Cast Specimens Research Articles

Behavior of localized strain under hot compression of cast specimen from Mg–Al–Zn alloy

Axisymmetric hot compression experiments of Mg–Al–Zn specimens in intervals of temperature 250–450 °С and deformation rate (10-3-5)·10–1 s–1 were carried out. Structure formation was studied by optical microscopy. Macroscopically localized strain of cylindrical specimens depending on temperature, strain rates and initial grain size (400 μm and 1400 μm) are investigated. Localized strain diagrams for different initial grain size can be used for development and optimization of hot processing technology parameters are plotting. It is shown that increase of the grain size direct to strain localization increment tendency.

Manufacturing of (Al–10Zn) / TiB2 in-situ nanocomposites by reactive liquid metallurgy and hot-extrusion for enhanced interfacial bonding and mechanical properties

This work systematically deals with the development of an (Al–10Zn) die-casting alloy reinforced with in-situ synthesized hexagonal-shaped TiB2 nano-rods through casting and hot-extrusion processes. The cast specimens were extruded at 673 K with an extrusion ratio of 2:1 to orient the micro-texture, generate sub-grains within grains, reorder the reinforced in-situ TiB2 nanoparticles in the matrix, and engender strain fields to improve the mechanical properties. The nanoscale hexagonal TiB2 nano-rods (∼89 nm length and 14 nm edge) were synthesized by the chemical reaction of two halide salts (K2TiF6 and KBF4) with (Al–10Zn). The fabricated AMNCs were characterized using diffracted beams (XRD), scattered beams (FESEM and EBSD) and transmitted beams (TEM) received from the specimen. The diffracted beams from the X-rays reveal the formation of a TiB2 phase with a major α-Al phase and an individual Zn phase. The scattered beams from FESEM and EBSD revealed the homogenous distribution of TiB2 with less particle-free spacing, refinement of grains to an ultrafine level, and the absence of imperfections such as voids and interfacial de-bonding. The strain fields were observed through transmitted beams in the TEM analysis which were engendered by the thermal misfit between the matrix and TiB2 reinforcement. Among the fabricated AMNCs, (Al–10Zn) + 6 wt% TiB2 nanocomposite exhibited higher mechanical strength (160 MPa UTS) whereas (Al–10Zn) + 4.5 wt% TiB2 nanocomposite retained the ductility with improved strength (151.7 MPa UTS and 40% elongation). The strengthening mechanisms were computed using the (a) Zheng and Chen model and (b) Modified Cylne model to estimate the contribution of individual strengthening, and compared with the experimental results. The grain size strengthening contributed more to the total strength owing to the Zener pinning effect by in-situ TiB2 nano-rods.

Vascular supply of the metacarpophalangeal joint.

To describe in detail the arterial vasculature of metacarpophalangeal joints 2-5 on cadaver specimens and to compare it to ultrasound imaging of healthy subjects. Eighteen hands of donated human cadavers were arterially injected and investigated with either corrosion casting or cryosectioning. Each layer of cryosectioned specimens was photographed in high-resolution. Images were then segmented for arterial vessels of the metacarpophalangeal (MCP) joints 2-5. The arterial pattern of the joints was reconstructed from the segmented images and from the corrosion cast specimens. Both hands of ten adult healthy volunteers were scanned focusing on the vasculature of the same joints with high-end ultrasound imaging, including color Doppler. Measurements were made on both cryosectioned arteries and Doppler images. The arterial supply of MCP joints 2-5 divides into a metacarpal and a phalangeal territory, respectively. The metacarpal half receives arteries from the palmar metacarpal arteries or proper palmar digital arteries, while the phalangeal half is supplied by both proper and common palmar digital arteries. Comparing anatomical and ultrasonographic results, we determined the exact anatomic location of normal vessels using Doppler images acquired of healthy joints. All, except three branches, were found with less than 50% frequency using ultrasound. Doppler signals were identified significantly more frequently in MCP joints 2-3 than on 4-5 (p < 0.0001). Similarly, Doppler signals differed in the number of detectable small, intraarticular vessels (p < 0.009), but not that of the large extraarticular ones (p < 0.1373). When comparing measurements acquired by ultrasound and on cadaver vessels, measurements using the former technique were found to be larger in all joints (p < 0.0001). Using morphological and ultrasonographic techniques, our study provides a high-resolution anatomical maps and an essential reference data set on the entire arterial vasculature of healthy human MCP 2-5 joints. We found that Doppler signal could be detected in less than 50% of the vessels of healthy volunteers except three locations. Intraarticular branches were detected with ultrasound imaging significantly more frequently on healthy MCP 2-3 joints, which should be taken into account when inflammatory and normal Doppler signals are evaluated. Our study also provides reference data for future, higher-resolution imaging techniques.

