Fatigue limit by thermal analysis of specimen surface in mono axial traction test

Abstract

Abstract. In this work is indicated how it could be possible to evaluate the limit stress of the thermo-elastic phase of deformation by thermo-analysing the surface of the specimen during a static traction test. Adding the temperature curve measured on a small area of the surface (the hottest) to the classic stress-strain curve, it is possible to evaluate a limit temperature T 0 coincident with the beginning of the non linear trend of the curve. The corresponding stress value is coincident with the fatigue limit of the analyzed component. As an example, the results of traction tests performed on two notched specimens, where the change of linearity in the temperature curve during static traction test was evident, are reported. The corresponding value of stress was a good approximation of the fatigue limit for R = -1, determined by the conventional method. The aim of the reported examples in this paper must be interpreted as support to the basic principle of the method and not as the results of a complete experimental planning of which we will comment in an another occasion.1 Nomenclature E l energy required for fatigue fracture ĭ l integral of a surface point temperature, proportional to E l , at fatigue fracture ı stress ı 0 fatigue limit for R = -1 (limit stress above which some crystal is plasticized)) ı i minimum stress ı s maximum stress ı m mean stress ı p plastic stress ı 0,2 yield stress ı r fracture strength/original cross sectional area and t r is the test time with thermo plastic behaviour f loading frequency R stress ratio İ strain İ 0 strain corresponding to ı 0 a

Fatigue damage in GFRP

“…Another method for the application of thermography to assess damage in homogeneous materials was recently proposed by Risitano et al (2010). This work is based on the experimental observation that during a static tensile test, the surface temperature of the specimens (i.e.…”

“…A following sudden increase in DT happens in the last part of the static test. The end of the first linear part of the curve is related, according to experimental tests in Risitano et al (2010), to the fatigue limit of the tested material. Also, another recent application of this static method deals with polymeric materials (i.e.…”

Change of Specimen Temperature during the Monotonic Tensile Test and Correlation between the Yield Strength and Thermoelasto-Plastic Limit Stress on the Example of Aluminum Alloys

“…The observation of the macroscopic temperature change during the tensile is the underlying principle of, among other things, the fatigue limit estimation method called Static Thermographic Method, where the variation of the slope of the stress strain versus temperature curve identifies the transition zone between thermoelastic and thermoplastic behavior when the beginning of irreversible micro-plasticization occurs. This moment is considered by the authors as the value of the fatigue limit of the tested material [26][27][28][29][30]. This method has also been used for notched metal specimens [31] Another approach to investigate the fatigue limit during tensile static tests was proposed in [32] where the authors estimated the dissipation and the area where the first increase of energy occurs.…”

Modern Experimental Techniques With an Emphasis on Infrared Thermography to the Assessment of Fatigue Components With Dents

“…More recently, a new and fast method to determine the fatigue limit using IR thermography was proposed by Risitano and coworkers [34][35][36][37][38]. It analyzes the thermal variation in quasi-static uniaxial tensile tests.…”

“…The use of IR thermography methods in fatigue characterization consists on the measurement of the temperature rise on the external surface of the tested specimen during load application in order to identify a singular transition from a conservative and non-damaging state of energy to a dissipative and damaging one [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38].…”