Steady State Crack Growth in Shape Memory Alloys

2013 ◽  
Author(s):  
Selcuk Hazar ◽  
Wael Zaki ◽  
Ziad Moumni ◽  
Gunay Anlas
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth ◽  
Crack Tip ◽  
Reverse Transformation ◽  
Small Scale ◽  
Local Algorithms ◽  
Non Local

Shape memory alloys experience phase transformation from austenite to martensite around crack tip. When the crack advances, martensitic transformation occurs at the tip and the energy that goes into transformation results in stable crack growth like in the case of plastic deformation. In literature, there are studies on steady-state crack growth in elasto-plastic materials with small scale yielding around crack tip that use stationary movement methods similar to non-local algorithms. In this work, Mode I steady-state crack growth in an edge cracked Nitinol plate is modeled using a non-local stationary movement method. The Zaki-Moumni (ZM) constitutive model is utilized for this purpose. The model is implemented in ABAQUS by means of a user-defined material subroutine (UMAT) to determine transformation zones around the crack tip. Steady-state crack growth is first simulated without considering reverse transformation to calculate the effect of transformation on stress distribution in the wake region, then reverse transformation is taken into account. Stress distribution and transformation regions calculated for both cases are compared to results obtained for the case of a static crack.

Mode I Steady Crack-Growth in Superelastic Shape Memory Alloys

2012 ◽  
Author(s):  
Theocharis Baxevanis ◽  
Dimitris Lagoudas ◽  
Chad Landis
Keyword(s):  
Shape Memory Alloys ◽  
Energy Release Rate ◽  
Shape Memory ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Crack Tip ◽  
Scale Transformation ◽  
Small Scale ◽  
Mode I

A numerical analysis of quasi-static, steady state crack growth in superelastic Shape Memory Alloys (SMAs) under small-scale transformation conditions is carried out for plane strain, mode I loading. Crack growth is assumed to proceed at a critical level of the crack-tip energy release rate. Finite-element results concerning the mechanical fields near the advancing crack tip are presented and the ratio of the far-field applied energy release rate to the crack-tip energy release rate is obtained for a range of thermomechanical parameters. A substantial fracture toughening is observed associated with closure stresses placed on the crack tip by the transformed material left behind in the wake of the advancing crack tip.

Prediction of Creep Crack Initiation Under Transient Stress Conditions

2006 ◽  
Author(s):  
Catrin M. Davies ◽  
Noel P. O’Dowd ◽  
Kamran M. Nikbin ◽  
George A. Webster
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Crack Initiation ◽  
Creep Strain ◽  
Crack Tip ◽  
Steady State Creep ◽  
Creep Model ◽  
Small Scale ◽  
Creep Crack ◽  
Initial Loading

A method to predict the time for creep crack initiation (CCI) from a stationary crack tip is presented. The method is relevant to situations where small scale yield or widespread plasticity conditions prevail on initial loading. Initiation is considered to occur at the attainment of a critical creep strain at a small distance from the crack tip. The model proposed here considers the integrated effects of creep strain accumulation as the stress distribution changes from that on initial loading (controlled by J) to the steady state creep stress distribution (controlled by C*). Material properties are chosen to represent Type 316H stainless steel at 550°C and plane strain conditions are considered. For the conditions examined, the CCI times predicted are significantly shorter times than those predicted using a steady state creep model.

scholarly journals Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State

2018 ◽  
Author(s):  
Behrouz Haghgouyan ◽  
Ibrahim Karaman ◽  
Sameer Jape ◽  
Alexandros Solomou ◽  
Dimitris C. Lagoudas
Keyword(s):  
Finite Element ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Crack Tip ◽  
Stress Conditions ◽  
Mode I ◽  
Niti Shape Memory Alloys

Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs) subjected to mode-I, isothermal loading is studied using finite element analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite element suite and crack growth under displacement boundary condition is investigated for plane strain and plane stress conditions. Parameters for the SMA material constitutive law implemented in the finite element setup are acquired from characterization tests conducted on near-equiatomic NiTi SMA. Virtual crack closure technique (VCCT) is implemented where crack is assumed to extend when the energy release rate at the crack-tip becomes equal to the experimentally obtained material-specific critical value. Load-displacement curves and mechanical fields near the crack-tip in plane strain and plane stress cases are examined. Moreover, a discussion with respect to the crack resistance R-curves calculated using the load-displacement response for plane strain and plane stress conditions is presented.

