Gabriel Dragos Vasilescu

The current trend in both academic research and industrial applications is to expand the use of additive manufacturing processes across an increasing number of functional domains. This has led to substantial efforts aimed at improving the overall performance of additively manufactured components, particularly those produced by Material Extrusion (MEX). One of the main limitations of MEX-fabricated parts is the presence of air voids formed between deposited lines and layers, which reduce mechanical strength and structural uniformity. In this context, the present study investigates the influence of inter-layer ironing process parameters, an approach intended to modify near-surface morphology and improve the surface quality and dimensional accuracy of two commonly used materials, namely lightweight polylactic acid (PLA-LW) and standard. The experimental setup involved varying the ironing direction, nozzle diameter, and ironing spacing, while keeping all other manufacturing parameters constant. A complete 4 × 3 × 3 factorial experimental design was employed, considering three process parameters: ironing direction at four levels, nozzle diameter at three levels, and ironing spacing at three levels, resulting in 36 parameter combinations applied to each material separately. Performance evaluation included surface roughness (S_a), Shore D hardness, waviness (W_a), microscopic morphology analysis, and qualitative ultrasonic inspection used to observe internal void-related features, whereas the quantitative analysis focused on Sa, Wa, and hardness variations. The results were compared with those obtained for specimens produced using final-layer-only ironing and no ironing. Inter-layer ironing generally improved surface quality compared with non-ironed specimens, reducing Sa by up to 85.22% and increasing Shore D hardness by up to 10.40% for individual PLA-LW specimens manufactured using the 0.4 mm nozzle. The waviness response was strongly material-dependent; increasing the ironing spacing from 0.1 to 0.3 mm reduced Wa by 47.71% for PLA-LW and 13.39% for standard PLA, while the same spacing increase reduced Sa by 25.61% for PLA-LW but increased Sa by 10.87% for standard PLA. While PLA-LW specimens exhibited localized surface defects possibly associated with the compaction or collapse of near-surface voids, standard PLA specimens showed more pronounced waviness and material accumulation, highlighting the different responses of compact and foamed polymer structures to repeated thermo-mechanical ironing actions.

In the current context of sustainability management and energy insecurity, amplified by the military instability determined by the war between Russia and Ukraine, and the increasingly frequent occurrence of a series of plausible scenarios for disasters or energy blackouts worldwide, this work is a real and applicable model for regional states that would like to critically analyze the situation of their energy security through identifying all the plausible risk scenarios targeting the energy critical infrastructures. The study has identified and assessed two of the most plausible risk scenarios (a natural disaster and a terrorist attack) in the case of a strategic power substation of 220 kV, 400 kV, or 750 kV undergoing a blackout effect. After having assessed the risks, the safety strategy for Romania’s national power system has been elaborated together with the safety strategy for the European Power system-ENTSO-E (European Network of Transmission System Operators for Electricity). The results of the study match other specialized works from different European countries and might represent a model for other types of energy safety risk assessments and for other types of critical infrastructures that are vital for the modern European society and for sustainability management.

A new non-sparking metallic material, Cu-Ti, with applications in potentially explosive environments is proposed as an alternative to CuBe, to reduce the processing and toxic effects of Be. Using high-purity Cu and Ti materials, a Cu (~3–4 wt%) Ti alloy with good chemical and structural homogeneity was fabricated in an induction furnace under an Ar atmosphere. The hot-rolled material was tested in an explosive gas mixture (10% H₂ or 6.5% CH₄) under extremely severe wear tests for 15,000 cycles, and no hot sparks were produced to ignite the medium. The material was investigated as hot-rolled plates (600 s at 950 °C and 10% reduction). The microstructures and surface of the wear test samples were investigated by light optical microscopy (LOM) and scanning electron microscopy (SEM). The chemical compositions were determined by energy dispersive spectrometry (EDS). The corrosion behavior was studied using electrochemical techniques: open-circuit, linear, and cyclic potentiometry in saline electrolyte solutions. The mechanical properties, such as microhardness and friction coefficient, were determined using UMT equipment. The results showed that the alloy is suitable for applications requiring non-ignition properties, with good hot rolling deformability and chemical composition homogeneity. Regarding the corrosion analysis and mechanical properties of the experimental CuTi alloy, minor differences were observed between the cast- and hot-rolled material.

