Surface Tensile Stress Research Articles

Properties and Characterization of Nanocellulose

Abstract In the field of nanotechnology, nanocellulose plays crucial role. Some features of nanocellulose like high surface area, crystallinity, porosity and tensile stress makes remarkable changes in medical and Industrial area. It is known for its biocompatibility, renewability, high aspect ratio, infinitesimal toxicity and sustainability. Nanocellulose can be prepared by microcrystalline cellulose. For the synthesis of nanocellulose, Acid hydrolysis procedure was used. Various methods of characterizations were used for the prepared nanocellulose such as “Fourier transforms infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and X-ray diffraction”. Nanocellulose drew the attention of scientists for their biochemical properties due to its physical and chemical structure. Various applications of nanocellulose in different field such as biochemical, waste water management, electronics, packaging, automotive etc.

Fatigue properties of SiC graded ceramic lattice structures with a triply periodic minimal surface manufactured by laser powder bed fusion

SiC graded ceramic lattice structure (GCLS) offers superior mechanical strength and its impact on fatigue warrants investigation. In this work, SiC triply periodic minimal surface (TPMS) GCLSs were prepared via laser powder bed fusion technology and liquid silicon infiltration process, alongside SiC TPMS uniform ceramic lattice structure (UCLS) as a reference. Fatigue properties, fatigue failure, and strengthening mechanisms were systematically investigated through compression fatigue tests, finite element (FE) simulations, and theoretical analysis. Fatigue failures of SiC UCLSs and GCLSs are influenced by cyclic ratcheting and fatigue damage, with cyclic ratcheting dominance. The fatigue strength ratios of UCLS and GCLS are 0.7 and 0.74, indicating that GCLSs exhibit stronger deformation resistance and superior fatigue performance. FE results show that surface tensile stress level in GCLS is lower than in UCLS, resulting in slower fatigue crack initiation. Stress redistribution and higher crack thresholds contribute to enhanced fatigue resistance in SiC TPMS GCLSs.

Observed meltwater-induced flexure and fracture at a doline on George VI Ice Shelf, Antarctica

Abstract Global Navigation Satellite System (GNSS) observations and ground-based timelapse photography obtained over the record-high 2019/2020 melt season are combined to characterise the flexure and fracture behaviour of a previously formed doline on George VI Ice Shelf, Antarctica. The GNSS timeseries shows a downward vertical displacement of the doline centre with respect to the doline rim of ~60 cm in response to loading from a central meltwater lake. The GNSS data also show a tens-of-days episode of rapid-onset, exponentially decaying horizontal displacement, where the horizontal distance between the doline rim and its centre increases by ~70 cm. We interpret this event as the initiation and/or widening of a fracture, aided by stress perturbations associated with meltwater loading in the doline basin. Viscous flexure modelling indicates that the meltwater loading generates tensile surface stresses exceeding 75 kPa. This, together with our timelapse photos of circular fractures around the doline, suggests the first such documentation of meltwater-loading-induced ‘ring fracture’ formation on an ice shelf, equivalent to the fracture type proposed as part of the chain-reaction lake drainage process involved in the 2002 breakup of the Larsen B Ice Shelf.

Epitaxial AlN film with improved quality on Si (111) substrates realized by boron pretreatment via MOCVD

This study investigated the growth of AlN epitaxial films on 2-in. Si(111) via metal-organic chemical vapor deposition. By introducing triethylboron (TEB) during trimethylaluminum pretreatment, a nearly crack free AlN epilayer with a thickness of 500 nm was acquired. The x-ray diffraction rocking curves of AlN (002) and (102) exhibited full width at half maximum values of 0.22° and 0.36°, respectively. Atomic force microscopy image analysis showed that after the introduction of TEB, larger grains appeared on the surface of Si(111) substrate, promoting the 3D growth pattern of the subsequent AlN buffer layer. Laytec reflection curves depicted the morphological transition from 3D to 2D growth mode during AlN deposition. At the same time, the curvature value was significantly reduced by 20 km−1, and the Raman spectrum peak of E2(high) shifted from 648.7 to 652.5 cm−1, indicating that the surface tensile stress was greatly reduced, effectively suppressing the crack problem of AlN on Si(111).

