Indentation and Splitting of Freshwater Ice Floes

1995 ◽  
Vol 117 (1) ◽  
pp. 63-69
Author(s):  
D. S. Sodhi ◽  
S. N. Chin
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Small Scale ◽  
Effective Pressure ◽  
Deformation And Failure ◽  
Low Speed ◽  
Freshwater Ice ◽  
Compressive Stresses ◽  
Ice Floes

Small-scale indentation and floe-splitting experiments were conducted on columnar ice floes of various sizes and at different speeds. During low-speed indentation (0.2–8 mm s−1), the ice floes always split apart, while at higher indentation speeds (> 100 mm s−1) they did not. The reason is attributed to differences in the process of deformation and failure. At low speed, a large zone of microcracked ice forms in front of the indentor. Development of compressive stresses in the microcracked ice zone leads to buildup of transverse forces that drive crack propagation. These zones of microcracked ice are not observed during high-speed indentation. Rather, the ice fails by continuous crushing. The theoretical effective pressure required to split an ice floe, as predicted by Bhat (1988), agrees to some extent with those measured during experiments.

scholarly journals Breakage of Ice Sheets by Underwater Explosions

1977 ◽  
Vol 19 (81) ◽  
pp. 661-663
Author(s):  
E. Vittoratos ◽  
M. E. Charles
Keyword(s):  
Elastic Plate ◽  
High Speed ◽  
Plate Theory ◽  
Ice Sheets ◽  
Theoretical Development ◽  
Small Scale ◽  
Theory Approach ◽  
Classical Plate Theory ◽  
Theoretical Understanding ◽  
Deformation And Failure

AbstractWe have attempted to develop a theoretical understanding of the field experience on the destruction of floating ice sheets by explosives, by performing small-scale laboratory explosions and developing a theory based on the elastic plate. Glass spheres 4.5 × 10¯2 m in diameter and c. 4 × 10¯4 m thick were immersed in water underneath a floating ice sheet c. 2 × 10¯2 m in thickness. The air pressure was raised till the sphere burst at pressures around 15 atmospheres. A high-speed camera (up to several thousand frames per second) recorded the details of the explosion: the growth of the gas bubble and the corresponding deformation and failure of the ice. We observed radial and circumferential cracks develop within 2 ms of the bursting of the sphere.As a first step in the theoretical development, we have considered the response of an infinite elastic plate to impulsive pressure loading due to an underwater explosion. We have assumed potential, incompressible flow which is a valid approximation for the case of the above experiments and the analogous compressed-gas blasting in the field (Mellor and Kovacs, 1972). However the effects caused by the intense shock wave that is radiated by the detonation of a high explosive are thus not considered. We relate the maxima in the tensile stress with the crack pattern and the eventual damage, and have achieved qualitative agreement with the laboratory observations. The model does reproduce and clarify some aspects of the field data, in particular the role of the thickness (Mellor, unpublished); but it fails to relate the crater diameter to the weight of the explosive. It appears that at optimum blasting conditions with high explosives an incompressible-fluid, classical-plate-theory approach is inadequate.

scholarly journals Breakage of Ice Sheets by Underwater Explosions

1977 ◽  
Vol 19 (81) ◽  
pp. 661-663
Author(s):  
E. Vittoratos ◽  
M. E. Charles
Keyword(s):  
Elastic Plate ◽  
High Speed ◽  
Plate Theory ◽  
Ice Sheets ◽  
Theoretical Development ◽  
Small Scale ◽  
Theory Approach ◽  
Classical Plate Theory ◽  
Theoretical Understanding ◽  
Deformation And Failure

