Search Results (47)

The study focused on the development and optimization of plastic deformation of pure M1E copper using an unconventional hydrostatic extrusion (HE) process aimed at improving the performance of electrodes used in electrical discharge machining (EDM). The process was designed to refine the microstructure while maintaining the high electrical conductivity required for EDM applications. Optimization of a three-stage HE process (cumulative strain ε = 2.51) resulted in the formation of an ultrafine-grained structure (d₂ ≈ 370 nm), leading to a significant increase in mechanical strength (UTS ≈ 400 MPa) while preserving very high electrical conductivity (~99% IACS). This combination of properties is particularly important for EDM electrodes, as it allows improved wear resistance without compromising electrical performance. Due to the application-oriented nature of the study, the HE-processed copper was tested under industrial EDM conditions. Wear tests were conducted using seven electrodes of different geometries required for the production of a sample injection mold. The results demonstrated a substantial reduction in electroerosion wear of HE-processed electrodes (30–90%) compared with undeformed copper, together with up to 25% improvement in surface quality. These findings indicate that hydrostatic extrusion is an effective method for producing high performance EDM electrode materials with improved durability and machining quality. Full article

This paper proposes a complex plastic forming process for grade 2 titanium using a combination of severe plastic deformation techniques, equal-channel angular pressing (ECAP) and hydrostatic extrusion (HE). The aim of the combination of these methods is to reduce the strength of the phenomenon of microstructural anisotropy and the resulting anisotropy of mechanical properties characteristic of the HE process. Two routes of plastic deformation (HE and ECAP + HE) were compared using the same total strain rate of ε ~ 3.5. Results: The analysis of mechanical properties and microstructure studies using TEM and SEM/EBSD techniques showed that it is possible to obtain large microstructure refinement of titanium with almost identical mechanical properties via both studied techniques. In addition, this also leads to a significant improvement in the strength of UTS by ~ 1000 MPa, YS by ~ 945 MPa and ductility (E) by ~ 25%. These findings indicate that applying a sequential ECAP + HE strategy can effectively reduce anisotropy and improve the overall performance of grade 2 titanium. Full article

AA1050 aluminum was hydrostatically extruded at room temperature to true strains of 0.9 and 3.2, and at cryogenic temperature to a true strain of 0.9. As a result of the extrusion process, the yield strength (YS) increased by 130–160% to 120–130 MPa, and the ultimate tensile strength (UTS) rose by 64–81% to 125–140 MPa. The hardness reached 46–49 HV. YS and UTS values correspond to mechanical properties typical of the H6 or H8 temper designations, with unusually high elongation at break ranging from 15% to 16.4%. Differences in lattice parameters, crystallite size, and lattice strain between samples deformed under various conditions—as well as those annealed after deformation—were within the margin of measurement uncertainty. This indicated that differences in defect density between the samples were relatively small, due to dynamic recovery occurring during extrusion. However, positron annihilation spectroscopy demonstrated that the cryo-cooled material extruded at a true strain of 0.9, as well as the one extruded at RT at a true strain of 3.2, exhibited significantly higher mean lattice defect concentrations compared to the sample extruded at RT at a true strain of 0.9. The predominant defects detected were vacancies associated with dislocations. The extrusion parameters also significantly affected the crystallographic texture. In particular, they altered the relative proportions of the <111> and <100> components in the axial texture, with the <100> component becoming dominant in cryogenically extruded samples. This trend was further intensified during recrystallization, which enhanced the <100> component even more. Recrystallization of the deformed materials occurred in the temperature range of 520–570 K. The activation energy for grain boundary migration during recrystallization was estimated to be approximately 1.5 eV. Full article

This review aims to give evidence of the current developments and potential applications of emerging technological methods to improve the technological performance and the sensorial acceptability of wholegrain products. The review explores the technologies based on physical, i.e., micronization, steam explosion, high hydrostatic pressure, extrusion cooking, ohmic heating, and 3D printing, and biotechnological methods, such as fermentation and enzymatic treatments in the pre-milling, milling, and transformation steps of wholegrain products. The literature from the past decade for this review article was collected from electronic databases such as ScienceDirect, PubMed, Google Scholar, and Web of Science. Full article

