Hardness Of Specimens Research Articles

Evaluation of Struthiocamelus eggshell as an in vitro alternative to extracted human teeth in preliminary screening studies on dental erosion.

This in vitro work investigates the potential of ostrich eggshellas a substitute for extracted human teeth in preliminary screening studies on dental erosion. Additionally, it aims to demonstrate the potential of ostrich eggshell compared to human enamel in evaluating the efficacy of a preventive agent in protecting against dental erosion, using an artificial mouth model. The experiment utilized 96 erosion testing specimens from each substrate, human enamel, and ostrich eggshell. The specimens were subjected to six different experimental regimens of increasing erosive challenge, simulating the consumption of an acidic drink. The acidic drink was delivered at a consistent volume and duration range. Both artificially stimulated and unstimulated saliva flowed throughout the experimental regimens. Surface hardness was measured using a Through-Indenter Viewing hardness tester with a Vickers diamond, while surface profiling was done using a surface contacting profilometer with a diamond stylus. An automated chemistry analyzer system was used to detect calcium and phosphate ions. The study found that ostrich eggshell specimens demonstrated predictable surface loss, hardness drop, and ion loss due to the acidic challenge. Meanwhile, enamel appeared to fall short in terms of surface hardness predictability. The transient hardness loss phase, which manifests as an overlooked decrease in surface hardness despite significant ion and structural loss, may explain this phenomenon. The experiment showed that assessing surface loss is essential in addition to hardness testing, particularly as certain experimental conditions may produce a false perception of tissue recovery despite the actual surface loss. By analyzing the response of ostrich eggshell specimens to erosive challenges, researchers were able to identify an "overlooked" reduction in hardness in enamel specimens. The differences in the structure, chemical composition, and biological response to erosion in the presence of artificial saliva between enamel and ostrich eggshell could explain their distinct behaviors.

Development and Comparative Analysis of MWCNT-Polymer Composites for Bioelectronics Application

The development of biosensors is essential while determining the inside body assaying and assessing implants in-vivo applications. Researchers are doing remarkable studies in certain areas, but output for receiving, adaptability and circulation of nutrients are also essential. For examining the similar functionality, multi-walled carbon nanotube epoxy-composite with varying filler percentages is examined and compared using electromechanical and morphological assessment. Mechanical investigations like tensile and flexural tests were performed in addition to the hardness of specimens. The DC conductivity test is performed to determine the charge conductivity along with NMR for measuring the signal responses. The surface characterization is performed to determine the morphological properties of specimens. It is observed that the mechanical properties increased and decreased after exceeding the filler composition to addition to 2% of total weight. In comparison, the conductivity and magnetic resonance enhance to a further extent showing proportional to addition of nanofillers, thus making them potential applications for flexible organic bioelectronics products.

Microstructure characteristics at different depths of 40CrNiMo steel after laser hardening

This study focuses on laser-hardened 40CrNiMo steel, which meets the requirements for use in sprag clutch wedges; specifically, the microhardness characteristics as well as the phase and element characteristics and formation mechanism at different depths are investigated after laser hardening. The results show that the hardness of the arc-shaped specimen with a laser-hardened layer fluctuates significantly after reaching a certain depth. With increasing depth, the original austenite grain size decreases exponentially, it becomes easier for acicular martensite to form near the surface, and the martensite bulge phenomenon near the surface is more pronounced. The proportion of small-angle grain boundaries decreases, while that of large-angle grain boundaries increases after laser hardening. The angle of the small-angle grain boundaries of the adjacent grains of the hardened layer is mostly below 5°, while that of the large-angle grain boundaries is predominantly between 50° and 60°. After laser hardening, the preferred orientation of the grains in the hardened layer is not clear. The aggregation of C atoms is an important factor determining the structural characteristics of the hardened layer.

Effect of surface treatment of ethylene vinyl acetate on the delamination of custom-fitted mouthguards.

