Presence Of Dimples Research Articles

Enhanced high-temperature mechanical properties and strengthening mechanisms of chemically prepared nano-TiC reinforced IN738LC via laser powder bed fusion

Fabrication of high-strength nickel-based composites to meet the demanding service requirements in aerospace environments is a significant challenge. This paper introduces the wet chemical method to prepare the nano-TiC reinforced IN738LC. In contrast to the conventional ball milling approach, this method attains superior attachment of nanoparticles. By employing a full-factorial experimental design, the correlation between Laser-powder bed fusion (L-PBF) processing parameters and the porosity, micro-hardness, and high-temperature tensile strength of as-built samples was examined. The results indicate that the optimal processing parameters are a laser power of 225 W, scanning speed of 750 mm/s, and hatch space of 0.09 mm, with a Volumetric energy density (VED) of 111.1 J/mm3. Compared to IN738LC, the chemically prepared TiC-IN738LC exhibits a 45 % increase in room temperature tensile strength (400 MPa) and a 65 % increase in high-temperature tensile strength (120 MPa). Compared with ball-milled TiC-IN738LC, the chemically prepared samples present superior microstructure with more equiaxed grains. The morphological analysis of the tensile samples reveals that the presence of dimples are crucial in enhancing the ductility properties. Furthermore, this study identifies the Orowan strengthening mechanism and the grain refinement strengthening mechanism as the principal mechanisms of reinforcement by nano-ceramics.

Investigation on the effects of deposition strategy on the mechanical characteristics and microstructure of austenitic stainless steel 308LSi manufactured via wire arc additive manufacturing

This study examines the impact of deposition strategy on ASS 308LSi thin-walled structure manufactured via the Wire Arc Additive Manufacturing (WAAM) technique on the microstructural characteristics, tensile strength, microhardness, Charpy impact testing, and fracture morphology of the WAAM 308LSi. The analysis of the microstructure reveals that the deposition strategy promotes transitioning from columnar to equiaxed fine grain structure. The tensile strength results show that specimens with a 45° deposition strategy exhibit lower anisotropy and higher tensile properties compared to those with a 0° deposition strategy, with improvements of 33.1% in the transverse direction and 26.7% in the longitudinal deposition directions, respectively. The microhardness in WAAM SS308LSi demonstrates variations in the bottom, middle, and top regions, with the highest average value observed at a 45° deposition strategy (213.3 ± 6.5 HV, 201.1 ± 10.7 HV, and 191.5 ± 5.2 HV) as well. The impact testing results indicate that the highest absorbed energy occurs at a 45° deposition strategy, with 75 ± 4.2 J and 74 ± 4.0 J for the transverse and longitudinal directions, respectively. The fractures observed during testing exhibit ductile characteristics, with the presence of dimples and particles. This study demonstrates the significant potential of the 45° deposition strategy with the implementation of double-sided substrate deposition, resulting in a refined microstructure, nearly isotropic behavior, and excellent mechanical performance.

Hydrogen embrittlement susceptibility of AISI 4140 alloy-steel under cathodic protection and in H2S and CO2 environment

The susceptibility to hydrogen embrittlement (HE) of AISI 4140 steel when subjected to environments such as those found in offshore oil and gas fields is investigated. Hydrogen charging was carried out for 15 days using two different hydrogen sources, cathodic protection (CP) and corrosion in a saline solution containing high concentrations of H2S and CO2 (SC-sour corrosion). The steel specimens were austenitized at 850 °C, oil-quenched at ambient temperature, followed by tempering for 18 min at 350, 450, and 600 °C. The effect of tempering temperatures on hydrogen embrittlement susceptibility was also investigated. Tensile strength testing, scanning electron microscopy (SEM), and fractography analysis were used to correlate the HE with microstructural and environmental conditions. The results revealed that both hydrogen charging conditions increased the steel hardness and decreased ductility, with this effect being more pronounced at lower tempering temperatures and SC-hydrogen charging. Fracture surfaces of the steel tempered at 600 °C with hydrogen charged exhibited predominantly ductile behavior with the presence of dimples, while at 350 and 450 °C surface fractures showed cleavage facets as a consequence of brittle behavior. In general, the AISI 4140 steel hydrogen embrittlement index (%EI) was higher for hydrogen charging induced by SC compared to CP.

