Powder Bed Selective Laser Processing of Alumina: Scanning Strategies Investigation

Powder Bed Selective Laser Processing (PBSLP) is a promising technique for the additive manufacturing of alumina. For the method’s success, PBSLP process parameters such as laser power, scanning speed, hatching distance, and scanning strategies need to be investigated. This paper focuses on studying the scanning strategies’ effects on the PBSLP of alumina numerically and experimentally. Scanning strategies such as linear with different orientation, concentric, and islands were investigated. A numerical model was developed in which the PBSLP parameters, scanning strategy effects, and interpreting the experimental results could be observed. The numerical model proved its ability to reach the proper process parameters instead of using experimental trails which are time and cost consuming. For relative density, the island strategy succeeded to print alumina samples with a high relative density reaching 87.8%. However, there are round passages formed inside the samples that remain a barrier for the island strategy to be effectively used in PBSLP of alumina. Both linear and concentric strategies achieved a relative density of 75% and 67%, respectively. Considering the top surface roughness, samples printed with linear strategies gave low top surface roughness compared to the island and concentric strategies. Linear-45° is considered the effective strategy among the studied strategies as it achieved good relative density and low roughness at top and side surfaces. For PBSLP of alumina, new scanning strategies should be considered, and this study presents a new scanning strategy that is mainly based on space filling mathematical curves and should be studied in future work.

Chemical profile and antioxidant, antibacterial, and cytotoxic activities on Artemia salina from the essential oil of leaves and xylopodium of Cochlospermum regium

Cochlospermum regium is a shrub plant species from the Cerrado domain used in traditional medicine. This study aimed to evaluate the chemical profile and antioxidant, antibacterial and cytotoxic activities on Artemia salina from the essential oil of fresh leaves and xylopodium. Fresch leaves and xylopodium of C. regium were collected in an area of ​​Cerrado domain in Goiás State, Brazil, 2021. The essential oil was obtained by hydrodistillation, the yield was quantified and the chemical profile determined by gas chromatography with mass spectrometry (GC-MS). Physicochemical analyzes were carried out for organoleptic analysis (color and appearance), solubility, relative density (g mL-1), refractive index, optical rotation (αD), antioxidant activity in DPPH radical reduction (IC50 µL mL-1), antibacterial activity on Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Salmonella serovar Enteritidis and Salmonella serovar Thyphymurium by the disc method (mm), and cytotoxicity bioassay on Artemia salina (LC50 µg mL-1). The major compounds for the essential oil of fresh leaves were viridiflorol 10.21%, Copaen-4-α-ol <β>, longiborneol 9.07 and β-bisabolene 11.48%, and for the essential oil of xylopodium β-selinene 26.17%, aromadendrene 8.66 % and thujopsene 8.09%. The yield was 0.58 and 0.33%, color slightly yellow and yellow for fresh leaves and xylopodium, respectively. Positive solubility, refractive index of 1.3468 and 1.3347, optical rotation +48.8 and +21.5, relative density 0.932 and 0.936 g mL-1, antioxidant activity IC50 = 47.65 and 111.16 µL mL-1 for fresh leaves essential oil and xylopodium, respectively. The essential oil from fresh leaves showed high antibacterial potential for all strains, as well as for cytotoxic activity on A. salina with LC50 = 90.17 and 625.08 µg mL-1, respectively.

Enzyme Linked Immunosorbent Assay for Fumonisin B1 Detection in Local Corn Seeds from Baghdad-Iraq

Fungi produce a series of toxic compounds on corn, especially Fumonisin B1 (FB1) toxin produced by Fusarium spp. and promoting cancer activity in humans and animals. This study aimed to the isolation and identification of fungi associated with local corn seeds and the detection for the presence of FB1 by using ELISA technique. Thirty samples of corn ears were collected from silos and markets in Baghdad city during the period from November 2018 to March 2019. The present study found that Fusarium was the dominant isolate among fungi in terms of the relative density 57.07%, followed by Aspergillus 31.17%, Rhizopus 3.36%, Alternaria 2.88%, Mucor 2.16%, Penicillium 1.92%, Trichothecium 0.96%, and Helminthosporium 0.48%. FB1 was detected in all samples of the silos and markets with a concentration range of 13.69 - 175.54 µg/kg. There were no significant differences in FB1concentration among samples collected from the silos and markets. Also, no relationship was found between the number of infected seeds by Fusarium spp. and FB1concentrations.

KEANEKARAGAMAN JAMUR MAKROSKOPIS DI KAWASAN AIR TERJUN CURUG EMBUN KOTA LUBUKLINGGAU

This study aims to determine the types, diversity index, species evenness index, dominance index, and relative density of macroscopic fungi in the Waterfall area of ​​Curug Embun, Marga Bakti Village, North Lubuklinggau District I. This research is quantitative descriptive. Data collection techniques in this study using the roaming method with sampling using purposive sampling technique. The results of the analysis of the macroscopic fungal diversity index in the Curug Embun Waterfall area were 1.3530, the species evenness index was 0.4516, the dominance index was 0.4776 and the highest relative density was 68.027%. There are 3 edible species and 17 non-edible mushrooms. 17 species of macroscopic mushrooms in the Waterfall area of ​​Curug Embun were found. The diversity index, dominance, and Simpson index are in the medium category. Schizophyllum commune is the most commonly found species.

