Thermomechanical Cracking in the Vicinity of a Near-Surface Void Due to High-Speed Friction Load

1988 ◽  
Vol 110 (2) ◽  
pp. 306-311 ◽  
Author(s):  
T. Y. Chen ◽  
F. D. Ju
Keyword(s):  
Stress State ◽  
High Speed ◽  
Stress Singularity ◽  
Rectangular Cavity ◽  
Stress Fields ◽  
Stress Effect ◽  
Thermal And Mechanical Properties ◽  
Near Surface ◽  
Energy Balance Method ◽  
Thermal Tensile Stress

This paper discusses the temperature distribution and the stress state in the vicinity of a near-surface rectangular cavity. They occur when the solid is subjected to the Coulomb frictional loading of an asperity moving at moderately high speed. The finite difference method is employed to calculate both the temperature and stress fields. The energy balance method is applied at the corners of the rectangular cavity to resolve the problem of singularities in the temperature field there. The stress singularity at each corner is represented by a special element that is introduced representing the behavior of the known stress singularity at the corner and its surrounding vicinity. Results show that the thermal stress effect dominates the stress field and eventually leads to failure. When a defect, such as a cavity, exists, the stress state that determines the failure phenomenon is more severe and can be quantified depending on the location of the cavity. These results were determined through a numerical computation based on the material properties of Stellite III. However, the parametric effect of material variations including changes in both thermal and mechanical properties were also considered. The study of the cavity location also established the existence of a critical cavity location. This location is defined by the critical ligament thickness (thickness between the wear surface and the top edge of the cavity), at which the cavity-influenced thermal tensile stress reaches a maximum. This thickness is important to designers when cavities at coating/substrate interface are either unavoidable or are too expensive to control in fabrication.

High-Speed Visualization of the Oscillatory Supersonic Flow Over a Rectangular Cavity

2011 ◽  
Author(s):  
Taro Handa ◽  
Hiroaki Miyachi ◽  
Hatsuki Kakuno ◽  
Takaya Ozaki
Keyword(s):  
Supersonic Flow ◽  
Pressure Wave ◽  
High Speed ◽  
Pressure Oscillation ◽  
Rectangular Cavity ◽  
Schlieren Method ◽  
Trailing Edge ◽  
The Relationship ◽  
Type Pressure ◽  
Semiconductor Type

A mechanism of cavity-induced pressure oscillation in supersonic flows is not well understood in spite of a lot of former investigations. Especially, the process by which the pressure wave is generated and the path of the pressure wave propagating inside the cavity remain unclear. In order to clarify these, the oscillatory behaviors in the supersonic flow over a rectangular cavity are visualized by the schlieren method with a high-speed camera in the present study. The inlet Mach number of the flow is 1.68. The length and depth of the cavity are 14.0mm and 11.7mm respectively; i.e., the length-to-depth ratio of the cavity is 1.20. The pressure oscillation near the trailing edge of the cavity is also measured by use of the semiconductor-type pressure transducer simultaneously with the visualization. As a result, the pressure waves propagating inside as well as outside the cavity are successfully visualized. In addition, the relationship between the shear layer displacement, pressure wave generation and pressure oscillation at the trailing edge of the cavity are clarified experimentally.

scholarly journals About mathematical simulation of processes for high-speed loading of materials on Department of Physical Mechanics of St. Petersburg State University

2020 ◽  
Vol 65 (4) ◽  
pp. 699-713
Author(s):  
Victor A. Morozov ◽  
◽  
Vsevolod I. Bogatko ◽  
Andrey B. Yakovlev ◽  
◽  
...  
Keyword(s):  
Mathematical Simulation ◽  
High Speed ◽  
Surface Region ◽  
Pulse Method ◽  
Magnetic Pulse ◽  
State University ◽  
Natural Experiments ◽  
Near Surface ◽  
Metal Rings ◽  
Physical Mechanics

The researches of shock-wave processes in the constructional materials are actual, but carrying out of natural experiments is extremely inconvenient and expensive, and sometimes it is even impossible to replicate. Therefore basically all researches of these problems are reduced to various cases of simulation of processes for high-speed loading of materials in the laboratory circumstances. In the paper we consider following directions of mathematical simulation of processes for high-speed loading of materials that were made on department of physical mechanics of St. Petersburg State University: the simulation of shock-loaded media by using of dynamics of dislocations; the simulation of high-speed loading of media with the account of the relaxation phenomena in a near-surface region; the simulation of propagation of the short elastoplastic impulse in medium under the condition of influence of a weak magnetic field; the generation of mathematical models of deformation and destruction of thin metal rings by a magnetic-pulse method; the simulation of crack propagation during the short-term pulse loading.

