Search results for: H. Sehitoglu

Items from 1 to 20 out of 103 results

article

FeMnNiAl Iron-Based Shape Memory Alloy: Promises and Challenges

W. Abuzaid, Y. Wu, R. Sidharth, F. Brenne, more

Shape Memory and Superelasticity > 2019 > 5 > 3 > 263-277

Among all shape memory alloys, the iron-based FeMnNiAl has emerged as one of the most promising compositions with a huge superelasticity temperature window (> 400 °C). In this article, we first point to the high local transformation strains (> 10%) and high transformation stress levels (500–700 MPa) that result in a large work output. When subjected to either tensile or compressive loading,...

article

Effects of Temperature on Fatigue Crack Propagation in Pseudoelastic NiTi Shape Memory Alloys

E. Sgambitterra, C. Maletta, P. Magarò, D. Renzo, more

Shape Memory and Superelasticity > 2019 > 5 > 3 > 278-291

The effects of temperature on fatigue crack propagation in a pseudoelastic NiTi shape memory alloy (SMA) were analyzed. Single edge crack specimens were used and near crack tip displacements were captured by in situ digital image correlation (DIC). The effective stress intensity range was estimated from displacement data by a fitting procedure involving the William’s solution. Stress intensity range...

article

Recent Progress on Modeling Slip Deformation in Shape Memory Alloys

H. Sehitoglu, S. Alkan

Shape Memory and Superelasticity > 2018 > 4 > 1 > 11-25

This paper presents an overview of slip deformation in shape memory alloys. The performance of shape memory alloys depends on their slip resistance often quantified through the Critical Resolved Shear Stress (CRSS) or the flow stress. We highlight previous studies that identify the active slip systems and then proceed to show how non-Schmid effects can be dominant in shape memory slip behavior. The...

article

Nonuniqueness of the fatigue threshold

S. Alkan, H. Sehitoglu

International Journal of Fatigue > 2017 > 104 > C > 309-321

The fatigue crack growth prediction near the threshold regime remains one of the most challenging fields in fatigue research. In previous studies, the threshold effects have been incorporated into fatigue crack growth models upon modification of the Paris Law in an empirical fashion. In this work, without a priori assumptions and empirical constants, we derived the threshold levels with a combination...

article

Dislocation core effects on slip response of NiTi- a key to understanding shape memory

S. Alkan, H. Sehitoglu

International Journal of Plasticity > 2017 > 97 > C > 126-144

The understanding of the non-Schmid behavior in shape memory alloy NiTi is considered a significant breakthrough because this alloy still remains enigmatic. We utilize an Eshelby-Stroh formalism in conjunction with Molecular Statics-Peierls stress calculation to predict the experimental CRSS results for three different crystal orientations and tension-compression cases. These combination of tools...

article

Giant non-Schmid effect in NiTi

S. Alkan, Y. Wu, H. Sehitoglu

Extreme Mechanics Letters > 2017 > 15 > Complete > 38-43

The work addresses the departure from Schmid law during plasticity of shape memory alloy, NiTi, that has been overlooked despite its cardinal importance. High resolution Digital Image Correlation (DIC) technique is utilized to pinpoint the critical resolved shear stress (CRSS) levels in uniaxial tension and compression experiments. To our knowledge, the non-Schmid behavior of B2 NiTi is characterized...

article

Elastocaloric cooling capacity of shape memory alloys – Role of deformation temperatures, mechanical cycling, stress hysteresis and inhomogeneity of transformation

Y. Wu, E. Ertekin, H. Sehitoglu

Acta Materialia > 2017 > 135 > C > 158-176

Elastocaloric (EC) effect refers to the rapid cooling in shape memory alloys (SMAs) during reverse transformation from martensite to austenite under adiabatic conditions. We present a very comprehensive study of the EC response far extending the existing literature by studying the effect of loading states (tension and compression), long-term cycling, strain localization, and deformation temperatures...

article

Superelasticity and Shape Memory Behavior of NiTiHf Alloys

H. Sehitoglu, Y. Wu, L. Patriarca, G. Li, more

Shape Memory and Superelasticity > 2017 > 3 > 2 > 168-187

The NiTiHf high-temperature shape memory alloys represent a significant advancement in extending the functionality of binary NiTi to elevated temperatures above 100 °C. Despite this potential, the previous results in the literature point to a disappointingly low shape memory strains with addition of Hf. On the other hand, based on theoretical analysis using the lattice constants, the transformation...