Abstract We have attempted to develop a theoretical understanding of the field experience on the destruction of floating ice sheets by explosives, by performing small-scale laboratory explosions and developing a theory based on the elastic plate. Glass spheres 4.5 × 10¯2 m in diameter and c. 4 × 10¯4 m thick were immersed in water underneath a floating ice sheet c. 2 × 10¯2 m in thickness. The air pressure was raised till the sphere burst at pressures around 15 atmospheres. A high-speed camera (up to several thousand frames per second) recorded the details of the explosion: the growth of the gas bubble and the corresponding deformation and failure of the ice. We observed radial and circumferential cracks develop within 2 ms of the bursting of the sphere. As a first step in the theoretical development, we have considered the response of an infinite elastic plate to impulsive pressure loading due to an underwater explosion. We have assumed potential, incompressible flow which is a valid approximation for the case of the above experiments and the analogous compressed-gas blasting in the field (Mellor and Kovacs, 1972). However the effects caused by the intense shock wave that is radiated by the detonation of a high explosive are thus not considered. We relate the maxima in the tensile stress with the crack pattern and the eventual damage, and have achieved qualitative agreement with the laboratory observations. The model does reproduce and clarify some aspects of the field data, in particular the role of the thickness (Mellor, unpublished); but it fails to relate the crater diameter to the weight of the explosive. It appears that at optimum blasting conditions with high explosives an incompressible-fluid, classical-plate-theory approach is inadequate.

Crack Propagation in Freshwater and Saline Ice

1999 ◽  
Vol 578 ◽  
Author(s):  
Patrick J. Donovan ◽  
Masahiko Arakawa ◽  
Victor Petrenko
Keyword(s):  
Crack Propagation ◽  
Crack Velocity ◽  
High Speed ◽  
Acoustic Emissions ◽  
Crack Tip ◽  
High Speed Photography ◽  
Propagation Time ◽  
Reliable Technique ◽  
Resistance Method ◽  
Freshwater Ice

AbstractCrack propagation in columnar saline and freshwater ice has been investigated with high-speed photography, acoustic emission detection and the resistance method. High-speed photography was found to be a single reliable technique. The resistance method proved effective for freshwater ice samples, but not for saline ice samples due to the presence of conductive fluid inclusions. Acoustic emissions pinpointed the moment of crack initiation, but did not correspond to the crack propagation time. Crack velocity has been characterized over a temperature range of -5°C to -30 °C for freshwater and saline ice. Freshwater ice exhibited an overall average velocity of 198 m/s, and did not vary with temperature. Crack velocity in saline ice demonstrated temperature dependence, increasing from an average of 86 m/s in the -5°C to -20°C range, to 131 m/s at -30°C. The crack velocity was also shown to have a general dependence on fracture toughness K' of the material, however, the microstructural variation between samples is also shown to influence significantly the crack behavior in both saline and freshwater ice. Nonuniform crack tip advance and crack reorientation were observed as crack slowing mechanisms in freshwater ice, while in saline ice fracture crack tip blunting on voids greatly reduced average crack velocities.

Observation of crack propagation in saline ice and freshwater ice with fluid inclusion

2003 ◽  
Vol 81 (1-2) ◽  
pp. 159-166
Author(s):  
M Arakawa ◽  
V F Petrenko
Keyword(s):  
Crack Propagation ◽  
Electrical Resistance ◽  
Crack Velocity ◽  
High Speed ◽  
High Speed Photography ◽  
Low Density ◽  
Conductive Liquid ◽  
Freshwater Ice ◽  
Maximum Crack ◽  
Very High

A key process of crack propagation in saline ice is the interaction between the crack and fluid inclusions. We observed their interaction in freshwater ice using very high-speed photography (VHSP) and found that the low-density fluids (air and inert liquid, Fluorinert, 1.78 g/cm3) could not impede the crack effectively, interrupting the propagation for less than 10 µs. The high-density liquid mercury, (13.8 g/cm3) impeded the crack more effectively, stalling the development of the crack for more than 20 µs. The crack velocity in saline ice was measured using two different methods: electrical resistance method (ERM) and VHSP. These two methods returned very different mean velocities, 15 m/s for the ERM and 250 m/s for the VHSP. We found that in ice with conductive liquid inclusions, the ERM measured the time it took to break liquid bridges stretched across a crack rather than the crack velocity. Results from the VHSP show that the maximum crack velocity in saline ice was 500 m/s, which is one-half of that found in freshwater ice. From our results using freshwater ice with inclusions, we conclude that liquid inclusions in saline ice may play a role in this retardation. PACS No.: 62.20Mk

