Specimen Surface Research Articles

Modeling and Simulation of Fatigue Crack Initiation Process Based on Field Theory of Multiscale Plasticity (FTMP): Part II: Modeling Vacancy Formation and Coupling with Diffusion Analysis

Cyclic straining simulations using incompatibility-incorporated crystal plasticity-FEM, which exhibit PSB ladder structure evolutions as detailed in Part I, are coupled with diffusion analyses of produced vacancies. A new vacancy source model is introduced based on the Field Theory of Multiscale Plasticity (FTMP), interpreting the relationship between the incompatibility rate and the flux of dislocation density as edge dipole annihilation processes. Both direct and indirect coupling diffusion analyses, with and without cyclic straining, demonstrate that varying incompatibility rates tend to further promote vacancy diffusion, leading to surface grooving, enhanced extension rates, and eventual transition to cracks. The findings reveal that (i) the evolved PSB ladder structure serves as a site for vacancy formation, (ii) it provides a diffusion path toward the specimen surface, and (iii) it significantly enhances groove extension rates. These factors effectively facilitate the transition from a “groove” to a “crack”, evidenced by the abrupt acceleration of the extension rate, mirroring systematic experimental observations. These achievements validate the FTMP’s capability to simulate complex phenomena and significantly deepen our understanding of slip band–fatigue crack transition mechanisms.

Laser‐Based Closed‐Loop Controlled Heat Treatment for Residual Stress Relief of Additively Manufactured AlSi10Mg Components

In laser powder bed fusion of metals small melt pools with extremely short solidification times and steep temperature gradients to the surrounding material exist due to the layer‐wise and selective melting process with small areas of energy input compared to the cooler, solid ambient material. This causes high thermally induced residual stresses (RS), which can lead to the immediate rejection of the component due to critical part deformation and inhomogeneous mechanical properties under load. To prevent this, furnace‐based stress relief heat treatments are commonly applied before cutting‐off the part from the built platform. In this study a novel closed‐loop controlled laser‐based heat treatment using temperature feedback through inline pyrometer measurement is investigated, enabling a fast and highly efficient postprocess stress relief. Therefore, a laser beam is guided by a scanner optics in a meandering pattern over the top surface of AlSi10Mg cantilever specimens. It enables a decrease of near‐surface RS from 158 to 5 N mm−2, resulting in a reduction of displacement by over 90% at material affecting depths up to 3 mm and area rates of 8 to 163 mm2 s−1.

Effect of loading area on triaxial compression behavior of microcapsule-based self-healing concrete

Concrete is customarily subjected to a complex triaxial stress state in structures under service. True triaxial experiments using cubic specimens in laboratory settings often utilize shims marginally smaller than the specimen surface for loading purposes. However, the influence of shim dimensions on the triaxial mechanical characteristics of concrete remains obscure. Therefore, in this study, for urea-formaldehyde (UF)/epoxy microcapsule-based self-healing concrete, shims of varying sizes were designed to conduct true triaxial compression experiments, examining the effects of loading area size and microcapsule content on triaxial mechanical behavior. The crack damage morphology was observed using a scanning electron microscope (SEM), the rupture of microcapsules was analyzed through energy-dispersive X-ray spectroscopy (EDS), and the micropore structure was determined via nuclear magnetic resonance (NMR). The research findings reveal that reducing the loading area induces stress concentration near the shim edge, significantly decreasing the first peak strength with a maximum reduction of 37%; while also increasing the second peak strength, with a maximum increase of 52%. Notably, a “sleeve-like” delamination occurs when the loading area is below 95% of the specimen surface area. Incorporating microcapsules into concrete enhances ductility and porosity, achieving a maximum 1.9% increase in first peak strain and 1.98% in porosity. This study may offer valuable insights and data for the optimization of concrete materials and structural design, thereby contributing to the safety and durability of engineering structures.

