BITS Faculty Publications

Permanent URI for this communityhttp://localhost:4000/handle/123456789/1867

Browse

Filters

2017 - 201922020 - 20233

Settings

Author: search.filters.author.Kumar, GulshanSubject: search.filters.subject.Residual stresses

Search Results

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Experimental characterization and finite element modeling of through thickness deformation gradient in a cold rolled zirconium sheet
    (Elsevier, 2017-11) Kumar, Gulshan
    A commercial Zirconium alloy was subjected to different thickness reductions (20%, 40% and 60%) by cold rolling. A through-thickness gradient in microstructure, crystallographic texture and residual stress was observed. This gradient was till 1/8th of the specimen thickness, and implied a corresponding anisotropy in the imposed strain state. An elasto-plastic FE (finite element) model was developed to capture such through thickness deformation gradients. A reasonably good agreement was observed between the experimental and predicted residual stress distributions when the material anisotropy was accounted for. Through-thickness residual stress evolution was shown to be significantly affected by material anisotropy and to a lesser extent by the rolling parameters (coefficient of friction and rotational speed).
  • No Thumbnail Available
    Item
    Study on the effect of Ar9+ ion irradiation of Zr–2.5 wt.% Nb alloy pressure tube
    (Taylor & Francis, 2018-11) Kumar, Gulshan
    Response of Zr–2.5 wt.% Nb alloy pressure tube, used in PHWR nuclear reactors, to 315 keV Ar9+ ion irradiation at room temperature was investigated in the fluence range of 3.1 × 1015–4.17 × 1016 Ar9+ cm−2. Changes in microstructural parameters, viz., the size of coherently scattering domains, microstrain and dislocation density, upon irradiation were ascertained through grazing incidence X-ray diffraction. In general, a decrease in domain size was observed with fluence with a corresponding increase in microstrain and dislocation density. Residual stress measurement showed the development of compressive stresses in place of tensile after irradiation. Transmission electron microscopy showed the formation of dislocation loops of ⟨a⟩-type and ⟨c⟩-type during irradiation. The hardness of irradiated samples, probed through nanoindentation technique, was found to be higher in comparison with unirradiated samples. The above findings have been rationalised on the basis of the defects generated during the Ar9+ ion irradiation.
  • No Thumbnail Available
    Item
    An assessment of residual stresses and micro-structure during single point incremental forming of commercially pure titanium used in biomedical applications
    (Elsevier, 2020) Kumar, Gulshan
    Single point incremental forming (SPIF) is a branch of incremental sheet forming where a very small portion of the sheet is deformed plastically at any moment. The highly localized point deformation is done by a simple hemispherical tool, whose path is numerically monitored by a Computer numerical control (CNC) machine, performs this progressive extremely localized deformation. Since no die is required during forming, highly customized and user-oriented sheet metal products can be manufactured employing the process. SPIF can be readily employed in the manufacturing of customized orthopaedic implants and braces, e.g., cranial implants, ankle implants, elbow and knee support braces. The forming of these sheets through SPIF would results in the generation of residual stresses in the sheet metal. With time and other physical factors, these residual stresses would be relieved resulting in dimensional inaccuracy. This inaccuracy is highly detrimental in the case of implants and highly undesirable for supporting braces. The objective of this work is to investigate, experimentally, the state and magnitude of residual stresses on commercially pure titanium grade 2 by SPIF for biomedical applications. The important process parameters: forming angle and incremental step depth are used for this investigation in the present study. The X-ray diffraction technique was used for the experimental measurements of the residual stresses. Microstructural behaviour of the final product at different incremental step depth and forming angles are also observed by EBSD (Electron backscattered diffraction) technique. The experimental findings showed the formation of increased tensile residual stresses with an increase in incremental step depth and steepness of forming angles.
  • No Thumbnail Available
    Item
    Finite element analysis of residual stresses during incremental sheet forming of Ti-6Al-4V alloys using different tool path profiles
    (Springer, 2023-08) Kumar, Gulshan
    The incremental sheet metal forming is highly flexible and a die-free production method for fabricating various sheet metal components using a CNC spindle tool. Compared to the conventional process, it is beneficial for small-batch components. In biomedical and aeronautical sectors, titanium grade-5 (Ti-6Al-4V) is highly recommended due to its optimal specific strength, biomedical applications, and excellent resistance rate against corrosion. This paper simulates a truncated conical, hemisphere, and hyperbolic geometry in the incremental sheet metal forming process. MATLAB programming is then used to compute the profile, modify, and export the data to the Abaqus input file format for further FE analysis. This research uses an explicit-based computational approach to simulate SPIF and determine the output response parameters such as residual stresses, von Mises stress distribution, and variation in sheet thickness along the deforming depth. The Johnson–Cook (J-C) parameters have been used for carrying out the incremental forming simulations. Compared to other tool path profiles, more compressive stresses were observed in the conical shape profile. The distribution of effective residual stresses and part thickness were also explored in a detailed comparison of various tool path profile predictions.
  • No Thumbnail Available
    Item
    A review on the effect of residual stresses in incremental sheet metal forming used in automotive and medical sectors
    (Elsevier, 2023) Kumar, Gulshan
    Incremental sheet forming (ISF) is a process that can produce sheet metal components with a series of stepwise small incremental deformation. This literature paper presents a thorough review of analyzing the influence of residual stresses in correlation with different process variables like tool diameter, tool path, the thickness of the sheet, depth of cut and wall angle, etc., during the procedure of single point incremental forming used in the automotive and medical industry. Moreover, this paper clearly explains the process parameters, which further help improve the ISF process compared to other conventional metal forming processes. This review initiates with the introduction of ISF for different types of materials and follows the residual stress measurement in various sectors. This paper also provides specific insights into the impact of residual stresses on forming forces, geometric shape accuracy, formability, and other factors in the process. The gap from this intensive review will provide the groundwork for the investigators for future research to recognize the implication of residual stresses in the automotive and medical fields. Based on the investigation, residual stresses should be considered in the design step of the manufacturing process with diverse scales. Finally, the future scope and probable research directions were discussed.