S. Vishnuvardhan

Evaluation of Cyclic Hardening Parameters for Type 304LN Stainless Steel

Engineering components are often subjected to cyclic load excursions beyond elastic limit and hence cyclic plastic deformation of engineering materials becomes inevitable. Since the resultant elastic-plastic stress-strain response of the material plays a pivotal role in analysis, design and failure of the component, it becomes important to understand the cyclic plastic deformation behaviour of engineering materials. Also, cyclic hardening parameters are required in the design of structural components subjected to large plastic deformation. Constitutive equations were proposed by Prager, Armstrong and Frederick, Chaboche, and Ohno-Wang based on the stabilized strain-controlled hysteresis curve to evaluate the hardening parameters. In the present study, cyclic hardening parameters for SA 312 Type 304LN stainless steel have been determined based on the results of constant amplitude strain-controlled fatigue tests carried out earlier at CSIR-SERC under five different strain amplitude values, viz, 0.20%, 0.35%, 0.65%, 0.80% and 0.95%. It is observed that in isotropic hardening, the values of Q decreased with increase in strain amplitude. In kinematic hardening, the values of C1and γ1 are constant for all values of strain amplitude.

Monotonic Fracture Studies on Bi-metallic Pipe Weld Joints Having Circumferential Through-Wall Crack

Bi-metallic welded joints are necessary in pressurized and boiling water reactors where heavy section low alloy carbon steel components are connected to stainless steel primary piping systems. The behaviour of such bi-metallic weld joints is very difficult to understand, and very limited experimental data are available in the literature on the fracture behaviour of such joints. It is essential to develop fracture assessment methodologies for these joints and validate them experimentally to ensure safe operation of power plants. In this background, fracture studies were carried out under monotonic bending on seven numbers of bi-metallic pipe weld joints of 324 mm nominal outer diameter having circumferential through-wall crack. The specimens were made of SA 508 Gr.3 Cl-1 low alloy steel (ferritic) pipe on one half and SA312 Type 304LN stainless steel (austenitic) pipe on the other half. The initial through thickness notch was located in the different regions of the weld joints such as weld centre, buttering, heat-affected zones and base metals (low alloys steel and stainless steel). Initial notch angle was either 60° or 90°. Prior to the fracture tests, fatigue pre-cracking was carried out to create sharp crack front. Subsequently, fracture tests were conducted under four-point bending and displacement control. The collapse load of the weld joint having crack in the buttering layer is 12% less compared to that having crack in the heat-affected zone. Increase in the crack angle present in the heat-affected zone from 60° to 90° reduced the collapse load of the weld joint by 19%.

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.

Is GFRP Rebar a Potential Replacement for Steel Reinforcement in Concrete Structures

The use of Glass Fibre Reinforced Plastic (GFRP) rebars as a potential replacement for steel reinforcement has raised quite a bit of controversy among the professionals and engineers engaged in the construction industry. Divergent views have been opined by the professionals for its usage in civil engineering structures. Even though, the GFRP rebar has some advantages with regard to corrosion, its usage in the construction industry is still a big question mark due to its low modulus of elasticity and serviceability aspects towards construction of structural elements. In this background, experimental investigations have been taken up at the CSIR—Structural Engineering Research Centre, Chennai to study the static and fatigue behavior of concrete beams reinforced with GFRP and Thermo Mechanically Treated (TMT) bars. Concrete beams with GFRP bars of dimensions 100 mm × 200 mm × 1500 mm have been subjected to static monotonic loading to study the flexural behaviour and companion concrete beams of same dimensions with TMT bars have also been investigated. The investigations have revealed that the concrete beams with GFRP bars resulted in unacceptable deflections and crack widths, with regard to serviceability, compared to the companion beams with TMT bars of same amount of area of reinforcement. The fatigue studies conducted on concrete beams, at four different load ranges, with GFRP bars were also not encouraging. This paper presents the details of experimental investigations and the results.