Tension Fracture Research Articles

Experimental study on compressive behavior and failure characteristics of imitation steel fiber concrete under uniaxial load

The concrete columns suffer from spalling and flaking in the room and pillar mining method, which affects service performance. The energy absorption and deformation failure laws of fiber concrete structures under compression load need further study. In this study, four types of imitation steel fiber concrete specimens were prepared, and uniaxial compression experiments were carried out. Simultaneous photographic and acoustic emission monitoring was conducted to investigate the compression energy absorption, crack evolution, fracture surface fractal and RA/AF value characteristics of fiber concrete. The results obtained in the present work are as follows. Imitation steel fiber concrete showed the best compressive and energy absorption performance with a 0.4–0.6% fiber/mortar mass ratio. A higher dosage of fibers prolonged the yield time but also led to earlier macroscopic cracking. The bond between imitation steel fiber and matrix can disperse the stress, which significantly improved the toughness of concrete. For every 0.2% increase in fiber content, the pre-peak toughness index CTI and post-peak damage absorption energy FCEC increased by about 10% and 50%, respectively. Both plain concrete and fiber concrete specimens developed macroscopic cracks under local tensile stresses. The proportion of shear fracture in plain concrete reached 80.1% and dominated during the secondary crack development. The proportion of tension and shear fracture in fiber concrete was less disparate and showed a mixed pattern with synergistic action. The proportion of shear fractures gradually increased with the increase in fiber content. The calculated results of the RA/AF method corresponded well with the crack morphology. With the increase in fiber content, the bridging effect of fiber became more obvious, and the ability of specimens to resist cracking improved significantly. The fractal characteristics of the fracture surface of each specimen were investigated. The plain concrete specimens had a relatively complete surface when destroyed, and their fractal dimension was only 1.62, the lowest among all the specimens. The surface of fiber concrete was more fragmented, and their fractal dimension was higher, with the fractal dimension D increasing by 0.2–0.4 for each 0.2% increase in fiber content. This study can provide a reference for the fiber concrete pillar designs.

Comparison of high-frequency components in acoustic emissions from rock fracture under Mode Ⅰ and Mode Ⅱ dominated loading

High-frequency components in acoustic emission (AE) or seismic radiation attract much attention as they are directly related to the fracture process. One of the main issues in our knowledge of high-frequency radiation is a lack of definition on the relationship between high-frequency content and source mechanisms. In this study, high-frequency emission waves due to rock fracture in tension and shear are studied experimentally and theoretically. An improved AE-signal processing method, focusing on direct-arrived waves, is proposed to pinpoint the exact high-frequency radiation in a rupture event. Current data support that for each individual AE signal the later arriving waves contain lots of low-frequency components, while the high-frequency components are mostly carried by the direct arrivals. In comparison with tensile cracks, shear cracking generates more high-frequency components and tends to radiate energy in the form of waves with larger RA values (designated as rise time/amplitude). Combining the theories from dynamic fracture and acoustic radiation, the difference in high-frequency energy release from shear and tensile cracking can be attributed to the rate of stress drop at the tips. The present findings provide a framework for a new way to identify the tensile failure in rock. It will be helpful in solving the difficulty tracking seismic or micro-seismic events from tensile sources associated with karst collapsing, hydraulic fracturing and roof falling in mines.

Experimental and Numerical Fracture Characterization of DP1180 Steel in Combined Simple Shear and Uniaxial Tension

Current tests for plane stress characterization of fracture in automotive sheet metals include simple shear, uniaxial, plane strain, and biaxial tension, but there is a significant gap between shear and uniaxial tension. Presently, it remains uncertain whether the fracture strain experiences a reduction between simple shear and uniaxial tension or undergoes an exponential increase as the triaxiality decreases. Fracture in combined simple shear and tension is complicated by premature edge cracking in tension along with a strong sensitivity of fracture strain to the measurement lengthscale. To address these issues, several existing simple shear geometries were modified and evaluated, with a focus on obtaining approximately linear strain paths corresponding to combined uniaxial tension and simple shear suitable for experimental fracture characterization using digital image correlation (DIC). An experimental and numerical investigation was conducted using two planar geometries that do not require through-thickness machining and can be easily tested on a universal test frame. Finite-element analysis was used to investigate the influence of the notch eccentricity on the stress state and predicted fracture location. The most promising geometry in each coupon type was then selected and tested for a dual-phase advanced high-strength steel, DP1180. The performance of the two planar geometries was evaluated based on the linearity of strain and stress state, along with the location of fracture initiation. The best geometry was then used to evaluate and recalibrate the modified Mohr-Coulomb (MMC) fracture locus with data in combined shear and tension. The initial MMC calibration using four fracture tests that suppressed necking provided an accurate estimate for the fracture strain in combined uniaxial tension and simple shear. The MMC model correctly predicted a valley in the fracture strain between these two loading conditions.

