Formation Of Microcracks Research Articles

Mechanistic insights into waterjet-guided laser grooving of silicon: Impact of ablation dynamics, oxide formation, and thermal stress

Waterjet-guided laser machining of silicon offers precision with minimal heat-affected zones (HAZs), but understanding the mechanisms behind laser-material interactions remains essential. This study first utilizes orthogonal experiments to reveal fundamental relationships between processing parameters (scanning cycle, laser fluence, scanning velocity, and waterjet pressure) on groove depth and the depth-to-HAZ ratio. These findings guide the in-depth investigation of laser-material mechanisms. The results indicate that the ablation rate decreases with increasing scanning cycles, a phenomenon primarily attributed to the different absorption rates of 532 nm laser light between silicon and silicon dioxide. This conclusion is supported by x-ray photoelectron spectroscopy(XPS) results, which reveal that the accumulation of silicon dioxide occurs as the scanning cycles increase. Additionally, a near-linear relation between the ablation rate and laser fluence is observed, as the ablated area is continuously exposed to high laser intensity regions. However, increasing laser fluence also leads to diminished processing quality due to greater thermal deformation in non-ablating regions. Last, increased scanning velocity is found to cause rougher surfaces, as insufficient heat diffusion leads to higher thermal stress and results in micro-crack formations. The results provide a detailed understanding of the laser-induced transformations in the material and highlight optimal conditions for reducing thermal damage while maintaining machining efficiency. This study advances the field of laser processing by offering insights into the mechanisms governing oxide formation, thermal cracking, and material deformation during silicon grooving, providing the foundation for future exploration of laser-material interaction dynamics.

Оценка качества и механических свойств получаемых слоев металла из низкоуглеродистой стали методом WAAM с использованием дополнительной механической и ультразвуковой обработки

Introduction. Additive manufacturing is a technology that enables three-dimensional (3D) components to be printed layer by layer according to digital models. Completely different from traditional manufacturing methods such as casting, forging, and machining, additive manufacturing is a near net shape manufacturing process that can greatly enhance design freedom and reduce manufacturing runtime. The material processing challenges in Wire and Arc Additive Manufacturing (WAAM) are related to achieving performance metrics related to geometric, physical, and material properties. Tight tolerances and stringent surface integrity requirements cannot be achieved by utilizing stand-alone AM technologies. Therefore, WAAM parts typically require some post-processing to meet requirements related to surface finish, dimensional tolerances and mechanical properties. It is therefore not surprising that the integration of AM with post-processing technologies into single and multi-setup machining solutions, commonly referred to as hybrid AM, has become a very attractive proposition for industry. The purpose of the work is to evaluate the quality and mechanical properties of the resulting metal layers of mild steel by WAAM method using additional mechanical and ultrasonic processing. Research Methods. To conduct the experiments, a set of welding equipment was used — a single-phase inverter device KEMPPI Kempomat 1701, designed for welding with wire in shielding gases. A mixture of argon and carbon dioxide (80 % argon and 20 % CO2) was used as a shielding gas. SV-08G2S (0.8 C-2 Mg-Si) wire was used as the surfacing material. A plate made of steel St3 with overall dimensions 150×100×5 mm was used as a base for surfacing. The surface of the plate before surfacing was thoroughly cleaned from the layer of oxides, oil, rust and other contaminants. For this purpose mechanical cleaning of the surface was used with BOSCH abrasive wheel with a diameter of 125 mm diameter and a grit size of 120. Before surfacing the surface of the product was degreased with white spirit. The gas flow rate was set at 8 dm3/min. To select the optimal wire feed rate and volt-ampere characteristic, surfacing was performed at each adjustment step of wire feed rate, and voltage. Mechanical statistical tensile tests, chemical composition analysis and metallographic studies were also performed. Results and Discussion. Gas porosity is a typical defect that occurs during the WAAM process and should be eliminated because it adversely affects the mechanical properties. Initially, gas porosity leads to a reduction in the mechanical strength of the part due to damage from microcrack formation. In addition, it often causes the surfaced layer to have worse fatigue properties due to the spatial distribution of different shape and size structures. In our experiments we found that a wire feed speed range of 5–6 m/min is optimal. Increasing the flow rate of shielding gas in the range of 8–14 l/min allows reducing porosity in the surfaced metal to almost zero. The mechanical properties of the surfaced beads show that the average value of yield strength after machining is higher than that of unprocessed specimens. The data obtained from these experiments are in good agreement with those reported in the literature. The presented results can be used in real WAAM technological processes.