Background/Objectives: Most orthodontic forces are absorbed–dissipated before reaching the dental pulp and its neuro-vascular bundle (NVB); nonetheless, no data are available about this issue during the periodontal breakdown. The current study’s objective was to investigate how much orthodontic force reaches the dental pulp and NVB during the orthodontic movements in periodontal breakdown. Methods: Herein, an assessment was performed on the second lower premolar of nine patients (72 3D models) and included 1440 numerical simulations. A gradual horizontal periodontal breakdown (1–8 mm loss) was simulated. Five orthodontic movements (intrusion, extrusion, rotation, translation, and tipping) under 0.5 N/5 KPa and 4 N/40 KPa were assessed. The numerical methods used were Von Mises/VM (overall homogenous) and Tresca (shear non-homogenous), suitable for the ductile resemblance of dental tissues. Results: Both methods showed similar color-coded projections for the two forces. Quantitatively, Tresca was 1.14 times higher than VM and lower than the maximum physiological hydrostatic circulatory pressure. During the bone loss simulation, the NVB stress was 5.7–10.7 times higher than the pulpal stress. A gradual tissue stress increase was seen, strictly correlated with the bone loss level. For 1 mm bone loss, only 2–3% of the applied force manifested at the NVB level (0.27–0.5% for pulp), while for 8 mm loss, the received stress was 4–10% for the NVB (0.6–0.9% for pulp) when compared to the applied force. Only translation displayed pulpal stress. Conclusions: When assessing NVB stress, the tooth absorption–dissipation ability of dental tissues varied between 90 and 93% (8 mm loss) and 97% (1 mm bone loss) and 99% when assessing pulpal stress. Full article

Three-dimensional printing enables rapid prototyping, customization, and on-demand production. Polylactide is a popular biopolymer filament used in 3D printing. However, due to its brittleness and low mechanical strength, it often needs to be reinforced with filler particles. Diatomaceous earth shows great potential as a filler material due to its abundant and natural occurrence, biocompatibility, and environmental friendliness, as well as its excellent mechanical properties. Cold hydrostatic extrusion was used to improve the compressive strength of 3D-printed parts. Both neat and reinforced with 10% diatomaceous earth filaments were used to 3D print cylindrical billets, followed by post-processing using hydrostatic extrusion. X-ray microtomography showed a significant reduction in total and open porosity and average pore size, from ~20 µm to less than 10 µm in the Polylactide (PLA) and Diatomaceous (DE) composite. Compression tests showed a significant improvement in the compressive strength of PLA from ~60 MPa to ~100 MPa, while PLA with DE achieved an impressive almost twofold increase to 80–120 MPa. This was attributed to a reduction in pore size, as well as pore closure, which mitigates crack initiation in semi-brittle PLA. In addition, it has been proposed that hydro extrusion-induced structural rearrangement is an important strengthening factor. Full article

Background/Objectives: Dental pulp and its neuro-vascular bundle (NVB) are among the least studied dental tissues. This study identified the best method for evaluating ischemic risks in the dental pulp and NVB of healthy lower premolars under orthodontic forces and in intact periodontium. Methods: Nine 3D models of the second lower premolar were reconstructed based on the CBCT scans from nine patients. Nine patients (CBCT scan) were subjected to 3 N of intrusion, extrusion, rotation, tipping, and translation. Five numerical methods, Tresca, von Mises (VM), Maximum and Minimum Principal, and hydrostatic pressure were used to biomechanically assess (totaling 225 simulations) the color-coded stress distribution in pulp and NVB. The results (both qualitative and quantitative) were correlated with the physiological maximum hydrostatic pressure (MHP) and known tissular biomechanical behavior. Results: All five methods displayed quantitative amounts of stress lower than MHP and did not seem to induce any ischemic risks for the NVB and pulp of healthy intact premolars. Among the five movements, rotation seemed the most stressful, while translation was the least stressful. The NVB displayed higher amounts of stress and tissular deformations than the pulp, seeming to be more exposed to ischemic risks. Higher tissular deformations are visible in NVB during intrusion and extrusion, while pulpal coronal stress is visible only during translation. Only the VM and Tresca methods showed a constant stress display pattern for all five movements. The other three methods displayed various inconsistencies related to the stress distribution pattern. Conclusions: Only the Tresca and VM methods can provide correct qualitative and quantitative data for the analysis of dental pulp and NVB. The other three methods are not suitable for the study of the pulp and NVB. Full article

