Local Breakage Research Articles

Study on multi-state of meshing-impacting dynamic characteristics of spur gear systems considering friction under localized tooth breakage

Localized tooth breakage is one of the common failures of spur gears, which affects the smooth and safe operation of spur gear transmission systems. The tooth collision cannot be neglected, and it is especially important to reveal the meshing-impacting dynamic characteristics of the gear system under localized tooth breakage to improve the safe and stable operation of the gear system. Based on the gear meshing principle and the dissipative collision contact force model, the drive-side tooth meshing model and back-side tooth impacting model are established with considering the transient nature of tooth back-side contact. The tooth surface meshing model and tooth back collision model under partial breakage are established. According to the contact state and force environment of the gear pair, the multi-state meshing-impacting behaviour under local breakage is classified, and the discrete meshing-impact dynamics model of an involute spur gear system under local breakage is established to explore the influence of local breakage on the meshing stiffness and load distribution. The mechanism of contact force under partial tooth breakage is revealed, and the influence of load coefficient and meshing frequency on the nonlinear dynamics is studied by defining two Poincaré maps. It is found that local tooth breakage affects the contact force of single-and double-tooth meshes and reduces gear load carrying capacity. Larger loads inhibit back-side impact, and smaller loads induce the coexistence behaviour and back-side impact. Larger or smaller meshing frequency induce back-side impact behaviour. The coexistence of chaotic and periodic motions induces back-side impact behaviour, and localized tooth breakage affects the coexistence phenomenon and aggravates the complexity of the dynamic behaviour. The dynamic model of gear system considering energy dissipation and nonlinear vibration under the presence of local tooth breakage of the pinion is explored, and the conditions of back-side impact are studied. This research provides new methods and ideas for nonlinear dynamic modelling and analysis of faulty gear systems.

A rate-dependent constitutive model for saturated frozen soil considering local breakage mechanism

A rate-dependent constitutive model for saturated frozen soil is vital in frozen soil mechanics, especially when simultaneously describing the nonlinearity, dilatancy and strain-softening characteristics. The distribution of the non-uniform strain rate of saturated frozen soil at the meso-scale due to the local ice-cementation breakage is described by a newly binary-medium-based homogenization equation. Based on the field-equation-based approach of the meso-mechanics theory, the interaction expression of the strain rate at macro- and meso-scale is derived, which can give the strain rate concentration tensor at different crushed degrees. With the thermodynamics and empirical assumption, a breakage ratio in the rate-dependent form is determined. This overcomes the limitations of the existing binary-medium-based models that are difficult to simulate rate-dependent mechanical response. Based on these assumptions, a newly binary-medium-based rate-dependent model is proposed considering both the ice bond breakage and material composition characteristics of saturated frozen soil. The proposed constitutive model has been validated by the test results on frozen soils with different temperatures and strain rates.

Metal-Organic Framework Glass Anode with an Exceptional Cycling-Induced Capacity Enhancement for Lithium-Ion Batteries.

Metal-organic frameworks (MOFs) hold great promise as high-energy anode materials for next-generation lithium-ion batteries (LIBs) due to their tunable chemistry, pore structure and abundant reaction sites. However, the pore structure of crystalline MOFs tends to collapse during lithium-ion insertion and extraction, and hence, their electrochemical performances are rather limited. As a critical breakthrough, a MOF glass anode for LIBs has been developed in the present work. In detail, it is fabricated by melt-quenching Cobalt-ZIF-62 (Co(Im)1.75 (bIm)0.25 ) to glass, and then by combining glass with carbon black and binder. The derived anode exhibits high lithium storage capacity (306 mAh g-1 after 1000 cycles at of 2 A g-1 ), outstanding cycling stability, and superior rate performance compared with the crystalline Cobalt-ZIF-62 and the amorphous one prepared by high-energy ball-milling. Importantly, it is found that the Li-ion storage capacity of the MOF glass anode continuously rises with charge-discharge cycling and even tripled after 1000 cycles. Combined spectroscopic and structural analyses, along with density functional theory calculations, reveal the origin of the cycling-induced enhancement of the performances of the MOF glass anode, that is, the increased distortion and local breakage of the CoN coordination bonds making the Li-ion intercalation sites more accessible.

