Non-linear creep damage model of sandstone under freeze-thaw cycle

To study rock damage characteristics under long-term freeze-thaw cycles and loads,rock freeze-thaw and creep damage factors were defined based on nuclear magnetic resonance porosity and volume strain,respectively.The damage factor is introduced into the basic rheological element,and the non-linear creep damage constitutive model and freeze-thaw rock equation are established to describe non-linear creep characteristics under a constant load.Simultaneously,the creep test of freeze-thaw rock under step loading is performed.Based on the test data,the applicability and accuracy of the creep damage freeze-thaw rock model are analyzed and verified.The results show that freeze-thaw cycles result in continuous rock pore structure damage and deterioration,and nuclear magnetic resonance porosity enhancement.The constant load induces increasing rock plastic deformation,volume,and creep aging damage.As the loading stress increases,the instantaneous rock elastic parameters increase,and the rheological elastic and viscosity parameters decrease.Furthermore,the damage degradation of freeze-thaw cycles weakens the rock viscoplasticity,resulting in a rapid decrease in the viscosity parameter with an increase in freeze-thaw cycles.Generally,the continuous damage of the rock is degraded,and the long-term strength decreases continuously.

Poly(ADP-ribosyl)ation of Apoptosis Antagonizing Transcription Factor Involved in Hydroquinone-Induced DNA Damage Response

The molecular mechanism of DNA damage induced by hydroquinone （HQ） remains unclear. Poly（ADP-ribose） polymerase-1 （PARP-1） usually works as a DNA damage sensor, and hence, it is possible that PARP-1 is involved in the DNA damage response induced by HQ. In TK6 cells treated with HQ, PARP activity as well as the expression of apoptosis antagonizing transcription factor （AATF）, PARP-1, and phosphorylated H2AX （v-H2AX） were maximum at 0.5 h, 6 h, 3 h, and 3 h, respectively. To explore the detailed mechanisms underlying the prompt DNA repair reaction, the above indicators were investigated in PARP-l-silenced cells. PARP activity and expression of AATF and PARP-1 decreased to 36%, 32%, and 33%, respectively, in the cells; however, y-H2AX expression increased to 265%. Co-immunoprecipitation （co-IP） assays were employed to determine whether PARP-1 and AATF formed protein complexes. The interaction between these proteins together with the results from IP assays and confocal microscopy indicated that poly（ADP-ribosyl）ation {PARylation） regulated AATF expression, in conclusion, PARP-1 was involved in the DNA damage repair induced by HQ via increasing the accumulation of AATF through PARylation.

A CONTINUOUS DAMAGE APPROACH TO RELATIONSHIP BETWEEN SIZE REDUCTION AND ENERGY CONSUMPTION DURING ORE COMMINUTION

Based upon the aspect of continuous damaging,the process of ore comminution may be des- cribed as the growth and propagation of the microcracks in the ore grains under external load- ing,and a theoretical expression has been developed on the relationship between the grain size distribution and the total energy consumption during entire ore comminution process.The en- ergy consumed totally may be considered consisting of two portions,i.e.with fresh crack sur- faces growth and with crack propagation.The proposed expression seems to be an advance over previous conventional ones,especially that from the viewpoint of energy distribution.

New Blast Damage Criterion for Damage Prediction

There are several underground mines in India which operate in close proximity to an operating surface mine.Under such scenario,the blast induced stress waves generated due to surface blasting may be a potential source to cause instability of adjoining underground mine structures.Using seismographs,54 blast induced vibration data were recorded at various locations in the roof,floor and pillars of the underground mine at Hingir Rampur mine of Coal India Limited by synchronizing the timing of surface blasting carried at an adjacent Samleshwari opencast mine.Results of this study show that Artificial Neural Network(ANN)has better prediction potential of peak particle velocity(PPV)and damage to adjacent underground structures due to surface blasting as compared to conventional regression methods.In order to assess and predict the impact of surface blasts on underground workings,Blast Damage Factor(BDF)has been evolved.The study shows that site specific charts can predict the blast damage class at an underground location due to surface blasting for known distances and explosive charge per delay.The severe damage in case study mine site took place when peak particle velocity exceeded 162 mm/s and PPV less than 51 mm/s had no probability of damage to underground structures due to surface blasting.

Stability control of gob-side entry retained under the gob with close distance coal seams

In multi-seam mining,the interlayer rock strata between the upper coal seam(UCS)and the lower coal seam(LCS)appear damage and strength weakening after mining the UCS.Ground stability control of the gob-side entry retaining(GER)under the gob with close distance coal seams(CDCS)is faced with difficulties due to little attention to GER under this condition.This paper focuses on surrounding rock stability control and technical parameters design for GER under the gob with CDCS.The floor rock strata damage characteristics after mining the UCS is first evaluated and the damage factor of the interlayer rock strata below the UCS is also determined.Then,a structural mechanics model of GER surrounding rock is set up to obtain the main design parameters of the side-roadway backfill body(SBB)including the maximum and minimum SBB width calculation formula.The optimal SBB width and the water-to-cement ratio of high water quick-setting material(HWQM)to construct the SBB are determined as 1.2 m and 1.5:1.0,respectively.Finally,engineering trial tests of GER are successfully carried out at#5210 track transportation roadway of Xingwu Colliery.Research results can guide GER design under similar mining and geological conditions.