Evaluation of orthotropic elasticity of gradient-structured bamboo by microtensile testing combined with digital image correlation technique

Bamboo, a biomaterial with a unique gradient structure, possesses exceptional mechanical properties. The gradient structure impacts the mechanical properties of bamboo in the longitudinal (L), radial (R) and tangential (T) directions. To investigate the elasticity associated with gradient structure, we derived the orthotropic elastic constants: Young’s modulus (E), Poisson’s ratio (ν) and shear modulus (G) at different radial positions (outer, central and inner) through micro-tensile testing and the digital image correlation (DIC) technique. Our results revealed that the Young’s modulus of bamboo exhibited a characteristic orthotropic behavior irrespective of radial position. The ratio of E in the L, T and R directions (EL:ET:ER) was 6.05:1.08:1, 5.12:1.17:1 and 8.02:1.58:1, respectively at the outer, central and inner positions. With increasing fiber fraction, ν (except νRT) demonstrated an upward trend. Under main axis tension, fiber pull-out and brittle fracture were the main failure modes, whereas off-axis tension exposed the vulnerable interface between fibers and parenchyma cells. The enhancement effect of the gradient structure in the L and T directions was more prominent, resulting in a consistent deformation pattern from the inner to outer positions. However, strain localization was found when tensioning through the R direction. Leveraging the derived orthotropic elastic constants, we visualized the three-dimensional elastic behavior of bamboo by body deformation. Bamboo at the outer position exhibited quasi-isotropic behavior in the RT plane due to the high fiber fraction. This study provides critical experimental evidence for the orthotropic behavior of bamboo at different radial positions and valuable data for mechanical modeling and practical applications involving bamboo.

A SVM-based method for identifying fracture modes of rock using WVD spectrogram features of AE signals

In order to achieve the highly efficient and accurate identification of fracture modes including tension or shear fractures during rock failure, an intelligent identification method based on Wigner-Ville distribution (WVD) spectrogram features of acoustic emission (AE) signals was proposed. This method was mainly constructed by the following steps: Firstly, AE hits corre-sponding to tension and shear fractures were obtained through conducting the Brazilian disc test (tension fracture) and direct shear test (shear fracture) of limestone. Secondly, the WVD spectro-grams of these tensile-type and shear-type AE hits were respectively extracted and then trans-formed into the image features of relatively low-dimension as the sample set based on the gray-level cooccurrence matrix (GLCM) and histogram of oriented gradient (HOG). Finally, on the basis of the processed and classified sample set of the WVD spectrogram features, an identifica-tion model of rock fracture modes was established by a support vector machine (SVM) learning algorithm. To verify this method, the fracture modes of limestone subjected to biaxial compres-sion were identified by the method. The results showed that the method not only can greatly re-veal the fracture modes change from tension-dominated to shear-dominated fractures, but also has advantages over the RA-AF value method, such as applicability, accuracy and practicality.

Bio-inspired, metal additive manufacturing interlocked structures: Geometrically design and fracture performance analysis

Suture-inspired interlocked interfaces in nature exhibit promising industrial applications potentials in advanced mechanical structures, devices and equipment. In this paper, the parametric design of interlocked interfaces is performed, and selective laser melting (SLM) additive manufacturing tensile specimens and compact tension (CT) fracture specimens with sutured interfaces are harvested, where AlSi10Mg raw materials are used as constituent materials. Afterwards, compact tension tensile fracture experiments and corresponding finite element simulations were performed and compared, where force-displacement curves for different interface structural geometrical parameters were harvested. The mechanical properties and failure modes of the interlocked interface structures were analyzed through experiments and simulations verification. Crack-tip opening displacement (CTOD) and fracture energy criteria were used to evaluate the fracture toughness of the interlocked specimen interfaces. In addition, parametric analysis was carried out to investigate the influence of different interlocked structural parameters on the interface mechanical performances and failure features. Accordingly, it can be concluded that the interface strength, toughness, and failure mechanisms can be rationally tuned through given geometrical parameters of the re-entrant interface microstructures.

