Numerical investigation of dimple-texturing on the turning performance of hardened AISI H-13 steel

Forming micro-dimples nearer to the cutting edge on the rack face of the tungsten carbide cutting inserts will positively influence the machinability. However, it is challenging to machine the perfect micro-dimple dimensions by utilizing the available machining techniques. Finite element analysis can be an efficient way to observe the influence of dimple-texture area density, micro-dimple size, and various micro-dimple shapes on cutting inserts' machinability. This paper numerically analyses the impact of micro-dimple-textured cutting inserts in dry machining of AISI H-13 steel using AdvantEdge (virtual machining and finite element analysis software). Micro-dimples are formed on the rack face of tungsten carbide cutting inserts to observe the effect of dimple-textured cutting inserts on machinability compared to non-textured cutting inserts in terms of micro-dimple shape, micro-dimple size, and micro-dimple area density ratio. Their outcomes are analysed in terms of chip-insert contact length, main cutting force, and thrust force. It is observed that micro-dimple textured cutting inserts exhibit minimal main cutting force and thrust force in line with increasing the cutting insert life span. The abrasive wear was reduced in dimple-textured cutting inserts due to minimal contact between the cutting insert and chip developed compared to non-textured cutting inserts.

Size Effect in Plastic Deformation and Failure of Metallic Glasses

Depending on the composition and structure of metallic glasses cells with the dimensions in the range from tenths nanometers to tenths micrometers were observed on the ductile fracture surface. The variation in dimple size was compared with the serrations presented on the loading curve at the nanoindentation of the metallic glasses with different compositions. Higher instantaneous deformation can be connected with simultaneous shearing at more suitable shear band configurations. The cell morphology with the various cell sizes is observed at the failure of the metallic glasses. At the failure of high strength metallic glasses, the cells are formed in short time due to the release of high amount of stored elastic energy. In this case the uniform cell morphology with the cell size of about 20 nm is observed.

Reduction of Friction and Soil Adhesion of Medium Carbon Steel via Hard Coating and Surface Texture

Rapid development of mechanical cultivation demands satisfactory wear performance and lower soil adhesion on the soil-engaging components of terrain machinery. A thick 2Cr13 hard coating was used in conjunction with surface textures in this sector. The results showed that 2Cr13 coating and surface texture decreased the friction coefficient and wear rate enormously. The surface wettability of the coating was reduced by a dimpled-surface texture. The adhesion test suggested that dimples greatly decreased the adhesion force by decreasing the friction component and the decrement increased with the increase of dimple size. The adhesion force increased with the soil moisture and then decreased when exceeding the moisture content threshold.

Effect of Friction Stir Processing on Gas Tungsten Arc-Welded and Friction Stir-Welded 5083-H111 Aluminium Alloy Joints

This paper presents the analysis of the friction stir-processed aluminium alloy 5083-H111 gas tungsten arc-welded and friction stir-welded joints. The comparative analysis was performed on the processed and unprocessed gas tungsten arc-welded and friction stir-welded joints of similar aluminium alloy 5083-H111. The results showed a clear distinction between the friction stir processed joints and unprocessed joints. There is a good correlation observed between the microstructural results and the tensile results. Ultrafine grain sizes of 4.62 μm and 7.177 μm were observed on the microstructure of the friction stir-processed friction stir-welded and gas tungsten arc-welded joints. The ultimate tensile strength for friction stir-welded and gas tungsten arc-welded before friction stir processing was 153.75 and 262.083 MPa, respectively. The ultimate tensile strength for friction stir processed friction stir-welded joint was 303.153 MPa and gas tungsten arc-welded joints one was 249.917 MPa. The microhardness values for the unprocessed friction stir-welded and gas tungsten arc-welded joints were both approximately 87 HV, while those of the friction stir-processed ones were 86.5 and 86 HV, respectively. The application of friction stir processing transformed the gas tungsten arc morphology from brittle to ductile dimples and reduced the ductile dimple size of the unprocessed friction stir-welded joints from the range of 4.90–38.33 μm to 3.35–15.59 μm.