Optimized Design of Anchor Plates for 2200 MPa-Class Prestressing Anchorage Zones

The strength of prestressed steel strands has developed towards high strength, increasing from 1860 MPa to over 2200 MPa. The stress in the prestressed anchorage zone is more concentrated and complex, and the anchor plates for dispersed loads need to be optimized in design. This article proposes a design scheme for adding a middle pressure-bearing step based on the existing anchor plate and then establishes a 1/4 model of the concrete anchoring area of the anchor plate for finite element analysis. Based on the theory of the strut-and-tie model, the position of the middle pressure-bearing step is determined according to the maximum angle of the strut-and-tie model. Then, carry out force transfer tests in the anchorage zone for verification. The research results indicate that after adding a middle pressure bearing step to the anchor plate, the angle between the strut-and-tie model in the anchorage zone increases, and the bearing capacity improves. The position of the middle pressure-bearing step in the anchor plate is different, and the angle between the strut-and-tie models is different. According to the middle step position parameter, λ (the ratio of the effective width of the middle step to the distance from the middle step to the end face of the anchor plate) is 0.533 to optimize the anchor plate, and the bearing capacity of its anchorage zone is relatively high. The main tensile and main compressive stresses of the anchor plate after optimization increased by 6.2% and 5.74%, respectively, compared to the anchor plate before optimization. The main tensile stress of the spiral reinforcement under the anchor plate decreased by 0.59%, the main compressive stress decreased by 2.89%, and the von-Mises stress decreased by 2.32%. The side surface tensile stress of concrete under the anchor plate was reduced by 4.3 percent. Finally, three concrete specimens were poured for force transfer testing in the anchorage zone, verifying the safety and reliability of the optimized anchor plate in the 2200 MPa-level prestressed anchorage zone.

Ultrafast Carbothermal Shock Synthesis of Wadsley–Roth Phase Niobium‐Based Oxides for Fast‐Charging Lithium‐Ion Batteries

AbstractWadsley–Roth phase niobium‐based oxides show potential as anode candidates for fast‐charging lithium‐ion batteries. Traditional synthesis methods, however, usually involve a time‐consuming calcination process, resulting in poor production efficiency. Herein, a novel carbothermal shock (CTS) method that enables the ultra‐fast synthesis of various Wadsley–Roth phase Nb‐based oxides within seconds is introduced. The extremely rapid heating rates enabled by CTS alter the reaction mechanism from a sluggish solid‐state process to a swift liquid‐phase assisted one and drive the chemical reactions away from equilibrium, thereby generating abundant oxygen vacancies and dislocations. Theoretical calculations reveal that oxygen vacancies significantly lower the energy barrier for Li+ diffusion and enhance the intrinsic electronic conductivity. Moreover, dislocations help convert the surface tensile stress arising from Li+ intercalation into compressive stress, effectively improving the structural integrity during cycling. Notably, this approach can also be applied to synthesize LiFePO4 cathode materials under ambient conditions, eliminating the requirement for inert atmospheres. Consequently, the CTS‐synthesized Nb14W3O44||LiFePO4 battery demonstrates reversible structural evolution validated by in situ XRD and exceptional cycling ability (e.g., 0.0065% capacity decay per cycle at 4 A g−1 over 3000 cycles). Importantly, the Nb14W3O44||LiFePO4 configuration also shows enhanced thermal stability in the Ah‐level pouch cell nail penetration test, confirming its feasibility.

The role of retained austenite on the formation of the nanostructured hard-turned induced white layer in AISI 52100 bearing steel

Interest in hard-turning is steadily increasing due to its obvious benefits in terms of desirable surface integrity and improved operational efficiency. Surface microstructural variations can occur during machining due to cutting speed, tool geometry, and process conditions. These variations create nanostructured white layers (WL), categorized as mechanically induced white layers (M-WL) or thermally induced white layers (T-WL). This study explored the role of retained austenite (RA) content (<2%, 12%, and 25%) on WL generation in AISI 52100 bearing steel, offering insights for optimizing hard-turning. The findings showed that, regardless of RA content, samples exhibited M-WL with no dark layer beneath the white layer when utilizing a cutting speed (VC) of 60m/min using a fresh insert. Increasing tool flank wear to 0.2mm led to the formation of T-WL and surface tensile residual stresses in specimens with higher RA content (12% and 25%). This effect was also observed at 260m/min with a fresh cutting insert. Machining at 260m/min with a worn tool (VB) of 0.2mm resulted in T-WL and surface tensile residual stresses, independent of RA content. Additionally, a 0.2mm tool wear caused a significant shift in the maximum subsurface compressive residual stresses to greater depths, irrespective of RA content.