Comprehensive analysis of Sn58Bi/Cu solder joints reinforced with Mg particles: Wettability, thermal, mechanics, and microstructural characterization

In this study, the Sn58Bi-xMg (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) composite solders were synthesized to explore the impact of Mg particles. The study examined the wettability, thermal properties, mechanical properties, microstructure, and growth of interfacial IMC (intermetallic compound) of composite solder. Experimental results showed that adding Mg particles had no significant impact on the melting point of Sn58Bi solder. However, increasing the Mg content increased the undercooling of the solder. Moreover, the incorporation of Mg particles resulted in a consistent rise in the coefficient of thermal expansion (CTE) of the composite solder, ranging from 11.4 × 10−6/°C to 15.6 × 10−6/°C. It was worth noting that including Mg particles enhanced the wetting ability of Sn58Bi alloy on Cu substrates. With a 0.4 % addition of Mg particles, the wetting area could be increased by 60.14 %, and the lowest wetting angle was approximately 10.43°. Adding Mg particles resulted in an amelioration in the brittleness of the Bi-rich phase within the solder matrix, coupled with a decrease in both the thickness of IMC and the grain size at the joint interface. Compared to the joints without mixed Mg particles, the shear strength of Sn58Bi-0.4Mg solder joints and the microhardness of the alloy increased by 30 % and decreased by 10 %, respectively. Also, the presence of dimples within the fracture indicated a rise in the ductility of the solder joints. Overall, adding 0.4 wt% Mg particles in this experiment resulted in a more effective modification of the Sn58Bi solder comprehensive properties.

Effect of welding parameters on the microstructure and mechanical behavior of dissimilar AISI 304/AISI 430 thin plates welded by gas Tungsten arc welding

In this work, the microstructure and mechanical behavior of dissimilar AISI 430 and AISI 304 thin sheets welded by Gas Tungsten Arc Welding using AISI 304 and AISI 316L as filler metals were studied. The obtained joints were characterized by optical and scanning electronic microscopy, Energy-dispersive X-ray spectroscopy and fluorescence, tensile tests and the Vickers microhardness test. Measurements carried out by energy dispersion X-ray spectrometry in the melting zone indicated a slightly heterogeneous distribution of nickel and iron. It was observed that the beginning of solidification of the zone fusion occurred through epitaxial growth. The WM solidification morphology was basically cellular influenced by temperature gradient, solidification rate and chemical composition. Variations in chemical composition and solidification morphology did not significantly alter the Vickers microhardness values in the melting zone. Results obtained in tensile tests indicated adequate mechanical behavior for the joints using AISI 304 as filler rod; those exhibited a ductile fracture behavior with the presence of dimples. However, the AISI 316L joints failure prematurely resulting in a fragile behavior.

Numerical simulation of turbulent flow and particle deposition in heat transfer channels with concave dimples

The efficiency of heat transfer will be significantly reduced if airborne particles deposit in the heat transfer channel. Better understandings on particle deposition characteristics in heat exchanger channel are crucial for the energy efficiency improvement. In this study, the particle deposition in a three-dimensional dimpled rough channel was simulated using the Reynolds stress model (RSM) and discrete particle model (DPM). For the turbulent diffusion of particles, the random walk model (DRW) was employed, and for the particle–wall contact, user-defined functions(UDF) are developed in this study to achieve motions such as bouncing and deposition of particles. Grid independence testing and numerical verification were followed by an analysis and study of the flow structures, secondary flow, temperature distribution, and particle deposition distribution in the dimpled rough channel. On the turbulent structure and particle deposition characteristics, the impacts of several significant parameters, including particle size, airflow velocity, the ratio of dimple depth to inner diameter (h/d), and the ratio of inner diameter of dimple to distance between dimples (d/s), were examined. The findings demonstrate that the primary mechanisms influencing the deposition characteristics of particles in dimpled channels are gravity deposition, thermophoresis force distribution, turbulence structure, secondary flow, and particle inertia, and the effects of these mechanisms change significantly with particle size. For small particles (dp ≤ 10 μm), the presence of dimples will encourage deposition; however, for large particles (dp > 10 μm), the presence of dimples will only have a little impact on the distribution of where the particles are deposited.

