This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure...This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure characteristics and phase composition were analyzed,and the influence of particle size ratios on dynamic mechanical behavior and damage mechanism were investigated.The prepared sample with a=0.1 exhibited continuous wrapping of the Hf phase by the Al phase.Hf—Hf contact(continuous Hf phase)within the sample gradually increased with increasing a,and a small amount of fine Hf appeared for the sample with a=1.The reactive materials exhibited clear strain-rate sensitivity,with flow stressσ0.05and failure strainεfincreasing approximately linearly with increasing strain rate.ε.It is found that the plastic deformation of the material increased with increasing strain rate.As a increased from 0.1 to 1,the flow stress gradually increased.Impact failure of the material was dominated by ductile fracture with a large Al phase plastic deformation band for lower a,while brittle fracture with crushed Hf particles occurred at higher a.Finally,a constitutive model based on BP neural network was proposed to describe the stress-strain relationships of the materials,with an average relative error of 2.22%.展开更多
In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specime...In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.展开更多
Understanding the stress-strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time.Previous investigations of this topic were mainly focused on ...Understanding the stress-strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time.Previous investigations of this topic were mainly focused on experimental tests;however,theoretical approaches were rarely reported.Based on this,this paper focuses on the contact fracture at closing stage when rock is uniaxially loaded,and then a theoretical model is proposed.Based on the change of fracture elasticity modulus,it shows that as crack apertures are gradually reduced in the loading process,the permeability of rock sample will decrease progressively.This scenario shows that theoretical computation matches well with the experimental results.Finally,the effects of ratio of sample size to fracture aperture(n).pore pressure(P),and initial aperture(b) on stress-strain relationship and permeability change for contact compression fracture at closing stage are analyzed.展开更多
Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out o...Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out on several systems under various test setups.Al is chosen as it is extruded and adheres to well defined shape tolerances and elastic properties.A robust method,using the Savitzky-Golay filter,is introduced to identify significant slope changes in the stressestrain curve.Since the load in the test system is well defined,the recorded deformation is corrected to the expected value of Al resulting in a system-compliance factor.The results across the testing systems and test setups showed significant variance,with the recorded E always lower than the anticipated EAl.The number of components within the system over which the deformation is measured had the most significant impact,lowering the expected E by up to 50%.Additionally,the system-compliance factor is inconsistent across different systems and setups.Thus,it is evidently proved that each setup must be separately evaluated for its system-compliance and that no single value exists across systems and setups.The findings are then projected onto a series of uniaxial compressive strength(UCS)tests carried out on Stanstead granite(SS GR)samples.The corrected Et50 and Eavg values for system-compliance of the samples are within1%for each system as opposed to being50%pre-correction.The findings conclude that it is deemed necessary and of utmost importance that the deformation be corrected to accommodate the systemcompliance to obtain reliable results.展开更多
Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showe...Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height(W/H) ratio of coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. The shear failure along the interface triggered the compressive failure in coal. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. Hence, with a proper combination of interface friction and the W/H ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure which is brittle failure to non-violent failure which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of W/H ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.1 and 0.25, and the results are presented and discussed.展开更多
基金funded by the National Natural Science Foundation of China(Grant No.12302437)China Postdoctoral Science Foundation(Grant No.2021M701710)。
文摘This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure characteristics and phase composition were analyzed,and the influence of particle size ratios on dynamic mechanical behavior and damage mechanism were investigated.The prepared sample with a=0.1 exhibited continuous wrapping of the Hf phase by the Al phase.Hf—Hf contact(continuous Hf phase)within the sample gradually increased with increasing a,and a small amount of fine Hf appeared for the sample with a=1.The reactive materials exhibited clear strain-rate sensitivity,with flow stressσ0.05and failure strainεfincreasing approximately linearly with increasing strain rate.ε.It is found that the plastic deformation of the material increased with increasing strain rate.As a increased from 0.1 to 1,the flow stress gradually increased.Impact failure of the material was dominated by ductile fracture with a large Al phase plastic deformation band for lower a,while brittle fracture with crushed Hf particles occurred at higher a.Finally,a constitutive model based on BP neural network was proposed to describe the stress-strain relationships of the materials,with an average relative error of 2.22%.
基金support provided by the Strategic Program of Chinese Academy of Sciences (Grant No. XDB10030400)the Hundred Talent Program of Chinese Academy of Sciences (Grant No. Y323081C01)
文摘In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.
基金the National Natural Science Foundation of China(Grant Nos.51374215,11572343,51622404)Beijing Major Scientific and Technological Achievements into Ground Cultivation Project(Grant No.Z151100002815004)+2 种基金Fok Ying Tung Education Foundation(Grant No.142018)the State Key Research Development Program of China(Grant No.2016YFC0801404)Outstanding Young Talents of"Ten Thousand People Plan"
文摘Understanding the stress-strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time.Previous investigations of this topic were mainly focused on experimental tests;however,theoretical approaches were rarely reported.Based on this,this paper focuses on the contact fracture at closing stage when rock is uniaxially loaded,and then a theoretical model is proposed.Based on the change of fracture elasticity modulus,it shows that as crack apertures are gradually reduced in the loading process,the permeability of rock sample will decrease progressively.This scenario shows that theoretical computation matches well with the experimental results.Finally,the effects of ratio of sample size to fracture aperture(n).pore pressure(P),and initial aperture(b) on stress-strain relationship and permeability change for contact compression fracture at closing stage are analyzed.
基金This work has been supported through the Natural Sciences and Engineering Research Council of Canada(NSERC)PGS D3-518886,NSERC Discovery Grants 341275
文摘Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out on several systems under various test setups.Al is chosen as it is extruded and adheres to well defined shape tolerances and elastic properties.A robust method,using the Savitzky-Golay filter,is introduced to identify significant slope changes in the stressestrain curve.Since the load in the test system is well defined,the recorded deformation is corrected to the expected value of Al resulting in a system-compliance factor.The results across the testing systems and test setups showed significant variance,with the recorded E always lower than the anticipated EAl.The number of components within the system over which the deformation is measured had the most significant impact,lowering the expected E by up to 50%.Additionally,the system-compliance factor is inconsistent across different systems and setups.Thus,it is evidently proved that each setup must be separately evaluated for its system-compliance and that no single value exists across systems and setups.The findings are then projected onto a series of uniaxial compressive strength(UCS)tests carried out on Stanstead granite(SS GR)samples.The corrected Et50 and Eavg values for system-compliance of the samples are within1%for each system as opposed to being50%pre-correction.The findings conclude that it is deemed necessary and of utmost importance that the deformation be corrected to accommodate the systemcompliance to obtain reliable results.
基金sponsored by Coal and Energy Research Bureau and CDC-NIOSH under Grant No.R01OH009532
文摘Bumps in coal mines have been recognized as a major hazard for many years. These sudden and violent failures around mine openings have compromised safety, ventilation and access to mine workings.Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height(W/H) ratio of coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. The shear failure along the interface triggered the compressive failure in coal. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. Hence, with a proper combination of interface friction and the W/H ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure which is brittle failure to non-violent failure which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of W/H ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.1 and 0.25, and the results are presented and discussed.