Singular jets during the collapse of drop-impact craters

When a drop impacts on a deep pool at moderate velocity it forms a hemispheric crater which subsequently rebounds to the original free-surface level, often forming Worthington jets, which rise vertically out of the crater centre. Under certain impact conditions the crater collapse forms a dimple at its bottom, which pinches off a bubble and is also known to be associated with the formation of a very fast thin jet. Herein we use two ultra-high-speed video cameras to observe simultaneously the dimple collapse and the speed of the resulting jet. The fastest fine jets are observed at speeds of approximately $50~\text{m}~\text{s}^{-1}$ and emerge when the dimple forms a cylinder which retracts without pinching off a bubble. We also identify what appears to be micro-bubbles at the bottom of this cylinder, which we propose are caused by local cavitation from extensional stress in the flow entering the jet. The radial collapse of the dimple does not follow capillary-inertial power laws nor is its bottom driven by a curvature singularity, as has been proposed in some earlier studies. The fastest jets are produced by pure inertial focusing and emerge at finite dimple size, bypassing the pinch-off singularity. These jets emerge from the liquid contained originally in the drop. Finally, we measure directly the compression of the central bubble following the pinch-off and the subsequent large volume oscillation, which occurs at frequencies slightly above the audible range at approximately 23 kHz.

Anisotropic Behavior of Aluminum Alloy 2024-Graphene Composites at Varying Strain Rates

In fabrication of high strength materials coupled with improved mechanical properties; focus on integration of multifunctional reinforcements are increasing along with novel processing methods. Single layer 2-D material Graphene are among one such novel material with huge aspect ratio, posse’s high strength. But the real challenge is processing and incorporation of these reinforcements with appropriate content in metals or its alloys matrix. Current research work focus to study the anisotropic behavior on addition of pristine Graphene/MWCNT and processing methods like ball milling under constant ball to powder precursor ratio (BPR) of AA 2024 nanocomposites. The extent change in aspect ratio, size of the nanoparticle mixtures during ball milling were analyzed under SEM and Raman spectroscopy. Thus obtained (ball milled) precursors are consolidated through vacuum hot press and hot extruded to get typical flat specimen at optimized processing parameters. XRD analysis, relative density and hardness measurement is done on extruded composites. Thus developed composites are subjected to study the anisotropic behavior at various orientations and strain rates (0.5, 1.0, 1.5 mm/min) using uniaxial tensile testing instrument and corresponding stress strains graphs were obtained. The fracture surfaces were characterized by scanning electron microscope (SEM) and its shows the nucleation of the dimple size are varies with increasing the strain rate and also deeper dimple size were noticed. Negative strain sensitivity were observed for the lower strain rate (0.1 and 0.3 mm/min) and positive strain sensitivity for higher strain rates. Microstructural anisotropy infers that AA2024-Graphene/MWCNT composites are sensitive to strain rate and shear type of failure is observed on increasing the strain rate.

The effect of dimple size on the tribological performances of a laser surface textured palm kernel activated carbon-epoxy composite

Purpose The purpose of this study is to investigate the effect of dimple size on the tribological performances of laser surface-textured palm kernel-activated carbon-epoxy (PKAC-E) composite. Design/methodology/approach A PKAC-E disc 74 mm in diameter was fabricated using the hot compression moulding technique. Five different types of surface contacts were prepared using a CO2 laser surface-texturing machine: a non-textured surface, and surfaces with dimples between 500 and 1,200 μm in diameter. The area density, contact ratio and depth were kept constant. A sliding test was carried out using a ball-on-disc tribometer under boundary lubricated conditions with constant sliding speed, sliding distance and applied load. Findings In general, the results showed that the friction coefficient decreased with an increasing dimple diameter of surface-textured PKAC-E composite. However, the appropriate dimple diameter for maintaining low friction coefficient is proposed in the range of 800 to 1,000 μm. Originality/value This is the first study, to the authors’ knowledge, to investigate the effects of dimple size, which is larger than 500 μm, on the tribological performances of laser surface-textured PKAC-E composite.