Synthesis and characterization of bulk mechanical properties of a bio-based resin filled by graphene nanoplatelets and cellulose nanocrystals

In the present paper, a novel bio-based resin derived from epichlorohydrin was reinforced by Graphene NanoPlatelets (GNPs) and Cellulose NanoCrystals (CNCs) in different weight ratios and characterized experimentally through tension tests and fracture toughness tests on bulk specimens. The nanofillers were applied separately. The experimental results showed that the neat resin has a Young’s modulus of 3.29 GPa, a tensile strength of 45.15 MPa, a stress intensity factor of 0.61 MPa m1/2 and a critical strain energy release rate of 0.091 kJ/m2. The level of the properties reveal that the bio-based adhesive can be used for cosmetic and for some structural applications. The addition of cellulose nanocrystals in the epoxy resin didn’t improve the mechanical properties of the neat resin mainly due to the development of intense aggregation of cellulose nanocrystals. On the other hand, the addition of graphene has led to the increase of the Young’s modulus and the fracture toughness and to the decrease of the tension strength of the resin. Development of agglomerations of graphene were also present in this case. The contradictory findings on the mechanical properties of the reinforced resin gives a clear message about the need for optimizing the manufacturing process. Both nanocomposites have undergone a complete life-cycle analysis which has shown that they are far more environmentally friendly than a conventional epoxy resin.

Microstructure evolution, mechanical properties, and strengthening mechanisms of 6061 aluminum alloy processed via corrugated constrained groove pressing

In this study, a corrugated constrained groove pressing (CCGP) technology based on a semicircle groove was proposed, improving the uniformity of strain accumulation in deformed metal sheets through staggered groove pressing. First, 6061-O aluminum alloy was processed at room temperature via conventional CCGP (Conv-CCGP) and 90° cross CCGP (Cross-CCGP). The effects of strain route and deformation pass on the microstructure evolution of the CCGPed alloy were investigated and correlated with mechanical properties. Changes in the mechanical properties of the CCGPed alloy at room temperature measured via tensile in different directions and hardness tests were studied. Results showed that the strength and hardness of the CCGPed sheet in both routes were considerably improved, but ductility was decreased. Cross-CCGP can effectively alleviate the anisotropy of the deformed sheet and achieve optimal strength in roll direction (RD) and transverse direction (TD) at two passes. Yield strength (YS) and ultimate tensile strength (UTS) along RD were increased by 190.2% and 15.5% relative to the initial alloy, reaching 119 MPa and 134 MPa, respectively. Along TD, YS and UTS were increased by 255.0% and 36.0%, reaching 142 MPa and 151 MPa, respectively. Characterization techniques, including electron backscatter diffraction and high-resolution transmission electron microscopy, were used to establish comprehensive models of dynamic recovery-based substructure evolution and dynamic recrystallization-dominated grain refinement. Meanwhile, the integrated microstructural changes and theoretical calculations identified dislocation strengthening and local grain refinement as the major contributors to the strengthening of the CCGPed alloy. In addition, tensile fracture surface analysis showed that the CCGPed alloy still underwent plastic fracture, but the fracture mode shifted from tension fracture into shear fracture.

