For brittle materials, the tensile strength plays an important role in mechanical analyses and engineering applications. Although quasi-static direct and dynamic indirect tensile strength testing methods have already ...For brittle materials, the tensile strength plays an important role in mechanical analyses and engineering applications. Although quasi-static direct and dynamic indirect tensile strength testing methods have already been developed for rocks, the dynamic direct pull test is still necessary to accurately determine the tensile strength of rocks. In this paper, a Kolsky tension bar system is developed for measuring the dynamic direct tensile strength of rocks. A dumbbell-shaped sample is adopted and attached to the bars using epoxy glue. The pulse shaping technique is utilized to eliminate the inertial effect of samples during test. The single pulse loading technique is developed for the effective microstructure analyses of tested samples. Two absorption devices are successfully utilized to reduce the reflection of waves in the incident bar and transmitted bar, respectively. Laurentian granite （LG） is tested to demonstrate the feasibility of the proposed method. The tensile strength of LG increases with the loading rate. Furthermore, the nominal surface energy of LG is measured, which also increases with the loading rate.展开更多
A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method...A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.展开更多
Ductile iron bars(DIBs) with a diameter of 145 mm, used for plunger pump production, were made by the horizontal continuous casting(HCC). The microstructure of the samples cut at three locations with different distanc...Ductile iron bars(DIBs) with a diameter of 145 mm, used for plunger pump production, were made by the horizontal continuous casting(HCC). The microstructure of the samples cut at three locations with different distances away from the surface(~20 mm from the surface, half of the radius and the center of the HCCDIBs)were investigated. The mechanical properties were measured by tensile and torsion tests. Results show that after the spheroidization of graphite, the iron matrix incorporates the nodules of Format I, Size 8 close to the surface, Format I, Size 7 at the half of the radius from the surface, and Format II, Size 6 in the centre of the bar,according to the ASTM A247 standard. The content of pearlite in the matrix changes from 55%(~20 mm from the surface) to 70%(half of the radius) and 80%(the center of the HCCDIBs). The strengths in tension are 552, 607 and 486 MPa with the elongations of 12.5%, 10.5% and 5.8% in samples cut at these three locations from the surface to the centre, respectively. The strength in torsion is equal to 558, 551 and 471 MPa at corresponding torsion angles of 418°, 384° and 144° respectively to the same distance from the bar surface. Fracture in tension is manifested via crack propagation through the interface between graphite nodules and matrix(Mode I), while in torsion the fracture is caused by the shear of graphite nodules(Mode II). It is shown that the transition between two fracture modes is also dependent on the size of graphite nodule. Typically, fracture Mode I was observed for nodules of smaller diameter(less than 22.7 μm) and fracture Mode II was seen for nodules of greater diameter(more than 24.8 μm).展开更多
基金Supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)through Discovery Grant(72031326)
文摘For brittle materials, the tensile strength plays an important role in mechanical analyses and engineering applications. Although quasi-static direct and dynamic indirect tensile strength testing methods have already been developed for rocks, the dynamic direct pull test is still necessary to accurately determine the tensile strength of rocks. In this paper, a Kolsky tension bar system is developed for measuring the dynamic direct tensile strength of rocks. A dumbbell-shaped sample is adopted and attached to the bars using epoxy glue. The pulse shaping technique is utilized to eliminate the inertial effect of samples during test. The single pulse loading technique is developed for the effective microstructure analyses of tested samples. Two absorption devices are successfully utilized to reduce the reflection of waves in the incident bar and transmitted bar, respectively. Laurentian granite （LG） is tested to demonstrate the feasibility of the proposed method. The tensile strength of LG increases with the loading rate. Furthermore, the nominal surface energy of LG is measured, which also increases with the loading rate.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.
基金financially supported by the Shaanxi Provincial Science and Technology Achievement Transfer and Promotion Plan-absorb Achievement Transformation Project(No.2017CGZH-XNGJ-03)Shaanxi Provincial Education Department Scientific Research Program Project-service Local Special Industrialization Cultivation Project(No.17JF018)+1 种基金Xi'an Science and Technology Planning Project Science and Technology Innovation Guide Projects(No.201805037YD15CG21(19))Xi'an University of Technology Scientific and Technological Achievement Transformation Project-technical Requirement Solving Project of Enterprises(No.2018-1)
文摘Ductile iron bars(DIBs) with a diameter of 145 mm, used for plunger pump production, were made by the horizontal continuous casting(HCC). The microstructure of the samples cut at three locations with different distances away from the surface(~20 mm from the surface, half of the radius and the center of the HCCDIBs)were investigated. The mechanical properties were measured by tensile and torsion tests. Results show that after the spheroidization of graphite, the iron matrix incorporates the nodules of Format I, Size 8 close to the surface, Format I, Size 7 at the half of the radius from the surface, and Format II, Size 6 in the centre of the bar,according to the ASTM A247 standard. The content of pearlite in the matrix changes from 55%(~20 mm from the surface) to 70%(half of the radius) and 80%(the center of the HCCDIBs). The strengths in tension are 552, 607 and 486 MPa with the elongations of 12.5%, 10.5% and 5.8% in samples cut at these three locations from the surface to the centre, respectively. The strength in torsion is equal to 558, 551 and 471 MPa at corresponding torsion angles of 418°, 384° and 144° respectively to the same distance from the bar surface. Fracture in tension is manifested via crack propagation through the interface between graphite nodules and matrix(Mode I), while in torsion the fracture is caused by the shear of graphite nodules(Mode II). It is shown that the transition between two fracture modes is also dependent on the size of graphite nodule. Typically, fracture Mode I was observed for nodules of smaller diameter(less than 22.7 μm) and fracture Mode II was seen for nodules of greater diameter(more than 24.8 μm).
