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You searched for +publisher:"Drexel University" +contributor:("Lau, Alan"). Showing records 1 – 3 of 3 total matches.

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Drexel University

1. Shannahan, Logan Spencer. A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture.

Degree: 2017, Drexel University

The fracture behavior of materials resulting from rapidly applied loads remains poorly understood, and requires consideration of the inertial forces and rapidly changing crack front. At the same time, with the advent of improved high-speed cameras and full-field optical techniques such as digital image correlation (DIC), the spatial and temporal resolution of measurable field data has increased. As such, this thesis presents a novel hybrid experimental-computational technique that extracts dynamic fracture criterion from DIC data using improved, iterative elastodynamic expressions relating stress intensity factors (SIFs) to displacement fields around the crack front. Two variations of the solution are explored: an over-deterministic least squares regression is used when the crack tip location is known, such as at initiation of fracture, and an iterative Newton-Raphson optimization is used when the crack tip location is unknown. Dynamic fracture experiments are conducted on single-edge-notch specimens, impacted on the opposite face by a striker in mode I (or crack opening), to determine the efficacy of the method. Three materials with varying microstructures are studied: brittle polymer polymethyl methacrylate (PMMA), nanolayered metal-ceramic MAX phase Ti3SiC2, and human femoral cortical bone, a natural hierarchical ceramic matrix composite. PMMA is a historically well-studied material in classical dynamic fracture mechanics and is chosen as a model material, and when combined with data from literature is used to conduct validation and uncertainty quantification arising from key experimental and numerical parameters. Material rate dependency and the effect of transient wave interactions are investigated in the dynamic fracture behavior of MAX phase Ti3SiC2, and found to hold little influence due to the energy absorbing mechanisms of kink banding and delamination unique to the layered microstructure. Mode-mixity arising from an orthotropic microstructure is investigated in human femoral cortical bone, and lead to significant mode II SIFs even in the absence of any applied mode II loading, though mode I fracture remains dominant. These collective results demonstrate the wide variety of material microstructures with varying deformation mechanisms to which the hybrid experimental-computational dynamic fracture analysis is well-suited to handle.

Ph.D., Mechanical Engineering and Mechanics  – Drexel University, 2017

Advisors/Committee Members: Lamberson, Leslie, Lau, Alan, College of Engineering.

Subjects/Keywords: Mechanical engineering; Digital image correlation; Fracture mechanics – Research; Fractures

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Shannahan, L. S. (2017). A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture. (Thesis). Drexel University. Retrieved from http://hdl.handle.net/1860/idea:7566

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Shannahan, Logan Spencer. “A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture.” 2017. Thesis, Drexel University. Accessed February 19, 2019. http://hdl.handle.net/1860/idea:7566.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Shannahan, Logan Spencer. “A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture.” 2017. Web. 19 Feb 2019.

Vancouver:

Shannahan LS. A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture. [Internet] [Thesis]. Drexel University; 2017. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1860/idea:7566.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Shannahan LS. A Hybrid Experimental-Computational Approach for the Analysis of Dynamic Fracture. [Thesis]. Drexel University; 2017. Available from: http://hdl.handle.net/1860/idea:7566

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


Drexel University

2. Chanthasopeephan, Teeranoot. Characterization of soft tissue cutting for haptic display: experiments and computational models.

Degree: 2006, Drexel University

Real-time medical simulation for robotic surgery planning and surgery training requires realistic yet computationally fast models of the mechanical behavior of soft tissue. This work presents a study to develop such a model to enable fast haptics display in simulation of softtissue cutting. An apparatus was developed and experiments were conducted to generate force-displacement data for cutting of soft tissue such as pig liver. The force-displacement curve of cutting pig liver revealed a characteristic pattern: the overall curve is formed by repeating units consisting of a local deformation segment followed by a local crack-growth segment. The modeling effort reported here focused on characterizing the tissue in the local deformation segment for fast haptic display. The deformation resistance of the tissue was quantified in terms of the local effective modulus (LEM) consistent with experimental forcedisplacement data. An algorithm was developed to determine LEM by solving an inverse problem with iterative finite element models. To enable faster simulation of cutting of a threedimensional (3D) liver specimen of naturally varying thickness, three levels of model order reduction were studied. Additionally, the variation of the LEM with cutting speed was determined. The values of LEM decreased as the cutting speed increased. This thesis also includes the characteristic response of soft tissue to the growth of a cut (cracking) with a scalpel blade. The experimentally measured cut-force versus cut-length data was used to determine the soft tissue’s resistance to fracture (resistance to crack extension) in scalpel cutting. The resistance to fracture of the soft tissue is defined as the amount of mechanical work needed to cause a cut (crack) to extend for a unit length in a soft-tissue sample of unit thickness. The equipment, method, and model are applicable for all soft tissue.Finally, the method of determining the property of the pig liver tissue during cutting was verified. Dual C-arm fluoroscopes were used to obtain the motion of the beads embedded inside the specimen during cutting. The experimentally measured displacement field was compared to the displacement field obtained through finite element model based on the LEM values at each localized area.