Background and Objectives: Most orthodontic forces are absorbed–dissipated before reaching the dental pulp and its neuro-vascular bundle (NVB); however, no data are available about their amounts. The objective of this study was to assess the amount of orthodontic force that reaches the dental pulp and its NVB during orthodontic movements in a healthy periodontium. Materials and Methods: This study involved the second lower premolars of nine patients and 180 numerical simulations. Five orthodontic movements (intrusion, extrusion, rotation, translation, and tipping) under 0.5 N/5 KPa and 4 N/40 KPa were assessed. The numerical methods included only two failure criteria suitable for dental tissue (of ductile resemblance): Von Mises (VM) (overall, homogenous) and Tresca (shear, non-homogenous). Results: Both forces displayed a similar color-coded stress display for the two methods. The Tresca quantitative results were 1.11 times higher than the VM but lower than the maximum physiological hydrostatic circulatory pressure. The biomechanical behavior of the pulp and NVB showed that, in the intact periodontium, the NVB-induced stress was 5.7 higher than in the pulp. Quantitatively, the rotation movement seemed to be the most stressful for the NVB, closely followed by intrusion and extrusion. For the dental pulp, rotation remained the most stressful, closely followed by tipping and translation. Tissue deformations were visible for NVB areas during intrusion and extrusion. The dental pulp showed pulpal stresses under translation and rotation. The numerical simulations with the two methods showed that, in the intact periodontium, only a small amount of the initial orthodontic load produced effects in the NVB and dental pulp. Only about 2.85% of the initial orthodontic load of 40 KPa/4 N applied at the bracket level induced stresses in the NVB, while the dental pulp was reached by 0.5% of the applied force. A similar distribution was seen at 5 KPa/0.5 N. Conclusions: The absorption–dissipation ability of the dental tissue varies between 97.15 and 99.98%. Full article

Background/Objectives: This study assessed the biomechanical behavior of dental pulp and the neuro-vascular bundle/NVB as well as the ischemic risks during orthodontic movements in a gradual horizontal periodontal breakdown, using five methods and aiming to identify the most accurate one. Methods: Seventy-two models of second lower premolar (from nine patients) were subjected to 3 N of intrusion, extrusion, rotation, tipping, and translation. Five numerical methods, Tresca, Von Mises/VM, Maximum and Minimum Principal, and hydrostatic pressure were used in a total of 1800 numerical simulations. The results were color-coded projections of the stress areas that were then correlated with maximum physiological hydrostatic pressure/MHP and known clinical biomechanical behavior. Results: During periodontal breakdown, all five methods displayed, for all movements, quantitative stresses lower than MHP, suggesting that 3 N are not inducing any local tissular ischemic risks for the healthy intact tissues. All five methods displayed rotation as the most stressful movement during periodontal breakdown, while translation was the least. The NVB was more exposed to ischemic risks than dental pulp during the periodontal breakdown due to constant tissular deformations. Only VM and Tresca methods showed translation as more prone to expose dental pulp (both coronal and radicular) to ischemic risks (than the other movements) during the periodontal breakdown simulation. However, all five methods showed intrusion and extrusion as more prone to expose the NVB to higher ischemic risks than the other movements during the periodontal breakdown simulation. Conclusions: During periodontal breakdown, Tresca and Von Mises were more accurate, with Tresca being the most accurate of all. Full article