A Finite Element Study of Stable Crack-Growth in Superelastic Shape Memory Alloys

2012 ◽  
Author(s):  
Antonino Parrinello ◽  
Theocharis Baxevanis ◽  
Dimitris Lagoudas ◽  
Austin Cox
Keyword(s):  
Finite Element ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth ◽  
Small Strain ◽  
Stable Crack Growth ◽  
Constitutive Law ◽  
Scale Transformation ◽  
Small Scale ◽  
Element Analysis

A finite-element analysis of stable crack growth in superelastic Shape Memory Alloys (SMAs) is carried out for plane strain, mode I loading. The small-scale transformation assumption is employed in the calculations using displacement boundary conditions on a circular region that encloses the stress-induced phase transformation zone. The constitutive law adopts the classical rate-independent small-strain flow theory for the evolution equation of the transformation strains. The crack is assumed to propagate quasi-statically with the energy release rate maintained at a critical value; the analysis is accomplished by means of the Virtual Crack Closure Technique (VCCT). Resistance curves, obtained for a range of thermomechanical parameters, show enhanced fracture toughness.

A Single Specimen CTOA Test Method for Evaluating the Crack Tip Opening Angle in Gas Pipeline Steels

2004 ◽  
Author(s):  
Sayyed H. Hashemi ◽  
Ian C. Howard ◽  
John R. Yates ◽  
Robert M. Andrews ◽  
Alan M. Edwards
Keyword(s):  
Steady State ◽  
Crack Growth ◽  
Crack Tip ◽  
Gas Pipeline ◽  
Test Method ◽  
Opening Angle ◽  
Single Specimen ◽  
Data Set ◽  
Test Technique ◽  
Pipeline Steels

Failure information from recent full-scale burst experiments on modern TMCP gas pipeline steels having a yield strength level of 690MPa and higher has shown that the CTOA fracture criterion can be effectively used to predict the arrest/propagation behaviour of the pipe against possible axial ductile fractures. The use of CTOA as an alternative or an addition to the Charpy V-notch and DWTT fracture energy in pipelines is currently under review. A significant difficulty currently limiting the more extensive use of CTOA in pipeline assessment is its practical evaluation either in the real structure or in a laboratory scale test. Different combinations of experimental and finite element analyses have been proposed for the measurement of the CTOA of a material. Although most of these models are able to predict the CTOA effectively, their implementation requires extensive calibration processes using the test load-deflection data. The authors have recently developed a novel test technique for direct measurement of the steady state CTOA using a modified double cantilever beam geometry. The technique uses optical imaging to register the uniform deformation of a fine square grid scored on the sides of the specimen. The slope of the deformed gridlines near the crack tip is measured during crack growth from captured images. Its value is a representative of the material CTOA. This paper presents recent results from the implementation of the technique to determine the steady state CTOA (steady state in this work refers to regions of ductile crack growth where CTOA values are constant and independent of crack length) of API X80 and X100 grade gas pipeline steels. In each case the approach was able to produce large amounts of highly consistent CTOA data from both sides of the test sample even from a single specimen. This extensive data set allowed an evaluation of the variance of the stable CTOA as the crack grew through the microstructure. The test method generated a steady CTOA value of 11.1° for X80 and 8.5° for X100 steels tested, respectively.

scholarly journals Modelling fatigue crack growth in shape memory alloys

2022 ◽  
Author(s):  
Marlini Simoes ◽  
Christopher Braithwaite ◽  
Advenit Makaya ◽  
Emilio Martínez‐Pañeda
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Crack Growth

Environmentally Assisted Cracking of Subsea Pipelines in Oil & Gas Production Environments—Effect of Static Loading

CORROSION ◽  
10.5006/2896 ◽  
2020 ◽  
Vol 76 (3) ◽  
pp. 312-323
Author(s):  
Ramgopal Thodla ◽  
Feng Gui ◽  
Colum Holtam
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Steady State ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Tip ◽  
Metal Dissolution ◽  
Low Frequencies ◽  
Static Crack

Fatigue crack growth rate of line pipe steels in sour environments typically exhibits a steady-state value at low frequencies. However, in highly inhibited sour environments, there is no evidence of a steady-state fatigue crack growth at low frequencies. This is likely a result of static crack growth rate at Kmax. Stable static crack growth measured under constant stress intensity factor (K) conditions in inhibited sour environments was in the range of 10−7 mm/s to 10−8 mm/s. The crack growth rate in inhibited sour environments is likely associated with crack tip processes associated with metal dissolution/film formation and associated hydrogen evolution. The results obtained were modeled based on a crack tip strain rate based approach, where the rate limiting step was the metal dissolution/FeS formation and the corresponding hydrogen generation reaction.

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