Verification of mechanical properties and surface topography of PH1 stainless steel samples obtained by selective laser melting

Nowadays, additive technologies are used to create physical models, prototypes, samples, tooling, and the production of plastic, metal, ceramic, glass, composite components, and components made of biomaterials. The greatest technological interest is the production of final parts from metal alloys. This paper presents the results of studies of the topography of differently oriented surfaces of PH1 stainless steel samples made using the method of selective laser melting. The surfaces were studied in the plane of construction, perpendicular to the platform, at angles of 45o and 135o. For each surface under consideration, the roughnesses Ra, Rz were determined and a profile was constructed. The findings showed high stability of the topography of the surface layer of the grown material. To confirm the quality of the obtained samples, they were synthesised and tensile tests were carried out. The established characteristics of the elastic modulus, the tensile strength and the corresponding deformations are consistent with the previously determined properties of samples grown using selective laser melting technology and datasheet specifications. According to the results of mechanical tests, the microstructure of the fracture surfaces of the samples was investigated. It is established that the destruction of samples under tension occurs by a viscous mechanism with the implementation of a combination of shear and pit-porous types of destruction. The study of the topography of differently oriented surfaces is carried out – in the plane of construction, perpendicular to it and at angles to the platform 45 and 135o. It is shown that the best surface quality corresponds to two planes – parallel and perpendicular to the plane of the construction platform. The average values of their roughness were Ra ~ 0.6 µm and Rz ~ 4 µm. The quality of the surfaces located at an angle is significantly inferior to the first two. A change in the surface quality depending on the angle of inclination was also observed

Digital method for analysing speckle-interferometric images of material deformation

Residual stresses arising from the technological processes of manufacturing aircraft structures can considerably affect the bearing capacity of the structure, which justifies the need to assess the level of these stresses. The study analysed the speckle interferometric images in terms of the parameter image intensity. This method allows assessing the picture of the change in this parameter both in a particular band, and performing a comparative analysis in a number of bands. Due to the presence of a correlation between the material deformation and the intensity of the image, the dynamics of the variation of the stress state (residual stresses) is estimated. When decoding the holograms, the authors used the Aleksandrov-Bonch-Bruevich vector equation. Double exposure of speckle holograms was applied and photo processing of the hologram was performed. It is shown that, depending on the position of the beam from the hole, there is a change in the image intensity. It was proved that the method employed in the study does not depend on external factors. The proposed approach allows taking a fresh look at the picture of stress state analysis and evaluating the qualitative and quantitative processes in the deformation zone, namely around the drilled hole in the plate

Improved mechanical performance of quasi-cubic lattice metamaterials with asymmetric joints

Abstract In this paper, we propose a simple method for the modification of the unit cells in the lattice metamaterials that provides an improvement of their impact strength. The idea is based on the introduction of small mutual offsets of the interconnected struts inside the unit cells. In such way, the joints between the struts become asymmetric and the overall geometry of the unit cells can be defined as the quasi-cubic with the axis of chirality. Considering four types of cubic lattices with BCC, BCT, FCC and octahedron structures, we modified their geometry and investigated the influence of the offsets and the unit cell size on the overall performance in static and dynamic tests. From the experiments we found that the small offsets (less than the strut diameter) can allow to increase the impact strength of 3d-printed polymeric specimens in 1.5–3 times remaining almost the same density and static mechanical properties. Based on the numerical simulations, we show that the explanation of the observed phenomena can be related to the increase of plastic deformations and damage accumulation in the unit-cells with asymmetric joints leading to the transition from the quasi-brittle to the ductile type of fracture in tested specimens

Modified Fe3O4 Magnetite Core@Shell Type Nanomaterials for Highly-Responsive LPG Sensing: A Comparative Analysis

The present work focuses on the synthesis of Fe _3 O _4 magnetite core@shell type nanoparticles modified with three types of ligands: Magnetite with activated carbon (MAC), Magnetite with silica (tetraethoxysilane, TEOS, and 3-aminopropyltriethoxysilane, APTES) (MTA) and Magnetite with silica, APTES and humic acids (MTAH). The MTAH sample shows greater porosity in comparison to MTA, and MAC samples. The band gap of MTAH is 4.08 eV, which is higher than MTA (2.92 eV), and MAC (2.80 eV). Rietveld quantitative phase analysis of all derivatives was performed and compared with all three samples. The LPG sensing at room temperature shows the highest sensor response of 9.42, in comparison to 3.87 sensor response for MAC, and 4.60 for MTA. This approximately double sensor response increment is justified with the help of band gap, porosity, and size of all 3 the samples. The MTAH sample shows the lowest response-recovery time of 9.33 and 10.78 s respectively in comparison to MAC and MTA samples. In conclusion, this manuscript describes the synthesis procedure of different derivatives of Fe _3 O _4 core@shell materials along with the relation of LPG sensing with different parameters of the materials