A Comparison of Fracture Limit Analysis on Titanium Grade 2 and Titanium Grade 4 Sheets During Single Point Incremental
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TECHNICAL ARTICLE—PEER-REVIEWED
A Comparison of Fracture Limit Analysis on Titanium Grade 2 and Titanium Grade 4 Sheets During Single Point Incremental Forming G. Yoganjaneyulu . C. Sathiya Narayanan
Submitted: 21 May 2019 / Accepted: 13 August 2019 Ó ASM International 2019
The influence of tensile properties, void coa lescence parameters, strain triaxiality eeeffm and its fracture Abstract
limits for various spindle rotational speeds in single point incremental forming were compared for titanium grade 2 and grade 4 sheets. The microstructure reveals the presence of a and b phase particles, as was confirmed using x-ray diffraction analysis. Forming limit diagrams and fracture limit curves were plotted for the sheets and the results were compared for both titanium grade sheets. The void coalescence in fractured samples showed an improved fracture resistance for the titanium grade 2 sheets compared with the titanium grade 4 sheets. The void size, ligament thickness, void (L/W) ratio, d-factor, strain triaxiality and further void coalescence parameters were also compared. In all cases, because of their better ductility, the titanium grade 2 sheets exhibited better forming and fracture limits (void coalescence) than that of grade 4 sheets. Keywords Titanium grade sheets Forming limit diagrams Fracture limit curves Stress-based fracture limit curve Fracture limit analysis Strain triaxiality
Introduction Incremental sheet forming (ISF) is an emerging forming process for small batch production and rapid prototype development. An ISF process progressively forms sheet
G. Yoganjaneyulu (&) C. Sathiya Narayanan Department of Production Engineering, National Institute of Technology, Tiruchirapalli, Tamil Nadu 620015, India e-mail: [email protected]
metal into a pre-designed, three-dimensional shape using computer numerical control (CNC). This process is highly flexible and, with careful tool path programming, can achieve very complex shapes. Therefore, ISF has been widely accepted as a more promising forming process compared with the conventional processes such as deep drawing and stamping [1]. Titanium and its alloys are the most frequently used materials in the aircraft, orthopedic, marine and dental implant industries because these materials have a high strength-to-weight ratio and good corrosion resistance compared to those of steel and aluminum alloys. Ambrogio et al. [2] Proposed a novel variant of ISF technology in which a continuous current is supplied in order to generate local heating, allowing easier formability and lowering the forces required for the manufacturing of light weight alloys. Liu [3] has developed heat-assisted incremental sheet forming methods for deforming hard materials at elevated temperatures and also showed a clear improvement in the geometrical accuracy and formability during the heat-assisted incremental forming process. Belhassen et al. [4, 5] experimentally and numerically analyzed the damage and spring-back occurring during the flexible forming process. An elasto-pla
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