scholarly journals 3D characterisation of hydrogen environmentally assisted cracking during static loading of AA7449-T7651

2021 ◽  
Author(s):  
Unai De Francisco ◽  
Felix Beckmann ◽  
Julian Moosmann ◽  
Nicolas O. Larrosa ◽  
Matthew J. Peel
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Environmental Exposure ◽  
Exposure Time ◽  
Transgranular Fracture ◽  
Crack Growth Behaviour ◽  
X Ray ◽  
Environmentally Assisted Cracking ◽  
Boundary Triple ◽  
Gauge Section

AbstractIn this investigation, synchrotron X-ray microtomography was used to perform 3D in situ observations of crack initiation and growth during hydrogen environmentally assisted cracking (HEAC) in tensile samples of AA7449-T7651. Two smooth tensile samples with a 1 mm diameter gauge section were held at a fixed displacement ($$\approx 30$$ ≈ 30 % of yield stress) in warm, moist air ($$\approx 76\,^\circ $$ ≈ 76 ∘ C, 73% relative humidity). The samples were then imaged repeatedly using X-ray tomography until they fractured completely. The tomograms showing the nucleation and evolution of intergranular cracks were correlated with electron microscopy fractographs. This enabled the identification of crack initiation sites and the characterisation of the crack growth behaviour relative to the microstructure. The samples were found to fracture within an environmental exposure time of 240 min. Some cracks in both samples nucleated within an exposure time of 80 min (33–40% of the total lifetime). Many cracks were found to nucleate both internally and at the sample surface. However, only superficial cracks contributed to the final fracture surface as they grew faster owing to the direct environmental exposure and the larger crack opening. HEAC occurred prominently via brittle intergranular cracking, and cracks were found to slow down when approaching grain boundary triple junctions. Additionally, crack shielding from nearby cracks and the presence of coarse Al–Cu–Fe particles at the grain boundaries were also found to temporarily reduce the crack growth rates. After prolonged crack growth, the HEAC cracks displayed ductile striations and transgranular fracture, revealing a change in the crack growth mechanism at higher stress intensity factors.

Specimen Geometry Effects on Creep Crack Initiation and Growth in Parent Materials and Weldments

2011 ◽  
Author(s):  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
David W. Dean ◽  
Kamran M. Nikbin
Keyword(s):  
High Temperature ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Parent Material ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference ◽  
Constraint Effects

High temperature crack growth in weldments is of great practical concern in high temperature plant components. Cracking typically occurs in the heat affected zone (HAZ) and often propagates into adjacent parent material (PM). Recently, the importance of constraint effects on creep crack growth behaviour has been recognised and creep crack growth testing on a range of specimen geometries has been performed. Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens using sections taken from a non-stress-relieved 316 steel weldment. These specimens include the compact tension, C(T), middle tension, M(T) and circumferentially cracked bar, CCB, geometries. Results are presented from two long-term creep crack growth (CCG) tests performed on M(T) weldment specimens and these are compared with available data on C(T) and CCB weldment specimens together with both long and short term tests on parent material for a range of specimen geometries. The creep crack initiation (CCI) and growth (CCG) behaviour from these tests has been analysed in terms of the C* parameter. As high levels of residual stress exist in non-stress-relieved weldments, the residual stresses remaining in the weldment specimens have therefore been quantified using the neutron diffraction technique. Long-term (low-load) tests are required on PM specimen to observe specimen constraint effects in 316 steel at 550 °C. When interpreted in terms of the C* parameter the CCG behavior of PM and Weldment materials follow the same trendline on low constraint geometries. However, significant difference is observed in the CCG behavior of PM and weldments on the high constraint C(T) geometry. Long term tests on C(T) specimen weldments are required to confirm the results found.