CFD analysis on the intensified mechanism of gas-liquid mass transfer in a microporous tube-in-tube microchannel reactor

A three-dimensional CFD model coupled with a mesoscale mass transfer model was developed to simulate the absorption of CO2 in the microporous tube-in-tube microchannel reactor (MTMCR). The simulation results were validated by experimental data and empirical correlations, with the discrepancies within ±20%. The local breakage and coalescence of the gas-liquid interfaces enhanced mass transfer in the annular microchannel. The higher ReG and ReL means lower ratio between energy for mass transfer and surface, and also, larger contribution of interfacial area to the mass transfer. Additionally, an entrance-effect zone was revealed, and the entrance-effect zone enlarged with the increase in ReG and ReL. The overall mass transfer coefficient and entrance-effect zone enlarged significantly with appropriate decrease in the length of the gas-liquid collision zone. Results of this work could provide a theoretical basis for the further optimization of MTMCR.

Formation of TiAlSi intermetallics during heating Ti-A356 Al mixed powder compact at semisolid temperature

• The local breakage of oxide films determine the formation of τ1 and τ2 crystals and their morphologies. • Both τ1 and τ2 crystals have an intrinsic plate morphology, but τ2 crystals were thinner due to their more anisotropic growth. • τ1 lamellar domains generate during growth of τ2 crystals accompanied by decrease in density of SFs. • τ1 crystals coarsen at the expense of τ2 crystals, leading all reaction products to finally convert into large τ1 plates. Due to the similarity in composition and crystal structure of some TiAlSi ternary intermetallics, it is quite difficult to accurately confirm their physic characteristics, and thus, to tailor microstructure to improve mechanical properties of metal materials related to the TiAlSi intermetallics. Therefore, the formation process of TiAlSi intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595 °C. The results indicated that two kinds of intermetallics of τ1 (tetragonal, I41/amd) and τ2 (orthorhombic, Cmcm) generated, and both the concentration and supply direction of Ti atoms, which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders, determined the phase and morphology of the intermetallics. τ1 and τ2 crystals all had an intrinsic plate morphology, but τ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults (SFs). τ1 lamellar domains generated during growth of τ2 crystals, which were accompanied by decrease in density of SFs. The combined effect of size difference and internal energy difference between τ1 and τ2 crystals made large τ1 crystals coarsen at the expense of τ2 crystals in Ostwald ripening, leading them to finally evolve into an agglomerate of large τ1 plates.

Experimental characterization of dynamic behavior of single bubble breakage in an agitated tank

Experimental tests for characterizing bubble breakage dynamics in different locations of a stirred tank with a 6-bladed impeller were carried out for a range of impeller Reynolds number (Re) using water as a continuous phase. The dynamic behavior of the bubble from the injection point until arriving at the impeller region was studied by using a high speed imaging method. The deformation behavior, local breakage probability, and the local number of daughter bubbles produced from the injection point until crossing the impeller region were quantified for the whole range of power input. The dominant breakage mechanisms at different locations in the stirred tank were identified and discussed. The results revealed that during the bubble’s motion in the turbulent field, it experiences different scales of deformation depending on the location of the bubble. Highly deformed shapes were observed in the injection and impeller regions due to the bubble’s interaction with turbulent eddies. Three distinct regions between the injection position and the impeller region were observed in which different breakage mechanisms were found to govern the breakage behavior including turbulent fluctuation, shear forces, and bubble collision with the blade. High breakage probability was observed in front of the blade’s tip, with about 90% occurring within a distance of 0.35Ri from the blade’s tip (Ri is the impeller radius). In the impeller region, around 20% of the breakages occurred above the impeller close to the blade’s top, while the breakage percentage below the impeller was very small (2% as a maximum). The breakage probability and the number of daughter bubbles increased with increasing Re with a dependence of 1.3.