Micro-computed tomographic evaluation of dentinal microcracks in response to progressive taper enlargement in root canals of maxillary molars.

To investigate the development of dentinal microcracks resulting from the progressive enlargement of the buccal canals of maxillary molars with and without the MB2 canal employing instruments with the same tip and four different tapers. Twenty maxillary molars with (n = 10) and without (n = 10) the MB2 canal underwent micro-CT scanning. Their mesiobuccal and distobuccal canals were sequentially enlarged using nickel-titanium instruments with sizes 25/.03, 25/.05, 25/.06 and 25/.08v. Subsequent scans were conducted after each canal enlargement. The preoperative scans were coregistered with their respective datasets, and the cross-sectional images were carefully examined to identify dentinal defects. This process, conducted twice at two-week intervals, involved two examiners. Intra- and inter-examiner calibrations were validated using the Kappa index. The incidence of microcracks was reported as a percentage frequency. The intra- and inter-examiner Kappa values were 0.85 and 0.88, respectively, indicating excellent agreement. Dentinal microcracks were detected in 1206 out of 42 975 cross-sectional image slices (2.8%). Molars with MB2 canal exhibited more slices (4.5%) than teeth without MB2 (0.9%). Every dentinal microcrack observed in the images after root canal preparation was already present in the corresponding images takenbefore root canal preparation. The progressive enlargement of root canals using instruments with different tapers did not induce the formation of new dentinal microcracks in maxillary molars, regardless of the presence of the MB2 canal.

Quantification of coarse aggregate constraint on mortar shrinkage in concrete under drying condition

Quantifying the constraint effect of coarse aggregates on mortar shrinkage is essential for predicting the bulk shrinkage of concrete. This study investigated the formation and evolution of tensile strain/stress shells around coarse aggregate in concrete under dry conditions by using digital image correlation and lattice fracture modelling. The average constraint shell thickness and constraint index were proposed to quantify the range and degree of coarse aggregate constraint on mortar shrinkage. The results indicated that constraint range increased as size of coarse aggregates increased, with the growth rate of 0.079. The constraint degree of coarse aggregate is positively correlated with aggregate size and mortar drying shrinkage. Notably, the formation of drying-induced micro-cracks also consumes more drying shrinkage forces, resulting in lower bulk drying shrinkage in concrete. At last, a mathematical model was developed to predict the bulk drying shrinkage of concrete based on constraint index and then validated against experimental results.

Creep-fatigue interactive behavior and damage mechanism of TP321 stainless steel under hybrid-controlled conditions

In this study, Hybrid-controlled creep-fatigue (HCCF) tests were conducted on TP321 austenitic stainless steel under a variety of test conditions. The effects of strain amplitude, holding time, holding stress and temperature on the creep-fatigue behavior of TP321 austenitic stainless steel were not only analyzed in detail but also revealed the creep-fatigue damage interactive mechanism. The results demonstrated that a rise in test temperature and load holding time markedly induced creep deformation, resulting in a notable reduction in failure life. Additionally, an increase in test temperature led to the cessation of the cyclic hardening phenomenon. Secondly, the analysis of fracture morphology and X-ray computed tomography (X-CT) scanning results demonstrated that the transgranular cracks expanded inwards and connected with the intergranular voids under creep-fatigue interaction, forming a mixed intergranular and transcrystalline fracture mode. The presence of large creep cavities impeded the propagation of fatigue cracks when creep damage was the dominant phenomenon. Subsequently, the damage evolution mechanism was elucidated through microstructural analysis, which revealed that the impact of the slip bands on the triangular grain boundaries and the precipitation of carbides facilitated the nucleation of voids and the internal formation of intergranular microcracks, thereby causing creep-fatigue damage interaction. Finally, the TP321 austenitic stainless steel creep-fatigue damage interactive mechanism diagram was proposed in conjunction with the fracture morphological characteristics and microstructure.

