ASU Electronic Theses and Dissertations
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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- Creators: Darnal, Aryabhat
- Creators: Mobasher, Barzin
Description
High-temperature mechanical behaviors of metal alloys and underlying microstructural variations responsible for such behaviors are essential areas of interest for many industries, particularly for applications such as jet engines. Anisotropic grain structures, change of preferred grain orientation, and other transformations of grains occur both during metal powder bed fusion additive manufacturing processes, due to variation of thermal gradient and cooling rates, and afterward during different thermomechanical loads, which parts experience in their specific applications, could also impact its mechanical properties both at room and high temperatures. In this study, an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain boundary misorientation angles, and inherent defects, as byproducts of electron beam powder bed fusion (EB-PBF) AM process, impact its anisotropic mechanical behaviors and softening behaviors due to interacting mechanisms. Mechanical testing is conducted for EB-PBF Ti6Al4V parts made at different build orientations up to 600°C temperature. Microstructural analysis using electron backscattered diffraction (EBSD) is conducted on samples before and after mechanical testing to understand the interacting impact that temperature and mechanical load have on the activation of certain mechanisms. The vertical samples showed larger grain sizes, with an average of 6.6 µm, a lower average misorientation angle, and subsequently lower strength values than the other two horizontal samples. Among the three strong preferred grain orientations of the α phases, <1 1 2 ̅ 1> and <1 1 2 ̅ 0> were dominant in horizontally built samples, whereas the <0 0 0 1> was dominant in vertically built samples. Thus, strong microstructural variation, as observed among different EB-PBF Ti6Al4V samples, mainly resulted in anisotropic behaviors. Furthermore, alpha grain showed a significant increase in average grain size for all samples with the increasing test temperature, especially from 400°C to 600°C, indicating grain growth and coarsening as potential softening mechanisms along with temperature-induced possible dislocation motion. The severity of internal and external defects on fatigue strength has been evaluated non-destructively using quantitative methods, i.e., Murakami’s square root of area parameter model and Basquin’s model, and the external surface defects were rendered to be more critical as potential crack initiation sites.
ContributorsMian, Md Jamal (Author) / Ladani, Leila (Thesis advisor) / Razmi, Jafar (Committee member) / Shuaib, Abdelrahman (Committee member) / Mobasher, Barzin (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2022
Description
Non-Destructive Testing (NDT) is a branch of scientific methods and techniques
used to evaluate the defects and irregularities in engineering materials. These methods
conduct testing without destroying or altering material’s structure and functionality. Most
of these defects are subsurface making them difficult to detect and access.
SONIC INFRARED (IR) is a relatively new and emerging vibrothermography
method under the category of NDT methods. This is a fast NDT inspection method that
uses an ultrasonic generator to pass an ultrasonic pulse through the test specimen which
results in a temperature variation in the test specimen. The temperature increase around
the area of the defect is more because of frictional heating due to the vibration of the
specimen. This temperature variation can be observed using a thermal camera.
In this research study, the temperature variation in the composite laminate during
the SONIC IR experimentation using an infrared thermal camera. These recorded data are
used to determine the location, dimension and depth of defects through SONIC IR NDT
method using existing defect detection algorithms. Probability of detection analysis is
used to determine the probability of detection under specific experimental conditions for
two different types of composite laminates. Lastly, the effect of the process parameters
such as number of pulses, pulse duration and time delay between pulses of this technique
on the detectability and probability of detection is studied in detail.
used to evaluate the defects and irregularities in engineering materials. These methods
conduct testing without destroying or altering material’s structure and functionality. Most
of these defects are subsurface making them difficult to detect and access.
SONIC INFRARED (IR) is a relatively new and emerging vibrothermography
method under the category of NDT methods. This is a fast NDT inspection method that
uses an ultrasonic generator to pass an ultrasonic pulse through the test specimen which
results in a temperature variation in the test specimen. The temperature increase around
the area of the defect is more because of frictional heating due to the vibration of the
specimen. This temperature variation can be observed using a thermal camera.
In this research study, the temperature variation in the composite laminate during
the SONIC IR experimentation using an infrared thermal camera. These recorded data are
used to determine the location, dimension and depth of defects through SONIC IR NDT
method using existing defect detection algorithms. Probability of detection analysis is
used to determine the probability of detection under specific experimental conditions for
two different types of composite laminates. Lastly, the effect of the process parameters
such as number of pulses, pulse duration and time delay between pulses of this technique
on the detectability and probability of detection is studied in detail.
ContributorsDarnal, Aryabhat (Author) / Liu, Yongming (Thesis advisor) / Zhuang, Houlong (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2019