Background/Objectives: There are few data about the ischemic risks induced by the large orthodontic forces during periodontal breakdown in dental pulp and neuro-vascular bundle (NVB) and none on the individual tissular stress distribution, despite their great importance for orthodontic treatment planning. Our aim was to assess, by a numerical analysis, the biomechanical behavior of dental pulp and the NVB during a simulated horizontal periodontal breakdown (1–8 mm), under 2–4 N of applied orthodontic forces and five movements (rotation, translation, tipping, intrusion, and extrusion). Additionally, the ischemic and degenerative-resorptive risks were assessed. Methods: The analysis involved 72 3D models of nine patients, totaling 720 simulations. The models were CBCT-based, having the second lower premolar and surrounding periodontium, and they suffered 1 mm of gradual horizontal periodontal breakdown (up to 8 mm loss). Results: Both forces displayed a similar qualitative stress distribution in all five movements, but with a quantitative increase (doubling of stress amounts for 4 N when compared with 2 N). The highest amounts of stress were displayed at 8 mm of periodontal loss, which is lower than the 16 KPa of the maximum hydrostatic pressure. The NVB stress was higher than the pulpal stress. Rotation was the most stressful, closely followed by tipping, intrusion, and extrusion. Conclusions: A total of 4 N of applied force seems to not induce any ischemic or degenerative-resorptive risks for healthy intact teeth, in up to 8 mm of periodontal breakdown. Intrusion and extrusion determined the highest visible tissular deformation in the NVB, with potential ischemic and resorptive-generative risks for previously traumatized/injured teeth (i.e., occlusal trauma). Rotation and translation (in particular) showed the highest coronal and radicular pulpal stress with potential ischemic and resorptive-generative risks for previously injured/traumatized dental pulp (i.e., direct-indirect pulp capping). It seems that 4 mm of periodontal breakdown could signal a clinical stress increase with potential ischemic and degenerative-resorptive risks for the previously traumatized/injured tissues. Full article

Background/Objectives: This numerical analysis of stress distribution in the dental pulp and neuro-vascular bundle (NVB) of lower premolars assessed the ischemic and degenerative–resorptive risks generated by 2 and 4 N during orthodontic movements (rotation, translation, tipping, intrusion and extrusion) in intact periodontium. Methods: The numerical analysis was performed on nine intact periodontium 3D models of the second lower premolar of nine patients totaling 90 simulations. Results: In intact periodontium, both forces displayed a similar stress distribution for all five orthodontic movements but different amounts of stress (a doubling for 4 N when compared with 2 N), with the highest values displayed in NVB. In intact periodontium, 2 N and 4 N induced stresses lower than the maximum hydrostatic pressure (MHP) with no ischemic risks for healthy intact teeth. The rotation was seen as the most stressful movement, closely followed by intrusion and extrusion. Translation was quantitatively seen as the least stressful when compared with other movements. Conclusions: Larger orthodontic forces of 2 N and 4 N are safe (with any expected ischemic or resorptive risks) for the dental pulp and NVB of healthy intact teeth and in intact periodontium. Nevertheless, rotation and translation movements can induce localized circulatory disturbances in coronal pulp (i.e., vestibular and proximal sides) generating ischemic and resorptive risks on previously treated teeth (i.e., direct and indirect dental pulp capping). The intrusion and extrusion movements, due to the higher NVB-induced deformation when compared with the other three movements, could trigger circulatory disturbances followed by ischemia on previously traumatized teeth (i.e., occlusal trauma). Full article

A comparative study of the structural integrity of an opaque recycled poly(ethylene terephthalate) (rPET-O) has been carried out with two types of modified rPET-O by applying reactive extrusion techniques, namely (a) using a multi-epoxide reactive agent (REx-rPET-O) and (b) a 90/10 (wt/wt) rPET-O/polycarbonate (PC) blend. The chemical modifications introduced during reactive extrusion were confirmed using differential scanning calorimetry (DSC) and rheological dynamic analysis (RDA). For the quantification of the fracture parameters, an instrumented pendulum impact testing machine was used using specimens in SENB configuration. The structural modifications generated during reactive extrusion promote an increase of between 16 (REx-rPET-O) and 20% (rPET-O/PC) in the stress-intensity factor (K_Q) compared to unmodified rPET-O. The most significant differences between both modifications are registered in the “specific work of fracture” (w_f) (alternative parameter to the standardized impact strength), where an increase of 61% is reached for the case of rPET-O/PC and only 11% for REx-rPET-O. This trend can be attributed to the type of reactive modification that is generated, namely chain branching (REx-rPET-O) vs. the generation of a random copolymer “in situ” (rPET-O/PC). This copolymer decreases the crystallization capacity and degree of crystalline perfection of rPET-O, promoting an increase in the critical hydrostatic stress conditions for the generation of crazing and crack propagation. Full article