Effect of cryogenic treatment on the mechanical properties of 3D-printed polylactic acid part

The article investigates the effect of cryogenic treatment on the 3-D printed Polylactic Acid (PLA) specimen. It was found that exposure of PLA specimens to the cryogenic temperature (10 K) using a cryocooler led to a 35 % increase in tensile strength in 5 h, with most improvement occurring within the first hour. The cryogenic treatment enhanced the PLA specimen’s strength and ductility due to increased crystallinity and better molecular alignment. It is likely due to the interaction of the cooling medium (helium) used in the cryocooler with the PLA specimens. Towards this, EDS analysis is performed on cryo-treated PLA specimens. The EDS analysis reveals that nickel and iron compounds were detected on the surface of the cryogenic-treated PLA specimen. These findings highlight that cryogenic treatment significantly improves PLA specimen’s mechanical properties and tensile strength. However, challenges arise, including delamination-layer separation caused by internal stresses, and must be addressed. This work will be helpful for researchers working in polymer 3-D printing.

Deformation mechanisms at the tip of internal fatigue cracks in vacuum and in the presence of an air environment in a Ti alloy

Ultrasonic fully reversed tension fatigue tests have been performed in the Very High Cycle Fatigue (VHCF) regime (NR>107−108cycles) on Ti-6Al4V specimens containing a controlled internal notch. Two sets of samples have been used. The first one contains a central chimney along the specimen longitudinal axis which brings air to the internal notch; in the second series the notches are not connected to the surface. The microstructure present below the fracture surface of the broken specimens has been studied by electron microscopy (EBSD, TKD and TEM). The formation of nanograins and nanovoids was observed below the surface of the cracks growing in a vacuum environment but not below the surface of cracks connected with ambient air. In the latter case extensive striations were observed. Below each striation the formation of tensile {101̄2} twins was observed.

The relationship between crack front twisting, plastic zone and [formula omitted] curve of fatigue cracks in AA2024-T3

While fatigue crack growth is inherently a three-dimensional challenge, it is often modelled in two dimensions for simplicity. This study explores the relationship between the two-dimensional primary plastic zone (PPZ) on the surface of specimens and the three-dimensional twisting of the crack front leading to a slanted crack front. Fatigue crack growth experiments were conducted using 2-mm-thick MT-160 AA2024-T3 sheet specimens in both L-T and T-L crack orientations. High-resolution digital image correlation (HR-DIC) was employed to capture the PPZ within the surface displacement data and correlate its morphology with the twisting angle of the slanted crack front.Further, this study investigates how the twisting of the crack front affects the crack propagation curve, represented as da/dN−ΔK, by examining its influence on the mixed-mode I/II/III loading state along the crack front. Here, we utilize finite element simulations to derive a mapping function that adjusts ΔK to ΔKeqv, accounting for the twisted crack front caused mixed-mode loading conditions. The modified da/dN−ΔKeqv curves for both L-T and T-L orientations demonstrated similar behaviour, suggesting that differences in their crack front twisting may explain the discrepancies observed in their traditional da/dN−ΔK crack propagation curves.

Non-electric mass transfer between stainless steel 316H and glassy carbon in NaF-KF-UF4 salt

This study focuses on non-electric mass transfer between stainless steel 316H (SS316H) and carbon materials in molten NaF-KF-UF4 salt. To simulate the molten-salt flow and accelerate the mass transfer, an SS316H specimen was rotated with a tangential speed of 2 m/s in the molten salt contained in a glassy carbon crucible at 1073 K for 120 hours. The concentrations of Cr, Fe, Ni, and Mn in the salt were measured as a function of time during the test. The depletion of Cr was observed near the surface of the post-test SS316H specimen, and Fe-concentrated layers were formed on the specimen. (Cr, Fe)7C3 layers, Cr-metal particles, and dendritic structures concentrated with Fe and Cr were observed on the post-test crucible, indicating the non-electric mass transfer between SS316H and glassy carbon.