Contamination of ethylene vinyl acetate (EVA) during mouthguard fabrication can cause delamination. The study evaluated the effects of different EVA surface treatments on the contact angle, laminate bond strength, and elongation capacity. Specimens of two bonded EVA plates were prepared (n=30). The Shore A hardness of standardized EVA plate specimens was measured before and after thermo-plasticization. The EVA plates were randomly allocated to one of five different surface treatment groups: no treatment (control); isopropyl alcohol, 100%; chloroform, 99.8%; self-cure acrylic resin monomer (methacrylate, ethylene glycol dimethacrylate, and chemical initiator-amine type); and ethyl alcohol, 70%. The maximum breaking force and elongation at the site of fracture were recorded using a universal testing machine. The contact angle surface was measured using ImageJ software. Scanning electron microscopy of the EVA surface was performed. The laminate bond strength was obtained by dividing the maximum breaking force by the bonding area between the two EVA plates. The laminate bond strength and maximum elongation data were analyzed by one-way ANOVA, followed by the Tukey's and the Dunnet test. The failure mode data was analyzed using the chi-square test (α=.05). EVA surface treatment significantly influenced the laminate bond strength and maximum elongation (p < .001). The control group had a higher contact angle and significantly lower laminate bond strength and maximum elongation than the other groups (p < .001). The acrylic resin monomer and chloroform-treated specimens had similar laminate bond strength and maximum elongation. The acrylic resin monomer group had a significantly lower contact angle (p < .001). All treatments had a significantly higher laminate bond strength and maximum elongation than the control group. The acrylic resin monomer and chloroform groups had a significantly higher laminate bond strength and maximum elongation and the acrylic resin monomer group had a lower contact angle than the other groups. The chloroform should be avoided due its hazardous effects.

Mechanical Characteristics of Composite Resins Produced by Additive and Subtractive Manufacturing.

The aim of the study was to evaluate the mechanical characteristics of resin composites produced by additive and subtractive manufacturing. Six composite resin materials produced by subtractive (Vita Enamic-VE, Cerasmart-CE, Lava Ultimate-LU) and additive manufacturing (Varseo Smile Crown plus-VSC, Saremco Print Crowntec-SPC, Formlabs 3B Permanent crown-FLP) were selected. The three-point bending test was performed, and surface hardness of test specimens was measured. The flexural strength values of CE, SPC and LU test groups were found to be statistically higher when compared to VE, FLP and VSC test groups (p⟨0.0033). The modulus of elasticity values of the test specimens was listed as VE>LU>CE>SPC>FLP>VSC. The FLP group [35.11(4.46)] had the lowest surface hardness values, whereas the VE group [252.50 (21.5)] had the highest values. Other groups were listed as LU⟩CE⟩SPC⟩VSC in terms of surface hardness. According to the ISO 6872:2015, the flexural strengths of all resin composites were found to be acceptable for single unit fixed restorations. However, the VSC group's flexural strength is suitable for inlay, onlay, veneer restorations or single-unit anterior fixed dental prostheses. Also, VSC may not be a suitable choice for posterior restorations due to its low flexural strength.

Crystallization behavior and structural evaluation of cordierite base glass-ceramic in the presence of CaO and B2O3 additives

The purpose of the present work is to highlight the role of CaO and B2O3 additives on the crystallization behavior and microstructural properties of stoichiometric cordierite glass-ceramics using differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Vickers micro-hardness and scanning electron microscopy (SEM). The results show that the presence of B2O3 and CaO in the initial glass led to the precipitation of only one exothermic peak (α-cordierite: Mg2Al4Si5O18). During the heat treatment process, the presence of calcium oxide favors crystallization of anorthite (CaAl2Si2O8) besides α-cordierite phase. It is worth mentioning that, CaO and B2O3 additives strongly encourage the formation of α-cordierite and have the opposite effect on the crystallization of μ-cordierite. In order to determine the effect of crystallization and B2O3 and CaO additives on the hardness of specimens, the micro-hardness measurement of glasses and glass-ceramics shows that the glass-ceramic containing CaO (MAS5C) exhibits the highest micro-hardness value, which depends on the high crystallinity value in this specimen.

