Direct physical evidence for the back-transformation of stress-induced martensite in the vicinity of cracks in pseudoelastic NiTi shape memory alloys

Gollerthan, S.; Young, Marcus L.; Neuking, K.; Ramamurty, Upadrasta; Eggeler, Gunther

doi:10.1016/j.actamat.2009.08.015

Cited by 88 publications

(44 citation statements)

References 24 publications

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“…In addition, a cohesive zone model has been developed by Freed and Banks-Sills (2007) to analyze the effects of the SIM on crack growth resistance in NiTi alloys, as well as to simulate the effects of the wake of the crack, which is mainly associated with the reverse martensitic transformation occurring during crack propagation. This latter mechanism was also experimentally demonstrated by infrared thermographic observations (Gollerthan et al, 2009b), carried out during in-situ loading of miniature compact tension specimens. Furthermore, some experimental studies have been carried out with the aim to analyze the formation and propagation of cracks under cyclic loading conditions (Gall et al, 2008;Ritchie, 2007, 2008) as well as to investigate the mechanical behavior of cracked components under static loadings (Chen et al, 2005;Daymond et al, 2007;Gall et al, 2001;Gollerthan et al, 2008Gollerthan et al, , 2009Maletta et al, 2009a).…”

Section: Introductionmentioning

confidence: 85%

Fracture control parameters for NiTi based shape memory alloys

Maletta

Furgiuele

2011

International Journal of Solids and Structures

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a b s t r a c tIn this paper new fracture control parameters for Nickel-Titanium (NiTi) based shape memory alloys (SMAs) are proposed, based on a recent literature analytical model on fracture mechanics of SMAs. In fact, the stress induced martensitic transformation, occurring in the crack tip region of NiTi alloys, causes a complex and unusual stress distribution with respect to common engineering materials. For this reason two different stress intensity factors (SIFs) have been defined to describe the stress distribution in both transformed and untransformed regions, i.e. in the martensitic and austenitic phases, respectively. Systematic studies have been carried out to analyze the effects of the main thermo-mechanical parameters of NiTi alloys on the two proposed SIFs, i.e. on the crack tip stress distribution, and comparisons with linear elastic fracture mechanics have been illustrated. Finally, the proposed model was used to analyze different loading conditions of a commercial superelastic NiTi alloys, which demonstrated a marked effect of the temperature on the crack tip stress distribution.

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Section: Introductionmentioning

confidence: 85%

Fracture control parameters for NiTi based shape memory alloys

Maletta

Furgiuele

2011

International Journal of Solids and Structures

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“…[39,40] This type of localized transformation to B19¢ is well established for pseudoelastic NiTi alloys subjected to tensile loading. [32][33][34][35][36][37][38][39][40] However, whether the stressinduced formation of R-phase also occurs in a localized manner still remains an open question.…”

Section: Introductionmentioning

confidence: 99%

“…In order to characterize this type of transformation-related deformation, a local assessment of strain is required. This can be achieved by using more than one strain gage, [33,34] by thermal imaging, [35,36] by evaluating the strain fields using optical methods, [37,38] or by using appropriately positioned multiple electrical resistance probes. [39,40] This type of localized transformation to B19¢ is well established for pseudoelastic NiTi alloys subjected to tensile loading.…”

Section: Introductionmentioning

confidence: 99%

On the Stress-Induced Formation of R-Phase in Ultra-Fine-Grained Ni-Rich NiTi Shape Memory Alloys

Olbricht

Yawny

Pelegrina

et al. 2011

Metall Mater Trans A

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Phase transformations in binary ultra-fine-grained (UFG) pseudoelastic NiTi wires were studied in a wide temperature range using mechanical loading/unloading experiments, resistance measurements, differential scanning calorimetry (DSC), thermal infrared imaging, and transmission electron microscopy (TEM). The formation of R-phase can be detected in the mechanical experiments. It is shown that the stress-strain response of the R-phase can be isolated from the overall stress-strain data. The R-phase always forms prior to B19¢ when good pseudoelastic properties are observed. The stress-induced B2 to R-phase transition occurs in a homogeneous manner, contrary to the localized character of the B2/R to B19¢ transformations. The temperature dependence of the critical stress values for the formation of the martensitic phases shows a Clausius Clapeyron type of behavior with constants close to 6 MPa/K (B19¢) and 18 MPa/K (R-phase). A stress-temperature map is suggested that summarizes the experimentally observed sequences of elementary transformation/deformation processes.

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“…[9][10][11]26, all experimental data presented here was taken from a pseudoelastic NiTi SMA with 50.7 at.% Ni, which had been subjected to thermo-mechanical treatments (forming and aging) and a final heat-treatment for 6 min at 773 K resulting in an average austenite grain size of 70 lm with Ni 4 Ti 3 precipitates ranging in size from 60 to 130 nm. The DSC curve for the pseudoelastic NiTi SMA has been reported in Gollerthan et al (Ref 9).…”

Section: Materials and Experimentsmentioning

confidence: 99%

“…In particular, it is widely accepted that thermoelastic martensitic transformation, and specifically stress-induced martensitic transformation, plays a significant role in the fracture process of NiTi SMAs ( . Experimental studies have focused on understanding the formation and propagation of cracks under variable loadings (Ref 4,5) as well as under static loading conditions (Ref [6][7][8][9][10][11][12]. The formation of stress-induced martensite in the crack tip vicinity, as a consequence of the highly localized stresses, has been observed using digital image correlation (DIC) (Ref 6), by infrared (IR) thermography (Ref 10), and by synchrotron x-ray diffraction (XRD) (Ref [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Stress-Induced Martensite in Front of Crack Tips in NiTi Shape Memory Alloys: Modeling Versus Experiments

Maletta

Young

2011

J. of Materi Eng and Perform

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NiTi-based shape memory alloys (SMAs) exhibit an unusual stress distribution at the crack tip as compared to common engineering materials, due to a stress-induced martensitic transformation resulting from highly localized stresses. Understanding the fracture mechanics of NiTi-based SMAs is critical to many of their applications. Here, we develop an analytical model, which predicts the boundaries of the transformation region in the crack tip vicinity of NiTi-based SMAs. The proposed model is based on a recent analytical approach which uses modified linear elastic fracture mechanics concepts to predict the crack tip stress distribution and transformation region in SMAs but, unfortunately, it applies only to the plane stress condition. To overcome this limitation, the proposed model accounts for stress triaxiality, which plays an important role in restricting crack tip plastic deformations in common ductile metals as well as the stressinduced martensite in NiTi SMAs. The effects of triaxial stress at the crack tip are taken into account by including a new parameter, the transformation constraint factor, which is based on the plastic constraint factor of elasto-plastic materials. The predictions of the model are compared with synchrotron x-ray microdiffraction observations and satisfactory agreement is observed between the two results. Finally, the evolution of crack tip transformation boundaries during fracture tests of miniature compact tension specimens is predicted and the effects of applied load and crack length are discussed.

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Direct physical evidence for the back-transformation of stress-induced martensite in the vicinity of cracks in pseudoelastic NiTi shape memory alloys

Cited by 88 publications

References 24 publications

Fracture control parameters for NiTi based shape memory alloys

Fracture control parameters for NiTi based shape memory alloys

On the Stress-Induced Formation of R-Phase in Ultra-Fine-Grained Ni-Rich NiTi Shape Memory Alloys

Stress-Induced Martensite in Front of Crack Tips in NiTi Shape Memory Alloys: Modeling Versus Experiments

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