High-throughput determination of uniaxial creep laws by cantilever bending coupled to digital image correlation

Speaker: Professor Vikram Jayaram, Department of Materials Engineering, Indian Institute of Science, Bangalore, India  (qjayaram@iisc.ac.in)

The century-old technique of bending creep has re-surfaced thanks to our ability to couple position-sensitive strain measurements by image correlation with the varying stress in a bent cantilever. Multiple stress-strain-time histories can be captured in a single test in samples as thin as ~ 1 mm.

This talk covers the evolution of this technique and its application to practical situations of increasing complexity, beginning with classical steady-state creep in “simple” materials, its extension to complex metallurgical and ceramic systems that display tension-compression asymmetry, and to inhomogeneous systems such as weldments and sandwich structures.  Stress, in a creeping beam, evolves with time. Nevertheless, the existence of the so-called invariant or skeletal points, postulated over 60 years ago in complex structures subject to bending, allows effective uniaxial behaviour to be simply recovered from a single experiment.

In addition to high throughput, cantilevers permit small coupons to be extracted from in-service steam turbine boiler tubes for residual life estimation, from additively manufactured alloys for quick correlation of process variables with creep properties and, finally, from titanium alloys containing micro-textured regions which have been implicated in dwell-fatigue failure of aerospace components.

Vikram Jayaram graduated in Natural Sciences from Cambridge in 1978 and obtained his doctorate in Materials Science & Engineering from Stanford. Following postdoctoral research at Lawrence Berkeley Laboratory and University of California, Santa Barbara, he joined the Indian Institute of Science in 1990 where he is presently Honorary Professor at Department of Materials Engineering. He is a fellow of the American Ceramic Society, Indian Institute of Metals and many of the academies of science and engineering in India. He served as chair of the Department of Materials Engg. and later as Dean, Division of Mechanical Sciences. He is a member of the advisory council of many government laboratories and university materials departments, former president of Indian Structural Integrity Society and current Vice-President of Indian Academy of Sciences. His current research interests cover high-temperature testing, fracture, creep, thin films and electron microscopy.