Ti2SC MAX phase enhanced wear characteristics of Al 2024 via friction stir processing

ABSTRACT In this research work, wear characteristics of the Al2024 alloy exposed to friction stir processing (FSP) with/without addition of the Ti2SC MAX phase have been investigated. Microstructural investigations revealed a good correlation between SZ and base alloy, and no defects such as cracks, etc. were detected. SEM micrographs confirmed the uniform dispersion of the Ti2SC particles in the Al2024 matrix after FSP. Also, redistribution of the precipitates of Al2024 alloy was observed. A decrease in the hardness of the 3-pass FSPed specimen without Ti2SC was observed due to the grain size increase and coarsening of the precipitates. The considerable improvement in wear rate and friction coefficient was realised by adding the Ti2SC MAX phase in the base alloy. Abrasive abrasion properties such as ploughing, plastic deformation, and grooves on surfaces indicate abrasive abrasion is the predominant wear mechanism for all specimens.

Surface hardness of pristine and laser-treated zinc as a function of indentation load and its correlation with crystallite size valued by Williamson-Hall analysis, size-strain plot, Halder-Wagner and Wagner-Aqua models

To get a range of crystallite size, 5 N pure polycrystalline zinc specimens were shined with 50–100 Nd:YAG laser shots. Williamson-Hall, Size-Strain Plot, Halder-Wagner, and Wagner-Aqua models were employed to evaluate the crystallite size and lattice strain of pristine and laser-treated specimens. Surface hardness of the specimens were measured under 0.2 and 0.3 kgf indentation loads for 10 s. In each case, the surface hardness followed inverse Hall – Petch Relation. For a fixed number of laser shots, the surface hardness was greater for 0.2 kgf indentation load than that for 0.3 kgf. The surface hardness of pristine zinc specimen increased on treatment with 50 laser shots. With further rise in laser shots up to 80, the surface hardness progressively decreased close to that of pristine specimen. Later, it again increased for 90 laser shots and then slightly decreased for 100 laser shots.

Fast Curing with High-power Curing Lights Affects Depth of Cure and Post-gel Shrinkage and Increases Temperature in Bulk-fill Composites.

High-power LED curing lights and bulk-fill resin composites are intended to reduce chair time. This study investigated depth of cure, post-gel shrinkage (responsible for shrinkage stress), and heat generation in bulk-fill composites when cured according to minimum curing times recommended by manufacturers of curing lights and composites. A regular LED curing light (Demi Ultra, 1350 mW/cm2, Kerr Dental) and two LED curing lights with high-power modes (VALO Grand, 3117 mW/cm2 Xtra Power, Ultradent; and Bluephase PowerCure, 2435 mW/cm2 Turbo and 3344 mW/cm2 3sCure, Ivoclar Vivadent) were tested on three bulk-fill composites (Filtek One Bulk Fill, 3M Oral Care Solutions; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; Tetric Powerfill, Ivoclar Vivadent). Using minimum times recommended by manufacturers (3, 5, 6, 10, or 20 seconds), depth of cure was determined by Vickers hardness of specimens cured in a slot (n=10). Post-gel polymerization shrinkage was measured using a strain gauge (n=10) and temperature with a thermocouple (n=5). Results were analyzed using two- and one-way analysis of variance (ANOVA) followed by pairwise comparisons or Student-Newman-Keuls post hoc tests (α=0.05). Curing lights and curing protocols significantly affected depth of cure, post-gel shrinkage, and temperature rise (p<0.001). Cure decreased with depth whereby best overall curing performance was achieved by the 20 second exposure at lowest irradiance (Demi Ultra). Fast curing (3-5 seconds) at high irradiance resulted in lesser depth-of-cure performance, except for the BluePhase-Tetric PowerFill combination. Post-gel shrinkage was higher in all composites when cured at high irradiance (p<0.001), while heat generated also tended to be higher. Although the high-power LED curing lights advertise time savings, not all manufacturer recommended minimum curing times cured bulk-fill materials to the same extent. Moreover, these time savings came at a cost of higher post-gel shrinkage and generated more heat in the bulk-fill composites than the lower irradiance curing protocol.

