Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2005 - 200912010 - 20121

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Subject: search.filters.subject.Energy Release Rate

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    Determination of Mixed Mode Energy Release Rates in Laminated Carbon Fiber Composite Structures Using Digital Image Correlation
    (2012) Puishys, Joseph Francis; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Carbon fiber composites have recently seen a large scale application in industry due to its high strength and low weight. Despite numerous beneficial attributes of composite materials, they are subject to several unique challenges; the most prevalent and troubling is delamination fracture. This research program is focused on developing an appropriate damage model capable of analyzing microscopic stress strain growth at the crack tip of laminated composites. This thesis focuses on capturing and identifying the varying stress and strain fields, as well as other microstructural details and phenomena unique to crack tip propagation in carbon fiber panels using a novel mechanical characterization technique known as Digital Image Correlation (DIC).
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    PLASTIC TEARING ENERGY IN TOUGH STEELS
    (2005-12-05) Chen, Xiaohu; Albrecht, Pedro; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Plastic tearing occurs in compact tension (C(T)) specimens fabricated from ductile steels. This tearing, however, is not an elastic fracture problem governed by a crack tip singularity parameter. The current application of the J-integral and the J-R curve to plastic fracture mechanics is misleading. This dissertation reviews the existing energy rate and geometric factor approaches, and then reanalyzes the unloading compliance data for C(T) specimens of various types of steel. The objective of the analysis is to investigate the criteria that can characterize the crack extension under plastic tearing. The author suggests that the energy release rate that remains constant with significant crack growth, in conjunction with the mechanism motion of crack extension to represent the degree of tearing, can serve as the objective parameter in a standard fracture toughness test. Both the energy release rate and the plastic tearing mechanism motion are calculated directly from the test data. The effects of the initial crack length, the specimen size, the testing temperature, and the steel type on the results are investigated. The purpose is to determine the sensitivity of both parameters to the testing configurations. To discuss the tri-axial stress status ahead of the crack front, a finite element model using non-singular elements is presented and verified by the experimental load-displacement curve. Simplifications to the costly C(T) specimen fabrication are proposed based on the analytical conclusions from both the test data and the finite element model.