Analysis on Milling Performance of 2024-T351 Aluminum Alloy Using TiAlN Coated Carbide Cutting Tools

2011 ◽  
Vol 697-698 ◽  
pp. 218-222 ◽  
Author(s):  
Jin Yang Xu ◽  
Qing Long An ◽  
Ming Chen
Keyword(s):  
Surface Roughness ◽  
Aluminum Alloy ◽  
Residual Stresses ◽  
High Speed ◽  
Cutting Tools ◽  
High Speed Milling ◽  
Low Speed ◽  
Milling Performance ◽  
Compressive Stresses ◽  
Coated Carbide

This research is concerned with the analytical and experimental study on milling of 2024-T351 aluminum alloy with TiAlN coated carbide cutting tools in both low-speed machining and high-speed machining. The results are analyzed in terms of surface roughness and residual stresses of the workpiece. Surface roughness studies indicate that in high-speed milling of 2024-T351 aluminum alloy the surface roughness can maintain a lower value and the workpiece can obtain excellent surface quality compared to the low-speed machining. The high-speed milling was found to be able to enhance the original residual stresses of the workpiece; while the low-speed milling may weaken or undermine the original residual stresses, or even transform the initial compressive stresses into the tensile stresses.

Investigation on Acoustic Emission Characteristics from Q345R during Fatigue Crack Propagation

2013 ◽  
Vol 331 ◽  
pp. 61-64 ◽  
Author(s):  
Meng Yu Chai ◽  
Li Chan Li ◽  
Yong Quan Li ◽  
Wen Jie Bai ◽  
Quan Duan
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
High Speed ◽  
Low Speed ◽  
Signal Parameters ◽  
Crack Generation

The fatigue crack propagation process of specimen made from Q345R was monitored by acoustic emission (AE) equipment. The AE characteristic of the specimen generated during the fatigue crack propagation was obtained by parameter analysis method and wavelet transform method .The results show that the fatigue crack growth curve comprises four phases of the crack generation phase, the low-speed crack propagation phase, the high-speed crack propagation phase and the fracture phase, and the variation of signal parameters presents the similar tendency to the fatigue crack growth rate. The values of signal parameters, such as count, energy, and amplitude, are stable and low in the crack generation phase and low-speed crack propagation phase, and relatively unstable and high in the high-speed crack propagation phase and fracture phase. The type of signals is burst emission and the frequency ranges from 100kHz to 180kHz. From these correlations, it may be possible to predict the remaining service life of a pressure vessel from the results of short-term AE monitoring of crack propagation.

Experimental Measurement of CTOA During Ductile Crack Propagation in Pipeline Burst Tests

2018 ◽  
Author(s):  
Kazuki Shibanuma ◽  
Hikaru Yamaguchi ◽  
Takahiro Hosoe ◽  
Katsuyuki Suzuki ◽  
Shuji Aihara
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Crack Velocity ◽  
High Speed ◽  
Crack Arrest ◽  
Opening Angle ◽  
Small Scale ◽  
Outer Diameter ◽  
Burst Test ◽  
Pipe Burst

Dynamic measurement of drop-weight tear test (DWTT) and pipe burst test for 356 mm outer diameter and 9.5 mm wall thickness steel pipe were conducted using high-speed camera. Crack velocity in the DWTT were 10 m/s during the steady state. Crack Tip Opening Angle (CTOA) values measured in the DWTT showed the constant value of about 20.1° during steady state propagation. On the other hand, crack velocity in the burst test showed monotonically decreasing during crack propagation from 200 m/s but it was found that CTOA value kept constant value of about 13.2° until crack arrest irrespective of the crack velocity. These results showed the validation of the CTOA criterion for the high-pressure gas pipelines. The results also showed that CTOA in a burst test is generally different from that in a test using small-scale specimen. Future developments of the experimental procedure using a small-scale specimen to provide CTOA value corresponding with that in a burst test would be effective.

scholarly journals Design And Implementation Of Ls-Pmsg For Small Scale Hydro Power Plant