Influence of Mg Content on the Metallurgical, Hardness, and Tensile Behaviour of Zn-Al-Si-Mg Alloy in the As-Cast Condition

In this current article, an effort was made to briefly study the impact of magnesium content on the mechanical and metallurgical performance of as-cast Zn-Al-Si-Mg alloy. Zinc, aluminium, and silicon of appropriate weight quantities were melted in an electric furnace, and magnesium of varying quantities (1-5wt%) was added to the melt to obtain rectangular cast specimens. Microstructural, hardness and mechanical property analysis was conducted for the developed alloy in the as-cast condition. It was noted that an addition of Mg to the Zn matrix refines the grains but more than 3wt-% of Mg to the matrix forms clusters which deteriorate the property of the alloy in the as-cast condition. The value of hardness and tensile strength were noted to enhance, and ductility was observed to decrease from the baseline alloy to the alloy with 3wt% of Mg. Further addition of Mg decreased the properties of the alloy.

Dielectric constant and flexural strength of micro porous slip cast partially sintered silicon nitride

Slip casting of commercial Si3N4 powder dispersed in de-ionized water with Y2O3 and Al2O3 as sintering aids was carried out using optimum slurry conditions arrived through zeta potential and viscosity measurements. The cast specimens were sintered in graphite furnace in the temperature range of 1600 °C to 1800 °C under 0.15 MPa static N2 pressure. The sintered Si3N4 show density variation from 59% to 82% of theoretical value in the sintering temperature range studied. The 3-point flexural strength varied between 80 MPa and 320 MPa and dielectric constant 3.9 to 5.7 as a function of decreasing porosity from 39% to 17%. The samples exhibit uniform distribution of micro porosity in the range 0.5 μm–2.0 μm and grain size of 0.5 μm–3.0 μm. The microstructure changed from equiaxed and platelet shaped α-Si3N4 grains to needle shaped β- Si3N4 with increase in sintering temperature from 1600 °C to 1800 °C. The dielectric and flexural strength properties found promising for high temperature radome applications.

Steel Fiber Addition in Eco-Friendly Zero-Cement Concrete: Proportions and Properties

The main objective of this paper is to study the behavior of eco-friendly zero-cement concrete, its proportions, and its properties. The experimental program involves casting and testing many specimens divided into three main groups according to the percentage of added steel fibers in order to investigate the effect of steel fibers on the density, compressive strength, modulus of elasticity, and splitting tensile strength of concrete. The experimental outcomes indicated that the percentage of steel fibers has a small impact on the dry density: adding 0.5% and 1% of steel fibers increased the dry density by about 0.9% and 1.6% respectively. The percentage of steel fibers has an important impact on the compressive strength: after 28 days, steel fibers increased the compressive strength by about 4.9% and 12.8% for added steel fiber percentages of 0.5% and 1%. Also, the results indicated that steel fiber had an important impact on the splitting tensile strength in concrete after 28 days of curing: adding 0.5% and 1% steel fibers increased the splitting tensile strength by about 11.8%and 23.2% respectively. Finally, adding steel fibers has an impact on the modulus of elasticity: after 28 days, adding 0.5% and 1% steel fibers improved the modulus of elasticity approximately by 1.7% and 5%.

Fracture behavior of Hastelloy X elaborated by laser powder bed fusion: Influence of microstructure and building direction

