Research

Ductile and Brittle Fracture of Structural Steel Under Earthquake Loading

Failure in steel structures by fracture occurs in three stages: (1) initiation of a crack by ductile fracture or ultra-low cycle fatigue, (2) propagation of the ductile crack and (3) transition from ductile tearing to brittle cleavage fracture. Computational models have been developed and validated over the past two decades which can predict the initiation of cracks under complex stress states and loading scenarios, including ultra-low cycle fatigue loading characteristic of large earthquakes. As a part of his doctoral research, Dr. Ziccarelli developed and implemented a computational framework to simulate ductile crack propagation using the finite element platform WARP3D. However, a number of key issues in this area remain.

Our group is continuing to investigate in these areas, including a study on brittle cleavage fracture after large-amplitude load cycles, and quantifying the effect of cyclic prestrain on ductile fracture toughness.

Cyclic Local Buckling in Steel Structures

Local buckling is a critical failure mode in steel components which resist earthquake ground motions. Slender steel elements (as measured by their width-to-thickness ratio) are more susceptible to buckling. As a result, the slenderness of elements which are expected to undergo significant inelastic deformation is limited by Table D1.1 in AISC 341. However, it is unclear whether elements satisfying the limits in this table will display consistent, reliable performance.

Our group is performing an analytical study of cyclic local buckling, with the potential to inform more rational and consistent seismic slenderness limits.

Modelling Fatigue Crack Propagation in Marine Hydrokinetic Turbines

Marine hydrokinetic (MHK) turbines are renewable energy devices which are critical in our national effort to increase the share of energy which comes from renewable resources. MHK turbine blades resist loads which vary over time, which can lead to the formation and propagation of fatigue cracks. These cracks, if sufficiently long, can lead to reduced performance and structural failure.

Inspection of MHK turbine blades for fatigue cracking is challenging, due to the harsh marine conditions in which these devices operation. Thus, it is critical that computational tools are developed which can reliably simulate the initiation and propagation of fatigue cracks. We are currently working on developing and testing computational methods which can achieve this goal.