Filler Material Research Articles

ВОССТАНОВЛЕНИЕ ВАЛА РОТОРА ТУРБОКОМПРЕССОРА ТКР-7С-6 ДВИГАТЕЛЯ ВНУТРЕННЕГО СГОРАНИЯ

The use of a turbocharger has a positive effect on the power of the internal combustion engine, reduces fuel consumption and positively affects the environmental friendliness of operation. Along with the positive effect on the operation of the internal combustion engine, turbochargers reduce the overall life of the engine. Small extreme wear and a small diameter of the rotor shaft limit the use of traditional recovery processes. (Research purpose). The research purpose is developing a method for restoring the rotor shaft of a turbocharger of internal combustion engines. (Materials and methods) A short-pulse laser surfacing of an antifriction ceramic coating with subsequent finishing treatment in the form of diamond smoothing was used to apply the restoration coating. The powder composition BN-B4C-LiO-MgO was used as a filler material. Preliminary studies have shown high adhesive strength of the coating and wear resistance in conditions of oil starvation. The surface was subjected to finishing treatment by diamond smoothing after the formation of the restoration coating. A laboratory installation has been developed to accelerate the rotor shaft in the turbocharger housing to 60,000 revolutions per minute, followed by an assessment of the acceleration time and the pressure increase in the compressor manifold. (Results and discussion) The presented method made it possible to restore the turbocharger rotor shaft with a surface roughness of Ra 0.32. Bench tests were conducted to evaluate the efficiency of a turbocharger with a restored shaft, the results of which showed that the intensity of unwinding of the turbocharger rotor shaft and the pressure increase in the compressor manifold are on average 10 percent higher than for a unit with a standard rotor shaft. (Conclusions) The presented technological process of restoring the worn surface of the rotor shaft of the 7C-6 turbocharger is of high practical importance and its application will improve the reliability and durability of turbochargers. The results can be used in the operating and repair enterprises.

Development of electroslag remelting technology for obtaining multilayer billets

The paper analyzes the methods of external influence on the electroslag remelting process in order to obtain multilayer ingots. The method of electroslag remelting with rotation of the consumable electrode is proposed, which leads to the appearance of centrifugal force that affects the heat pattern in the metal bath by changing the place of delivery of electrode metal droplets and form the crystallization front, providing greater crystalline homogeneity in the axial direction. Application of the electrode rotation technology allows to obtain multilayer ingots with a minimum transition zone between layers of different chemical composition. For realization of this method it is necessary to give the electrode unidirectional or reversible rotation around its axis or the axis of the bath at asymmetric location of the electrode. The rotation speed of the electrode depends on its diameter. For electrodes with a diameter of 40–250 mm it is 30–90 rpm. Rotation of the consumable electrode has a complex positive effect on remelting performance: it increases productivity without increasing the suitable power for the slag bath; it increases refining capacity; it changes the place of electrode metal delivery into the metal bath and forms the crystallization front, providing greater crystalline homogeneity in the axial direction. Application of the technology of rotation of the consumable electrode makes it possible to introduce chemical composition-correcting additives into the liquid metal bath from the ingot surface by applying a coating consisting of filler material and water-based non-stick paint to the remelting electrode.

Full scale testing of ultra-high performance concrete closure joint for prefabricated full-depth precast concrete bridge deck panel system