Laser Power Bed Fusion (LPBF) results in complex meso and microstructures, which significantly change the fracture mechanisms of Hastelloy X superalloys. This article aims to investigate the role played by original crack orientation (perpendicular or co-linear to sample lasing planes) on the fracture toughness values of LPBF HX. Single notched three-point bending samples were manufactured vertically (V) or horizontally (H) to estimate the fracture toughness for these two original crack directions. The highest value (about 1360 kJ/m²) is computed in V specimens with an original crack parallel to the lasing plane whereas a value of 1042 kJ/m² is estimated in H specimens with the second crack orientation. Compared to the values obtained in cast specimens, the fracture toughness of LPBF specimens is virtually 5–6 times higher. A non-self-similar cracking is specific to V specimens revealing a more tortuous crack path than in H specimens with self-similar cracking. In both cases, ductile failure is driven by both transgranular and intergranular modes. Nevertheless, the strong morphological texture contributes to promote intragranular fracture mode in V specimens which requires more energy than the one dissipated by an intergranular failure associated to H samples. Consequently, the fracture toughness is significantly higher in V specimens. • Fracture tests were conducted on Hastelloy X specimens elaborated by Laser Power Bed Fusion with two build directions. • In H specimens, intergranular fracture is dominant due to the grain boundaries aligned with the initial notch. • In V specimens, transgranular fracture occurs along with grain boundaries perpendicular to the initial notch. • The morphological texture is responsible for the fracture toughness anisotropy.

High oxidation resistance of AlCoCrFeNi high entropy alloy through severe shear deformation processing

In the current study, the high temperature oxidation behavior of AlCoCrFeNi high entropy alloy (HEA) following severe shear deformation was investigated. X-ray diffraction and transmission electron microscopy analysis confirmed spinodal distribution of B2 and BCC phase in the as cast specimen. In contrast, the processed specimen showed a dual phase microstructure (B2/BCC+FCC) after shear deformation. Electron backscattered diffraction analysis revealed significant grain refinement from 90 µm for the as-cast HEA to nearly 2 µm for the processed specimen. The processed specimen showed up to 66% reduction in the oxidation kinetics compared to the as cast alloy. The remarkable improvement in the high-temperature oxidation performance following processing is attributed to complete microstructure refinement. The current study provides a sustainable solution and a new pathway for addressing the looming problem of material deterioration at high temperatures. • Stationary Friction Processing (SFP) refined the grain size from 90 µm up to 2 µm. • Transformation from BCC/B2 to FCC phase microstructure was observed after SFP. • SFP enhanced the activation energy due to significant grain refinement. • Microstructural refinement after SFP resulted in superior oxidation resistance.

Utilization potential of steel fibers in 3D printed functionally graded cementitious composite: An experimental approach

• Fibers enhanced the structural integrity and low tensile strength. • No fiber clustering was observed during extrusion and printing due to short fiber. • Due to reduced voids, mold cast specimens present the highest compressive strength. • Flexural strength increased due to the interlocking of fiber-rich extruded filaments. • Peak stress was highest with 1% fiber content. By employing the 3D concrete printing (3DCP) technique, modern structures can be built with lower costs, lower construction waste, and higher efficiency. Considering the brittle failure modes of 3DCP, a significant difference in properties between the fiber and the host cementitious composite may cause delamination. A functionally graded material can be used to overcome this by distributing fibers according to the loads they are to bear. In this study, copper-coated short discontinuous fibers are used to examine the effect on the flexural strength of the 3D printed mortar. The results show that the flexural strength of 3D printed mortar increased by 31.05% without any decrease in the corresponding compressive strength when adding fibers up to 1.00%. Short discontinuous fibers present potential in developing 3D printed functionally graded cementitious composite.

Pore structure, internal relative humidity, and fiber orientation of 3D printed concrete with polypropylene fiber and their relation with shrinkage

The shrinkage properties and its mitigation strategies for 3D printed concrete (3DPC) are of great significance, especially for structural applications in construction. This study aims to understand the effect of polypropylene fiber (PP fiber) on the total shrinkage of 3DPC under drying. The rheological properties, mechanical properties, internal relative humidity (RH), pore size distribution and fiber orientation of 3DPC were investigated and compared with cast concrete. Without PP fiber, the total shrinkage of the printed specimens is similar to the cast ones. The addition of PP fiber reduces the total shrinkage for cast specimens more significantly than for printed specimens. This phenomenon is explained from both pore structure and fiber orientation perspectives. A lower total shrinkage is also observed on specimens cut along the printing direction when compared with those cut perpendicularly to the printing direction due to higher quantity of fiber oriented along the printing direction. The total shrinkage of 3DPC is found inversely proportional to the fiber orientation factor.

