Effect Of Single Tensile Overload Research Articles

Effect of single tensile overload on fatigue crack growth behavior of CP-Ti at negative load ratio

In present study, the fatigue crack growth (FCG) behavior of commercial pure titanium (CP-Ti) at negative load ratio with a single tensile overload was investigated through the combination of experiment and finite element method (FEM). The influence of load ratio and overload ratio was considered to investigate the overload retardation effect of FCG with compact-tensile-shear (CTS) specimens. Changes of the fatigue crack growth rate (FCGR) and crack opening force before and after overload were obtained experimentally under different loading conditions. The mechanical behaviors of stress–strain distribution and evolution of plastic zone size ahead of crack tip were explored by FEM for revealing the mechanism of overload at negative load ratios. The results demonstrate that retardation effect of FCG increases with overload ratio, and decreases with load ratio. The retardation effect of overload occurs after a transient acceleration of FCGR. The excessive residual compressive stress induced within the unloading stage of overload cycle ahead of crack tip, causes a shielding effect, which is one of the main factors of overload retardation effect. The difference of plastic strain at crack tip before and after overload makes the monotonic plastic zone (MPZ) and reverse plastic zone (RPZ) compete with each other, resulting in an increase of residual plastic strain, which hinders the crack propagation. At negative load ratios, the overload retardation effect will be weakened by the compressive load because of the decreasing residual plastic strain.

Effect of single tensile overload on fatigue crack growth behavior based on plastically dissipated energy and critical distance theory

The paper systematically investigates the fatigue crack growth (FCG) behavior of Q345 steel under a single tensile overload during constant amplitude cyclic loadings by combining the experimental, numerical and theoretical methods. Compact tension specimens are applied to explore the retardation effect of FCG rate after the overload application. A predictive technique based on plastically dissipated energy method, critical distance theory and node-release technology is developed to characterize the FCG behavior following the overload. Crack opening displacement and crack opening load level along the crack flank are obtained to explore the effect of overload on plasticity-induced crack closure. Additionally, the stress-strain response at critical distance and compressive residual stress field ahead of crack-tip are further explored to reveal the intrinsic mechanism and accumulative damage. Results show that the magnitude of residual stretched material wedge and value of maximal crack opening load level increase obviously with the increasing of overload; discontinuous closure takes place behind and before plastic wedge at overload location, which limits the stress/strain ranges at crack-tip and thereby retards crack growth. The magnitude of compressive residual stress and size of stress field ahead of crack-tip increase with increasing overload ratio, which aggravates the retardation effect after overload.

Effect of single overload on fatigue crack growth in QSTE340TM steel and retardation model modification

To analyze the effect of single tensile overload on fatigue crack growth behavior, a series of experiments have been conducted under different load ratios and overload ratios on QSTE340TM automobile steel. The results showed that the application of overload extended the fatigue life of the specimens in all cases. The fatigue crack growth rate curves presented different patterns between the case load ratio R = 0.7 and the cases R = 0.1, 0.3, 0.5. Difference between the trends of the closure load and the fatigue crack growth rate in the cases R = 0.1, 0.3, 0.5 was found and discussed. The images of fracture surface were obtained by Scanning Electron Microscope. A new effective stress intensity factor expression was proposed and discussed. A combined model based on both the residual stress effect and the plasticity-induced crack closure effect was proposed by modifying the Wheeler model and applying the new effective stress intensity factor expression. The proposed model gave reliable estimates of QSTE340TM steel for all overload cases and two other materials from references.

Effect of single tensile overload on fatigue crack growth behavior in DP780 dual phase steel

The purpose of this study was to analyze the effect of single tensile overload on fatigue crack growth (FCG) behavior in DP780 dual phase steel. The compact tension samples were tested under constant amplitude load and overload condition. The results showed that all the material conditions responded favorably to the single tensile overloads; the magnitude and extent of crack retardation was amplified due to an increase in overload ratio (OLR) and a longer crack length at overload application. The error between the overload affected crack growth increment and the magnitude of overload monotonic plastic zone size decreased about 30% after introducing the factor (n−1)/(n+1) into Irwin model. A plastic zone size factor was used to modify the Wheeler model to calculate the FCG rate during retardation period after an overload, the predicted results were in good agreement with the experimental data. During the application of an overload, a crescent moon shaped damage zone was formed ahead of the crack tip characterized by cleavage surfaces, tearing ridges, dimples and voids. The fracture morphology after crack front reformation was severely damaged due to the premature contact of the crack flanks. Crack branching was not significant interaction effect for the crack growth retardation under overload.

Analysis of short and long crack behavior and single overload effect by crack opening stress

The study analyzed the behaviors of short and long crack as well as the effect of single tensile overload on the crack behaviors by using fatigue crack opening behavior. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many data using strain gages during experiment. The unusual growth behaviors of short crack and crack after the single tensile overload applied, was explained by the variations of crack opening stress. In addition, fatigue crack growth rate was expressed as a linear form for short crack as for long crack by using effective stress intensity factor range as fracture mechanical parameter, which is based on crack closure concept. And investigation is performed with respect to the relation between plastic zone size formed at the crack tip and crack retardation, crack length and the number of cycles promoted or retarded, and the overload effect on the fatigue life.