On the microstructure and tensile behaviour of nanostructured NiTi alloy produced by electroplastic rolling

Electroplastic rolling was employed to produce nanostructured (NS), near-equiatomic NiTi alloy from a coarse grained NiTi nugget (ingot), which was produced using vacuum induction melting, followed by quenching in water from a temperature of 800°C. The microstructure of NS NiTi was characterized using X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis revealed that the NS NiTi is predominantly martensitic at room temperature, with less than ≈10 % of the austenite phase. The NS NiTi alloy has an average grain size of ≈36 nm. TEM investigation confirmed the presence of grains that are less than 10 nm in size and no amorphous zones were detected. The NS martensitic NiTi alloy specimens were tested in tension at two different strain rates (10−2 and 10−1 s−1). In contrast to a stress-strain profile expected in a martensitic NiTi alloy, the stress-strain curves show conventional tensile behaviour. The observed UTS was high, around ≈1800 MPa, with a less than usual elongation to failure of ≈6 %. The presence of dimples on the fracture surfaces can be seen in scanning electron microscopy (SEM) images, which is indicative of ductile fracture. The role of grain size in the observed deformation and fracture features is also discussed.

Study of forming limit curves and mechanical properties of three-layered brass (CuZn10)/ low carbon steel (St14) /brass (CuZn10) composite considering the effect of annealing temperature

In this study, the effect of annealing temperature on the mechanical properties and formability of brass (CuZn10)/low carbon steel (St14)/brass (CuZn10) composite sheets fabricated by the cold roll bonding (CRB) process were studied. The results showed that CRB process increases the tensile strength and hardness drastically while elongation decreases sharply. However, due to the recrystallization phenomenon, annealing operation can moderate the effect of these changes in mechanical properties. The most significant decline in ultimate tensile strength (UTS) and enhancement in elongation compared to the as-received sample were 90% and 295%, respectively. These results appeared at a temperature of 600 °C. Also, examination of the microstructure of the composite shows that at this temperature, full crystallization happens in the St14 steel layer that, as a result, new equiaxed free strain grains grow. The presence of dimples in the SEM images of the fracture surface indicates ductile fracture mechanism in all samples. The dimples become deep and equiaxial as the annealing temperature increases, indicating more ductility. In addition, after obtaining the forming limit diagram, it was found that annealing heat treatment improves the formability of CuZn10/St14/CuZn10 composite.

Investigation of Co-Cr-Fe-Mn-Ni Non-Equiatomic High-Entropy Alloy Fabricated by Wire Arc Additive Manufacturing

Fabrication of high-entropy alloys (HEAs) is a crucial area of interest for materials scientists since these metallic materials may have many practical uses. Wire arc additive manufacturing (WAAM), unlike other additive technologies, has tangible benefits for making large-sized components, but manufacturing the wire from HEAs is still very limited. Recent studies suggested tackling this problem using a combined cable composed of wires consisting of pure elements as feeding material. However, not all compositions of HEAs can be obtained by the pure elements’ wires because the number of them is limited. This study aims to examine phase composition, chemical elements distribution, microstructure, and mechanical properties of a Co-Cr-Fe-Mn-Ni HEA, which was not previously obtained by the WAAM. The cable-type wire used in this study is composed of two wires which consist of Cr, Fe, Mn, and Ni, and one pure Co wire. The phase composition, chemical elements distribution, microstructure, and mechanical properties were investigated. The prepared high-entropy alloy has non-equiatomic chemical composition with a single-phase FCC crystal structure with homogeneously distributed elements inside the grains. The microstructure examinations showed dendrite structure which is typical for WAAM processes. The compressive yield strength of the alloy is ~279 MPa, the ultimate compressive strength is ~1689 MPa, the elongation is 63%, and the microhardness is ~150 HV, which was found to be similar to the previously fabricated Co-Cr-Fe-Mn-Ni alloys by other methods. Fracture analysis confirmed the ductile behavior of deformation by the presence of dimples.