article

Finite element simulation of single crystal and polycrystalline Haynes 230 specimens

P.G. Luccarelli, G.J. Pataky, H. Sehitoglu, S. Foletti

International Journal of Solids and Structures > 2017 > 115-116 > C > 270-278

Metallic materials are typically described on the macroscopic scale without consideration that they are an aggregate of grains at the micro scale. Taking this into account, finite element simulations with a crystal plasticity model were used to reproduce the behavior of a Nickel-based superalloy, Haynes 230. The aim of this work was to replicate the local behavior of a real polycrystalline aggregate...

article

Shape memory strains and temperatures in the extreme

H. Sehitoglu, L. Patriarca, Y. Wu

Current Opinion in Solid State and Materials Science > 2017 > 21 > 2 > 113-120

It is well known that the achievement of high transformation strains in shape memory alloys (SMAs) has been curtailed by plastic deformation mediated via dislocation slip. In particular, the utilization of SMAs at high temperatures is also hindered by plastic slip. In this paper, an overview of the most important SMAs is provided by constructing transformation strain, transformation temperature, and...

article

Shape memory functionality under multi-cycles in NiTiHf

H. Sehitoglu, Y. Wu, L. Patriarca

Scripta Materialia > 2017 > 129 > C > 11-15

The functionality of NiTiHf (25%Hf) shape memory alloy (SMA) was studied under isobaric temperature cycling experiments. Both the local and overall strains, determined with digital image correlation (DIC), displayed excellent stability and no measurable unrecovered elongation. The external stress levels were higher than 250MPa and transformation temperature was 420°C which exceeds other NiTi based...

article

Non-Schmid response of Fe3Al: The twin-antitwin slip asymmetry and non-glide shear stress effects

S. Alkan, H. Sehitoglu

Acta Materialia > 2017 > 125 > C > 550-566

The non-Schmid effects in DO₃ ordered Fe₃Al (DO₃-Fe₃Al) are investigated by utilizing experimental measurements of the onset of slip and atomistic scale simulations to study slip directionality and core effects. Uniaxial tension and compression experiments were conducted on DO₃-Fe₃Al single crystals utilizing high resolution Digital Image Correlation (DIC) to measure local slip strain evolution. The...

article

Slip and Twinning in the [ 1 ¯ $$ \overline{\mathbf{1}} $$ 49]-Oriented Single Crystals of a High-Entropy Alloy

I. V. Kireeva, Yu. I. Chumlyakov, Z. V. Pobedennaya, Yu. N. Platonova, more

Russian Physics Journal > 2016 > 59 > 8 > 1242-1250

Using [ 1 ¯ $$ \overline{1} $$ 49] - oriented single crystals of an FCC Fe₂₀Ni₂₀Mn₂₀Cr₂₀Co₂₀ (at.%) high-entropy alloy subjected to tensile deformation, the temperature dependence of critical resolved shear stresses τ_cr(T) and the deformation mechanism of slip and twinning are investigated in the early stages of deformation at ε ≤ 5% within the temperature interval T = 77–573 K. It is shown...

article

Transformation stress modeling in new FeMnAlNi shape memory alloy

A. Ojha, H. Sehitoglu

International Journal of Plasticity > 2016 > 86 > C > 93-111

We investigate the bcc-fcc transformation in the new shape memory alloy FeMnAlNi utilizing density functional theory calculations for double shear. We formulate an energy expression to derive the fcc martensite formation stress, incorporating the transformation shear energy and the elastic interactions of the dislocations. The critical bcc-fcc transformation stress was determined as 191 MPa, which...

article

Near-tip closure and cyclic plasticity in Ni-based single crystals

S. Rabbolini, P.G. Luccarelli, S. Beretta, S. Foletti, more

International Journal of Fatigue > 2016 > 89 > C > 53-65

Fatigue crack growth was investigated in a 001 oriented single crystal specimen, made of a Ni-based superalloy, Haynes 230. Crack propagation was characterized with digital image correlation: crack closure, measured by analyzing the relative displacements of crack flanks, showed closure levels much lower than polycrystal alloys. Reversed plastic zones were calculated from regressed stress intensity...

article

Ultrahigh tensile transformation strains in new Ni50.5Ti36.2Hf13.3 shape memory alloy

