Critical Width Research Articles

A novel method for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test during laser welding

A novel evaluation method was developed for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test laser welding. By changing different chemical compositions and welding speeds, the critical restraint width was named and regarded as a new index to evaluate cracking susceptibility. First of all, the average critical restraint width of SUS310S, 316 and 302 was measured as 22.97 mm, 18.17 mm and 17.38 mm during laser welding at a speed of 1.0 m/min, respectability. Single phase austenite under mode A appeared in 310S while the other could form austenite and a small amount of ferrite based on mode FA, therefore, the solidification cracking susceptibility was 310S > 316 > 302. Then, the critical restraint widths of SUS310S and 304 had a tendency of decrease with increasing welding speed from 0.5 m/min to 1.0 m/min during laser welding. The lower heat input could decrease primary and secondary dendrite arm spacings, causing a reduction in the segregation degree. In addition, the fine dendrite along grain boundary of weld center could contribute to form zigzag interface which would be beneficial to interrupt the continuous residual liquid film. Thus, the solidification cracking susceptibility tended to decrease with an increase in laser welding speed from 0.5 m/min to 1.0 m/min. Above all, the developed evaluation method could improve the applicability, feasibility and progressiveness of hot cracking test.

Ligand-induced incompatible curvatures control ultrathin nanoplatelet polymorphism and chirality

The ability of thin materials to shape-shift is a common occurrence that leads to dynamic pattern formation and function in natural and man-made structures. However, harnessing this concept to rationally design inorganic structures at the nanoscale has remained far from reach due to a lack of fundamental understanding of the essential physical components. Here, we show that the interaction between organic ligands and the nanocrystal surface is responsible for the full range of chiral shapes seen in colloidal nanoplatelets. The adsorption of ligands results in incompatible curvatures on the top and bottom surfaces of the NPL, causing them to deform into helicoïds, helical ribbons, or tubes depending on the lateral dimensions and crystallographic orientation of the NPL. We demonstrate that nanoplatelets belong to the broad class of geometrically frustrated assemblies and exhibit one of their hallmark features: a transition between helicoïds and helical ribbons at a critical width. The effective curvature [Formula: see text] is the single aggregate parameter that encodes the details of the ligand/surface interaction, determining the nanoplatelets' geometry for a given width and crystallographic orientation. The conceptual framework described here will aid the rational design of dynamic, chiral nanostructures with high fundamental and practical relevance.

Impact of long-range attraction on desorption kinetics.

Desorption of molecules from surfaces is widespread both in nature and technology. Despite its omnipresence and conceptual simplicity, fundamental details can be surprisingly complex and are often poorly understood. In many cases, first-order kinetics is assumed, which implies that the adsorbates do not interact with each other and desorption is the rate-limiting process. While this might be a good approximation in some cases, it is far from reality in the case of adsorbates that form ordered structures. Here, we study the desorption of a submonolayer film of 3-nitrophenol from the natural cleavage plane of calcite kept in ultrahigh vacuum. Interestingly, two distinctly different desorption regimes are observed during isothermal desorption monitored by dynamic atomic force microscopy. Initially, at high coverages, the coverage decreases almost linearly in time, indicating a constant desorption rate. Beyond this linear regime, at low coverages, a drastic increase in desorption rate is observed until the surface is completely empty. The transition between these two regimes is associated with a critical island width. We propose an existence of a long-range attractive interaction between the molecules as a possible explanation for the sudden increase in the desorption rate when a critical island width is reached. The herein observed phenomenon of two different desorption regimes is expected to be of general nature when interactions beyond next-neighbour attraction are present.

Understanding detonation wave dynamics in annular channels with geometric and pressure variations

This study delves into detonation wave behavior within C2H2/O2/Ar-filled annular channels using the generalized ZND model to establish the link between detonation velocity Dn and curvature κ during wave propagation. Incorporating detonation shock dynamics (DSD), it examines the outer wall's influence on wave propagation. Predictive models accurately identify the critical channel diameter width dcr and detonation wave angular velocity ω across diverse pressures. Wide-diameter channels (d > dcr) exhibit a supersonic region segregating the outer wall's impact from the inner wall, contrasting narrow-diameter channels (d < dcr) allowing the outer wall's influence on the inner wall. The behavior of the detonation wave is influenced not only by the Dn-κ relationship but also by the compressive effect of the outer wall. Notably, factors shaping the wave's ω manifest through the inner normal angle φi. The source term causing a loss in detonation wave velocity results in a decrease in the φi, while the source term accelerating the detonation wave leads to an increase in the φi. For stable wave propagation in wide-diameter channels, this study advocates φi at 0° as optimal, revealing insights pivotal for comprehending detonation wave dynamics in annular channels.