Influence on Mechanical Behaviour and Characterization of A6063/Bagasse and Titanium Nitride Hybrid Composites

In this study, aluminium matrix (A6063) composites reinforced with titanium nitride and sugarcane bagasse ash were fabricated using liquid metallurgy technique. Reinforcements were added to a maximum of 10 wt% in aluminium alloy. The composites were then subjected to various mechanical properties study. Microscopic examinations were employed to analyse the distribution of reinforcement and phases in the composites. The tensile and impact test specimen after fracture was exposed to scanning electron microscopy to study the fracture mechanism. The tensile strength, hardness, yield strength and flexural strength of composites increased to a maximum of 29.7%, 31%, 34% and 7.7%, respectively. Ductility and impact strength decreased to a maximum of 47% and 11.5%, respectively. The presence of dimples, shearing, tearing microcracks, pull-out, stress concentration, hillock and particle fracture influenced the tensile and impact fracture mechanisms. Contribution of titanium nitride was higher in influencing the tensile strength, hardness, flexural strength and impact strength than that of bagasse ash.

Multilayer friction stir plug welding: A novel solid-state method to repair cracks and voids in thick aluminum plates

In the present paper, a novel solid-state welding method is introduced and investigated which can be used as a repair method for thick aluminum plates. The process is named “multilayer friction stir plug welding”. This process was proposed to overcome issues regarding friction hydro-pillar processing of aluminum alloys including a high oxidation rate and extreme softening at elevated temperatures. In this process, a hole with a special cross-section is drilled to remove the crack or void. Then, the hole is filled using several plugs with the same composition of the parent material. These plugs are welded to the parent material and each other using a set of non-consumable rotary tools. Heat input is the most important parameter which should be controlled during the process. Therefore, tool rotational speed and dwell time were investigated as the main process parameters that dominate the heat input during the process. Tensile tests and optical microscopy were used to investigate the mechanical properties and microstructure of the welds. The fractographic analysis was also carried out to investigate the failure mode. The results indicate the fabrication of sound welds. Higher tool rotational speed and lower dwell time lead to a stronger joint. The highest achieved strength was 124MPa with rotational speed of 3000rpm and dwell time of 5s. The presence of dimples and micro-voids with some evidence of shear failure in fractographic analysis indicates the ductile failure.

A Novel Flat Friction Stir Spot Welding of Triple Sheet Dissimilar Aluminium Alloys: Analyzing Mechanical Properties and Residual Stresses at Weld Region

In present research work, a novel flat friction stir spot welding was performed on three dissimilar Aluminum alloy sheets (two sheets of AA6082-T6 and one sheet of AA6061-T6). The microstructural features and mechanical properties of joints were investigated at various parameters like tool tilt angle, tool rotational speed, dwell time and tool plunge depth. The optimized value of the response parameter was obtained using Taguchi orthogonal array L27. An increase in tool tilt angle, tool rotational speed and dwell time had improved the microhardness. Optical microscopy, scanning electron microscopy, microhardness tests, lap shear strength test and X-ray diffraction were employed to study the characterization of joints. The present investigations were carried out to correlate the microhardness with microstructural characterization of joints at different welding conditions. It was observed from the XRD analysis that the compressive residual stresses were developed due to reaction for forces exerted by the tool shoulder. Fractograph of joints exhibited mixed mode of fracture with the presence of dimples, transgranular texture and cleavage facets. The comparision of joint efficiency of FFSSW weldment with other variants was done.

The Effect of Surface Texturing on Dry Gross Fretting

The effect of steel disc surface texturing on dry gross fretting in a ball-on-disc configuration was studied. Dimples were created with abrasive jet machining. The tribological performance of sliding pairs, steel–steel and steel–ceramics, was experimentally studied. The character of surface texturing effect was related to the dominant wear type. During steel–steel contact, the presence of dimples on disc surfaces could lead to increases in wear and friction. However, the escape of wear debris into dimples could result in reductions of friction and wear in the steel–ceramics configuration.

