Vijay Radhakrishnan

On cyclic stress–strain behaviour and low cycle fatigue life

Abstract In low cycle fatigue of metallic materials, the Manson–Coffin and Basquin relations are considered to be in conjunction with the cyclic stress–strain curve. Design considerations under constant load range or constant total displacement range are discussed based on the above relations.

The relationship between minimum creep rate and rupture time in Cr-Mo steels

The Monkman-Grant equation is widely used to relate the minimum creep rate, εmin,and the rupture time, tr, in creep. However, for materials that exhibit large tertiary creep and limited secondary creep, the above equation has not been found to be valid, and a correction in terms of the rupture strain εr and the strain at the onset of tertiary stage, ε23, has to be incorporated. The relation is given in the form.

Creep deformation behavior and failure diagnostic diagrams of a columnar-grained nickel-based superalloy

Uniaxial creep deformation of a columnar-grained cast Ni-based superalloy has been analyzed in the temperature range of 1035-1315 K. Two-stage heat treatment of the material resulted in an average γ′ particle size of 0.4 µm and inter-particle distance of 0.04 µm. At 1035 K, the alloy showed predominantly primary creep with very low tertiary creep strains. At temperatures above 1035 K, a pseudo-tertiary creep regimen is predominant. Faceted fracture, coarsening of γ′ particles, decohesion of the matrix around the particles, and rafting of the coarsened γ′ particles have been observed as failure modes over the temperature range studied. An analysis is presented to understand creep deformation behavior of the material in the secondary and tertiary creep stages, by expressing them as power functions of time. Failure diagnostic diagrams have also been constructed for the material over the temperature range investigated.

Absent Right Side Iliac Arterial System, an Intraoperative Surprise during Live Related Recipient Renal Transplantation

Introduction. Renal transplantation has become the standard of care for patients with end stage renal disease. We present a rare case of an absent right sided iliac arterial system encountered during recipient renal transplantation. The presence of such vascular anomaly intraoperatively can present a technically challenging situation to the surgeon. Case Presentation. During a routine renal transplantation of a 34-year-old man, we encountered a complete absence of right side iliac arterial system and a prominent branch arising from left hemipelvis and coursing to the right lower limb and the urinary bladder. The artery to the bladder was divided and anastomosed end to end to the donor renal artery. Intraoperatively the renal perfusion and the urine output were good. A posttransplant magnetic resonance angiogram done six weeks later revealed good vascular supply to the kidney and the lower limb. Conclusion. Absent iliac artery on one or both sides is a rare phenomenon. The presence of it during an unanticipated renal transplant surgery can pose a significant technical challenge to the surgeons. We advocate routine assessment of pelvic vasculature before recipient renal transplant surgery so as to avoid a difficult situation like this.

Low cycle fatigue life: Dependence on test mode

Fatigue hardening and softening in materials result in different lives in low cycle fatigue, depending on the test mode. The problem is discussed based on the cyclic stress-strain relation, and a suitable testing mode is suggested for the design of structural parts, which are subjected to either constant load or constant displacement fatigue.

Fracture toughness relation in biaxial loading

The fracture toughness relation (FTR) in biaxial loading of a body containing a slanting crack has been analyzed. A basic requirement for the validity of the FTR is discussed. A criterion based on the energy release rate in each mode is presented and compared with the experimental data.

Creep life prediction of low-alloy steels based on the β-envelope method

The creep life of low-alloy steels has been analyzed based on the β-envelope method. A parameter that compensates both the stress and the time axes is proposed involving the coefficients of the creep strain-time relations.