Multiphysics analytical and numerical studies of biomolecule preconcentration utilizing ion concentration polarization: a case study of convergent microchannels.

A convergent sector in microfluidic devices utilizing ion concentration polarization (ICP) can help increase the preconcentration rate and the concentration enhancement factor (CEF) of biomolecules. In this work, we present a detailed study of the nozzle-like-squeeze effect of a convergent channel on the preconcentration of biomolecules. By numerically solving coupled Nernst-Planck-Poisson-Navier-Stokes governing equations for the 2D channel model, we report the first study on the critical width of a convergent region in the channel to retain the advantage of the nozzle-like-squeeze effect in speeding up preconcentration and augmenting CEF. In addition, we investigated the impact of the location and the dimensions of a convergent sector on the mechanism of biomolecule preconcentration. The location of an ion-selective membrane was also determined to ensure that biomolecules are focused on the convergent region of the channel. Moreover, we introduce analytical studies to compare and verify simulation findings. Specifically, the formulas for the critical dimensions of a convergent channel, location of a preconcentrated biomolecule plug, and position of an ion-selective membrane are presented. Furthermore, important working parameters, including electric potentials and hydrostatic pressures, were examined to scrutinize their effect on convergent concentrators. These detailed analytical solutions and numerical simulation results are consistent with experimental observations, providing deep insights into the ICP phenomenon and the preconcentration mechanism of biomolecules in convergent microfluidic concentration devices.

Substantial toughening by thick nanoscale amorphous intergranular films in nanocrystalline materials

Amorphous intergranular films (AIFs) have been proven in experiments to improve the damage tolerance of nanocrystalline materials. However, a quantitative study is still lacking. Molecular dynamics simulations were performed here to investigate the effect of CuNb AIFs on the fracture toughness of nanocrystalline Nb. In order to clarify the role of AIFs, a bicrystal Nb model with one straight symmetrical tilt grain boundary and a mode-I crack in one of the grains was constructed, in which the AIF effect was introduced by replacing the normal grain boundary with a CuNb AIF. Then, AIF thickness-dependent tensile deformation of the bicrystal Nb samples was simulated. The work-of-fracture, which is defined as the released strain energy due to the newly generated unit area in the crack during stretching, was employed to quantify the fracture toughness of the bicrystal systems. The results show that the fracture toughness of the AIF sample can be tripled due to the blunted crack tip and the relieved stress concentration at the crack tip as compared to the AIF-free one that exhibits a brittle crack propagation behavior. Also, the thicker the AIFs, the more pronounced this reinforcing effect. More importantly, it is found that there exists a critical AIF width of 1.7 nm, below which the crack will eventually break through the AIF, and above which the crack failed to do this. It is revealed that the enhanced fracture toughness originated from the transformation of brittle crack propagation to abundant dislocation emission from AIFs.

Cascade Formation of Topological Defects and Satellite Droplets in Liquid Crystals at Dynamic Capillary Instability

The formation of topological defects at the nematic–isotropic liquid interface and near satellite droplets has been detected at the breakup and fragmentation of the bridge of the isotropic phase between nematic domains. This process has been implemented in thin optical cells filled with a liquid crystal. The critical width of the bridge at which a universal time dependence of its width is determined by the capillary velocity (ratio of the surface tension to the viscosity) has been determined.

Energy evolution mechanism during rockburst development in structures of surrounding rocks of deep rockburst-prone roadways in coal mines

Influenced by the deep high-stress environment, geological structures, and mining disturbance in coal mines, the frequency of rockburst disasters in roadways is increasing. This research analyzed energy evolution characteristics during rockburst development in the elastic bearing zone and energy conversion in the plastic failure zone. The critical energy criteria for structural instability of roadway surrounding rocks were deduced. Numerical software was also applied to simulate the energy evolution during rockburst development in surrounding rocks of rockburst-prone roadways under conditions of different mining depths and coal pillar widths. The occurrence mechanism of rockburst deep in coal mines was analyzed from the perspective of energy in structures of deep roadway surrounding rock in coal mines. The research results show that the critical energy criteria are closely related to the elastic strain energy stored in deep roadway surrounding rocks and the energy absorbed by support systems. The impact energy in roadways is directly proportional to the square of the stress concentration factor k. Moreover, as the mining depth increases, the location of the peak point of maximum energy density gradually shifts to coal ahead of the working face. The larger the mining depth is, the more significantly the energy density is influenced by advanced abutment pressure of the working face and the wider the affected area is. With the increment of the coal pillar width, the distance from the peak point of energy density to the roadway boundary enlarges abruptly at first and then slowly, and the critical coal pillar width for gentle change in the distance is 30 m. Changes in the peak elastic energy density in coal pillars with the coal pillar width can be divided into four stages: the slow increase stage, abrupt increase stage, abrupt decrease stage, and slow decrease stage. The elastic energy density is distributed asymmetrically in deep roadway surrounding rocks in coal mines. Under the action of structures of roadway surrounding rocks, energy evolution in these structures differs greatly during rockburst development under conditions of different coal pillar widths. This research provides an important theoretical basis for the support of rockburst-prone roadways during deep coal mining.