Case Report: Newborn with Anorectal Malformation

Anorectal malformations are defined by the relationship of the rectum to the sphincter complex and can be classified as high and low anomaly based on whether meconium is present or absent, presence of dimple, anocutaneous reflex, sacral abnormality or presence of meconium in urine. The diagnosis should be made in the delivery room by inspecting the perineum. Meconuria with absence of anal opening invariably indicates a high malformation which requires a colostomy in the newborn period. Low malformations do not become evident until 24 hours when the meconium may show up in the perineal fistula. These defects can be managed by a perineal anoplasty without a colostomy in the newborn period. A prone cross table lateral shoot abdominal film is required if clinical information at 24 hours is insufficient to decide whether a colostomy is needed. We present a case of newborn, day 4 of life, who did not pass meconium since birth, had abdominal distension, vomiting, poor feeding and lethargy since last 2 days. Anal area showed pigmentation with presence of median raphe, anal dimple and slightly formed anal opening. Baby was initially thought as a case of low type imperforate anus. On further evaluation, was found to have meconuria too. Invertogram done showed high type defect. Rest of the examination was normal. Supportive therapy was initiated and baby underwent transverse loop colostomy for high type imperforate anus on day 5 of life. So it is always advisable to confirm the type of anorectal malformation both clinically and by doing required investigation before deciding for any operative intervention like colostomy or anoplasty, as clinical examination and investigation may not correlate in all occasions. Evaluation should also include screening out for associations and other sacral anomalies. BJHS 2018;3(2)6: 500-503.

Electron beam welding study of grade 1 CP Titanium

Mechanical properties at room temperature as well as at cryogenic temperatures (77K, 20K) were evaluated on parent metal as well as electron beam weldments of α–Ti (commercially pure grade I) in this work. The strength of the weldment as well as parent metal increased with decrease in temperature. Weld efficiency >95% at all the temperatures (ambient, 77K, 20K) was observed. Microscopy revealed single phase α in parent metal, which transformed to widmanstatten martensitic structure with feathery morphology in the weld.Increase in dislocation density near the failure tip of tensile test specimen and presence of dimples were observed indicating ductile failure/ sufficient amount of ductility even at 20K.

Facial dimple creation surgery: A review of literature

Cosmetic surgery is not a new thing. The boom of cosmetic surgery is at its pace in India; people have been getting habituated to esthetics for so many years. Esthetic adjustment of various body parts such as rhinoplasty and lip modifications are more common nowadays. A dimple is a small depression on the surface of the body which can be easily noticeable; people appreciate the presence of dimple on the face and believe that it is a sign of good fortune and prosperity. With the advancements in the cosmetic surgery, there has been a upsurge in having artificial dimple on face. With this increased demand in having facial dimples in people, surgeons now are in an idea of creating an artificial dimple with dimple surgery or “dimpleplasty.” The procedure of dimpleplasty is as simple as making a cut in the skin, suturing the underside of the skin to a deeper layer to create a small depression. The suture creates a permanent scar which maintains the dimple. It is a thumb rule that any surgery has minor risks which are avoidable; the current review enumerates the various procedures for dimpleplasty and their outcomes. This article emphasizes on routine as well as recent procedures used for dimpleplasty and its relative complications.

Property enhancement of cast iron used for nuclear casks

Ductile iron (DI) is a preferred material for use in various structural, automotive, and engineering fields because of its excellent combination of strength, toughness, and ductility. In the current investigation, we elucidate the relationship between the morphological and mechanical properties of DI intended for use in safety applications in the nuclear industry. DI specimens with various alloying elements were subjected to annealing and austempering heat treatment processes. A faster cooling rate appeared to increase the nodule count in austempered specimens, compensating for their nodularity value and subsequently decreasing their ductility and impact strength. The ductility and impact energy values of annealed specimens increased with increasing ferrite area fraction and nodularity, whereas an increase in the amounts of Ni and Cr resulted in an increase of hardness via solid solution strengthening. Austempered specimens were observed to be stronger than annealed specimens and failed in a somewhat brittle manner characterized by a river pattern, whereas the ductile failure mode was characterized by the presence of dimples.

