Direction Of Curvature Research Articles

On the transverse indentation moduli of high-performance KM2 single fibers using a curved area function

Nanoindentation of single microscale fibers is a challenging task due to the dimensional similarity of the probing instruments to the single-fiber cross sections. Algorithms customarily used in nanoindentation equipment assume that the indentation occurs in flat surfaces, thus simplifying the local geometry and approximating material properties in curved specimens. A modified Curved Area Function (mCAF) is developed using finite element analysis and tested using nanoindentation measurements of high-performance single microfibers. The mCAF accounts for the dimensions and curvature in the transverse direction of the cylindrical microfiber in conjunction with the contact depth and the impression of the indented area. The transverse direction indentation modulus of a $$12\,\upmu \hbox {m}$$ of $$\hbox {Kevlar}^{\textregistered }$$ KM2 fiber was estimated as $$7.76\, \pm \,0.22$$ GPa. The computational results were corroborated with experimental measurements performed on KM2 single fibers and agreed with literature findings that assumed minor differences in testing equipment, area analysis, and projected surface area. Two geometry-related coefficients $$ C_{0}$$ and $$C_{1}$$ were determined that facilitate simulation of fiber nanoindentations with diameters of $$d = 7, 15, 30, 40,$$ and $$50\,\upmu \hbox {m}$$ with indentation depths up to, and including, $$2\,\upmu \hbox {m}$$. The mCAF provided a narrow measurement error of $$\pm \,0.22$$ GPa (2.8%) when compared to published studies using the semi-infinite plane approximation, reinforcing the suitability of the developed model.

Height of water-conducting fractured zone in a coal seam overlain by thin bedrock and thick clay layer: a case study from the Sanyuan coal mine in North China

The accurate determination of the height of the water-conducting fractured zone (HWCFZ) in a coal seam covered by thin bedrock and thick clay layer is crucial for aquifer protection, mine safety, and eco-environmental conservation. Using the Sanyuan coal mine in North China as a case study, theoretical analysis, numerical simulation, and field measurements were used to analyze the regularity of the HWCFZ in this area. Per mechanical theory, a geometrical model for calculating rock bending and subsidence was established. Two arcs of equal curvature and lengths and opposite curvature direction were used to fit the curve section of intermediate rock layer after bending. The theoretical method for solving the HWCFZ was given by calculating the rock layer's tensile ratio. In addition, rock failure process analysis (RFPA) software was used to simulate the development of the water-conducting fractured zone (WCFZ) during the mining process, and the HWCFZ was measured by the drilling fluid loss measurement, both which verified the feasibility of the theoretical calculation. To determine the primary controlling factors affecting the HWCFZ, the seepage characteristics and plastic properties of the Quaternary clay layer were also analyzed using laboratory tests. Results show that the Quaternary clay with a depth greater than 130 m has a permeability coefficient of E−10 m/s, a liquidity index less than 0.25, and a plasticity index more than 17, indicating the clay layer is impermeable and of great importance to inhibiting the development of WCFZ. The research can provide significant theoretical insights for effectively preventing water hazards on mine roofs.

The effect of liner surface texture on journal bearing performance under thermo-hydrodynamic conditions

PurposeThe purpose of this paper is to study the effect of liner surface texture on journal bearing performance. Modeling the profile curvature of the dimples or grooves is planned for different cases of texture surface under thermo-hydrodynamic condition (THD). The aim of this paper is to determine the effect the texture surface on the performance of journal bearing and specify the optimum shape for texture dimples.Design/methodology/approachThe paper was opted for an exploratory study by applying finite difference method to solve the energy equation, the heat conduction equations and the Reynolds equation numerically. The lubricant film thickness is divided to a mesh of 640,000 points. The equations were solved for each point of the mesh by using a MATLAB code. For texture shape optimization, 24 cases of different texture shapes were selected which includes elliptical, triangle and square curvature shape.FindingsThe paper provides theoretical insights about the effect of texture shape on journal bearing performance. It was concluded that to get a high load-carrying capacity, the direction of curvature is preferably to be perpendicular to the sliding direction. The convex texture has higher load carrying capacity than concave texture. Finally, the surface with textures in channel form yields better overall performance than the surface with several dimples.Originality/valueThis paper fulfils an identified need to study how texture surface affects the performance of journal bearing under thermo-hydrodynamic conditions.

