In order to enhance the heat transfer performance of a plate heat exchanger, porous copper fiber sintered sheets (PCFSSs) with a three-dimensional (3D) network structure has been developed. Slim copper fibers are manufactured with a new type of multi-tooth tool. Then, they are pressed and sintered in a designed mold to produce the PCFSSs. In addition, the heat transfer performance and the pressure drop of the plate heat exchanger are investigated experimentally. The results show that copper fibers with a rough surface can be manufactured efficiently. PCFSFs with a 3D network structure can be successfully machined. Moreover, PCFSSs with porosity of 70% nearly quadruple the heat transfer performance and PCFSSs with porosity of 90% are optimum, considering both the heat transfer performance and the pressure drop.
A novel peripheral milling process with an end milling cutter for manufacturing aluminum fibers is proposed. Most of the cutting is done by the peripheral teeth of the cutter and the chips removed by the teeth form aluminum fibers, while the cutter end has little effect on aluminum fibers. The machining principle and the formation mechanism of aluminum fiber cross-section are presented. The feasibility of this new fabrication process is experimentally investigated under different machining conditions. In addition, influences of cutting parameters on the equivalent diameter, the length, and surface morphology of aluminum fibers are analyzed. Experimental results indicate that aluminum fibers can be successfully manufactured by peripheral milling and the productivity can be improved by increasing the rotational speed n. Smaller radial depth of cut a e , larger rotational speed n, and smaller feed speedv f are in favor of obtaining slim aluminum fibers. The length of aluminum fibers is theoretically determined by the axial depth of cut a p and also actually affected by other cutting parameters. Of all the cutting parameters considered in these experiments, the optimum parameters of a e , n, and v f are 0.3 mm, 118 r/min, and 60 mm/min, respectively.
The water jet peening (WJP) technology can induce compressive residual stress (RS) in metal surfaces and, thus, improve the fatigue life of components. In this paper, a mathematical model is proposed for calculating the RS induced by WJP. To validate the proposed mathematical model, experimental and finite element simulation verifications were carried out on Al6061-T6. The distribution of RS along the depth direction, the maximum compressive RS, and the depth of the compressive RS layer were also investigated based on the mathematical model. Results showed that the error of maximum compressive RS between the mathematical model and experiment was within 9% under a jet pressure of 60 MPa, and the error of depth of the compressive RS layer between the mathematical model and experiment was within 13% under a jet diameter of 0.3 mm. Hence, the mathematical model is reliable and accurate. The maximum compressive RS increases with the increase in jet pressure, and the depth of the compressive RS layer approximately linearly increases with the increase in jet diameter.
Abstract Pneumatic shot peening is a widely used surface strengthening method. During the peening process, shots often collide with each other, resulting in large energy loss and small compressive residual stress. In order to achieve the optimum compressive residual stress with as little energy loss as possible, firstly the collision mechanism of shots and the forming and coupling mechanism of the target’s residual stress are revealed, and then pneumatic shot peening is simulated by using DEM-FEM coupling model. Then, the effects of impact angle θ , initial shot velocity v 0 , shot diameter d p , and mass flow rate r m on the percentage η of shots with different ratios of the impact velocity to initial shot velocity v m / v 0 , the energy loss (EL), the energy transferred from shots to the target (ET), the residual energy (ER) and the compressive residual stress (RS) are investigated. The results show that as many random shots successively impact the target, the RS field induced by each shot couples with some adjacent RS fields induced by other shots, so that disperse RS fields are gradually transformed into a continuous RS layer with the compressive RS in the surface and the tensile RS in the subsurface. With the increase of θ and r m and with the decrease of v 0 and d p , the collision probability of shots increases, so EL also increases and η of shots with a large v m / v 0 decreases. While, ET increases with the increase of v 0 and d p , decreases with the increase of r m , and first increases and then decreases with the increase of θ. ET does not entirely determine but greatly affects the compressive RS field. So, the surface compressive RS and the maximum compressive RS first increase and then decrease with the increase of θ and r m , while the two parameters increase with the increase of v 0 and d p . The optimum parameters of shots are θ = 75°, v 0 = 60 m s −1 , d p = 0.25 mm and r m = 2 kg min −1 , in which ET reaches 45%, the surface compressive RS of S 11 and S 33 reach 512 MPa and 510 MPa respectively, and the maximum compressive RS of S 11 and S 33 reach 665 MPa and 746 MPa respectively.
