Research On Fatigue Life Prediction Method Of Low-Velocity Impact Based On Damage Dissipated Energy

Fatigue is the most common typical failure form in production and life.Modern mechanical structural parts are subjected to impact loads due to complex service environments.Impact fatigue has become one of the main causes of structural failure.Accurate and stable prediction of impact fatigue life is an important guarantee for giving full play to the strength of materials and ensuring the safety of structural parts in service.Due to the complexity of the impact fatigue problem,the mathematical model is difficult to characterize the impact fatigue failure law and deterioration characteristics,resulting in an incomplete impact fatigue theoretical system,which cannot meet the needs of fully exploiting the impact fatigue resistance potential of materials and effectively ensuring the safety design of service structures.It will seriously threaten the service safety of structural components and may lead to catastrophic consequences.Therefore,it is of great theoretical significance and engineering value to research the impact fatigue life prediction method of metal structural parts,and the establishment of an accurate fatigue life prediction model is the key and core to solving the impact fatigue problem.In this paper,the impact stress fluctuation effect and dynamic response are considered,and the dynamic fracture strength factor is introduced to analyze and clarify the dynamic response scaling law of metal materials under impact load.Based on the theory of damage thermodynamics,a life prediction method of intrinsic damage dissipated energy coupled with low-cycle fatigue micro-damage accumulation and macro-damage evolution is proposed to realize the characterization from dynamic response to dynamic failure.Combined with the characteristics of impact fatigue,focusing on the critical region damage method,a prediction model of the dissipated energy life of impact fatigue intrinsic damage is constructed,which is highly targeted and has clear physical and mechanical significance.At the same time,through the finite element modeling of ABAQUS and the secondary development of VUMAT,combined with the impact fatigue test data of typical notched parts,the advanced nature of the impact fatigue life prediction method is compared and demonstrated.Under the framework of irreversible damage thermodynamics,based on the evolution analysis of intrinsic damage dissipation energy in the critical region of fatigue damage,the research on the impact fatigue life prediction method is carried out.The main work and research results are as follows:1.Use the SHPB test combined with fracture dynamics and wave theory to analyze the dynamic response of crack under impact stress.By analyzing the fluctuation effect of shock stress wave,the evolution equation of stress wave fluctuation behavior is established,and the evolution law of stress-strain field under the action of stress wave is analyzed.Through dynamic fracture toughness analysis,the dynamic crack propagation characteristics under impact load are discussed.The results show that the impact stress wave promotes the failure of the cracked structure and reaches the dynamic equilibrium state in a very short time.2.Based on the damage irreversible thermodynamic framework,an intrinsic damage dissipation evolution model is established to describe the fatigue damage failure behavior.Based on the Lemaitre-Chaboche damage theory,through the study of the thermodynamic state potential and dissipation potential of the damage process,the coupled constitutive relationship between the loss evolution dynamic response of damaged materials and the damage is analyzed.The damage model of material fatigue performance degradation is established,and the critical condition of intrinsic damage dissipation is identified.The research work lays a theoretical foundation for impact fatigue research.3.A low-speed impact fatigue life prediction model is constructed to target the nature of impact damage evolution.Based on the equal-life condition of equal maximum intrinsic damage dissipation energy in the critical region,a low-cycle fatigue life prediction method considering the effect of average strain is proposed,and the relationship between the maximum strain,strain amplitude,and material properties and fatigue life is revealed.Through the comparative analysis of five commonly used metal fatigue tests,the life prediction model proposed in this paper is located in the error band of 2 times,which is better than the existing prediction model.Aiming at the low-velocity impact fatigue characteristics,based on the equivalent relationship of the maximum intrinsic damage dissipation energy in the critical region,an impact fatigue life prediction model is established.It overcomes the impact notch sensitivity and volume effect and has a strong physical meaning and mechanical basis.Through the comparison and demonstration of the low-velocity impact fatigue test data of two kinds of metal materials,the results show that the prediction accuracy of the model is within 1.5 times the error band,which is consistent with the test data,which provides a new method for impact fatigue life prediction.4.Taking typical notched parts as an impact fatigue example,the application analysis of the low-speed impact fatigue life prediction model is realized.Using the theory of maximum intrinsic damage dissipation energy in the critical domain,through ABAQUS finite element modeling and VUMAT secondary development,the theoretical prediction of the impact fatigue life of three typical notched parts was carried out and compared with the four impact fatigue life prediction methods.The calculation results show that the new impact fatigue life prediction model can accurately and stably predict the impact fatigue life of notched parts,and the impact fatigue life prediction effect is better than the existing prediction model.It provides a new idea for the prediction of the impact fatigue life of metal materials.