3D volumetric isotopological meshing for finite element and isogeometric based reduced order modeling

This paper presents a generic framework to construct 3D structured volumetric meshes of complicated geometry and arbitrary topology. Structured meshes are well-suited for reduced order model applications with geometric parameters. For that purpose, we use the triangulated solid 3D model’s boundary provided from B-Rep CAD (Boundary-Representation in Computer Aided Design) models. The input triangulated mesh is decomposed into a set of cuboids in two steps: pants decomposition and cuboid decomposition. Both segmentations understand the geometry and features of meshes. Cuboid decomposition splits a surface into a set of quadrilateral patches which can define a volumetric layout of the associated boundary surface. Using aligned global parameterization, patches of the cuboid decomposition are re-positioned on the surface in a way to achieve low overall distortion, and alignment to principal curvature directions and sharp features. The optimization process is thought to design cross fields with topological and geometrical constraints. Using the optimized cuboid decomposition, a volumetric layout is extracted. Based on the global parameterization and the structured volumetric layout previously computed, a 3D volumetric parameterization is deducted. For different geometrical instances with the same topology but different geometries, the proposed method allows to have the same representation: 3D volumetric isotopological meshes holding the same connectivity. MEG-IsoHex method is introduced to compare fields on 3D hexahedral meshes. The efficiency and the robustness of the proposed approach are illustrated through a remeshing case for large deformations and reduced order models using isogeometric analysis.

BcpLH organizes a specific subset of microRNAs to form a leafy head in Chinese cabbage (Brassica rapa ssp. pekinensis)

HYL1 (HYPONASTIC LEAVES 1) in Arabidopsis thaliana encodes a double-stranded RNA-binding protein needed for proper miRNA maturation, and its null mutant hyl1 shows a typical leaf-incurvature phenotype. In Chinese cabbage, BcpLH (Brassica rapa ssp. pekinensis LEAFY HEADS), a close homolog of HYL1, is differentially expressed in juvenile leaves, which are flat, and in adult leaves, which display extreme incurvature. BcpLH lacks protein–protein interaction domains and is much shorter than HYL1. To test whether BcpLH is associated with defects in microRNA (miRNA) biogenesis and leaf flatness, we enhanced and repressed the activity of BcpLH by transgenics and investigated BcpLH-dependent miRNAs and plant morphology. BcpLH promoted miRNA biogenesis by the proper processing of primary miRNAs. BcpLH downregulation via antisense decreased a specific subset of miRNAs and increased the activities of their target genes, causing upward curvature of rosette leaves and early leaf incurvature, concurrent with the enlargement, earliness, and round-to-oval shape transition of leafy heads. Moreover, BcpLH-dependent miRNAs in Chinese cabbage are not the same as HYL1-dependent miRNAs in Arabidopsis. We suggest that BcpLH controls a specific subset of miRNAs in Chinese cabbage and coordinates the direction, extent, and timing of leaf curvature during head formation in Brassica rapa.

Isthmuses, accessory canals, and the direction of root curvature in permanent mandibular first molars: an in vivo computed tomography study.

ObjectivesThis study was performed to assess the anatomy of mandibular first molars.Materials and MethodsIn this in vivo study, cone-beam computed tomography (CBCT) volumes of 312 bilateral intact first mandibular molars from 156 patients (79 men and 77 women; average age, 35.6 ± 11.2 years) were investigated in terms of the direction of each canal's curvature in the buccolingual and mesiodistal dimensions (direction of the position of the apex in relation to the longitudinal axis of the root), the presence of an isthmus (a narrow, ribbon-shaped communication between 2 root canals) in 3 segments (0–2, 2–4, and 4–6 mm) from the apex), and the presence and number of accessory canals (smaller canals besides the main root canals, connecting the pulp to the periodontium). Data were analyzed statistically (α = 0.05).ResultsMesiolingual canals were mostly buccally and distally inclined, while mesiobuccal and distolingual canals were mostly distally curved. Isthmuses were more common in younger patients (χ2 test, p < 0.05). The average numbers of accessory canals in the apical, middle, and coronal segments were 9.9 ± 4.2, 6.9 ± 2.9, and 9.3 ± 3.0 canals per segment, respectively (analysis of variance, p < 0.001). Age and sex were not associated with the number of accessory canals (p > 0.05).ConclusionsThe complex anatomy of these teeth deserves attention during non-surgical or surgical endodontic treatment. Around the apex, isthmuses might be more prevalent in younger and female individuals.

