Droplet Breakup Regime in a Cross-Junction Device with Lateral Obstacles

Numerical simulation using Ansys Fluent code is performed,to investigate droplet generation in cross-junction based VOF method.Droplets of water are generated by the shear stress applied by continuous phase(oil),two configurations of cross-junction are suggested;the first is a simple model no modification is performed at the outer channel,while the second model is characterized by a lateral obstacle.we study the effect of velocity ratio,viscous parameter,interfacial tension,flow condition on droplet size and frequency,the effect of lateral obstacles on droplets generation is also focused and analysed.The numerical simulations showed that the velocity ratio and interfacial tension play a significant role in determining the droplet breakup and non-breakup.On the other side,the increase of flow rate ratio can be effectively used to decrease the droplet size.In addition,droplets produced in cross-junction with lateral obstacles are generally found to be larger than that produced with the first model.Moreover,the frequency of droplet production was increasing by increasing of flow rate ratio.The numerical results show very good agreements with previous numerical and experimental works for the growth of droplet breakup,size and frequency.

Friction welding influence on microstructure,microhardness and hardness behavior of CrNiMo steel(AISI 316)

For joining high Cr,Ni and Mo austenitic stainless steel(AISI 316)by direct drive friction welding(DDFW),with friction weld-ing conditions:rotation speed of 3000 r/min,friction time of 10 s,friction pressure of 130 MPa,forge time of 5 s and forge pressure of 260 MPa.The results of microstructure showed that the temperature at the interface reached 819℃while forge applied between 357-237℃,which subdivided welded joint into four distinct regions of highly plastically deformed zone(HPDZ),thermo-mechanically affected zone(TMAZ),heat affected zone(HAZ)and the base metal,with grain size about 10µm,100µm,90µm and 30µm respectively.These re-gions were created due to dynamic recrystallization(DRX)at the interface and thermo-mechanical deformation with heat diffusion in the neighboring regions.Whereas,high level of microhardness about 300 HV0.1 and hardness roughly 240 Hv10 at the interface due to HPDZ creation while low level of 240 HV0.1 for microhardness and moderately of 205 HV10 for hardness in neighboring regions.

Study of thin Films of Nickel Oxide (NiO) Deposited by the Spray Pyrolysis Method

In this work,thin films of nickel oxide(NiO)were deposited by a simple and inexpensive technique,which is spray pyrolysis on ordinary glass substrates heated to a fixed temperature of500°C,from a solution containing nickel nitrate hexahydrate as a precursor dissolved in distilled water with deferent values of concentrations.The NiO thin films obtained were characterized to determine the structure with X-ray diffraction technique(XRD),the absorption domain(UV-Visible Spectroscopy),and the surface morphology(SEM).The X-ray diffraction patterns confirm the presence of NiO phase with preferential orientation along the(111)direction.The optical gap for nickel oxide calculated with a concentration of0.1M from the measurement of optical absorption is3.6eV,which is quite comparable to the value of the ratio.

Unveiling the Residual Stresses,Local Micromechanical Properties and Crystallographic Texture in a Ti-6Al-4V Weld Joint

In this work,the micromechanical properties,crystallographic texture,welding residual stresses and their evolution after plastic strain were investigated in a Ti-6Al-4V alloy tungsten inert gas weld joint.It was found that the welding process affected the Young modulus and microhardness values in bothαandβphases in the different regions of the weld joint.The highest microhardness and Young modulus values of a phase were recorded in the heat-affected zone,whereas the highest values of these characteristics for theβphase were found in the fusion zone(FZ).The change in the micro mechanical properties was accompanied by a change in the crystallographic texture components of the dominant a phase from(0001)<10-10>and(11-20)<10-10>components in the base material to(10-10)<11-20>and(11-20)<3-302>components in the FZ.The introduction of tensile testing resulted in a continuous stress relaxation and improved the weld joint performances.

Microstructure and Mechanical Behavior in Dissimilar SAF 2205/API X52 Welded Pipes

The welding of a duplex stainless steel SAF 2205 DSS （UNS 31803） and high strength low alloy steel API X52 by shielded metal arc welding process was conducted using two different filler metals, the duplex E2209 and austenitic E309 grade. The microstructures of the dissimilar metal joints have been investigated by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy （EDS） and X-ray diffraction. EDS analysis at the interface X52 weld metal showed an evident gradient variation of Cr and Ni between boundaries of fusion and type II, where the highest hardness value was recorded. Tensile strength and toughness values of the weld metal produced by E309 electrode are slightly higher than those of the weld metal produced by E2209 electrode. Potentiodynamic polarization tests of different regions of the welded joints evaluated in 3.5% NaC1 solution exhibit a high corrosion resistance of both weld metals.

Mechanical and Metallurgical Characterization of HSLA X70Welded Pipeline Steel Subjected to Successive Repairs

The aim of this work is to study the influence of successive weld repairs on the microstructure and the mechanical behavior of the heat-affected zone（HAZ） of an HSLA X70 steel. Detailed microstructural examination combined to grain size measurement showed that beyond the second weld repair, the microstructure of the HAZ undergoes significant change in the grain morphology and grain growth. The results of the X-ray diffraction analyzed using MAUD software indicated an increase in the crystallite size and a decrease in the dislocation density according to the number of weld repair operations. Consequently, a loss of mechanical properties, namely the yield strength and the toughness with the number of weld repairs, was recorded. Beyond the second weld repair operation, the properties of the welded joint do not fulfill the standards applied in piping industry.

Synthesis,microstructure and dielectric properties of Sb-doped multiferroic Bi_(0.8)Ba_(0.2)Fe_(1-x)Sb_(x)O_(3)ceramics

The multiferroic ceramics Bi_(0.8)Ba_(0.2)Fe_(1-x)Sb_(x)O_(3)with x=0,0.01,and 0.02 were synthesized using the solid-phase reaction technique.The samples were sintered at two different temperatures,850℃and 900℃.Scanning electron microscopy revealed the effect of antimony concentration on grain size and formation.The effect of Sb-doping on the crystal structure and ferroelectric properties of these ceramics was investigated using X-ray diffraction,Raman spectroscopy,and dielectric measurements.The dielectric constant was enhanced upon Fe^(3+)substitution by Sb^(3+)without affecting the dielectric loss of the ceramics.The tetragonal distortion of the rhombohedral symmetry of BiFeO_(3)caused by Ba-doping at Bi 3þsite was lifted by Sb-doping at Fe^(3+)site.