Education - Lecture/Discussion - WPI Only
Thursday, April 10, 2014
1:00 PM-1:50 PM
Eric N. Landis, University of Maine: Eric N. Landis is the Frank M. Taylor Professor of Civil Engineering at the University of Maine. His research interests are in experimental mechanics and fracture, with particular focus on the use of innovative laboratory techniques to capture mechanisms of fracture and failure in heterogeneous materials. He also dabbles in biomimetics, burrowing marine invertebrates, and other things he should probably keep his nose out of. He has PhD and BS degrees from Northwestern University and the University of Wisconsin, respectively. Prior to his graduate work he spent several years in civil engineering consulting. At UMaine he has been honored for both his teaching and research, and 2006 he was named the Carnegie Foundation U.S. Professor of the Year in Maine. He is a registered Professional Engineer in Maine.
Adding sufficient quantities of steel fibers to concrete has long been known to transition a relatively brittle material to a relatively ductile one. That transition is made possible by a number of well known toughening mechanisms including, fiber-matrix debonding and pull-out, additional matrix cracking, as well as fiber bending and fracture. In the work here, we seek to measure these different energy dissipation mechanisms through the analysis of 3D microstructural images. Reinforced and unreinforced flexure specimens of an ultra high performance concrete were scanned using an x-ray computed tomography (CT) imaging system that allowed quantitative measurement and characterization of internal features. The x-ray CT imaging was done in conjunction with three point bending tests of notched specimens. Unreinforced specimens were used to measure specific fracture energy in a way that accounts for the irregular shape of the fracture surface. For fiber-reinforced specimens, 3D digital image analysis techniques were used to measure fiber volume fraction, as well as the orientation of each individual fiber. In post-fracture scans, the total amount of internal cracking was measured, as was the degree of fiber pullout relative to undamaged specimens. Measurements show that with a nominal steel fiber volume fraction between 3.5 and 4.0%, there is a hundred-fold increase in energy dissipated. Through quantitative analysis of the tomographic images, we could account for roughly 90% of the net work of load. The analysis shows that roughly half of the internal energy dissipation comes from matrix cracking, including the crack branching and multiple crack systems facilitated by the fibers, while the remaining energy dissipation is due to fiber pull-out and bridging. The measurements should allow us to tune fracture and damage models in a way that incorporates the physical structure of the material.
Suggested Audiences: College
Last Modified: March 20, 2014 at 3:15 PM