Y. Wu, L. Patriarca, H. Sehitoglu, Y. Chumlyakov

Scripta Materialia > 2016 > 118 > C > 51-54

We report on unprecedented transformation strains exceeding 20% in tension for Ni_50.5Ti_36.2Hf_13.3 shape memory alloy (SMA). The strain measurements were made at multiscales utilizing advanced digital image correlation. The display of excellent strain reversibility in shape memory (isothermal deformation between M_f and A_f), isobaric thermal cycling (between M_f and A_f), and superelasticity experiments...

article

Mechanisms of fatigue crack growth – a critical digest of theoretical developments

P. Chowdhury, H. Sehitoglu

Fatigue & Fracture of Engineering Materials & Structures > 39 > 6 > 652 - 674

Recent advances in the processing technology are permitting the manufacture of novel metallic materials with superior fatigue properties via microstructure tailoring. In the light of these promising developments, there is a rising need for establishing a synergy between state‐of‐the‐art experimental characterizations and physically based theoretical underpinnings. A revisit to the existing predictive...

article

Strength prediction in NiCo alloys – The role of composition and nanotwins

P. Chowdhury, H. Sehitoglu, H.J. Maier, R. Rateick

International Journal of Plasticity > 2016 > 79 > C > 237-258

Experimentally, hardening behaviors of nano-twinned Ni–Co alloys in tension demonstrate strong composition dependence. The strengthening characteristics improve substantially with increasing Co content (up to 2.9% Co), however, accompanied by an abrupt decline (at 5.52% Co), suggesting the existence of a critical composition. On theoretical grounds, atomistic modeling is performed to rationalize the...

article

Critical Stresses for Twinning, Slip, and Transformation in Ti-Based Shape Memory Alloys

A. Ojha, H. Sehitoglu

Shape Memory and Superelasticity > 2016 > 2 > 2 > 180-195

We investigate the effect of Nb and Ta contents on the (i) critical resolved shear stress (CRSS) for the β − α″ transformation, (ii) the CRSS for austenite slip, and (iii) the CRSS for twin nucleation in martensite (α″ phase) that govern shape memory and superelasticity in Ti-based alloys. The critical stresses for slip and twinning are achieved with a modified Peierls Nabarro formalism utilizing...

article

High-temperature functional behavior of single crystal Ni51.2Ti23.4Hf25.4 shape memory alloy

L. Patriarca, H. Sehitoglu, E. Yu. Panchenko, Y.I. Chumlyakov

Acta Materialia > 2016 > 106 > C > 333-343

In this work the functional behavior of the new Ni_51.2Ti_23.4Hf_25.4 high temperature shape memory alloy is investigated along three crystal orientations in compression and compared with the polycrystal behavior. Transformation temperatures were measured following specific aging treatments with the aim to optimize the shape memory and pseudoelastic behaviors. Two aging treatments were then selected...

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Search results for: H. Sehitoglu

FeMnNiAl Iron-Based Shape Memory Alloy: Promises and Challenges

Effects of Temperature on Fatigue Crack Propagation in Pseudoelastic NiTi Shape Memory Alloys

Recent Progress on Modeling Slip Deformation in Shape Memory Alloys

Nonuniqueness of the fatigue threshold

Dislocation core effects on slip response of NiTi- a key to understanding shape memory

Giant non-Schmid effect in NiTi

Elastocaloric cooling capacity of shape memory alloys – Role of deformation temperatures, mechanical cycling, stress hysteresis and inhomogeneity of transformation

Superelasticity and Shape Memory Behavior of NiTiHf Alloys

Finite element simulation of single crystal and polycrystalline Haynes 230 specimens

Shape memory strains and temperatures in the extreme

Shape memory functionality under multi-cycles in NiTiHf

Non-Schmid response of Fe3Al: The twin-antitwin slip asymmetry and non-glide shear stress effects

Slip and Twinning in the [ 1 ¯ $$ \overline{\mathbf{1}} $$ 49]-Oriented Single Crystals of a High-Entropy Alloy

Transformation stress modeling in new FeMnAlNi shape memory alloy

Near-tip closure and cyclic plasticity in Ni-based single crystals

Ultrahigh tensile transformation strains in new Ni50.5Ti36.2Hf13.3 shape memory alloy

Mechanisms of fatigue crack growth – a critical digest of theoretical developments

Strength prediction in NiCo alloys – The role of composition and nanotwins

Critical Stresses for Twinning, Slip, and Transformation in Ti-Based Shape Memory Alloys

High-temperature functional behavior of single crystal Ni51.2Ti23.4Hf25.4 shape memory alloy

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