Effect of aberrations on the beam quality factor of Hermite-Gauss beams.

The effect of aberrations on the beam quality factor (M2) of Hermite-Gauss (HG) beams is examined. Using the method of moments, we derive closed-form analytical expressions of M2 due to astigmatism and spherical aberration. Our analysis reveals that the radius of the HG beams plays a significant role in determining the effect of the aberrations on M2. For each aberration, we establish a critical width that separates the region where M2 changes infinitesimally from the region where it changes sharply. The analytical results are validated through numerical simulations.

Dynamics of droplet generation in a wedge-shaped step-emulsification microchannel

The droplet generation in a wedge-shaped step-emulsification microchannel is investigated experimentally and the generation dynamics of dripping flow as a main applicable flow regime is primarily studied. The sodium alginate aqueous solution and liquid paraffin are used as dispersed phase and continuous phase respectively. The droplet generation process is divided into four stages: two-dimensional retracting stage, two-dimensional spreading stage, three-dimensional necking stage, and three-dimensional pinch-off stage. The head of the dispersed phase retracts and spreads faster under higher dispersed phase flow rate or viscosity. The critical neck width between the necking and the pinch-off stages is independent of the dispersed phase flow rate and viscosity. With the increase of dispersed phase flow rate, the droplet size increases while its formation period decreases. The droplet size and formation period increase with the increase in the dispersed phase viscosity. The flow regime of droplet generation relies primarily on the flow rate ratio and viscosities. A correlation is proposed for predicting the droplet size.

Failure analysis of overlying strata in fault fracture zone during coal mining

Abstract Faults encountered during coal mining can compromise the continuity and integrity of the overburden, resulting in considerable differences in the stress, displacement, and failure fields of the rocks surrounding the fault zone. When a working face is located adjacent to a fault, the fault-disturbed overburden becomes activated and unstable along the fault plane, which could lead to mining disasters. The fault-adjacent overburden morphology during mining was analyzed using a physical model. A mechanical model of the stability of the fault-disturbed overburden was constructed. The criteria for determining the sliding failure of the overburden during mining were defined, from which the critical coal pillar width required to maintain the overburden stability was determined. The results indicate that an inverted trapezoidal block forms in the overburden due to the combined effects of mining and faulting. The morphology of this block is influenced by the coal pillar width, the height of the fractured zone, and the dip angles of fault and coal seam. The block is prone to sliding or rotational failure along the fault plane during mining. As the coal seam and fault dip angles increase, the critical coal pillar width for maintaining overburden stability decreases. Conversely, increasing coal seam thickness increases the critical coal pillar width. The critical width of coal pillar was determined to be 176 m, which was verified through field observations performed in the #3307 working face.

Tailoring angle dependent ferroelectricity in nanoribbons of group-IV monochalcogenides

Ferroelectricity is significant in low dimensional structures due to the potential applications in multifunctional nanodevices. In this work, the tailoring angle dependent ferroelectricity is systematically investigated for the nanoribbons and nanowires of puckered group-IV monochalcogenides MX (M = ; X = ). Based on first-principles calculations, it is found that the ferroelectricity of nanoribbon and nanowire strongly depends on the tailoring angle. Firstly, the critical width for the bare nanoribbon of group-IV monochalcogenide is obtained and discussed. As the nanowires are concerned, the ferroelectricity will disappear when the tailoring angle becomes small. At last, H-passivation on the edge and the strain engineering are employed to improve the ferroelectricity of nanoribbon, and it is obtained that H-passivation is beneficial to the enhancement of polarization for nanoribbons tailored near the armchair direction, while the polarization of nanoribbons tailored along the diagonal direction will decrease when the edges are passivated with H atoms, and the tensile strain along the length direction always favors the improvement of ferroelectricity of the considered nanoribbons. Therefore, tailoring angle has great influence on the ferroelectricity of nanoribbons and nanowires, which may be used as an effective way to tune the ferroelectricity and further the electronic structures of nanostructures in the field of nanoelectronics.

