This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strengt...This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock.Regardless of three-point-bending,four-point-bending,or a combination of the above two specimen types,fracture toughness KICand tensile strength ftof rock were determined using only two sets of specimens with ae,max:ae,min≥3:1.The values KICand ftwere consistent with those determined using multiple sets of specimens.The full structural failure curve constructed by two sets of small-size specimens with ae,max:ae,min≥3:1 can accurately predict large-size specimens fracture failure,and±10%upper and lower limits of the curve can encompass the test results of large-size specimens.The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min≥3:1,and±15%upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data.The model and method proposed in this paper require only two sets of small-size specimens,and their selection is unaffected by the specimen type,geometry,and initial crack length.展开更多
In this paper, a comparative study on the fracture toughness of woven glass fibre reinforced polypropylene, chopped glass fibre reinforced polypropylene and nanoclay filled polypropylene composites is presented. Nanoc...In this paper, a comparative study on the fracture toughness of woven glass fibre reinforced polypropylene, chopped glass fibre reinforced polypropylene and nanoclay filled polypropylene composites is presented. Nanoclays (Cloisite 15A) of 1 wt. % to 5 wt. % were filled in polypropylene (PP) matrix and they were subjected to fracture toughness stu-dies. The specimen with 5 wt. % nanoclay showed 1.75 times and 3 times improvement in critical stress intensity factor (KIC) and strain energy release rate (GIC), respectively, over virgin PP. On the other hand, 3 wt. % nanoclay PP composites showed superior crack containment properties. These structural changes of composite specimens were examined using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) methods. It showed that exfoli-ated nanocomposite structures were formed up to 3 wt. % nanoclay, whereas, intercalated nanocomposite structures formed above 3 wt. % nanoclay in the PP matrix. Furthermore, the woven fibre reinforced PP composites demonstrated superior crack resistant properties than that of clay filled nanocomposites and chopped fibre PP composites. However, KIC and GIC values for woven fibre composites were lesser than that of chopped fibre composites. Moreover, KIC and GIC values for both nanoclay filled PP composites and woven fibre composites are comparable even though the clay filled PP demonstrated catastrophic failure. Also, the crack propagation rate of PP-nanoclay composites is comparable to that of chopped fibre composites.展开更多
The method to detect the crack initiation point of Charpy pre-cracked specimen under dy- namie loading was studied using strain gauge.The load-time curve and nominal strain-time curve at the crack tip for impact testi...The method to detect the crack initiation point of Charpy pre-cracked specimen under dy- namie loading was studied using strain gauge.The load-time curve and nominal strain-time curve at the crack tip for impact testing specinens may be shnultaneously measured by twin-channel oscilloscope with high speed sampling and diskette storing.Based on the dynam- ic finite element simulation of impact response of Charpy specimen,the measuring method of dynamic fracture toughness was analysed and some problems in previous dynamic fracture toughness measurement were discussed.展开更多
In part Ⅰ and Ⅱ of this series, experimental investigation in both EPFM and LEFM had been discussed. In this part, further theoretical analysis is given. The theoretical development of Two Parameter Fracture Mechani...In part Ⅰ and Ⅱ of this series, experimental investigation in both EPFM and LEFM had been discussed. In this part, further theoretical analysis is given. The theoretical development of Two Parameter Fracture Mechanics by Hancock etc, has rationalized our experimental results. This method can be applied to engineering practice, and will allow the advantage of enhanced toughness for specimens with low levels of constraint to be taken into account for defect assessment.展开更多
In this experimental study, chromium oxide powder was sprayed on a low-carbon steel substrate using the atmospheric plasma spray process. The current and standoff distances(SODs) were varied to study their effect on t...In this experimental study, chromium oxide powder was sprayed on a low-carbon steel substrate using the atmospheric plasma spray process. The current and standoff distances(SODs) were varied to study their effect on the fracture toughness of the coatings. Theoretically, as the arc current increases, the melting of the ceramic oxide should increase and this in turn should lead to the formation of a dense coating. However,it was observed that if the arc power is too high and because the particle size of the powder is small(approximately 30 μm), the particles tend to fly away from the plasma core. Similarly, an appropriate SOD should provide the particles with more melting time, thus resulting in a dense coating. On the other hand, a larger SOD leads to the solidification of the molten particles before the droplets can reach the substrate. All these effects may lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate the plasma spraying parameters and microstructure of the coating with the fracture toughness and other primary coating properties.展开更多
The embedded atom potentials for binary Ti V were developed and used to predict the mechanical properties of binary Ti V solid solutions with hcp and bcc structures including lattice parameters, elastic constants and ...The embedded atom potentials for binary Ti V were developed and used to predict the mechanical properties of binary Ti V solid solutions with hcp and bcc structures including lattice parameters, elastic constants and fracture toughness for Mode Ⅰ fracture under plane strain. The calculation results show that with the increment of V content, the lattice parameters and elastic constants decrease but the fracture toughness increases for hcp solid solutions, the lattice parameters decrease but the elastic constants and fracture toughness increase for bcc solid solutions. The calculation results agree well with the available experiment values. [展开更多
