Research on fatigue crack propagation behaviour of 4003 ferritic stainless steel based on infrared thermography

Abstract

A B S T R A C T Fatigue crack propagation (FCP) behaviour of 4003 ferritic stainless steel was investigated using infrared thermography. Four stages of superficial temperature evolution were observed during the FCP tests: an initial temperature decrease stage, a temperature equilibrium stage, a slow temperature increase stage and an abrupt temperature increase stage; a thermal model is developed to explain the observed temperature evolution. The experimental results indicate that: when the range of stress intensity factor (ΔK) is at a low level where the crack is located in slow propagation region, thermoelastic effect will be in dominant status; when the ΔK is at a high level where the crack is located in stable propagation region, the temperature rise can be used to describe FCP rate. The fatigue fracture surfaces were examined using scanning electron microscope (SEM) in order to understand the effect of the fatigue mechanisms on temperature variation.Keywords fatigue crack propagation; fatigue fracture mechanisms; infrared thermography; stress intensity factor. N O M E N C L A T U R Ea crack length da/dN crack propagation rate ΔK the range of stress intensity factor ΔK th the threshold value of ΔK for crack starting to increase ΔK th,temp the threshold value of ΔK where the temperature begin to increase sharply C Paris coefficient m Paris exponent T the highest superficial temperature value around the crack tip T 0 room temperature ΔT maximum temperature increment R loading ratio f the frequency of loading Q the energy conversion rate per unit volume q the dissipated power per unit length of crack front k the thermal conductivity of the material r c the radius of the cyclic plastic zone v the crack propagation velocity Cp the heat capacity at a constant pressure α l the coefficient of linear expansion ρ the density Δσ the principal stress ξ the dissipated energy per unit length of crack front during one cycle η a material-dependent proportionality factor σ y the cyclic yield stress of the material

Evaluation of plastic strain work and multiaxial fatigue life in CuZn37 alloy by means of thermography method and energy‐based approaches of Ellyin and Garud

“…Thermodynamic analysis of fatigue process may relate to, for example, estimation of the dissipated energy, 28,29 analysis of heat dissipation sources in fatigue tests, [30][31][32] energy balance, 33 entropy of fatigue process, 34,35 often together with other experimental methods [36][37][38] and fatigue crack propagation. 39,40 Crupi et al 41 showed that the temperature increment and hysteresis loop of the materials are closely correlated because they are both a manifestation of the energy dissipation process in metals under fatigue loading. Much attention is devoted to analyses related to phenomena taking place in the materials during the fatigue loadings.…”

Temperature‐dependent characteristics of DH36 steel fatigue crack propagation

“…1 Once microcracks occur in these structures, they will continue to expand until the structures fail under alternating loads. 2 Therefore, microcracks have become a serious concern as they pose a great threat to the safety of such structures in polar regions.…”