Experimental study on axial resistant behavior of multi-celled corrugated-plate CFST walls

Multi-celled corrugated-plate concrete-filled steel tubular (MC-CFST) wall is an innovative type of steel–concrete composite wall for achieving lower steel consumption and higher load-resistance efficiency. Experiments on 14 specimens were conducted to investigate the performance of MC-CFST walls under axial compression. The key parameters included wall depth, corrugated cell width and corrugated plate form. The specimens exhibited good ductility and showed similar failure patterns with local buckling on steel tubes and corrugated plates. By analyzing the test results, failure modes and ultimate and residual resistances of the specimens were discussed in detail. In addition, the performance of corrugated plates during the whole loading process was analyzed based on the measured strain results. It can be found that the vertical performance of corrugated plates is the combination of the accordion effect and vertical compression effect, and the horizontal performance is the combination of the overall expansion effect and beam effect. A method for calculating the critical width of corrugated cells was presented. Moreover, the test results were compared with the typical equations specified in several existing design codes. It was found that AISC 360-16, EC4-2004 and GB50936-2014 could safely predict the ultimate resistance of MC-CFST walls, among which the results of GB50936-2014 were the closest to the experimental results.

Identifying the critical lakeshore zone to optimize landscape factors for improved lake water quality in a semi-arid region of Northeastern China

The degradation of water quality and decline in purification capacity of lakeshore zones due to anthropogenic activities and climate change is a growing concern in China. The identification of the critical width of the lakeshore zone remains a challenge due to natural geographic features and pollutant types, that is why a general identification approach has yet to be developed. To facilitate the planning of lakeshore restoration plans, it becomes necessary to conduct studies focusing on the development of relationships between water quality and landscape factors within the lakeshore zone in different regions. In this study, spatio-temporal patterns of water quality of 49 lakes in Western Jilin Province, China, were determined through field monitoring from 2015 to 2019. Multivariate statistical methods were applied to quantitatively identify the relationships between lakes water quality and landscape factors within lakeshore zones of different widths. The results indicated that nitrogen (N) contributed more to eutrophication, while fluoride concentrations were found to be abnormally high. Furthermore, the width of the lakeshore zone was found to have a significant impact on water quality, with a critical width of 150 m having the greatest effect. Cropland and saline land explained almost 50% of the water quality variability throughout different seasons. The results also revealed that dual control of N and phosphorus (P) will be required to prevent eutrophication in the study area. Agricultural activities and severe soil salinization were identified as the main causes of diffuse pollution. The establishment of a width threshold identification framework for lakeshore zones is not only of great significance for development of scientific and acceptable restoration plans for lakeshore vegetation filters in ecologically vulnerable areas of western Jilin, but should also provide an effective and user-friendly tool for implementing diffuse pollution control.

Stability analysis of riverbanks with a dual structure under water-root-soil coupling.

The collapse mechanism of dual-structure vegetation riverbanks at different water levels is unclear. A method for calculating the critical collapse width of a dual-structure vegetation bank under different failure modes that consider the variations in river and groundwater levels and the influence of vegetation roots is proposed. Combined with the influence of flow lateral erosion and slope toe accumulation, a calculation model of riverbank stability was established. The results show that shear failure is the main failure mode when the cohesive soil layer on a dual-structure bank is thick, and the critical collapse width of the bank with root soil is higher than that of the soil bank. The critical collapse width of the bank varied with the water level during different water level periods. Compared with a soil riverbank, a rooted soil riverbank can significantly prolong the bank collapse time. The collapse width of a soil bank without vegetation roots is smaller than that of a rooted soil bank, and the cumulative collapse width is related to calculation time. The greater the thickness of rooted soil, the slower the decay rate of bank stability under water flow erosion.

Daily Climatic Data Better Explain the Radial Growth of Swiss Stone Pine (Pinus cembra L.) in High-Elevation Cliffs in the Carpathians

Information about climate–growth relationships is crucial for predicting the potential climatic impact on tree species, especially those growing on the edges of their distribution range, for instance, in high-elevation forests. This study aimed to determine changes in the relationships between tree-ring widths and daily climatic data in high-elevation forests in the Western Carpathians over time. Climate–growth relationships were calculated to obtain the TRWI (tree-ring-width index) chronology (based on 104 trees) and day-wise aggregated data for temperature (mean, minimum, and maximum) and sums of precipitation. The radial growth of stone pine was mostly determined by the mean temperature in the period between mid-June (21st) and the beginning of July (4th) for the critical 14-day window width (r = 0.44). The negative influence of precipitation on the radial growth occurred in summer (r = −0.35) and overlapped with the period of the positive influence of temperature. Dendroclimatic studies based on daily data may define the exact periods (expressed in calendar days) that influence the radial growth of trees much better than the commonly used monthly means. This is particularly important in analysing the growth of trees at high elevations, where the climatic factor strongly limits radial growth.

