Dynamic Simulation of Crack Propagation with Dislocation Emission and Migration

1995 ◽  
Vol 408 ◽  
Author(s):  
N. Zacharopoulos ◽  
D. J. Rolovitz ◽  
R. A. Lesar
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Dynamic Simulation ◽  
Loading Rate ◽  
High Loading ◽  
Spatial Evolution ◽  
Dislocation Emission ◽  
Loading Rates ◽  
Simulation Procedure ◽  
And Migration

AbstractWe present a simulation procedure for fracture that self-consistently accounts for dislocation emission, dislocation migration and crack growth. We find that the dislocation microstructure in front of the crack tip is highly organized and shows a complex temporal-spatial evolution. The final dislocation microstructure and the number of emitted dislocations immediately proceeding fracture varies rapidly with the loading rate. For high loading rates, fracture occurs at smaller loads with increasing loading rate. However, the load at fracture shows a maximum with respect to loading rates.

Dynamic Simulation Of Crack Propagation With Dislocation Emission And Migration

1995 ◽  
Vol 409 ◽  
Author(s):  
N. Zacharopoulos ◽  
D.J. Srolovitz ◽  
R.A. LeSAR
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Dynamic Simulation ◽  
Loading Rate ◽  
High Loading ◽  
Spatial Evolution ◽  
Dislocation Emission ◽  
Loading Rates ◽  
Simulation Procedure ◽  
And Migration

AbstractWe present a simulation procedure for fracture that self-consistently accounts for dislocation emission, dislocation migration and crack growth. We find that the dislocation microstructure in front of the crack tip is highly organized and shows a complex temporal-spatial evolution. The final dislocation microstructure and the number of emitted dislocations immediately proceeding fracture varies rapidly with the loading rate. For high loading rates, fracture occurs at smaller loads with increasing loading rate. However, the load at fracture shows a maximum with respect to loading rates.

Dairy Waste Treatment with Anaerobic Stationary Fixed Film Reactors

1983 ◽  
Vol 15 (8-9) ◽  
pp. 359-368 ◽  
Author(s):  
L van den Berg ◽  
K J Kennedy
Keyword(s):  
Cheese Whey ◽  
Loading Rate ◽  
Cod Removal ◽  
High Loading ◽  
Loading Rates ◽  
Dairy Wastes ◽  
Plant Waste ◽  
Fixed Film ◽  
Dairy Plant ◽  
Removal Efficiencies

Cheese whey and a dilute waste from a cheese factory with a Chemical Oxygen Demand of 66,000 and 4,000 mg (COD)/L respectively, were treated at high loading rates in 0.7 to 1.2 L downflow anaerobic stationary fixed film reactors and an upflow sludge bed reactor. In downflow stationary fixed film reactors treating cheese whey, COD removal efficiencies of 97% were achieved at a loading rate of 5 kg COD/m3/day and 92% at a maximum loading rate of 22 kg COD/m3/day. With dairy plant waste, loading rates of up to 15 kg COD/m3/day were possible with COD removal efficiencies averaging 75%, decreasing slightly with increasing loading rates. In an upflow sludge bed reactor the COD removal efficiency of dairy plant waste, decreased from 87% at 5 kg COD/m3/day to 73% at 15 kg COD/m3/day. A stationary fixed film reactor treating a skim milk powder waste (4,000 ppm) could only be operated at up to 10 kg COD/m3/day with a treatment efficiency of 72%. Methane was produced from all wastes at rates corresponding to 0.32 m3 CH4 (0°C, 1 atm) per kg COD removed. Results show that stationary fixed film reactors are capable of treating dairy wastes at high loading rates and high COD removal efficiencies.

