Fatigue fracture is one of the main failure modes of Ti-6A1-4V alloy,fracture toughness and crack closure have strong effects on the fatigue crack growth（FCG）rate of Ti-6A1-4V alloy.The FCG rate of Ti-6A1-4V is inve...Fatigue fracture is one of the main failure modes of Ti-6A1-4V alloy,fracture toughness and crack closure have strong effects on the fatigue crack growth（FCG）rate of Ti-6A1-4V alloy.The FCG rate of Ti-6A1-4V is investigated by using experimental and analytical methods.The effects of stress ratio,crack closure and fracture toughness on the FCG rate are studied and discussed.A modified prediction model of the FCG rate is proposed,and the relationship between the fracture toughness and the stress intensity factor（SIF）range is redefined by introducing a correcting coefficient.Notched plate fatigue tests（including the fracture toughness test and the FCG rate test）are conducted to investigate the influence of affecting factors on the FCG rate.Comparisons between the predicted results of the proposed model,the Paris model,the Walker model,the Sadananda model,and the experimental data show that the proposed model gives the best agreement with the test data particularly in the near-threshold region and the Paris region,and the corresponding calculated fatigue life is also accurate in the same regions.By considering the effects of fracture toughness and crack closure,the novel FCG rate prediction model not only improves the estimating accuracy,but also extends the adaptability of the FCG rate prediction model in engineering.展开更多
computer controled procedure is developed for automatic measurementsof the crack opening stress Sop dunng fatigue tests. A crack opening displacement gauge(COD meter) is used to obtain digital data on the load-COD cur...computer controled procedure is developed for automatic measurementsof the crack opening stress Sop dunng fatigue tests. A crack opening displacement gauge(COD meter) is used to obtain digital data on the load-COD curves. Three methods forderiving S op from the data sets are compared:(1) slope method, (2) tangent lines inter-secting method, and (3) tangent point method. The effect of the position of the CODmeter with respect to the crack tip on Sop is studied in tests of 2024-T3 specimens. Re-sults of crack growth and Sop are presented for CA loading with an overload and withan overload followed by an underload.展开更多
In situ high-temperature(maximum: 650°C) experiments for fatigue crack growth on single edge-notched GH4169 superalloy specimens have been performed in scanning electron microscopy(SEM). In order to investigate t...In situ high-temperature(maximum: 650°C) experiments for fatigue crack growth on single edge-notched GH4169 superalloy specimens have been performed in scanning electron microscopy(SEM). In order to investigate the crack closure behavior,digital image correlation(DIC) method was applied to measure the full-field displacement and strain fields around the crack tip.The deformation carrier(speckle) was fabricated on the polished specimen surface with Zr O2 powders having a good hightemperature resistance, and the speckle patterns were recorded during the fatigue test by SEM. In consideration of the distortion of SEM images, the unabridged model and the bicubic model were used to correct the spatial distortion, and the distortion parameters can be determined by a calibration test. It is shown that the unabridged model makes a better contribution towards improving SEM-DIC measurement accuracy. Based on the deformation field, the mode Ι stress intensity factor range ?K and the crack opening displacement(COD) can be calculated for evaluating the crack closure effect. Additionally, the crack propagation was monitored using SEM and optical microscope. It indicates that the cracks grew initially in trans-granular mode at room temperature and 650°C, then propagated in both trans-granular and inter-granular modes.展开更多
This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution,...This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.展开更多
On the basis of stress-strain analysis under cyclic loading,the mechanism,origin and cyclic number of microcraek nucleation of duplex structure materials,saying ferrite plus martensite, have been experimentally studie...On the basis of stress-strain analysis under cyclic loading,the mechanism,origin and cyclic number of microcraek nucleation of duplex structure materials,saying ferrite plus martensite, have been experimentally studied and calculated.Both results are in fair mutual agreement. The morphology,distribution,size and relative quantities of the constitutional phase,especial ly strengthening phase,as well as the stress-strain distribution and variation in micro-region are directly influential in the origin of microcracks in duplex structure materials.展开更多
基金Supported by the Joint Funds of National Natural Science Foundation of ChinaCivil Aviation Administration Foundation of China(Grant No.U1233201)Science and Technology Support Plan of Tianjin,China(Grant No.13ZCZDGX00200)
文摘Fatigue fracture is one of the main failure modes of Ti-6A1-4V alloy,fracture toughness and crack closure have strong effects on the fatigue crack growth（FCG）rate of Ti-6A1-4V alloy.The FCG rate of Ti-6A1-4V is investigated by using experimental and analytical methods.The effects of stress ratio,crack closure and fracture toughness on the FCG rate are studied and discussed.A modified prediction model of the FCG rate is proposed,and the relationship between the fracture toughness and the stress intensity factor（SIF）range is redefined by introducing a correcting coefficient.Notched plate fatigue tests（including the fracture toughness test and the FCG rate test）are conducted to investigate the influence of affecting factors on the FCG rate.Comparisons between the predicted results of the proposed model,the Paris model,the Walker model,the Sadananda model,and the experimental data show that the proposed model gives the best agreement with the test data particularly in the near-threshold region and the Paris region,and the corresponding calculated fatigue life is also accurate in the same regions.By considering the effects of fracture toughness and crack closure,the novel FCG rate prediction model not only improves the estimating accuracy,but also extends the adaptability of the FCG rate prediction model in engineering.
文摘computer controled procedure is developed for automatic measurementsof the crack opening stress Sop dunng fatigue tests. A crack opening displacement gauge(COD meter) is used to obtain digital data on the load-COD curves. Three methods forderiving S op from the data sets are compared:(1) slope method, (2) tangent lines inter-secting method, and (3) tangent point method. The effect of the position of the CODmeter with respect to the crack tip on Sop is studied in tests of 2024-T3 specimens. Re-sults of crack growth and Sop are presented for CA loading with an overload and withan overload followed by an underload.
基金supported by the National Natural Science Foundation of China(Grant No.11672153)the China Postdoctoral Science Foundation(Grant No.2018M641331)the National Key Research and Development Program of China(Grant No.2017YFB1103900)。
文摘In situ high-temperature(maximum: 650°C) experiments for fatigue crack growth on single edge-notched GH4169 superalloy specimens have been performed in scanning electron microscopy(SEM). In order to investigate the crack closure behavior,digital image correlation(DIC) method was applied to measure the full-field displacement and strain fields around the crack tip.The deformation carrier(speckle) was fabricated on the polished specimen surface with Zr O2 powders having a good hightemperature resistance, and the speckle patterns were recorded during the fatigue test by SEM. In consideration of the distortion of SEM images, the unabridged model and the bicubic model were used to correct the spatial distortion, and the distortion parameters can be determined by a calibration test. It is shown that the unabridged model makes a better contribution towards improving SEM-DIC measurement accuracy. Based on the deformation field, the mode Ι stress intensity factor range ?K and the crack opening displacement(COD) can be calculated for evaluating the crack closure effect. Additionally, the crack propagation was monitored using SEM and optical microscope. It indicates that the cracks grew initially in trans-granular mode at room temperature and 650°C, then propagated in both trans-granular and inter-granular modes.
文摘This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.
文摘On the basis of stress-strain analysis under cyclic loading,the mechanism,origin and cyclic number of microcraek nucleation of duplex structure materials,saying ferrite plus martensite, have been experimentally studied and calculated.Both results are in fair mutual agreement. The morphology,distribution,size and relative quantities of the constitutional phase,especial ly strengthening phase,as well as the stress-strain distribution and variation in micro-region are directly influential in the origin of microcracks in duplex structure materials.