Method for generating transparent porcine tibia showing the intraosseous artery

BackgroundThe occurrence of nonunion after tibial fracture surgery is mainly related to insufficient blood supply. Therefore, anatomical study of the internal and external tibial artery is very important, but there is no good method for displaying the intraosseous artery clearly and intuitively. This hinders the protection and reconstruction of it by surgeons, as well as the development of new instruments and techniques by researchers.ObjectiveTo develop a transparent specimen that could clearly display the intraosseous artery of the tibia.MethodsIn 10 isolated pig calves with popliteal vessels, the popliteal artery was exposed and a tube was placed. A casting agent was then injected at constant pressure, and the tissue around the blood vessel was preliminarily removed after solidification. The perivascular tissue and periosteum were further removed via alkali corrosion, and the tibia was fixed with an external fixator to protect the non-corrosive areas at both ends. Alternate acid corrosion and flushing were then applied until the intraosseous artery was completely exposed. The distribution and branches of intraosseous nutrient arteries were observed with the naked eye and via microscopy. Three-dimensional (3D) scanning and 3D printing filling techniques were used to make transparent tibia specimens with preservation of intraosseous arteries.ResultsA cast specimen of the intraosseous artery of porcine tibia was successfully generated via epoxy resin perfusion combined with acid–alkali etching, and the intraosseous artery was clearly visible. The 3D printing and filling technique successfully produced a transparent tibia specimen with preservation of internal bone arteries, and accurately restored the external shape of the tibia. The foramen of the nutrient artery appeared near the middle upper third of the lateral edge of the tibia. After entering the tibia, the nutrient artery proceeded forward, medial, and downward for a certain distance, twisted and turned near the midpoint of the medullary cavity, and divided into the ascending and descending branches. After going in the opposite direction for a distance, the ascending trunk sent out 2–3 branches, and the descending trunk sent out 2–3 branches.ConclusionThe cast specimen of pig intraosseous artery generated via the above-described perfusion corrosion method provides methodological guidance for the study of anatomical characteristics of the intraosseous artery, and a theoretical basis for the study of new methods of internal fixation and reconstruction of the blood supply of the lower tibia.

Effect of high temperature heat treatment on microstructure and properties of FeCoCrNiAl high-entropy alloy laser cladding layer

Here, the heat treatment for FeCoCrNiAl high-entropy alloy (HEA) laser cladding (LC) layer was given at a temperature which is higher than that of the first phase transition. The effects of heat treatment on the phase transition, microstructure and mechanical properties of the LC-ed FeCoCrNiAl were studied. Meanwhile, the LC-ed sample was compared with the casting specimen. The results showed that the cladding layer had lower activation energy of phase transformation, and it had higher proportion of Fe element because of the dilution of the matrix metal, which promoted the formation of face-centered cubic (FCC) phase. Then more FCC phase structures precipitated in the cladding layer after heat treatment. However, the formation of FCC phase did not change the texture characteristics of the cladding layer. The differences in physical properties, slip system, Burgers vector and dislocation types between the two phases, as well as the serious atomic disarrangement at the two-phase interface, caused a significant increase of dislocation density. The mechanical properties of the FeCoCrNiAl-HEA were improved by the the presence of proper amount of FCC phase combined with fine grains strengthening and dislocation strengthening. Nevertheless, the excess amount of FCC phase promoted plastic deformation and weakened the strengthening effects of dislocation and fine grain strengthening. • Alloying elements and activation energies promoted phase transformations under thermal action. • Solid phase transition under heat treatment did not change the grain growth orientation in coating. • Variations in physical properties between two phases promoted the existance of dislocations. • Dislocations, fine grains and phase proportions influenced mechanical properties of FeCoCrNiAl.

