Highest Relative Density Values Research Articles

The Mechanical Properties of Functionally Graded Lattice Structures Derived Using Computer-Aided Design for Additive Manufacturing

This study aims to investigate the mechanical properties of Functionally Graded Lattice Structures (FGLSs) and to determine their industrial application possibilities through additive manufacturing. For this purpose, lattice structures with uniform and horizontal, vertical and radially graded configurations are designed using auxetic unit cells were fabricated with RGD720 photopolymer resin using Material Jetting. FGLSs are compared with uniform structures in regards with deformation behavior, structural strength and energy absorption. The results showed that the most significant deviation in the strut diameters of the uniform lattice structures was seen in the rotation lattice structure at 8.2%. The lowest deviation was seen in the chiral structure, which deviated by 5.4%. The lowest deviations (between 3.4% and 9%) in FGLSs were obtained in chiral structures. The highest relative density value (0.3049 g/cm3) among all configurations was observed in the vertically graded chiral structure. The lowest relative density value (0.1865 g/cm3) was obtained in uniform re-entrant structures. According to the compression test results, the highest compressive stress (2.61513 MPa) and elastic modulus (84.63192 MPa) were formed in the rotation structure. The maximum energy absorption capacity value (19.381 KJ) and the maximum specific energy absorption value (3649.905 KJ/kg) were obtained in the uniform chiral structure.

The relationship between structural evolution and high energy ball milling duration in tin reinforced Mg alloys

In this study, 9 wt% Sn reinforced Mg alloys are produced by high energy ball milling and conventional sintering method. Effect of ball milling time (30 min, 2 h, 4 h, 8 h, and 12 h) on particle and grain morphology is detected by SEM examination. Phase evolution and solid solution mechanism is monitored by XRD analysis. Sintering process is carried out at 400 °C with 2 h sintering duration under Ar atmosphere. Platelet structure in powder morphology is observed up to 4 h ball milling, which is linked with the texture formation on < 002 > direction in hexagonal structure of Mg. This platelet formation is broken into smaller and monodispersed particle morphology with further milling process due to excessive plastic deformation which eventually provide homogenous dispersion of reinforcement element. Furthermore, ball milling process after 4 h triggers solid solution along with formation of intermetallic phase (Mg2Sn) according to crystallographic approach. The highest relative density values is measured in 8 h milling duration. Besides, the highest hardness value is achieved along with proper distribution of reinforcement element in 8 h condition. The hardness values is increased almost 85% comparing with pure ball milled Mg and 74% increment comparing with as cast Mg. The highest elastic modulus values is measured at 8 h milling condition by ultrasound method and this value is found in reasonable range. By introducing 12 h ball milling process, density, hardness and elastic modulus properties of 9 wt% Sn-Mg alloy is diminished because excessive amount of intermetallic phase formation on grain and grain boundaries. Therefore, 8 h high energy ball milling process is chosen the most suitable condition for this materials system to obtain proper powder packing and sinterability along with superior physical and mechanical properties.

Structure and Properties of Barium Titanate Lead-Free Piezoceramic Manufactured by Binder Jetting Process.

This article presents the results of manufacturing samples from barium titanate (BaTiO3) lead-free piezoceramics by using the binder jetting additive manufacturing process. An investigation of the manufacturing process steps for two initial powders with different particle size distributions was carried. The influence of the sintering and the particle size distribution of the starting materials on grain size and functional properties was evaluated. Samples from fine unimodal powder compared to coarse multimodal one have 3–4% higher relative density values, as well as a piezoelectric coefficient of 1.55 times higher values (d33 = 183 pC/N and 118 pC/N correspondingly). The influence of binder saturation on sintering modes was demonstrated. Binder jetting with 100% saturation for both powders enables printing samples without delamination and cracking. Sintering at 1400 °C with a dwell time of 6 h forms the highest density samples. The microstructure of sintered samples was characterized with scanning electron microscopy. The possibility of manufacturing parts from functional ceramics using additive manufacturing was demonstrated.