Influence of a cutting fluid on the surface integrity and fatigue strength of 42CrMo4 drilled parts.

This study investigates the influence of a cutting fluid during the drilling operation on the surface integrity and fatigue strength of 42CrMo4 hardened steel. The investigation includes characterizing surface topography, microstructure at different hole locations, and residual stresses. Fatigue tests were conducted, and the results were correlated with observations on surface integrity. The findings reveal that crack initiation occurs in a transition zone within the hole, where the cutting process evolves from pure cutting to a region with a strongly adhesive layer. The absence of cutting fluid leads to increased surface roughness and tensile residual stresses, resulting in a 28% reduction in fatigue strength.

Comparative analysis of time dependent temperature profiles of hydrating mass concretes of different mix ratios

In mass concrete, heat due to cement hydration in most cases is not easily released and is otherwise confined within its core. Consequently, mass concrete may exhibit quite remarkable increase in temperatures internally depending on majorly the vicinity temperature and the proportion of cement in mixture ratio. When the surface tensile stresses resulting from temperature difference between its core and surface exceeds the strength of the concrete, cracks could develop at the surface. Two mass concrete blocks of dimensions 1.10 m × 1.10 m × 1.10 m each and mixes of 1: 2: 4 and 1: 3: 6 with constant water cement ratio (w/c) of 0.60 were used in the study. Type-K thermocouples were used to monitor the temperature variance in mass concretes. BK Precision 710 temperature meter dual input was used to determine the temperature readings at time intervals. Thermometer was used to measure the environment temperatures within the vicinity of the mass concretes. Generally, the trends of the temperature profiles exhibit an initial uniform temperature which rises to peak values at 24 hours of concrete placement and then declined to constant temperature at mostly 120 hours and beyond. The sole source of heat in hydrating concrete is the cement paste, and higher cement content leads to higher quantity of heat release. Therefore, the mass concrete block of mix ratio 1:2:4 exhibited higher quantity of heat release than that of 1:3:6 especially at the core.

Corrosion and wear interplay: Tribo-electrochemical evaluation of NiTiNOL60 alloy in sulfuric acid

The combined corrosion and wear behaviour of NiTiNOL60 alloy is important in various engineering applications. While previous studies have explored its performance in artificial seawater environments, limited information exists regarding its tribocorrosion characteristics in acidic conditions. This paper investigates the synergistic interaction between sliding wear and electrochemical processes for NiTiNOL60 alloy in a sulfuric acid environment, employing experimental procedures compliant with ASTM standards. Microscopic analysis confirms the alloy's Ni-rich composition, featuring a dense network of B2 NiTi + Ni4Ti3 cubic and rhombohedral crystal matrix structures. Our research and results reveal that material degradation during tribocorrosion arises from the combined effects of sliding wear and electrochemical reactions. Consequently, multiple wear mechanisms influenced by tribochemical wear are observed, with delamination and micro-cracks being notably prominent under higher applied loads due to surface tensile stress and contact pressure, leading to crack propagation perpendicular to the sliding direction. These findings have practical implications for optimising the performance and durability of NiTiNOL60 alloy in acidic environments, offering valuable insights for load-bearing engineering applications.