Cortical bone is semi-brittle and anisotropic,that brings a challenge to suppress vibration and avoid undesired fracture in precise cutting process in surgeries.In this paper,a novel analytical model is proposed to re...Cortical bone is semi-brittle and anisotropic,that brings a challenge to suppress vibration and avoid undesired fracture in precise cutting process in surgeries.In this paper,a novel analytical model is proposed to represent cortical bone cutting processes.The model is utilized to predict the chip formations,material removal behavior and cracks propagation under varying bone osteon cutting angles and depths.Series of orthogonal cutting experiments were conducted on cortical bone to investigate the impact of bone osteon cutting angle and depth of cut on cutting force,crack initialization and propagation.The observed chip morphology highly agreed with the prediction of chip formation based on the analytical model.The curly,serrated,grainy and powdery chips formed when the cutting angle was set as 0°,60°,90°,and 120°,respectively.Cortical bone were removed dominantly by shearing at a small depth of cut from 10 to 50μm,and by a mixture of pealing,shearing,fracture and crushing at a large depth of cut over 100μm at different bone osteon angles.Moreover,its fracture toughness was calculated based on measured cutting force.It is found that the fluctuation of cutting force is suppressed and the bone material becomes easy to remove,which attributes to lower fracture toughness at bone osteon cutting angle 0°.When the cutting direction develops a certain angle to bone osteon,the fracture toughness increases then the crack propagation is inhibited to some extent and the fluctuation of cutting force comparatively decreases.There is a theoretical and practical significance for tools design and operational parameters choice in surgeries.展开更多
Damage tolerance of titanium alloy structures is very important for the safety of modern aircraft under complex loading and environmental conditions. However, there is no available systematic knowledge about the effec...Damage tolerance of titanium alloy structures is very important for the safety of modern aircraft under complex loading and environmental conditions. However, there is no available systematic knowledge about the effect of alloy thickness under mixed-mode loading at elevated temperatures. In the present study, a newly developed fracture experimental technique based on high-temperature moiré interferometry was employed to investigate experimentally I-II mixed-mode fracture in titanium alloy TC11 of various thicknesses at room and elevated temperatures. Compact shear specimens with thickness ranging from 1.8 to 7.1 mm were tested. The effects of temperature, thickness, and loading angle on the load capacity and crack initiation angle were investigated systematically. The TC11 alloy was shown to possess varied fracture performance at elevated tem-perature, and an opposite thickness effect at room temperature. Increasing temperature would enhance the fracture load capacity of thick specimens but reduce the fracture load capacity of thin specimens. Crack initiation angles under I-II mixed-mode loading showed the thickness-temperature coupling effects. These complex effects call for new development in three-dimensional mixed-mode fracture theory and technologies for damage tolerance assessment.展开更多
In this paper, the location parameter δ_(a) in Weibull distribution i.e. the lower limiting CTOD toughness of high strength steel weldments is evaluated from Gleeble simulated coarse grained specimens. The Charpy-V t...In this paper, the location parameter δ_(a) in Weibull distribution i.e. the lower limiting CTOD toughness of high strength steel weldments is evaluated from Gleeble simulated coarse grained specimens. The Charpy-V transition temperature obtained from these specimens is transformed to a fracture toughness K_(IC) value at a given temperature using Sanz' relation. Then, the location parameter a is δ_(a) evaluated. The predicted location parameter arrives at agreement with the lowest CTOD value as obtained from thick multilayer weldments. The improvement of the fracture toughness of multilayer weldments needs the increase of the lowering limiting CTOD.toughness i.e. the toughness of the coarse grained zone.展开更多
Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated ...Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.展开更多
基金supported by National Natural Science Foundation of China(No.52179132)Program for Science&Technology Innovation Talents in Universities of Henan province(No.20HASTIT013)Sichuan University,State Key Lab Hydraul&Mt River Engn(No.SKHL2007)。
文摘This paper develops a model that only requires two sets of small-size rock specimens with the ratio of the structural geometry parameter maximum to minimum ae,max:ae,min≥3:1 to determine the rock fracture and strength parameters without size effect and predict the actual structural performance of rock.Regardless of three-point-bending,four-point-bending,or a combination of the above two specimen types,fracture toughness KICand tensile strength ftof rock were determined using only two sets of specimens with ae,max:ae,min≥3:1.The values KICand ftwere consistent with those determined using multiple sets of specimens.The full structural failure curve constructed by two sets of small-size specimens with ae,max:ae,min≥3:1 can accurately predict large-size specimens fracture failure,and±10%upper and lower limits of the curve can encompass the test results of large-size specimens.The peak load prediction curve was constructed by two sets of specimens with ae,max:ae,min≥3:1,and±15%upper and lower limits of the peak load prediction curve can cover the small-size specimen tests data.The model and method proposed in this paper require only two sets of small-size specimens,and their selection is unaffected by the specimen type,geometry,and initial crack length.