Investigation of mechanical properties of Cu/Mo-SiCp composites produced with P/M, and their wear behaviour with the Taguchi method

In this study, metal matrix composite materials were produced by adding 0, 5, 10, and 15 wt% Mo and SiCp powder particles into the Cu main matrix. Powder metallurgy processes were used as the production methods. These metal matrix composites were produced using a simple mixing method. Scanning electron microscopy was used to examine the surface morphology of the composites in different proportions. Density and hardness tests of the produced composite materials were performed. Taguchi's L16 orthogonal array experimental design was used to describe the wear experiments. The parameters that affected the wear performance the most were determined. The highest relative density value was recorded as 89.18%. Significant increases in hardness (77.038 HRB) occurred in direct proportion to the increase of Mo and SiCp powder particles. As a result of the wear tests, specific wear rate values of the obtained composite materials were determined. According to the optimised results, A4B3C3D2E2F2 (optimum) equation was obtained and the specific wear rate value was determined as 1.18642 × 10−7 mm3/Nm. Also it was found that the reinforcement ratios were relatively more effective compared to the other parameters.

Kelkit Çayı (Tokat) Epilitik Diyatomeleri

Bu çalışmada, Kelkit Çayı (Tokat) epilitik diyatomelerin aylık değişimi, yerleşim yeri altı ve tarım alanları altından seçilen iki istasyondan Mart-Aralık 2018 tarihleri arasında aylık periyotlarda alınan taş örneklerinde incelenmiştir. Çalışma süresince epilitik diyatomelere ait toplam 18 takson kaydedilmiştir. En fazla taksonla temsil edilen diyatome cinsleri Cymbella (3 takson) ve Nitzschia (3 takson) olurken, her iki istasyonda tüm aylarda kaydedilen diyatomeler arasındaki en yüksek nispi yoğunluklar ise Ulnaria ulna türüne ait olmuştur. İstasyonlardaki diyatomeler arasında Sorensen Benzerlik İndeksi ise %56,41 olarak bulunmuştur. Ayrıca istasyonlardan alınan su örneklerinde sıcaklık ve çözünmüş oksijen ölçümleri yapılmıştır. Ölçülen bu değişkenlerin epilitondaki diyatome gelişimini olumlu yönde etkilediği tespit edilmiştir. Epilitik florada tespit edilen diyatome türlerin nispi yoğunlukları belirlenmiştir. Elde edilen sonuçlara göre en düşük nispi yoğunluk 1. İstasyonda 4,76 olarak Mart ayında (Cymbella affinis ), 2. İstasyonda ise 2,83 olarak yine Mart ayında (Lindavia glomerata) kaydedilmiştir. En yüksek nispi yoğunluk değerleri dikkate alındığında ise 1. İstasyonda Navicula radiosa ve Ulnaria ulna türünde Aralık ayında (13,56), 2. İstasyonda ise Ulnaria ulna türünde Mart ayında (9,43) belirlenmiştir.

Selective Laser Melting of NiTi Shape Memory Alloy: Processability, Microstructure, and Superelasticity

Nowadays, thanks to the growing interest regarding the manufacturing of 3D complex parts with integrated functionalities, the additive manufacturing of NiTi shape memory alloy is a challenging technological issue. Particularly, 3D printing of NiTi components requires a strong interaction between technological and metallurgical approaches, due to the significant correlation among the process conditions, the microstructure, and the functional performances. The goals of the present work are to define the processability of NiTi powder for realizing fully dense samples using Selective Laser Melting process and the correlation between the microstructure and the superelastic response of specimens processed in different process conditions. It was found that highest relative density values can be obtained for a laser fluence in the range 63–160 J/mm3. The resulting microstructures exhibit variable degrees of orientations, according to the different cooling rates and melt pool size, specific for each condition. Finally, mechanical testing in compression indicated that the as-built alloy exhibits a limited superelastic behavior. A typical flag-like behavior, characterized by 6% of complete recoverable strain, was obtained through heat treatment at 500 °C. This suggests that the microstructure of as-built samples is highly efficient to promote superelasticity after annealing.