Stress Relaxation during Artificial Aging of an AlSi7Cu0.5Mg Cast Alloy

After casting and solidification, Al cast cylinder heads undergo a sequence of heat treatments to achieve the desired material properties. This sequence comprises solution heat treatment (SHT), quenching, and artificial aging. Internal stresses are formed due to temperature gradients in the complex geometry of the cylinder heads during quenching from the SHT temperature to room temperature. Especially high tensile stresses can produce damage during service. However, part of these internal stresses relaxes during the aging treatment. This work aims to systematically measure the relaxation of the stresses, as well as to phenomenologically model the amount and rate of relaxation. Cast specimens of AlSi7Cu0.5Mg are heat-treated in a furnace before relaxation in a creep testing machine. SHT and SHT plus aging at 180, 200, and 230 °C for 0 h, 0.5 h, 1 h, 4 h, and 6 h are carried out before testing. The relaxation of the stress at constant temperature and strain over 5 h is recorded at three different testing temperatures (180 °C, 200 °C, and 230 °C). The relaxation process is strongly dependent on the testing temperature: at 180 °C and 200 °C the equilibrium stress was already reached after around 1 h, and at 230 °C the equilibrium was reached after 3.5 h. The initial stress values do not influence the relaxation rate. A phenomenological relaxation model is developed to calculate the stress decrement over time and the equilibrium stress in the AlSi7Cu0.5Mg-alloy. The model allows for calculating the levels of residual stress at any time during artificial aging as a function of the thermal history of the alloy, the relaxation temperature, and the initial stress level. Complete relaxation of the initial stress is not reached within 5 h.

Fatigue behavior of removable partial denture cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) clasp materials.

To investigate the fatigue behavior of cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) material for a removable partial denture (RPD) clasps. Dumbbell-shaped specimens were digitally designed with the center part of the dumbbell being a half-round shape at the cross-sectional dimension of 1.25 mm to simulate a typical clasp design and dimensions. A fatigue machine with an offset axis rotation system simulated a typical undercut depth of 0.25, 0.50, and 0.75 mm. Each group was subjected to 30,000 fatigue cycles (simulating 21 years) or till specimen failure. Before testing, the stress value at each undercut depth for each specimen was established in a universal testing machine and SN curves were plotted for each group. Data were statistically analyzed using Kruskal-Wallis and post hoc tests. The fractured surfaces were analyzed using SEM. The average fatigue cycles with 0.25, 0.50, and 0.75 mm undercuts were 27,155 ± 6277, 9298 ± 4033, 5642 ± 8785 for cast CoCr and 26,765 ± 6150, 11,318 ± 7931, 2861 ± 4803, for laser-sintered CoCr, respectively. Apart from three specimens, the PEEK groups did not fail during the simulation period. Clasps with 0.25 mm deflection showed significantly higher fatigue resistance than other groups (p < .001). There was no significant difference in fatigue behavior between the cast and laser-sintered CoCr. Microporosities at the fractured site along with irregular crack propagation were observed for cast and laser-sintered CoCr specimens. Fatigue-induced broken polymer crosslinking chains were observed in PEEK specimens. PEEK material exhibited the highest fatigue resistance and significantly lower deflection resistance. Cast and laser-sintered CoCr showed similar fatigue resistance and behavior.

Shape-Dependent Strength of Al Si9Cu3FeZn Die-Cast Alloy in Impact Zone of Conformal Cooling Core.

This article presents the results of shape-dependent strength analyses in die-castings from traditional (straight-drilled) and conformal core-cooling moulds. Cores with a traditional cooling layout were made of H13 steel using machining, and the working sections of the conformal cores were made using the selective laser melting method (SLM). Two series of casts were produced in the same mould. For Series A, the mould was fitted with traditional cooling cores, and for Series B, the same mould was fitted with conformal ones. The cast specimens were subjected to two weeks of natural ageing. The strength testing of the casts determined the levels of the destructive forces. The destructive forces in the core-cooling impact zones were approximately 28% higher in the B samples than they were in the A samples. The impact of the alloy’s porosity, density, and microstructure on the strengths of the casts was demonstrated. The alloy densities in the central (broken-off) fragments of the casts from Series A were 2.6646 g/cm3; these were 2.6791 g/cm3 in the cases of casts from Series B. The values of the secondary dendrite arm space (SDAS) ranged from 6 to 13 μm in the analysed cross-section of the set of the A casts, and between 3 and 12 μm in the same zone of the set of the B casts. The results of the experimental determinations of the casts porosity levels and SDAS parameters were compared with the results of numerical simulations that were carried out in ProCAST software.

