Metal Fatigue Damage Characterization And Life Prediction Method Based On Surface Micromorphology

Metal fatigue is a common form of failure in engineering structures and materials,and often leads to catastrophic accidents in unforeseen circumstances,so people have been searching for ways to prevent and evaluate it.Fatigue failure involves a complex process,after the material undergoes cyclic loading,the internal microstructure will inevitably change,and the micromorphology of the surface of the material will also change.The key question is how to choose appropriate physical parameters that can quantitatively describe the cumulative damage of material fatigue,and whether the physical parameter can directly or indirectly measure and reasonably evaluate the fatigue life and remaining life of materials.Therefore,in this paper,the following experiments and analysis models are studied on the fatigue damage failure mechanism of materials,the surface characteristics of damage evolution,meso-scale numerical models and calculations:(1)310s stainless steel samples were subjected tensile-compressive fatigue and torsional fatigue tests at different strain amplitudes.The hysteretic behaviors of the materials under corresponding circumstances were studied,and model parameters calibrated to reflect their mechanical properties were obtained.Based on this,the difference in fatigue resistance characteristics of the material under two different loading effects were analyzed.And The cyclic stable stress-strain hysteresis curves under different strain amplitudes are compared and analyzed to explore the non-massing characteristics of the material.(2)Samples of 310 s stainless steel and HRB335 steel that underwent different cycles under different strain amplitudes were uniaxially stretched to fracture.Based on experimental research found that samples that had undergone different pre-fatigue cycles and passed large deformation stretch were observed under an optical microscope,and the difference in the distribution of cracks related to the number of cycles was obvious in the necking site.And the more the life is consumed,the more obvious the difference.This phenomenon is of great significance for describing the cumulative fatigue damage.(3)Aiming at the phenomenon that the image characteristics of surface cracks on metal specimens are strongly related to fatigue life loss of the metal material,it is proposed to use the "unit crack area" as a new quantitative description parameter for characterizing fatigue cumulative damage,and a new method for evaluating the remaining life of materials after low-cycle tensile and compression cycles is suggested.The method of measuring the unit crack area under the specified strain amplitude cycle with the increase of the cycle number can be used to predict the fatigue life and remaining life of the material under different strain amplitude cycles.(4)Through numerical simulation calculations and statistical analysis methods,the evolution law of the non-uniform deformation of the free surface of the material under cyclic loading and its relationship with fatigue life were studied from a meso-level,and a method for predicting the fatigue life of the material before the fatigue test was developed.Based on this,a new method for fatigue life prediction of non-Masing materials is proposed,which significantly improves the reasonableness of the prediction results.