Search Results (26)

Severe friction and extreme temperatures occur at the tool–chip interface during metal cutting. Conventional cutting fluids struggle to penetrate interface micro-capillaries at the contact interface under high contact pressure. This issue causes severe tool–chip adhesion and accelerates tool wear. This study aims to solve fluid delivery limitations by introducing micro-textures with a depth of 15 microns on the tool surfaces. It reveals the mechanism of micro-textures in accelerating fluid penetration and reducing interface friction. An analytical capillary penetration model was established for conventional and micro-textured tools. Thermal penetration tests (30–150 °C) and turning experiments on hardened steel were conducted to evaluate interfacial fluid transport behavior. Theoretical modeling shows that micro-textures facilitate direct vapor-phase filling into micro-capillaries. This mechanism bypasses liquid ingress and droplet evaporation stages. This reduces the fluid penetration time into the capillaries by almost an order of magnitude. Thermal tests show that textured surfaces maintain dynamic vapor–liquid equilibrium. At 150 °C, the vapor penetration area reaches 978.5 × 10⁻³ mm² on micro-textures, over four times that of smooth surfaces. Energy dispersive spectrometry (EDS) detected fluid-derived sodium (0.98 at.%) inside micro-textured capillaries. Meanwhile, workpiece material adhesion decreases from 6.04 at.% to 0.11 at.%. In turning tests of AISI 1045 hardened carbon steel, micro-textured tools reduced the main cutting force by up to 17% and the axial force by up to 22%. Cutting temperatures decreased by up to 10.0%. The average tool–chip friction coefficient dropped by 9.2% at a cutting speed of 240 m/min. This work provides insights into a vapor-phase lubrication mechanism and offers quantitative guidance for designing high-efficiency self-lubricating tools. Full article

An alternative conductive ink based on carbon nanotubes (CNTs) was developed using a platinum-catalyzed silicone elastomer and isopropyl alcohol (IPA). The inclusion of IPA in the conductive CNT ink facilitated the optimization of its mechanical strength, electrical conductivity, and viscosity. Compared to conventional silicone rubber-based conductive polymers that often solidify in a few hours at room temperature or with heating, this liquid composite of CNT particles and IPA exhibited a prolonged duration of up to several months in a hermetic environment, maintaining chemical stability even with the elastomer and its curing agent. The gradual evaporation of IPA initiates a well-known cross-linking process, leading to stretchability and electrical conductivity derived from the silicone elastomer and CNT particles, respectively. The relationship between the mechanical strength and electrical conductivity of the hardened conductive CNT ink was studied, which helped determine the optimized concentration of CNT particles in the conductive CNT ink. Subsequently, a piezoresistive sensor was designed, fabricated, and evaluated. The conductive CNT ink-based piezoresistive sensor showed high sensitivity and good repeatability with respect to a wide range of external forces. The effect of the concentration of CNT particles on the viscosity of the conductive CNT ink was also investigated, providing a better understanding of the entanglement of CNT particles within the silicone elastomer. A coating test using the conductive CNT ink with a paper cutting machine demonstrated its potential for adaptation to various printing techniques, including screen printing. The proposed conductive CNT ink, characterized by a simple chemical composition, facile fabrication process, use of non-toxic elements, high electrical conductivity, and stretchability, combined with an extended duration, has the potential to be applied for multiple purposes, such as various types of flexible and wearable electronics. Full article

This article presents the results of experimental studies to determine the possibility of processing steelmaking slags into an artificial granulated filler for concrete by the method of forced carbonization and the stabilization of the obtained filler in the concrete matrix over time. The utilization of metallurgical waste and technogenic CO₂ is a global problem. In this work, the method of the granulation of finely ground converter (BOF) and electric steelmaking (EAF) slags was used to obtain artificial granules and their subsequent forced carbonization in the developed laboratory carbonization chamber. Within the framework of this study, the quantitative binding of CO₂ by granules based on BOF and EAF slags was established, which amounted to 5.2 and 7.8% by weight, respectively. It was determined that the mass loss during crushability testing, indirectly characterizing the actual compressive strength of the granule material, depending on the type of slag and grain size, ranges from 13.6 to 42.3%, which is quite sufficient for using this artificial filler in concrete production. Based on the developed batches of fillers, concretes were obtained that have a compressive strength of 30.7 to 37.8 MPa in 28 days of hardening, which generally corresponds to concrete class B25. The preliminary studies and the results obtained indicate the prospects of processing steel slags into artificial granulated fillers by forced carbonization and using this product in concrete production. Full article

