The Experts below are selected from a list of 1764 Experts worldwide ranked by ideXlab platform
Romesh C. Batra - One of the best experts on this subject based on the ideXlab platform.
-
Shear band spacing in thermoviscoplastic materials
International Journal of Impact Engineering, 2006Co-Authors: Romesh C. Batra, Z.g. WeiAbstract:Abstract A closed-form expression for shear band spacing in Strain-hardening, Strain-Rate-hardening and thermally softening thermoviscoplastic materials is derived by studying the stability of a homogeneous solution of equations governing its simple shearing deformations. The wavelength of the perturbation that maximizes its initial growth Rate is assumed to determine the shear band spacing, L s . The dependence of L s upon various material parameters and the Nominal Strain Rate, ɛ ˙ , is delineated. When written as L s = A 1 k χ 1 or A 2 ɛ ˙ χ 2 where A 1 and A 2 are parameters and k is the thermal conductivity, it is found that χ 2 ≃ - 0.787 and χ 1 depends upon the Strain-Rate hardening exponent m ; χ 1 ≃ 0.5 for m ≃ 10 - 6 and n ≃ 0.011 , decreases rapidly to 0.21 for m ≃ 10 - 4 and n ≃ 0.011 , and then increases slowly to 0.25 for m ≃ 0.05 and n ≃ 0.011 . However, for m = 0 and n ≠ 0 , χ 1 = 1 .
-
Crack propagation due to brittle and ductile failures in microporous thermoelastoviscoplastic functionally graded materials
Engineering Fracture Mechanics, 2005Co-Authors: Romesh C. Batra, B. M. LoveAbstract:Abstract Plane Strain transient finite thermomechanical deformations of heat-conducting functionally gradient materials comprised of tungsten and nickel–iron matrix are analyzed to delineate brittle/ductile failures by the nodal release technique. Each material is modeled as Strain-hardening, Strain-Rate-hardening and thermally-softening. Effective properties are derived by the rule of mixtures. At Nominal Strain-Rate of 2000 s −1 brittle crack speed approaches Rayleigh’s wave speed in the tungsten-plate, the nickel–iron-plate shatters at Strain-Rates above 1130 s −1 , and the composite plate does not shatter. The maximum speed of a ductile crack in tungsten and nickel–iron is about 1.5 km/s, and that in the composite is about 0.14 km/s.
-
Microstructural effects on shear instability and shear band spacing
Theoretical and Applied Fracture Mechanics, 2000Co-Authors: L. Chen, Romesh C. BatraAbstract:A constitutive relation that accounts for the thermally activated dislocation motion and microstructure interaction is used to study the stability of a homogeneous solution of equations governing the simple shearing deformations of a thermoviscoplastic body. An instability criterion and an upper bound for the growth Rate of the infinitesimal deformations superimposed on the homogeneous solution are derived. By adopting Wright and Ockendon's postulate, i.e., the wavelength of the dominant instability mode with the maximum growth Rate determines the minimum spacing between shear bands, the shear band spacing is computed. The effect of the initial dislocation density, the Nominal Strain-Rate, and parameters describing the initial thermal activation and the initial microstructure interaction on the shear band spacing are delineated.
-
Dynamic shear band development in dipolar thermoviscoplastic materials
Computational Mechanics, 1994Co-Authors: Romesh C. Batra, J. HwangAbstract:We study thermomechanical deformations of a viscoplastic body deformed in plane Strain compression at a Nominal Strain-Rate of 5000 sec-1. We develop a material model in which the second order gradients of the velocity field are also included as kinematic variables and propose constitutive relations for the corresponding higher order stresses. This introduces a material characteristic length l, in addition to the viscous and thermal lengths, into the theory. It is shown that the computed results become mesh independent for l greater than a certain value. Also, the consideration of higher order velocity gradients has a stabilizing effect in the sense that the initiation of shear bands is delayed and their growth is slower as compared to that for nonpolar (l=0) materials.