scholarly journals Study of Deformation and Breakup of Submillimeter Droplets’ Spray in a Supersonic Nozzle Flow

2020 ◽  
Vol 10 (18) ◽  
pp. 6149
Author(s):  
Oleg A. Gobyzov ◽  
Mikhail N. Ryabov ◽  
Artur V. Bilsky
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Supersonic Nozzle ◽  
Stress Effect ◽  
Size Distributions ◽  
Flow Measurements ◽  
Image Velocimetry ◽  
Accelerated Flow ◽  
High Speed Flows ◽  
Breakup Mode

The problem of secondary atomization of droplets is crucial for many applications. In high-speed flows, fine atomization usually takes place, and the breakup of small droplets determines the final products of atomization. An experimental study of deformation and breakup of 15–60 µm size droplets in an accelerated flow inside a converging–diverging nozzle is considered in the paper. Particle image velocimetry and shadow photography were employed in the experiments. Results of gas and liquid phase flow measurements and visualization are presented and analyzed, including gas and droplets’ velocity, shape and size distributions of droplets. Weber numbers for droplets’ breakup are reported. For those small droplets at low Weber numbers, the presence of well-known droplets’ breakup morphology is confirmed, and rare “pulling” breakup mode is detected and qualitatively described. For the “pulling” breakup mode, a consideration, explaining its development in smaller droplets through shear stress effect, is provided.

scholarly journals Defect-dependent Elasticity: Nanoindentation as a Probe of Stress State

2000 ◽  
Vol 15 (8) ◽  
pp. 1693-1701 ◽  
Author(s):  
K. F. Jarausch ◽  
J. D. Kiely ◽  
J. E. Houston ◽  
P. E. Russell
Keyword(s):  
Stress State ◽  
Elastic Properties ◽  
Elastic Response ◽  
Indentation Modulus ◽  
Strongly Correlated ◽  
Near Surface ◽  
Single Crystal Surfaces ◽  
Complex Interdependence ◽  
Low Temperature Annealing ◽  
Surface Steps

Using an interfacial force microscope, the measured elastic response of 100-nm-thick Au films was found to be strongly correlated with the films' stress state and thermal history. Large, reversible variations (2×) of indentation modulus were recorded as a function of applied stress. Low-temperature annealing caused permanent changes in the films' measured elastic properties. The measured elastic response was also found to vary in close proximity to grain boundaries in thin films and near surface steps on single-crystal surfaces. These results demonstrate a complex interdependence of stress state, defect structure, and elastic properties in thin metallic films.

Effect of Carbon Nanotube on Electrical, Thermal and Mechanical Properties of Epoxy

2007 ◽  
Author(s):  
Yuanxin Zhou ◽  
Peixuan Wu ◽  
Zhongyang Cheng ◽  
Biddut Kanti Dey ◽  
Shaik Jeelani
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Carbon Nanotube ◽  
High Speed ◽  
Mechanical Test ◽  
High Vacuum ◽  
Mechanical Analysis ◽  
Thermal And Mechanical Properties ◽  
Multi Walled Carbon Nanotubes ◽  
Mechanical Agitator

In this study, electrical, thermal and mechanical properties of multi-walled carbon nanotubes (CNTs) reinforced Epon 862 epoxy have been evaluated. Firstly, 0.1 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt% CNT were infused into epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Neat epoxy sample also was made as reference. Electrical conductivity, dynamic mechanical analysis (DMA, three point bending tests and fracture tests were performed on unfilled, CNT-filled epoxy to identify the loading effect on the properties of composites. Experimental results show significant improvement in electric conductivity. The resistivity of epoxy decreased to 15Ωm with 0.4% CNT. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 17° C increase in Tg, but CNT has little effect on decomposing temperature. Mechanical test results showed that modulus increased with higher CNT loading percentages, but the 0.3 wt% CNT-infusion system showed the maximum strength and fracture toughness enhancement. The decrease in strength and fracture toughness in 0.4% CNT/epoxy was attributed to poor dispersions of nanotubes in the composite.

scholarly journals Effective characteristics of a layered tube consisting of elastic-creeping materials

2018 ◽  
Vol 251 ◽  
pp. 04039 ◽  
Author(s):  
Tatiana Bobyleva ◽  
Alexei Shamaev
Keyword(s):  
Stress State ◽  
Strain State ◽  
Analytical Form ◽  
Effective Characteristics ◽  
Stress Fields ◽  
Stress Strain ◽  
Creep Theory ◽  
Composite Tube ◽  
Subsequent Deformation

The article suggests a method for modelling the stress-strain state of layered elastic-creeping tube. This method is based on a combination of the theory of averaging and creep theory. This theory takes into account the previous stress state and its effect on the subsequent deformation period. Creep kernels for the averaged problem are found in the explicit analytical form. These formulas can be used to estimate displacement and stress fields during long-term loading of a composite tube.

