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.

Study on turbulent flow in wave wall tube heat exchanger

The traditional straight wall tube heat exchanger has low heat exchange efficiency, in order to solve this problem, the turbulent flow in wave wall tube heat exchanger was studied by numerical simulation. It is found that the unique corrugated structure of the heat exchange tube in the wave wall tube heat exchanger can improve the flow state of the fluid in the heat exchanger. The average pressure drop of heat exchanger gradually increases with the increase of Reynolds number Re. Under the same conditions, the average pressure drop of wave wall tube heat exchanger is lower than that of straight wall tube heat exchanger. The improvement of heat exchange performance of heat exchanger can not be realized only by increasing the inlet flow of heat exchanger. The wave wall tube heat exchanger can strengthen the heat exchange of the fluid in the heat exchanger.

Microstructure and Mechanical Properties of Additively Manufactured Ni-Al Bronze Parts Using Cold Metal Transfer Process

In this paper, the microstructure and mechanical properties of the SG-CuAl8Ni6 Ni-Al bronze straight wall were studied, which was fabricated by the cold metal transfer (CMT) arc additive manufacturing technology. This Ni-Al bronze cladding layer of SG-CuAl8Ni6 is composed mainly of α-Cu, residual β phase, rich Pb phase and κ phase. The microstructure of this multilayer single-channel Ni-Al bronze straight wall circulating presents the overall periodic law, which changes from fine cellular crystals, columnar crystals to dendritic crystals with the increase of the distance from the substrate. The Vickers hardness value of the Ni-Al bronze straight wall decreases with the distance of substrate are between 155 and 185 HV0.5. The microhardness and elastic modulus of the Ni-Al bronze specimen are 1.57 times and 1.99 times higher than these of the brass matrix, respectively. The ultimate tensile strength (UTS) of the straight wall in the welding direction and 45° downward-sloping is greater than that of about 550 MPa in the stacking direction, and the elongation value in the welding direction is the highest. With the increase in interlayer temperature, the grain size increased gradually, and the tensile strength decreases slightly.

Study on the Collapse Process of Cavitation Bubbles Including Heat Transfer by Lattice Boltzmann Method

In this study, an improved double distribution function based on the lattice Boltzmann method (LBM) is applied to simulate the evolution of non-isothermal cavitation. The density field and the velocity field are solved by pseudo-potential LBM with multiple relaxation time (MRT), while the temperature field is solved by thermal LBM-MRT. First, the proposed LBM model is verified by the Rayleigh–Plesset equation and D2 (the square of the droplet diameter) law for droplet evaporation. The results show that the simulation by the LBM model is identical to the corresponding analytical solution. Then, the proposed LBM model is applied to study the cavitation bubble growth and collapse in three typical boundaries, namely, an infinite domain, a straight wall and a convex wall. For the case of an infinite domain, the proposed model successfully reproduces the process from the expansion to compression of the cavitation bubble, and an obvious temperature gradient exists at the surface of the bubble. When the bubble collapses near a straight wall, there is no second collapse if the distance between the wall and the bubble is relatively long, and the temperature inside the bubble increases as the distance increases. When the bubble is close to the convex wall, the lower edge of the bubble evolves into a sharp corner during the shrinkage stage. Overall, the present study shows that this improved LBM model can accurately predict the cavitation bubble collapse including heat transfer. Moreover, the interaction between density and temperature fields is included in the LBM model for the first time.

Numerical investigation of plastic flow and residual stresses generated in hydroformed tubes

During tube hydroforming process, the friction conditions between the tube and the die have a great importance on the material plastic flow and the distribution of residual stresses of the final component. Indeed, a three-dimensional finite element model of a tube hydroforming process in the case of square section die has been performed, using dynamic and static approaches, to study the effect of the friction conditions on both plastic flow and residual stresses induced by the process. First, a comparative study between numerical and experimental results has been carried out to validate the finite element model. After that, various coefficients of friction were considered to study their effect on the thinning phenomenon and the residual stresses distribution. Different points have been retained from this study. The thinning is located in the transition zone cited between the straight wall and the corner zones of hydroformed tube due to the die–tube contact conditions changes during the process. In addition, it is clear that both die–tube friction conditions and the tube bending effects, which occurs respectively in the tube straight wall and corner zones, are the principal causes of the obtained residual stresses distribution along the tube cross-section.

A Viscous, Two-Layer Western Boundary Current Structure Function

The classic oceanographic problem of a 1.5-layer western boundary current evolving along a straight wall is considered. Here, building upon the previous work of Charney, Huang and Kamenkovich, we have derived, solved and validated a new numerical formulation for accounting for viscous effects in such systems. The numerical formulation is validated against rotating table experimental results.