Insight into the microstructural and durability characteristics of 3D printed concrete: Cast versus printed specimens

This study presents the comparison of microstructural and durability characteristics of 3D printed concrete (3DPC) depending on its production method (printing or casting). Printed samples with different numbers of layers, as well as a cast specimen with an identical mix composition, were produced and compared, with their microstructural pore and solid characteristics quantitatively and qualitatively investigated. For this purpose, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) were utilized to evaluate the microstructures of the 3DPC. In particular, quantitative approaches using micro-CT data were newly proposed for a better understanding of the microstructural characteristics of 3DPC. Moreover, their durability-related characteristics and transport properties, including freeze-thaw and thermal resistance, were examined and compared. Despite noticeable differences between the microstructures of the printed and cast specimens, including their anisotropic and inter-layer porosity and heterogeneity, confirmed by MIP, SEM and micro-CT, no significant differences in the transport (capillary water porosity and water sorptivity) or durability-related properties (frost and thermal attack) were found. This was due to the dense and homogenous microstructure of 3DPC, which is attributable to the high binder content and low w/b of the mixture. Moreover, the newly proposed evaluation provided reasonable quantitative and qualitative characteristics, which can be used to demonstrate and predict the material properties of 3DPC.

A Method to Visualize and Quantify the Intraosseous Arteries of the Femoral Head by Vascular Corrosion Casting.

ObjectiveTo describe a method to display the three‐dimensional distribution of intraosseous arteries in the femoral head by vascular corrosion casting.MethodsAn experimental study was done to expose the intraosseous arteries of the femoral head by a microperfusion corrosion method between January 2021 and May 2021. Specimens were 23 swine femoral heads (12 female specimens and 11 male specimens, where age of swine ranged from 8 to 12 months, and the weight was approximately 150 kg). The femoral heads were microperfused with the vascular casting resin through retinacular arteries, and the bone of the femoral head was dissolved with 50% sodium hydroxide and 10% hydrochloric acid and rinsed under the microscope until the vessel casts were completely exposed. The distribution and anastomosis of the arteries in the femoral head were observed under direct vision and microscopy. The diameter of the artery in the femoral head was measured at 0.5 cm after its entry into the bone of the femoral head with a microscale under the microscope. The number of internal arteries with diameter ≥0.05 mm was counted. The number and diameter of the main trunk of the epiphyseal arteries in the femoral head between male and female swine were compared.ResultsThe vascular casting specimen of the swine femoral head was successfully produced by using epoxy resin as a casting agent, and the three‐dimensional intraosseous vascular structures were clearly visible. The number of epiphyseal arteries in male and female swine was 8.55 ± 2.15 and 8.83 ± 2.15 (t = −0.31, p = 0.38), respectively. The diameters of the superior epiphyseal arteries in male and female swine were 0.35 ± 0.09 and 0.31 ± 0.08 mm (t = 1.03, p = 0.16), the diameters of the inferior epiphyseal arteries were 0.47 ± 0.05 and 0.49 ± 0.09 mm (t = −0.57, p = 0.29), and the diameters of the anterior epiphyseal arteries were 0.34 ± 0.08 and 0.33 ± 0.13 mm (t = 0.32, p = 0.37). There was no significant difference in the number and diameter of the main trunk of intraosseous arteries between male and female swine (p > 0.05). The main trunk of intraosseous arteries formed an anastomosis in the center of the femoral head. Among 23 swine femoral head samples, three types of intraosseous anastomosis were observed, including 13 (57%) posterior superior‐posterior inferior, seven (30%) posterior inferior‐anterior, and three (13%) uniform intraosseous anastomosis.ConclusionThe microperfusion corrosion method can produce the vascular casting specimen of swine femoral head revealing the three‐dimensional structure of the intraosseous artery, which clearly shows the origin, course and branches, and diameter, as well as the anastomosis, of nutrient arteries in the femoral head. This method provides a simple and rapid technique for quantifying and visualizing intraosseous arteries.

Synthesis and characterization of structural metal matrix composite using agricultural waste targeting for environmental sustainability

Coconut shell is one of the major agricultural wastes like rice husk, corn hub, groundnut shell etc., which can be found in abundance in various countries those have significant potential in agricultural sector. In the recent times, it has been found that these kind of agricultural wastes are effectively utilized by recycling them targeting for various engineering and scientific applications and in turn to achieve environmental sustainability. In the present study, the mechanical behavior of aluminum hybrid metal matrix composites reinforced with coconut shell ash (CSA) and silicon carbide is investigated. The composite specimens are fabricated by stir casting technique under normal atmospheric conditions with different weight fractions of reinforcements. The as cast specimens are heated to 500°C and maintained for four hours followed by normal cooling and subsequent aging at 170°C for two hours. Microstructural examination of the composites confirmed the uniform distribution of reinforcements and grain boundaries with no significant agglomeration. Properties such as mass density, hardness, and ultimate tensile strength are computed in order to appraise the mechanical behaviour of composites. The results revealed the fact that, with increasing the quantity of CSA in reinforcing phase, the ultimate tensile strength is increased and hardness is decreased. On the other side, the percentage of elongation is improved marginally and stiffness decreased. Inclusion of CSA offered significant influence on the mechanical behavior of Al-SiC-CSA hybrid composites. To some extent, AA 6061/CSA competes with AA 6061/SiCp in mechanical behavior rather than hybrid composites because of lack in both chemical and structural affinity between the reinforcements.