Performance evaluation of cBN-Ti3AlC2–Al composites fabricated by HTHP method

In this paper, polycrystalline cubic boron nitride (PcBN) with Ti3AlC2–Al as the compound binder was manufactured by high-temperature and high-pressure (HTHP) method. Effects of Ti3AlC2 decomposition on PcBN microstructural features and mechanical properties at different sintering temperatures were systematically analyzed. Results revealed that sintering temperature of 1350 °C was critical temperature for complete Ti3AlC2 decomposition under HTHP conditions. Sintering driving force improved with increasing temperature, resulting in significant enhancement of PcBN compactness. In addition, decomposition products of Ti3AlC2 reacted with cBN to form TiC, TiB2, and AlN, improving the adhesion between cBN grains. At 1450 °C, as-prepared composites with the highest relative density value (99.6%), bending strength (586.22 MPa) and Vickers hardness (48.8 GPa) were attained. Moreover, at 1300 °C, fracture toughness of PcBN was 7.18 MPa m1/2.

Characteristics of quadruplet Ti–Mo–TiB2–TiC composites prepared by spark plasma sintering

The spark plasma sintering process was implemented to produce four different composites, namely Ti-10 wt% Mo-(0.5, 1, 2, and 4) wt% (TiB2 + TiC). All samples were sintered at 1300 °C for 5 min under 50 MPa. A full study was carried out on the mechanical properties and the relative density of these SPSed composite samples. The best relative density of around 98.7% was related to the sample with 1 wt% (TiB2 + TiC). The role of relative density was so predominant that the best values for all mechanical properties, i.e., bending strength, hardness, elongation, and ultimate tensile strength (UTS), were achieved for those with the highest relative density values. The formation of the in-situ TiB phase was proved by the XRD analysis. Besides, microscopical investigations (optical and SEM) showed that adding more ceramic additives led to an increased amount of porosity while Mo solubility decreased in the titanium matrix. Finally, different fracture modes on the surfaces of composite samples were studied using SEM images.

Diversity of Insects in Shallot (Allium ascalonicum L) Plantations at Various Altitudes

Recently the improvement of shallot seed quality using true shallot seed has been developed. This research was aimed to know diversity of insects and the role of insects on the cultivation of shallot seeds in various altitudes. This research was conducted in three different districts (Deli Serdang, Simalungun and Toba Samosir districts) in Plant Pests and Diseases Laboratory, Faculty of Agriculture, University of North Sumatra, Medan from July 2017 until January 2018. This research used four different insect traps (sweep net, pitfall trap, hand picking, and yellow trap), and repeated for six times. The results showed that insects caught on shallot farmings in Balige highland were 11 orders and 31 families with the highest relative density value was 22.5% and the lowest relative density was 0.35%. The value of insect diversity index of Shannon-Weiner (H') on shallot farming in Balige was 2.72 (moderate) and the value of insect evenness index (E) was 0.71 (high). The insects caught on shallot farming in Pematang Siantar middleland were 11 orders and 22 families with the highest relative density value was 28.7% and the lowest relative density was 0.35%. The value of insect diversity index of Shannon-Weiner (H') on shallot farming in Pematang Siantar 2.42 (moderate) and the value of insect evenness index (E) was 0.71 (high), and on shallot plantations at Lubuk Pakam lowland were 10 orders and 21 families with the highest relative density value was 24.7% and the lowest relative density 0.39%. The value of insect diversity index of Shannon-Weiner (H') was 2.32(moderate) and the value of insect evenness index (E) was 0.85 (high).

Study on mechanical and ballistic performances of boron carbide reinforced Al 6061 aluminum alloy produced by powder metallurgy

