Research On The Process Of Multiple Crack Propagation In 7n01 Aluminum Alloy Material

With the requirement of lightweight for large equipment,7N01 aluminum alloy material has been widely used in the fields of aviation,aerospace and railway transportation due to its excellent mechanical properties.During the long-term use of aluminum alloy structural parts,due to the effects of processing technic,service environment,fatigue load and other factors,damage may occur in multiple parts at the same time.Compared with single crack damage,the interaction between multiple cracks will accelerate the crack growth rate and seriously affect the safety of the structure.In this paper,the multiple cracks propagation process of aluminum alloy is studied by combining experiment and simulation.The main research contents include:(1)Test design of multi-crack propagation process for aluminum alloy,the finite element simulation was used to analyze the influence of the main geometric parameters of the test specimen on the fatigue crack initiation and propagation,and the design of the multiple cracks propagation test specimen was completed.Combined with Digital Image Correlation(i.e.DIC)method and fatigue crack propagation test standards,multiple cracks research test scheme were determined.(2)Based on the static tensile stress-strain test data of aluminum alloy,the elastic-plastic finite element model of multiple cracks speimen was established,and the DIC strain data extracted during the crack growth propagation were compared to verify the validity of the simulation model.(3)Based on the experimental measurement and simulation analysis,the failure criterion of multiple cracks propagation was studied.The data showed that when two cracks were close to each other,the stress field distribution at the crack tip interfered with each other,resulting in obvious deflection of the crack propagation path and the crack propagation along the direction of maximum circumaxial stress.When the connected area of two crack tips is in a plastic yielding state,the crack growth rate increases,so it is reasonable to use the plastic zone connection at the crack tip as the failure criterion of multiple crack propagation.(4)The growth rate data of collinear equal length crack,collinear unequal length crack and non-collinear equal length crack were obtained through the multiple cracks propagation test.When the two cracks are far apart,the stress field at the crack tip has no obvious influence on each other,and each crack coincides with the growth rate curve of the single crack.When the two cracks are close to each other,the plastic zone at the tip of the multiple cracks are connected and the crack propagation rate increases obviously.(5)Based on the finite element method,the influence of the relative position of multiple cracks on the stress intensity factor(SIF)is studied.As the driving force parameter of crack propagation,the interaction between cracks will produce enhancement or shielding effect.By changing the vertical distance,horizontal distance and deflection Angle between the cracks,the change trend of stress intensity factor at the crack tip was obtained.An equivalent method for calculating stress intensity factor of multiple cracks by plastic zone connection and coefficient correlation method was established for collinear cracks.