The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear...The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear.In this paper,a dynamic shear box was used to perform direct shear tests on saw-cut(planar)and natural(rough)granite fractures,with different normal load oscillation amplitudes.Based on the recorded shear forces and normal displacements,the shear forces,apparent friction coefficients and normal displacements are found to change periodically with oscillated normal loads and are characterized by a series of time shifts.The observed changing patterns are similar for the rough and planar fractures.Compared with the test data under constant normal load(CNL),small/large normal load oscillation amplitude enhances/reduces the peak shear strength,with a critical point.The magnitude of critical normal load oscillation for the rough fractures is smaller than the planer fractures.The results imply that dynamic fault weakening/strengthening can be achieved by both normal load oscillation amplitudes and slip surface topography.The rough fractures with larger normal oscillation amplitude can easily cause frictional weakening under stress disturbance.展开更多
The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instabilit...The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.展开更多
The purpose of the present study was to evaluate the effect ofA1203 content on the fracture property of all-ceramics ZrO2. To improve the all-ceramics ZrO2 restoration mechanics properity ,96 samples containing 0,5,10...The purpose of the present study was to evaluate the effect ofA1203 content on the fracture property of all-ceramics ZrO2. To improve the all-ceramics ZrO2 restoration mechanics properity ,96 samples containing 0,5,10 and 15 wt% of A1203 particles were prepared by cold isostatic pressing （200 MPa） and 1 550 ℃ sintered .The phase was analyzed by X-ray diffraction analysis and the bulk densities of the samples were made using Archimedes principle. Samples were randomly divided into four groups. In each group, 24 specimens were prepared so that the angle between notch and specimen＇s long axis is 90° and 60°. Notch depths were 1 mm for all samples. Samples were loaded with three-point bending method. 90° cut samples were used to measure fracture toughness while 60°cut samples were used to observe fracture curve by taking points on the fracture extension path under microscope, plotting points on coordinates, generating fitting curve by software ＂Origin＂, and analyzing the microstructure of the specimen fracture surfaces by scanning electron microscopy （SEM）.The results show that the increment ofA1203 has insignificant effect on the densification of all-ceramic ZrO2.XRD analysis shows that the specimen is comprised of t-ZrO2 and a- A1203 before fracture while fracture surface is m-ZrO2, t-ZrO2 and a-A1203. ZrO2 containing 10% A1203 has the optimum mechanical properties and unconspicuous crack propagation and distribution. The observations may provide a reference for the materials selection, shaoe design, and production orocess of all-ceramic crown and bridge.展开更多
Periprosthetic femoral fracture(PFF)is a major complication following total hip arthroplasty(THA),particularly in patients with Dorr type C femurs,which have normal bone quality.Implant selection plays a critical role...Periprosthetic femoral fracture(PFF)is a major complication following total hip arthroplasty(THA),particularly in patients with Dorr type C femurs,which have normal bone quality.Implant selection plays a critical role in early postoperative stability,but the biomechanical influence of different femoral stem designs in this high-risk population remains unclear.In this study,CT data from a Dorr type C femur with normal bone quality,obtained from a patient with hip osteoarthritis,were used to reconstruct a three-dimensional femoral model.Six femoral stems representing different designs were implanted to construct corresponding THA finite element models.The models were subjected to a simulated stumbling condition,with progressively applied axial displacement until PFF occurred.The maximum fracture load was recorded and compared among the stem designs.The maximum fracture load,ranked from highest to lowest,was as follow:Corail(6079.26 N),Omnifit(5605.11 N),Synergy(5165.03 N),Taperloc(5030.77 N),Excia(4192.37 N),and Profemur(4034.64 N).The Excia and Profemur stems showing lower fracture loads than the peak stumbling load of approximately 8.7 times body weight(4785 N).These results suggest that,for THA in patients with Dorr type C femurs with normal bone quality,the use of Corail,Omnifit,Synergy,or Taperloc stems may be preferable for minimizing the risk of postoperative PFF.展开更多
The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughne...The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil,i.e.stress corrosion cracking,decrease linearly with the increasing applied electric field,either positive or negative.For the PZT-5 ferroelectric ceramics,delayed fracture in silicone oil under sustained positive or negative field can occur,and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor.The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes fieldenhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.展开更多
基金the funding support from the National Natural Science Foundation of China (Grant No. 51904359)the Guangdong Provincial Department of Science and Technology (Grant No. 2019ZT08G090)the Open Research Fund of the State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (CUMT) (Grant No. SKLCRSM20KF002)
文摘The dynamic frictional behaviors of natural discontinuities(joints,fractures,faults)play an important role in geohazards assessment;however,the mechanisms of the dynamic fault weakening/strengthening are still unclear.In this paper,a dynamic shear box was used to perform direct shear tests on saw-cut(planar)and natural(rough)granite fractures,with different normal load oscillation amplitudes.Based on the recorded shear forces and normal displacements,the shear forces,apparent friction coefficients and normal displacements are found to change periodically with oscillated normal loads and are characterized by a series of time shifts.The observed changing patterns are similar for the rough and planar fractures.Compared with the test data under constant normal load(CNL),small/large normal load oscillation amplitude enhances/reduces the peak shear strength,with a critical point.The magnitude of critical normal load oscillation for the rough fractures is smaller than the planer fractures.The results imply that dynamic fault weakening/strengthening can be achieved by both normal load oscillation amplitudes and slip surface topography.The rough fractures with larger normal oscillation amplitude can easily cause frictional weakening under stress disturbance.
