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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
351

Performance of Polymer Coatings Under Forming Conditions

Purohit, Zalak 2010 December 1900 (has links)
Prepainted metal sheets being environment friendly and cost effective as compared to postpainted metal sheets, are widely used in construction, packaging, transportation and automotive industries. One of the key requirements for prepainted coatings is to retain its surface quality and properties during forming process. During forming process, major surface damage occurs when the coated sheet is bent and un-bent around the die corner. To reduce surface damage of coatings, proper control of the parameters during forming and detail study of the surface conditions is required. In the present study, influence of forming parameters such as die radius, lubrication and specimen material are investigated. The influence of these parameters on friction, surface damage and properties of polymer coatings are evaluated. Experiment set-up is built to conduct bending under tension test. This test gives a better way to evaluate coating performance, as it closely simulates the die region of real forming process and considers bending effects. Experimental results show increase in friction and surface damage with decrease in die radius. Moreover, with decrease in die radius hardness of the coating decreases and strain in the specimen increases. Lubrication has some effect on coefficient of friction, but the influence is not as significant as that of die radius. This is attributed to the fact that, the polymer coating itself acts as a solid lubricant in the test. Material effect was studied, polypropylene coating being the softer material compared to PVDF coating shows more surface damage in the form of scratches. Numerical simulations were performed using Finite Element Analysis package (FEA) Abaqus. A 2D model was built, exploiting the plane strain condition for bending under tension test. Numerical simulations indicate that maximum contact pressure and von Mises stress are concentrated at the beginning of the drawing edge. Apart from the location, the value of contact pressure was higher for smaller die radius. Thus, experiments help in studying the effect of forming parameters on coating performance and numerical simulations provide more insight into the critical areas where stresses are high. Numerical simulations also provide a scope to study the effect of material and geometric parameters on performance of coatings without running experiments.
352

Numerical And Experimental Investigation Of Fatigue Life In Deep Drawn Parts

Aytekin, Oguz 01 May 2005 (has links) (PDF)
Sheet metal forming has an important place among metal forming processes. As the usage of sheet metal increases, the fatigue simulation and optimization of these parts become more important. This thesis study examines the change of the fatigue life of a sheet metal part after forming. A sphere-like shape is deep drawn and change in thickness and residual stresses are analyzed. To understand the effect of residual stresses, deep drawn parts with and without residual stress tested against the fatigue failure. In parallel, the forming process is simulated with an implicit finite element method (FEM). The success of forming simulation is discussed in the study. Thickness changes and residual stresses calculated with FEM are included in computer aided fatigue analysis. The effect of thickness changes is examined with the results of FEM analysis. The effectiveness of the whole simulation process is discussed by comparing the outputs of experiments and computational analysis.
353

Desig And Analysis Of Fixturing In Assembly Of Sheet Metal Components Of Helicopters

Bayar, Fatih Mehmet 01 February 2007 (has links) (PDF)
Assembling of the compliant parts used in aviation industry is a challenging process. Assembly fixtures are quite important tools in this effort and widely used in industry. In fixturing of easily deformable sheet metal parts, besides restraining the rigid body motion of the parts, the possible deformations that may occur during the assembly process and the spring-back effect on the final product need to be taken in to consideration. In order to guarantee a successful assembling, in other words, to obtain the final product within specified tolerances, a systematic approach to the fixture design problem is required. The designer should predict the correlation between the input variations and the final assembly variation, especially, for the complex assemblies. This study proposes a design and analysis approach in fixturing of sheet metal assemblies for helicopter components. The design of an assembly fixture for a particular tail cone has been completed convenient to the existing locating principles. Finite Element Analysis (FEA) has been realized in simulating the assembling process in order to predict the possible variation of the interested feature on a complex assembly due to deformations.
354

Determining Surface Residual Stress In Steel Sheets After Deep Drawing And Bulging Processes

Adiguzel, Sinem 01 February 2011 (has links) (PDF)
The aim of this thesis is to investigate the effects of bulging and deep drawing processes on St4 cold rolled steel by simulation and experimental characterization. In the simulations, commercial software programs MSC Marc and Simufact.forming were used. The experimental studies cover metallographic investigations, hardness measurements, and residual stress measurements. Residual stress measurements were carried out by different non- destructive characterization methods / X-ray diffraction and Magnetic Barkhausen Noise. The experimental and simulation results were correlated with each other.
355

