Study On Fatigue Life Prediction Method Considering Material Properties And Non-Proportional Additional Strengthening

In engineering practice,components often serve in complex cyclic loading environments,resulting in various forms of fatigue failure,which can bring significant safety hazards and lead to serious consequences.Fatigue life can be affected by factors such as whether the component itself is smooth,material properties,loading methods and so on.Smooth body components’ fatigue life can be estimated through theoretical models owing to their stress and strain distribution has certain regularity;However,when there are notches in the component,the stress and strain situation at the notch is very complex,resulting in multi axial distribution of the component and additional strengthening effects under non-proportional loading,making the component more prone to cracking.Therefore,establishing a fatigue life prediction model suitable for smooth/notched parts and different material characteristics is of great significance and practical value.To address the above issues,This article considers the influence of material properties on fatigue life and conducts research on the prediction method of uniaxial fatigue life of smooth parts;Then based on the critical interface theory,a study was conducted on the fatigue life prediction method for notched components;Finally,a new fatigue life prediction model is established for fatigue damage under non proportional loading conditions.The following is the research content of this article:(1)Establishing a uniaxial fatigue life prediction model considering material properties.Considering the material characteristics and average stress and the material sensitivity coefficient is introduced through the relevant research on four smooth parts of FGH96,GH909,TA11,and GH4133 alloys based on the Lv model,to explore the effect of material properties on fatigue life under uniaxial tension;(2)Propose a critical interface determination method,and establish a multi axis fatigue life prediction model considering stress gradient effects and material characteristics.The stress and strain distribution state of the local notch of the notched piece is obtained by using ANSYS finite element analysis software.The orientation of crack initiation and propagation of the notched piece is determined using the plane with the largest plastic strain energy density by combining the energy critical surface method.Using the plane with the maximum plastic strain energy density as the crack initiation surface to establish a line integral field diameter on the crack initiation surface and extract the corresponding stress-strain parameters from the field diameter.Based on this,the effects of material properties and average stress on multiaxial fatigue life are considered,and new material property factors and relative average shear stress gradient factors are established using parameters extracted from the field diameter.Based on FS and SWT models,a new model is established by combining material characteristic factors and relative shear stress gradient factors.This article uses the experime ntal results of three different materials(Q345 steel,TC4 alloy,and 7050-T7451 aluminum alloy)for notched specimens to verify new model’s effectiveness;(3)Establishing a fatigue life prediction model considering the influence of multi axis non-proportional loading.By using theories such as dislocation slip under nonproportional loading,a new non-proportional additional strengthening coefficient is proposed by linking microscale related parameters with macroscopic scale related parameters,combining material properties and average stress.Based on the Itoh and Susmel models and the factors were considered,a new life prediction model is established,and its effectiveness is verified using various material test data.