Thermal Effects on Tension Softening Response and Fracture Characteristics of Quartz-Diorite

Thermal Effects on Tension Softening Response and Fracture Characteristics of Quartz-Diorite

Perturbations in fatty acid metabolism and collagen production infer pathogenicity of a novel MBTPS2 variant in Osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a heritable and chronically debilitating skeletal dysplasia. Patients with OI typically present with reduced bone mass, tendency for recurrent fractures, short stature and bowing deformities of the long bones. Mutations causative of OI have been identified in over 20 genes involved in collagen folding, posttranslational modification and processing, and in bone mineralization and osteoblast development. In 2016, we described the first X-linked recessive form of OI caused by MBTPS2 missense variants in patients with moderate to severe phenotypes. MBTPS2 encodes site-2 protease, a Golgi transmembrane protein that activates membrane-tethered transcription factors. These transcription factors regulate genes involved in lipid metabolism, bone and cartilage development, and ER stress response. The interpretation of genetic variants in MBTPS2 is complicated by the gene's pleiotropic properties; MBTPS2 variants can also cause the dermatological conditions Ichthyosis Follicularis, Atrichia and Photophobia (IFAP), Keratosis Follicularis Spinulosa Decalvans (KFSD) and Olmsted syndrome (OS) without skeletal abnormalities typical of OI. Using control and patient-derived fibroblasts, we previously identified gene expression signatures that distinguish MBTPS2-OI from MBTPS2-IFAP/KFSD and observed stronger suppression of genes involved in fatty acid metabolism in MBTPS2-OI than in MBTPS2-IFAP/KFSD; this was coupled with alterations in the relative abundance of fatty acids in MBTPS2-OI. Furthermore, we observed a reduction in collagen deposition in the extracellular matrix by MBTPS2-OI fibroblasts. Here, we extrapolate our observations in the molecular signature unique to MBTPS2-OI to infer the pathogenicity of a novel MBTPS2 c.516A>C (p.Glu172Asp) variant of unknown significance in a male proband. The pregnancy was terminated at gestational week 21 after ultrasound scans showed bowing of femurs and tibiae and shortening of long bones particularly of the lower extremity; these were further confirmed by autopsy. By performing transcriptional analyses, gas chromatography-tandem mass spectrometry-based quantification of fatty acids and immunocytochemistry on fibroblasts derived from the umbilical cord of the proband, we observed perturbations in fatty acid metabolism and collagen production similar to what we previously described in MBTPS2-OI. These findings support pathogenicity of the MBTPS2 variant p.Glu172Asp as OI-causative and highlights the value of extrapolating molecular signatures identified in multiomics studies to characterize novel genetic variants.

Mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene propellant under confining pressure

AbstractTo better understand the mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene (HTPB) propellant under various confining pressures, the uniaxial tension tests with low to medium strain rate and various confining pressures were carried out. The coupling effects of strain rate and confining pressure on mechanical properties were presented. Meanwhile, the confining pressure influence mechanism was analyzed and revealed using the meso numerical simulation method and scanning electron microscopy images of fracture surfaces. The meso damage evolution processes under various confining pressures were presented. The results show that strain rate and confining pressure affect mechanical responses of HTPB propellant significantly. As confining pressure increases, the maximum tension strength and fracture strength increase. The maximum tension strain and failure strain vary slightly with confining pressure under low strain rate, while they increase significantly with confining pressure at medium strain rate. The fracture energy density increases with the increase of strain rate and confining pressure. Meanwhile, the value of saturation pressure depends on strain rate. The confining pressure influence mechanism is to suppress dewetting damage initiation and evolution. Besides, the failure mode of HTPB propellant under different confining pressures is still particles dewetting.

Uniaxial compression deformation and fracture mechanism of cold metal transfer (CMT) arc additive Mg–Gd–Y–Zn–Zr alloy

Mg–Gd–Y–Zn–Zr alloy were fabricated using the cold metal transfer (CMT) arc additive technology. The deformation mechanism and fracture characteristics of the Mg–Gd–Y–Zn–Zr alloy under uniaxial compression were studied by numerical simulation and experiment. The results revealed that the unique delamination and solidification characteristics of CMT and the Marangoni effect of the molten pool promoted the continuous distribution of β-Mg24(Gd, Y)5, at the grain boundary of the α-Mg matrix. Compared with the longitudinal section, the cross section had a uniform grain size distribution, and more dense and regular dimples were formed after the fracture. The Vickers hardness of the cross section was higher than that of the longitudinal section before and after compression. The compressive strength of the cross section was 426.12 MPa, and the fracture elongation was 20.25%, which was 10.14% higher than that of the longitudinal section. This was attributed to the equiaxed and eutectic structure with the uniform cross-section distribution. β-Mg24 (Gd, Y)5 played a better role in fine grain strengthening and precipitation strengthening than the irregularly distributed longitudinal section. The prediction of the fracture tendency of the Mg–Gd–Y–Zn–Zr alloy by using the finite element method was in agreement with the experimental results of uniaxial compression. The concentration of stress and strain at the shear site was the direct cause of fracture. Further, the obvious ‘cleavage step'and ‘tongue-like patterns'existed in the fracture morphology, which proved that the Mg–Gd–Y–Zn–Zr alloy formed by CMT had certain brittleness, and the fracture type was transgranular fracture.

