Ashok Kumar C



Name            : Ashok  Kumar C.

Designation  : Design Engineer

Qualification: Master of Technology (PEST)


ME Dissertation Project (2005):


“Characteristics of Singular Stress Field around a Crack in a Smart Material”




There is a rapid growth in the use of smart materials, structures and systems in the current day engineering technology due to their advanced and intelligent features. Of the several smart materials used in practice, the shape memory alloys are finding increasing applications. The novel characteristic associated with these materials is that they have the ability to return to their shape even after severe deformation.


One of the most commonly used shape memory alloys with a wide variety of applications is Nitinol. It is an alloy of two materials Nickel (Ni) and Titanium (Ti).  The important mechanical properties, which make it more attractive for structural applications are its ductility, high fatigue life and corrosion resistance. Nitinol possess a peculiar and unique constitutive behavior, which strongly depends on the applied load and operating temperature.  It exhibits typically two elastic moduli when loaded up to failure. It has the ability to remember its original shape even after subjected to severe deformation and restores to its original condition. The basis for its shape memory behavior is that it can easily transform from phase to phase (Austenitic to Martensitic and vice-versa) with little change in volume. The load dependent phase change behavior of Nitinol gives rise to a characteristic stress field around a crack in it. The material very close to crack tip shows a martensitic behavior due to high stress magnitudes encountered where as the other region away from the crack will be under austenitic condition. Since the constitutive behavior strongly depends on the phase conditions the singular stress field around the crack in this case will be very much different from the one seen in conventional monolithic materials.


This work presents the results of an extensive investigation carried out to study the singular stress field behavior near the tip of a central crack in a square plate subjected to uniform in plane traction. The traction applied was large enough to cause plastic deformation at crack tip. The fracture parameter J-Integral for an elastic-plastic behavior was evaluated. A parametric study was carried out by varying the crack length and keeping the applied traction constant. 


Some of the important results of the investigation:






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