Computer Simulation to Determine LHP of 4 Different Types of Transient Industrial Quenched Molybdenum Steel Bars

Simulation of hardness distribution in quenched specimens has been investigated using three-dimensional finite-element (FE) analyses which reduced into a 2-dimensional axisymmetric analysis based on Ansys Software capable of predicting temperature history; evolution hardness of four different types of Molybdenum steel bars during thermal processing of materials in quenching process is presented. The Jominy test results are used to estimate specimen hardness. specimen points hardness used to be determined through conversion of evaluated characteristic cooling time for phase transformation t8/5 into hardness. The lowest hardness point (LHP) of each quenched Molybdenum steel bar has been determined to be in mid its length in the center. Experimentally, it is quite impossible to determine this hardness value, and earlier approaches could only assess surface hardness. Normally, this value of hardness at the surface is greater than (LHP), that, under certain conditions might lead to component failure and deformation. The model can be employed to establish a cooling method to attain the required microstructure as well as mechanical properties, which include hardness.

Investigation of the microstructure, machinability and hole quality of AISI 1045 steel forged at different temperatures

In this study, AISI 1045 steel material was hot forged at 1100, 1150, 1200 and 1250°C temperatures. The microstructure and hardness of the test specimens after forging were investigated. The non-forged samples and forged samples were drilled with 6.8 mm diameter solid tungsten carbide drills. Drilling tests were performed in 80 and 120 m/min cutting speed combinations and 0.15, 0.20 and 0.3 mm/rev feed rate. After drilling operations progress forces, surface roughness, roundness deviation, the deviation from cylindricity and taper were investigated. It has been determined that AISI 1045 steel consists of ferrite + pearlitic microstructure and its hardness increases due to the removal of microvoids and pores by forging. It was also determined that the hardness of the samples decreased due to the coarsening in grain size depending on the cooling time with the increase of the forging temperature. It was observed that the feed force obtained during the drilling of the untreated sample in the perforation process was less than the values obtained during the drilling of the hot forging process samples. However, it was found that the measured surface roughness, roundness, cylindricity and conicity values of an untreated sample were more than the hot forging treated sample. It was observed that this situation was caused by the difficulties experienced in sawdust evacuation due to the longer hole length of the untreated sample. Feed rates, surface roughness, roundness, cylindricity and taper values decreased with increasing forging temperature. This situation arises from the decrease in the feed rate due to the decrease in the hardness of the samples, which occurs with the increase in the forging temperature. With the hot forging process applied to the untreated A sample, the hardness values of the forged samples increased between about 8.7 and 10%. The increase in feed force was between 11 and 20%. Surface roughness, Circularity, Cylindricity and Taper values decreased between 40 and 98% compared to the untreated A sample.

Spray electrolyte plasma polishing of GH3536 superalloy manufactured by selective laser melting

Electrolyte plasma polishing (EPP) is an innovative and efficient technology mainly used to polish complex metal products and obtain surfaces with low roughness and high gloss. However, limited by the electrolyte bath size, EPP method is not suitable for polishing workpieces with large size. This paper introduces a spray electrolyte plasma polishing (SEPP) method that can process large-scale and complex surface. The theoretical mechanism of SEPP is presented. GH3536 superalloy plates manufactured by SLM were used as the experimental specimens. The influence of cathode feed velocity on surface roughness is studied. Key parameters, like distance between anode and cathode, voltage, temperature, and flow rate of the electrolyte were investigated experimentally. Properties such as surface roughness, micro morphology, chemical composition, and surface hardness of the GH3536 specimens were detected and analyzed. The results show that SEPP technology can decrease the specimen surface roughness from Ra = 13.93 μm to 0.107 μm and obtain a smooth and glossy surface without obvious machining traces. The oxides and other impurities on the specimen surface were removed, and the contents of Ni, Cr, and Fe elements were increased. Additionally, the surface hardness values of the polished specimen were increased and showed good consistency.

