About Prof. Ramarathnam Narasimhan

RN's Career Bio-Sketch 

RN's Salient Academic Contributions 

Ramarathnam Narasimhan is a Professor of Mechanical Engineering and J.C. Bose National Fellow at the Indian Institute of Science, Bangalore. Over the course of his academic career, he has made important contributions to the fields of Solid Mechanics, Fracture Mechanics and Mechanics of Materials. His research interests are focused on nonlinear and dynamic fracture, mechanics of indentation, and deformation and fracture behavior of bulk metallic glasses, HCP metals and shape memory alloys (SMAs).

In an early work, he studied elastic-plastic crack tip fields and clearly pinpointed for the first time the importance of three-dimensional effects near a crack tip. His simulations have delineated the competition between micro-void coalescence and shear localization near a crack tip under mixed-mode (combined tension-shear) loading. He demonstrated that ductile fracture processes are retarded at high loading rates due to acute loss of stress triaxiality near a crack tip and proposed a new dynamic crack initiation model. This holds the key for understanding phenomena such as increased fracture toughness of engineering materials at high strain rates and paves the way for developing fracture resistant materials under impact and shock loading.

Professor Narasimhan has established the structure of crack tip fields in ductile FCC single crystals for different lattice orientations and constraint levels. A notable discovery is the occurrence of lattice rotation bands near a crack tip through detailed EBSD maps, which were predicted by Professor J.R. Rice more than three decades back, but has never been experimentally verified previously. He studied in detail, using simulations and experiments, failure of magnesium alloys (HCP) which deform plastically by a combination of crystallographic slip and twinning. An important contribution of his work is to establish the role of twinning on crack growth, dissipation and toughening. Thus, his studies have provided new insights on the mechanics of fracture of FCC and HCP alloys from the perspective of individual grains. They can guide the choice of texture and microstructure of polycrystalline alloys which will display higher fracture resistance. His ongoing research on fracture of SMAs has shed light on the roles of plasticity, phase transformation and detwinning on crack initiation and toughness. He is also currently working on mixed-mode fracture of TWIP (austenitic) steels using experiments and crystal plasticity simulations.

Bulk metallic glasses (BMGs) are novel materials with tremendous potential for high technological applications, which however is impeded by their poor ductility and toughness. Professor Narasimhan’s research has focused on these two important issues. He has studied the role of several factors such as pressure sensitive yielding, Poisson’s ratio and mode-mixity on the fracture response of BMGs. He showed through careful experiments that ductile BMGs fracture by a fluid meniscus instability mechanism occurring inside a dominant shear band at a notch tip. Experimental studies have indicated that an intriguing pattern of nano-corrugations form on the fracture surface of brittle bulk metallic glasses. Professor Narasimhan’s simulations have demonstrated that this is caused by spontaneous nucleation of multiple cavities which coalesce via dynamic crack growth along curved shear bands. Further, his studies on tensile response of BMG composites have shown that highly strain hardening elongated dendrites would make them ductile without any penalty on the strength. These results provide design guidelines for strong yet ductile BMG composites.

Professor Narasimhan’s work has revealed several interesting aspects about the mechanics of fracture of thin hard films bonded to soft substrates during nano-indentation. The transition from contact-dominant behavior to that governed by flexure of the film on a plastically deforming substrate was clearly delineated from his numerical simulations. He investigated the stability of crack growth in the coatings under contact loads and proposed a method for interpreting nano-indentation load-displacement records to deduce the fracture energy of the coatings. In an important contribution, he developed a modified expanding cavity model (ECM) which can explain the high ratios of hardness to yield strength exhibited by pressure sensitive plastic solids such as polymers and amorphous metals during indentation. Recently, he has developed an ECM which can be applied to estimate the transformation stress in shape memory alloys.

Tubular hydroforming is being increasingly used in automotive applications in order to achieve weight reduction, reduced part count and cost. From a combination of experiments, simulations and theory, Professor Narasimhan studied the mechanics of tubular hydroforming and showed that the non-proportional strain paths experienced by the tubes can have a profound effect on the forming limit diagram associated with failure of the tubes by bulging and localized necking.

He has collaborated quite extensively with the industry through sponsored projects. His work on Al and Mg alloys and tubular hydroforming was supported by GM R&D. He developed a constitutive theory and numerical algorithm for modeling the behavior of ice in the high strain rate regime and to simulate the effect of ice impact on engine blades for Honeywell Aerospace. He established an experimental procedure for testing the fatigue and fracture behavior of steel-belted radial tyres for J.K.Tyres Limited.

Professor Narasimhan has published more than one hundred and twenty articles in refereed international journals and has guided more than seventy-five doctoral and Masters (research and course) students. His students have gone on to excel both in academia and industry, which is a testimony to his mentorship skills. He has been an inspiring teacher and has taught courses on Solid Mechanics, Fracture Mechanics and Finite Element Methods over last three decades for undergraduate and graduate students at IIT, Bombay, IISc, NUS, Singapore, and Caltech, USA, as well as engineers from the industry, research laboratories and college teachers. He has served as Chairman of Engineering Sciences Research Council of CSIR (2015-2024) and the Program Advisory Committee for Mechanical Engineering of Department of Science and Technology (2012-2015), which evaluate and award research projects. He was also Convener of Sectional Committee on Engineering and Technology for election of fellows (2010-2012) and member of council (2018-2020) of the Indian National Science Academy. He has served as a member of academic councils of engineering institutions like Anna University, Chennai, IIT, Indore and VIT, Vellore, and has helped in framing their course programs and curricula.