Muhammad Hasibul Hasan

Single-Degree-of-Freedom Based Pressure-Impulse Diagrams for Blast Damage Assessment

Pressure-impulse (P-I) diagrams, which relates damage with both impulse and pressure, are widely used in the design and damage assessment of structural elements under blast loading. Among many methods of deriving P-I diagrams, single degree of freedom (SDOF) models are widely used to develop P-I diagrams for damage assessment of structural members exposed to blast loading. The popularity of the SDOF method in structural response calculation in its simplicity and cost-effective approach that requires limited input data and less computational effort. The SDOF model gives reasonably good results if the response mode shape is representative of the real behaviour. Pressure-impulse diagrams based on SDOF models are derived based on idealised structural resistance functions and the effect of few of the parameters related to structural response and blast loading are ignored. Effects of idealisation of resistance function, inclusion of damping and load rise time on P-I diagrams constructed from SDOF models have been investigated in this study. In idealisation of load, the negative phase of the blast pressure pulse is ignored in SDOF analysis. The effect of this simplification has also been explored. Matrix Laboratory (MATLAB) codes were developed for response calculation of the SDOF system and for repeated analyses of the SDOF models to construct the P-I diagrams. Resistance functions were found to have significant effect on the P-I diagrams were observed. Inclusion of negative phase was found to have notable impact of the shape of P-I diagrams in the dynamic zone.

Determination of Fracture Toughness Values of Two Ni – Base Super Alloys for High Temperature Applications

Nickel-base Alloys 617 and 276 have been considered as structural material for turbine blades and nuclear hydrogen generation. The structural integrity of an engineering component is known to be influenced by the presence of surface irregularities such as cracks in the material. Hence Elastic plastic fracture mechanics base single compact tension specimen has been used to determine J1C value for ductile crack growth behavior of austenitic Alloy 617 and 276 as a function of temperature. Alloy 617 showed fairly constant resistance to fracture from ambient temperature up to 500°C for duplicate testing satisfying EPFM criteria. Whereas the J1C values of alloy 276 were gradually reduced with increasing temperature, the reduction being more pronounced from ambient temperature to 100°C. Efforts have been made to calculate the values of K1C and crack tip opening displacement for these alloys. Finally, fracture morphology in the loading and unloading sequences has been analyzed by SEM.