We developed and analyzed a novel non-sparking material based on CuAlBe for applications in potentially explosive environments. Using a master alloy of CuBe, an established material for anti-sparking tools used in oil fields, mines, or areas with potentially explosive gas accumulations, and pure Al, we used an Ar atmosphere induction furnace to obtain an alloy with ~10 wt% Al and ~2 wt% Be percentages and good chemical and structural homogeneity. The new material was tested in an explosive gaseous mixture (10% H₂ or 6.5% CH₄) under extremely strong wear for 16,000 cycles, and no hot sparks capable of igniting the environment were produced. The material was used in the form of hot-rolled plates obtained from melted ingots. The experimental results reflect the use of a suitable material for non-sparking tools. This material has good deformability during hot rolling, abnormal grain growth during deformation under heat treatment and special thermo-mechanical processing, and no high chemical composition variation. Additionally, there are slightly different corrosion resistance and mechanical properties between the melt and hot-rolled state of CuAlBe material. Through hot rolling, the material’s corrosion resistance increased, reducing the chances of generating sparks capable of causing explosions.

The paper presents the results of the theoretical and practical research on the development of the infrastructure for assessing the risk of terrorist attacks associated with undesirable events such as major accidents that can occur at explosives storehouses. The scientific research was carried out within the framework of Project PN 16 43 02 15 - CORE Program titled “Researches regarding the increase of security degree in the technical infrastructures for storing explosives for civil uses”. The use of the DIRE version 1.0 software package specialized in the field of risk assessment of terrorist attacks on explosives storehouses has provided the necessary premises for an objective and highly accurate assessment of this type of risk in the technical infrastructure and the quantification of the degree of damage to the human component and on-site or neighbouring targets, as well as to the area in their proximity.

This paper carries out a study on the microstructural characteristics and mechanical properties of phosphate layers deposited on steel reinforcements for civil constructions. Analyses were performed on 4 sets of samples: 1 control sample (unphosphated) and 2–4 samples that were phosphated with three different solutions. The structural and chemical analysis, as well as the examination of the mechanical properties (surface roughness, microindentation, and scratch resistance) of the phosphate layers deposited on steel rebars for civil constructions, was carried out. The following conclusions were drawn from the experimental results: the coatings show flashes of crystals deposited on the metal surface; chemical homogenization of the phosphated layers is observed; the profiles present a higher roughness after deposition of the phosphated layers; the indentation Young modulus and hardness values recommend the phosphating procedure to improve the CS surface quality; the COF is three times larger for phosphated samples compared with the initial metallic one; and scratch traces are uninterrupted, except for one zone of sample that was phosphated with solution II, wherein the phosphated layer does not present lateral scratches or exfoliations.

The modelling of the throw effect of material fragments following the detonation of explosive materials with a harmful effect on the human component and/or nearby industrial/civil targets is based on the quantification of the impact of the throwing speed and mass of the material fragments. Models developed to generate trajectory calculations for ranges of mass, launch angles and launch velocity based on Monte Carlo simulations are sensitive to the predetermined ranges assigned to each trajectory variable, requiring long time intervals to run the simulations at the time of analysis and IT resources to match. Following the production of an explosion-type event, thousands of individual fragments characterized by their own mass and velocity parameters can be generated, resulting individual energy values that can be taken into account in a quantitative risk assessment, by grouping them into ten distinct classes, thus: Class 1st represents fragments with the highest kinetic energy and/or mass, and class 10th represents fragments with the lowest kinetic energy and/or mass. The paper will highlight the ten distinct classes of the kinetic energy parameter, with the maximum, average and minimum values for each class, as well as the average mass for each detached fragment associated with the energy classes.

Sciendo provides publishing services and solutions to academic and professional organizations and individual authors. We publish journals, books, conference proceedings and a variety of other publications.

Sciendo provides publishing services and solutions to academic and professional organizations and individual authors. We publish journals, books, conference proceedings and a variety of other publications.