The influence of plastic flow localization on the surface morphology of aluminum alloy specimens subjected to complex loading

This study investigates the effects of complex (nonproportional) loading on plastic deformation in aluminum alloys (Al-6% Mg), with a focus on understanding surface morphology changes driven by the Portevin–Le Chatelier effect. Mechanical tests on the deformation of thin-walled tubular specimens were carried out on an Instron 8850 two-axis servohydraulic testing system. Quantitative analysis of the lateral surface of the specimens roughness was carried out based on data obtained using a NewView 5010 interferometer-profilometer. Localized plasticity zones in a wide spectrum of spatial scales were determined using the Hurst exponent as a roughness characteristic. The results of measuring changes in the surface geometry of specimens under various programs of complex (disproportionate) loading are presented. A compact representation of data on the specimens surface relief in the form of amplitude-frequency characteristics was obtained using wavelet analysis. The results obtained can be used to assess the surface roughness of products, especially at the final stages of their manufacturing process by plastic deformation.

Influence of artificial and process-induced defects on very high cycle fatigue characteristics of 316L stainless steel produced by laser powder bed fusion

This study investigates the impact of artificially embedded defects on the very high cycle fatigue (VHCF) of 316L stainless steel produced by laser powder bed fusion (PBF-LB) technology. Each specimen contains a single embedded artificial defect of 180 μm or 350 μm in diameter, positioned at specific distances from the surface (ranging from 350 μm to 1200 μm). The defect position and size are quantified by X-ray computed tomography. Following VHCF testing, the fracture surfaces of the specimens are examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction analysis. The results demonstrate that the fracture surfaces predominantly display a fish-eye fracture type, with a fine granular area (FGA) surrounding the internal defects, typical for VHCF. The FGAs dimensions including thickness are estimated by means of microscopy analysis. However, despite the presence of relatively large artificial defects, cracks sometimes initiate from much smaller process-induced defects closer to the surface than the artificial ones. In conclusion, our study quantifies the relationship between the probability of crack initiation from artificial defects and the distance of the artificial defect from the specimen's surface.

Comparative analysis of the performance of Thin Spray-on Liner with shotcrete and mesh support

In order to study the effect of different surface protection components, such as Thin Spray-on Liner (TSL), in the support system of prestressed bolts on the critical rock mass, based on the similarity theory, physical modeling tests were designed and carried out for the support of the critical rock mass by the combination of NPR bolts and PR bolts with three types of surface protection components, such as TSL, sprayed concrete, and metal mesh, respectively. The test results show that the three types of surface protection components can significantly increase the threshold value of crack development of the critical rock specimen and effectively improve the peak bearing capacity of the critical rock body, and at the same time, the NPR bolts with higher strength and elongation have a more significant effect on the improvement of the peak bearing capacity of the critical rock specimen. In addition, TSL and spray-mixed support and specimen surface can realize close fit, in the loading of the early support response is more timely, in the late loading, compared with the spray-mixed material in the rupture of debris collapse, TSL in the occurrence of tearing can still be tightly adhered to the specimen proximity surface of the rock specimen, to prevent specimen debris fall. For the phenomenon of TSL coating rupture in the experiments, the energy balance equation was established to analyze the connection between the actual energy absorption effect and the theoretical value of the combination of TSL and bolts under the pre-stressed bolts support system, and it was found that the combination of pre-stressed bolts and TSL greatly improved the actual energy absorption effect of the support system as a whole, and the analytical results of the various experimental subgroups showed better results than the theoretical values. The analysis results of the subgroups show a good fit.

Identification of optimal cutting parameters regarding lacquer wettability of CNC processed MDF panels by artificial neural network

ABSTRACT The primary objective of this study was to evaluate the surface roughness and lacquer wettability of medium-density fiberboard (MDF) panels processed on computer numerical control (CNC) machine. Then, it is aimed to determine the optimal CNC cutting parameters by modeling the data obtained from the experiments with ANN. For these purposes, two cutting tool types, two toolpath strategies, three spindle speed and four cutting depth values were used as CNC cutting parameters. The roughness and lacquer wettability tests were performed on the surfaces of MDF specimens after CNC machining. Using the obtained experimental data, the ANN models with the highest predictive ability were determined and the optimum CNC cutting parameters were defined according to surface roughness and lacquer wettability. The smoothest surfaces were obtained for the spiral router bit with offset toolpath strategy, 22,500 rpm spindle speed and 1.6 mm cutting depth, and for the straight router bit with raster toolpath strategy, 21,500 rpm spindle speed and 1.7 mm cutting depth. The optimal cutting parameters that gave the best lacquer wettability were an offset toolpath strategy, 20,500 rpm spindle speed and 1.5 mm cutting depth for spiral router, and a raster toolpath strategy, 20,500 rpm spindle speed and 3.1 mm cutting depth for straight router.

