Experimental investigation of crossflow characteristics in multi-jets system at small nozzle-to-plate spacing

To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.

Atomistic simulations of the lubricative mechanism of a nano-alkane lubricating film between two layers of Cu-Zn alloy

We describe simulations of lubrication by a hexadecane molecular lubricating film during the shearing process of a Cu-Zn alloy performed using the atomistic method.The results indicate that with increasing Zn contents,the interface slip between the alloy wall and the lubricating film first decreases and then increases,according to variations of the radius distribution function(RDF),while the interface slip reaches its lowest value of 0.12 during the shearing of CuZn30 alloy.We also discuss the relationship between interface roughness and the lubricating film.During film lubrication,the interface's roughness effectively inhibits interfacial slip.For the convex contact model,the presence of the hexadecane lubricating film reduces the interfacial contact pressure from 11.9 GPa to 8.7 GPa and the friction coefficient from 0.81 to 0.52.

Temperature-Dependent SRS Behavior of 316L and Its Constitutive Model

The strain rate sensitivity（SRS）and temperature sensitivity（TS）of 316L austenitic stainless steel were investigated by constant strain rate test（CSRT）and strain rate jump test（SRJT）under four temperatures（293,373,473 and 573 K）and four strain rates（5 ×10^-4/s,1 × 10^-3/s,5 × 10^-3/s and 1 × 10^-2/s）.The results show that temperature sensitivity（TS）indexes at different strain rates are coincidence to be negative,related to temperature softening.On the contrary,SRS indexes change from positive to negative with the increase in temperature associated with dynamic strain aging（DSA）.Moreover,based on the comparison between CSRT and SRJT,SRS and TS indexes obtained by two methods agree well.It proves that the SRJT can describe the SRS and TS phenomenon of 316L efficiently.Furthermore,the effects of tem-perature and strain rate on fracture mechanism were discussed.At last,an improved Johnson-Cook model was proposed to consider the temperature-dependent SRS behavior of 316L.

Microstructure,tensile properties and free bulge formability of Sr-and Y-containing AZ31 alloy sheet produced by twin-roll casting and sequential hot rolling

The effects of Sr and Y on microstructure,tensile property and free bulge formability of AZ31 alloy sheet produced by twin-roll casting and sequential hot rolling were investigated to improve the mechanical properties and formability of the AZ31 alloy.Sr and Y addition can form Al4 Sr,Al2 Y and Al3 Y phases which can impede dislocation movement and promote dynamic recrystallization during the rolling deformation and decrease the lattice resistance to dislocation motion by decreasing Al solubility in the alloy,resulting in finer grains,lower dislocation density and no twinning generating in the twin-roll casting and sequential hot rolling(TRC-HR)AZ31-1.3 Sr-1.0 Y alloy.The maximum stress and elongation of the alloy increase significantly after adding Sr and Y.The average cavity and grain sizes of the TRC-HR AZ31-1.3 Sr-1.0 Y alloy are smaller,resulting in higher elongation in the alloy.The addition of Y and Sr can effectively improve the free bulge formability and the thickness uniform of the alloy.The Al4 Sr,Al2 Y and A13 Y phases can inhibit the grain growth by obstructing dislocation motion or grain boundary slip,resulting in smaller grain size of AZ31-1.3 Sr-1.0 Y alloy bulge parts.