Abstract In this study, the density, hardness, impact toughness, transverse rupture strength, tensile strength and ballistic resistance of Al 6061 alloy reinforced with boron carbide (B4C) powders were studied to elucidate the influence of the ceramic content and production process on the physical and ballistic properties of the resulting composites. Powder-metallurgy and hot-extrusion techniques were used to manufacture the Al 6061-based metal matrix composites reinforced with 5 wt%, 10 wt%, 15 wt% and 20 wt% B4C. The hot-rolling process was performed on a group of specimens to examine the effect on the mechanical and ballistic behaviors. The results revealed that a uniform particle distribution was achieved in a matrix structure and higher relative density values were measured in all specimens. The hardness, transverse rupture strength and tensile strength were improved and impact toughness was decreased with increasing volume fraction of B4C particle reinforcement for both hot-extruded and hot-rolled specimens. The highest flexural strength was measured in hot-extruded specimens and the maximum tensile strength was obtained in hot-rolled composites. The deformation tests showed that transgranular cracking occurred on B4C particles and particles were retained in the matrix. The hot-extruded, hot-rolled and laminated with two hot-rolled specimens were subjected to a ballistic test with a 7.62 mm × 51 mm M80 projectile for Type III and the ballistic resistance investigated by analyzing the hole surface in the armor. The hot-rolled and hot-extruded specimens were perforated in ballistic tests and exhibited ductile behavior with the petal failure mechanism. The two-layer hot-rolled specimens successfully absorbed the impact energy of the bullet with the lowest depth of penetration and smooth bulging.

Development of Cu-Exfoliated Graphite Nanoplatelets (xGnP) Metal Matrix Composite by Powder Metallurgy Route

In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.

Optimizing Mixing during the Sponge Cake Manufacturing Process

Sponge cakes have traditionally been manufactured using multistage mixing methods to enhance potential foam formation by the eggs. Today, use of all-in (single-stage) mixing methods is superseding multistage methods for large-scale batter preparation to reduce costs and production time. In this study, multistage and all-in mixing procedures and three final high-speed mixing times (3, 5, and 15 min) for sponge cake production were tested to optimize a mixing method for pilot-scale research. Mixing for 3 min produced batters with higher relative density values than did longer mixing times. These batters generated well-aerated cakes with high volume and low hardness. In contrast, after 5 and 15 min of high-speed mixing, batters with lower relative density and higher viscosity values were produced. Although higher bubble incorporation and retention were observed, longer mixing times produced better developed gluten networks, which stiffened the batters and inhibited bubble expansion during mixing. As a result...

Frequency distribution curves and the identification of hotspots: response to comments

This is a response to the criticism by Cayuela et al. (2011) of our proposal for a frequency distribution approach (Bartolino et al. 2011) to the identification of hotspots in conservation and ecology. The main criticism from Cayuela et al. (2011) does not concern or affect the validity of the method per se, but mainly relates to a presumed lack of objectivity in the identification of a spatially global threshold derived from geometric properties of cumulative relative frequency distribution (CRFD) curves. As we will demonstrate, their critique mainly originates from the loose biological/ecological meaning of hotspots, and from misreading and misinterpreting the methodology we proposed. As we noted at the very beginning of our paper (Bartolino et al. 2011), it is not easy to identify a sharp boundary between hotspots and non-hotspots for phenomena that are essentially continuous (Fortin and Dale 2005), such as species richness and/or abundance. A number of statistical techniques have been proposed to perform this task (Nelson and Boots 2008), but clearly there is no insurance that the resulting hotspots will be ecologically and/or biologically significant. Moreover, the identification of hotspots is mostly driven by practical, socioeconomic or conservation objectives, partially accounting for the properties of the spatial processes under investigation. Cayuela et al. (2011) based their criticism of our paper on the widely recognised difficulty involved in adequately defining hotspots. In particular, they claim that our method is as subjective as any other global method (sensu Nelson and Boots 2008), because the hotspots identified using CRFD curves have no particular ecological meaning— although we have never claimed that they do. We do, however, claim that our method is more objective than other global methods (all subjective from an ecological point of view), because it is not left up to the author to identify the threshold used to define hotspots. We reiterate here that the a priori selection of a threshold, based on whatever percentile (e.g., the classical 5, 10, or 15% thresholds), is different from the identification of a threshold according to the geometric property of CRFD curves. In any case, neither are necessarily related to ecological and/or biological significance. However, according to Cayuela et al. (2011), utilizing the 45 slope tangent to the curve corresponding to the highest richness/ density value as the global threshold is no better than using any arbitrary 5%. In this respect, Cayuela et al. (2011) claim that there are two elements of subjectivity: considering the highest relative density value (when there may be many tangents to the CRFD curve with a slope of 45 ), and considering only a slope of 45 . The first critique is irrelevant, since during the identification of hotspots, we are interested by definition in the highest values of the phenomenon under study. The criticism of the use of a slope of This reply refers to the ‘‘notes and comments’’ at doi:10.1007/s10144-011-0272-7.

