Experimental Study On Fatigue Crack Growth Rate Of ADB610 Steel Under Different Stress Ratios

ADB610 is a new generation of crack-free welding high strength low alloy structural steel, and it is currently known as the 21st century "green steel", which is produced by using micro-alloyed and controlled rolling and cooling process. With the development of modern industrialization, the development of alloy structural steels increasingly focused on improving its reliability and economy, that is to say in addition to meeting the structural strength requirements, more attention should be paid to its safety and life of the structure. ADB610 steel has been widely used in many areas, because of its good mechanical and welding properties. Currently the majority of research on the kind of steel is limited to the conventional mechanical properties, welding property and toughness etc.. However, as the important basis for the design of resisting to fracture and estimating the residual life--the crack growth rate is very rare, especially, it is not reported that the study on the fatigue crack growth behavior under different conditions. Therefore, this paper, taken stress ratio-R into consideration, has research on the fatigue crack growth behavior of ADB610 steel.First, using the standard compact tension specimens (CT specimen) experiment,the fatigue crack propagation for ADB610 steel under different stress ratios has been completed, and the fatigue crack growth data under different stress ratios R have been acquired, (a, N) and (da/dN, AK).Moreover, this paper studied the effect of stress ratios R on the fatigue crack growth rate based on Paris formula, got da/N-AK curves under different stress ratios R, the relationship between parameter C, m in the Paris formula with stress ratio R, and the reliability analysis for fatigue crack growth data for:1) the reliability study on fatigue crack growth rate data based on (a, N); 2) the reliability study on fatigue crack growth rate data based on (da/dN,ΔK); 3) the reliability study on fatigue crack growth rate data based on random variables, acquired the P-da/N-AK curves under different reliability. The results shown that:1) the fatigue crack growth rate of ADB610 steel decreases with the stress ratio R increasing; 2) parameter C, m of Paris formula and stress ratio R has a correlation with stress ratio-R, parameter C will decrease with stress ratio-R increasing, m will increase with stress ratio-R decreasing; 3) higher reliability, fatigue crack growth rate ADB610 steel faster.Secondly, this paper used scan electron microscopy (SEM) to research the fractographs of ADB610 steel, the analysis showed that:ADB610 fatigue fracture is mixed fracture with cleavage fracture and fatigue fracture, the first stage of crack growth are transgranular fracture or cleavage fracture and fatigue crack is mainly produced by the slip bands of surface; in the stable crack growth and fast-propagating stages of fatigue crack growth, crack extension mechanism is based on the strip.Finally, this paper taken the driving force of two-parameter model to establish a relationship between stress ratio R and the crack growth rate da/dN with the stress intensity factor rangeΔK, got identifies specific crack growth model for the materials used in this paper, using this model to calculate the crack growth rate under different stress ratios, The calculation results was close to the test results, which proves the feasibility of the model.