Faculty Publications

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Subject: search.filters.subject.Strain rate

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    Influence of die angle on containerless extrusion of commercially pure titanium tubes
    (2007) Srinivasan, K.; Venugopal, P.
    Containerless tube extrusion has been investigated with commerically pure titanium at room temperature and a strain rate of 0.07 s-1 using 20 conical dies of five different strains and four different angles with MoS2 lubricant. Theoretical punch pressures have been calculated using appropriate equations from slab analysis of the process and compared with experimentally determined punch pressures. It is found that there exists an optimum angle at which the punch pressure is the least at a given strain.
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    The effect of the particle shape and strain rate on microstructure and compressive deformation response of pure Ti-foam made using acrowax as space holder
    (Elsevier Ltd, 2015) Mondal, D.P.; Patel, M.; Jain, H.; Jha, A.K.; Das, S.; Dasgupta, R.
    Titanium foams of varying amount of porosities have been made using acrowax bits as a space holder through powder metallurgy route. Two types of Ti-particles were used: (i) angular and (ii) spherical in order to see the effect of particle shape on microstructure and deformation behavior. The compressive deformation behavior of Ti-foams with varying porosities and type of particles are studied under different strain rates. It is observed that the microstructural characteristics of Ti-foam varied marginally with the shape of Ti-particles. But the shape of particles influenced reasonably the deformation responses of Ti-foam. The plateau stress, modulus and energy absorption follow power law with relative density irrespective of shape of Ti-particles. All these parameters in Ti-foams are almost invariant to the strain rate. The empirical constants associated with different empirically developed power law relations are different for different shape of Ti-particles. © 2014 Elsevier B.V.
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    Quasi-Static and High Strain Rate Compressive Response of Injection-Molded Cenosphere/HDPE Syntactic Foam
    (Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2016) Bharath Kumar, B.R.; Singh, A.K.; Doddamani, M.R.; Luong, D.D.; Gupta, N.
    High strain rate compressive properties of high-density polyethylene (HDPE) matrix syntactic foams containing cenosphere filler are investigated. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10?4 s?1, 10?3 s?1 and 10?2 s?1 strain rates. Further, a split-Hopkinson pressure bar is utilized for characterizing syntactic foams for high strain rate compression. The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10?4 s?1 for HDPE resin and syntactic foams. Theoretical models are used to estimate the effectiveness of cenospheres in reinforcing syntactic foams. © 2016, The Minerals, Metals & Materials Society.
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    Prediction of strain rate sensitivity of high density polyethylene using integral transform of dynamic mechanical analysis data
    (Elsevier Ltd, 2016) Zeltmann, S.E.; Bharath Kumar, B.R.; Doddamani, M.R.; Gupta, N.
    Recent interest in understanding the effect of strain rate on mechanical properties has motivated this study to develop a correlation between frequency domain dynamic mechanical analysis (DMA) results and elastic modulus values that are obtained from a separate set of elaborate tensile tests conducted over a wide range of strain rates. Using the time-temperature superposition principle and the integral relations of viscoelasticity, the DMA results are converted into a time-domain relaxation function in order to predict the strain-rate dependent modulus. The transformation technique is validated with experimental results for high density polyethylene (HDPE) resin and is found to be accurate over a wide range of strain rates. Cross correlation between DMA results and tensile test results over a wide range of strain rates can help in substantially reducing the requirement for tests that are needed to characterize the material behavior with respect to strain rates, temperature and loading frequency. © 2016 Elsevier Ltd
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    Indentation creep studies to evaluate the mechanical properties of stainless steel welds
    (Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2016) Udaya Prasanna, H.U.; Udupa, K.R.
    Size being limited for preparing standard specimens for mechanical tests, the weld poses problems to researchers and scientists in estimating the strength parameters and workhardening coefficients. The integrity of the weld is difficult to probe into, particularly when the temperature of operation is much higher than the room temperature. The indentation creep test route is successfully tried by the authors to present a detailed commentary on the mechanical properties of a stainless steel weld at different test temperatures using a methodology whereby the creep test results are correlated to the compression test results and correlation equations developed. As the indentation creep tests can be carried out on a small-sized sample, the method enables one to carry out only this test to judge the mechanical properties of the welds. © 2015 Engineers Australia.
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    Prediction of modulus at various strain rates from dynamic mechanical analysis data for polymer matrix composites
    (Elsevier Ltd, 2017) Zeltmann, S.E.; Prakash, K.A.; Doddamani, M.; Gupta, N.