2018 ◽  
Vol 1 (2) ◽  
Author(s):  
Yusuf Ismail Nakhoda ◽  
Feri Prasetyo Nugroho ◽  
M. Abd. Hamid ◽  
Awan Uji Krismanto ◽  
Eko Yohanes Setiawan
Keyword(s):  
Power Plant ◽  
Permanent Magnet ◽  
Output Voltage ◽  
High Speed ◽  
Synchronous Generator ◽  
Small Scale ◽  
Stable Operation ◽  
Electrical Machine ◽  
Hydro Power ◽  
Low Speed

- In conventional power system, synchronous generator which characterized by high-speed operating condition has been widely implemented. However, those high-speed synchronous machines are not suitable for a power plant powered by renewable energy (RE) due to uncertain feature of renewable resources. To overcome this problem, an electrical machine with low-speed characteristic is required for ensuring stable operation and maintaining output power of the RE based distribution generation (DG) unit. In this paper, a low-speed permanent magnet synchronous generator (LS-PMSG) is designed and implemented. To realize low-speed operation capability, the multi-stages permanent magnet synhcronous machine is proposed. The multi-stages machine equipped with two stators and three rotors construction. From the experimental results, it was monitored that output voltage of single rotor of the designed machine was 35 V. Moreover, to increase the output voltage to 50 V, those three rotors can be connected in series.

Do You Name Speedy Objects Faster Than Slow Objects: SPEEDED NAMING OR NAMING SPEED? THE AUTOMATIC EFFECT OF OBJECT SPEED ON PERFORMANCE

2018 ◽  
Author(s):  
Moshe Shay Ben-Haim ◽  
Eran Chajut ◽  
Ran Hassin ◽  
Daniel Algom
Keyword(s):  
High Speed ◽  
Mental Representations ◽  
Reading Aloud ◽  
Naming Task ◽  
Naming Speed ◽  
Low Speed ◽  
Everyday Objects ◽  
Pictures And Words

we test the hypothesis that naming an object depicted in a picture, and reading aloud an object’s name, are affected by the object’s speed. We contend that the mental representations of everyday objects and situations include their speed, and that the latter influences behavior in instantaneous and systematic ways. An important corollary is that high-speed objects are named faster than low-speed objects despite the fact that object speed is irrelevant to the naming task at hand. The results of a series of 7 studies with pictures and words support these predictions.

scholarly journals Splatters and Aerosols Contamination in Dental Aerosol Generating Procedures

2021 ◽  
Vol 11 (4) ◽  
pp. 1914
Author(s):  
Pingping Han ◽  
Honghui Li ◽  
Laurence J. Walsh ◽  
Sašo Ivanovski
Keyword(s):  
Particle Size ◽  
Disease Transmission ◽  
High Speed ◽  
Low Speed ◽  
Dental Procedures ◽  
Dental Equipment ◽  
Produce Contamination ◽  
Fluorescein Dye ◽  
Filter Papers ◽  
Airborne Disease

Dental aerosol-generating procedures produce a large amount of splatters and aerosols that create a major concern for airborne disease transmission, such as COVID-19. This study established a method to visualise splatter and aerosol contamination by common dental instrumentation, namely ultrasonic scaling, air-water spray, high-speed and low-speed handpieces. Mock dental procedures were performed on a mannequin model, containing teeth in a typodont and a phantom head, using irrigation water containing fluorescein dye as a tracer. Filter papers were placed in 10 different locations to collect splatters and aerosols, at distances ranging from 20 to 120 cm from the source. All four types of dental equipment produced contamination from splatters and aerosols. At 120 cm away from the source, the high-speed handpiece generated the greatest amount and size (656 ± 551 μm) of splatter particles, while the triplex syringe generated the largest amount of aerosols (particle size: 1.73 ± 2.23 μm). Of note, the low-speed handpiece produced the least amount and size (260 ± 142 μm) of splatter particles and the least amount of aerosols (particle size: 4.47 ± 5.92 μm) at 120 cm. All four dental AGPs produce contamination from droplets and aerosols, with different patterns of distribution. This simple model provides a method to test various preventive strategies to reduce risks from splatter and aerosols.

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