Fibre-reinforced composites are facing new challenges in the context particular in sustainability and recyclability. Vitrimers could be useful as new matrices to support the increase in sustainability. Due to their high strength, which is comparable to that of thermosets often used in composites, and their covalent adaptive networks, which make them reshapeable for scaled-up manufacturing and recycling purposes, they are very useful. Orthogonal cutting is used for precise reshaping and functional integration into carbon fibre reinforced plastics. Vitrimers could improve processing results at the cutting edge as well as surface quality thanks to their self-healing properties compared to brittle matrices, as well as enabling the recycling of formed chips and scrap. This study showcases the manufacturing of a carbon fibre-reinforced vitrimer using 4-aminophenyl disulfide as a hardener, with vacuum-assisted resin infusion. The temperature of chip formation and the cutting parameters are then shown for different fibre orientations, cutting widths and speeds. The observed cutting forces are lower (less than 140 N) and more irregular for fibre orientations 45°/135°, increasing with cutting depth, and fluctuating periodically during machining. Despite varying cutting speeds, the forces remain relatively constant in range between 85 N and 175 N for 0°/90° fibre orientation and 50 N and 120 N for 45°/135° fibre orientation, with no significant tool wear observed and lower-damage depth and overhanging fibres observed for 0°/90° fibre orientation. Damage observation of the cutting tool shows promising results, with lower abrasion observed compared to thermoset matrices. Microscopic images of the broached surface also show good quality, which could be improved by self-healing of the matrix at higher temperatures. Temperature measurements of chip formation using a high-speed camera show a high temperature gradient as cutting speeds increase, but the temperature only ever exceeds 180 °C at cutting speeds of 150 m/min, ensuring reprocessability since this is below the degradation temperature. Therefore, orthogonal cutting of vitrimers can impact sustainable composite processing. Full article

The current research trends of production engineering are based on optimizing the machining process concerning human and environmental factors. High-performance materials, such as hardened steels, nickel-based alloys, fiber-reinforced polymer (FRP) composites, and titanium alloys, are classified as hard-to-cut due to their ability to maintain strength at high operating temperatures. Due to these characteristics, such materials are employed in applications such as aerospace, marine, energy generation, and structural. The purpose of this article is to investigate the machinability of these alloys under various cutting conditions. The purpose of this article is to compare cryogenic cooling and cryogenic processing from the perspective of machinability and sustainability in the manufacturing process. Compared to conventional machining, hybrid techniques, which mix cryogenic and minimal quantity lubricant, led to significantly reduced cutting forces of 40–50%, cutting temperatures and surface finishes by approximately 20–30% and more than 40%, respectively. A carbon footprint is determined by several factors including power consumption, energy requirements, and carbon dioxide emissions. As a result of the cryogenic technology, the energy consumption, power consumption, and CO₂ emissions were reduced by 40%, 28%, and 35%. Full article

This article explores the possibility of using metallurgical waste slags formed during the smelting of cast iron and steel as cementless binders that harden due to forced carbonization and the subsequent hydration processes of some minerals that form the basis of these slags. This study presents the results of multi-objective optimization using statistical methods of mathematical experimental design, with the purpose of obtaining a carbonized material with good mechanical and physical properties. As a result of the research, carbonized stone with compressive strength up to 116.5 MPa was obtained. Water absorption by weight is within the range of 6.0–17.0%, and quantitative CO₂ binding was 6–11.9%, depending on the type of slag. A pilot batch of wall product samples (hollow bricks and paving elements of various territories) was manufactured under production conditions. During the tests, we found that the compressive strengths of products based on BOF and EAF slags were 96.3 and 81.1 MPa, respectively, and that of bricks based on BS slag was 37.1 MPa. A comprehensive analysis of the performance properties of products from the pilot batch showed that these samples meet the requirements of national standards. Full article

