Analysis of Adiabatic Shearing Failure Mechanism for Aluminum Matrix Composites Based on Experimental and Numerical Simulation

Adiabatic shear behavior and the corresponding mechanism of TiB2/Al composites were researched by split Hopkinson pressure bar （SHPB）.Results show that the flow stresses of the TiB2/Al composites exhibit softening tendency with the increasing of strain rates. All the composites fail in splitting and cutting with a 45 degree, and the phase transformed bands of molten aluminum are found on the adiabatic shear layers. The deformation behavior and shear localization of the TiB2/Al composites specimens were simulated by finite element code MSC.Marc. The Johnson-Cook model was used to describe the thermo-viscoplastic response of the specimen material. There was unanimous between the numerical result and the experimental result on the location of the adiabatic shear band. From the numerical simulation and experiment, it was concluded that the instantaneous failure of the composite was ascribed due to the local low strength area where the formation of adiabatic shear band was, and the stress condition had significant effect on the initiation and propagation of adiabatic shear band （ASB）.

BOP shear force evaluation under complex scenarios

As the“throat”of the drilling well control system,ram blowout preventers(BOPs)can effectively prevent blowout accidents.However,the ram shear mechanism under complex working conditions is unclear,and it is difficult to evaluate the ram BOP shear force,leading to frequent shear failure accidents in oilfields.Aiming at the above problems,this paper takes the double-V ram BOP as the research object,and integrates the methods of theoretical analysis,simulation modeling,and test verification to analyze the shear force in the pipe shear process under both static and moving conditions.A ram BOP shear force evaluation method is proposed based on equivalent stress.Finally,by comparing with calculation data and experimental data,the error between them is less than 5%,demonstrating the applicability and effectiveness of the proposed method.The research results can provide a theoretical basis for oilfield operations of ram BOPs.

Pulsatile blood flow in large arteries:comparative study of Burton's and McDonald's models

To get a clear picture of the pulsatile nature of blood flow and its role in the pathogenesis of atherosclerosis, a comparative study of blood flow in large arteries is carried out using the two widely used models, McDonald＇s and Burton＇s models, for the pressure gradient. For both models, the blood velocity in the lumen is obtained analytically. Elaborate investigations on the wall shear stress （WSS） and oscillatory shear index （OSI） are carried out. The results are in good agreement with the available data in the literature. The superiority of McDonald＇s model in capturing the pulsatile nature of blood flow, especially the OSI, is highlighted. The present investigation supports the hypothesis that not only WSS but also OSI are the essential features determining the pathogenesis of atherosclerosis. Finally, by reviewing the limitations of the present investigation, the possibility of improvement is explored.

Pressure shear assisted extraction of polysaccharide from Auricularia auricula and its biological activities

In this paper,using to the comprehensive scoring method,pressure shear assisted extraction was used to prepare polysaccharide from Auricularia auricula(PS-AAP)by orthogonal test to optimize the extraction.The highest comprehensive score(90.70)was obtained under 1:70 g/mL solid-liquid ratio,110°C reaction temperature,60 min reaction time and 1.0 MPa reaction pressure.Compared to AAP by water bath(WB-AAP),PS-AAP led to a higher extraction efficiency and decreased the relative molecular weight.In addition,infrared spectrum(FT-IR)analysis showed that pressure shear assisted did not change the polysaccharide structure.Scanning electron microscope(SEM)showed that PS-AAP was smaller and more broken by pressure shear assisted.Furthermore,the ratio of glucose to mannose in PS-AAP was relatively higher than WB-AAP,which also proved that PS-AAP had certain antioxidant and hypoglycemic activities.Compared with WB-AAP,the inhibitionα-glucosidase andα-amylase activity of PS-AAP increased by 11.37%and 24.43%respectively.These results revealed that PS-AAP has the poten-tial value of being a antioxidant and hypoglycemic agent.

A numerical study of violent sloshing problems with modified MPS method

A numerical study on violent liquid sloshing phenomenon in a partially filled rectangular container is carried out by using moving particle semi-implicit（MPS） method. The present study deals with the implementation of five modifications all together over the original MPS method. The modifications include improved source terms for pressure Poisson equation, special approximation technique for the representation of gradient differential operator, collective action of mixed free surface particle identification boundary conditions, effecting Neumann boundary condition on solving the PPE and fixing judiciously the parting distance among particles to prevent collision. The suitability of the kernel function used in the original MPS method along with these five modifications is investigated for violent sloshing problems. The present model ensures a good agreement between numerical results with the existing experimental observations. The model is successfully applied to a partially filled tank undergoing horizontal sinusoidal excitation to compute the sloshing wave amplitudes and pressure on tank walls. The assessment of dynamic behaviour manifested in terms of base shear, overturning moment and impact pressure load exerted on tank ceiling induced by violent sloshing motion using MPS method is not reported in the open literature and has been efficiently carried out in the present study.