Analytical solutions of stress and displacement in strain softening rock mass around a newly formed cavity

The closed form solutions of the stress and displacement in strain softening rock mass around a newly formed cavity are derived with a three step-wise elasto-plastic model. Hoek-Brown criterion is adopted as the yielding criterion of rock mass. Damage factors are proposed to account for degradation of the material parameters to reflect the degree of strain softening. The surrounding rock mass around the cavity is divided into three regions: elastic region, strain softening region and residual state region. The analytical solutions of stress, strain, displacement and radius of each region are obtained. The effects of the strain softening and shear dilatancy behavior on the results are investigated with parametric studies. The results show that the radii of the residual state region and strain softening region in the surrounding rock mass with higher damage degree are larger. The radii of the residual state region and strain softening region are 1-2 times and 1.5-3 times of the cavity radius, respectively. The radial and tangential stresses decrease with the increase of the damage factor. The displacement of the cavity wall for the case with maximum plastic bulk strain is nearly twice than that with no dilation. Rock mass moves more toward the center for the case with larger damage factor and shear dilation. The area of the plastic region is larger when the damage factors are considered. The displacements in the surrounding rock mass increase with the increase of the damage factors and shear dilation factors. The solutions can be applied to the stability analysis and support design of the underground excavation.

Study on Failure Possibility of Full Containment LNG Storage Tanks with API 581 Risk-based Inspection

The total storage of full containment LNG storage tanks is very huge. Once the tank rupture or leakage, the consequence will be unimaginable. Therefore it is necessary to perform the risk-based inspection （RBI） and evaluation on LNG storage tanks, and the analysis on LNG storage tanks failure possibility is especially important in the RBI. Recently, Risk-based inspection （RBI） technology based on API 581 is gradually adopted and has become a new technology to determine economic feasibility and safety of equipment in petrochemical plants. However, there are limitations of applying API 581 to LNG equipment because of the unique structure of LNG storage tank （the metal inner tank and concrete outer tank）. Therefore, a failure probability calculation model suitable for full containment LNG storage tanks is proposed. The domestic inner tank is usually made of 9%Ni, and its failure possibility can be calculate based on API581; the outer tank is usually made of pre-stressed concrete, and the failure possibility of structure durability can be calculated by the method of fuzzy mathematics ; Then the failure possibility of the inner tank and the outer tank will be comprehensive considered by using cellulose model. Finally, by citing a real example, it also detailedly introduces the application of this proposed calculation model in the failure possibility analysis of full containment LNG storage tanks. This study provides a new approach for the evaluation of failure possibility on full containment LNG storage tanks.

Reliability analysis of k-out-of-n system with load-sharing and failure propagation effect

In complex systems,functional dependency and physical dependency may have a coupling effect.In this paper,the reliability of a k-out-of-n system is analyzed considering load-sharing effect and failure mechanism(FM)propagation.Three types of FMs are considered and an accumulative damage model is proposed to illustrate the system behavior of the k-out-of-n system and the coupling effect between load-sharing effect and FM propagation effect.A combinational algorithm based on Binary decision diagram(BDD)and Monte-Carlo simulation is presented to evaluate the complex system behavior and reliability of the k-out-of-n system.A current stabilizing system that consists of a 3-out-of-6 subsystem with FM propagation effect is presented as a case to illustrate the complex behavior and to verify the applicability of the proposed method.Due to the coupling effect change,the main mechanism and failure mode will be changed,and the system lifetime is shortened.Reasons are analyzed and results show that different sensitivity factors of three different FMs lead to the change of the development rate,thus changing the failure scenario.Neglecting the coupling effect may lead to an incomplete and ineffective measuring and monitoring plan.Design strategies must be adopted to make the FM propagation insensitive to load-sharing effect.

Influence of cyclic dynamic disturbance on damage evolution and zoning effect of coal-rock under local static load constraint

In order to obtain the characteristics of the effects of cyclic impact loading on the damage of coal-rock in the presence of a local static load constraint,the evolution of the damage factor and the fracture rate during the process and incremental cyclic impact on raw coal and briquettes has been studied.Experimental results show that the presence of local static load restraint improves the impact resistance of the coal-rock,and the damage factor of the coal-rock shows obvious zoning characteristics.When the coal-rock is in an elastic state,the partition with a larger static load restraint area has stronger impact resistance,when the coal-rock is in a plastic state,the partition with a larger static load restraint area has a weaker impact resistance.Increasing impulsive cyclic impacts have a higher damage efficiency to coal-rock than constant impulsive cyclic impacts.The difference in rock breaking efficiency between the two cyclic impact methods is mainly reflected in the partition with the largest constrained area.The crack propagation on the coal-rock surface is more consistent with the partition characteristics of the damage factor.When the static load constrained zone is in an elastic state,the static load has an inhibitory effect on the crack growth.When the static load confinement zone is in a plastic state,the cracks mainly propagate in the static load confinement zone,and the constrained zone mainly consists of tensile cracks that grow in the vertical direction,while the cracks in the non-constrained zone mainly grow in an oblique direction.Finally,fracture mechanics was applied to analyze the failure type of the sample.