The performance of high-performance concrete has been enhanced in the present study by incorporating non-metallic fibres without altering the binder content. The impact of these fibres on high-performance concrete flexural and compression characteristics and the arrangement of fibres within the composite were systematically analysed. Unlike conventional practices, the authors of the research introduce various non-metallic fibres, including alkali-resistant glass fibres, carbon microfibers, three types of polypropylene microfibers, and one type of polyvinyl alcohol fibre while maintaining an equal amount of binder. The research aims to comprehensively evaluate the fibre’s influence on cement composite properties. Various types of non-metallic fibres, highlighting differences in diameters and their physical-mechanical properties with a constant amount by volume, have been considered in the research. Alkali-resistant glass and carbon fibres exhibit low values of residual post-cracking force but polyvinyl alcohol fibres demonstrate the best post-cracking behaviour, with a residual post-cracking force value. This detailed examination of fibre distribution and composition sheds light on the nuanced effects on fresh and hardened concrete properties. Notably, this work diverges from existing research by maintaining a constant binder amount and considering the quantitative distribution of fibres in a unit volume of the cement matrix, along with their aspect ratio. These findings provide valuable insights for selecting the most suitable non-metallic fibres for enhancing high-performance concrete properties. Full article

Austenitic stainless steels, such as 304 and 304L, are extensively utilized in diverse industries due to their favorable properties, including biocompatibility, high durability, ductility, toughness at cryogenic temperatures, and excellent corrosion resistance. Additionally, these steels exhibit notable resistance to fatigue and oxidation. Despite these advantages, they are challenging to machine due to characteristics such as high work hardening, built-up edge formation, and low heat conductivity. The material 304L distinguishes itself from material 304 through its lower carbon content, making it more resistance to corrosion. 304L is experiencing a consistent rise in industrial demand. It is anticipated that this advanced material will progressively supersede 304 in various applications. The variability in alloy compositions and surface integrity of blanks can influence the tool wear and may even lead to abrupt tool breakage, necessitating supervision during machining operations. This study delves into the correlation between the alloy compositions, micro structure, surface integrity, and machinability of these special steels, focusing on turning processes. Various blanks of 304 and 304L in the form of bars, sourced from different manufacturers, were utilized in the study. These blanks exhibited slight variations in alloy composition (albeit within the standard range) and differed in the state of surface integrity characterized by variations in microstructure, grain size, microhardness, and residual stress. All blanks (across this array of materials) were subjected to turning using the same tool specifications and sets of machining parameters for comparative analysis. Various machinability indicators, including cutting forces, surface roughness, burr formation, tool wear, and chip morphology, were thoroughly examined. The findings highlight that the key factors influencing machinability include the microhardness of the surface and the residual stress state in the subsurface of the bars before the turning process. In contrast, changing the alloy composition within the standard range has hardly any effect on the machinability of these steels. The machinability of the examined specimens was adversely affected when the hardness exceeded 350 HV from the surface up to 2 mm below the surface and simultaneously the surface compressive residual stress exceeded −130 MPa. Full article

Reinforced concrete two-way slabs are important elements in the construction field, and their impact response under drop-weight impact is a complex mechanical issue that can cause the collapse of heavy structures. Previous research has documented the analysis of conventional steel-reinforced concrete slabs under impact loads. However, the investigation of layered hybrid concrete composite flat solid slabs reinforced with carbon-fiber-reinforced polymer (CFRP) rebars is an innovative subject. This paper examines the structural behavior of layered novel hybrid concrete composite flat solid slabs with a combination of reactive powder concrete (RPC) in the top layer and normal concrete (NC) in the bottom layer, reinforced with internal CFRP or traditional steel bars in the tension zone, under an impact load test. For this purpose, ten full-scale square flat solid slab samples with a 1550 mm length and a 150 mm depth were fabricated and divided into eight layered hybrid concrete samples with 50% RPC and 50% NC and two samples cast with NC only. The impact tests were carried out using a hardened steel cylindroconical impactor (projectile) with a height of 650 mm and a diameter of 200 mm, a flat nose diameter of 90 mm, and a total mass of 150 kg released from two different heights of 5 and 7 m. The variables considered were the types and ratios of reinforcement, as well as the free-drop weight and height. The experimental results obtained showed that layered RPC flat solid slabs are superior in resisting and sustaining impact forces and also have fewer scattered parts when compared to NC flat solid slabs. Additionally, the flat solid slab samples reinforced with CFRP bar grids were overall more resistant to impact loads, by an average of 19%, compared to flat solid slabs with steel bars and showed lower deflection, by an average of 10%, compared to the other flat solid slabs. Full article