The main objective of the transverse joint between prefabricated full-depth precast concrete deck panels is to prevent the relative vertical movement between the panels and to transfer the loads between adjacent panels without cracking. The most common failure mode for these types of joints during their service life are the interface cracks. Such cracks serve as a conduit for ingress of water into the superstructure, leading to further deterioration requiring frequent maintenance. UHPC is known for its high tensile and bond strengths and is often considered as a joint fill material that has the potential to make this connection more durable. This research has been initiated to investigate if closure joints cast using UHPC material can compete with the performance of monolithic deck systems. The experimental program consisted of two full-scale concrete bridge decks that were statically tested until failure. One bridge deck was a jointed panel deck (JPD) consisting of two half-size panels connected by UHPC closure joint, while the control deck was a full panel deck (FPD) cast as one monolithic specimen. Both decks were connected to the steel girders with UHPC shear pockets that contained four to six shear studs welded to the girder flange. The JPD had rectangular tapered shear pockets and the FPD had circular shaped pockets. The results indicated that the JPD and FPD reached the same ultimate loads, and both failed via concrete punching at the load point situated adjacent to the closure joint of JPD. The results demonstrated that using UHPC closure joint resulted in similar performance and behaviour under loading as the monolithic deck. The interfacial failure was not indicated even at ultimate loads. This confirms the ability of the UHPC closure joint to transfer the load to the adjacent panel. The results also indicated the use of circular or rectangular pockets led to similar behaviours.

Stability Evaluation Method of High Fill Loess Foundation Based on Numerical Simulation

In order to understand the stability evaluation method of high fill loess foundation, the author proposes a study on the stability evaluation method of high fill loess foundation based on numerical simulation. The author first established a three-dimensional finite element model of a multi-level high fill slope using PLAXIS 3D software based on a loess high fill slope engineering project in a certain section of northwest China. The study investigated the effects of changes in fill materials, fill boundaries, slopes, and unloading platforms on slope stability. Secondly, based on the vertical and horizontal displacement of the top and foot of each level of slope under step-by-step filling, the distribution pattern of the most dangerous points of each level of slope and the overall deformation trend of the slope were analyzed. The results indicate that the cohesion and internal friction angle of the filling material are key factors affecting the stability of high fill slopes. Reducing the height of the steps at the boundary between the filling and the undisturbed soil, deepening the width of the steps, reducing the slope, and widening the unloading platform can all improve the stability of the slope. During the construction of lower slopes, there is a significant vertical displacement mutation, while the horizontal displacement mutation is relatively slow; After the construction is completed, the deformation situation is good, and the vertical and horizontal displacement of the higher slope during construction changes greatly, with uneven distribution; After the completion of construction, the consolidation settlement period is long and the deformation is large; Emphasis should be placed on strengthening deformation monitoring at high altitudes after construction is completed. Finally, the platform width can be selected within this range based on the actual engineering situation. After the platform width is greater than 3.6m, as sufficient platform width has been reached at this point, further increasing the platform width has little impact on the safety factor, and the curve gradually flattens out. The research results have determined the stability influencing factors, deformation trends, and development laws of loess high fill slopes in the northwest region, providing a scientific basis for further research on deformation control of loess high fill slopes.

Calculations of phase composition of austenitic high-nitrogen welding wire and study of a welded joint made from it

The processability of a material is directly related to the possibility of its production, operation and maintainability. One of the most important indicators of the processability of any metal is weldability. Austenitic steels with a high nitrogen content proved themselves as high-strength, corrosion- and cold-resistant materials, but the issue of their weldability is still not fully understood. The lack of welding filler materials on the market specifically designed for welding high-nitrogen steels is the primary obstacle to solving this problem. Thus, the goal of the work was to develop and obtain a laboratory sample of high-nitrogen welding wire. Based on calculations of nitrogen solubility and the phase composition of the weld metal, the chemical composition of Cr – Mn – Ni – Mo – V, N steel was selected for this wire. A defect-free ingot with 0.57 % N was obtained, and wire with a nitrogen content of 0.57 wt. % was produced using hot plastic deformation and drawing methods. Testing of this wire to obtain a welded joint of austenitic cast steel, close to it in chemical composition, with the welding process carried out according to the developed technological recommendations, made it possible to obtain a defect-free welded joint without loss of nitrogen in the weld metal. With a microhardness of the base metal of 252 HV50 , due to the alloying of the welding wire steel with nitrogen and vanadium, the metal of the weld and fusion line had a high microhardness (278 and 273 HV50 , respectively), significantly exceeding the microhardness of Cr – Ni cast austenite. The metal of the welded joint has high strength (0.9 of the base metal strength) and high impact toughness. The fracture of impact samples is characterized by a dimple structure characteristic of viscous materials. According to the obtained results, the new welding wire showed itself to be a promising material for welding austenitic high-nitrogen steels.