In recent years, there has been a lack of information in the literature regarding the extrusion and connection of closed profiles from oxygen-free copper in bridge dies. Available studies contain information on the processes of extrusion and connection of profiles from aluminium alloys and various types of steel. However, there is a lack of detailed data on the values of technological parameters for which copper is joined in the extrusion process. Therefore, one of the goals of this work is to fill the gap in the literature regarding the extrusion of oxygen-free copper in bridge dies. In this work, the authors determined the thermo-mechanical conditions at which oxygen-free copper will be joined. This paper describes the effects of charge temperature and hydrostatic pressure in the weld zone of a bridge die on copper bonding in the fabrication of tubular profiles. Physical tests of the welding process under the conditions of upsetting a material consisting of two parts were carried out using the Gleeble 3800 metallurgical process simulator with the PocketJaw module in the standard configuration for SICO (strain-induced crack opening) tests. For the numerical simulations, the commercial computer programme FORGE^®NxT 2.1. using the finite element method (FEM) was used. Based on the analysis of the test results obtained, it was found that complete material bonding during the extrusion process could be achieved for a charge temperature higher than 600 °C and a hydrostatic pressure of 45–65 MPa. Full article

Currently, the field of microgear manufacturing faces various processing challenges, particularly in terms of size reduction; these challenges increase the complexity and costs of manufacturing. In this study, a technique for microgear manufacturing is aimed at reducing subsequent processing steps and enhancing material utilization. This technique involves the use of trough dies with extrusion-cutting processing, which enables workpieces to undergo forming in a negative clearance state, thus reducing subsequent processing time for micro products. We conducted finite element simulations using microgear dies, measuring stress, velocity, and flow during the forming process of four types of dies-flat, internal-trough, external-trough, and double-trough dies. The results indicated that the buffering effect of the troughs reduced the rate of increase in the material’s internal stress. In the cavity, the material experiences a significant increase in hydrostatic pressure, leading to the formation of a “hydrostatic pressure wall”. This pressure barrier imposes substantial constraints on the flow of the material during dynamic processes, making it difficult for the material to move into the remaining areas. This effectively enhances the blockage of material flow, demonstrating the critical role of hydrostatic pressure in controlling material distribution and movement. In addition, combining the characteristics of both into a double-trough die enhances the overall stability of forming velocity, reduces forming load and energy consumption, and maximizes material utilization. Results further revealed that microgears manufactured using double-trough dies exhibited defect-free surfaces, with a dimensional error of less than 5 μm and tolerances ranging from IT5 to IT6. Overall, this study offers new insights into the traditional field of microgear manufacturing, highlighting potential solutions for the challenges encountered in current microstamping processes. Full article

The development of bioabsorbable implants from Zn alloys is one of the main interests in the new generation of biomaterials. The main drawbacks of Zn-based materials are their insufficient mechanical properties. In the presented studies, a quaternary alloy composed of zinc with magnesium (0.2–1 wt. %), calcium (0.1–0.5 wt. %) and strontium (0.05–0.5 wt. %) was prepared by gravity casting followed by hot extrusion and then by hydrostatic extrusion. Microstructural characterization using scanning electron microscopy (SEM) and X-ray diffraction (XRD) phase analysis was performed. The mechanical properties were examined, using static tensile tests. Corrosion properties were analyzed using immersion tests. Samples were immersed in Hanks’ solution (temperature = 37 °C, pH = 7.4) for 14 days. All alloys were subjected after corrosion to SEM observations on the surface and cross-section. The corrosion rate was also calculated. The microstructure of the investigated quaternary alloy consists of the α-Zn grains and intermetallic phases Mg2Zn11, CaZn13 and SrZn13 with different grain sizes and distribution, which impacted both mechanical and corrosion properties. Thanks to the alloying by the addition of Mg, Ca, and Sr and plastic deformation using hydrostatic extrusion, outstanding mechanical properties were obtained along with improvement in uniformity of corrosion rate. Full article