Effects of Er:YAG laser debonding on changes in the properties of dental zirconia.

To investigate changes in the optical and mechanical properties of novel zirconia ceramics applied in dentistry after Er:YAG laser debonding and to evaluate the feasibility and value of reusing zirconia restorations debonded by an Er:YAG laser. Four types of zirconia ceramics were investigated: self-glazed zirconia (SGZ), 3Y-TZP, 4Y-PSZ and 5Y-PSZ. Forty rectangular (25 mm*8 mm*1.5 mm) specimens were fabricated for each zirconia type, and a total of 160 specimens were manufactured. The zirconia specimens were divided into four subgroups according to the applied Er:YAG laser debonding process: the control group, 4 W laser group, 5 W laser group, and 6 W laser group. For each subgroup, 10 specimens were subjected to color tests (color difference (△E) and transparency parameter (TP) tests) and subsequent mechanical tests (flexural strength (FS), elastic modulus (EM), Vickers hardness (VH) and surface roughness (Ra) tests). The △E, TP, FS, EM, VH and Ra values were measured and calculated. One random sample from each subgroup was observed by SEM. Statistical analyses were performed by one-way ANOVA followed by post hoc comparisons (α = 0.05). The △E and TP values after Er:YAG laser debonding were not significantly different among the subgroups (P > 0.05). However, the 6 W laser group had the highest △E and lowest TP. The ranges of changes in △E and TP were below the clinically detectable threshold (△E = 1.2, △TP = 1.33). In terms of the mechanical properties, there were no significant differences in the FS, EM, VH or Ra among the subgroups. No obvious microcracks were detected on the surfaces of the zirconia specimens during SEM. Er:YAG laser debonding does not obviously affect the optical or mechanical properties of novel zirconia ceramics in dentistry. Moreover, it is potentially feasible and valuable to reuse zirconia restorations after Er:YAG laser debonding.

Comparative Analysis of Modern 3D-Printed Hybrid Resin-Ceramic Materials for Indirect Restorations: An In Vitro Study.

The study investigated the impact of aging on surface roughness, color stability, and biocompatibility of hybrid resin-ceramic materials. A total of 225 specimens were produced from three three-dimensional (3D)-printed (HarzLabs Dental Sand Pro (HL), BEGO VarseoSmile Crown plus (BV), Voco V-Print c&b temp (VV)) and one milled material (Voco Grandio Blocs (VG)). Specimens were grouped into untreated, polished, and glazed surfaces. 5000 thermal cycles simulated aging. Surface roughness and color stability were analyzed, and surface topography was observed using scanning electron microscopy (SEM). Biocompatibility was evaluated with L929 cells. Surface roughness differed significantly between untreated and other groups, with no changes before and after artificial aging. Untreated milled samples were significantly smoother than 3D-printed ones. SEM analysis revealed roughest surfaces in untreated 3D-printed specimens. Polished and glazed specimens were smoother than untreated ones. Color values showed significant differences between untreated and treated/aged groups. No material showed cytotoxicity. In summary, untreated VG was smoother than 3D-printed materials, but polishing and glazing reduced roughness to levels comparable to VG. Surface treatments induced color changes, with glazing causing more changes than polishing. Aging affected color stability and biocompatibility but not surface roughness. All materials showed acceptable color changes and good biocompatibility.