Effect of Fibres on the Failure Mechanism of Composite Tubes under Low-Velocity Impact.

Filament-wound composite tubular structures are frequently used in transmission systems, pressure vessels, and sports equipment. In this study, the failure mechanism of composite tubes reinforced with different fibres under low-velocity impact (LVI) and the radial residual compression performance of the impacted composite tubes were investigated. Four fibres, including carbon fiber-T800, carbon fiber-T700, basalt fibre, and glass fibre, were used to fabricate the composite tubes by the winding process. The internal matrix/fibre interface of the composite tubes before the LVI and their failure mechanism after the LVI were investigated by scanning electric microscopy and X-ray micro-computed tomography, respectively. The results showed that the composite tubes mainly fractured through the delamination and fibre breakage damage under the impact of 15 J energy. Delamination and localized fibre breakage occur in the glass fibre-reinforced composite (GFRP) and basalt fibre-reinforced composite (BFRP) tubes when subjected to LVI. While fibre breakage damage occurs globally in the carbon fibre-reinforced composite (CFRP) tubes. The GFRP tube showed the best impact resistance among all the tubes investigated. The basalt fibre-reinforced composite (BFRP) tube exhibited the lowest structural impact resistance. The impact resistance of the CFRP-T700 and CFRP-T800 tube differed slightly. The radial residual compression strength (R-RCS) of the BFRP tube is not sensitive to the impact, while that of the GFRP tube is shown to be highly sensitive to the impact.

Dynamics responses analysis in frequency domain of helical gear pair under multi-fault conditions

This work aims to investigate dynamic characteristics of a helical gear pair under multiple faults condition, through model-based dynamic analysis. Two kinds of faults, tooth spalling and local breakages are considered. Firstly, influences of each kind of fault on meshing stiffness of gear pair with one or more faulted teeth were revealed. Then an 8 degree of freedom lumped-parameter model was developed to obtain dynamic responses. Furthermore, frequency spectrum analysis of the responses was conducted and compared with those under healthy condition. Results indicate that spalling or local breakage introduce different affects into mesh stiffness, and consequently displacement & velocity amplitudes of pinion appear with different waveforms, especially for the case only tooth breakages happen. This work could provide useful instructions for fault detection diagnosis of geared transmissions under multiple fault conditions.

Investigation on Vortex-Induced Vibration Experiment of a Standing Variable-Tension Deepsea Riser Based on BFBG Sensor Technology.

A vortex-induced vibration (VIV) experiment on a standing variable-tension deepsea riser was conducted to investigate the applicability and sensitivity of Bare Fiber Bragg Grating (BFBG) sensor technology for testing deepsea riser vibrations. The dominant frequencies, dimensionless displacements, in-line and cross-flow couplings of the riser VIV under different top tensions were observed through wavelet transform and modal decomposition. The result indicated that, excited by the same external flow velocities, the cross-flow and in-line dominant frequencies of the riser both decreased with increasing top tension. In terms of displacement responses, increasing top tension caused the root mean square (RMS) displacement to decrease and the vibration amplitude to reduce. In terms of cross-flow and in-line coupling, the closer a location is to the ends of the riser, the smaller the trajectory is and the more standard the “8” becomes. During top tension increases, there exists a “lag” in the time when the riser’s vibration trajectory becomes an “8”. The Slalom Surround Installation approach can effectively prevent the local breakage of the optical fiber string. BFBG sensor technology can give an accurate presentation of the displacement time history, vibration amplitude and frequency of the riser, provides a clear picture of how the riser’s mode and VIV evolve as a function of flow velocity.