Docol 1300M Micro-Jet-Cooled Weld in Microstructural and Mechanical Approaches concerning Applications at Cyclic Loading.

The application of advanced high-strength steel grades (AHSS) in different kinds of industry is connected to more than their attractive mechanical properties. The present paper focuses on improving the welding Docol 1300M steel to reach an acceptable microstructure and mechanical parameters. It was decided to manufacture joints with different welding parameters using different filler materials. The electrode wires were varied to increase the carbon content in the weld, and nitrogen was added to the argon shielding mixture to obtain non-metallic inclusions that strengthen the fusion zone. Specimens of joints welded with the gas metal arc welding (GMAW) process for non-destructive and destructive tests were examined. Tensile and bending tests as well as microscopic inspections using a light (LM) and scanning electron microscope (SEM) were also conducted. The results from the fatigue test confirmed the validity of the proposed welding process for the Docol 1300M joint. The collected data enabled the following conclusion: The article's novelty is represented by the use of shielding gas mixtures containing argon and nitrogen in the GMAW welding process of AHSS steel to create titanium non-metallic inclusions, which will translate into better performance properties of the entire joint.

Push-out test of eco-friendly steel-concrete–steel composite sections enhanced by polypropylene fibers: An experimental study and statistical analysis

Steel-concrete-steel (SCS) structural element solutions are rising due to their advantages over conventional reinforced concrete in terms of cost and strength. The impact of SCS sections with various core materials on the structural performance of composites has not yet been fully explored experimentally, and in this work, both slag and polypropylene fibers were incorporated in producing eco-friendly steel-concrete-steel composite sections. This study examined the ductility, ultimate strength, failure modes, and energy absorption capacities of steel-concrete-steel filled with eco-friendly concrete, enhanced by polypropylene fiber (PPF) to understand its impact on modern structural projects. Eco-friendly concrete was produced by the partial replacement of cement with waste material such as ground granulated blast-furnace slag (GGBS) to reduce carbon dioxide emitted as one of the by-products of cement which harms the environment. A constant rate of cement replacement with GGBS was used. Polypropylene fibers were used as a fill material in the structural elements to enhance the performance. Seven specimens of SCS were analyzed for their mechanical properties using push-out monotonic loading. The control specimen was constructed with a conventional concrete core, even as testing specimens had different amounts of polypropylene fiber added to the core. The current investigation indicates that the impact of polypropylene fiber (PPF) material filling concrete on SCS performance is somewhat smaller than that of ordinary concrete (less than 10 percent). Applying PPF to concrete can increase its tensile strength, slow the spread of cracks, and strengthen the material overall. The compressive strengths of the samples were affected by the proportion of PPF, with the strength increasing from 47.6 MPa to 56.43 MPa as the PPF levels increased from 0 to 2 percent. Compared to the control sample, the PPF SCS specimens had an increased energy absorption. On the other hand, in comparison to PPF SCS specimens, the ductility level of the control sample was smaller.

Deuterium permeation and retention behavior in copper-based brazing filler materials

Copper-based brazing filler materials are commonly employed in vacuum brazing techniques to achieve joining of plasma-facing components for ITER. In this work, gas-driven permeation (GDP) and thermal desorption spectroscopy (TDS) experiments have been performed to study the hydrogen isotopes permeation and retention behavior in two types of brazing filler materials (CuMnNi and CuGeNi metals). Experimental results show that CuMnNi filler exhibits the similar deuterium (D) permeability with CuMnNi filler but lower diffusion coefficients than CuGeNi filler. Three distinct peaks are observed between 380 K and 980 K for CuMnNi filler. However, no evident desorption peak is observed for CuGeNi filler. CuGeNi filler may be considered as a potential brazing filler material for reducing tritium inventory.