Microstructure, properties and fracture failure mechanism of MAG welded joints of four types of stainless steels

In this study, four types of austenitic stainless steels (SUS 301L, SUS 304, SUS 316L and SUS 321) with different chemical compositions were butt welded by using MAG (metal active gas) welding. Unique information was gained by studying the solidification mode, microstructure and mechanical properties of the four welded joints under the same welding process, and their fracture mechanisms were analyzed from the perspective of crystallography. The results indicate that the microstructure of the four austenitic stainless steel base metals is uniformly sized equiaxed austenite with δ-ferrite distributed inside or at the boundary of austenite grains in 301L and 304 base metals. The welds of the four kinds of stainless steels are solidified in Austenitic-Ferrite (AF) solidification mode, and the final microstructures of the 301L, 304 and 316L weld are equiaxed grains while the 321 stainless steel weld grows into a dendritic structure due to its low temperature gradient. The microstructures of the fusion zone (FZ)/fine equiaxed zone (FQZ) and heat affected zone (HAZ) of the four types of stainless steels are closely related with the solidification mode of FZ, i.e. small FZ and HAZ regions result from Ferrite (F) solidification mode present in the 301L and 321 welded joints. However, larger FQZ regions generate in the 304 and 316L welded joints due to the Ferrite-Austenitic (FA) solidification mode. The 304 and 316L stainless steel tend to fracture at the HAZ positions due to the formation of FQZ; large angle grain boundary formed at the weld of 301L stainless steel is the reason for its fracture, and the good anisotropy of the weld and heat affected zone of 321 stainless steel also makes it easier to fracture in the base metal (BM). The section hardness distribution characteristics of the four stainless steels welded joints also verify their fracture tendency.

A biocultural study of nasal fracture, violence, and gender using 19th–20th century skeletal remains from Portugal

AbstractNasal fracture is usually described as the most common type of fracture of the facial bones, either alone or associated with other fractures. This work aims to study the nasal fracture among Portuguese individuals from the 19th and 20th centuries. The focus is on patterning in trauma in relation to gender and in the attempt to distinguish violent from accidental injury. The sample comprises 2023 (52.6% males, 47.4% females) individuals from three Portuguese identified skeletal collections who were born between 1804 and 1951 and died between 1895 and 1969. Age at death ranges between 1 and 109 years old. Nasal and other facial fractures were studied, and violent versus accidental trauma were distinguished following Magalhães et al. (2020). Nasal fracture was more frequent in males (10.4%, 101/969) than in females (5.9%, 47/800). This was true both for fracture inferred due to violence (laterally deviated fracture) and due to accident. Sixty‐one point five percent (91/148) of the individuals show a lateral impact force deviation. Comminutions correspond to 18.4% (26/141) of the total, and 12.8% (19/148) have other facial fractures. There is no association between nasal fracture and risk of death for both sexes, but the males seem to show a higher tendency for nasal fracture earlier in life than the females. The differences of nasal fracture between sexes are in accordance with the historical data showing that men had more social and cultural opportunities to engage in violent encounters. Although the percentage in women is lower, the majority of laterally deviated noses and isolated, non‐comminuted nasal fractures in both sexes show that interpersonal violence may have played an important role in the results.

