A new numerical simulation model for high pressure squeezing moulding

High pressure squeeze is the most popular moulding process applied in modern moulding machines.Because of the unique characters of moulding sand and nonlinearity of squeezing process,the mechanical model is of key importance for computer simulation.Drucker-Prager/Cap is a typical soil mechanical theory model and it was used to simulate the squeezing process in this study,while ABAQUS software is used to simulate dynamic stress/strain evolution during the process.The simulation agrees well with the experimental results.We conclude that Drucker-Prager/Cap is an appropriate model for the squeezing compaction of moulding sand,and that the associated nonlinearity can be solved well with ABAQUS software.

3D numerical simulation of high pressure squeezing process with revised Drucker-Prager/Cap model

In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.

Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China,the in-situ stress field in deep formations is complex.When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field,tunnels will suffer serious asymmetric deformation.There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness.This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve(GSC)and ground loosening curve(GLC).Then,based on the convergence confinement theory,the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures.In addition,this method can provide the clear support time and support stiffness of the second layer of initial support.The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China.Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field.Field applications showed that the secondary lining could be constructed properly.

Polyaxial strength criterion and closed-form solution for squeezing rock conditions

In this paper,a nonlinear strength criterion is proposed using the average of intermediate(σ2)and minor(σ3)principal stresses in place of σ3 in Ramamurthy(1994)’s strength criterion.The proposed criterion has the main advantages of negligible variation of strength parameters with confining stress and ability to link with conventional strength parameters.Additionally,a new closed-form solution based on the proposed criterion is derived and validated for Chhibro Khodri tunnel.Further,analytical solutions including Singh’s elastoplastic theory,Scussel’s approach,and closed-form solutions based on conventional and modified Ramamurthy(2007)criteria are compared with the results of proposed approach.It is shown that the in situ squeezing pressure predictions made by the proposed approach are more accurate.Also,a parametric study of the present analytical solution is carried out,which displays explicit dependency of tunnel stability on internal support pressure and tunnel depth.The influence of tunnel geometry is observed to be dependent on the applied support pressure.

Effect of applied pressure and ultrasonic vibration on microstructure and microhardness of Al-5.0Cu alloy

The squeeze pressure field and power ultrasonic field were applied during the conventional casting process of Al-5.0Cu alloy simultaneously. The effects of individual squeeze pressure or power ultrasonic and their coupling on the microstructures and microhardness of Al-5.0Cu alloy were studied by optical microscopy, scanning electron microscopy, image analysis and micro Vickers hardness test. The results show that compared with the conventional casting, refined microstructures, homogeneous distribution of α（Al） and θ（Al2Cu） and improved microhardness can be obtained when squeeze pressure or power ultrasonic is applied individually. For the case of combined fields, both the treated region and the improvement of microstructure and properties can be enhanced.

Effect of zirconium on microstructures and mechanical properties of squeeze cast Al-5.0Cu-0.4Mn-0.1Ti-0.1RE alloy

Al–5.0Cu–0.4Mn alloys with different Zr additions have been prepared by direct squeeze casting.The effects of Zr on microstructures and mechanical properties of the as-cast and T6 heat-treated alloys were investigated by tensile test,optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the optimal tensile property of the as-cast alloy occurs at the Zr content of 0.15%(mass fraction)due to the"Zr poisoning"action and the appearance of bulky primary Al_3Zr,which decreases the grain refinement strengthening effect of the as-cast alloy.The peak values of ultimate tensile strength and yield strength of the T6 alloy occur at the Zr content of 0.25%,and that of the elongation occurs at Zr content of 0.05%.This is mainly attributed to the strengthening effect of dispersed precipitation of Al_3Zr and??phases.The optimal mechanical properties of T6 heat-treated alloy are the tensile strength of 429 MPa,the yield strength of 327 MPa and the elongation of 18%,respectively when the squeeze pressure is 100 MPa and Zr content is 0.25%.