The Mechanical and Physical Properties of 3D Printing Filament made from Recycled Polypropylene and Ground Tyre Rubber Treated with Alkali

When molten, used vehicle tyres are unable to decompose or be recycled. Despite global efforts to find new uses for these materials, many worn tyres are still dumped in landfills. Therefore, this study proposes using ground tyre rubber (GTR) as a fill material for recycled polypropylene 3D printing filament. The filament composite’s physical and mechanical properties will be assessed in this investigation. GTR is expected to give the filament elastic characteristics, which could lead to rubber-like filaments. This study filled recycled polypropylene (rPP) polymer matrix composites with GTR to make filament. The mechanical and physical properties of a 3D-printed specimen made from rPP and GTR filament with varying compositions were analysed. Compared to pure rPP, rPP/GTR samples with 3 wt% GTR had a maximum tensile strength of 716.76 MPa. The flexural test findings showed that rPP/GTR with 3 wt% GTR had the highest flexural strength at 80.53 MPa, followed by rPP/1 wt% GTR at 65.38 MPa. In physical tests, the rPP/GTR at 5 wt% GTR had the highest water absorption at 5.41 %, and the wt% of GTR connected directly with water absorption. This study has shown that affordable, environmentally friendly rPP/GTR filaments can be developed with less amount of GTR content (3 wt%) and used for 3D printing applications, helping to lessen the impact of plastic and waste while having valuable mechanical and physical properties that are comparable to those of the pure polypropylene material produced.

Influence of geometric imperfections of flange joints on the fatigue load of preloaded bolts

In an ideal flange joint configuration, the fatigue endurance of preloaded bolts is contingent upon factors such as the magnitude of preload, applied working load, and the geometric dimensions of the flange. However, real-world flanged joints often deviate from this ideal geometry, introducing imperfections that can markedly escalate the fatigue burden on bolts. This study endeavors to simulate the geometric imperfections inherent in a standard DN40 flange and ascertain their impact on bolt fatigue through a combination of empirical measurements and finite element (FE) analysis. The investigation reveals that even minor deviations in flange geometry, such as non-parallelism on the order of 0.03 mm, can exert a considerable influence on bolt fatigue, particularly when the flange gap aligns with the applied eccentric working load (same side). To mitigate the deleterious effects of these imperfections, the proposal and evaluation of employing filler material between the flanges are made. Specifically, it is demonstrated that a thin layer of liquid metal filler (KemisKit Fe21), substantially alleviates the fatigue burden on bolts. Empirical findings illustrate that this corrective measure enhances the fatigue life of bolts by a factor of more than 30 under the highest applied working load condition.

FeCo/PANI composites as electromagnetic shields in the X-band: An understanding of the loss mechanisms

The growing dependence on electronic devices functioning within the microwave frequency range, coupled with the need for miniaturization, has resulted in increased instances of electromagnetic interference (EMI) in such devices. Besides altering device performance, the associated health hazards due to electromagnetic radiations have necessitated the urgency for developing efficient electromagnetic shielding materials. Here, highly magnetic FeCo nanoparticles, approximately 200 nm in diameter, have been used as magnetic filler materials in emeraldine base (PANI – EB) and emeraldine salt (PANI – ES) forms of polyaniline to understand the EMI shielding response in X-band frequency range (8.2–12.4 GHz). Composites using 10 % and 25 % FeCo by weight have been prepared using a physical mixing approach and uniform dispersion within the polymer matrix is ascertained using FE-SEM imaging and EDX elemental maps. Structural and magnetic properties of FeCo remain unaltered after the grind mixing process, as confirmed by XRD and VSM measurements. With the total shielding effectiveness remaining sufficiently low at 2–3 dB in FeCo/PANI – EB, significant enhancement to up to 40 dB is achieved in composites prepared in PANI – ES. Detailed investigations of electromagnetic parameters of the composites reveal the importance of the magnetic filler to achieve an absorption-dominated shielding of electromagnetic waves.

