Volume 64, Issue 3

In recent years, dental cements have gained more and more importance due to the increasing clinical expectations. They are used as restorative materials and as materials providing critical functions such as chemical and physical adhesion in restorations and protective lining in the cavity. In this work, the effect of water absorption on the mechanical and microstructural properties of different commercial dental cements is systematically investigated. Furthermore, the effect of addition of biocompatible hydroxyapatite on the mechanical and microstructural properties of the cements is characterized. The results show that Voco Meron containing glass ionomer provides the highest values in water absorption and volume change tests. Ketac Cem Radiopaque (209 HV) containing glass ionomer exhibits the highest hardness increase after immersion for 28 days in water, whereas the highest water uptake value is observed in Adhesor Carbofine cement containing zinc polycarboxylate. The hardness of Adhesor ZincPhospate increases with increasing content of hydroxyapatite, whereas in Ketac Cem Radiopaque, the hardness decreases with increasing content of hydroxyapatite significantly. Test results are verified by microstructural analysis of different types of dental cements using scanning electron microscopy and the effect of particle size/distribution on the properties that are of crucial clinical importance is characterized in detail.

The optimization of friction stir processing (FSP) parameters of magnesium alloy composite (AZ31B–SiC) based on orthogonal test was researched. The results show that the distribution of silicon carbide (SiC) particles, microhardness, tensile property, and fracture mode are greatly affected by the change in process parameters. The results show that the composite was made with a rotating speed of 750 rev·min −1 , a traversing speed of 30 mm·min −1 , and a processing time of three; the distribution of SiC particles is even, the microhardness difference of composite is small, the tensile property is better, and the ductile fracture is the main fracture mode. Besides, the existence of SiC and the number of FSP have a certain influence on the corrosion performance of the magnesium alloy composite (AZ31B–SiC), and the corrosion resistance of the FSP sample is obviously better than that of the AZ31B magnesium alloy.

Additive manufacturing is a production technology based on creating three-dimensional parts directly from computer-aided design data layer-by-layer. In recent years, it has been used in many industries with the production of functional, high-quality metallic parts with the powder bed fusion process by laser. The build orientation of the three-dimensional part has a major impact on many factors such as part quality, waste amount, production time, and cost. In this study, a multi-objective optimization is carried out using non-dominated sorting genetic algorithm-II to simultaneously optimize different objectives that may conflict with each other, such as the amount of support structure and build time. Estimation methods are developed for computing the amount of support structure and the build time, which reflect the current state of the technology. With the developed method, build orientation is optimized for a complex part, and the wide range of alternative results are visualized and evaluated. The design for additive manufacturing knowledge required to correctly perform the build orientation process is eliminated by automating the pre-processing stage. Therefore, the contribution is made to the accessibility and sustainability of the PBF-L, which has high process costs by minimizing support structure volume and build time.

In this study, the fatigue properties, microstructure, and surface damage tolerance of the 6N01 profile, 7N01 profile, and 7N01 plate aluminum alloy were studied. The fatigue test results show that the fatigue limit of the 7N01 profile was the highest and the 7N01 plate was the lowest. More importantly, most fatigue specimens failed in the safe life area provided by the Kitagawa–Takahashi line diagram, which indicates that there is a “short-notch effect” in the fatigue behavior of the pre-cracked aluminum alloys. For the sake of safety, according to the Kitagawa–Takahashi line diagram corrected by the fatigue test results, the effective harmless notch sizes a 0,eff of 6N01 profile, 7N01 profile, 7N01 plate is 23.92, 10.81, 24.32 μm, respectively, and their effective fatigue notch propagation threshold Δ k eff,th is 0.81, 0.39, 0.77 MPa m 1/2 , respectively. These corrected values reestablished the fatigue tolerance of the three materials and provided the critical data reference for the practical application. Combined with this study and the analysis of the literature, it can be concluded that the short-notch effect of the three materials should be related to the microstructure, crack closure mechanism, internal defects.

Magnesium (Mg) alloy parts have become very interesting in industries due to their lightness and high specific strengths. The production of Mg alloys by conventional manufacturing methods is difficult due to their high affinity for oxygen, low melting points, and flammable properties. These problems can be solved using nontraditional methods such as wire electric discharge machining (WEDM). The parts with a quality surface have better properties such as fatigue, wear, and corrosion resistance. Determining the surface roughness (SR) by analytical and experimental methods is very difficult, time-consuming, and costly. These disadvantages can be eliminated by predicting the SR with artificial intelligence methods. In this study, AZ91D was cut with WEDM in different voltage (V), pulse-on-time (µs), pulse-off-time (µs), and wire speed (mm s −1 ) parameters. The SR was measured using a profilometer, and a total of 81 data were obtained. Multilayer perceptron, ensemble neural network and optimization-based evolving product-unit neural network (EPUNN) were used to predict the SR. It was observed that the EPUNN method performed better than the other two methods. The use of this model in industries producing Mg alloys with WEDM expected to provide advantages such as time, material, and cost.

