Quantitative thermography: a powerful but simple tool to assess the fatigue strength of metals in a one-specimen test–capabilities and limitations in the test setup

Abstract

PurposeThe aim of the study is the question, that is, which evaluation method for the measured temperature profile is more suitable and feasible for quantitative thermometry (QT): A simple measurement setup based on 3-point temperature sensing by means of semiconductor sensors (NTCs) or thermographic methods which offer 2-dimensional (2D) temperature measurements of the sample with good spatial resolution but an inferior temperature sensitivity. What experimental effort is required to adjust the test setup to satisfy the boundary conditions of the underlying thermodynamic equations?Design/methodology/approachIn this paper results of both methods are contrasted and the error of QT measurement is assessed by finite element analysis (FEA) in this follow-up.FindingsThe low-cost NTC method allows a straightforward determination of a lower estimate of the fatigue strength with only a very small measurement error. Even asymmetries in the thermal boundary conditions of the test setup are broadly tolerated, as well as a lack of thermal isolation.Practical implicationsThe method is restricted to metallic materials without phase transitions during fatigue in the fatigue strength regime.Originality/valueQT is not a new method. The assessment of the methods proposed in the literature regarding their practicability in terms of accuracy is innovative focus of this work. Nevertheless, highly accurate thermometric measurements can be performed by using simple commercial sensors in combination with a standard digital multimeter.