Numerical analysis of mechanical behavior of unidirectional thermoplastic-based carbon fiber composite for 3D-printing

The paper is dedicated to the simulation of mechanical behavior of a unidirectional thermoplastic-based composite material reinforced with carbon fibers. The influence of microstructure imperfections on mechanical characteristics of the composite material has been studied, and numerical parameters that ensure a good correlation between nonlinear two-scale simulation of progressive damage and experimental data have been identified. Results of the study revealed limited importance of accounting for such imperfections of composite microstructure as deviation in fiber laying direction and fiber curvature. The two-scale simulation approach based on submodeling technique was proved to describe the nonlinear behavior of the thermoplastic-based carbon fiber material with a reasonable accuracy.

The study of the moment of resistance of the grinder of legumes

The paper presents experimental studies of the determination of the flywheel masses and the moment of inertia along the coastline, the mechanical characteristics of the shredder are constructed depending on the abrasive roughness, the direction of curvature of the groove and the size of the gap between the disks.

Analysis on Smoke Visibility in Fire Environment from the Perspectives of Path Curvature and View Direction

Analysis on Smoke Visibility in Fire Environment from the Perspectives of Path Curvature and View Direction

Toward the Optimal Construction of a Loss Function Without Spurious Local Minima for Solving Quadratic Equations

The problem of finding a vector $\boldsymbol {x}$ which obeys a set of quadratic equations $| \boldsymbol {a}_{\text {k}}^\top \boldsymbol {x} |^{2}=\text {y}_{\text {k}}$ , $\text {k}=1,\cdots,\text {m}$ , plays an important role in many applications. In this paper we consider the case when both $\boldsymbol {x}$ and $\boldsymbol {a}_{k}$ are real-valued vectors of length n. A new loss function is constructed for this problem, which combines the smooth quadratic loss function with an activation function. Under the Gaussian measurement model, we establish that with high probability the target solution $\boldsymbol {x}$ is the only minimizer (up to a global sign) of the new loss function provided $\text {m}\gtrsim \text {n}$ . Moreover, the loss function always has a negative directional curvature around its saddle points.

Tunable Anelasticity in Amorphous Si Nanowires.

In situ bending tests of amorphous Si nanowires (a-Si NWs) found different elastic behavior depending on whether they were straight or curved to begin with. The axially straight NWs exhibit pure elastic deformation; however, the axially curved NWs exhibit obvious anelastic behavior when they are bent in the direction of original curvature. On the basis of STEM-EELS analysis, we propose that the underlying mechanism for this anelastic behavior is a bond-switching assisted redistribution of the nonuniform density (structure) in the curved NWs under the inhomogeneous stress field. This mechanism was further supported by the fact that the originally straight a-Si NWs also display similar anelasticity with the as-grown curved NWs after focused ion beam irradiation that can cause nonuniform structure distribution. As compared to what has been reported in other 1D materials, the anelasticity of a-Si NWs can be tuned by modifying their morphology, controlling the loading direction, or irradiating them via ion beam. Our findings suggest that a-Si NWs could be a promising material in the nanoscale damping systems, especially the semiconductor nanodevices.

Research on Well Trajectory Deduction Method Based on Pythagorean-Hodograph Quintic Space Curves

Considering the influence of key parameters such as bore angle, azimuth and sounding of wellbore, based on the spatial five-time PH curve with continuous unit tangent and directional curvature, no need for iteration, using Bessel polynomial interpolation method, optimization the spatial model and the curve description can accurately deduct the spatial parameters of the fifth point according to the determined four points of the space, and then establish the wellbore trajectory analytical equation to generate the well trajectory curve. Taking a directional well as an example, the wellbore trajectories of the wells from 403.9 meters to 976 meters were fitted by PH, cubic spline and linear interpolation method respectively, and compared with the real measuring points. The results show that the wells fitted by PH method, the differences of the bevel angle and the measured point, the azimuth angle and the measured point are 0.910° and 5.7°. The differences of the cubic spline and the measured point, the straight line method and the measured point are 4.240°, 5.86° and 6.54°, 9.09°. For the PH method, the trajectory inclination and azimuth differences are the smallest, which are 3.51% and 3.17%.

