An Investigation Into the Effect of Pre-bending on the Tube Hydro-forging Technology

Tube hydro-forging (THFG) combining with the pre-bending is an advanced method to manufacture the complex cross-sectional tubular component with curved axis. However, the effect of pre-bending on the subsequent THFG, especially on the critical internal pressure required to inhibit wrinkling, has not been clarified yet. Therefore, this paper makes a detailed study on it. At first, based on the energy method, the change rule between the critical internal pressure and the hoop strain was established when pre-bending was considered. Subsequently, the mechanics condition difference between single and double curvature differential segment during THFG was analyzed. Via the plastic theory, the distribution of hoop strain could be obtained. Mainly due to the uneven distribution of thickness and cold work-hardening caused by pre-bending, the maximum hoop strain at the outer straight-wall was greater than that at the inner straight-wall during THFG. Substituting the maximum hoop strain at the outer/inner straight-wall into the change rule, then their mathematical model of the critical internal pressure to restrain the wrinkling could be solved respectively. Finally, the critical internal pressure considering pre-bending was determined by that of outer straight-wall, and its value was always greater than the critical internal pressure without considering pre-bending under the same punch stroke. With the increase of bending radius, the critical internal pressure difference between considering and not considering pre-bending also increases. When the bending radius was 250 mm, the critical internal pressure difference was 33%, while it increased to 74% as the bending radius reduced to 100 mm, all of which were verified by experiment. The effect of friction coefficient on the critical internal pressure was also studied. In conclusion, this work provided a new and more accurate prediction model of critical internal pressure to guide practical production for when existing the pre-bending.

Hot Gas Pressure Forming of Ti-55 High Temperature Titanium Alloy Tubular Component

In this paper, hot gas pressure forming (HGPF) of Ti-55 high temperature titanium alloy was studied. The hot deformation behavior was studied by uniaxial tensile tests at temperatures ranging from 750 to 900 °C with strain rates ranging from 0.001 to 0.05 s−1, and the microstructure evolution during tensile tests was characterized by electron backscatter diffraction. Finite element (FE) simulation of HGPF was carried out to study the effect of axial feeding on thickness distribution. Forming tests were performed to validate this process for Ti-55 alloy. Results show that when the temperature was higher than 750 °C, the elongation was large enough for HGPF of Ti-55 alloy. Dynamic recrystallization (DRX) occurred during the tensile deformation, which could refine the microstructure. The thickness uniformity of the formed part could be improved by increasing feeding length. The maximum thinning ratio decreased from 27.7% to 11.5% with the feeding length increasing from 0 to 20 mm. A qualified Ti-55 alloy component was successfully formed at 850 °C, the microstructure was slightly refined after forming, and the average post-form yield strength and peak strength were increased by 8.7% and 6.9%, respectively. Pre-heat treatment at 950 °C before HGPF could obtain Ti-55 alloy tubular component with bimodal microstructure and further improve the post-form strength.

Efficient Evaluation of Long-Term Response for Design of Components of Offshore Structures

This paper compares two approaches for the estimation of long-term response of wave load effects on offshore structures. These approaches are applied to estimate the extreme value of the cross section interaction ratio of a tubular component of the bracing system of a semisubmersible platform. The tubular component is subjected to axial loads and bending moments due to static loads and wave effects. The iteration ratio in the ultimate limit state is defined by applying design criteria derived from API RP-2A LRFD [6]. The approaches are also applied to estimate the long-term response of a single degree of freedom system due to wave actions. The first approach is based on the proposals of Videiro and Moan [3]. The results of the first approach are compared with a new model of long-term response estimation, based on the up-crossing rate distribution of the response process.

ANALYSIS OF INFLUENCE OF RUTIN AND GRAVITY ACTION ON THE RENAL EXCRETORY FUNCTION

Aim - to analyze the effect of rutin on the renal excretory function in the conditions of normogravity and hypergravity. Materials and methods. 9 series of experiments were conducted, including 4 series with the use of a centrifuge of ultra-short radius. The effect of rutin in the dose of 10 mg/kg on the renal excretory function was studied in normal conditions and in combination with the gravity action 3g. All the animals received 3% water load intragastrically and were placed into exchange cages for 24 hours. We obtained urine samples and determined the amount and the concentration of sodium, potassium and creatinine. Results. It was found that under normal conditions rutin, administered intragastrically in a dose of 10 mg/kg, promotes significant increase in diuresis and saluresis solely due to the inhibition of tubular reabsorption. Rutin in a dose of 10 mg/kg in combination with the gravity action enhances its original diuretic activity by complex influence on tubular and glomerular kidney structures. Rutin alone and rutin in combination with hypergravity stimulates the excretory function of the kidneys similarly to hydrochlorothiazide, but has a shorter latent period. Conclusion. The use of rutin combined with the gravity action contributes to the stimulation of the renal excretory function not only due to the tubular component, but also due to the glomerular one.