FeTi-FeB was added to molten high chromium white cast iron in amounts of 0.5–2.5 wt% at 50 °C above the melting temperature. The samples were produced in four groups. The first group samples were investigated as cast, the second group homogenized at 1000 °C for 1 h, and the other two groups were also homogenized at 1000 °C but for 3 and 6 h, respectively. To study the effect of FeB and FeTi on the microstructure, the samples were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and hardness tests. Wear tests were performed using a pin-on disc. A homogeneously dispersed carbide microstructure was produced by the homogenization heat treatment method. The addition of FeTi-FeB inoculants to high Cr white cast iron played an important role in the distribution of hard carbides. The chemical rate and the carbide volume varied on account of the added hard inoculant particles. TiB 2 , Cr 3 C 2 , M 7 C 3 , M 23 C 6 , and γ-FeCr phases formed on the surfaces. The hardness and wear resistance were improved considerably due to FeTi-B inoculation.

In this study, a self-healing mechanism was developed by means of melting the eutectic structure for microcrack repair in a hypoeutectic Al–Si cast alloy. The alloy was heated just above the eutectic temperature to provide melting of the eutectic in this mechanism. The melted eutectic Si particles repair the microcrack under appropriate conditions. The microcrack formation was provided by tensile loading in Al–Si alloy tensile bars and then eutectic-based self-healing treatment was performed to ensure microcrack healing. Microcrack healing was monitored by X-ray radiography and microstructural examinations were carried out by scanning electron microscopy. The mechanical properties were investigated by tensile testing before and after the healing treatment. Eutectic-based self-healing treatment provides the healing of some microcracks in the microstructure of hypoeutectic Al–Si cast alloy. Also, 44% of yield strength, 59% of ultimate tensile strength, and 86% of total elongation have been recovered by the eutectic-based self-healing process in Al–Si alloy.

As a new concept and multidisciplinary research area that combines advanced manufacturing, materials science and mechanics, 4D printing has attracted academic interest in the recent years. Shape Memory Polymer (SMP) is widely used in 4D printing due to its high stiffness and fast response. In order to make better analysis and research on additive manufacturing of SMP structures based on FDM, the DMA, DSC and TMA tests were conducted first to determine the basic thermodynamic properties of SMP. And then nine parameters, divided into three groups including printing parameters, temperature parameters and structural parameters were examined to character and assess the effect on the mechanical properties of SMP samples, respectively. The results show that the best parameters combination of temperature and printing parameters for the SMP printing is that platform temperature T P  = 65 °C, nozzle temperature T N  = 210 °C, feed rate Fr  = 50 mm/s, layer thickness Lt  = 0.18 mm. Compared with temperature and printing parameters, the structural parameters directly affect the tensile strength of the specimen with improve of 17.298 MPa while these two are 3.639 and 5.528 MPa. The tensile strength of the specimen can be effectively improved through adjusting the structural parameters.

Porcelain tiles are prepared from kaolin, silica sand, feldspar, clay raw materials, and various additives. Ceramic powders are calcined at different temperatures after grinding, drying, and sieving. After the powders are formed and dried, they are sintered at different temperatures. Firing shrinkage (FS), water absorption (WA), and three-point flexure tests of the samples are compared. The mineralogical definitions are completed by performing a phase analysis via X-ray diffraction (XRD). After the microstructural investigations, pore-sizes and distributions are examined by the Barrett–Joyner–Halenda (BJH) method. The powder sintering process increases the crystallization of the compact material. Low porosity and high strength structures are obtained for the samples with powder calcination temperatures of 800 and 900 °C and a compact sintering temperature of 1200 °C. The pore volume increases by increasing the powder calcination temperature in samples compact-sintered at 1200 °C. When the powder calcination temperature of these samples is increased to 1000 °C, the flexural strength decreases. Therefore, the powder sintering temperature of 900 °C is the critical value.

In this investigation, mechanical properties of composite materials produced from woven jute type were investigated. These composites were produced in the form of epoxy adhesive layers by using hand lay-up method in which aluminum, mica and ceramic particles were added into epoxy as a structural adhesive by 2, 4 and 6 wt%. Samples produced according to ASTM D procedures were subjected to tensile and three point bending loads to examine the effect of the particles. Experimental results were presented in tables and graphs. As a result, it was observed that the tensile and bending failure loads of the composite materials obtained by using the particle reinforced adhesive increased. Also, the biggest rise in tensile strength was achieved with 4 wt% aluminum and the biggest increase in bending strength was observed for 2 wt% aluminum particles.

