Life Prediction And Fatigue Analysis Based On Thermographic Method

The infrared thermal image displays the distribution of temperature on the surface of object,and the temperature is one of the most universal state parameter in the natute.As an inspection means of object state,infrared thermography has the advantages of non-destructive, real-time and non-contact,which has been widely applied to the scientific research.Fatigue thermography,as one of the most promising research directions of the thermograpic method, is utilized for obtaining the fatgiue limit of metals just in a short time,stirring up the strong interest from the academe and industry community.In this paper,we start our study from the engineers' most interest:the rapid measuring method for fatigue limit.Using the intrinsic dissipation as the fatigue evaluation indicator,the fatigue limit of a mild steel is determined by the rising lock-in thermography.In the most situation,the ultimate limit is not enough for engineering design,the engineers also need the fatigue life curve of materials or structures.Under the hypothesis of energy tolerance for fatigue failure,the paper proposes the concept and method of quantitative thermographic methodology,aiming the rapid determination of fatigue life curve of metallic materials.Based on the obtained fatigue curve,the method is extended to the new fields such as residual life prediction and non-linear stress analysis.The objective is to establish a systemic and quantitative fatigue thermographic evaluation method.Under the real working condition,fatigue often happens on the structural components, especially in the the stress concentration area of the structure.Generally,the fatigue crack occurs from the local area and propagates slowly,and the fatigue damage accumulates gradually,finally leading to the sudden fatigue failure.Consequently,the research of thermographic method based on local fatigue damage is practical significant.The paper firstly introduces the thermodynamic model of local energy method,then advances two fatigue evaluation indicators based on local thermographic method:standard deviation of temperature and standard deviation of stress,respectively.The experiment shows the two parameters are both very sensitive to local dagame,and have the strong description ability for the characteristic and evolution process of the local damage.The method is hopefully applied to the fatigue evaluation and health monitoring for online service structures.From the standpoint of thermodynamics,the paper studies the energy dissipation characteristic of metal fatigue and refers to the classic fatigue theory and experimental method, establishing a fatigue evaluation system based on thermographic method preliminarily. Through the research of fatigue thermographic method,we links the microstructure evolution with the macroscopical fatigue behavior,providing a new research approach and content for giving a further understanding of metal fatigue mechanism.