The infrared measurement cascade: Connecting large scale meteorologically induced surface temperature perturbations to local spatial velocity structures

2020 ◽  
Author(s):  
Benjamin Schumacher ◽  
Marwan Katurji ◽  
Jiawei Zhang
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Brightness Temperature ◽  
High Speed ◽  
Surface Brightness ◽  
Large Scale ◽  
Mean Velocity ◽  
Near Surface ◽  
Multi Scale ◽  
Infrared Cameras

<p>The evolution of micrometeorological measurements has been recently manifested by developments in methodological and analytical techniques using spatial surface brightness temperature captured by infrared cameras (Schumacher et al. 2019, Katurji and Zawar-Reza 2016). The Thermal Image Velocimetry (TIV) method can now produce accurate 2D advection-velocities using high speed (>20Hz) infrared imagery (Inagaki 2013, Schumacher 2019). However, to further develop TIV methods and achieve a novel micrometeorological measurement technique, all scales of motion within the boundary layer need to be captured.</p><p>Spatial observations of multi-frequency and multi-scale temperature perturbations are a result from the turbulent interaction of the overlying atmosphere and the surface. However, these surface signatures are connected to the larger scales of the atmospheric boundary layer (McNaughton 2002, Träumner 2015). When longer periods (a few hours to a few days) of spatial surface brightness temperatures are observed, the larger scale information needs to be accounted for to build a comprehensive understanding of surface-atmospheric spatial turbulent interactions. Additionally, the time-frequency decomposition of brightness temperature perturbations shows longer periods of 4-15 minutes superimposed over shorter periods of ~ 4–30 seconds. This suggests that that boundary layer dynamic scales (of longer periods) can influence brightness temperature perturbations on the local turbulent scale. An accurate TIV algorithm needs to account for all scales of motion when analysing the time-space variability of locally observed spatial brightness temperature patterns.</p><p>To analyse these propositions temporally high resolved geostationary satellite infrared data from the Himawari 8 satellite was compared to near-surface and high speed (20 Hz) measured air and brightness temperature using thermocouple measurements and infrared cameras. The satellite provides a temporal resolution of 10-minutes and a horizontal resolution of 2 by 2 km per pixel and therefore captures the atmospheric meso γ and micro α scale which signals are usually active for ~10 minutes to < 12 hours. Moreover, the Himawari 8 brightness temperature was used to create the near-surface mean velocity field using TIV. Afterwards, the velocity field was compared to the in-situ measured wind velocity over several days during January 2019.</p><p>The results show that the atmospheric forcing from the micro α scale to lower atmospheric scales has a major impact on the near-surface temperature over several minutes. A significant (p-value: 0.02) positive covariance between the Himawari 8 measurement and the local measured temperature 1.5 cm above the ground on a 10 minute average, specifically concerning cooling and heating patterns, has been found.</p><p>Further analysis demonstrates that the retrieved near-surface 2-D velocity field calculated from the Himawari 8 brightness temperature perturbations is correctly representing the mean velocity. This finding allows the classification of meso-scale atmospheric forcing and its direct connection to local scale turbulent 2-D velocity measurements. This extends the TIV algorithm by a multi-scale component which allows to address inter-scale boundary layer analysis from a new point of view. In respect to the current findings a new experiment will focus on the repeated induced local velocity patterns from large scale forcing which will be measured through the surface brightness temperature.</p>

Residual Stress Gradients in PVD-Coated Carbide Cutting Tools

2006 ◽  
Vol 524-525 ◽  
pp. 607-612 ◽  
Author(s):  
Berend Denkena ◽  
Bernd Breidenstein
Keyword(s):  
Residual Stress ◽  
Stress State ◽  
Cutting Tools ◽  
Surface Residual Stress ◽  
Vector Method ◽  
Near Surface ◽  
Residual Stress State ◽  
Coated Tools ◽  
Cohesive Damage ◽  
Coated Carbide

PVD-coated cutting tools show a typical kind of failure in use: cohesive damage, which is believed to be a result of the residual stress state of substrate and coating. As the sin2ψ-technique does not give satisfactory information on near surface residual stress trends of coated tools the scattering vector method was applied to determine residual stress depth distributions of coating and substrate. The results are presented and an attempt for an interpretation is given.

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