Emplacement and accumulation of magmatic products in contractional structures: How does it occur? Insights from Central Andes of northern Chile

Structural and stratigraphic data demonstrate that the magmatism in northern Chile was accompanied by shortening related to the development of fold and thrust belts. However, how magmatic products were emplaced and accumulated in the contractional structures is an unresolved question. We, therefore, integrated field and seismic data from the regions of the Pampa del Tamarugal, Salar de Punta Negra Basin, and the Hornitos Fold and Thrust Belt to determine the main structures that facilitated the magma accumulation. The syn-kinematic granitic intrusions in the Hornitos Fold and Thrust Belt were preferably emplaced along fold-related thrusts. In this region, magma migrated along thrust ramps and finally accumulated into the core of the anticlines and broken synclines. Subsidiary and vertical tensional fractures controlled the magma accumulation in the hinge zone and at the axis of the folds. The seismic data from the Pampa del Tamarugal and Salar de Punta Negra Basin present evidence of buried volcanoes on inversion anticlines. During the tectonic inversion of the pre-existing Late Paleozoic to Mesozoic half-graben structures in the regions, magma migrated along the master faults and finally accumulated into the core of the inversion anticlines as sills or was expulsed to the surface as volcanoes, as evidenced by the Punta Negra Monogenetic Volcano.

Microstructure and properties of low alloy CrMo steel processed with varied isothermal temperatures

The microstructure and properties of low alloy CrMo steel after isothermal treatment at different temperatures were studied. The experiment process is to rapidly cool the samples that have been held at 940 ℃ for 2 h to a salt bath furnace at different temperatures (300–500 ℃) for isothermal treatment, and then air cooling to ambient temperature. The microstructure after isothermal treatment is granular bainite, which is a mixed microstructure composed of bainitic ferrite (BF) and martensite/austenite (M/A) island. The morphology, size and volume fraction of M/A islands change with the change of isothermal temperature. The mechanical properties are also closely related to isothermal temperature. With the increase of isothermal temperature, the impact toughness and yield strength (YS) decreased. By studying the effects of different strengthening mechanisms and multiphase on YS, the results show that YS mainly depends on BF. According to the SEM and EBSD characterization of the fracture, it is found that the stress in the sample is mainly concentrated near the M/A, which makes the crack easy to initiate on the M/A island or its interface. The brittle fracture tendency of materials is related to M/A island. The larger the size of the M/A island, the more likely brittle fracture will occur and the less ductile it will be.

Development and experimental verification for the coaxially formed self-centering buckling-restrained brace

The development for a new construction of self-centering buckling restrained braces (SCBRBs) was made by letting either an assembled steel BRB part or an integrally formed composite BRB part coaxially pass through an outer self-centering (SC) part with steel disc springs, and tests on the SCBRBs were conducted to validate the seismic performance and the configurations, mainly including the pattern of BRBs and that of pull rods in SC parts to keep the initial stiffness under two loading sides as close as possible. Tests show that, contrary to BRBs, the SCBRBs presenting flag-shape hysteretic curves have a significant reduction of residual drifts. Variation laws show that the residual drifts of the SCBRBs at horizontal drift levels of 2% are almost within 0.5% if self-centering ratios exceed 0.66. Besides, when the ratios under drift levels of 2% are close to 1.0, the residual drifts are approximately within the start displacements of the specimen with a SC part only. For the four SCBRBs adopting the same SC part within the drifts from 2% to 3.5%, approximately 56–73% axial strength and about 13–21% energy dissipation are from the SC part. Both types of BRB parts work stably. Except for tension fracture of plate braces, other members remain intact in SCBRBs, facilitating replacement of plate brace and reuse of intact SC part. Moreover, the interaction between two tubes in the SC part provides additional energy dissipation and horizontal resistance. Both tests and theoretical predictions reveal that the adjustment of pull rods in the SC part can adjust its initial stiffness in tension, and the pattern of employing two groups of six rods applying tension forces by two stages is preferred to decrease the difference between the initial stiffness in tension and that in compression.

The characteristics of gas-liquid dispersive mixing and microbubble generation in turbulent adjustable jet flow field

In this study, the gas-liquid two-phase mixing process and the microbubbles formation process in a jet flow field has been investigated by using a self-designed on-line measurement system for measuring bubble generation characteristics and the Volume of Fluid (VOF) model in numerical simulation methods for analyzing flow field distribution characteristics. The effect of turbulence intensity on the dynamic size distribution of microbubble has been considered. The characteristics and duration of the three stages during the bubble breaking process, namely, surface oscillation stage, surface tension stage and fracture stage, were analyzed. The results show that the increase of turbulence intensity in jet flow will further promote the imbalance between the external deformation force and the surface tension resisting the deformation of the bubble, and promote the breaking probability of bubble. However, when the bubble breaks to a sufficiently small size, the surface tension against bubble deformation will increase sharply, the surface free energy needed to overcome for bubble breakage is very large, and the breakage probability of bubble will significantly decrease. Compared with the breaking process of bubbles, the increase in turbulence intensity will greatly promote the bubble coalescence process, which will ultimately become the main reason for affecting the bubble size distribution. Moreover, the influence of flow field distribution characteristics on bubble size distribution and average bubble size change is analyzed by using Population Balance Model.