The use of polarized light for biomedical applications

Baba, Justin Shekwoga 15 November 2004 (has links)
Polarized light has the ability to increase the specificity of the investigation of biomedical samples and is finding greater utilization in the fields of medical diagnostics, sensing, and measurement. In particular, this dissertation focuses on the application of polarized light to address a major obstacle in the development of an optical based polarimetric non-invasive glucose detector that has the potential to improve the quality of life and prolong the life expectancy of the millions of people afflicted with the disease diabetes mellitus. By achieving the mapping of the relative variations in rabbit corneal birefringence, it is hoped that the understanding of the results contained herein will facilitate the development of techniques to eliminate the effects of changing corneal birefringence on polarimetric glucose measurement through the aqueous humor of the eye. This dissertation also focuses on the application of polarized light to address a major downside of cardiovascular biomechanics research, which is the utilization of toxic chemicals to prepare samples for histological examination. To this end, a polarization microscopy image processing technique is applied to non-stained cardiovascular samples as a means to eliminate, for certain cardiac samples, the necessity for staining using toxic chemicals. The results from this work have the potential to encourage more investigators to join the field of cardiac biomechanics, which studies the remodeling processes responsible for cardiovascular diseases such as myocardial infarct (heart attacks) and congestive heart failure. Cardiovascular disease is epidemic, particularly amongst the population group older than 65 years, and the number of people affected by this disease is expected to increase appreciably as the baby boomer generation transitions into this older, high risk population group. A better understanding of the responsible mechanisms for cardiac tissue remodeling will facilitate the development of better prevention and treatment regimens by improving the early detection and diagnosis of this disease.
356

Development and Application of Plate Element by the Vector Form Intrinsic Finite Element Method.

Chang, Po-Yen 24 August 2009 (has links)
In this study, a new vector form intrinsic finite element (VFIFE) for the plate is developed and applied to study the responses of a traditional plate member applied to engineering structures. The VFIFE method is a solution procedure for the mechanic problems by adopting the traditional co-rotational explicit finite element method developed by Belyschko and Hsieh (1973). Three different shape-functions including the simplest polynomial form shape-function (Poly), non-conforming area coordinate shape-function (BCIZ) and the conforming area coordinate shape-function (BCIZC) are utilized to simulate the displacement field of the plate. For a system with nonzero rigid-body displacement, the equilibrium will be difficult to achieve in the global coordinate system when the traditional finite element method is applied. By separating the rigid-body motions from the deformed motions, this problem can be easily taken care. In numerical examples, the accuracy and efficiency of this new developed vector form intrinsic finite element for plate simulation are also examined. It is found that compared to the analytical solution, the accuracy is excellent, while compared to traditional finite element method, the efficiency is also encouraging. This new VIFIFE plate element was also applied to the analysis for the sheet plate members in the harbor structures such as the sheep-pile wharf structural system. It was found that not only can the global behaviors of the pile be clearly observed but also local variations in deformations of the steel sheet are clearly shown.
357

KPI´s- Measuring and evaluating in order to increase efficiency

Winblad, Carl-Johan, Rensfelt, Anna, Lindman, Louise January 2008 (has links)
<p>Background: AA Logistics Sweden is having logistic efficiency problems, and at this point they do not have performance measurement in terms of KPI´s. Due to constant development and demand on their products, there have not been enough resources available to perform these measurements.</p><p>Purpose: Our purpose is, on the basis of service level and turnover speed, to measure efficiency in terms of KPI’s at AA. It is also to design record sheets that can assist AA to increase the efficiency over time.</p><p>Methodology: Interviews with managers and employees, in order to have a solid foundation for what to look for and analyse in the ERP system. The empirical material that was received was analysed on the basis of different theories.</p><p>Result, conclusions: We have developed values for each KPI and also suggested SMART goals that in the long run will contribute to increasing the logistic efficiency.</p>
358

Microstructural effects on fatigue damage evolution in advanced high strength sheet (AHSS) steels

Godha, Anshul 08 June 2015 (has links)
An understanding of the damage evolution prior to crack initiation in advanced structural materials is of vital importance to the fatigue community in both academia and industry. Features known as the Persistent Slip Bands (PSBs) play an integral role in this damage evolution. Therefore, PSBs have been the focus of a lot of science-based investigations over the years. However, most existing studies in this area are restricted to analysis of PSBs in single crystal face centered cubic (FCC) materials. Moreover, these studies lack a quantitative analysis of the evolution of the fatigue damage (or PSBs) as a function of the material microstructure. This is especially true for relatively modern materials such as the Advanced High Strength Structural (AHSS) steels that are gaining a lot of importance in the automotive sector. Accordingly, the objective of this research is to quantitatively characterize evolution of PSBs in three AHSS steels having different microstructures as a function of number of fatigue cycles and strain amplitude. For this purpose strain controlled interrupted fatigue tests have been performed on two dual phase steels (DP-590 and DP-980) having different relative amounts of tempered martensite and a ferritic high strength low alloy steel (HR-590). Digital image analysis and Stereology have been used for unbiased quantitative characterization of the evolution of global geometry of the PSB colonies as function of number of fatigue cycles and strain amplitude. Evolution of PSB colonies has been couched in terms of variation of PSB colony volume fraction and total surface area unit volume, and total surface area of individual PSBs per unit volume and three-dimensional angular orientation distribution of the PSBs. For this purpose, new stereological techniques have been developed for estimation of the three-dimensional angular orientation distribution. The stereological data reveal that during strain controlled in these AHSS steels, volume fraction of the PSB colonies varies linearly with the their total surface area per unit volume. Detailed analysis of the stereological data leads to a simple geometric model for evolution of the PSB colonies in the three AHSS steels, which accounts for all observed data trends.
359