Tailoring sintering-resistant thermal barrier coatings by considering critical healing width of two-dimensional interlamellar pores

Tailoring sintering-resistant thermal barrier coatings by considering critical healing width of two-dimensional interlamellar pores

Cascade Formation of Topological Defects and Satellite Droplets in Liquid Crystals at Dynamic Capillary Instability

The formation of topological defects at the nematic–isotropic liquid interface and near satellite droplets has been detected at the breakup and fragmentation of the bridge of the isotropic phase between nematic domains. This process has been implemented in thin optical cells filled with a liquid crystal. The critical width of the bridge at which a universal time dependence of its width is determined by the capillary velocity (ratio of the surface tension to the viscosity) has been determined.

Investigation of the Shear Behavior of Concrete Beams Reinforced with FRP Rebars and Stirrups Using ANN Hybridized with Genetic Algorithm.

The shear strength prediction of concrete beams reinforced with FRP rebars and stirrups is one of the most complicated issues in structural engineering applications. Numerous experimental and theoretical studies have been conducted to establish a relationship between the shear capacity and the design variables. However, existing semi-empirical models fail to deliver precise predictions due to the intricate nature of shear mechanisms. To provide a more accurate and reliable model, machine learning (ML) techniques are adopted to study the shear behavior of concrete beams reinforced with FRP rebars and stirrups. A database consisting of 120 tested specimens is compiled from the reported literature. An artificial neural network (ANN) and a combination of ANN with a genetic optimization algorithm (GA-ANN) are implemented for the development of an ML model. Through neural interpretation diagrams (NID), the critical design factors, i.e., beam width and effective depth, shear span-to-depth ratio, compressive strength of concrete, FRP longitudinal reinforcement ratio, FRP shear reinforcement ratio, and elastic modulus of FRP longitudinal reinforcement rebars and FRP stirrups, are identified and determined as input parameters of the models. The accuracy of the proposed models has been verified by comparing the model predictions with the available test results. The application of the GA-ANN model provides better statistical results (mean value Vexp/Vpre equal to 0.99, R2 of 0.91, and RMSE of 22.6 kN) and outperforms CSA S806-12 predictions by improving the R2 value by 18.2% and the RMSE value by 52.5%. Furthermore, special attention is paid to the coupling effects of design parameters on shear capacity, which has not been reasonably considered in the models in the literature and available design guidelines. Finally, an ML-regression equation considering the coupling effects is developed based on the data-driven regression analysis method. The analytical results revealed that the prediction agrees with the test results with reasonable accuracy, and the model can be effectively applied in the prediction of shear capacity of concrete beams reinforced with FRP bars and stirrups.

Coupling of underground coal mining and mine reclamation for farmland protection and sustainable mining

Mining-induced subsidence inevitably caused damage to farmland and created newborn ponding in mining areas with high groundwater tables. However, traditional mining and reclamation (TMR) is characterized by low reclamation and long-term farmland abandonment. Here, two critical width models of the skip-panel and the back-panel were proposed to protect farmland and increase the reclamation rate. Secondly, concurrent mining and reclamation (CMR) and TMR were simulated according to mining-induced subsidence and farmland damage patterns. The advantages of CMR were discussed in comparison with TMR. The results show that: 1) The layout of underground mining was optimized to successfully achieve farmland protection; 2) The overall and staged layouts of mine reclamation were optimized by incorporating final settlement and earthwork balance; 3) The proposed earthwork allocation allowed lower pre-filling heights and rapid reclamation; 4) CMR can prolong the life of farmland by 12.5 years and increase reclamation rate and farmland area by 50.31% and 869.40 ha; 5) CMR has high costs in the short term, but has good social and ecological benefits in the long term. In terms of policy, we recommend the government increase the reclamation rate index and encourage enterprises to adopt CMR. CMR is the realistic need for sustainable mining and will gradually become a new hotspot for scientific mining. This study can provide a reference for sustainable mining and land use management in coal resource-based cities with high groundwater tables.