文摘In this paper, a comparative study on the fracture toughness of woven glass fibre reinforced polypropylene, chopped glass fibre reinforced polypropylene and nanoclay filled polypropylene composites is presented. Nanoclays (Cloisite 15A) of 1 wt. % to 5 wt. % were filled in polypropylene (PP) matrix and they were subjected to fracture toughness stu-dies. The specimen with 5 wt. % nanoclay showed 1.75 times and 3 times improvement in critical stress intensity factor (KIC) and strain energy release rate (GIC), respectively, over virgin PP. On the other hand, 3 wt. % nanoclay PP composites showed superior crack containment properties. These structural changes of composite specimens were examined using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) methods. It showed that exfoli-ated nanocomposite structures were formed up to 3 wt. % nanoclay, whereas, intercalated nanocomposite structures formed above 3 wt. % nanoclay in the PP matrix. Furthermore, the woven fibre reinforced PP composites demonstrated superior crack resistant properties than that of clay filled nanocomposites and chopped fibre PP composites. However, KIC and GIC values for woven fibre composites were lesser than that of chopped fibre composites. Moreover, KIC and GIC values for both nanoclay filled PP composites and woven fibre composites are comparable even though the clay filled PP demonstrated catastrophic failure. Also, the crack propagation rate of PP-nanoclay composites is comparable to that of chopped fibre composites.
文摘The method to detect the crack initiation point of Charpy pre-cracked specimen under dy- namie loading was studied using strain gauge.The load-time curve and nominal strain-time curve at the crack tip for impact testing specinens may be shnultaneously measured by twin-channel oscilloscope with high speed sampling and diskette storing.Based on the dynam- ic finite element simulation of impact response of Charpy specimen,the measuring method of dynamic fracture toughness was analysed and some problems in previous dynamic fracture toughness measurement were discussed.
文摘In part Ⅰ and Ⅱ of this series, experimental investigation in both EPFM and LEFM had been discussed. In this part, further theoretical analysis is given. The theoretical development of Two Parameter Fracture Mechanics by Hancock etc, has rationalized our experimental results. This method can be applied to engineering practice, and will allow the advantage of enhanced toughness for specimens with low levels of constraint to be taken into account for defect assessment.
文摘In this experimental study, chromium oxide powder was sprayed on a low-carbon steel substrate using the atmospheric plasma spray process. The current and standoff distances(SODs) were varied to study their effect on the fracture toughness of the coatings. Theoretically, as the arc current increases, the melting of the ceramic oxide should increase and this in turn should lead to the formation of a dense coating. However,it was observed that if the arc power is too high and because the particle size of the powder is small(approximately 30 μm), the particles tend to fly away from the plasma core. Similarly, an appropriate SOD should provide the particles with more melting time, thus resulting in a dense coating. On the other hand, a larger SOD leads to the solidification of the molten particles before the droplets can reach the substrate. All these effects may lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate the plasma spraying parameters and microstructure of the coating with the fracture toughness and other primary coating properties.