Loading Rate Effect Investigation of Through-Hole-Mounted Solder Joints

2005 ◽  
Author(s):  
Frank Z. Liang ◽  
Larry M. Palanuk ◽  
Mike Gabriel
Keyword(s):  
Solder Joint ◽  
High Speed ◽  
Loading Rate ◽  
High Loading ◽  
Static Tests ◽  
Loading Rates ◽  
Wide Range ◽  
Load To Failure ◽  
The Impact ◽  
Through Hole

This paper presents two simple and unique tests to extract shock-level loading limits for eutectic and lead free solders. A wide range of loading rates, from quasi-static to high speed, was applied to a through-hole-mounted anchor assembly test coupon. The high speed shock tests were conducted on a drop shock table where the impacting velocities were derived through table input adjustments. The quasi-static tests were done using controlled hydraulic linear actuator with a load cell. As would be assumed, the dynamic load to cause solder joint failure was found to increase with higher loading rate. However, at such a high loading rate range, the impact velocity did not change the load to failure. This study leads to an interesting hypothesis that at high loading rates, the solder joint strain rate may not see a significant change as observed at low rates.

scholarly journals Methane conversion efficiency as a simple control parameter for an anaerobic digester at high loading rates

2011 ◽  
Vol 64 (2) ◽  
pp. 534-540 ◽  
Author(s):  
W. Charles ◽  
N. P. Carnaje ◽  
R. Cord-Ruwisch
Keyword(s):  
Anaerobic Digestion ◽  
Production Rate ◽  
Conversion Efficiency ◽  
Methane Conversion ◽  
Control Parameter ◽  
Loading Rate ◽  
High Loading ◽  
Loading Rates ◽  
Ch4 Production ◽  
On Line

The anaerobic digestion process is globally applied to the treatment of highly concentrated wastes such as industrial and rural effluents, and sewage sludge. However, it is known to be relatively unstable. When loaded with high concentrations of organic material, unwanted volatile fatty acids (VFA) are often produced rather than methane (CH4) gas which can lead to digester acidification and failure. This study investigated digester behaviour under high loading rates, testing the usefulness of stoichiometric methane conversion efficiency as a digester control parameter at high loading rates. Our results show that, in general, the CH4 production rate was proportional to the feed rate (loading rate). However, at very high loading rates, the CH4 production rate was not proportional to the increase in the feeding rate. Consequently, VFA accumulated and the H2 partial pressure increased. The proportionality of the loading rate and gas production rate is stoichiometrically expressed as the conversion efficiency. We found that conversion efficiency was a useful indicator as an early warning of digester imbalance. The digester remained stable at conversion efficiencies above 75%. Dropping below 70% signified the onset of digester failure. As loading rate and methane production data are readily available on-line in most anaerobic digestion plants, the conversion efficiency can be monitored on-line and used as an efficient control technique to maintain safe operation of anaerobic digesters at high loading rates.

scholarly journals The Effect of High Loading Rate on the Behaviour and Mechanical Properties of Coal-Rock Combined Body

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Fengqiang Gong ◽  
Hao Ye ◽  
Yong Luo
Keyword(s):  
Incident Energy ◽  
Loading Rate ◽  
Peak Stress ◽  
High Loading ◽  
Peak Strain ◽  
Rate Range ◽  
Loading Rates ◽  
High Loading Rate ◽  
Coal Rock ◽  
Second Peak

In order to investigate the high loading rate effect on the behaviour and mechanical properties of coal-rock combined body, the dynamic compressive tests were conducted by using the Split-Hopkinson Pressure Bar (SHPB) device under the loading rate range from 2.7×105 MPa/s to 4.0×105 MPa/s. The stress-strain curves, dynamic peak stress and strain, elastic modulus, and energy distribution law of coal-rock combined body under different loading rates were analyzed and discussed. The results show that the dynamic stress-strain curves of coal-rock combined body have a double-peak feature under high loading rate range, which can be divided into the initial bearing stage, the bearing decline stage, the bearing enhance stage, and the unstable stage. The first peak stress of the coal-rock combined body is independent of the loading rate, while the dynamic compressive strength (the second peak stress) and dynamic peak strain (the second peak strain) have a strong loading rate effect and will generally increase linearly with the loading rate. The first and second elastic moduli of coal-rock combined body are not sensitive to the loading rate. With the increase of the loading rate, the incident energy and reflective energy of coal-rock combined body increase rapidly, while the change of transmitted energy is very small. The absorption energy ratio of the coal-rock combined body shows a good linear law with the incident energy under different loading rates.