Predictions of Creep Crack Initiation Periods in Pre-Compressed 316H Stainless Steel

2013 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
G. A. Webster ◽  
D. W. Dean
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Crack Growth ◽  
Crack Opening ◽  
Creep Crack Growth ◽  
Prediction Methods ◽  
Opening Displacement ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference

Pre-compression of 316H stainless steel significantly alters its tensile, uniaxial creep and crack growth behaviour. It has previously been shown that reliable and conservative creep crack initiation predictions can generally be obtained for as-received 316H stainless steel using a variety of prediction methods. Given the changes in material behaviour caused by pre-compression, this paper applies similar prediction methods to pre-compressed 316H stainless steel at 550°C. Several procedures are available for estimating creep crack initiation time periods. The suitability of a procedure depends on the availability of the necessary material data. The procedures considered in this paper include the use of the creep fracture mechanics parameter C*, the crack opening displacement concept, the sigma-d approach and the time dependent failure assessment diagram. Creep crack growth tests have been performed on compact tension specimens manufactured from 316H stainless steel which was uniformly pre-compressed by 4% and 8% at room temperature. For each test, the time for creep crack initiation to occur was recorded. Predicted creep crack initiation times have been compared with the experimentally determined values. Comparisons with as-received material are also included. For pre-compressed material, conservative creep crack initiation predictions were only consistently achieved using steady state creep crack growth rates predicted from C*. This is a significant difference to as-received material for which conservative predictions were generally obtained by a variety of methods. At this time, there is only a limited set of pre-compressed data making it difficult to draw firm conclusions about the appropriateness of the various creep crack initiation prediction methods. The differences in the results between the pre-compressed and as-received material do however highlight the need for further tests on pre-compressed material.

Prediction of Residual Life Assesment Using Thermography and Crack Growth Analysis

2012 ◽  
Vol 157-158 ◽  
pp. 202-209
Author(s):  
Marina Kutin ◽  
Ivana Vasovic ◽  
Mirko Maksimovic ◽  
Marko Ristic
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Infrared Thermography ◽  
Residual Life ◽  
Fatigue Cracks ◽  
Testing Machine ◽  
Crack Tip ◽  
Crack Tip Opening Displacement ◽  
Variable Loading ◽  
Crack Growth Behaviour

The most important characteristics for service safety of complex metal structures are those describing crack initiation and growth caused by static or dynamic, variable loading. Crack initiation and growth is subject of numerous investigations by different methods. The paper shows the possibility of applying infrared thermography to the problems of fracture mechanics. The main aim of testing was to qualitative relate the temperature changes of the spacemen measured by infrared thermography with the evaluation of fatigue cracks in steel specimen. Based on the distribution of temperature on the surface of the sample, during the action of force, the spread of plastic zones and crack tip are determined. The increase of temperature produced by the plastic deformation at the crack tip has been measured by infrared camera Thermal CAM SC640, FLIR Systems. SE(B) specimens were tested in three-point bending (TPB), following the procedures of ASTM E1820, on electrical mechanical testing machine with crack tip opening displacement (CTOD) control, at room temperature. Numerical simulation of stress distribution on the same model under same condition is presented, too. The results showed that thermography is a method suitable for monitoring and prediction of crack initiation and growth, as well as critical stress in elastic and elastic-plastic deformations. Fatigue crack growth behaviour of cracked TPB specimen made of S355 J2 G3 steel using Paris relation is considered.

On angled crack initiation under biaxial loading

1984 ◽  
Vol 19 (1) ◽  
pp. 51-59 ◽  
Author(s):  
C W Woo ◽  
L H Ling
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Test Specimen ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Crack Problem ◽  
Complex Loading ◽  
Loading Conditions ◽  
Fracture Criteria ◽  
Crack Growth Behaviour

The angled crack problem has been of growing interest to both designers and researchers for the prediction of the structural integrity of components under complex loading conditions. In the study of angled crack growth behaviour, it is invariably of interest to predict the initial crack growth direction θ0 and the fractures stress σc at which crack initiation occurs. In this paper the merits of the various proposed fracture criteria are reviewed. The biaxial loading effect on the parameter used in each criterion for the prediction of the fracture behaviour is studied. It is observed that the popular testing method employing uniaxial loading of a test specimen is inadequate to demonstrate the suitability of fracture criteria in the prediction of θ0 and σc. It is suggested that with the biaxial loading of a test specimen with an angled crack, a better appraisal of the fracture criteria can be obtained. The experimental results obtained in this study seem to support the maximum stress criteria for both uniaxial and biaxial loading conditions. Both tensions and compression biaxial loading effects have been considered.