A Lumped-Mass Model for Large Deformation Continuum Surfaces Actuated by Continuum Robotic Arms

AbstractCurrently, flexible surfaces enabled to be actuated by robotic arms are experiencing high interest and demand for robotic applications in various areas such as healthcare, automotive, aerospace, and manufacturing. However, their design and control thus far has largely been based on “trial and error” methods requiring multiple trials and/or high levels of user specialization. Robust methods to realize flexible surfaces with the ability to deform into large curvatures therefore require a reliable, validated model that takes into account many physical and mechanical properties including elasticity, material characteristics, gravity, external forces, and thickness shear effects. The derivation of such a model would then enable the further development of predictive-based control methods for flexible robotic surfaces. This paper presents a lumped-mass model for flexible surfaces undergoing large deformation due to actuation by continuum robotic arms. The resulting model includes mechanical and physical properties for both the surface and actuation elements to predict deformation in multiple curvature directions and actuation configurations. The model is validated against an experimental system where measured displacements between the experimental and modeling results showed considerable agreement with a mean error magnitude of about 1% of the length of the surface at the final deformed shapes.

Induction of membrane curvature by proteins involved in Golgi trafficking.

The Golgi apparatus serves a key role in processing and sorting lipids and proteins for delivery to their final cellular destinations. Vesicle exit from the Golgi initiates with directional deformation of the lipid bilayer to produce a bulge. Several mechanisms have been described by which lipids and proteins can induce directional membrane curvature to promote vesicle budding. Here we review some of the mechanisms implicated in inducing membrane curvature at the Golgi to promote vesicular trafficking to various cellular destinations.

Coronal root canal morphology of permanent two-rooted mandibular first molars with novel 3D measurements.

To measure the coronal root canal morphology of permanent mandibular first molars using 3D coordinates for more precise conservative endodontic cavity preparation. In total, 57 cone beam computed tomography (CBCT) images of sound mandibular molars with fully formed apices without previous endodontic treatment were taken from 33 patients aged 16 to 75years. The CBCT machine (MCT-1[EX-2F], J. Morita Manufacturing Corp, Kyoto, Japan) provided 14-bit greyscale images with the voxel size of 0.125mm. All images were taken at 80 kV and 5.0 mA, with a 17-s exposure time, which were then reconstructed in 3D models and viewed by an endodontist. The gender of the patients and the tooth position, and number of root canals, were recorded. The landmarks of coronal root canals were determined, then the distribution of landmarks, maximum curvature in the axial direction and curvature directions in the horizontal direction of coronal root canals were measured. Distributions of landmarks were analysed using a spatial statistics method. Data about curvature were compared using a t test. Overall, the distribution of root canal orifices and the centre of the canal primary curve were more centralized than other landmarks. The landmarks were located more mesiobuccally to the centre of the occlusal plane of mandibular first molars. Specifically, the measurements of the maximum curvature of coronal root canals in the axial direction were as follows: in 3-canal teeth, the average angles of curvatures were 22°,23°,15° for mesiobuccal (MB), mesiolingual (ML) and distobuccal (DB) canals, respectively; in 4-canal teeth, the average angles of curvatures were 24°,26°,15°,22°for MB, ML, DB and distolingual (DL) canals, respectively. The degrees of coronal root canal curvatures in the horizontal direction were as follows: in 3-canal teeth, the average angles of curvatures were -8°,47°,-2° for MB, ML and DB canals, respectively; in 4-canals teeth, the average angles were -11°,50°,-28°,45° for MB, ML, DB and DL canals, respectively. Statistically, there was no reliable side or sex difference in any of the measurements (P>0.05). In permanent two-rooted mandibular first molars, the coronal canals clustered in the direction of the mesiobuccal side of the occlusal surface of the teeth.

Parabolicity, Brownian Exit Time and Properness of Solitons of the Direct and Inverse Mean Curvature Flow

We study some potential theoretic properties of homothetic solitons $$\Sigma ^n$$ of the MCF and the IMCF. Using the analysis of the extrinsic distance function defined on these submanifolds in $$\mathbb {R}^{n+m}$$ , we observe similarities and differences in the geometry of solitons in both flows. In particular, we show that parabolic MCF-solitons $$\Sigma ^n$$ with $$n>2$$ are self-shrinkers and that parabolic IMCF-solitons of any dimension are self-expanders. We have studied too the geometric behavior of parabolic MCF and IMCF-solitons confined in a ball, the behavior of the mean exit time function for the Brownian motion defined on $$\Sigma $$ as well as a classification of properly immersed MCF-self-shrinkers with bounded second fundamental form, following the lines of Cao and Li (Calc Var 46:879–889, 2013).