scholarly journals Crack propagation and fracture resistance in saline ice

1994 ◽  
Vol 40 (136) ◽  
pp. 451-462 ◽  
Author(s):  
Samuel J. DeFranco ◽  
John P. Dempsey
Keyword(s):  
Sea Ice ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Loading Rate ◽  
Stable Crack Growth ◽  
Fracture Geometry ◽  
Water Ice ◽  
Two Temperatures ◽  
Resistance Curves

AbstractCrack propagation in saline ice (a model sea ice) is investigated in this study in an attempt to understand the processes of crack growth at one loading rate and two temperatures. As has been previously observed in cold sea ice and warm or cold fresh-water ice, crack growth occurs in initiation/arrest increments. The energetic stability criteria of crack growth are examined in saline ice and crack growth is characterized in terms of the fracture-resistance parameterKR. This paper offers the development of a new fracture geometry capable of sustained stable crack growth and the presentation of fracture-resistance curves for saline ice at −25° and −15 C. The important findings of this paper are that: (i) in warm saline ice, extensive local crack-tip damage is accompanied by a limited amount of slow, stable crack extension; (n) fracture in cold saline ice is characterized by locally negativeKRbehavior; and (iii) fracture in cold or warm saline ice is characterized by globally positiveKRcurve behavior.

Dynamic Crack Propagation Behavior of the Mg-Li Alloys under High-Speed Impact Loading

2005 ◽  
Vol 488-489 ◽  
pp. 717-720 ◽  
Author(s):  
Gui Ying Sha ◽  
Yong Bo Xu ◽  
En Hou Han
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Loading Rate ◽  
High Loading ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Hopkinson Pressure Bar ◽  
Propagation Behavior ◽  
High Loading Rate ◽  
Crack Propagation Behavior

The dynamic experiments for the Mg-Li alloys with single phase structure were carried out using the Hopkinson pressure bar. The dynamic crack propagation behavior and fracture mechanism of the alloys were investigated. The results show that the dynamic crack propagation is a deceleration process for the Mg-Li alloys under high loading rate. The fastest crack propagation velocity for Mg-3.3Li alloy is m/s 37 . 1253 , and 935.36m/s for Mg-14Li alloy. Observations of the fracture by SEM reveal that the dynamic fracture surface for Mg-3.3Li alloy mainly appears to be brittle fracture along grain boundaries. Whereas, the Mg-14Li alloy is ductile fracture mode under high loading rate. The main reason for these may be the transformation of hcp→bcc structure and the precipitation of the MgLi2Al and AlLi, as increase of Li in Mg-Li alloy.

The characteristics of high speed crack propagation at ultra high loading rate

2020 ◽  
Vol 108 ◽  
pp. 102650 ◽  
Author(s):  
Mao Zhou ◽  
Yongqiang Li ◽  
Wu Jiankui ◽  
Yin Yu ◽  
Hongliang He
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Loading Rate ◽  
High Loading ◽  
High Loading Rate

scholarly journals Crack propagation and fracture resistance in saline ice

1994 ◽  
Vol 40 (136) ◽  
pp. 451-462 ◽  
Author(s):  
Samuel J. DeFranco ◽  
John P. Dempsey
Keyword(s):  
Sea Ice ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Loading Rate ◽  
Stable Crack Growth ◽  
Fracture Geometry ◽  
Water Ice ◽  
Two Temperatures ◽  
Resistance Curves

AbstractCrack propagation in saline ice (a model sea ice) is investigated in this study in an attempt to understand the processes of crack growth at one loading rate and two temperatures. As has been previously observed in cold sea ice and warm or cold fresh-water ice, crack growth occurs in initiation/arrest increments. The energetic stability criteria of crack growth are examined in saline ice and crack growth is characterized in terms of the fracture-resistance parameterKR. This paper offers the development of a new fracture geometry capable of sustained stable crack growth and the presentation of fracture-resistance curves for saline ice at −25° and −15 C. The important findings of this paper are that: (i) in warm saline ice, extensive local crack-tip damage is accompanied by a limited amount of slow, stable crack extension; (n) fracture in cold saline ice is characterized by locally negativeKRbehavior; and (iii) fracture in cold or warm saline ice is characterized by globally positiveKRcurve behavior.

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