Application of fast thermal imaging techniques in the strain rate sensitivity studies of materials

Veli-Tapani Kuokkala, Amos Gilat, Jarrod Smith, Jeremy Seidt

    Research output: Chapter in Book/Report/Conference proceedingConference contributionScientific


    The mechanical behavior of materials depends on both temperature and strain rate, the effects of which for example on the flow stress are normally opposite, i.e., increasing strain rate increases the flow stress while increasing temperature reduces it. One of the practical problems in the experimental determination of material properties is the separation of the temperature, strain hardening, and strain rate effects. For example in the tensile tests at high strain rates, the effects are coupled, as the temperature of the specimen tends to increase due to the internal heating of the specimen. The coupling of strain hardening and temperature softening depends on the strain rate and mechanical and physical properties of the test material. New optical methods, such as full-field strain determination based on digital image correlation and full-field thermal imaging with infrared cameras working at increasingly higher frame rates provide new possibilities to tackle the above-mentioned problems. This paper describes in detail the novel techniques used to measure simultaneously the full-field strains and temperatures on the sample surfaces deforming at different strain rates extending from very low quasi-static to highly dynamic regions. Examples of the results will be presented for example for austenitic stainless steels and hybrid materials with layered structures of various material types, showing that the temperature increase in the tensile test can be several hundreds of degrees especially in the final necking stage of the specimen. Another important topic of research is the fraction  of plastic deformation work converted to heat, also known as the Inelastic Heat Fraction (IHF) or the Taylor-Quinney coefficient, which has been studied using many different materials and experimental techniques. It has, however, been pointed out in many papers that  is not a constant for a certain material but depends on many internal and external variables such as the general strain rate sensitivity of the material, amount of plastic (cold) work, strain rate, etc. In principle, storage of energy in the material requires that its internal microstructure, i.e., dislocation or other defect contents, or its interface properties, such as the effective external or internal surface area, somehow change during the deformation process. Based on the new possibilities provided by the novel optical methods discussed above, one of the aims of the present study was the accurate determination of the value of  or IHF as well as its dependence on the internal and external variables of the experiments.
    Original languageEnglish
    Title of host publicationAdvanced Plasticity, Damage, and Fracture with Applications
    Subtitle of host publicationProceedings of ICPDF 2018, the Twenty Fourth International Conferences on Plasticity, Damage, and Fracture, San Juan, Puerto Rico, January 3-9, 2018
    EditorsAkhtar S. Khan
    Place of PublicationFulton, MD, USA
    Number of pages1
    ISBN (Electronic)978-0-9911654-5-2
    Publication statusPublished - 2018
    Publication typeB3 Article in conference proceedings
    EventInternational Conferences on Plasticity, Damage, and Fracture -
    Duration: 13 Mar 2018 → …


    ConferenceInternational Conferences on Plasticity, Damage, and Fracture
    Period13/03/18 → …


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