Comparative Quantitative Analysis of the Evolution of Precipitates in Inconel 625 Superalloy Manufactured by Laser Powder Bed Fusion Subjected to High-Temperature Creep and Annealing

AbstractThe aim of the study is to contribute to understanding how prolonged exposure to high temperature and stress affects the morphology, size, and distribution of secondary phase precipitates in Inconel 625 manufactured by laser powder bed fusion. Creep tests were performed under a constant stress of 100 MPa at temperatures of 600 °C, 700 °C, and 800 °C. Samples creep tested at 600 °C and 700 °C were terminated after 2000 hours, while at 800 °C, the creep test was carried out until rupture. Isothermal annealing was carried out at temperatures of 700 °C and 800 °C for the same duration as creep tests. Microstructural analysis of creep-deformed and annealed samples was performed with the use of light microscopy, scanning, and transmission electron microscopy. The first-ever comparison of the evolution of precipitates in Inconel 625 LPBF after creep tests and annealing at 700 °C and 800 °C was shown. The qualitative and quantitative analysis revealed that the stress applied during creep tests leads to more pronounced nucleation of δ phase precipitates, although the growth of δ particles occurs more slowly compared to annealing. Furthermore, in creep-tested samples, the growth and coalescence of carbides and Laves phase particles were more intensive, compared to stress-free annealing, particularly at a temperature of 800 °C. Moreover, we show that the evolution of carbides and Laves phase particles along grain boundaries contributes to cavity and microcrack formation during high-temperature creep of Inconel 625 LPBF.

Effect of Size-Controlled Nanofluid on Mechanical Properties, Microstructure, and Rheological Behavior of Cement Slurry for Oil Well Cementing.

The optimal design of cement slurry by balancing various cement additives and cement is critical for effective oil well cementation job. However, given adverse circumstances of application, existing additives may not be sufficient to perform suitably in challenging conditions, leading to premature cement hydration, formation of microcracks, and gas channeling pathways. Thus, this study explores the use of a single-step silica nanofluid (NP size: 5-10, 90-100, and 250-300 nm and concentration: 1, 3, and 5 wt %) as an additive and explores its effect on thickening time, fluid loss, and rheological behavior of class G cement slurry at high-pressure and high-temperature (HPHT) conditions (135 °C and 3625 psi). The improvement in thickening time, fluid loss, and rheology of conventional slurry was greater for low NP size than the nanofluid of high NP size: the nanofluid size, e.g., 5-10 nm, and concentration (1 wt %) were found to accelerate the thickening time by 30-40% while reducing fluid loss from 38 mL (no silica, slurry CS) to 30 mL (with silica, slurry C1). The rheological behavior was studied via shear (viscosity) and dynamic (elastic moduli, G') modes to evaluate the viscosity, hysteresis, and elastic response of slurry with and without nanofluid. The inclusion of nanofluid slightly reduced the slurry viscosity; however, all slurries exhibited shear thinning with superior fitting with the power law model. As compared to slurry CS, hysteresis of slurry C1 was least dependent on shear deformation, and thus, it showed that it almost matched viscosity profiles during loading and unloading cycles. The addition of silica was found to maintain the original properties of cement slurry, establishing that cement had not agglomerated, and no sedimentation was observed even at shear rates of 1000 s-1. The results of this study greatly promote the use of silica nanofluid as an important additive in class G cement for cementation operations, which is unlikely with a two-step nanofluid where nanoparticles are expensive, and upon mixing, they tend to agglomerate and make large size clusters.

Comparative Evaluation of Microcrack Formation by K Files Using Mechanical Technique with Help of Reciprocating Contra-Angle Handpiece and Manual Technique: An Invitro Study

Introduction Effective root canal preparation is essential for successful treatment, focusing on thorough cleaning and shaping to prevent complications like vertical root fractures. Different tools, such as stainless steel and nickel-titanium files, offer advantages and drawbacks, impacting the risk of dentinal microcracks. This study examines the incidence of these cracks using both manual and reciprocating techniques with K files.  Material and Method This study involved 150 mandibular premolars, divided into five groups to evaluate dentinal crack formation with different file systems. Groups included manual and mechanical instrumentation with stainless steel (S.S.) and nickel-titanium (NiTi) files, with one control group. After standard root canal preparation and irrigation, each root was sectioned and examined under a stereomicroscope to document crack formation. Data was analysed using Chi-square test, and Fisher's Exact test.  Result There is no statistical significant difference among groups.  Conclusion Maintaining root integrity in root canal treatment is vital, with similar crack formation seen in both manual and reciprocating techniques. Reciprocating handpieces offer a cost-effective, efficient option, beneficial for student training in modern endodontics.