Simulating time-dependent quasi-brittle failures based on a multilinear releasing mechanism of viscous force (VF) fields

The time-dependent progressive failures in heterogeneous brittle materials are modeled by considering the temporal stress redistribution mechanism due to local breakages. The influence of local breakages lies in two kinds of stress redistributions: (1) Internal forces in the breaking element are assumed to release infinitely fast when compared with external loadings, and the corresponding viscoelastic deformation of the specimen happens in a finite speed. This deformation delay is implemented by introducing a VF field all over the specimen. (2) Then the gradual release of VF fields stored previously follows, resulting in the viscous recovery of the entire specimen, which is approximated as a multilinear process. The main characteristic of the present algorithm is its linearity, i.e. no nonlinear iterations are included. Numerical results of uniaxial tensile/compressive, anchor bolt pull-out and Brazilian tests show that the proposed model is capable of overcoming the over-brittle issue in existing lattice models and capturing the strain rate sensitivity, which agree well with experimental observations.

Preparation of Porous Ceramic Based on Al2O3 as a Result of Zonal Compaction During Sintering of Powder Workpieces of Very Fine Aluminum Powder PAP-2 Combustion Products

Production aspects are considered for preparing porous ceramic based on α-Al2O3 using the effect of zonal compaction during powder workpiece sintering of very fine combustion products in air of flaky aluminum powder PAP-2 particles. It is shown that formation of a porous structure in sintered material proceeds by a local breakage mechanism through boundaries of aggregates with formation of pores between agglomerates, and also due to occurrence of a closed intergranular pore system. Properties of the ceramic obtained are: density 2.45 g/cm3, total porosity 39%, open porosity 30%, closed porosity 9%, the and ultimate strength in bending 50 – 60 MPa.

Modeling of progressive failures in quasi-brittle media based on a temporal stress-redistribution mechanism

• Quasi-brittle failure model based on a temporal stress-redistribution mechanism. • Simulating damage-induced softening without nonlinear iterations. • Implementing viscosity by introducing viscous force fields. • Strain-rate sensitivity, immediate elasticity and cyclic responses investigated. A new attempt is made to simulate progressive failure processes in heterogeneous brittle materials such as concrete, ceramics, rocks etc., by considering the time-dependence of stress redistributions induced by local breakages. Two mechanisms of stress redistribution are incorporated into the proposed model in order to account for the influence of each local breakage on the remaining specimen: (1) one is the immediate release of internal forces in the breaking element, which is assumed to happen within an infinitesimal time when compared with the characteristic time of external loadings. The release of such internal forces is hence suddenly applied to the remaining specimen, which is considered to take time to deform correspondingly due to material viscosity. This deformation delay is implemented by introducing a viscous force (VF) field prevailing in the entire specimen. (2) The other is the gradual release of previously stored VF fields, whose characteristic time is assumed to be material-dependent. Here the release of VF is approximated as stepwise for simplicity. The proposed model is found to be capable of overcoming the unreasonably-low-ductility problem encountered in many existing lattice models when it comes to the uniaxial tensile test . Furthermore, the force–displacement response obviously depends on the ratio of the VF releasing time to the characteristic time of external loading, showing trends agreeing with experimental observations. Compared with results without viscosity, the failure pattern is more scattering, and the force–displacement curve has a higher peak load and a more ductile post-peak tail.

Degradation processes in high-temperature creep of cast cobalt-based superalloys

Degradation processes in high-temperature creep of two cast high-chromium cobalt-based superalloys strengthened by niobium and tantalum for use in the glass industry were analysed via various experimental techniques. Constant load creep tests were conducted at 900, 950 and 1000 °C in a tensile stress range from 40 to 80 MPa. It was found that the CoNb superalloy possesses considerably longer creep life compared to the CoTa superalloy under the same loading conditions. Conversely, the creep ductility of the fractured specimens shows the opposite order of the creep life. The creep behaviour of both superalloys obeys the Monkman-Grant formula indicating that the creep deformation mechanism and fracture processes are mutually interlinked. The homogeneously distributed creep damage of the CoNb superalloy is closely connected with primary carbides and is predominantly initiated either as interface decohesion between the carbide/matrix and carbide eutectics/matrix or by breakage of bulk M23C6 carbides. The dominant type of creep damage in the CoTa superalloy is localized breakage of M23C6 carbides in close proximity of the fracture path. The final brittle fracture in the CoNb superalloy occurs via relatively fast propagation of the longest cracks after the ultimate state of damage is reached. Due to premature fracture, the inherent creep ductility of the CoNb matrix is not exhausted. The final ductile transgranular creep fracture of the CoTa superalloy is caused by a local strain-induced instability of the dislocation microstructure leading to a loss of an external section of specimen (necking).

