Date: Thursday, Apr 23rd
Presenter: Professor John A. Nairn, Richardson Chair in Wood Science and Forest Products, Oregon State University
The Material Point Method (MPM) is a particle-based, computational mechanics tool with some advantages over Finite Element Analysis (FEA), particularly in areas of contact physics, explicit crack propagation, and large deformation materials. These advantages make MPM well suited to simulations of cutting because those simulations need to model contact between tool and chip, rubbing forces between tool and remaining material, explicit crack propagation ahead of the tool, and large-deformation, elastic plastic materials. In brief, MPM simulations can initiate and propagate cutting into steady-state chip formation. The simulation output for tool forces can be compared to prior analytical models, which have been modified to work with hardening materials and to account for rubbing forces Recent developments for MPM modelling of contact between a rigid tool and crack surfaces along with improved large-deformation material models now permits simulations into the regime where the tool tip contacts the crack tip. The figure below shows equivalent plastic strain during cutting simulations of an elastic plastic material with (left) or without (right) hardening. As hardening is reduced the tool tip approaches the crack tip eventually entering the touching regime. Comparisons between simulations with simple materials and analytical models have verified the numerical approach. The model can therefore be used for problems with no analytical results such as veneer peeling. Veneer peeling is cutting of hot and wet wood transverse to the grain and uses a pressure bar to guide cutting and limit lathe checking in the peeled veneer. Modelling can help optimize veneer peeling, such as to adjust tool and pressure bar configurations to minimize lathe checking or minimize forces.
Dr. Nairn's research focuses on mechanical properties as engineering materials. He investigates why materials such as wood composites and fiberboards fracture or fail. His other research interests include the study of nanocomposites, the effect of residual heat stresses in composites, and the durability of composites.
Funding from the Richardson chair will allow Dr. Nairn to focus on bringing new areas of composites science and computational mechanics to wood science. He is also interested in developing more environmentally-friendly materials by combining natural fibers such as hemp, flax, or wood fibers with the appropriate matrix to have expanded applications in the construction and automotive industries.
Before his arrival at OSU in 2006, Dr. Nairn was an engineering professor at University of Utah for more than 20 years. He earned his bachelor?s degree in chemistry from Dartmouth College and his doctorate in chemistry from University of California, Berkeley. Dr. Nairn also worked as a staff scientist for the Central Research and Development Department at E. I. duPont de Nemours Co., Inc., in Wilmington, Delaware before moving to Utah in 1986.
Dr. Nairn has written over 120 papers including six book chapters. He is the author of several scientific computer applications that are available for free download on his web site. He has attracted over $4 million is grants and contracts funded by such organizations as the National Science Foundation, the Department of Energy, NASA, Boeing, and the DuPont Company. His awards include a Fulbright Fellowship at the Imperial College in London and a Student?s Choice Award for Teaching at the University of Utah.