maintaining low surface roughness. Finally, a series of case studies are presented documenting the production several parts for a variety of design groups and researchers at Queen's University. These case studies provide examples for the uses of SPIF, as well as document the methods used to produce these parts in greater detail than is present in the literature. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-11-29 16:06:51.964

Thesis (M.A.)--Boston University

Accurately forecasting the contribution of the Greenland Ice Sheet to global sea-level requires precise observations to constrain present-day processes and incorporate them into models. However, the spatial and temporal resolution of satellite imagery and representativeness of in situ measurements often precludes or obscures our understanding of mass loss processes. This thesis investigates whether imagery from unmanned aerial vehicles (UAVs) have the potential to 1) bridge the scale gap between in situ and satellite observations and, 2) resolve processes of mass loss which are beyond the resolution of satellite imagery. It is found that the footprints of ground-based pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Point-to-pixel albedo comparisons are therefore often invalid, meaning that satellite-derived albedo measurements may be more accurate than previously thought. A 25 km transect intersecting the dark zone reveals that distributed impurities, not cryoconite nor surface water, govern spatial albedo patterns and may have implications for the future expansion of the dark zone. Repeat surveys over Store Glacier show that UAVs can be used to quantify calving rates and surface velocities of tidewater glaciers. The surveys indicate that large calving events cause short-term terminus velocity accelerations and can explain the seasonal pattern of acceleration and retreat. Any process which accelerates calving, such as removal of the ice m ́elange, therefore has important implications for the glaciers future behaviour.

Thesis (M.M.)--Boston University

Chapter 2 contains the continuum mechanical notions for the description of the plastic behavior of sheet metal under large deformations at room temperature. As such, it includes the kinematics of a continuum body, strain and stress definitions, and a general elasto-plastic constitutive model description. This last point is complemented by the definition of anisotropy, as well as the description of some yield criteria and hardening laws. Next, Chapter 3 defines the stress strain states required to be experimentally reproduced in order to describe the initial yield locus and its displacement in the stress axis representation during plastic deformation. A review of the available experimental equipment capable of reproducing the required stress strain states is presented in order to choose the best for further construction. After consideration, those deemed the highest performing are the Miyauchi device, able to perform simple shear tests and the bi-axial testing machine, able to perform plane strain and simple shear tests separately or simultaneously. This chapter presents the mechanical features of the Miyauchi device and the bi-axial test machine that were built at the M&S Laboratory, followed by a description of the optical strain gauge chosen that allows the computation of the strain field throughout the specimens deformation area. Chapter 4 focuses on the validation of the experimental equipment. First, the homogeneity of the stress and strain fields is verified. Then, the availability of performing the plane strain, simple shear, Bauschinger and orthogonal tests is checked. The repeatability (precision) of the tests is corroborated and the accuracy is validated by comparison with finite elements simulations. In Chapter 5, the identification methods are proposed and DC06 (0,8mm thick), DP1000 (1,6mm thick) and S320GD (0,69mm thick) steels are identified according to those methods. The initial yield surface for DC06 is identified by two methods (one using the strain measurements, the other using stress measurements) for two yield criteria, which are then compared with a texture-based yield criterion and the experimental points. The initial yield surface for the other two materials is described by the Hill 1948 yield criterion identified using strain measurements. The yield surface evolution (hardening) for DC06 and S320GD is described by the Teodosiu and Hu hardening law due to the observed mechanical behavior, i.e., the Bauschinger effect and strong influence of the pre-strain when strain-path changes take place. DP1000 exhibits a high Bauschinger effect and its flow stress is not influenced by the amount of pre-strain when reversing the load; hence, its behavior is described by a kinematic hardening law. Finally, in Chapter 6, conclusions about the present work are established and equipment improvement and further topics for research are proposed, namely, the study of texture evolution, the material axis rotation and the experimental validation of new yield criteria.

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The structural behaviour of single shear bolted connections, double shear bolted connections and single shear screwed connections of thin sheet steels at elevated temperatures has been investigated in this study. The current design rules on bolted and screwed connections of thin sheet steels for cold-formed steel structures are applicable for ambient temperature condition only. These design rules may not be applicable for elevated temperature conditions. Therefore, design guidelines should be prepared for bolted and screwed connections of cold-formed steel structures at elevated temperatures. A total of 30 tensile coupon tests were conducted to investigate the material deterioration of the thin sheet steels at elevated temperatures, and also to determine the critical temperatures for connection tests. A total of 510 tests on single shear bolted connections, double shear bolted connections and single shear screwed connections of thin sheet steels at elevated temperatures was performed in the temperature ranged from 22 to 900?C using both steady state and transient state test methods. The test results were compared with the predicted values calculated from the North American, Australian/New Zealand and European specifications for coldformed steel structures. In calculating the nominal strengths of the connections, the reduced material properties of the thin sheet steels were used due to the deterioration of material at elevated temperatures. It is shown that the design strengths predicted by these specifications are generally conservative at elevated temperatures. Finite element models for single shear bolted connections, double shear bolted connections and single shear screwed connections were developed and verified against the experimental results. Explicit dynamic analysis technique was used in the numerical analyses. Extensive parametric studies that included 490 finite element specimens were carried out using the verified finite element models to evaluate the bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections of thin sheet steels at elevated temperatures. Design equations for bearing strengths of bolted connections as well as design equations for tilting and bearing strengths of screwed connections were proposed based on both the experimental and the numerical results in the temperature ranged from 22 to 900?C. The bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections obtained from the test specimens and the finite element analyses were compared with the predicted strengths calculated using the proposed design equations and also compared with the design strengths calculated using the current North American, Australian/New Zealand and European specifications with consideration of the reduced material properties at elevated temperatures. It is shown that the proposed design equations are generally more accurate and reliable in predicting the bearing strengths of bolted connections as well as the tilting and bearing strengths of screwed connections of thin sheet steels at elevated temperatures than the current design rules. The reliability of the current and proposed design rules was evaluated using reliability analysis. The proposed design equations are suitable for bolted and screwed connections assembled using thin sheet steels of thickness ranged from 0.35 to 3.20mm. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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