Nitrogen-doped Graphene/Natural Rubber and Sodium Dodecyl Sulfate Modified Nanocomposites: Study on the Electrochemical Properties for the Potential Sensor Response

In this study, a piezoelectric composite was developed based on nitrogen-doped graphene/natural rubber (NGr-NR) and an anionic surfactant sodium dodecyl sulfate (SDS) through a simple sonication method. Taking advantage of the high electrical conductivity and high surface area of NGr, the hybrid network of NGr-NR-SDS nanocomposite showed excellent mechanical properties and enhanced electrochemical behavior. Here, NGr was used as functional filler materials incorporated into NR polymeric matrix. SDS was used with NGr-NR composite to reduce the aggregation and promote the interfacial interaction between NGr-NR which enhanced the stability of sensor. The surface morphology of NGr-NR-SDS was investigated by field emission scanning electron microscopy, transmission emission microscopy, and Fourier transform infrared spectroscopy. Cyclic voltammetry and electrochemical impedance spectroscopy of NGr-NR-SDS showed the highest current response of 17 μA and the lowest Rct value of 1920 Ω demonstrating the excellent electrochemical response. The significance of this result is that the developed nanocomposite shows great potential for flexible piezoelectric devices due to excellent electrochemical response and cyclic stability.

Numerical modeling of bamboo fences with various infill porosities deployed for mangrove restoration

As part of mangrove restoration initiatives eco-friendly fence has been implemented in eroded coastal areas in recent years. These fences provide the capacity to mitigate incoming wave energy and facilitate sediment deposition, thereby promoting the establishment and maintenance of mangrove habitats. Nevertheless, it is crucial to investigate the influence of the infill porosity on the wave dissipation performance of these fences, as the infill porosity can vary considerably across different restoration projects. The aim of this research is to explore the relationship between the infill porosity and wave dissipation effectiveness to identify more efficient designs for these eco-friendly restoration measures. The experiments involving wave interactions with fence models were conducted in a wave flume measuring 0.8 m in width and 25 m in length. Four wooden fences with distinct infill porosities ranging from 0.60 to 0.90 were strategically positioned to assess wave transmission, reflection, and dissipation phenomena under 18 distinct wave conditions. Additionally, the simulating waves till shore (SWASH)model was employed to calibrate critical bulk drag coefficient parameters and simulate the flow velocity distribution surrounding the fences under the experimental wave conditions. The findings indicated that a fence with a reduced infill porosity exhibits a higher wave transmission coefficient. However, this is accompanied by a higher reflection coefficient and lower wave energy dissipation within the fence. Both the infill porosity and incident wave conditions influence the flow velocity distribution characteristics in the vicinity of the fences. The area where the interaction between waves and fences is the most prominent is concentrated in the upper water layer immediately adjacent to the frontal section of the fences. Understanding the velocity distribution and hydrodynamic characteristics of the fence area aids in better determining the suitable porosity of fill materials for engineering applications.

Nonsurgical Rhinoplasty: An Updated Systematic Review of Technique, Outcomes, Complications, and Its Treatments.