Biocompatibility and antibacterial properties of medical stainless steel and titanium modified by alumina and hafnia films prepared by atomic layer deposition

New methods for producing surfaces with suitable biocompatible properties are desirable due to increasing demands for biomedical devices. Stainless steel 316 L and cp- titanium specimens were coated with thin films of alumina and hafnia deposited using the atomic layer deposition method at two temperatures, 180 and 260 °C. The morphology of the films was analysed using scanning electron microscopy, and their surface energies were determined based on drop contact angle measurements. Biocompatibility assays performed using mesenchymal stem cells were evaluated by incubating the specimens and then exposing their extracts to the cells or directly seeding cells on the specimen surfaces. No detrimental effect was noticed for any of the specimens. Antibacterial properties were tested by directly incubating the specimens with the bacteria Staphylococcus aureus. Overall, our data show that all prepared films were biocompatible. Alumina films deposited on cp-titanium at 260 °C outperform the other prepared and tested surfaces regarding antiadhesive properties, which could be related to their low surface energy.

Thermo-mechanical fatigue behavior and life prediction of selective laser melted inconel 718

The thermo-mechanical fatigue (TMF) property and corresponding damage mechanisms of selective laser melted (SLM) Inconel 718 superalloy were investigated systemically. The results show that the TMF life under in-phase (IP) loading is lower than that under out-of-phase (OP) loading, and the life difference gradually decreases with decreasing the strain amplitude. The fatigue cracks mainly exhibit inter-granular cracking characteristics under IP loading, and the δ phase embedded to the grain boundary promotes the creep cavity formation and then causes the fatigue crack propagation. While under OP loading, the fatigue crack is mainly characterized by trans-granular cracking, the oxidation induced crack extends from the specimen surface to the interior. A parameter, known as the shape factor k, has been discovered to exhibit high stability in temperature variations. Given the high stability of the k value and the quantitative relationship between stress and plastic strain range across different loading modes, a rapid prediction method for TMF hysteretic energy based on low cycle fatigue (LCF) has been proposed. Finally, combined with the energy cumulative damage model, the TMF life is successfully predicted. This approach significantly reduces the experimental quantity and complexity required for the TMF life prediction process, demonstrating substantial industrial application value.

Synthesis and evaluation of new type plant extraction corrosion inhibitor

The use of corrosion inhibitors in the development of oil and gas fields is an important means of effectively preventing metal corrosion, at present, the green growth of the oil and gas industry requires low-toxicity, low-residue, easy-to-post-treatment and other environmentally friendly corrosion inhibitors, however, most industrially used corrosion inhibitors such as mercury salts quaternary ammonium salts, and imidazolines are toxic to some degree. In this paper, a plant extract corrosion inhibitor was synthesized, firstly, the purple sweet potato extract was extracted by ethanol, and then the purple sweet potato extract and alkyl halide such as methane were used to produce the purple sweet potato corrosion inhibitor through condensation extraction and other processes, and the corrosion inhibitory performance of the inhibitor was evaluated by the loss-in-weight method, scanning electron microscopy, polarization curves, and impedance spectroscopy. The results show that there is a certain inhibition effect on N80 steel in the simulated stratum water environment, and the retardation rate can reach 91.38% in the gas phase, and the corrosion product morphology and chemical elements on the surface of N80 steel specimens were characterized by SEM, EDS, and it can be observed that a relatively dense protective film was formed after adding purple sweet potato corrosion inhibitor, and the corrosion inhibition rate can be known according to the weightlessness curve, Tafel curve and impedance curve. The corrosion inhibition rate increases with the increase of corrosion inhibitor concentration.

Specific U6 Small Nucleolar RNAs Are Present on the Surface of Primary AML Specimens and Are Accompanied By Short Fragments of Longer RNAs

Specific U6 Small Nucleolar RNAs Are Present on the Surface of Primary AML Specimens and Are Accompanied By Short Fragments of Longer RNAs

Pitting corrosion resistance of tempered N08825 alloy in the inner layer of bimetallic composite pipe