Cold forging is widely used in many industries. Multi-stage cold forming is usually utilized in forging fasteners. In this study, numerical simulation and experimental investigations were carried out on a five-stage cold-forming process for the manufacturing of low-carbon steel AISI 1010 relief valve regulating nuts. The forming process through five stages included preparation and centering for backward extrusion, backward extrusion over die pin, upset, backward extrusion over a moving punch, and piercing. The formability of the workpiece was studied, such as the effects on forming force response, maximum forming force, effective stress and effective strain distributions, metal flow patterns, and strength. A comparison of the forming forces obtained in the forming experiment with the numerical simulation results of the five-stage cold forming showed a good agreement with the trend of the forming force growth. For the maximum forming force and forming energy, the fourth stage of backward extrusion over the moving punch at the upper face was the largest among the five stages. The total maximum forming forces from the first to the fifth stages were numerically 440.9 kN and experimentally 449.4 kN, meaning the FE simulation and experimental results were in good agreement. The numerically simulated effective strain distributions were consistent with the experimentally tested hardness distributions. Highly compacted grain flow lines also resulted in higher hardness. The overall hardness of the workpiece formed by five-stage cold forming increased by 31% compared to the initial billet. The hardness of the workpiece increased with the forming stages, and the strain-hardening effect was obvious. The strength of the workpiece was significantly increased by five-stage cold forming. Full article

As a top construction material worldwide, concrete has core weakness relating to low tensile resistance without reinforcement. It is the reason that a variety of innovative materials are being used on concrete to overcome its weaknesses and make it more reliable and sustainable. Further, the embodied carbon of concrete is high because of cement being used as the integral binder. Latest research trends indicate significant potential for carbon fiber as an innovative material for improving concrete mechanical strength. Although significant literature is available on the use of carbon fiber in concrete, a limited number of studies have focused on the utilization of carbon fiber for concrete mechanical strength improvement and the reduction of embodied carbon. Following the gap in research, this study aimed to investigate and optimize the use of carbon fiber for its mechanical characteristics and embodied carbon improvements. The use of carbon fiber in self-compacting concrete lowers sagging. The greatest quantity of carbon fiber is that it reduces the blockage ratio, forcing the concrete to solidify as clumps develop. With time, carbon fiber improves the durability of concrete. Self-compacting concrete with no carbon fiber has a poor tensile strength. Experiments were conducted by adding carbon fiber at 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% by weight. Fresh concrete tests including slump test and L-box test, hardened concrete tests involving compressive strength and splitting tensile strength, and durability tests involving water absorption and acid attack test were conducted. Embodied carbon ratios were calculated for all of the mix ratios and decreasing impact, in the form of eco-strength efficiency, is observed with changes in the addition of carbon fiber in concrete. From the testing results, it is evident that 0.6% carbon fiber is the ideal proportion for increasing compressive strength and split tensile strength by 20.93% and 59%, respectively, over the control mix. Response Surface Methodology (RSM) is then applied to develop a model based on results of extensive experimentation. Optimization of the model is performed and final modelled equations are provided in terms of calculating the impact of addition of carbon fiber in concrete. Positive implications are devised for the development of concrete in the future involving carbon fiber. Full article

In a way so far unmatched in any single study, this paper presents the complex characteristics of commercially pure titanium (CP-Ti) containing 0.2 wt.% carbon, which is significantly above the carbon level in commonly used titanium alloys, while at the same time being the maximum permitted content in light of the recommendations in force. It has been demonstrated that the addition of carbon in CP-Ti can have many positive impacts. The investigated Ti-0.2C alloy was produced in a cold-copper crucible induction vacuum furnace and processed into a 12 mm diameter bar by hot rolling. The structure and properties of the Ti-0.2C alloy were compared to those of an CP-Ti Grade 1 produced and processed under the same technical conditions. The addition of 0.2 wt.% carbon to CP-Ti has been found to change the course of the crystallization process, the course and temperatures of phase transformations, and the values of lattice parameters; reduce susceptibility to grain growth; and create the possibility for additional hardening during solution treatment and aging. At the same time, it results in an assumed improvement in properties by increasing the tensile strength and yield strength, hardness, creep and oxidation resistance, and abrasive wear. It has a negative effect but is still within the acceptable range on impact strength and susceptibility to hot and cold deformation. Full article