Source terms modeling for spacer grids with mixing vanes for CFD simulations in nuclear reactors

In the present study, a numerical method was developed to simulate the presence of spacer grids with mixing vanes in nuclear reactors fuel assemblies. These mixing devices usually have a complex morphology that results in difficult mesh procedures and a high computational simulation cost. The presence of spacers and vanes was simulated using momentum sources to overcome the computational power problem from the perspective of a quarter of the full reactor core CFD (Computational Fluid Dynamic) simulations. Several approaches were tested using RANS models. The starting point is calculation with body-fitted mesh of one grid span of a fuel assembly with spacer grids featuring dimples, springs and mixing vanes. Velocities and Reynolds Stresses are extracted from these mesh, then converted to source terms. A new computational domain is created with a coarser mesh and without the presence of dimples, springs, and vanes, but source terms are added to the momentum and Reynolds Stress transport equations to force the solution as the detailed geometry computation. The forcing is imposed in only a few volumes of the domain where dimples, spring and vanes are located. The approach was numerically stable and relatively easy to implement in open source codes Code_Saturne (EDF) and commercial codes Star-ccm+ (Cd-Adapco). Best practice was defined and grid sensitivity analysis on different quantities was performed. The robustness of the numerical method was demonstrated. This new methodology creates an intermediate approach that provides higher spatial resolution than sub-channel codes and reduced computational cost compared to detailed CFD simulation. Development of the method was based on anisotropic second order closure models, due to the swirling flow generated by the mixing devices; nevertheless, this novel approach applies also to one and two equation turbulence models, without lack of generality.

Suboptimal control of wall turbulence with arrayed dimple actuators for drag reduction

ABSTRACTDirect numerical simulation of a turbulent channel flow with moving dimples at the bottom wall is carried out using the pseudo-spectral method and the curvilinear coordinate system. Suboptimal control based on the spanwise wall shear stress is applied for skin-friction drag reduction, and is implemented by the finite-size sensor-actuator system. The control law is realised in physical space by using a cross-shaped truncation of the wall shear stress information, which can be measured by the sensor. Only the information of wall shear stress inside the sensor area is utilised and that outside the sensor area is obtained by a linear reconstruction from the averaged value over the sensor. To effectively intervene the near-wall coherent structures, low-pass filtering of the spanwise wall shear stress is additionally implemented to eliminate the extra disturbances induced by the presence of dimple actuators, and the filtered stress is used as the control input. Numerical tests on the present control strategy show that the pressure form drag caused by the presence of dimples is reduced significantly as compared with the original suboptimal control, and the reduction of total drag is comparable with that of the opposition control. The underlying mechanism is further analysed by looking into the interaction between the moving dimples and the near-wall coherent structures.

Fatigue life behaviour of TiAlN and TiAlN/CrN coated notched P20 steel specimens

AbstractThe performance of single layer TiAlN and multilayered TiAlN/CrN physical vapour deposition coatings deposited on AISI P20 steel substrate in affecting overall fatigue resistance of notched specimens was assessed and compared with the performance of the uncoated counterparts. V‐shaped circumferential notches on cylindrical specimens were adopted for fatigue tests. Surface coating characteristics such as hardness, elastic modulus and microstrains were measured and found to be different and often larger than those of the steel substrate. Unlike the un‐notched (smooth) coated specimens, which are known to exhibit large improvements in fatigue life in the high cycle fatigue regime, considerable reductions in fatigue life of the coated notched samples were observed. This was understood to be because of the coating's brittleness, which induces at the notch tip early and frequent fatigue crack initiations, especially in the case of multiple layered coatings. Scanning electron microscope images showed more crack initiation sites in both the coated specimens compared with the uncoated specimen. Also, presence of dimples on the surface confirmed dimple rupture mechanism in the ductile steel substrate in the coated and uncoated specimens.