Hard turning was carried out on an X37CrMoV5-1 hot work tool steel with a hardness of 50 ± 2 HRC on a computer numerical control lathe, using a ceramic insert without the use of a coolant. The cutting parameters included three different cutting speeds, three different feed rates, and three different cutting depths. A full factorial design (FFD) was created, and 3 3 =27 experiments were carried out. The effects of cutting parameters on cutting force ( Fc ), surface roughness ( Ra ), material removal rate (MRR), specific cutting energy (SCE), current (Cu), and sound intensity (SI) were investigated. As a result of the analysis of variance (ANOVA), the effect ratios of cutting parameters on Fc , Ra , MRR, SCE, Cu, and SI were examined, and important parameters were determined. As a result, the effective rates of the feed rate, which is the most effective parameter, on Fc , Ra , and MRR were determined as 61.72, 95.90, and 61.70%, respectively. The cutting depth was 54.81 and 34.37% on SCE and SI, respectively, and the cutting speed was effective on Cu by 79.87%. By using FFD and response surface methodology (RSM), the regression equations of the results of Fc , Ra , MRR, SCE, Cu, and SI were extracted, and r 2 values were examined. In the validation experiments performed after the optimization experiments, the experimental results were estimated using FFD, RSM, and Taguchi method, and the differences between them were analyzed.

In this study, an Al-7075 matrix alloy reinforced and by 5, 10, and 15 wt% silicon carbides were produced as a composite material using the stir casting method. An investigation of the hardness, density, and microstructure of the matrix alloy and the composite materials was conducted. The following instruments were used for the microstructure studies: optical microscope and scanning electron microscope (SEM). The machinability behavior of the produced composite materials was investigated by using the drilling method with a three-axis computer numerical controlled (CNC) milling center. High-speed steel (HSS) and titanium nitride (TN)-coated HSS drill bits were used in the machinability tests. As drilling process cutting conditions three different feed rates (FRs) of 0.05, 0.10, and 0.15 mm·rev −1 and three different cutting velocities (CVs) 15, 20, and 25 m·min −1 were applied. The effects of cutting conditions such as FR, CV, reinforcement phase ratio, and cutting tool type on cutting forces such as thrust force (TF) and torque (TQ) in the drilling process were studied in detail. According to the experimental results, TF and TQ decreased with the increase in the CV and increased with the increase in the FR.

In this study, the ultimate tensile strength (UTS), elongation (ELG) and tensile modulus (TEM) of a recycled low-density polyethylene groundnut shell fiber composite (r-LDPE/GSF) were modeled and simulated when considered particle size (PS) and fiber content (FC) of groundnut shell fiber (GSF) by applying response surface techniques (RSM) for structural application. The deposit of recycled low-density polyethylene (r-LDPE) and GSF, an agro-waste, were combined in the production of r-LDPE/GSF composite at PS of 50–70 mesh (300–212 µm) and FC of 10–30 wt% of the GSF. The manufactured r-LDPE/GSF composite was tested for UTS, ELG and TEM and optimized by considering these process variables of GSF, PS and FC with RSM. The outcome indicated that at optimum condition, the UTS, ELG and TEM were 8.5072 MPa, 12.83% and 0.94007 GPa, respectively. The parameters at this point were PS and FC of 60.48 mesh (250 µm) and 30 wt%, respectively. The coefficient of determination ( R 2 ) was close to 0.99. The percentage of relative errors between raw experimental reading and the RSM was <0.16. Based on the result of the work, the predicted RSM data on tensile properties of r-LDPE/GSF composite shows that is a potential engineering material for structural application.

The remarkable mechanical properties of austempered ductile iron (ADI) render ADI as an alternative material for forged steels. On the other hand, the high strength and hardness make the machining of ADI to be challenging. In this study, the ADI is presented as an alternative material to fabricate the ring gear of the two-wheel tractors. A series of experiments were designed to evaluate the machinability of the alloyed ductile iron before the austempering process. 16MnCr5 alloy steel and alloyed ductile specimens were subjected to drilling tests. The effect of drilling parameters on thrust force was investigated based on a design of experiments approach. A regression model was established to predict thrust force at various drilling conditions. Then, the machinability rating was defined as the ratio of the predicted thrust forces. The results showed that at lower feed rates, the thrust force is very close for both materials, such that the estimated machinability rating is 86%.