Machining of additively manufactured alloy 718 in as-built and heat-treated condition: surface integrity and cutting tool wear

AbstractAdditive manufacturing (AM) using powder bed fusion is becoming a mature technology that offers great possibilities and design freedom for manufacturing of near net shape components. However, for many gas turbine and aerospace applications, machining is still required, which motivates further research on the machinability and work piece integrity of additive-manufactured superalloys. In this work, turning tests have been performed on components made with both Powder Bed Fusion for Laser Beam (PBF-LB) and Electron Beam (PBF-EB) in as-built and heat-treated conditions. The two AM processes and the respective heat-treatments have generated different microstructural features that have a great impact on both the tool wear and the work piece surface integrity. The results show that the PBF-EB components have relatively lower geometrical accuracy, a rough surface topography, a coarse microstructure with hard precipitates and low residual stresses after printing. Turning of the PBF-EB material results in high cutting tool wear, which induces moderate tensile surface stresses that are balanced by deep compressive stresses and a superficial deformed surface that is greater for the heat-treated material. In comparison, the PBF-LB components have a higher geometrical accuracy, a relatively smooth topography and a fine microstructure, but with high tensile stresses after printing. Machining of PBF-LB material resulted in higher tool wear for the heat-treated material, increase of 49%, and significantly higher tensile surface stresses followed by shallower compressive stresses below the surface compared to the PBF-EB materials, but with no superficially deformed surface. It is further observed an 87% higher tool wear for PBF-EB in as-built condition and 43% in the heat-treated condition compared to the PBF-LB material. These results show that the selection of cutting tools and cutting settings are critical, which requires the development of suitable machining parameters that are designed for the microstructure of the material.

Study on Residual Stresses of 2219 Aluminum Alloy with TIG Welding and Its Reduction by Shot Peening

Large residual stress of 2219 aluminum alloy induced by Tungsten Inert Gas (TIG) welding decreases its service performances. Shot peening was adopted to decrease the residual stress of TIG welding. Numerical models of TIG welding and shot peening were established using the combined discrete and finite element methods (DEM–FEM). The results show that TIG welding induces tensile residual stress due to the heat exchange effect and the longitudinal stress is larger than that in the transverse direction. The maximum tensile stress occurs at a depth of 0.1 mm. The surface tensile stress changes to compressive stress after shot peening as the severe deformation induced by the shots changes the stress state of the plate. The maximum value of compressive stress (σm) and the peened depth with compressive stress (Z0) are adopted to describe the peening effect. The absolute value of σm increases with the increased peening speed and nozzle height. Mixed shots with a diameter of 0.8 mm and 1.2 mm induce larger value of σm than those with only a diameter of 1.2 mm. The value of Z0 increases with the ascending shots diameter and nozzle height, while it varies nonmonotonically with the peening speed. The effect of shot peening on the residual stress in TIG welding is discussed.

Characterization and Control of Residual Stress in Plasma-Sprayed Silicon Coatings on SiC/SiC Composites

In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin2ψ technology and laser Raman spectroscopy. Then, the Raman shift–stress coefficient (P) and the Raman shift with free stress (ω0) were calculated as −201.41 MPa/cm−1 and 520.591 cm−1 via linear fitting with the least squares method. The results showed that all the as-sprayed Si coatings exhibited tensile stress on the surface, ranging from 53.5 to 65.9 MPa. The parameters of the spraying distance and second gas (H2) flow rate were considered to be the most important for controlling the residual stress on the coating surface. Additionally, the surface tensile stress of the Si layers could be eliminated and even changed into compressive stress by annealing above 800 °C. Furthermore, the residual stress distribution in the cross-section of the Si layers was evaluated using laser Raman spectroscopy. Additionally, the particle characteristics, such as in-flight velocity and temperature, were investigated using a diagnostic system. The results of this research contribute to increasing the understanding and control of residual stress in APS Si bond layers.

3D FEM heat transfer simulation of surface grinding of cryogenic pre-cooled parts

Cooling lubricants are used in grinding to minimize heat-related problems such as surface cracks, burn and tensile residual stresses. An alternative is the cryogenic cooling, where the cryogenics like LN2 are supplied at very low temperatures. The feasibility of different cryogenic cooling strategies depends on the workpiece volume-to-surface ratio. In this study 3D FEM heat transfer simulations are presented, which map the temporal and spatial temperature development, to assess the potential of LN2 pre-cooling when dry surface grinding. Different clamping strategies in terms of insulation are investigated simulatively and experimentally.It could be shown that clamping covers are required to maintain the cryogenic temperature in the workpiece during surface grinding due to their sufficient insulation. The temperatures during grinding of pre-cooled workpieces were successfully predicted by the developed FEM heat transfer simulation model.