Dynamic response of gravity dam model with crack and damage detection

Gravity dam is a typical structure that has been frequently used in the fields of water conservancy engineering, and the safety of the structure has received widespread attention recently. Due to earthquakes or other reasons, gravity dams normally have damage such as cracks in practical service. Damage in the structures can alter the structural dynamic behavior and seriously affect structural performance. Maintaining safety and integrity of the gravity dam structures requires a better understanding of dynamic response of structure with damage and associated damage detection method. In order to study thoroughly the dynamic behavior of gravity dam with damage, the sweep vibration responses of the gravity dam with and without damage are investigated. The experimental results show that the peak-peak acceleration responses all increase for the structure is with crack. At the same time, a structural damage detection method, i.e., the local damage factor (LDF) method, is considered in the study of gravity dam damage detection when the dam is subjected to the base excitation. It is shown that the LDF method can be used as a damage index and is capable of evaluating both the presence and relative severity of structural damage, and it can be used as a viable condition assessment and damage identification technique to detect and quantify the damage in the gravity dam.

The damage evolution behavior of polypropylene fiber reinforced concrete subjected to sulfate attack based on acoustic emission

To study the damage evolution behavior of polypropylene fiber reinforced concrete(PFRC)subjected to sulfate attack,a uniaxial compression test was carried out based on acoustic emission(AE).The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model.The changes to AE ringing counts during the compression could be divided into compaction,elastic,and AE signal hyperactivity stages.In the initial stage of sulfate attack,the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect,and this corresponded with detection of few AE signals and with concrete compression strength enhancement.With increasing sulfate attack time,AE activity decreased.The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete.PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber.After 150 d of sulfate attack,the cumulative AE ringing counts of plain concrete went down by about an order of magnitude,while that for PFRC remained at a high level.The initial damage factor of hybrid PFRC was-0.042 and-0.056 respectively after 150 d of corrosion,indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC.Based on a deterioration equation,the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles,which was 40%longer than that of plain concrete.

ACIDIC FIBROBLAST GROWTH FACTOR REDUCES RAT SKELETAL MUSCLE DAMAGE CAUSED BY ISCHEMIA AND REPERFUSION

Acute interruption of arterial blood flow to the extremities is often associated with significant morbidity and mortality. Broad spectrum mitogenic and non mitogenic activities of FGFs inspired us to study its protecting effects on tissue injuries in ischemia reperfusion condition. We found that systemic administration of aFGF after reperfusion onset prevented severe skeletal muscle injuries. In rats treated with aKGF, the tissue edema was reduced significantly, the tissue viability was increased, and the muscle fibers contained more succinate dehydrogenase (SDH) and adenosine triphosphatasc (ATPase). The pathological results supported the concept of improved prevention with aFGF treatment. The possible tissue protection by aFGF may come from its ability to regulate the concentration of evtra- and intracellular calcium ion. Besides, it may moderate other Ca2+ dependent enzyme conversion processes. Also, it may take part in the vascular tone regulation under ischemia and reperfusion conditions. These results suggest further study of tissue ischemia prevention with FGF and its possible mechanisms in the future.

Mechanical behavior of salt rocks: A geomechanical model

The geomechanical behavior of salt rocks is a significant concern during drilling and development operations in some hydrocarbon reservoirs and underground gas storage sites.In this study,the static and dynamic salt rock geomechanical properties from a field in southwest Iran were evaluated using experiments such as waves'velocities,and thermo-mechanical coupled uniaxial and triaxial compression tests.As a result and by considering both the petrophysical well logs and laboratory data of the waves’velocities,it is observed that the elastic properties of the core samples are concentrated within a narrow range unless an abnormality causes scatter.The results of uniaxial compression tests showed that rock strength decreases with increasing temperature linearly.In addition,the reduction of rock strength was observed with increasing porosity of the core samples as expected.In the case of triaxial compression tests,applying confining pressure on the core sample caused an increment in rock strength,while temperature decreased rock strength.The temperature also increased cohesion and decreases friction angle.The ratio of changes in stress to strain was used to investigate the dynamic changes in the geomechanical state.The maximum 0.25 damage factor was observed for the core samples for different definitions of the damage factor.Finally,we propose a novel analytical model to predict the stress-strain behavior of salt rocks at different conditions.The model was validated using experimental results and indicated a satisfactory accuracy.