Tribologically enhanced self‐healing hybrid laminates for wind turbine applications

AbstractWind turbines are subjected to extreme weather and load conditions; hence, high strength and impact resistance are required. Furthermore, wind turbine blades can be subjected to impact loads such as bird strikes, resulting in the formation of microcracks. Self‐healing capsules can be used to mend turbine blades for microscale damage. The incorporation of self‐healing capsules may cause a decrease in the mechanical characteristics of the composites prior to impact resistance, which can be compensated for with efficient fillers such as silicon carbide whiskers (SiCw). Thus, a novel hybrid composite structure is examined with the advantage of using a self‐healing mechanism and SiCw reinforcement. Tensile, tribological, and Charpy impact tests were performed to characterize the mechanical and tribological properties, which were supported with microscopic observations. Multiple experimental characterizations were performed to investigate the impact, and the ultimate tensile strength (UTS) and energy absorption capacity of the structure were shown to increase by 32% and 45%, respectively, with the addition of SiCw. The presence of self‐healing agents provides a 5% rise in UTS after enough time for healing following the collision. The structure's tribological performance is improved by 10% in wear resistance and 20% in friction coefficient.Highlights Hybrid laminated composite structure with silicon carbide whisker and self‐healing capsules. Tensile and Charpy impact tests conducted with microscopic observations Increased ultimate tensile strength and energy absorption capacity by 32% and 45%. Tribological improvement by 10% in wear resistance and 20% in friction coefficient.

Linear and nonlinear ultrasound parameters attributed to anisotropy in granite

The anisotropic nature of granite, a key factor affecting its mechanical properties, is inherently governed by its mineral alignment and the presence of orthogonal cleavage planes: rift, grain, and hardway. This study examines how these cleavage planes influence anisotropy, particularly in the context of microcracking formation and acoustic properties. A new measurement procedure for the acoustic nonlinearity parameter (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:\\beta\\:$$\\end{document}) is developed to address the well-known limitations of conventional linear ultrasound methods, including wave velocity and attenuation coefficient, in detecting microstructural changes induced by existing cleavage planes. Unlike other parameters, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:\\beta\\:$$\\end{document} exhibits remarkable changes depending on the plane type, highlighting its high sensitivity to the mineral distribution in each cleavage plane and to the microcracks. A correlation between the linear and nonlinear parameters provides further evidence of the superiority of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:\\beta\\:$$\\end{document} in detecting inherent microscale defects that develop in each plane and affect the anisotropic characteristics of granite. The findings of this study confirm that nonlinear ultrasound is capable of elucidating the mechanisms underlying the origin of anisotropy in granite due to microcracks, with broader implications for understanding unidentified chemical and mechanical phenomena in geological materials.

The effects of in-situ SiAlON on the properties and fracture behavior of alumina-based castables: Based on microcrack toughening mechanism

This study investigates the effect of adding Si powder on the microstructure and fracture behavior of in-situ SiAlON bonded alumina-based castables and clarifies the toughness improvement mechanism. The in-situ SiAlON bonded alumina-based castables were obtained using a nitriding reaction method with Si powder as the precursor. The fracture behavior of the specimens was characterised using the wedge-splitting test (WST) and digital image correlation technique (DIC). It was found that introducing in-situ SiAlON bonding phases can significantly improve the fracture behavior and toughness. The toughness parameter (GF/σNT) increased from 18.9 μm to 38.6 μm as the addition of Si powder increased from 0 wt% to 6 wt%. The primary toughness mechanism of the castables is microcrack toughening. The formation of microcracks is the consequence of a mismatch in the thermal expansion coefficients (CTE) of the corundum and in-situ SiAlON phases.