Design and Synthesis of Protein-Protein Interaction Inhibitor Scaffolds

Badger, David B. 01 January 2012 (has links)
Many currently relevant diseases such as cancer arise from altered biological pathways that rely on protein-protein interactions. The proteins involved in these interactions contain certain functional domains that are responsible for the protein's biological activities. These domains consist of secondary structural elements such as α-helices and Β-sheets which are at the heart of the protein's biological activity. Therefore, designing drugs that inhibit protein-protein interactions by binding to these key secondary structural elements should provide an effective treatment for many diseases. Presented in this dissertation are the designs, syntheses, and biological evaluations for both novel α-helix and novel Β-sheet mimics. The α-helix mimics were designed to inhibit the interactions between the tumor suppressor protein p53 and its inhibitor protein, MDM2. We also targeted the interactions between the Bak/Bcl-xL proteins. Using the knowledge gained from Hamilton's 1,4-terphenylene scaffold, we designed our inhibitors to be non-peptidic small molecule α-helix mimics. These molecules were designed to bind to the NH2-terminal domain of MDM2 protein thus preventing it from binding to the p53 protein thereby allowing p53 to induce apoptosis. The α-helix mimetic scaffold is designed around a central functionalized pyridazine ring while maintaining the appropriate distances between the ith, ith+4, and ith+7 positions of a natural alpha helix. The Β-sheet mimics were designed as inhibitors for the integrin mediated extracellular matrix cell adhesion found in Multiple Myeloma. We have designed, synthesized, and incorporated novel Β-turns to induce the formation of Β-hairpins as well as to cyclize the peptides in order to increase their binding affinities and reduce proteolytic cleavage. Given that many protein-protein interactions occur through hydrophobic interactions; our primary Β-turn promoter was designed with the ability to alter the Β-hairpin's hydrophobicity depending on the sulfonyl group used in the turn. The synthesis of several different sulfonyl chlorides for use in our Β-turn promoter is included in this section. We have also provided a detailed structural analysis and characterization of these new cyclic peptides via NMR and CD spectrometry. Using standard 2D NMR methods, we have elucidated the 3D conformation of several peptides in solution. We have also studied the structure activity relationships (SAR) for these cyclic peptides and then correlated these results with those obtained from the NMR studies.
360

An approach to automate the synthesis of sheet metal parts

Patel, Jay K., 1978- 13 September 2012 (has links)
In this research, an approach is developed to automate the design for sheet metal parts that are not only novel and manufacturable but also satisfies multiple objective functions such as material cost. Unlike commercial software tools such as Pro/SHEETMETAL which aids the user in finalizing and determining the sequence of manufacturing operations for a specified component, our approach starts with spatial constraints in order to create the component geometries and helps the designer design. While there is an enormous set of parts that can feasibly be generated with sheet metal, it is difficult to define this space systematically. To solve this problem, we currently have 108 design rules that have been developed for five basic sheet metal operations: slitting, notching, shearing, punching and bending. The technique revealed here represents candidate solutions as a graph of nodes and arcs where each node is a rectangular patch of sheet metal, and modifications are progressively made to the sheet to maintain the parts manufacturability. They are presented in the form of Standard Tessellation Language files (.stl) that can be transferred into available modeling software for further analysis. The overall purpose of this research is to provide creative designs to the designer granting him/her a new perspective and to check all the solutions for manufacturability in the early stage of design process. The abovementioned automation approach uses a new topological optimization technique to solve graph based engineering design problems by decoupling parameters and topology changes. This technique namely Topological and Parametric Tune and Prune (TP²) is the first topology optimization method that has been developed specifically for domains representable by a graph grammar schema. The method is stochastic and incorporates distinct phases for modifying the topologies and modifying parameters stored within topologies. Thus far, with the problems that been tested, (TP²) had proven better than genetic algorithm in terms of the quality of solutions and time taken to acquire them. / text

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