Correlation between residual stress and geometric tolerances in ultrasonic assisted turning

High accuracy in production parts and manufacturing quality are the requirements of production. Residual stress affects the surface quality and dimensional accuracy of manufactured parts. Production of parts with geometric tolerance, optimal residual stress, and suitable surface quality is always required by manufacturing industries. When machining parts, tensile residual stresses are created in them, which is one of the main reasons for the loss of geometric tolerances and distortion in the workpiece. This study investigated the effect of the ultrasonic-assisted vibration compared with conventional machining in various conditions of a 2024 aluminum workpiece on the surface quality, runout, straightness, and tensile residual stresses. In this article, the effects of geometric tolerance parameters, tensile residual stress, and surface roughness have been investigated simultaneously. A total of 18 experiments in different cutting speeds and feed rates in two machining states of conventional and ultrasonic vibration states were performed. The results showed that ultrasonic vibrations could be used to achieve 31% lower run out and 36% lower straightness in the parts. Also, the values of tensile residual stress in the ultrasonic vibration machining were 11% lower compared to conventional machining. Ultrasonic vibrations can also be used in most cases to achieve better surface quality, tolerance, and tensile residual stress according to machining parameters compared to conventional machining. The experimental results show that ultrasonic-assisted turning is a reliable method for machining, which can obtain lower tensile residual stress and improve the machined surface integrity and better tolerances.

Influence of laser shock peening on the residual stresses in additively manufactured 316L by Laser Powder Bed Fusion: A combined experimental–numerical study

Detrimental subsurface tensile residual stresses occur in laser powder bed fusion (LPBF) due to significant temperature gradients during the process. Besides heat treatments, laser shock peening (LSP) is a promising technology for tailoring residual stress profiles of additively manufactured components. A multi step process simulation is applied aiming at predicting the residual stress state after applying LSP to a cuboid shaped specimen manufactured by LPBF in two different building directions as well as comparing it with a post-build heat treatment. The validity of the numerical simulation is evaluated based on comparisons of residual stresses determined by incremental hole drilling technique within different stages of the multi step process: in the as-build condition, after subsequent heat treatment as well as after applying LSP to the as-build and heat treated specimens, showing overall a good experimental-numerical agreement throughout each of the process stages. Applying a heat treatment to the as-build LPBF sample at 700 °C for 6 h showed not to be effective in eliminating the surface tensile stress entirely, reducing the tensile residual stresses by 40%. However, the application of LSP on LPBF components showed promising results: LSP was able even to convert the detrimental near surface tensile residual stresses in the LPBF component into compressive residual stresses next to the surface, which is known to be beneficial for the fatigue performance.

Enhancing stress corrosion cracking resistance of machined surface via surface mechanical grinding treatment for AISI 316 L stainless steel

The mechanical properties, microstructures and corrosion resistance of turned, milled and surface mechanical grinding treatment (SMGT) processed surfaces were investigated through the surface stress measurement, microhardness, SEM, TEM, TKD, XRD and electrochemical corrosion analysis. The stress corrosion cracking (SCC) initiation behavior of three types of treated surfaces in boiling MgCl 2 solution were assessed and compared. The experimental results indicated that the SMGT processed surface inhibited the SCC initiation at the surface stress as high as 874 MPa. The enhancement of SCC resistance was attributed to the SMGT-induced dense ultrafine-grained (UFG) layer, gradient grain refinement and better corrosion resistance, resulting in the high yield strength and high critical stress of SCC initiation. • The surface mechanical grinding treatment generated a dense ultrafine-grained (UFG) layer and low residual stress on processed surface. • The dense UFG layer successfully suppressed the SCC initiation at the surface tensile stress as high as 874 MPa. • The mechanisms of SMGT improving the SCC resistance were attributed to the high yield strength combined with better corrosion resistance of the UFG layer, increasing the σ SCCof crack initiation. • The SMGT can serve as a promising strategy to enhance the SCC resistance for machined 316 L stainless steel surface.

