Dr. Vaidyanathan’s research program utilizes new approaches (such as instrumented nano- and microindentation, in situ diffraction at stress and temperature) to characterize the multi-scale mechanical properties of novel materials (such as shape-memory alloys/composites, bulk metallic glasses). Currently, the following investigations are ongoing:

(1) Simultaneous mechanical loading and diffraction to obtain in situ measurements of internal strains and texture (including residual stress measurements in engineering components): In situ diffraction experiments, performed under externally applied loads, offer an unique opportunity to better understand materials by providing a valuable link between their microscopic and macroscopic deformation behaviors. These experiments are carried out using the neutron source at Los Alamos National Laboratory and synchrotron x-rays at the Advanced Photon Source, Argonne National Laboratory. Additionally, measurements on unloaded samples probe the state of residual stress in engineering components.

(2) New methods for characterization of mechanical properties and residual stresses in materials with nano- and microindentation: Conventional testing methods such as tensile testing cannot be used to obtain mechanical properties at nano- and micro-size scales. The overall load-displacement curves obtained during instrumented indentation are used to extract both local and volume-averaged properties such as Young's modulus, yield strength, strain-hardening exponent, tensile strength and hardness.

(3) Processing and mechanical testing of smart composites (shape-memory and superelastic alloys) for actuator applications: The objective of this study is to develop and characterize smart actuator materials. Hot Isostatic Processing (HIP) was used to fabricate a composite that consisted of stiff TiC particles in a shape-memory NiTi matrix. These smart composites were subjected to uniaxial compressive loading (both monotonic and cyclic) and fatigue-fracture testing. By studying the effect of inexpensive reinforcing particles, a cost-effective alternative is provided while simultaneously tailoring the mechanical properties of these novel smart composites. Additionally, the mechanics of load partitioning in such materials is studied using in situ neutron and synchrotron x-ray diffraction.

Selected Publications

R. Vaidyanathan, M. Dao, G. Ravichandran and S. Suresh, “Study of Mechanical Deformation in Bulk Metallic Glass through Instrumented Indentation”, Acta Materialia 49 (2001) 3781-3789.

R. Vaidyanathan, M.A.M. Bourke and D.C. Dunand, “Texture, Strain and Phase Fraction Measurements During Mechanical Cycling in Superelastic NiTi ”, Met. Mat. Trans A 32A (2001) 777-786.

R. Vaidyanathan, D.C. Dunand, and U. Ramamurty, "Fatigue Crack-Growth in Shape-Memory NiTi and NiTi-TiC Composites", Mat Sci. Eng. A 289[1-2] (2000) 208-216.

R. Vaidyanathan, M.A.M. Bourke and D.C. Dunand, “Phase Fraction, Texture and Strain Evolution in Superelastic NiTi and NiTi-TiC Composites Investigated by Neutron Diffraction”, Acta Materialia 47, 12 (1999) 3353-3366.

R. Vaidyanathan, M.A.M. Bourke and D.C. Dunand, “Analysis of Neutron Diffraction Spectra Acquired in situ During Stress-Induced Transformations in Superelastic NiTi”, J. Appl. Phys 86, 6 (1999) 3020-3029.