Optimization of the ITER Precompression Ring Test Rig Flange

The precompression ring (PCR) is an important element of the ITER magnetic system since it improves the force distribution among the toroidal field magnets during plasma operation. An experimental campaign has been planned at the ITER organization to characterize the mechanical behavior of the ring in a test rig able to simulate the ITER assembly conditions. In particular, the testing machine aims at simulating the effect of the preload by means of a system of hydraulic cylinders capable to deliver 36 000 tons of radial pushing force. A steel “cushion” flange acts as interface between the cylinders and the ring distributing the pressure on the surface and preventing the PCR from local breakage. In this paper, the shape optimization of such flange is addressed, identifying the optimal geometry basing on the contact stress on the inner surface of the PCR. The study shows how the stress peaks can be avoided by obtaining a reasonably homogeneous distribution limiting the risks of peak stresses that might compromise the integrity of the component. The results of this study can also be used as a basis of future studies aiming at optimizing the ITER flange design and the behavior of the PCR in operative conditions.

Experimental study on the bubble breakage in a stirred tank Part 2: Local dependence of breakage events

Experimental observation of the local breakage behavior of a single bubble injected in different locations in a stirred tank was carried out using high speed imaging method. The bubble was injected in six positions located at different radial and tangential distances from a Rushton turbine impeller. The effect of relative location from the impeller on the breakage probability and the number of daughter bubbles (fragments) was investigated and discussed. The effect of power input (or Reynolds number) and mother bubble size on the breakage events for each injection position was studied. Trajectories of the bubbles were analyzed and quantified. It was found that the breakage probability and the number of produced daughter bubbles were large close to the impeller but decreases sharply when injecting the bubble away from the impeller, i.e. at r/R = 0.64 (where r is the distance from the impeller center and R is the tank's radius) or more from the impeller blade. The presence of baffles affected the breakage probability and the number of daughter bubbles in the regions around them. The breakage events were observed to occur in different sub-regions between the impeller and the wall after the bubble had exhibited different degrees of local deformation. For low Re, most of the bubbles injected close to the impeller were found to approach the impeller and then get pushed toward the tank's wall by the flow current ejected from the blades tip. For high Re, a considerable percentage of bubbles were found to be driven into the impeller by highly rotating flow currents and turbulent eddies. This led to an increase in the breakage probability in the impeller vicinity.

Tensile and bend behaviour of nanostructured HVOF and flame sprayed stellite coatings

Stellite 6 powder (CoCrSiW) was deposited using flame spray (FS) and high velocity oxygen fuel (HVOF) techniques on steel substrates. The microstructure of stellite coatings produced with these deposition techniques displayed a rather similar morphology consisting of cobalt-rich dendrites surrounded by hard (Cr3C7) carbide particles. The stellite (both FS and HVOF) coating was found to reduce the tensile strength of the steel. The failure of the coated steel specimens initiated by cracking on the coating surface, transverse propagation of the cracks towards the coating - substrate interface and diversion along the interface leading to local delamination and breakage. During the bend tests cracks developed along the coating and the main failure in the coating occurred due to the tensile-shear deformation, particularly in the coating-substrate material interface. The coating thickness does not appear to affect the bending strength. During bending the number of surface cracks per unit length decreased with increasing coating thickness. Stereoscopic analysis showed that the thicker the coating the deeper the surface cracks. When the critical stress for crack propagation reached defect sites at the substratecoating interface, the entire coating failed and peeled off from the substrate.