Solidification behavior and porosity in electron-beam powder bed fusion of Co–Cr–Mo alloys: Effect of carbon concentrations

An increased carbon content strengthens Co–Cr–Mo alloys for use in a broad range of industrial applications. In this study, we investigated the influence of the carbon content (0.04–2.5 mass%) on the porosity and microstructure of Co–27Cr–6Mo (mass%) alloys during atomization and electron-beam powder bed fusion (EB-PBF). Quantitative X-ray computed tomography clarified that the volume fraction of pores in the raw powders monotonically increased with the carbon content, as a potential effect of the significant reduction in the liquidus temperature. In contrast, the porosity evolution in the investigated alloys during EB-PBF under identical building conditions suggested an influence of carbon concentration that was distinct from that in the powder. These alloys exhibited negligible porosity fraction for 0.04 and 0.22 mass% and a maximum volume fraction (∼0.3 vol.%) at 2.0 mass%, followed by a remarkable reduction caused by further carbon addition. The porosity of the as-built alloys could be correlated to the solidification behavior varying with carbon concentration. The smoother and more flat solidification front during the cellular (0.04 and 0.22 mass%) and eutectic (2.5 mass%) solidification could effectively eliminate the gas bubbles from the melt pool, whereas the complicated morphology at the solid–liquid interfaces during the dendritic growth (1.5 and 2.0 mass%) hindered the pore elimination in the melt pool. Adding carbon significantly increased the Rockwell hardness of the as-built specimens, reaching a significantly high value of HRC59 at 2.5 mass% of carbon, primarily due to the formation of hard carbide precipitates. The obtained findings could be beneficial to reduce entrapped gas pores thereby contributing to the development of highly durable metal components.

Effect of organic matrix viscoelasticity on indentation recovery behavior in a crossed-lamellar structure of mollusk shell

Mollusk shells are known for their excellent mechanical properties from the complex hierarchical microstructures consisting of calcium carbonate and a small quantity of organic matrix. To investigate the influence of the adhesive organic matrix on the microscopic indentation properties of crossed-lamellar structure in the Cymbiola nobilis (C. nobilis) shell, Vicker`s indentation tests were performed on the specimens with different states (wet, fresh, and calcined at 180°C and 300°C). It is found that the hardness of specimens decreases in this order, which is mainly attributed to the decreased interface bonding strength induced by the loss of moisture and the melting of organic matrix with increasing heat-treatment temperature. Additionally, the indentations of WET, RT and 180°C specimens show a partial recovery with extending time of repose, reflecting a characteristic of viscoelasticity. There is no recovery in 300°C specimen since the molten organic matrix loses its elasticity. The effects of organic matrix on the hardness and indentation recovery behavior of different specimens come from the changes in its elasticity and the interface bonding strength.

Effect of Mouthwashes for COVID-19 Prevention on Surface Changes of Resin Composites

ObjectiveTo investigate the effect of various mouthwashes for COVID-19 prevention on surface hardness, roughness and color changes of bulk-fill and conventional resin composites and determine the pH and titratable acidity of mouthwashes.MethodsFour hundred and eighty specimens were fabricated in cylindrical molds (10 mm in diameter and 2 mm in thickness). Before immersion, baseline data of surface hardness, roughness, and color values were recorded. Each product of specimens (Filtek Z350XT, Premise, Filtek One Bulk Fill Restorative, SonicFil 2) were divided into 4 groups for 0.2% povidone iodine, 1% hydrogen peroxide, 0.12% chlorhexidine, and deionized water (serving as a control). The specimens were immersed in mouthwashes for 1 minute and then stored in artificial saliva until 24 hours. This process was repeated for 14 days. After immersion, surface hardness, roughness and color values of specimens were measured at 7 and 14 days. The data were statistically analyzed by two-way repeated ANOVA, Tukey's HSD and a t-test (p<0.05).ResultsAfter immersion, all mouthwashes caused significantly lower surface hardness, greater roughness and color values (p<0.05) on all resin composites tested.ConclusionsMouthwashes had an effect on all resin composites evaluated by a significant decrease of surface hardness, and an increase of roughness and color values (p<0.05).

