Research

Professor Needleman's main research interests are in the computational modeling of deformation and fracture processes in structural materials, in particular metals. Recent and current research areas include: ductile fracture by void nucleation, growth and coalescence; multi-scale modeling of plastic deformation of crystalline solids; modeling of time and rate dependent plastic flow; crack growth in plastically deforming solids; and dynamic crack growth.

Some recent and current research projects include:

		Multi-scale modeling of plastic deformation - modeling of plastic deformation of crystalline solids at a variety of scales using conventional crystal plasticity theory, various recently developed size-dependent gradient crystal plasticity theories and discrete dislocation plasticity. Conventional crystal plasticity theory is applicable for larger scale phenomena while the gradient crystal plasticity theories and discrete dislocation plasticity describe smaller scale phenomena. In some cases, smaller scale theories are used to inform larger scale models but multi-scale frameworks that directly couple models at different scales have also been explored.
click for larger version		Mechanical behavior of polymers - one study involves using 3D transient analyses accounting for finite strains to compare the stress and strain fields that develop in the various Izod specimen geometries used in practice. Other studies include analyses of strain localization in pressurized cylinders and the behavior of polymers in indentation.
click for larger version		Dynamic crack growth -  fast cracks in brittle solids can become supersonic in that their speed of propagation exceeds the shear wave speed of the surrounding material. A crack that starts propagating at a subsonic speed cannot reach the shear wave speed. When a critical condition is met the crack circumvents this limitation by nucleating a daughter crack that is supersonic from the outset which then coalesces with the main crack. An avi movie showing this process is here.
click for larger version		Deformation and fracture of porous solids -  void nucleation, growth and coalescence plays a major role in limiting the lifetime of a wide range of engineering alloys at room temperature and at elevated temperatures.  Accurate modeling of this process is needed to predict the lifetime of engineering components and can play a key role in the development of more failure resistant materials.