Comparative assessment of failure strain predictions using ductile damage criteria for warm stretch forming of IN718 all
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ORIGINAL RESEARCH
Comparative assessment of failure strain predictions using ductile damage criteria for warm stretch forming of IN718 alloy Gauri Mahalle 1 & Nitin Kotkunde 1
&
Amit Kumar Gupta 1 & Swadesh Kumar Singh 2
Received: 31 March 2020 / Accepted: 6 September 2020 # Springer-Verlag France SAS, part of Springer Nature 2020
Abstract It is vital to envisage accurately the fracture limits of high strength superalloys when noticeable localized necking or thinning tendency is not observed during sheet-metal stretch forming process. The present study mainly focuses on fracture limits evaluation of Inconel 718 alloy (IN718) in the effective plastic strain (EPS) vs. average triaxiality space. First, uniaxial tensile test, to analyze the material properties, were instigated at different test temperatures (RT-700 °C). Subsequently, stretch forming is performed to evaluate forming and fracture forming limit diagrams (FLD and FFLD) of IN718 using Nakazima test. It is observed that forming and fractured limits of IN718 are significantly influenced by variation of processing temperatures (with approximately 65–70% improvement in major safe and fracture strains) in all deformation regions (with respect to RT). In average triaxiality (η) vs effective plastic strain (EPS) space, higher fracture limits of IN718 are noticed in the entire triaxiality path of deformation region. Seven different ductile fracture models, namely McClintock (M-Mc), Brozzo, Rice-Tracey (R-T), Ko, Oh, Cockcroft and Latham (C-L), and Clift, are formulated so as to foresee the fracture loci of IN718 in EPS vs. triaxiality space. Overall, Oh model, showed best predictability at all temperatures with least Average absolute error (AAE < 13.5%). Keywords IN718 alloy . Forming limit diagram . Fracture forming limit diagram . Effective plastic strain . Triaxiality . Damage models
Introduction Inconel 718 alloy (IN718), a Ni-Fe-Cr based precipitatehardenable superalloy, is indispensable metal in various high temperature applications, mainly in castings of high-speed airframes, jet engine, nuclear reactor components, oil field, rocket motor, land-based gas turbine, cryogenic and pumps [1–3]. IN718 has an excellent combination of secondary precipitates into the metal matrix, which helps accomplishing an excellent combination of mechanical properties, e.g. high tensile strength, strain hardening and ductility [4, 5]. IN718 alloy is highly corrosion resistant (mostly crevice and pitting corrosion) and stable even in extreme temperature conditions [6].
* Nitin Kotkunde [email protected] 1
Mechanical Engineering Department, BITS Pilani -Hyderabad Campus, Hyderabad, India
2
Mechanical Engineering Department, GRIET, Hyderabad, India
The sheet metals forming process are used abundantly in manufacturing industries, specially to switch conventional welding process. Critical/complex geometry components can be manufactured easily using different forming processes. Forming of limited ductility or high strength material is very challenging. In li
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