This article reveals the formation mechanism of surface topography and the formation and coupling mechanism of residual stress field (RSF) after abrasive water jet sequential peening (AWJSP) that can sequential peening on the material surface at a certain distance interval, and proposes a mathematical model of surface dimple characteristic verified by simulation results. In addition, the influences of shot velocity v0, shot radius R and the distance between the center of adjacent shots DC on surface topography and RSF were also investigated. Results show the surface dimple forms resulting from the material plastic strain, and the residual stress (RS) is mainly induced by the unrecovered elastic strain resulting from the hindering of plastic strain. Decreasing v0, R or DC can decrease the surface roughness Rt, while increasing v0 and R is beneficial to induce a large and deep compressive RS layer. DC influences the whole distribution of compressive RS layer directly.
Abstract Water jet peening (WJP), a surface modification technique, can use the impact pressure induced by shock waves to introduce compressive residual stress in the surface of metal parts, thereby improving the fatigue life of metal parts, especially has broad application prospects in strengthening the concave surface area of metal parts. The impact pressure of the concave surface is different compared with the flat surface due to the effects of geometrical factors on the shock wave released. In this work, a mathematical model for calculating the peak pressure in the initial contact area of the concave surface is developed, and the effects of geometric factors (opening angle of V surface α and spherical radius R) and WJP parameters (jet velocity v and jet diameter d) on the peak pressure are analyzed by using finite element simulation models of WJP on concave V-shaped surface, concave spherical surface, V-groove surface, spherical groove surface, and spherical groove surface established with the coupled Eulerian–Lagrangian (CEL) algorithm of abaqus. A mechanism of impact pressure evaluation of the concave surface is developed to explain the peak pressure results obtained from finite element models. The results show that the peak pressure is mainly determined by α and v, while d does not affect the peak pressure for a concave V-shaped or V-groove surface. The peak pressure is mainly determined by R, v, and d for a concave spherical or spherical groove surface.
The grinding surfaces of the nickel-based superalloy usually generate tensile residual stress, which may reduce fatigue life of components. In order to transform tensile stress to compressive stress, this research develops a new technology that embeds a heat source inside the workpiece during grinding. The grinding process of Inconel718 is simulated by using COMSOL Multiphysics 5.0, and the distributions of residual stress with and without the added heat source are obtained. In addition, the influence of the density heat source, the length of heat source, the height of heat source and the distance between heat source and grinding zone on the residual stress are studied. The results are as follows: (1) The surface tensile residual stress can be transformed to the residual compressive stress by embedding a heat source in the workpiece. (2) The surface compressive residual stress is most sensitive to the density of heat source. (3) The maximum surface compressive residual stress is obtained by adjusting the density and position parameters of heat source.
In this paper, the theoretical models of the surface topography and residual stress (RS) were proposed, and the abrasive water jet sequential peening (AWJSP) finite element models were established by using ABAQUS. Then, the formation mechanism of the surface topography in multiple passes AWJSP process and the coupling mechanism of RS in a single and multiple passes AWJSP process were analyzed. After that, the influence of the number of shots (i.e. N), the distance between the center of adjacent shots D c , shot velocity v, and shot radius R on the surface topography and residual stress field (RSF) of the target were investigated. Results show that successive dimples were formed by single-pass AWJSP, the RSF formed by the impact of each shot will influence the previous RSF, and that will be coupled with it. In multiple passes AWJSP process, decreasing D c can decrease the surface roughness, the surface smoothness of the target material will gradually become better, and the RSF will also be uniform. Under full coverage condition, the surface roughness R t and mean width of the profile R sm will gradually decrease with the decrease of D c , while the change of D c has little influence on the RSF. Increasing the v can increase R t and R sm , and it is beneficial to induce a large and deep compressive RS layer. Increasing the R can decrease R t , R sm remains unchanged, and it is beneficial to induce a deep compressive RS layer.
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