Analysis of microstructure and fatigue of cast versus selective laser-melted dental Co-Cr alloy

Statement of problemThe forces exerted on teeth and prostheses during mastication are repeated and dynamic, resulting in fatigue damage to dental prostheses. Most fractures of dental restorations are fatigue failure. The 4-point bend fatigue behavior of Co-Cr-Mo-W alloys manufactured by investment casting (CAST) and selective laser melting (SLM) has received little attention. PurposeThe purpose of this in vitro study was to evaluate the 4-point bend fatigue property of dental Co-Cr alloys and determine the relationship between microstructure and the 4-point bend fatigue property of Co-Cr alloys created by traditional casting and SLM. These can guide the use of Co-Cr alloy in dentistry. Material and methodsCo-Cr-Mo-W alloys were fabricated with a dimension of 45×2×2 mm by investment casting and SLM. The 3-point bend test measured the ultimate bend strength with 3 specimens in each group. The 4-point bend fatigue test evaluated the fatigue life under various stresses, with 6 specimens in each group. The specimens were mechanically ground, polished, and electrochemically etched. Scanning electron microscopy was used to identify the microstructures of both etched specimens and fracture surfaces. X-ray diffraction investigations were used to determine the phases. Significant differences in the bend strength were analyzed by using the independent samples t test (α=.05), and the fatigue test was analyzed with ANCOVA (α=.05). ResultsThe mean ±standard deviation bend strength of SLM specimens was 1837 ±3 MPa, higher than the 1200 ±6 MPa for CAST specimens (P<.05). The maximum bend stress of the SLM specimens without fatigue failure was 735 MPa, which was statistically higher than the 394 MPa for CAST specimens (P<.05). The microstructure characteristics of the SLM alloy contributed to its excellent fatigue performance. In SLM alloy, the γ phase constituted the majority with some ε and Laves phases, while the cast alloy possessed higher ε and Laves phases. The grains of SLM alloy were equiaxed and fine, and the second phases were fine and dispersive. In contrast, the cast alloy possessed clear dendrites, and the second phases were sizable. ConclusionsThe SLM dental Co-Cr-Mo-W alloy had statistically better 4-point bend fatigue properties than cast alloy, which was associated with an improved microstructure.

Use of Artificial Intelligence Methods for Predicting the Strength of Recycled Aggregate Concrete and the Influence of Raw Ingredients.

Cracking is one of the main problems in concrete structures and is affected by various parameters. The step-by-step laboratory method, which includes casting specimens, curing for a certain period, and testing, remains a source of worry in terms of cost and time. Novel machine learning methods for anticipating the behavior of raw materials on the ultimate output of concrete are being introduced to address the difficulties outlined above such as the excessive consumption of time and money. This work estimates the splitting-tensile strength of concrete containing recycled coarse aggregate (RCA) using artificial intelligence methods considering nine input parameters and 154 mixes. One individual machine learning algorithm (support vector machine) and three ensembled machine learning algorithms (AdaBoost, Bagging, and random forest) are considered. Additionally, a post hoc model-agnostic method named SHapley Additive exPlanations (SHAP) was performed to study the influence of raw ingredients on the splitting-tensile strength. The model’s performance was assessed using the coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE). Then, the model’s performance was validated using k-fold cross-validation. The random forest model, with an R2 of 0.96, outperformed the AdaBoost models. The random forest models with greater R2 and lower error (RMSE = 0.49) had superior performance. It was revealed from the SHAP analysis that the cement content had the highest positive influence on the splitting-tensile strength of the recycled aggregate concrete and the primary contact of cement is with water. The feature interaction plot shows that high water content has a negative impact on the recycled aggregate concrete (RAC) splitting-tensile strength, but the increased cement content had a beneficial effect.