Directional Signatures of Surface Texture

Surface texture affects adhesion, friction and wear. A key component in the studies of these effects is a multiscale and directional characterization of surfaces. However, this task is beyond the ability of standard methods currently used. Methods based on fractal geometry, quantifying the surface topography at individual scales and directions, have been developed to overcome this problem. In this study, we propose a unified approach for surface texture analysis comprising three steps: directional surface representation, directional surface dimension and computer implementation. To address longstanding issues of texture analysis of surfaces with directionality and studies of surface texture effects on contact behaviour of rough surfaces, a directional blanket curvature covering method was used. Peak curvature signatures (sets of peak dimensions) were calculated. Higher value of peak dimension represents higher peak curvature complexity. Isotropic (sandblasted) and anisotropic (abraded) titanium alloy (Ti–6Al–4V) surface images were generated. Statistically significant differences in peak dimension were found between isotropic and anisotropic surfaces at scales of 15 μm and 20 μm. Contact areas and pressures were calculated between rigid flat plates pressed against Ti–6Al–4V rough surfaces. For low loads at a scale of 15 μm, contact areas decreased with dimension, while at scale of 25 μm they decreased and then increased. Changes in contact pressures exhibited trends opposite to the areas. For high loads, there are virtually no changes. Results showed that the curvature covering method detects minute differences in surface anisotropy and allows for detailed study of contact behaviour.

Development on a Prediction Model for Experimental Condition of Flexibly Reconfigurable Roll Forming Process

Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology by which sheet metal is shaped into a desired curvature using reconfigurable rollers and gaps. FRRF is conducive to producing multi-curvature surfaces by controlling the longitudinal strain distribution. However, it is difficult to predict the forming results since FRRF technology forms a secondary surface from the primary curvature. This study investigates the use of regression analysis as a basis for a model that can predict the longitudinal curvature of sheet metal. The following variables were considered as input parameters: Maximum compression value, radius of curvature in the transverse direction, and initial blank width. Regression model samples are obtained by performing experiments using FRRF equipment whilst the experimental design was generated by a three-level, three-factor full factorial design. The experimental surfaces are of a convex and of a saddle-type shape, with a total sample size of 54. Through regression analysis it has been shown that the longitudinal curvature can be expressed by means of a quadratic equation. The matching quadratic function was verified with R-squared values and root-mean-square errors, whilst the normality of the sample data was also verified. To apply the model to the actual forming process, the regression model was converted to deduce the compression characteristics for forming the target surface. Throughout the study, the proposed analytical procedure was validated, and a statistical formula for estimating the longitudinal curvature produced by the FRRF apparatus established.

Experimental Investigation of High Strength Precast Reinforced Concrete Walls used (Vierendeel Truss Form)

This paper presents an experimental investigation to study the behavior of Vierendeel Truss used instead of bearing wall in precast construction. The experimental program contains casting and testing (8) R.C wall panels specimens with opening with right angle corner, the dimension of the opening (300*350*75) mm which it is length, width, and thickness. The dimension of the R.C wall panel specimens was (1000*750*75) mm which they are length, width and thickness, respectively and all the specimens contain cantilever portion (100*60*75) mm length width and thickness respectively. In this study the main variable is the type of concrete and the compressive strength. The wall panel specimens were tested with uniformly distributed load with an eccentricity of (67.5) mm. The specimens were simply supported to represent the supports of the truss. The wall panels were divided into (2) groups, the first group is reactive powder concrete with (4) specimens and the second group is high strength self-compacted concrete with (4) specimens. The failure load, load – deflection curves crack pattern was studied. All the panels were deflected in single curvature in the vertical direction of loading. Opening causes concentrated stress at the corners of opening and initiated the cracks and failure.

Finite element simulation and experimental investigations of cold stamping forming defect of A588-A thick weathering steel bogie lower cover

In order to improve the stamping accuracy of the bogie cover plate of the rail vehicles. The cold stamping forming process of A588-A thick weathering steel plate with variable initial bending size (“H”) produced by the pre-straightening process was investigated by numerical simulation and experiment. The effects of “H”, curvature direction of the plate, and small curved fillets radius on the forming quality of the thick steel plate were analyzed. The results demonstrated that there are defects, such as serious springback, distortion of stamping fillet, and low profile accuracy. We propose some corresponding defect control methods. The larger initial bending size “H”, the higher springback value occurred. By applying 1.2–1.4 times springback compensation to the die geometry, the springback was reduced and the contour accuracy was enhanced exponentially. By replacing the original die fillet material with C12MoV and reducing the die clearance, the cross-section distortion of the stamping fillets due to bad die fittingness could be eliminated. The accuracy of the component can also be improved by controlling the curvature direction of the plate. The cold stamping test was carried out by using the best process parameters and defect control methods. The results show that the control methods are extremely effective.