NATIONAL INSTITUTE OF AEROSPACE

Banavara R. Seshadri

Banavara R. Seshadri

Tel: +1 (757) 864-3478; FAX: +1 (757) 864-8911seshadri_banavara _bg

Email: seshbr@nianet.org 

Research Interests

  • Exploration Systems
  • Characterization of Friction Stir Welded (FSW) aerospace structures;
  • Prediction of residual life and limit load for in-flight discrete source damage event;
  • Structural integrity of integral structures fabricated using different manufacturing procedures with the intention of reducing structural weight, improving performance and enhancing the life of aerospace structures;
  • Characterization, simulation, and evaluation of crack growth in Fiber Metal Laminates (FMLs);
  • Damage tolerant design concepts – Development of Computational methodologies and procedures to study and analyze the behavior of high performance aerospace structures;
  • Characterization of fatigue life based on local crack tip parameter near threshold regime; and
  • Elastic-plastic contact stress analyses of fasteners/joints – accounting for crack closure and plasticity effects in life estimation.

Education

  • Ph.D. (1996), Aerospace Engineering,  Indian Institute of Science, India
  • M.E (MS) (1990), Engineering Design, P.S.G. College of Technology, India
  • B.E. (BS)  (1988), Mechanical Engineering, Mysore University, India

Current Research

Life prediction tools for FSW structures: The goal of the current research program is to develop novel advanced analytical methodologies to enhance the structural integrity of integral structures fabricated using the Friction Stir Weld (FSW) manufacturing procedure. The intention is to reduce structural weight, improve performance, and enhance the life of aerospace structures. Methodologies developed based on thermal residual stress model have helped us to capture both tensile and compressive residual stress field distribution accurately in both C(T) and M(T) specimens with a single parameter, T. The stress intensity factor solution estimated using virtual crack closure technique (VCCT) due to FSW residual stress field compare well with test data. FSW M(T) and C(T) specimens with refined FE mesh were used to carry out crack closure analyses at different crack length to width ratios to study the effects of residual stress distribution on crack tip driving force. The crack growth rate prediction for closure free case agreed well with experimental data and constant crack growth rates were observed for constant Ktip. The developed methodology captured the effects of both tensile and compressive residual stress distribution on crack-tip driving force under constant amplitude loading. Also, the methodology was able to quantify the effects of material processing on the residual stress field. The developed methodology can also be used to analyze the effects of residual stress on crack tip driving force in large panels, by using the same parameters that were calibrated from small test coupons. Analyzing 24-inch wide FSW integral panel and comparing with test data demonstrated this. A life prediction tool for FSW structures has been developed, which accounts for variation in stress ratio, R and applied Kmax at the crack tip along with crack closure levels estimated under the influence of a residual stress field. Initial comparison of fatigue crack growth rate estimated using new tool compares well with the experimental behavior observed in C(T) specimens under the influence of tensile and compressive residual stress field. By developing such a tool, we can accurately account for the effects of residual stress on fatigue crack growth, which will make it possible to design lighter and more reliable structures.

Residual life and limit load for in-flight discrete source damage event: A methodology to predict residual life and limit load for in-flight discrete source damage event is under development. It is based on elastic-plastic fracture mechanics principles and well-established Crack Tip Opening Displacement (CTOD) failure criteria. These principles are being used in predicting residual strengths using a high fidelity ductile tearing simulation. For the purpose of validation, twenty-one panels/coupons made up of five different materials and eight thicknesses were analyzed for residual strength evaluation and compared with test data. After developing the methodology, it will be demonstrated for a large aircraft panel, which is a representative of a real time structure. The impact of developing high fidelity prediction tools will assist in maintaining right loads on aircraft for continued safe operation in the presence of discrete-source damage.

