SUNMONTUEWEDTHUFRISAT
Events for April 29, 2010
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An Analytically Enriched Finite Element Method for Cohesive Crack Modeling
Thu, Apr 29, 2010 @ 10:00 AM - 11:00 AM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Dr. James V. Cox, Soild Mechanics Department, Sandia National Laboratories, Albuquerque, NM 87185-0346jvcox@sandia.govAbstract:Meaningful computational investigations of many solid mechanics problems require accurate characterization of material behavior through failure. A recent approach to fracture modeling has combined the partition of unity finite element method (PUFEM) with cohesive zone models. Extension of the PUFEM to address crack propagation is often referred to as the extended finite element method (XFEM). In the PUFEM, the displacement field is enriched to improve the local approximation. Most XFEM studies have used simplified enrichment functions (e.g., generalized Heaviside functions) to represent the strong discontinuity but have lacked an analytical basis to represent the displacement gradients in the vicinity of the cohesive crack. As such, the mesh had to be sufficiently fine for the FEM basis functions to capture these gradients.In this study enrichment functions based upon two analytical investigations of the cohesive crack problem are examined. These functions have the potential of representing displacement gradients in the vicinity of the cohesive crack with a relatively coarse mesh and allow the crack to incrementally advance across each element. Key aspects of the corresponding numerical formulation are summarized. Analysis results for simple model problems are presented to evaluate if quasi-static crack propagation can be accurately followed with the proposed formulation. A standard finite element solution with interface elements is used to provide the accurate reference solution, so the model problems are limited to a straight, mode I crack in plane stress. Except for the cohesive zone, the material model for the problems is homogenous, isotropic linear elasticity. The effects of mesh refinement, mesh orientation, and enrichment schemes that enrich a larger region around the cohesive crack are considered in the study. Propagation of the cohesive zone tip and crack tip, time variation of the cohesive zone length, and crack profiles are presented. The analysis results indicate that the enrichment functions based upon the asymptotic solutions can accurately track the cohesive crack propagation independent of mesh orientation. Example problems incorporating enrichment functions for mode II kinematics are also presented. The results yield acceptable crack paths compared with experimental studies. The applicability of the enrichment functions to problems with anisotropy, large strains, and inelasticity is the subject of ongoing studies. Preliminary results for a contrived orthotropic elastic material reflect a decrease in accuracy with increased orthotropy but do not preclude their application to this class of problems
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Preliminary Reconnaissance Report: 12 January 2010 Haiti Earthquake
Thu, Apr 29, 2010 @ 01:00 PM - 02:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Eduardo A. Fierro1), and Cynthia L. Perry2)1) President of BFP Engineers, Inc., Berkeley, California USA2) Vice-President of BFP Engineers, Inc., Berkeley, California USAAbstract: After 240 years, the Enriquillo Plantain Garden Fault ruptured on 12 January 2010 at 4:53PM, resulting in a 7.0 Magnitude (USGS) earthquake in the vicinity of Port-au-Prince, Haiti. The epicenter was located at 18.457°N and 72.533°W and 25 km (15miles) WSW of Port-au-Prince. The earthquake has been a disaster for Haiti; at the time of this writing there are 170,000 confirmed deaths with estimates over 200,000 deaths. The National Palace, Palace of Justice, National Assembly, Supreme Court, Prison Civile de Port-au-Prince, and buildings housing the ministries of finance, education, public works, communication and culture have all been damaged. Power, water, and communications have been disrupted. This report is based on field reconnaissance by Eduardo Fierro. Mr. Fierro was on the ground in Port-au-Prince on Thursday January 14. His photos and observations were made from January 14 to 20, 2010. The primary objective of this initial trip was to observe the performance of building structures, industrial facilities, and infrastructure from a structural engineering perspective. This report documents places and structures that Mr. Fierro personally observed during his visits including Port-au-Prince, Cite Soleil, Petion Ville, Carrefour and other towns en route to Leogane
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