For patients looking for temporary results or who do not want surgery, nonsurgical rhinoplasty using filler injections has become increasingly popular. Filler materials and surgical techniques have improved in recent years, but serious complications remain. Therefore, the aim of this systematic review is to summarize the common types of fillers and injection techniques, complications, and treatment to help clinicians perform in a safer and more effective way. A systematic review was performed using keywords and Medical Subject Headings search terms. PubMed, Embase, and the Cochrane Library were searched using the appropriate search terms. Data collected from each study included injection materials, location, technique, patient satisfaction and complications, and treatment. From the 1812 studies identified, 30 were included in the systematic review. A total of 9657 patients underwent nonsurgical rhinoplasty, most commonly with hyaluronic acid (HA) (96.76%), followed by calcium hydroxyapatite (CaHA) (1.22%). Overall satisfaction was 99.08%. The overall incidence of complications was 39.11%, with the highest incidence of erythema and swelling (27.95%). Most of the complications are mild, but there are still 0.27% of the patients who have undergone severe complication-an arterial occlusion. Nonsurgical rhinoplasty is an effective and relatively safe option for improving the profile of the nose, with a short operative time and high patient satisfaction. Most of the complications were mild, but still serious vascular complications such as blindness, skin necrosis, and stroke were as high as 0.27%. A thorough understanding of the anatomy of the nasal vessels and a precise surgical technique is an important basis for prevention. A BULLET POINT LIST: (1) We summarize the common types of fillers and injection techniques, complications, and treatment of complications to guide physicians to perform nonsurgical rhinoplasty in a safer and more effective manner. (2) Out of 1812 studies through the search strategy, 30 articles were included in the systematic review. A total of 9657 patients underwent nonsurgical rhinoplasty. (3) Nonsurgical rhinoplasty is an effective and relatively safe option to improve the profile of the nose, with a short surgical time and high patient satisfaction. (4) Most of the complications were mild, but some severe complications due to the vascular factors such as blindness, skin necrosis, and cerebral infarction need to be vigilant. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Experimental analyses of high-filled cut-and-cover tunnel for reduction of the earth pressure

ABSTRACT The pressure distribution over buried structures like pipes and tunnels are considered a main factor in the economic design of such structures. This study shows the effect of using crumb rubber mixed with sand and geogrid layers to enhance the soil pressure distribution over that buried structure. That method is titled a high-filled cut-and-cover (HFCCT) construction method. Crumb rubber particles pieces mixed with sand as a lightweight fill material (LFM) in HFCCT are used to reduce the vertical earth pressure (VEP) on that buried tunnel. Geogrid reinforcement layer above the HFCCT system to strengthen the soil layers above the tunnels were implemental. A physical model is built to simulate such conditions by applying external loads to the treated soil layers above the tunnel. The strains are measured on the external body of the tunnel, while the soil pressure is assessed through pressure gauges around the tunnel. The results obtained from the crumb rubber models are compared with those obtained from the geogrid model. It was deduced that using crumb rubber and geogrid, reduces the earth pressure above the cut-and-cover tunnel (CCT). As compared to the use of geogrid, the utilization of rubber as a substitute for soil results in a 27% drop in pressure. The obtained results show that the use of geogrids in sandy soils leads to uniform stress, while using rubber sand could reduce the maximum stress of the soil above the tunnel.

Efficacy of root-end filling techniques using premixed putty type bioceramic cements: an ex vivo study.

Currently, premixed putty-type bioceramic cements (PPBCs) have become popular materials for root-end fillings. This study investigated three root-end filling techniques using PPBCs and calcium silicate-based sealers including EDTA pretreatment. Ninety root segments were prepared and standardized with an artificial fin and lateral canal, and assigned to three groups (n = 30). Root-end fillings were placed using BC-RRM Putty alone (Group PA), injection of BC sealer followed by BC-RRM Putty (Lid Technique: Group LT) or BC-RRM Putty with BC sealer coating (Deep putty packing technique: Group DP). Half of each group was pretreated with 17% EDTA. The radiographic images of the specimens were assessed by five graders and push-out bond strength tests were conducted. The data were analyzed with a general linear model including two-way ANOVA and chi-square test at a significance level of 5%. DP approach demonstrated significantly higher bond strength than LT (P < 0.05). However, there was no statistically significant difference in bond strength between PA and either DP or LT. EDTA pretreatment had no significant effect on push-out bond strength. Radiographically, for the main canal, PA and DP scored significantly higher than LT. In the fin, PA scored significantly higher than others (P < 0.05). Our study highlights variations in root-end filling techniques. Injecting a bulk of bioceramic sealer before the placement of PPBCs may reduce bond strength and radiopacity. The application of PPBCs alone or in the deep putty technique demonstrates potential for favorable outcomes. EDTA pretreatment did not enhance bond-strength. Careful selection and application of bioceramic materials and techniques in root-end fillings may influence the outcome of endodontic root-end surgery. When PPBCs and calcium silicate-based sealers are used together for root-end fillings, sealer followed by deep putty application may offer improved bond strength and radiographic fill compared to the lid technique.

