A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing(VCA) model is...A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing(VCA) model is briefly reviewed, which is based on the equivalent plastic zone concept. In this method, the retardation phenomenon is explained by the crack closure level variation, which is derived from the interactions between forward and reverse plastic zones ahead of the crack tip. As a comparison, the Forman equation in conjunction with the Willenborg model is also reviewed. The retardation phenomenon is described by directly modifying the stress intensity factor. It is known that the large plastic zone created by the overload can decelerate the fatigue crack growth rate until the crack grows beyond this region. A relationship between the plastic zone and the modified stress intensity factor is developed, which is a mathematical fitting equation instead of physical-based formulation. The experimental data in aluminum alloys are used to validate these two models. Overall, good agreement is observed between the model predictions and the testing data. It is noted that the approach based on modified VCA model can give more accurate prediction curves than the Willenborg model.展开更多
This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with a...This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with axle load from 60kN to 190kN were conducted on different pavement structures. The relationship between axle load and its deflection as well as its deflection basin curvature was obtained by statistical analyses. A methodology for deriving the equivalent conversion factors of overload axes to equivalent standard axle loads (ESAL) of 100kN is developed, obtaining the relationship between the equivalent conversion factors and the axle loads. Comparing the calculated defiections with the measured deflections, that elastic layered system theory is suitable for analyzing overload vehicles was verified. Consequently, the stresses and strains caused by overload axes were calculated by elastic layered system theory. The results showed that overload axes led to greater stresses and strains causing premature pavement fatigue distress. To guarantee the expected performance in overload axes pavement, the structure thickness needed increasing was obtained. The results are of referential values in the control of semi-rigid pavement overloadings.展开更多
The fatigue crack growth rate (CGR) of ultra high strength steel 30CrMnSiNi2A in distilled water at 18,35 and 55℃ were measured.It was confirmed that the temperature is strongly af- fected on the corrosion fatigue CG...The fatigue crack growth rate (CGR) of ultra high strength steel 30CrMnSiNi2A in distilled water at 18,35 and 55℃ were measured.It was confirmed that the temperature is strongly af- fected on the corrosion fatigue CGR of ultra high strength steel.An expression concerning the effects of Δ K and temperature on the CGR was proposed.The fact that the apparent activation energy (36.6 kJ/mol) resulted from regressive analysis of CGR data was similar to the activation energy of hydrogen diffusion in γ-Fe,strongly supporting the theory of hydrogen-assisted crack growth.The overload retardation effect was greatly reduced in cor- rosion fatigue crack growth,especially at lower frequency,e.g.,0.1 Hz.This phenomenon might be due to the increase of the SCC component of CGR after an overload.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51405009)the Fundamental Research Funds for the Central Universities of China
文摘A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing(VCA) model is briefly reviewed, which is based on the equivalent plastic zone concept. In this method, the retardation phenomenon is explained by the crack closure level variation, which is derived from the interactions between forward and reverse plastic zones ahead of the crack tip. As a comparison, the Forman equation in conjunction with the Willenborg model is also reviewed. The retardation phenomenon is described by directly modifying the stress intensity factor. It is known that the large plastic zone created by the overload can decelerate the fatigue crack growth rate until the crack grows beyond this region. A relationship between the plastic zone and the modified stress intensity factor is developed, which is a mathematical fitting equation instead of physical-based formulation. The experimental data in aluminum alloys are used to validate these two models. Overall, good agreement is observed between the model predictions and the testing data. It is noted that the approach based on modified VCA model can give more accurate prediction curves than the Willenborg model.
文摘This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with axle load from 60kN to 190kN were conducted on different pavement structures. The relationship between axle load and its deflection as well as its deflection basin curvature was obtained by statistical analyses. A methodology for deriving the equivalent conversion factors of overload axes to equivalent standard axle loads (ESAL) of 100kN is developed, obtaining the relationship between the equivalent conversion factors and the axle loads. Comparing the calculated defiections with the measured deflections, that elastic layered system theory is suitable for analyzing overload vehicles was verified. Consequently, the stresses and strains caused by overload axes were calculated by elastic layered system theory. The results showed that overload axes led to greater stresses and strains causing premature pavement fatigue distress. To guarantee the expected performance in overload axes pavement, the structure thickness needed increasing was obtained. The results are of referential values in the control of semi-rigid pavement overloadings.
文摘The fatigue crack growth rate (CGR) of ultra high strength steel 30CrMnSiNi2A in distilled water at 18,35 and 55℃ were measured.It was confirmed that the temperature is strongly af- fected on the corrosion fatigue CGR of ultra high strength steel.An expression concerning the effects of Δ K and temperature on the CGR was proposed.The fact that the apparent activation energy (36.6 kJ/mol) resulted from regressive analysis of CGR data was similar to the activation energy of hydrogen diffusion in γ-Fe,strongly supporting the theory of hydrogen-assisted crack growth.The overload retardation effect was greatly reduced in cor- rosion fatigue crack growth,especially at lower frequency,e.g.,0.1 Hz.This phenomenon might be due to the increase of the SCC component of CGR after an overload.
