Prediction of Geometric Distortion and Residual Stresses In Hot Rolled and Heat Treated Large Rings Through Finite Element Modeling
During quenching, hot rolled steel rings, especially those with a large outer diameter to wall thickness ratio, distort and develop undesired residual stresses. These phenomena are the result of three major mechanisms: metallurgical, mechanical and thermal. This paper presents the result of a comprehensive study on the heat treatment of rings by modeling via Finite Element Analysis. The simulation is carried out with coupled analysis of heat transfer, deformation mechanics and phase transformations. The material data required for the simulation of distortion during heat treatments, including TTT/CCT phase transformation diagrams, temperature dependent physical and thermophysical properties, as well as temperature and strain rate dependent mechanical properties are calculated by computer models.
A Distortion in Rolled and Heat-Treated Rings
are heat treated (i.e. normalized, quenched and tempered, see Figure 1). Because of this processing, some rings, especially those with a large outer-diameter to wall-thickness ratio, distort and become ovular (out of tolerance). This distortion is not the only problem resulting from this phenomenon. Even if the fi nished rings meet dimensional tolerances and are shipped to the customer, residual stresses resulting from heat treatment may become a problem during subsequent machining, causing additional deformation and distortion. A study on control of distortion and residual stresses in rolled and heat-treated rings is being conducted by the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) in partnership with the Forging Industry Association (FIA/FIERF), Education and Consulting LCC and four forging companies supplying the energy and aerospace industries. Understanding and ultimately solving this problem is a challenging task considering the three triggering mechanisms (thermal, metallurgical and mechanical) that affect the ring during heat treatment and cause the undesired results. In light of the complexity of the problem, most ring-rolling companies approach it with corrective rather than preventive measures. Some manufacture the ring with large tolerances so it can be machined to fi nal dimensions. Others correct the ring distortion by a mechanical method (compression or expansion), which also partially relieves the residual stresses. However, mechanical methods are fairly empirical, and there is a need for a physics-based understanding and methodology to produce rings with minimal distortion at an acceptable cost and lead time.
Dopamine Release is Involved in Antinociceptive Effect of Theophylline
ABSTRACT The methylxanthines, e.g., theophylline, are widely used for the treatment of bronchial asthma. Additionally, a pain relieving effect of theophylline has been reported in patients as well as in experimental animals. The mechanism of this antinociceptive action is not clear. In this study, involvement of dopaminergic system in theophylline-induced antinociception was evaluated using tail flick test model. Swiss albino mice, (either sex, weighing 25–30 g) with base line tail flick latencies (TFL) between 2.0 and 3.5 s, were used. TFL was recorded before and at intervals of 15, 30, 45, and 60 min. after drug treatment. The experimental protocol was duly approved by the Institutional Animal Ethics Committee, All India Institute of Medical Sciences, New Delhi, India. To determine the role of dopaminergic system, the mice were pretreated with either D1 or D2 dopaminergic receptor antagonists SCH 23390 and haloperidol, respectively, prior to treatment with theophylline. Another group of animals received apomorphine along with theophylline. The dose of theophylline used, i.e., 10 mg/kg, intraperitoneally (i.p.), had shown a significant increase in TFLs. The theophylline-induced antinociception, 10 mg/kg, i.p., was reversed by pretreatment with both D1 and D2 dopaminergic receptor antagonists SCH 23390 and haloperidol as well as with apomorphine (1 mg/kg) pretreatment. The results suggest that theophylline-induced antinociception is due to release of dopamine.