NIR‐Triggered Release of Nitric Oxide with Upconversion Nanoparticles Inhibits Platelet Aggregation in Blood Samples

AbstractThere is a great challenge to overcome the limitation of tissue penetration depth, while maximizing the benefit of light‐triggered biochemical cascades in a well‐defined mode simultaneously. Here, a new method of near‐infrared (NIR) light‐triggered release of nitric oxide (NO) by developing upconversion nanoparticles (UCNPs)‐based conjugate chemistry is reported. As the key nanotransducer in the design, core–shell‐structured UCNPs are encapsulated with a layer of SiO2 and then covalently linked with a potent NO‐releasing donor (S‐nitroso‐N‐acetyl‐dl‐penicillamine, SNAP). It is featured with highly localized breakage of chemical bonds of SNAP molecules by NIR–UV upconversion, enabling simultaneous NO release in a light dosage‐dependent manner. The biological effects of NO releasing are demonstrated by cellular imaging and inhibition of platelet aggregation from blood samples. This work provides a flexible and robust platform to generate cell‐signaling gas molecules trigged by NIR laser with deep tissue penetration.

Influences of tooth spalling or local breakage on time-varying mesh stiffness of helical gears

Abstract Time-varying mesh stiffness (TVMS) provides important information about the health condition of geared systems. Tooth faults, like crack, pitting, spalling and breakage, will change the TVMS. This work aims to reveal the influences of tooth spalling and local breakage on the TVMS of helical gears. Firstly, an analytical model is developed to incorporate the faults by combining slicing method, discrete integral method and potential energy method. Then, parametric study is conducted. Finally, conclusions are arrived and the results indicate that length, width and location of these defects are very important parameters that need to be considered for calculating TVMS of helical gears. This study provides a theoretical basis for fault diagnosis of helical geared transmissions.

Combined Highly Resistant Lining of Furnace Chamber for Drying Nutritional Yeast Suspension

Service conditions for the lining of SRTs12.5/1500 NK furnace chamber in the Mozyr’ Nutritional Yeast Plant (MZKI), the nature of its breakdown, and combustion processes are studied. A refractory adhesive is developed and tested as a brickwork mortar. Use for impregnation of a furnace refractory lining of an aluminium-chromium phosphate binder of optimum density makes it possible to reduce refractory porosity and thereby increase strength by 30%, and thermal shock resistance by a factor of three. Alining of highly resistant mullite-corundum refractory based on fuzed materials is tested: a “chequerboard” furnace brickwork scheme is accomplished; a protective highly-resistant coating is used for repairing local breakage. As a result of introducing these measures combustion chamber lining life is increased by a factor of 2.5 – 3.0, i.e., from 2 – 3 to 9 – 10 months.

A random virtual crack DEM model for creep behavior of rockfill based on the subcritical crack propagation theory

The post-construction settlement of rockfill dams and high filled ground of airport, which is a phenomenon of much significance, is mainly caused by the time-dependent breakage of the rockfill material. In this paper, a random virtual crack DEM model is proposed for creep behavior of rockfill in PFC2D according to the theory of subcritical crack propagation induced by stress corrosion mechanisms. The bonded clusters are adopted to represent the rockfill particles so as to simulate their irregular shapes. Virtual cracks are set at the bonds of the clusters, and the length of the crack is considered as a random value, which leads the crushing strength of a single particle to follow the Weibull’s statistical model and the corresponding size rules. Oedometric creep tests for rockfill are simulated by using this proposed model. The results show that the model, validated preliminarily by some test data, can reflect qualitatively the creep mechanism as well as the size effects reasonably. Particles can develop various breakage patterns during creep, including global breakage, local breakage and even complex mixed breakage. The increase in stress levels and particle size will lead to an obvious growth of the creep strain and creep rate of the rockfill. The scale effects on the creep behavior of rockfill are analyzed through 35 specimens, and formulas including the effects of scales and stress levels are tentatively proposed.