Application of 3D-printed resin guides for the removal of molar fiber posts

To evaluate the digital guide technique for removing fiber posts from molars and compare it with the conventional microscope-assisted ultrasound method. Two mandibular dentition models, each comprising six extracted molars, were prepared. Two thick and straight canals distributed separately in the distal and mesial roots of each molar were selected for placing the fiber posts. The 24 posts in the two dentition models were removed using 3D-printed resin guides, or a microscope and an ultrasonic device. The time taken to remove the fiber post from each tooth was recorded. The volume loss, deviation values (angular deviation and horizontal and vertical deviations of the tip), and formation of microcracks before and after fiber post removal were determined using micro-computed tomography images. The digital guide technique took significantly less time than the microscope-assisted ultrasound technique (p < 0.05). No significant differences in horizontal and vertical tip deviations were observed between the two groups. The angular deviation and volume loss in the guide group were significantly lower than those in the ultrasound group (p < 0.05). New dentin microcracks were formed in the ultrasound group but not in the digital guide group. Using a 3D-printed resin guide plate can shorten the fiber post removal time and improve the stability and safety compared to the microscope-assisted ultrasound technique. 3D-printed resin guides can reduce the fiber post removal time and provide better stability and safety than the conventional method.

Enhanced strength-ductility synergy in a Ni–W–Co–Ta medium-heavy alloy via cryogenic supersonic fine particle bombardment

This study explores the influence of cryogenic supersonic fine particle bombardment (CSFPB) on a Ni–W–Co–Ta medium heavy alloy (MHA), and focus on the effect of gas pressure and impact time on the surface integrity, microstructural evolution, and mechanical properties of the MHA. CSFPB treatment creates a gradient structure, including surface layer with nanograins down to 9.0 nm due to severe plastic deformation, subsurface layer with high density dislocation structures and deformation twins due to weakened impact energy, and undeformed matrix. A key advantage of CSFPB is seen to be the cryogenic environment, which promotes superior surface integrity by reduced roughness. As the impact duration and gas pressure increase, the depth of deformation layer, surface hardness and strength of the MHA progressively rise. The optimal combination of strength and ductility is achieved at a gas pressure of 1.0 MPa for a duration of 90 s. This setting results in a maximum ultimate tensile strength of 1351 MPa and yield strength 796 MPa, with uncompromising elongation. However, excessively long treatment durations or high gas pressures can lead to the formation of surface microcracks, ultimately reducing the MHA's strength. Therefore, CSFPB offers the benefit of improved surface integrity through the cryogenic environment while maintaining a desirable balance between enhanced strength and ductility.

Influence of municipal solid waste incineration bottom ash on the hydration and carbonation behavior of reactive magnesia cement

This study investigates the effects of Municipal solid waste incineration bottom ash (MSWIBA) on the hydration and carbonation behavior of reactive magnesia cement (RMC). The results indicate that the incorporation of MSWIBA accelerates the early hydration rate of RMC due to its dilution and nucleation effects. However, excessive MSWIBA content formed layered double hydroxides (LDH) inhibiting the hydration of magnesium oxide cement. Furthermore, while a 5% addition of MSWIBA enhances the compressive strength of RMC after carbonation, higher contents lead to a reduction in post-carbonation strength and long-term durability due to the formation of microcracks from hydrogen gas generation and the expansion from carbonation products. Additionally, the carbonation process is affected by LDH, which hinders the crystallization of hydromagnesite and favors the formation of more amorphous phases. The findings suggest that while MSWIBA can be beneficial at low dosages, its excessive use may compromise the long-term performance of RMC.

Family-based whole-exome sequencing implicates a variant in lysyl oxidase like 4 in atypical femur fractures.

