Knoop hardness optimal loading in measuring microhardness of maraging steel obtained by selective laser melting

© IMechE 2019. Knoop microhardness method possesses several advantages over Vickers testing: lower penetration depth, higher accuracy in indentation measurement, and a better suitability to measuring thin and elongated morphological features. This study explores the optimal loading and load independent hardness of selective laser melted specimens in non-heat-treated and heat-treated conditions, by using different Knoop test loads. The obtained results were used to plot load to indentation size charts, which, in turn, were used to obtain prediction curves in accordance to Meyer, proportional specimen resistance, and modified proportional specimen resistance models. The fitting of fitting curves to the measured values was used to calculate appropriate correlation factors. The results indicate that indentation size effect occurs in all measured specimens. This suggests that there is material true microhardness. Also, the most adequate model was modified proportional specimen resistance, with correlation factors just under one.The authors wish to acknowledge the support of European Commission through the project “Advanced design rules for optimal dynamic properties of additive manufacturing products – A_MADAM”, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 734455

Fermented sausage casings

Casing is part of sausages, giving it shape, size and integrity, but also having a role in volumetric, structural and chemical changes which occur in sausage during different production phases. For fermented sausages, natural or artificial casings can be used. Artificial casings have an advantage from the hygienic point of view, because microbiological contamination is negligible, storage at low temperatures unnecessary, and there is no problem with product spoilage during storage and transport. Today, artificial sausage casings are a better choice for production of large diameter sausages, while they are equivalent to natural casings for production of small diameter sausages

Influence of tool and welding parameters on the risk of wormhole defect in aluminum magnesium alloy welded by bobbin tool FSW

Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of FSW since the bottom shoulder forms the bottom surface of the weld, without the need for a backing plate. Moreover, the tool enters the base metal sideways and travels, forming the joint in a straight line while rotating, without the need for downward and upward motion at the beginning and end of the process. This paper presents a study on the BTFSW tool geometry and parameters on the risk of wormhole defect formation in the AA5005 aluminum–magnesium alloy and the wormhole effect on mechanical properties. It was shown that higher stress imposed by the tool geometry on the joint has a significant influence on heating, an effect similar to the increased rotational speed. Optimal kinematic and geometrical tool properties are required to avoid wormhole defects. Although weld tensile strengths were lower (between ~111 and 115 MPa) compared with a base metal (137 MPa), the ductile fracture was obtained. Furthermore, all welds had a higher impact strength (between ~20.7 and 27.8 J) compared with the base material (~18.5 J); it was found that the wormhole defect only marginally influences the mechanical properties of welds

Comparison of bacteriological status during ripening of traditional fermented sausages filled into different diameter artificial casings

The ripening process of fermented sausages is affected by diameter and type of sausage casings, and depends on changes in the microflora, important from hygienic and technological aspects. The aim of this study was to compare the bacteriological status sausages which were stuffed in artificial collagen sausage casings of different diameters (35 mm and 60 mm) during ripening and drying. The sausage stuffing was the same, as was the uncontrolled ripening conditions. In bigger diameter sausages, significantly higher average total bacterial count, enterobacteria and lactic acid bacteria counts were found than in smaller diameter sausages

Influence of tool geometry and process parameters on the properties of friction stir spot welded multiple (AA 5754 H111) aluminium sheets

Friction stir spot welding is an emerging spot-welding technology that offers opportunities for joining a wide range of materials with minimum energy consumption. To increase productivity, the present work addresses production challenges and aims to find solutions for the lap-welding of multiple ultrathin sheets with maximum productivity. Two convex tools with different edge radii were used to weld four ultrathin sheets of AA5754-H111 alloy each with 0.3 mm thickness. To understand the influence of tool geometries and process parameters, coefficient of friction (CoF), microstructure and mechanical properties obtained with the Vickers microhardness test and the small punch test were analysed. A scanning acoustic microscope was used to assess weld quality. It was found that the increase of tool radius from 15 to 22.5 mm reduced the dwell time by a factor of three. Samples welded with a specific tool were seen to have no delamination and improved mechanical properties due to longer stirring time. The rotational speed was found to be the most influential parameter in governing the weld shape, CoF, microstructure, microhardness and weld efficiency. Low rotational speeds caused a 14.4% and 12.8% improvement in joint efficiency compared to high rotational speeds for both tools used in this investigatio

Influence of Tool and Welding Parameters on the Risk of Wormhole Defect in Aluminum Magnesium Alloy Welded by Bobbin Tool FSW

Bobbin tool friction stir welding (BTFSW) utilizes a special tool that possesses two shoulders interconnected by a pin instead of one: the top shoulder and the pin in the conventional FSW tool. This greatly simplifies the kinematics in the otherwise complicated setup of FSW since the bottom shoulder forms the bottom surface of the weld, without the need for a backing plate. Moreover, the tool enters the base metal sideways and travels, forming the joint in a straight line while rotating, without the need for downward and upward motion at the beginning and end of the process. This paper presents a study on the BTFSW tool geometry and parameters on the risk of wormhole defect formation in the AA5005 aluminum–magnesium alloy and the wormhole effect on mechanical properties. It was shown that higher stress imposed by the tool geometry on the joint has a significant influence on heating, an effect similar to the increased rotational speed. Optimal kinematic and geometrical tool properties are required to avoid wormhole defects. Although weld tensile strengths were lower (between ~111 and 115 MPa) compared with a base metal (137 MPa), the ductile fracture was obtained. Furthermore, all welds had a higher impact strength (between ~20.7 and 27.8 J) compared with the base material (~18.5 J); it was found that the wormhole defect only marginally influences the mechanical properties of welds

Seasonal distributions of heavy metal concentrations in different snail (Helix pomatia) tissues from an urban environment in Serbia

The aim of this study was to evaluate the differences between concentrations of heavy metals (cadmium, copper, zinc, iron, and manganese) in terrestrial gastropods, Helix pomatia, collected in four different environment locations in Panevo city, Serbia. Metal concentrations in the foot and in the digestive gland were measured. Heavy metals cadmium, copper, zinc, iron, and manganese were measured in triplicate by atomic absorption spectrophotometry. Also, this study investigated correlations between the trace element content in the soft tissues and different seasons (summer and fall). The results showed that heavy metal concentrations of the measured elements in both snail tissues were significantly higher in polluted sites when compared to the background levels in the city. In digestive gland tissues, the concentration of heavy metals was higher compared with that in foot tissues. The bioaccumulation (heavy metal concentrations in soft tissues) of heavy metals (Cd, Cu, Zn, Fe, and Mn) in snails, Helix pomatia, has been assessed and related to seasons and sites. Heavy metal accumulation in the soft tissues of snails could provide a powerful monitoring tool for the assessment of environmental heavy metal pollution