-
On the Propagation of a Shear Band in a Steel Tube
Journal of Engineering Materials and Technology, 1994Co-Authors: Romesh C. Batra, Xiangtong ZhangAbstract:Marchand and Duffy tested thin-walled steel tubes in a split Hopkinson torsion bar at a Nominal Strain-Rate of approximately 1,600/s and could not determine conclusively whether a shear band initiating at a point in the tube propagated around the circumference in one direction or in both directions. They estimated the speed of propagation to be 520 m/s in the former case and 260 m/s in the latter. Here, the authors simulate their test numerically, and find that the shear band propagates in both directions around the circumference of the tube. When the tube is twisted at a Nominal Strain-Rate of 5,000/s, the band speed varies from 180 m/s at the site of the initiation to approximately 1,000 m/s at the nearly diametrically opposite point. The band speed increases with an increase in the Nominal Strain-Rate. The material defect is modeled by assuming that a small region near the center of the tubular surface is made of a material weaker than that of the rest of the tube.
V Sivan - One of the best experts on this subject based on the ideXlab platform.
-
stress corrosion cracking susceptibility of friction stir welded aa7075 aa6056 dissimilar joint
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Bala P Srinivasan, W Dietzel, R Zettler, J Dos F Santos, V SivanAbstract:Abstract Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow Strain Rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a Nominal Strain Rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower Nominal Strain Rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at Nominal Strain Rate levels in the order of 10−7 s−1.
-
Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: P. Bala Srinivasan, W Dietzel, R Zettler, J.f. Dos Santos, V SivanAbstract:Abstract Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow Strain Rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a Nominal Strain Rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower Nominal Strain Rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at Nominal Strain Rate levels in the order of 10−7 s−1.
R C Batra - One of the best experts on this subject based on the ideXlab platform.
-
effect of viscoplastic relations on the instability Strain shear band initiation Strain the Strain corresponding to the minimum shear band spacing and the band width in a thermoviscoplastic material
International Journal of Plasticity, 2001Co-Authors: R C BatraAbstract:We study thermomechanical deformations of a steel block deformed in simple shear and model the thermoviscoplastic response of the material by four different relations. We use the perturbation method to analyze the stability of a homogeneous solution of the governing equations. The smallest value of the average Strain for which the perturbed homogeneous solution becomes unstable is called the critical Strain or the instability Strain. For each one of the four viscoplastic relations, we investigate the dependence upon the Nominal Strain-Rate of the critical Strain, the shear band initiation Strain, the shear band spacing and the band width. It is found that the qualitative responses predicted by the Wright–Batra, Johnson–Cook and the power law relations are similar but these differ from that predicted by the Bodner–Partom relation. The computed band width is found to depend upon the specimen height. # 2001 Elsevier Science Ltd. All rights reserved.
-
The Evolution of Damage in Prenotched Steel Specimens Deformed at High Strain Rates
Computational Mechanics ’95, 1995Co-Authors: Y. H. Cao, R C BatraAbstract:We study dynamic thermomechanical deformations of a prenotched steel specimen deformed in plane Strain tension at Nominal Strain-Rates of 1000/s, 5000/s and 20000/s. The thermomechanical response of the porous material is modeled by the modified Gurson’s flow potential; the modification being due to Tvergaard and Needleman. The effective stress is assumed to depend upon the plastic Strain, plastic Strain-Rate and temperature through the Johnson-Cook relation. Voids are presumed to grow due to plastic dilation and nucleate when the plastic Strain reaches a critical value. The dependence of Young’s modulus, bulk modulus and thermal conductivity on porosity is accounted for. It is found that both the initial porosity and the Nominal Strain-Rate influence noticeably when and from where the damage, defined as the porosity attaining a critical value, begins to evolve.
-
An adaptive mesh refinement technique for the analysis of shear bands in plane Strain compression of a thermoviscoplastic solid
Computational Mechanics, 1992Co-Authors: R C Batra, K. -i. KoAbstract:We have developed an adaptive mesh refinement technique that geneRates elements such that the integral of the second invariant of the deviatoric Strain-Rate tensor over an element is nearly the same for all elements in the mesh. It is shown that the finite element meshes so geneRated are effective in resolving shear bands, which are narrow regions of intense plastic deformation that form in high Strain-Rate deformation of thermally softening viscoplastic materials. Here we assume that the body is deformed in plane Strain compression at a Nominal Strain-Rate of 5000 sec^-1, and model a material defect by introducing a temperature perturbation at the center of the block.
