
Speaker:

Joseph E. Bishop 

Sandia National Laboratories, USA 
Date:

Monday, July 3, 2017 
Place:

USI Lugano Campus, room SI003, Informatics building (Via G. Buffi 13) 
Time:

10:3011:30 


Abstract:

Part 1: Two fundamental sources of error and uncertainty in macroscale solidmechanics modeling are (1) the use of an approximate material model that represents in a mean sense the complex nonlinear processes occurring at the microscale, and (2) the use of homogenization theory with implicit approximations such as a separationofscales and the existence of a welldefined representative volume element. Macroscopic material models are typically in error when exercised outside of the calibration regime, and the assumptions in homogenization theory can be violated for additivelymanufactured (AM) metallic structures. In order to quantify these errors and uncertainties for solid mechanics, we adopt a posteriori modelform errorestimation techniques. A simple constitutive model is maintained at the macroscale, such as isotropic elasticity or von Mises plasticity, and the errors in engineering quantities of interest are assessed in a postprocessing step using a localization process and error bounds. Also, for a given loading scenario, the apparent macroscale properties can be adapted to minimize the goaloriented error and uncertainty.
Part 2: For geometrically complex parts and systems, the time required to develop an analysis capable finite element mesh can still take days to months to develop. Advanced tetrahedral meshing tools can alleviate this burden, but the development of robust and efficient tetrahedral finiteelement formulations for applications in largedeformation solidmechanics is still an active area of research. The recent development of general polyhedral formulations for solid mechanics offers new discretization opportunities. One approach is to use an existing tetrahedral mesh, but then subdivide each tetrahedron using partial rectification to obtain a polyhedral mesh. Two types of polyhedra are formed: (1) an aggregation of subtetrahedra attached to the original nodes, and (2) a polyhedron with 12 vertices and 8 faces. Several approaches may then be used to define the shape functions (e.g. using harmonic or maximum entropy barycentric coordinates) and quadrature schemes for the new polyhedra in order to obtain a consistent and stable finite element formulation.


Biography:

Joe Bishop received his Ph.D. in Aerospace Engineering from Texas A&M University in 1996. His graduate research was in the general areas of the mechanics of composite materials and the mechanisms and mechanics of material damping. From 1997 to 2004 he worked in the Synthesis & Analysis Department of the Powertrain Division of General Motors Corporation, performing thermalstructural analysis of internal combustion engines with a focus on predicting highcycle fatigue performance of the base engine. He joined Sandia National Laboratories in 2004 in the Engineering Sciences Center. He has worked on diverse research topics such as impact and penetration, pervasive fracture and fragmentation modeling, polyhedral finite elements, geologic CO2 sequestration, and metaladditive manufacturing. His current research interests include multiscale modeling in support of metaladditive manufacturing, experimental methods and computational techniques for determining residualstress fields, polyhedral finite element formulations and applications, modelform error estimation techniques in finiteelement analysis, meshfree technologies for shockphysics applications, and secondgeneration wavelets.




Faculty of Informatics
Università della Svizzera italiana
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