Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Author: search.filters.author.Neelakantha, V.L.

Search Results

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Experimental determination of spring back and thinning effect of aluminum sheet metal during L-bending operation
    (Elsevier Ltd, 2014) Dilip Kumar, K.; Appukuttan, K.K.; Neelakantha, V.L.; Naik, P.S.
    In automotive industry, significant efforts are being put forth to replace steel sheets with aluminum sheets for various applications. Besides its higher cost, there are several technical hurdles for wide usage of aluminum sheets in forming. Major problems in aluminum sheet metal forming operations are deformation errors and spring back effect. These problems are dependent on the number of parameters such as die and tool geometry, friction condition, loading condition and anisotropic properties of the metal.To predict the exact shape, the geometry based punch contact program must be used. The shape changes once the punch is withdrawn, because of the materials elasticity. Prediction of such a spring back effect is a major challenging problem in industry involving sheet metal forming operations. It also needs applying appropriate back tension during the forming complex shapes. Slight deformation of the metal leads to non-axisymmetric loading. One can predict the residual stress by determining plastic and elastic deformation. Thus appropriate spring back effect can be investigated.The present investigation was carried out to determine the spring back and thinning effect of aluminum sheet metal during L-bending operation. Number of specimens with thickness varying from 0.5. mm to 3.5. mm were prepared. The experiments were conducted for different clearances between punch and die. It is observed that, beyond a particular clearance for each thickness of the sheet metal, the spring back and thinning effects were linearly increasing. However, below the critical clearance, scratches on the surface of the sheet metal were seen due to wear. The scratches were analyzed through Scanning Electron micrographs. As the clearance between punch and die reduces further, more wear on the punching surface was observed. And, as the clearance increases it leads to increase the spring back effect and fracture propagation. © 2013 Elsevier Ltd.
  • No Thumbnail Available
    Item
    Determination of fracture toughness and fatigue crack growth rate using circumferentially cracked round bar specimens of Al2014T651
    (Elsevier Masson SAS infos@masson.fr 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2015) Neelakantha, V.L.; Jayaraju, T.; Naik, P.; Kumar K, D.; Rajashekhar, C.R.; Kumar, M.
    Fracture toughness (KIC) and fatigue crack growth rate (FCGR) are the important material properties in fracture mechanics. ASTM-E399 and ASTM-E647 are the standards for determination of KIC and FCGR of metallic materials. These standards recommend the use of compact tension (CT) or single edge notched bend (SENB) test specimens. Literature review indicates that CT or SENB specimens are complex in nature, difficult to manufacture, require typical fixtures for loading during experimentation and the test procedures using CT or SENB are time consuming and cumbersome. An alternate specimen geometry which can overcome the above said drawbacks is needed by the industry which can be used as standard test specimen geometry. This research work explains use of circumferentially cracked round bar (CCRB) specimens of high strength Al2014T651 alloy for determination of KIC and FCGR.The pre-cracked round bar specimen was loaded in tensile in a universal testing machine and pulled till failure. Using suitable stress intensity factor equations the fracture toughness can be calculated. In case of crack growth test, the pre-cracked round bar specimen is allowed to rotate under fatigue load. The ratio of length of crack propagated to the number of cycles to failure was the crack growth rate. The SEM analysis of fractured surfaces was also done.The results are comparable with the values reported in the literature obtained by using standard test specimens. There are numerous advantages of using round bar specimen in KIC and FCGR tests. It is concluded that, the methodology of determination of fracture toughness and fatigue crack growth rate using CCRB specimens is relatively simple, reliable, fast and economical. CCRB specimen may be recommended as a standard test specimen for fracture toughness as well as crack growth tests. © 2015 Elsevier Masson SAS. All rights reserved.