-
dynamic adiabatic shear band development in a bimetallic body containing a void
International Journal of Solids and Structures, 1991Co-Authors: R C BatraAbstract:Abstract We study the problem of the initiation and subsequent growth of a shear band in a thermally softening viscoplaslic prismatic body of square cross-section and containing two symmetrically placed thin layers of a different viscoplastic material and an elliptical void at the center. The yield stress of the material of the thin layer in a quasistatic simple compression test is taken to be either five times or one-fifth that of the matrix material. The body is deformed in plane Strain compression at a Nominal Strain Rate of 5.000 s '. These deformations are assumed to be symmetrical about the centroidal axes. It is found that shear bands initiate from the ends of the major axes of the ellipsoidal void and propagate in the direction of the maximum shear stress. These bands are arrested by the strong virtually rigid material of the thin layer, but pass through the weaker material of the thin layer rather easily. Other shear bands originale from points where the thin layers meet the free boundaries and propagate inio the matrix material along the direction ol maximum shearing when the material of the thin layer is stronger, but propagate into the thin layer when its maleriul is weaker than the matrix material. Tlie band in the weaker material of the thin layer bifurcates into two hands that propagate into the matrix material in the direction of the maximum shearing stress.
W Dietzel - One of the best experts on this subject based on the ideXlab platform.
-
Stress corrosion cracking of AZ61 magnesium alloy friction stir weldments in ASTM D1384 solution
Corrosion Engineering Science and Technology, 2009Co-Authors: P. B. Srinivasan, C. Blawert, R Zettler, W DietzelAbstract:AbstractStress corrosion cracking (SCC) behaviour of a wrought magnesium alloy (AZ61) friction stir weldment was assessed in ASTM D1384 test solution at two Strain Rates. The analyses have shown that both the parent and the weldment are susceptible to SCC at a Nominal Strain Rate of 10–6 s–1. Fractographic evidence clearly reveals the susceptibility, especially of the fine grained region of the friction stir weld nugget to SCC. The susceptibility to cracking has been observed to increase with decreasing Strain Rate and under this condition (10–7 s–1), the behaviour of the parent and the friction stir weldment were nearly the same.
-
Effect of plasma electrolytic oxidation treatment on the corrosion and stress corrosion cracking behaviour of AM50 magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: P. Bala Srinivasan, C. Blawert, W DietzelAbstract:Abstract The effect of a silicate-based plasma anodization treatment on the corrosion and stress corrosion cracking behaviour of a cast AM50 magnesium alloy was studied. Electrochemical tests revealed the beneficial effect of the plasma electrolytic oxidation (PEO) in improving the corrosion resistance of the alloy. Although the coating had provided an improved resistance to stress corrosion cracking in this test environment at a Nominal Strain Rate of 10 −6 s −1 , it could not completely eliminate the SCC susceptibility of the alloy. Cracking of the coating under conditions of Straining was found to be the reason for SCC of PEO-coated alloy.
-
stress corrosion cracking susceptibility of friction stir welded aa7075 aa6056 dissimilar joint
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005Co-Authors: Bala P Srinivasan, W Dietzel, R Zettler, J Dos F Santos, V SivanAbstract:Abstract Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow Strain Rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a Nominal Strain Rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower Nominal Strain Rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at Nominal Strain Rate levels in the order of 10−7 s−1.
-
Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: P. Bala Srinivasan, W Dietzel, R Zettler, J.f. Dos Santos, V SivanAbstract:Abstract Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow Strain Rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a Nominal Strain Rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower Nominal Strain Rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at Nominal Strain Rate levels in the order of 10−7 s−1.
P. Bala Srinivasan - One of the best experts on this subject based on the ideXlab platform.
-
Effect of plasma electrolytic oxidation treatment on the corrosion and stress corrosion cracking behaviour of AM50 magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: P. Bala Srinivasan, C. Blawert, W DietzelAbstract:Abstract The effect of a silicate-based plasma anodization treatment on the corrosion and stress corrosion cracking behaviour of a cast AM50 magnesium alloy was studied. Electrochemical tests revealed the beneficial effect of the plasma electrolytic oxidation (PEO) in improving the corrosion resistance of the alloy. Although the coating had provided an improved resistance to stress corrosion cracking in this test environment at a Nominal Strain Rate of 10 −6 s −1 , it could not completely eliminate the SCC susceptibility of the alloy. Cracking of the coating under conditions of Straining was found to be the reason for SCC of PEO-coated alloy.
-
Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: P. Bala Srinivasan, W Dietzel, R Zettler, J.f. Dos Santos, V SivanAbstract:Abstract Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow Strain Rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a Nominal Strain Rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower Nominal Strain Rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at Nominal Strain Rate levels in the order of 10−7 s−1.