文摘The embedded atom potentials for binary Ti V were developed and used to predict the mechanical properties of binary Ti V solid solutions with hcp and bcc structures including lattice parameters, elastic constants and fracture toughness for Mode Ⅰ fracture under plane strain. The calculation results show that with the increment of V content, the lattice parameters and elastic constants decrease but the fracture toughness increases for hcp solid solutions, the lattice parameters decrease but the elastic constants and fracture toughness increase for bcc solid solutions. The calculation results agree well with the available experiment values. [
基金China Scholarship Council,the National Natural Science Foundation of China(Grant No.52075161)Hunan Provincial Natural Science Foundation of China(Grant No.2022JJ40486)Changsha Municipal Natural Science Foundation of China(Grant No.2022cskj017).
文摘Cortical bone is semi-brittle and anisotropic,that brings a challenge to suppress vibration and avoid undesired fracture in precise cutting process in surgeries.In this paper,a novel analytical model is proposed to represent cortical bone cutting processes.The model is utilized to predict the chip formations,material removal behavior and cracks propagation under varying bone osteon cutting angles and depths.Series of orthogonal cutting experiments were conducted on cortical bone to investigate the impact of bone osteon cutting angle and depth of cut on cutting force,crack initialization and propagation.The observed chip morphology highly agreed with the prediction of chip formation based on the analytical model.The curly,serrated,grainy and powdery chips formed when the cutting angle was set as 0°,60°,90°,and 120°,respectively.Cortical bone were removed dominantly by shearing at a small depth of cut from 10 to 50μm,and by a mixture of pealing,shearing,fracture and crushing at a large depth of cut over 100μm at different bone osteon angles.Moreover,its fracture toughness was calculated based on measured cutting force.It is found that the fluctuation of cutting force is suppressed and the bone material becomes easy to remove,which attributes to lower fracture toughness at bone osteon cutting angle 0°.When the cutting direction develops a certain angle to bone osteon,the fracture toughness increases then the crack propagation is inhibited to some extent and the fluctuation of cutting force comparatively decreases.There is a theoretical and practical significance for tools design and operational parameters choice in surgeries.
基金Project supported by the National Natural Science Foundation of China (Nos. 51309073 and 51309203), the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20131317120012), and the Open Research Fund Program of State Key Laboratory of Hydroscience and Engineering (No. sklhse-2014-C-02), China
基金supported by the Natural Science Foundation of Jiangxi Province of China (Grant No. 2009GZW0022)
文摘Damage tolerance of titanium alloy structures is very important for the safety of modern aircraft under complex loading and environmental conditions. However, there is no available systematic knowledge about the effect of alloy thickness under mixed-mode loading at elevated temperatures. In the present study, a newly developed fracture experimental technique based on high-temperature moiré interferometry was employed to investigate experimentally I-II mixed-mode fracture in titanium alloy TC11 of various thicknesses at room and elevated temperatures. Compact shear specimens with thickness ranging from 1.8 to 7.1 mm were tested. The effects of temperature, thickness, and loading angle on the load capacity and crack initiation angle were investigated systematically. The TC11 alloy was shown to possess varied fracture performance at elevated tem-perature, and an opposite thickness effect at room temperature. Increasing temperature would enhance the fracture load capacity of thick specimens but reduce the fracture load capacity of thin specimens. Crack initiation angles under I-II mixed-mode loading showed the thickness-temperature coupling effects. These complex effects call for new development in three-dimensional mixed-mode fracture theory and technologies for damage tolerance assessment.
文摘In this paper, the location parameter δ_(a) in Weibull distribution i.e. the lower limiting CTOD toughness of high strength steel weldments is evaluated from Gleeble simulated coarse grained specimens. The Charpy-V transition temperature obtained from these specimens is transformed to a fracture toughness K_(IC) value at a given temperature using Sanz' relation. Then, the location parameter a is δ_(a) evaluated. The predicted location parameter arrives at agreement with the lowest CTOD value as obtained from thick multilayer weldments. The improvement of the fracture toughness of multilayer weldments needs the increase of the lowering limiting CTOD.toughness i.e. the toughness of the coarse grained zone.
文摘Several molybdenum silicides based alloys were produced by arc cast method with different vanadium additions. The microstructures revealed mainly single phase in samples with precipitation of second phases segregated to the grain boundaries. Lattice parameter and density measurements with different V concentrations have been correlated with lattice distortion. Mechanical properties studies were carried out, showing a decreasing behavior in microhardness while fracture toughness value increases at intermediate concentrations. Results indicated that vanadium alloying produces a significant effect on grain growth behavior and second phase precipitation.