P. Gandhi

Crack initiation and growth behaviour of circumferentially cracked pipes under cyclic and monotonic loading

Abstract Studies have been carried out on carbon steel pipes to demonstrate the leak before break design criterion and validate the analytical procedures. Fatigue crack initiation, fatigue crack growth rate and fracture resistance behaviour of the pipes have been experimentally and analytically evaluated. The tests have been carried out on pipes of outer diameter 219 and 15.1 mm wall thickness having a part through notch in the circumferential direction. The aspect ratios (2 c / a ) of the notches were 56, 28 and 18. Comparing the analytical and experimental results has validated analytical procedures. It has been observed that the analytical and experimental results compare well. The fatigue crack growth curve (d a /d N ∼Δ K ) obtained from three point bend specimens and pipe tests have been compared with the fatigue crack growth curve in ASME Section XI. The comparison shows that use of the ASME curve in analysis of components will give a conservative result in comparison to the curves obtained from the actual pipe tests. Fracture resistance behaviour of the pipe has been observed to be strongly dependent on the load histories to which the pipe has been subjected.

Studies on Fatigue Life of Typical Welded and Bolted Steel Structural Connections

This paper presents the results of fatigue tests conducted on typical welded and bolted connections made of IS 2062: 2011 steel and conforming to selected Constructional Details categorised in IS 800: 2007. The connection types include: longitudinal and transverse butt welded connections, fillet welded cruciform connections with load-carrying and non-load-carrying welds, and bolted (double cover butt type) connections. The tests were carried out at various values of maximum stress which were decided as a percentage of the yield strength of the base material. The S–N data obtained were compared with the characteristic S–N curves recommended in IS 800: 2007. In the case of transverse butt welded joints, all specimens which were tested at a maximum stress value equal to 65 % of the yield strength of the material and above, and one out of the two specimens tested at a maximum stress value equal to 60 % of the yield strength of the material failed to satisfy the codal provisions. Two out of the three cruciform joints with load-carrying welds tested at a maximum stress value equal to 80 % of the yield strength of the material failed to satisfy the codal provisions. Bolted specimens which were tested at a maximum stress value equal to 60 % of the yield strength of the material and above failed to satisfy the codal provisions.