Effect Of Incorporation Of Either Neem Or Aloe Vera Powders On Tear Strength And Hardness Of Acrylic Soft Denture Liner Material

Aim of the study: The heat acrylic soft lining materials are far from ideal due to poor soften and weak tearing strengths. This cause some practical problems when testing the adherence of soft liners to denture bases. The study objective was to assess the effect of either Neem or Aloe Vera extracts on tear strength and hardness of heat acrylic soft denture lining material.&#x0D; Materials and methods: Sixty acrylic soft liner specimens were prepared and divided into two main groups (30 specimens for tear strength test, 30 specimens for hardness test). These main groups sub-divided into three groups, each one consist of 10 specimens, according to incorporated material. The hardness specimens were fabrication with dimensions of (30 mm diameter × 3 mm thickness). The tear strength specimens were fabricated according to ASTM specification D-624. The scanning electron microscope (SEM) was used to estimate the distribution of either Neem or Aloe Vera particles within the soft liner. Energy dispersive X-ray spectroscopy (EDS) was used to analysis the elements of studied materials. Tear strength specimens were measured by utilizing universal Instron machine. Hardness specimens were measured by utilizing Shore A durometer. Statically all data were analyzed by using SPSS software.&#x0D; Results: The outcomes showed non-significant differences (p&gt;0.05) of all studied groups in tear strength and a highly significant (p&lt;0.001) decrease in hardness of all studied groups in comparison with the control group.&#x0D; Conclusion: Incorporation of Neem or Aloe Vera extracts powders showed slight increases in tear strength and highly significant decreases in hardness of soft liner material.

Temperature-Shift-Induced Mechanical Property Evolution of Lithium-Ion Battery Separator Using Cyclic Nanoindentation.

The evolution of mechanical properties of separators affected by temperature shifts is imperative for the performance of the lithium-ion battery. The flexible film characteristics hinder the evaluation of the micromechanical properties of separators. In the present study, considering the susceptibility of separators to temperature fluctuations, the temperature distribution of the battery during the discharging process at subzero temperature is obtained. Three sets of separator samples subjected to various temperature shifts are prepared. Through multicycle depth-sensitive nanoindentation, the temperature-dependent weakening of elastic modulus and hardness of separators is experimentally verified. Moreover, the variation trends of elastic modulus, hardness, and hysteresis response of the separator specimens in terms of temperature are investigated via extracting from the multicycle loading-unloading nanoindentation responses. The temperature-dependent variations in the elastic modulus of the separator were investigated by following heating, cooling, and thermostatic processes. Meanwhile, the indentation tests also verify that the effect of temperature shifts on the hardness exhibits an attenuation trend when heating or cooling is followed by a thermostatic process. The variation analysis of nanoindentation hardness as a function of temperature shifts shows typical size effects dependent on the nanoindentation depth. The temperature-induced residual stress and elemental distribution are also analyzed through characterization using X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. The obtained evolution law of temperature shift-induced mechanical properties of a separator could facilitate the optimal design of the separators and provide the supporting data to enhance the safety performance of lithium-ion batteries.

A study on resistance of asphalt concrete exposed to the effect of mycelial fungi

