• P Biswas

• Quasi-static crack tip ﬁelds in rate-sensitive FCC single crystals

In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip ﬁelds in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modiﬁed boundary layer framework by prescribing the two term $(K −T)$ elastic crack tip ﬁeld as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along $[10\bar{1}]$ direction. Solutions corresponding to different stress intensity rates $\dot{K}$, 𝑇-stress values and strain rate exponents 𝑚 are obtained. The results show that the stress levels ahead of the crack tip increase with $\dot{K}$ which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive 𝑇-stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative 𝑇-stress. Also, negative 𝑇-stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.

• Performance assessment of indigenously developed FBG strain sensors under short-term and long-term loadings

Fibre Bragg Grating (FBG) sensors are the most recent type of fibre optic sensors, which are gaining importance in the field of structural health monitoring of civil infrastructure. These are proven to be more versatile due to their distinct advantages such as high sensitivity, immunity to electromagnetic interference, ease of multiplexing and remote sensing. These are suitable for the short-term and longterm monitoring of the structures. Multiple Fibre Bragg Grating (FBG) sensors can be surface mounted and/or embedded in structures to measure strain, temperature, cracks and vibrations. Use of FBG sensors for real time health monitoring of various civil engineering structures is well-established in western world since last decade, whereas in the Indian context this technology is still in a nascent stage. In this paper, performance assessment of indigenously developed FBG sensors for the application of health monitoring of civil engineering structures by conducting short-term and long-term studies is presented. Brief details of the laboratory studies carried out on indigenously developed FBG sensors are covered in this paper. From the laboratory studies it is found that, these FBG sensors are suitable in health monitoring of civil engineering structures.