Reproductive biology of two tree species of Leguminosae in a Montane Rain Forest in southeastern Brazil

Studies on sympatric species that belong to the same taxonomic group and have the same pattern of pollination and seed dispersion, but different patterns of geographical distribution and structural parameters may be worthwhile to understand the evolution of their compatibility system. We studied the floral biology, pollinators and reproductive systems of two tree species in Itatiaia, an area covered with montane rain forest. Pseudopiptadenia contorta is widespread in Brazil but is present at a low relative density at the study site, while Pseudopiptadenia leptostachya is restrictively distributed but presents one of its highest relative density values in Itatiaia. Both species have small flowers arranged in compact spicate raceme inflorescences that constitute the pollination unit. Pollinators are native stingless bees and European honeybees that collect pollen from their nectarless flowers. Although both species have similar floral characteristics and pollination system, their compatibility system differs. Fruit set after manual pollinations and observation of the pollen tube growth showed that P. leptostachya is self-compatible while P. contorta only set fruits after cross-pollinations, and is thus a self-incompatible species. However, fruit set did not differ between the species, indicating that structural parameters are not affected by the compatibility system. Thus, the difference between these two species in terms of reproductive system may be related to other factors such as patterns of geographical distribution.

Influence of crossbreed on the degradation of myofibrillar proteins and on the cathepsin B+L activity in dry cured hams

Enzymatic activity and proteolysis undergone by the proteins extracted from the Semimembranosus and Biceps femoris muscles using high ionic strength buffer were studied in raw hams and hams dry-cured for 11 months. The hams were taken from three different crosses of three breeding enterprises: cross A (75% Duroc-25% Landrace); cross B (50% Duroc-25% Landrace-25% Large White); and cross C (75% Duroc-25% Landrace). Higher cathepsin B+L activity levels were recorded in the Semimembranosus muscle than in the Biceps femoris muscle both in the raw hams and in the cured hams, residual enzymatic activity in the hams being 1% of the initial levels; significant differences were not found for the three crosses. The proteolysis index was higher for the Biceps femoris muscle, similar values being observed for all three crosses. The raw hams from cross A exhibited the highest relative density values for low molecular mass peptides and the lowest relative density values for high molecular mass peptides. After 11 months of curing, proteolysis levels were highest in the hams from cross B, which had the highest levels of 8, 9 and 22 kDa fragments (in the Semimembranosus muscle) and 25 and 9 kDa fragments (in the Biceps femoris muscle). This finding confirms that genetic factors have an influence on proteolysis.

Pressureless (liquid-phase) sintering of X-Phase and mullite/X-phase powders

Abstract X-Phase and mullite/X-phase composite powders, derived by carbothermal reduction and nitriding of kaolinitic clays, have been respectively sintered to 100 and 95% theoretical density by pressure-less sintering. Powders with lower proportions of mullite gave higher relative density values. Optimal densification could only be achieved by attention to a combination of factors such as powder composition, type of embedding powder, two-step sintering, temperature and time. With the aid of X-ray diffraction, scanning and transmission electron microscopy, it is shown that in mullite/X-phase powders, further transformation of mullite to X-phase occurs during sintering (in a N2 atmosphere), because of reduction in the sample by CO (in the sintering gas) formed by the oxidation of carbon from the graphite linings of the furnace. X-Phase nucleates directly from mullite. Kinetics of the process revealed that it is controlled by a liquid phase. X-Phase in both powder and sintered forms is triclinic (a = 9·68, b = 8·56, c = 11·21 A , α = 91·4, β = 124·4 and γ = 99·2) and (pseudo) orthorhombic (a = 9·66, b = 2·84, and c = 11·17 A ) when analysed by X-ray and electron diffraction, respectively.