Corrosion Resistance and Tribological Properties of Laser Cladding Layer of H13 Die Steel Strengthened by Ultrasonic Rolling

Laser cladding is a new surface repair method that can improve the wear and corrosion resistance of substrate surfaces. However, the cladding layer typically exhibits a rough surface, high hardness and large residual tensile stress, and thus requires further machining and finishing. Ultrasonic rolling (U-rolling) is a highly efficient finishing and strengthening process that combines ultrasonic technology with traditional rolling (T-rolling). In this study, an iron-based alloy was coated onto the surface of H13 die steel using laser cladding, and the surface of the cladding layer was polished using U-rolling. The effects of U-rolling on the surface quality, corrosion resistance and friction and wear properties of the laser-cladding layer were investigated and compared with those obtained by T-rolling. The surface roughness of the U-rolled sample was only 1/4 that of the T-rolled sample. The hardness and residual compressive stress of the laser cladding layer after U-rolling were higher than those after T-rolling. Similarly, the surface corrosion resistance of the laser cladding layer after U-rolling was higher than that after T-rolling. U-rolling changed the surface roughness, grain size, and residual stress of the material and thus affected the corrosion resistance of the laser cladding layer. The friction coefficient and wear rate of the U-rolled surface of the cladding layer were lower than those of the T-rolled surface. In addition, the tribological properties of the cladding layer were found to be related to the rolling direction. When the friction direction of the sample was the same as the rolling direction, its friction and wear performance were higher than those when the two directions were perpendicular.

Mesoscale analysis of dry shrinkage fractures in concrete repair systems using FEM and VEM

ABSTRACT A novel numerical method that used a FEM coupled with a virtual element method was proposed to evaluate the drying shrinkage of concrete repair systems. The stress distribution, crack development of the concrete repair systems due to drying shrinkage were investigated using this method. (1) The mortar along the tangent direction of the aggregate boundary was subjected to the aggregate constraint, allowing shrinkage cracks to form easily. The overlay first developed a significant number of microcracks on surface, followed by debonding at both ends of the interface. (2) Owing to the confinement of the aggregate below the surface, the surface tensile stress of the overlay had a ‘hump’ distribution. After cracking, the surface was divided into several contraction zones, with tensile and compressive stresses applied to the boundary and interior of the contraction zone, respectively. (3) As the interface de-bonded, the tensile and shear stresses of the interface began to increase from both sides and moved inward. The rise in local compressive and shear stresses were induced by the constraint of the aggregate in the bonding interfacial region. (4) Tensile stress caused the first damage, and the shear stress caused interface debonding to evolve.

Machining-induced residual stress analysis and multi-objective optimization for milling process of Mg–Li alloy

Machining-induced residual stress in an Mg–Li alloy can lead to a significant deformation of its machined thin-walled parts. To solve this issue, an integrated method that combined the grey relational analysis (GRA), back propagation (BP) neural network, and non-dominated sorting genetic algorithm-III (NSGA-III) was proposed in this study aimed to analyze the dominant mechanism of residual stress and achieve a super-objective cooperative optimization of residual stress in the LA103Z Mg–Li alloy milling process. A typical spoon-shaped distribution of surface tensile stress and subsurface compressive stress was presented in the Mg–Li alloy owing to the coupling interaction between the cutting force and temperature. The increase in the cutting temperature owing to an increase in the cutting speed was proven to be the overarching factor that induced residual stress by the correlation analysis of cutting parameters, force–heat of cut and residual stress. The BP prediction models of the residual stress were established, and the predicted values were in good agreement with the test values, with a maximum error of 5.07 %. The NSGA-III optimization algorithm was used to search for the lowest values of in-plane tensile and compressive stresses (σtx, σty, σcx and σcy). The optimized cutting speed, feed, and cutting depth were determined to be 61 m/min, 0.068 mm/z, and 0.58 mm, respectively. The maximum predictive error of four residual stresses was experimentally verified to be 15.94 %, which proved the feasibility of the multi-objective optimization approach. The residual stress level of the optimized scheme evidently decreased compared with that of the current milling scheme, with the maximum reduction of 28.37 %. Therefore, the propsoed approach can effectively reduce the risk of warping and distortion of machined Mg–Li alloy parts.