This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.

In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.

Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.

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Description
Composite materials are widely used in various structural applications, including within the automotive and aerospace industries. Unidirectional composite layups have replaced other materials such as metals due to composites’ high strength-to-weight ratio and durability. Finite-element (FE) models are actively being developed to model response of composite systems subjected to a

Composite materials are widely used in various structural applications, including within the automotive and aerospace industries. Unidirectional composite layups have replaced other materials such as metals due to composites’ high strength-to-weight ratio and durability. Finite-element (FE) models are actively being developed to model response of composite systems subjected to a variety of loads including impact loads. These FE models rely on an array of measured material properties as input for accuracy. This work focuses on an orthotropic plasticity constitutive model that has three components – deformation, damage and failure. The model relies on the material properties of the composite such as Young’s modulus, Poisson’s ratio, stress-strain curves in the principal and off-axis material directions, etc. This thesis focuses on two areas important to the development of the FE model – tabbing of the test specimens and data processing of the tests used to generate the required stress-strain curves. A comparative study has been performed on three candidate adhesives using double lap-shear testing to determine their effectiveness in composite specimen tabbing. These tests determined the 3M DP460 epoxy performs best in shear. The Loctite Superglue with 80% the ultimate stress of the 3M DP460 epoxy is acceptable when test specimens have to be ready for testing within a few hours. JB KwikWeld is not suitable for tabbing. In addition, the Experimental Data Processing (EDP) program has been improved for use in post-processing raw data from composites test. EDP has improved to allow for complete processing with the implementation of new weighted least squares smoothing options, curve averaging techniques, and new functionality for data manipulation.
ContributorsSchmidt, Nathan William (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2016
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Description
The concept of Creep is a term used to define the tendency of stressed materials to develop an increasing strain through time under a sustained load, thus having an increase in deflection or having an elongation with time in relation to the short term strain. While the subject of compression

The concept of Creep is a term used to define the tendency of stressed materials to develop an increasing strain through time under a sustained load, thus having an increase in deflection or having an elongation with time in relation to the short term strain. While the subject of compression creep of concrete is well developed, use of concrete under tension loads has been limited at best due to brittleness of concrete. However with the advent of using fiber reinforced concrete, more and more applications where concrete is expected to carry tensile loads due to incorporation of fibers is gaining popularity. While the creep behavior of concrete in tension is important, the main case of the study is what happened when the concrete that is cracked in service is subjected to sustained loads causing creep. The relationship of opening cracks under these conditions are of utmost importance especially when the serviceability criteria is addressed. Little work has been reported in literature on the long-term behavior of FRC under sustained flexural loadings. The main objective of this study is to investigate the Long Term Flexural Behavior of Pre-Cracked Fiber Reinforced Beams under Sustained Loads. The experimental reports document the effect of loading and temperature on the creep characteristics of concrete. A variety of study has been carried out for the different responses generated by the creep tests based on factors like effect of temperature and humidity, effect of fiber content, effect of fiber type, and effect of different loading levels.

The Creep Testing Experimental Methodology is divided into three main parts which includes: (1) The Pre-cracking Partial Fracture Test; (2) Creep Test; (3) Post Creep Full Fracture Test. The magnitude of load applied to a specific specimen during creep testing was based on the results of average residual strength (ARS) tests, determined using EN14651. Specimens of the synthetic FRC mixture were creep tested at loads nominally equivalent to 30% and 50% of the FR1 value. The creep tests are usually continued until a steady Time versus CMOD response was obtained for the specimen signifying its presence in the secondary stage of creep. The creep recovery response is generated after unloading the specimen from the creep set up and later a full fracture test is carried out to obtain the complete post creep response of the beam under flexure.

The behavior of the Creep Coefficient versus Time response has been studied using various existing models like the ACI 209-R 92 Model and the CEB-FIP Model. Basic and hybrid rheological viscoelastic models have also been used in order to generate the material behavior response. A study has been developed in order to understand the applicability of various viscoelastic models for obtaining the material response of real materials. An analytical model for predicting the Flexural Behavior of FRC under sustained creep loads is presented at the end. This model helps generate the stress strain and Moment Curvature response of FRC beams when subjected to creep loads post initial cracking
ContributorsGohel, Megha Rajendrakumar (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2017