Atypical femur fractures (AFFs) are rare adverse events associated with bisphosphonate use, having unclear pathophysiology. AFFs also cluster in families and have occurred in patients with monogenetic bone diseases sometimes without bisphosphonate use, suggesting an underlying genetic susceptibility. Our aim was to identify a genetic cause for AFF in a Caucasian family with seven members affected by osteoporosis, including three siblings with bisphosphonate-associated AFFs. Using whole-exome sequencing, we identified a rare pathogenic variant c.G1063A (p.Gly355Ser) in lysyl oxidase like 4 (LOXL4) among 64 heterozygous rare, protein-altering variants shared by the three siblings with AFFs. The same variant was also found in a fourth sibling with a low-trauma femur fracture above the knee, not fulfilling all the ASBMR criteria of AFF and in one of 73 unrelated European AFF patients. LOXL4 is involved in collagen cross-linking and may be relevant for microcrack formation and bone repair mechanisms. Preliminary functional analysis showed that skin fibroblast-derived osteoblasts from the unrelated patient with the LOXL4 variant expressed less collagen type I and elastin, while osteogenic differentiation and mineralization were enhanced compared with two controls. In conclusion, this LOXL4 variant may underlie AFF susceptibility possibly due to abnormal collagen metabolism leading to increased formation of microdamage or compromised healing of microcracks in the femur.

Initial temperature conduction process and fracture response of rock impacted by ultra-low-temperature fluid: A case study of polymethyl methacrylate

Injecting ultra-low-temperature fluids, such as liquid carbon dioxide (CO2) and liquid nitrogen (LN2), into deep, low-permeability reservoirs for fracturing is an emerging waterless fracturing technology. When these fluids enter the reservoir, they rapidly exchange heat with the fracture walls, triggering intense cold shock, which influences fracture development. Although many scholars have studied the effects of nitrogen freezing and thawing on coal seams, the initial thermal exchange and cold shock process when LN2 first enters the rock mass remains unclear. This paper uses the visualizable material polymethyl methacrylate (PMMA) as the research object, conducting low-temperature impact experiments under different preset temperatures (20 °C, 40 °C, 60 °C, and 80 °C) to investigate the impact of thermal exchange during cold shock on PMMA fracturing. The results show: (1) During LN2 impact, PMMA's temperature changes in three stages: slow cooling (micro-cracks initiation), rapid cooling (formation of long fractures), and temperature recovery (crack formation completion). (2) In prolonged impacts, PMMA temperature decreases linearly, while in short-term cyclic impacts, temperature decreases exponentially with faster recovery, increasing the likelihood of micro-cracks formation. (3) Temperature differences have a dual effect on crack formation and propagation: they significantly enhance internal thermal stress, leading to rapid micro-cracks initiation and expansion, while also causing uneven temperature gradients in the crack propagation region, shifting fracture modes from tensile to complex composite failures and promoting secondary crack formation. However, a significant temperature differential may result in the development of a singular crack propagation path, hindering the formation of complex fracture networks. These findings offer theoretical insights into fracture network formation in waterless fracturing of low-permeability reservoirs.

The effect of soaking heat-polymerized acrylic resin denture base in avocado seed extract (Persea americana Mill.) on the inhibition of denture-plaque microorganisms biofilm growth

Background Heat polymerized acrylic (HPA) resins are known to have high porosity that contributes to increased surface roughness and microcrack formation in stress areas. This facilitates the attachment and growth of polymicrobial biofilms contributing to increased antimicrobial resistance. Many research had been carried out on avocado seeds, but no research that studies avocado seeds effect on denture-plaque microorganism biofilm on HPA resin has been found. Methods This study used 144 samples (n=144), namely HPA resin discs covered with mono-species and polymicrobial biofilms. The discs were soaked for 8 hours in the 5%, 10%, 15%, 20% avocado seed extract, positive control (alkaline peroxide), and negative control (aquadest). Each disc was shaken with a vortex mixer for 1 minute, and 100 μL was added into 96-well microplates with three times repetition and incubated for 24 hours. A microtiter plate biofilm formation assay was then conducted The inhibition values were determined from the percentage inhibition value formula which required absorption values from a microplate reader (595 nm). The research data were analyzed using a univariant test, and a one-way ANOVA test, accompanied by Welch ANOVA on non-homogenous data. Results In this research, it was found that the MBIC50 of avocado seed extract against the mono-species of C. albicans (5%), C. glabrata (5%), A. odontolyticus (15%), S. gordonii (15%), S. aureus (10%), while against polymicrobial was 20%. There was a significant effect of soaking HPA resin in avocado seed extract on the inhibition of mono-species and polymicrobial biofilms with a value of p&lt;0.001 (p&lt;0.05). Conclusion The MBIC50 of avocado seed extract in polymicrobial biofilm group was higher than that in the mono-species biofilm groups. Although alkaline peroxide showed higher inhibition value than that of the MBIC50 in polymicrobial biofilm group, 20% avocado seed extract was concluded effective as it inhibited &gt;50% polymicrobial biofilm.