Ph.D., Mechanical Engineering and Mechanics  – Drexel University, 2006

Advisors/Committee Members: Desai, Jaydev Prataprai, Lau, Alan C. W..

Subjects/Keywords: Mechanical engineering; Surgery – Simulation methods; Tissues – Simulation methods

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Chanthasopeephan, T. (2006). Characterization of soft tissue cutting for haptic display: experiments and computational models. (Thesis). Drexel University. Retrieved from http://hdl.handle.net/1860/1116

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Chanthasopeephan, Teeranoot. “Characterization of soft tissue cutting for haptic display: experiments and computational models.” 2006. Thesis, Drexel University. Accessed February 19, 2019. http://hdl.handle.net/1860/1116.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Chanthasopeephan, Teeranoot. “Characterization of soft tissue cutting for haptic display: experiments and computational models.” 2006. Web. 19 Feb 2019.

Vancouver:

Chanthasopeephan T. Characterization of soft tissue cutting for haptic display: experiments and computational models. [Internet] [Thesis]. Drexel University; 2006. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1860/1116.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Chanthasopeephan T. Characterization of soft tissue cutting for haptic display: experiments and computational models. [Thesis]. Drexel University; 2006. Available from: http://hdl.handle.net/1860/1116

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


Drexel University

3. Mosinyi, Bao Rasebolai. Fatigue damage assessment of high-usage in-service aircraft fuselage structure.

Degree: 2007, Drexel University

As the commercial and military aircraft fleets continue to age, there is a growing concern that multiple-site damage (MSD) can compromise structural integrity. Multiple site damage is the simultaneous occurrence of many small cracks at independent structural locations, and is the natural result of fatigue, corrosion, fretting and other possible damage mechanisms. These MSD cracks may linkup and form a fatigue lead crack of critical length. The presence of MSD also reduces the structure’s ability to withstand longer cracks.The objective of the current study is to assess, both experimentally and analytically, MSD formation and growth in the lap joint of curved panels removed from a retired aircraft. A Boeing 727-232 airplane owned and operated by Delta Air Lines, and retired at its design service goal, was selected for the study. Two panels removed from the left-hand side of the fuselage crown, near stringer 4L, were subjected to extended fatigue testing using the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility located at the Federal Aviation Administration (FAA) William J. Hughes Technical Center. The state of MSD was continuously assessed using several nondestructive inspection (NDI) methods. Damage to the load attachment points of the first panel resulted in termination of the fatigue test at 43,500 fatigue cycles, before cracks had developed in the lap joint. The fatigue test for the second panel was initially conducted under simulated in-service loading conditions for 120,000 cycles, and no cracks were detected in the skin of the panel test section. Artificial damage was then introduced into the panel at selected rivets in the critical (lower) rivet row, and the fatigue loads were increased. Visually detectable crack growth from the artificial notches was first seen after 133,000 cycles. The resulting lead crack grew along the lower rivet row, eventually forming an 11.8″ long unstable crack after 141,771 cycles, at which point the test was terminated Posttest fractograpic examinations of the crack surfaces were conducted, revealing the presence of subsurface MSD at the critical rivet row of the lap joint. Special attention was also given to the stringer clips that attach the fuselage frames to the stringers, since they also experienced cracking during the fatigue tests. The performance of the different conventional and emerging NDI methods was also assessed, and some of the emerging NDI methods were quite effective in detecting and measuring the length of subsurface cracks.Delta Air Lines conducted a separate destructive investigation on the state of damage along the right-hand side of the fuselage, near stringer 4R. A comparison of these two studies showed that the lap joint on the left hand-side of the aircraft, along stringer 4L, had better fatigue life than the one on the opposite side, along stringer 4R. The cause of the difference in fatigue life was investigated by close examination of the rivet installation qualities, and was found to be a result of better rivet installation… Advisors/Committee Members: Awerbuch, Jonathan, Lau, Alan C. W., Tan, Tein-Min.

Subjects/Keywords: Mechanical engineering; Airframes – Fatigue; Airplanes – Fuselage – Materials

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Mosinyi, B. R. (2007). Fatigue damage assessment of high-usage in-service aircraft fuselage structure. (Thesis). Drexel University. Retrieved from http://hdl.handle.net/1860/2762

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Mosinyi, Bao Rasebolai. “Fatigue damage assessment of high-usage in-service aircraft fuselage structure.” 2007. Thesis, Drexel University. Accessed February 19, 2019. http://hdl.handle.net/1860/2762.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Mosinyi, Bao Rasebolai. “Fatigue damage assessment of high-usage in-service aircraft fuselage structure.” 2007. Web. 19 Feb 2019.

Vancouver:

Mosinyi BR. Fatigue damage assessment of high-usage in-service aircraft fuselage structure. [Internet] [Thesis]. Drexel University; 2007. [cited 2019 Feb 19]. Available from: http://hdl.handle.net/1860/2762.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Mosinyi BR. Fatigue damage assessment of high-usage in-service aircraft fuselage structure. [Thesis]. Drexel University; 2007. Available from: http://hdl.handle.net/1860/2762

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.