Climate change is accelerating its adverse impact on ecosystems and infrastructure systems in cold regions. For extensive carbonate saline soil areas, their response to the freeze-thaw cycle remains uncertain. By considering the continuous intensification of freeze-thaw cycle frequency, the mechanical characteristics of carbonate saline soils are analyzed for different salt content (0.6% to 2.1%) based on the mechanical test in this paper. The purpose is to reveal the change law of shear strength and its parameters of carbonate saline soils under the scenario of continuous freezing and thawing cycles. The micro-characteristics of the carbonate saline soil before and after freeze-thaw cycling were analyzed by scanning electron microscopy, indicating changes in the structural soil properties caused by the combination of freeze-thawing and salinity. The scanning electron microscope images reveal the cumulative effect of frost heaving and salt expansion, i.e., increasing the number of pores between particles, reducing the effective contact between particles, and weakening the interaction force, resulting in cracks development. A series of mechanical tests demonstrate the stress-strain behavior of carbonate saline soils for different numbers of freeze-thaw cycles under different confining pressures. A transformation from strain-softening to strain-hardening is observed with an increase in the salt content from 0.6% to 2.1%. Furthermore, the shear strength of the carbonate saline soil decreases as the salt content and number of freeze-thaw cycles increase. The shear strength degradation mechanism is attributed to the cohesion and the internal friction angle. These shear strength parameters are critical in geotechnical analyses, such as evaluating of load capacity of foundations and slope stability in similar saline soils. Full article

This research is aimed at evaluating the effect of low-cycle fatigue on a newly designed hybrid sandwich ski structure to determine the changes that may occur due to cyclic loading and thus affect its use. This is primarily concerned with the fatigue behavior of the tested ski over different time intervals simulating its seasonal use and its effect on the mechanical properties of the ski, i.e., the durability and integrity of the individual layers of the sandwich ski structure. The ski was subjected to 70,000 deflections by moving the crossbar by 60 mm according to the ski deflection calculation in the arch. The results of the cyclic tests of the engineered ski design showed no significant changes in the ski during loading. The average force required to achieve deflection in the first 10,000 cycles was 514.0 ± 4.2 N. Thereafter, a secondary hardening of the structure occurred during relaxation and the force required increased slightly to 543.6 ± 1.7 N. The required force fluctuated slightly during the measurements and in the last series the value was 540.4 ± 0.8 N. Low-cycle fatigue did not have a significant effect on the mechanical properties of the ski; there was no change in shape or visual delamination of the individual layers of the structure. From the cross-section, local delamination was demonstrated by image analysis, especially between the Wood core and the composite layers E-Glass biaxial and Carbon triaxial. Full article

The retained austenite (RA) in advanced high-strength steel (AHSS) grades, such as dual-phase (DP) steels, plays an important role on their formability. Thanks to the transformation-induced plasticity (TRIP) effect that occurs during the mechanically induced transformation of RA into martensite, additional ductility is obtained. Martensite has a higher flow stress than austenite; hence, the transformation results in an apparent hardening, which is beneficial for the stability of deformation. The stability of RA at a given temperature strongly depends on its carbon content, which, in AHSS, is not uniform but distributed. The aim of this study is to build a model that predicts the transformation as well as TRIP in a DP steel grade with RA. A physics-based kinetic model is presented that captures the transformation of retained austenite based on the thermodynamic driving force of the applied stress. A direct analytical estimate of transformation plasticity is provided, which is consistent with the kinetic model. Transformation kinetics is incorporated in a self-consistent, mean-field homogenization-based constitutive model. Finally, an indication of the effect of transformation of retained austenite on formability is given. Full article