Simulation of Autogenous Self‐Healing in Lime‐Based Mortars

ABSTRACTThroughout history, architectural heritage has been constructed using masonry, clay or stone elements, and lime‐based mortars. Over time, old buildings are subjected to different degrees of movement and degradation, leading to the formation of microcracks. Water dissolves and transports lime in mortar, but when the water evaporates, the lime is deposited and heals cracks in a process known as autogenous healing. Lime‐based mortars can regain some mechanical properties due to their healing capacity, given certain conditions. In the present work, a constitutive formulation has been developed to simulate cracking and healing in lime‐based mortars. The proposed model captures the residual displacements within cracks, associated with interacting crack surface asperities, as well as the healing effect on mechanical properties. A new approach is described which expresses these mechanisms mathematically within a micromechanical formulation. The proposed model was validated by comparing the outputs with experimental data. The results show that the new continuum micromechanical damage‐healing model could capture the damage‐healing cycle with good accuracy.

Microstructural Anisotropy, Mechanical Properties, and Fatigue Crack Growth Behavior of AA2050‐T84 Alloy

ABSTRACTThis study focuses on characterizing the microstructure and mechanical properties of AA2050‐T84 alloy produced in two different thicknesses, 20 and 130 mm. A comparative analysis between the two thicknesses aims to understand how the rolling operation for achieving thin plates influences the alloy's microstructure and overall mechanical performance. Microstructural analyses showed a highly anisotropic grain structure and preferred crystallographic orientation in the 20‐mm‐thick plate, causing anisotropic tensile properties. Also, a significant fatigue crack deviation was observed for the 20‐mm‐thick plate during fatigue crack growth tests due to its microstructure. This result was attributed to the microcrack formations perpendicular to the crack growth direction and slip bands at the intermediate ΔK, when the loading was parallel to the rolling direction. The findings from this study offer critical insights into how the rolling operation for achieving thin plates influences the microstructure and overall performance of the alloy.

Periodically Sinusoidal Magnetic Stray Field and Improved Film Quality of CoMnP Micro-Magnet Arrays for Magnetic Encoders by Electrodeposition with the Assistance of Ultrasound

Magnetic encoders are composed of a magnetic sensor, a hard magnetic recording medium and a signal processing circuit. Electrodeposited micro-magnet arrays produced by micro-fabrication are promising recording media for enhancing encoder performance. However, two major engineering issues have yet to be resolved. One issue is an unknown relationship between the feature sizes of micro-magnet arrays and their stray field shapes, and another issue is the formation of micro-cracks due to the built-up residual stresses of thick films. In this study, we investigated the effect of feature sizes on the emanating stray field shape at various observation heights. Feature sizes include two height (i.e., film thickness) values of 78 μm and 176 μm, and both width and spacing with three values of 360 μm, 520 μm and 680 μm. Ultrasound-assisted agitation was adopted for investigating the effects of electrodepositing current densities on the film crystalline microstructures and magnetic properties. Narrowing the width of micro-magnets helps the stray field to become a sinusoidal profile. Thinner film, i.e., thickness 78 μm in this study, supports the stray field taking on a sinusoidal profile. Moreover, the spacing between the micro-magnets plays a key factor in determining the shape of the stray field. Under 37 kHz/156 W ultrasound agitation, the optimal hard magnetic properties of electrodeposited CoMnP films are residual magnetization 2329 G and coercivity 968 Oe by a current density of 10.0 mA/cm2. Ultrasound-assisted electrodeposition, along with duly designed feature size, facilitates the micro-magnet arrays having a sinusoidal stray field shape using high quality films. Furthermore, for the first time, a systematic understanding of feature-size-dependent stray field evolution and improved polarities quality has been realized for the recording media of sinusoidal magnetic encoders.