Fracture failure analysis of insulation with initial crack defect for stator end-winding in induction motor by using magnetic-structural coupling model

The insulation mechanic failure in stator end-winding of induction motor is usually an early and serious cause to weaken the residual breakdown electrical field strength and produce the short-circuit fault, especially subjecting to the combination of dynamical electromagnetic forces, mechanical stress and vibration. In this paper, the fracturebehavior of insulation layer with considering the initial crack defects and end-hoop support failures in end-windings were analyzed by using magnetic-structural coupling model and finite element method (FEM). Firstly, the distributions of magnetic flux density and electromagnetic force around the stator end region were determined by injecting three-phase alternating current. Secondly, the dynamic characteristics of deformation, stress and strain in winding insulation were respectively calculated by coupling the transient electromagnetic and structural analysis. Furthermore, the weak points of the concentrated stress and strain were located. Thirdly, the crack model mounted in winding insulation is defined and simulated by employing three-dimensional (3-D) semi-elliptical crack element. To evaluate the fracture mechanism and the degree of crack expansion quantitatively, the stress intensity factor (SIF) was introduced. Finally, the influence of crack location, direction, depth and end-hoop support failure on SIF and crack propagation were investigated. Results show that the concentrated stress at knuckle part of the coil insulation is lager quite larger than that of other parts. The SIF of transverse crack is larger than that of longitudinal cracks. The larger the initial crack depth in the stator end-winding insulation, the more serious the tendency and degree of crack fracture. Local end-hoop support failure also has an important influence on the crack propagation. Results in this study may contribute to the understanding of fracturefailure behaviors in insulation under dynamical electromagnetic vibration and provide necessary theoretical reference for fault diagnosis and prediction of stator winding in induction motors.

Ediacaran‐Ordovician Magmatism and REE Mineralization in the Wet Mountains, Colorado, USA: Implications for Failed Continental Rifting

AbstractStructures associated with Ediacaran‐Ordovician alkaline magmatism and the timing of rare earth element (REE) mineralization in the Wet Mountains, CO, were analyzed using field, geophysical, and U‐Th‐Pb isotope methods to interpret their tectonic setting in the context of previously proposed rift models. The Wet Mountains are known for thorium and REE mineralization associated with failed rift‐related, Ediacaran‐Ordovician alkaline intrusions and veins. Structural field data indicate that alkaline dikes and mineralized veins are controlled by a system of northwest‐striking, high‐angle faults and tension fractures formed in a 040°‐directed extensional regime. Magnetic and surface expressions of Democrat Creek and McClure Mountain complexes show tectonic elongation toward ∼045°, consistent with NE‐directed extension. Magnetic data also suggest the existence of a fourth, previously unrecognized mafic‐ultramafic complex of inferred Cambrian age with a similar elongated orientation. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) 208Pb/232Th analysis of low‐uranium zircon from carbonatite dikes and in situ 206Pb/238U LA‐ICP‐MS analysis of monazite in mineralized dikes yielded 465 ± 18 Ma and 489 ± 33 Ma ages, respectively. These ages are consistent with the expected age based on slightly older, cross‐cut syenite dikes and the hypothesized Ordovician end to failed rift‐related magmatism. The Ediacaran‐Ordovician age of alkaline magmatic rocks and the associated northeast‐directed extension direction are similar to those of the along‐strike, Ediacaran‐Cambrian Southern Oklahoma Aulacogen. Therefore, the failed rift system in the Wet Mountains is interpreted to be a northwestern continuation of the Southern Oklahoma Aulacogen with carbonatite magmatism and thorium/REE mineralization representing late intrusive phases.