Оценка сварочно-технологических свойств электродных покрытий основного типа различных производителей электродов для сварки трубных деталей и сборочных единиц поверхностей теплообмена котлоагрегатов

Introduction. New grades of high-strength steels, machining and repair processes are being introduced in the power industry. At the same time manual arc welding remains the main technological process for equipment repair in conditions of thermal power plants. Welding materials used in equipment repair should provide comparable to the base metal mechanical properties of the weld. The welding industry has long faced the problem of high sensitivity of basic type electrodes to moisture absorption. High susceptibility to cold cracking caused by diffusible hydrogen and hydrogen embrittlement are major obstacles to the wider use of basic-type electrodes for high-strength steels. Hydrogen production during arc welding is the result of the presence of hydrogen in the arc atmosphere, hydrogen-contaminated filler material, or local hydrogen residues on the source material. During welding, molecular hydrogen is dislocated by the arc energy and then easily absorbed by the molten material. Currently, the welding materials market produces electrodes with basic coating of well-known and proven brands, various national and foreign manufacturers. However, in practice there are cases of cold cracks in the weld seam after welding. Purpose of work is to assess the welding and technological properties of basic type electrode coatings of different manufacturers. The work investigates specimens weld overlaid with electrodes TMU-21U, TSU-5 of different manufacturers and the content of diffusion-mobile hydrogen in the weld overlaid metal is determined. The methods of research are mechanical static tensile tests, chemical composition analysis and metallographic studies. Determination of welding-induced hydrogen content can be accomplished by various quantitative elemental analysis methods. All test methods involve welding under defined conditions followed by deep freezing of the test specimens as quickly as possible. In this way, unintended diffusion processes are inhibited and the hydrogen introduced into the weld metal is retained. Subsequently, the diffusing hydrogen is desorbed from the test specimens in a controlled manner. Results and Discussion. An assessment of welding engineering properties of the electrodes revealed unstable arc burning. Mechanical properties of the welded metal of the investigated electrodes are at the minimum permissible level from the requirements of normative documents. The concentration of hydrogen present in the arc weld metal is multifactorially dependent on the welding procedure (process and parameters, consumables used, as well as environmental conditions (e.g. humidity). For qualitative assessment, hydrogen content of more than 15 cm3/100 g is considered high and hydrogen content less than 5 cm3 ml/100 g is considered very low. Presented results. The conducted evaluation of welding engineering properties of electrodes with basic coating showed satisfactory results. Mechanical properties of the welded metal in terms of impact toughness are at the lower permissible limit, relative elongation does not meet the requirements of normative documents. The content of diffusion-mobile hydrogen in the welded metal is higher than the declared indicators by the electrode manufacturers.