Design Optimization of Lattice Structures under Compression: Study of Unit Cell Types and Cell Arrangements

Additive manufacturing enables innovative structural design for industrial applications, which allows the fabrication of lattice structures with enhanced mechanical properties, including a high strength-to-relative-density ratio. However, to commercialize lattice structures, it is necessary to define the designability of lattice geometries and characterize the associated mechanical responses, including the compressive strength. The objective of this study was to provide an optimized design process for lattice structures and develop a lattice structure characterization database that can be used to differentiate unit cell topologies and guide the unit cell selection for compression-dominated structures. Linear static finite element analysis (FEA), nonlinear FEA, and experimental tests were performed on 11 types of unit cell-based lattice structures with dimensions of 20 mm × 20 mm × 20 mm. Consequently, under the same relative density conditions, simple cubic, octahedron, truncated cube, and truncated octahedron-based lattice structures with a 3 × 3 × 3 array pattern showed the best axial compressive strength properties. Correlations among the unit cell types, lattice structure topologies, relative densities, unit cell array patterns, and mechanical properties were identified, indicating their influence in describing and predicting the behaviors of lattice structures.

Opto-Thermal Investigation of Additively Manufactured Steel Samples as a Function of the Hatch Distance

Nowadays, additive manufacturing processes are becoming more and more appealing due to their production-oriented design guidelines, especially with regard to topology optimisation and minimal downstream production depth in contrast to conventional technologies. However, a scientific path in the areas of quality assurance, material and microstructural properties, intrinsic thermal permeability and dependent stress parameters inhibits enthusiasm for the potential degrees of freedom of the direct metal laser melting process (DMLS). Especially in quality assurance, post-processing destructive measuring methods are still predominantly necessary in order to evaluate the components adequately. The overall objective of these investigations is to gain process knowledge make reliable in situ statements about component quality and material properties based on the process parameters used and emission values measured. The knowledge will then be used to develop non-destructive tools for the quality management of additively manufactured components. To assess the effectiveness of the research design in relation to the objectives for further investigations, this pre-study evaluates the dependencies between the process parameters, process emission during manufacturing and resulting thermal diffusivity and the relative density of samples fabricated by DMLS. Therefore, the approach deals with additively built metal samples made on an EOS M290 apparatus with varying hatch distances while simultaneously detecting the process emission. Afterwards, the relative density of the samples is determined optically, and thermal diffusivity is measured using the laser flash method. As a result of this pre-study, all interactions of the within factors are presented. The process variable hatch distance indicates a strong influence on the resulting material properties, as an increase in the hatch distance from 0.11 mm to 1 mm leads to a drop in relative density of 57.4 %. The associated thermal diffusivity also reveals a sharp decrease from 5.3 mm2/s to 1.3 mm2/s with growing hatch distances. The variability of the material properties can also be observed in the measured process emissions. However, as various factors overlap in the thermal radiation signal, no clear assignment is possible within the scope of this work.

Evolution of Microstructure and Elements Distribution of Powder Metallurgy Borated Stainless Steel during Hot Isostatic Pressing

prepared by powder metallurgy process incorporating atomization and hot isostatic pressing (HIP) sintering at six different temperatures from 600 to 1160 °C, borated stainless steel (BSS) containing boron content of 1.86 wt% was studied. The phase of BSS, relative density of different temperature, microstructure, elemental distribution, and mechanical properties were tested and analyzed. The phases of the alloy were calculated by the Thermo-Calc (2021a, Thermo-Calc Software, Solna, Sweden) and studied by quantitative X-ray diffraction phase analysis. The distributions of boron, chromium, and iron in grains of the alloy were analyzed by scanning electron microscopy and transmission electron microscope. The grain size distributions and average grain sizes were calculated for the boron-containing phases at 900, 1000, 1100, and 1160 °C, as well as the average grain size of the austenite phase at 700 and 1160 °C. After undergoing HIP sintering at 900, 1000, 1100, and 1160 °C, respectively, the tensile strength and ductility of the alloy were tested, and the fracture surfaces were analyzed. It was found that the alloy consisted of two phases (austenite and boron-containing phase) when HIP sintering temperature was higher than 900 °C, and the relative density of the prepared alloys was higher than 99% when HIP temperature was higher than 1000 °C. According to the boron-containing phase grain size distribution and microstructure analysis, the boron-containing phase precipitated both inside the austenite matrix and at the grain boundaries and its growth mechanism was divided into four steps. The tensile strength and elongation of alloy were up to 776 MPa and 19% respectively when the HIP sintering was at 1000 °C.