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
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
A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a sim...A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a simple and efficient iterative algorithm based on method of contact resistance mitigation.On the surfaces of the closed crack,the Mohr-coulomb rule is satisfied by iteration when the crack is in condition of sliding.The stress intensity factors are obtained using displacement fitting method.It is shown that the numerical results agree with the experimental results well and that friction plays an important role in resisting crack propagation.展开更多
To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack...To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack section,crack propagation life,and stress variation were analyzed.Finite-element models were also developed,and some optimal values of certain parameters are suggested according to the simulated results.The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution.The fatigue lives of cracked specimens with long cracks are significantly improved by the technique.Considerable residual compressive stress is also induced,and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°.The stress at the weld root is distributed uniformly with the crack closed,and the optimal crack-closure depth is 4 mm.To evaluate the effect of different crack-closure depths in tests,it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.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.
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.
基金Project(2022YFC2903901) supported by the National Key R&D Project of ChinaProjects(52104111, 52274249) supported by the National Natural Science Foundation of China+3 种基金Project(2021JJ30819) supported by the Natural Science Foundation of Hunan Province,ChinaProject(kfkt2023-01) supported by the Open Fund of State Key Laboratory of Safety Technology of Metal Mines,ChinaProject(2023TJ-X80) supported by the Xiaohe Sci-Tech Talents Special Funding under Hunan Provincial Sci-Tech Talents Sponsorship Program,ChinaProject(2023ZZTS0516) supported by the Fundamental Research Funds for the Central Universities,China。
文摘A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a simple and efficient iterative algorithm based on method of contact resistance mitigation.On the surfaces of the closed crack,the Mohr-coulomb rule is satisfied by iteration when the crack is in condition of sliding.The stress intensity factors are obtained using displacement fitting method.It is shown that the numerical results agree with the experimental results well and that friction plays an important role in resisting crack propagation.
基金Projects(51478163,51678216)supported by the National Natural Science Foundation of ChinaProject(2017Y09)supported by the Transport Science Research Project of Jiangsu Province,China
文摘To evaluate the effect of treating long cracks with the impact crack-closure retrofit(ICR)technique,three rib-to-deck welded specimens with a crack length of about 100 mm were tested.The metallographic structure,crack section,crack propagation life,and stress variation were analyzed.Finite-element models were also developed,and some optimal values of certain parameters are suggested according to the simulated results.The results show that new crack sources are generated on both sides of the ICR-treated region because of the stress distribution.The fatigue lives of cracked specimens with long cracks are significantly improved by the technique.Considerable residual compressive stress is also induced,and so it is suggested that the optimal impact angle to be applied to real bridges should be 70°.The stress at the weld root is distributed uniformly with the crack closed,and the optimal crack-closure depth is 4 mm.To evaluate the effect of different crack-closure depths in tests,it is recommended that a hot-spot stress method which is extrapolated by three reference points should be adopted.