Low-cycle fatigue behaviour of stainless-clad bimetallic steel welded connections

The stainless-clad (SC) bimetallic steel is the most widely used laminated high-performance steel in construction, which often offers a variety of prominent structural performance and competitive advantages. Welding with electrodes of suitable mechanical properties and corrosion resistance is vital for SC bimetallic steel structures to ensure a complete corrosion-resistant surface. However, the research on welded connections under cyclic actions is very limited. Many recommendation designs and current standards for SC bimetallic steel are primarily developed for precision equipment, and they are not suitable for structural engineering. To this end, this paper aims to investigate the low-cycle fatigue behaviour of butt welded connections with different welding configurations for the SC bimetallic steel. Failure modes, cyclic characteristics and Masing behaviour of typical welded connections were analysed, and the low-cyclic fatigue behaviour was validated using the Basquin-Coffin-Manson model. A new proposed strain energy-based model was also proposed to describe. Differences in the low-cycle fatigue behaviour between the welded connections and the base bimetal were demonstrated, as well as that for various welding configurations. It was found that the low-cycle fatigue life of the welded connections with a transition weld zone is similar to that of these welded connections without a transition weld zone, both being about 60 % to 80 % of the base bimetal's fatigue life. However, the fatigue life of the welded connection with a single filler material is much shorter than that of the previous two, being only 15 % to 30 % of that of the base bimetal. It should be noted that both the adapted Basquin-Coffin-Manson model and the newly proposed strain energy-based model may predict well the low-cycle fatigue life of the three welded connections. Finally, the transition weld zone in these welded connections is recommended to be eliminated in order to simplify the welding procedures, and hence to improve welding efficiency.

Structuration and yield strength characterization of hybrid alkali-activated cement composites (HACC) for ultra-rapid 3D construction printing

This study investigates the critical time-dependent rheological properties, including structuration rate and yield stress, of hybrid alkali-activated cement composites (HACC). HACC, a blend of geopolymer and cement paste, is examined to evaluate its suitability for ultra-rapid 3D construction printing (3DCP), which refers to a material’s ability to attain rapid structuration and buildability within 5–10 min after mixing, essential for additive manufacturing of 3D structures. The investigation extends to the impact of filler materials like silica sand and PVA fibers on HACC’s rapid structuration. Vicat needle, fast- and slow-penetration resistance measurements indicate that setting time increases with decreasing the Silicon/Aluminum (S/A) molar ratio and the addition of silica sand. Conversely, the addition of fibers reduces setting time while enhancing yield strength. Specifically, HACC mixtures with 0.5% and 1% PVA fiber additions, alongside combined sand (30%, 40%) and fiber (0.5%) mixtures, demonstrate ultra-rapid setting behavior within 3–5 min. Notably, mixtures with 40% silica sand and 0.5% PVA fiber exhibit highest yield strength development, i.e., 14 MPa at 12 min. Remarkably, incorporating 1% fibers into the HACC mixture yields the highest 28-day compressive strength (∼80 MPa) and flexural strength (∼11 MPa). The synergistic interplay between geopolymer and cement facilitates rapid setting time and high early-age strength development in HACC mixtures. The varying effects of silica sand and PVA fiber on setting time and yield strength provide opportunities for designing suitable structuration profiles. These findings underscore the exceptional rapid setting, structuration, and mechanical properties of HACC, positioning it as a promising material for ultra-rapid 3D construction printing.

Combined Experimental and Numerical Modelling of the Electrical Behaviour of Laser-Soldered Steel Sheets.

The electric vehicle (EV) industry challenges battery joining technologies by requiring higher energy density both by mass and volume. Improving the energy density via new battery chemistry would be the holy grail but is seriously hindered and progresses slowly. In the meantime, alternative ways, such as implementing more efficient cell packaging by minimising the electrical resistance of joints, are of primary focus. In this paper, we discuss the challenges associated with the electrical characterisation of laser-soldered joints in general, and the minimisation of their resistive losses, in particular. In order to assess the impact of joint resistance on the overall resistance of the sample, the alteration in resistance was monitored as a function of voltage probe distance and modelled by finite element simulation. The experimental measurements showed two different regimes: one far from the joint area and another in its vicinity and within the joint cross-section. The presented results confirm the importance of the thickness of the filler material, the effective and total soldered area, and the area and position of the voids within the total soldered area in determining the electrical resistance of joints.