Introduction. In recent years, the issue of improving the quality and service life of road surfaces has been relevant in Russian and worldwide. The main reasons for the early destruction of road surfaces is the quality of individual components and the imperfect composition of asphalt concrete that has pre-set durability. The results of studies, characterizing changes in the roadway surface properties, are of practical value. In this case, we consider the surface hardness of asphalt concrete specimens of various types, subjected to microbiological destruction, which is the property to be studied. The purpose of the work is to study the microbiological resistance of various asphalt concretes, to select and substantiate methods for assessing the biological stability of asphalt concrete subjected to mycelial fungi.&#x0D; &#x0D; Materials and methods. Asphalt concrete specimens contain BND 60/90 bitumen that has the following characteristics: needle penetration depth 0.1 mm at 25 °С – 85; needle penetration depth 0.1 mm at 0 °С — 35; ring and ball softening point 0 °С — 48; extensibility — 83 cm; penetration index — 0.6. Mineral powder, glass cullet powder, and food flour are used as fillers. MP-1 inactivated mineral filler, made of carbonate rock, having the true and average density of 2.71 and 1.71 g/cm3, respectively, was also used. Glass powder was obtained by grinding the waste glass of JSC “Lisma”, Saransk. The chemical composition of glass waste is (in percent for weight): SiO2 — 68.75–72.90; Na2O — 11.9–16.7; K2O — 1.2–3.8; CaO — 5.0–6.0; BaO — 2.2–5.5; MgO — 3.2–3.8; Fe2SO4 — 0.1–0.12; Al2O3 — 1.0–1.5. Food flour was considered as an additive that serves as the nutritional medium for mycelial fungi. Some other components, added to the studied specimens of asphalt concrete, are discussed in the work. The studied property, or hardness, was identified using the Hoppler consistometer. Testing results are provided in the paper. Linear interpolation of experimental data was conducted to identify hardness at the intermediate points to rank the tested asphalt concrete, the standard error between the hardness curve during the exposure and the straight line for the same exposure points. The results of the proposed method are explained graphically using the experimental data. It is assumed that the smaller the root-mean-square error, the more resistant the corresponding composition of asphalt concrete to the effect of mycelial fungi.&#x0D; &#x0D; Results. As a result of the studies and the application of the proposed hardness control methods, the best compositions were identified in terms of resistance to the effects of mycelial fungi. Each group of specimens and compositions of asphalt concrete under study was broken down by their resistance to the effects of the external environment, or mycelial fungi.&#x0D; &#x0D; Conclusions. The results of this research project enable the authors to evaluate the quality of asphalt concrete compositions exposed to the biological environment. The proposed approach to assessing the quality of asphalt concrete compositions can be applied to other building materials and products subjected to certain aggressive media.

Effects of the Energy Density on Pores, Hardness, Surface Roughness, and Tensile Characteristics of Deposited ASTM 316L Specimens with Powder-Bed Fusion Process.

Powder bed fusion (PBF) is a typical metal-AM process. Studies on the process parameters are required to fabricate the desired shape without defects in the PBF process. The aim of this study is to investigate the effects of energy density on the pore, hardness, surface roughness, and tensile characteristics of deposited ASTM 316L specimens using a powder-bed fusion process. Twenty-seven types of specimens with different laser powers, scanning speeds, and overlap ratios were fabricated using the PBF process. The effects of the energy density on the porosity, hardness, surface roughness, tensile strength, and fracture properties of ASTM 316L specimens were examined. The relationships between these properties and energy density are discussed. A critical energy density level was suggested as 79 J/mm3 considering these characteristics. With the critical energy density level, relative density, surface roughness (Ra) and hardness were observed 99.5%, 1.2 μm, and 240 HV, respectively. Additionally, these characteristics were improved with increasing energy density. Five representative conditions were chosen to fabricate tensile specimens with the ASTM 316L powder through the PBF process. Tensile characteristics, including ultimate strength, yield strength, strain, and fracture shape, were examined for different energy densities. The best tensile characteristics were observed with the highest energy density level of 155 J/mm3.

Effect of different sizes of Nano-TiO2 on wear resistances and surface hardness of resinbased dental composites

Objective: The principal aim of this study was to evaluate the wear resistance and surface hardness of dental nanocomposites. Three difference sizes (5 nm, 21 nm and 80 nm) of nanoTiO2 particles were treated with the 3-methacryloyloxy-propyl-trimethoxysilane (MPTMS). The nano-TiO2 was then place in urethane dimethacrylate (UDMA) matrix. Methods: Nano-TiO2 was sonically dispersed in an ethanol solution containing MPTMS. The treated particles were washed in pure ethanol and then dried. Wear resistance and surface hardness of eighteen groups of experimental dental nanocomposites were evaluated. Each group had a particle size category and was treated with three different concentrations of the silane, (MPTMS), which are 2.5, 10 and 30 wt %. For comparison, a commercially available dental resin, SR Adoro® (Ivoclar Vivadent, Cape Town, South Africa), used as the control, was reinforced with untreated and treated nano-TiO2. Results: Statistical analysis showed that the effect of the concentrations of MPTMS on wear resistance and surface hardness of specimens was significant (p&lt;0.001), which is less than 0.05. The improvement of adding treated 80 nm TiO2 was better than that of adding treated 5 nm or 21 nm TiO2. Conclusions: It is concluded that the most available commercial product for dental restorations could be improved by the addition of nano-TiO2 with relatively large particles size