    Understanding and modeling the behavior of polymers and composites at a wide range of quasi-static and high strain rates is of great interest to applications that are subjected to dynamic loading conditions. The Standard Linear Solid model or Prony series frameworks for modeling of strain rate dependent behavior are limited due to simplicity of the models to accurately represent a viscoelastic material with multiple relaxations. This work is aimed at developing a technique for manipulating the data derived from dynamic mechanical analysis to obtain an accurate estimate of the relaxation modulus of a material over a large range of strain rate. The technique relies on using the time-temperature superposition principle to obtain a frequency-domain master curve, and integral transform of this material response to the time domain using the theory of viscoelasticity. The relaxation function obtained from this technique is validated for two polymer matrix composites by comparing its predictions of the response to uniaxial strain at a prescribed strain rate to measurements taken from a separate set of tension experiments and excellent matching is observed. © 2017 Elsevier Ltd
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    Additive Manufacturing of Syntactic Foams: Part 2: Specimen Printing and Mechanical Property Characterization
    (Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Saltonstall, B.; Patil, B.; Hoffmann, N.; Doddamani, M.; Gupta, N.
    High-density polyethylene (HDPE) and its fly ash cenosphere-filled syntactic foam filaments have been recently developed. These filaments are used for three-dimensional (3D) printing using a commercial printer. The developed syntactic foam filament (HDPE40) contains 40 wt.% cenospheres in the HDPE matrix. Printing parameters for HDPE and HDPE40 were optimized for use in widely available commercial printers, and specimens were three-dimensionally (3D) printed for tensile testing at strain rate of 10?3 s?1. Process optimization resulted in smooth operation of the 3D printer without nozzle clogging or cenosphere fracture during the printing process. Characterization results revealed that the tensile modulus values of 3D-printed HDPE and HDPE40 specimens were higher than those of injection-molded specimens, while the tensile strength was comparable, but the fracture strain and density were lower. © 2018, The Minerals, Metals & Materials Society.
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    Additive Manufacturing of Syntactic Foams: Part 1: Development, Properties, and Recycling Potential of Filaments
    (Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Patil, B.; Hoffmann, N.; Saltonstall, B.; Doddamani, M.; Gupta, N.
    This work focuses on developing filaments of high-density polyethylene (HDPE) and their hollow particle-filled syntactic foams for commercial three-dimensional (3D) printers based on fused filament fabrication technology. Hollow fly-ash cenospheres were blended by 40 wt.% in a HDPE matrix to produce syntactic foam (HDPE40) filaments. Further, the recycling potential was studied by pelletizing the filaments again to extrude twice (2×) and three times (3×). The filaments were tensile tested at 10?4 s?1, 10?3 s?1, and 10?2 s?1 strain rates. HDPE40 filaments show an increasing trend in modulus and strength with the strain rate. Higher density and modulus were noticed for 2× filaments compared to 1× filaments because of the crushing of some cenospheres in the extrusion cycle. However, 2× and 3× filament densities are nearly the same, showing potential for recycling them. The filaments show better properties than the same materials processed by conventional injection molding. Micro-CT scans show a uniform dispersion of cenospheres in all filaments. © 2018, The Minerals, Metals & Materials Society.
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    Insights into formation of gradient nanostructured (GNS) layer and deformation induced martensite in AISI 316 stainless steel subjected to severe shot peening
    (Elsevier B.V., 2018) Jayalakshmi, M.; Huilgol, P.; Badekai Ramachandra, B.R.; Udaya Bhat, K.
    Severe peening is a well-accepted top-down approach to engender surface nanocrystallization in austenitic stainless steels. In the present study, AISI 316 grade austenitic stainless steel is subjected to severe peening through air blast shot peening technique. Study is aimed at analyzing the microstructural features of the peened layer and deformation induced martensite through transmission electron microscopy technique. Gradient nanostructured (GNS) layer formed as a result of high strain rate, multi-directional deformation during severe peening found to extend to about 500 ?m from the surface. Nucleation of deformation induced martensite is not limited to shear band intersections as affirmed by the published literature related to severe peening. It is observed to nucleate at multiple locations in the austenite matrix. Martensite units thus formed, coalesce with each other to form continuous layer of lath martensite layer at about 15–20 ?m from the surface. Upon further deformation, lath morphology transforms to dislocation cell-type; resulting in fine martensite crystallites at the topmost layer of the peened surface. © 2018 Elsevier B.V.