Recent Publications

Seshadri, B.R., Smith, S. W., and Newman, J.A., “Development of Life Prediction Tool for Friction Stir Welded Structures’”, 2012 Aircraft Airworthiness & Sustainment conference, April, 2012, Baltimore, MD

Seshadri, B.R., Smith, S. W., and Newman, J.A., “Development of prediction methodology for the analyses and design of friction stir welded structures”, Aircraft airworthiness & sustainment conference, April, 2011, San Diego, CA

Seshadri, B.R., Smith, S. W., and Newman, J.A., “Three dimensional numerical simulation and evaluation of crack closure effects under residual stress field”, 2011 ASTM-ESIS Symposium, May, 2011, Anaheim, CA..

Seshadri, B.R., Wang, J. T., and Smith, S.W., “Three dimensional finite element simulation and evaluation of crack growth in fiber metal laminates”, 2010 Aircraft airworthiness & sustainment conference, May,  2010, Austin, TX.

Smith, S.W., Newman, J. A., Donald, K. J., Blair, A., James, M. A., Bucci, R. J.,  Brazill, R. L., Schultz, R. W., and Seshadri. B. R. and Johnston, W. M., “The prediction of fatigue crack propagation in a friction stir welded specimen containing a residual stress distribution”, Aeromat 2010, June, 2010, Bellevue, WA.

Newman, J.A., Smith, S.W., Seshadri, B.R., Donald, J.K., Blair, A., James, M.A., Bucci, R. J., Brazill, R.L., Schultz, R.W., “Residual stress effects on fatigue crack propagation in a friction stir welded material” presented at the Residual Stress Summit 2010, September,  2010, Tahoe City, CA

Seshadri, B.R., Smith, S.W., Johnston, Jr., W.M., and Hoffman, E. K., “Effect of residual stress on residual strength characterization of integral structures”, 12th Joint FAA/DoD/NASA conference on Aging Aircraft, May, 2009, Kansas City, Missouri.

Seshadri, B.R. and Smith S.W., “Three dimensional numerical simulation and evaluation    of the adjusted compliance ratio technique”, 9th International ASTM/ESIS Symposium on fatigue and fracture mechanics (37th ASTM National symposium on fatigue and fracture mechanics), May, 2009, Vancouver, BC.

Smith, S.W., Newman, J. A., James, M. A., Donald, K. J., Brazill, R. L., Schultz, R. W.,Blair, A., and  Seshadri. B. R., “An on-line methodology for measuring residual stress and producing reliable fatigue life assessments”, 9th International ASTM/ESIS Symposium on fatigue and fracture mechanics (37th ASTM National symposium on fatigue and fracture mechanics), May, 2009, Vancouver, BC.

Seshadri, B.R., Smith, S.W., and Johnston, Jr., W.M., “Residual strength characterization of unitized structures fabricated using different manufacturing technologies”, 11th Joint NASA/FAA/DoD conference on Aging Aircraft, April, 2008, Phoenix, Arizona.

Seshadri, B.R., Smith, S.W., and Johnston, Jr., W.M., “Residual strength characterization of integrally stiffened structures utilizing novel manufacturing technologies”, 6th International conference on computation of shell and spatial structures, May, 2008, Ithaca, New York.

Seshadri, B.R. and Smith, S.W., “Three dimensional constraint effects on the estimated CTOD during numerical simulation of different fatigue threshold testing techniques”, of a proposed paper to the 48th AIAA/ASME/AHS/ASC structures, Structural Dynamics, and Materials Conference, April, 2007, Waikiki, Hawaii

Seshadri, B.R., and Forth, S.C., “Numerical simulation and evaluation of different fatigue threshold testing techniques”, accepted for presentation and publication at 9th international fatigue congress, FATIGUE 2006, May, 2006, Atlanta, Georgia.

Forth, S.C., Johnston, W.M. and Seshadri, B.R., “Effect of the laboratory specimen on fatigue crack growth rate”, 16th European conference on Fracture, July, 2006, Alexandropoulos, Greece,

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