基金This project is supported by Doctoral Education Foundation of Ministry ofEducation of China (No.96021602).
文摘The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.
基金Funded by the Technology Department Science Fund of Sichaun(No.2011GZ011520)
文摘The purpose of the present study was to evaluate the effect ofA1203 content on the fracture property of all-ceramics ZrO2. To improve the all-ceramics ZrO2 restoration mechanics properity ,96 samples containing 0,5,10 and 15 wt% of A1203 particles were prepared by cold isostatic pressing （200 MPa） and 1 550 ℃ sintered .The phase was analyzed by X-ray diffraction analysis and the bulk densities of the samples were made using Archimedes principle. Samples were randomly divided into four groups. In each group, 24 specimens were prepared so that the angle between notch and specimen＇s long axis is 90° and 60°. Notch depths were 1 mm for all samples. Samples were loaded with three-point bending method. 90° cut samples were used to measure fracture toughness while 60°cut samples were used to observe fracture curve by taking points on the fracture extension path under microscope, plotting points on coordinates, generating fitting curve by software ＂Origin＂, and analyzing the microstructure of the specimen fracture surfaces by scanning electron microscopy （SEM）.The results show that the increment ofA1203 has insignificant effect on the densification of all-ceramic ZrO2.XRD analysis shows that the specimen is comprised of t-ZrO2 and a- A1203 before fracture while fracture surface is m-ZrO2, t-ZrO2 and a-A1203. ZrO2 containing 10% A1203 has the optimum mechanical properties and unconspicuous crack propagation and distribution. The observations may provide a reference for the materials selection, shaoe design, and production orocess of all-ceramic crown and bridge.
基金supported by the Fundamental Research Funds for the Central Universities(grant number AF0820060)the Natural Science Foundation of Ningbo(2022J030)the Zhejiang Medical health science and technology plan(2022RC248).
文摘Periprosthetic femoral fracture(PFF)is a major complication following total hip arthroplasty(THA),particularly in patients with Dorr type C femurs,which have normal bone quality.Implant selection plays a critical role in early postoperative stability,but the biomechanical influence of different femoral stem designs in this high-risk population remains unclear.In this study,CT data from a Dorr type C femur with normal bone quality,obtained from a patient with hip osteoarthritis,were used to reconstruct a three-dimensional femoral model.Six femoral stems representing different designs were implanted to construct corresponding THA finite element models.The models were subjected to a simulated stumbling condition,with progressively applied axial displacement until PFF occurred.The maximum fracture load was recorded and compared among the stem designs.The maximum fracture load,ranked from highest to lowest,was as follow:Corail(6079.26 N),Omnifit(5605.11 N),Synergy(5165.03 N),Taperloc(5030.77 N),Excia(4192.37 N),and Profemur(4034.64 N).The Excia and Profemur stems showing lower fracture loads than the peak stumbling load of approximately 8.7 times body weight(4785 N).These results suggest that,for THA in patients with Dorr type C femurs with normal bone quality,the use of Corail,Omnifit,Synergy,or Taperloc stems may be preferable for minimizing the risk of postoperative PFF.
基金This work was supported by the National Natural Science Foundation of China(Grant No.50131160738).
文摘The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen.The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil,i.e.stress corrosion cracking,decrease linearly with the increasing applied electric field,either positive or negative.For the PZT-5 ferroelectric ceramics,delayed fracture in silicone oil under sustained positive or negative field can occur,and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor.The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes fieldenhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.