Pitting corrosion resistance of N08825 alloy in the inner layer of bimetallic composite pipe SA210A/N08825 tempered at 570∼720 ℃ was investigated in NH4Cl solution by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The M23C6 precipitates, observed at the grain boundaries of inner layer alloy 825, exhibit a temperature-dependent behavior during tempering at 570∼720 ℃. The quantity of M23C6 precipitates and the pitting corrosion resistance change with the tempering temperature. When the tempering temperature increases from 570 to 660 ℃, the quantity of M23C6 precipitates increases, with the pitting potential (Ep) decreasing from about 499 ± 8.6–354 ± 6.7 mVSCE, the passive current density (ip) increases from about 1.9 ± 0.2–2.45 ± 0.3 μA cm−2, and the average number of pits on the specimen surface rises from 3 to 7. Conversely, when the tempering temperature increases from 660 to 720 ℃, the quantity of M23C6 precipitates decreases, leading to the Ep increases from about 354 ± 6.7–394 ± 14.6 mVSCE, the ip decreases from about 2.45 ± 0.3–2.34 ± 0.4 μA cm−2, and the average number of pits on the specimen surface decreases from 7 to 6. There is a strong relationship between the M23C6 precipitates and the pitting corrosion resistance. As the quantity of M23C6 precipitates increases, it results in the expansion of Cr-depleted zones on the specimen surface, the rise of passive film defects, and a subsequent reduction in the pitting corrosion resistance of inner layer alloy 825.

Space exposure test of hardwood specimens in the International Space Station

To design a wooden satellite and select the appropriate wood species, we conducted a space exposure test of wood on the International Space Station (ISS). The space exposure test used the Japanese Experiment Module “Kibo” on the Exposed Experiment Bracket Attached on i-SEEP (ExBAS), which is connected to the exposed facility of the ISS. Three wood species considered candidates for the structure of a wooden satellite were used in the exposure test: honoki (Magnolia obovata), yamazakura (Cerasus jamasakura), and dakekanba (Betula ermanii). In the outgassing test conducted in preparation for the space exposure test, the collected volatile condensable materials (CVCM) of the three wood species were below the critical value; however, the total mass loss (TML) exceeded the critical value. However, this was not a problem, because most of the mass loss was due to water evaporation. A space exposure test was conducted for 10 months in 2022. Consequently, no change was observed in the weight of the exposed specimen, and no erosion due to atomic oxygen (AO) was observed. The exposure test was scheduled to be carried out in the forward direction of the ISS travel; however, owing to equipment trouble, it was installed in the opposite direction. This is because an insufficient AO flux collided with the specimen. In terms of wood color, the brightness of the three species decreased owing to space exposure, and saturation increased in two wood species, except for yamazakura. A thin-film layer was observed on the surface of the aluminum cover to which the exposed specimen was fixed, which may have also formed on the surface of the wood specimen, reducing its brightness. However, because the hue angle did not change significantly, only a slight deterioration of the surface layer owing to vacuum ultraviolet was observed. The results confirmed that the wood had hardly deteriorated in space for approximately 10 months.

Unnotched fatigue behavior of the laser powder bed fused and hot isostatic pressed Inconel 718 at 600 °C

The microstructure and mechanical properties of hot isostatically pressed (HIP) Inconel 718 additively manufactured using the laser beam powder bed fusion (LPBF) process were investigated at 600 °C, with emphasis on the high cycle fatigue behavior evaluated using the rotating bend fatigue tests, and elucidation of the role of γ” precipitate size on the fatigue resistance. Experimental results show that the unnotched fatigue strength (σf) of the peak aged alloy improves only by 7 % after HIP, as compared to that of the non-HIP peak aged alloy, despite a significant improvement in the ductility due to HIP. Over-aging the HIP alloy, however, led to a further enhancement (by ∼14 %) in σf. Fractographic analyses suggest that the fatigue crack initiation occurs from the intrusions and extrusions on the fracture surface of both versions of the aged alloy. Microstructural investigations reveal the presence of persistent slip bands (PSBs) with different morphologies in peak- and over-aged microstructures. A change in the deformation mechanism due to the size of precipitates was identified to be the reason for the formation of nano-grains (through dynamic recrystallization) within the PSBs of the alloy with a coarse γ” microstructure. In several {110} grains, ∼5 μm thick nanocrystalline grain zones formed on the specimen surface; they completely suppressed the formation of PSBs and enhanced the fatigue resistance of the HIP LPBF IN718 alloy in the over-aged condition.