Comparison of DBEM and FEM Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2007 ◽  
Vol 348-349 ◽  
pp. 129-132 ◽  
Author(s):  
Roberto G. Citarella ◽  
Friedrich G. Buchholz
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Crack Path ◽  
Shear Loading ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Corner Points ◽  
Experimental Findings

In this paper detailed results of computational 3D fatigue crack growth simulations will be presented. The simulations for the crack path assessment are based on the DBEM code BEASY, and the FEM code ADAPCRACK 3D. The specimen under investigation is a SEN-specimen subject to pure anti-plane or out-of-plane four-point shear loading. The computational 3D fracture analyses deliver variable mixed mode II and III conditions along the crack front. Special interest is taken in this mode coupling effect to be found in stress intensity factor (SIF) results along the crack front. Further interest is taken in a 3D effect which is effective in particular at and adjacent to the two crack front corner points, that is where the crack front intersects the two free side surfaces of the specimen. Exactly at these crack front corner points fatigue crack growth initiates in the experimental laboratory test specimens, and develops into two separate anti-symmetric cracks with complex shapes, somehow similar to bird wings. The computational DBEM results are found to be in good agreement with these experimental findings and with FEM results previously obtained. Consequently, also for this new case, with complex 3D crack growth behaviour of two cracks, the functionality of the proposed DBEM and FEM approaches can be stated.

Effect of Hydrogenated Water on Fatigue Crack Growth for Austenitic Stainless Steel in Simulated BWR Water Environment

2004 ◽  
Author(s):  
Li H. Wang
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Austenitic Stainless Steel ◽  
Fatigue Crack Growth ◽  
Water Chemistry ◽  
Crack Growth ◽  
Growth Stage ◽  
Transgranular Fracture ◽  
Cyclic Loading Condition

Fatigue crack growth rates (FCGR) of sensitized austenitic stainless steel (SS) were measured in simulated BWR water at 288 °C using compact tension specimens under different cyclic loading modes, including saw-tooth, trapezoidal and constant loading pattern. This study tested sensitized SS in normal water chemistry (NWC) and hydrogen water chemistry (HWC) respectively, and attempted to clarify the effect of low electrochemical corrosion potential on the FCGR of sensitized stainless steel. Significant environment effects on FCGR of sensitized stainless steel were observed in both water chemistries when compared with air fatigue curve. The pronounced suppression effect of HWC on crack growth in statically sustained load was not observed in cyclic loading condition. ASME curve doesn’t seem to be conservative and could not bound all the FCGR data tested in this study. In contrast, all of the measured FCGR data were bound by the JSME disposition curve. PLEDGE model proposed by General Electric reasonably predicted the FCGR of sensitized SS in NWC, but underestimated the FCGR in HWC. ANL’s superposition model successfully estimated the FCGR measured in both water chemistries. The fractography exhibited transgranular fracture mode during the crack initiation and growth stage. No differences in the appearance of fracture surface were observed in HWC and NWC. Only in very high DO environments, the sensitized 304 SS exhibited the mixed mode of intergranular and transgranular during growth stage.

Estimation of Creep Crack Growth Properties Using Circumferential Notched Round Bar Specimen for 12CrWCoB Rotor Steel

2005 ◽  
Vol 297-300 ◽  
pp. 397-402
Author(s):  
Je Chang Ha ◽  
Joon Hyun Lee ◽  
Masaaki Tabuchi ◽  
A.Toshimitsu Yokobori Jr.
Keyword(s):  
Crack Growth ◽  
Axial Stress ◽  
Creep Crack Growth ◽  
Turbine Rotor ◽  
Rotor Steel ◽  
Creep Ductility ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Round Bar ◽  
Growth Properties

Most heat resisting materials in structural components are used under multi-axial stress conditions and under such conditions ductile materials often exhibit brittle manner and low creep ductility at elevated temperature. Creep crack initiation and growth properties are also affected by multi-axial stress and it is important to evaluate these effects when laboratory data are applied to structural components. Creep crack growth tests using circumferential notched round bar specimens are a simple method to investigate multi-axial stress effects without using complicated test facilities. Creep crack growth tests have been performed using a 12CrWCoB turbine rotor steel. In order to investigate the effects of multi-axial stress on creep crack growth properties, the tests were conducted for various notch depths at 650°C. The circumferential notched round bar specimen showed brittle crack growth behaviour under multi-axial stress conditions. Creep crack growth rate was characterized in terms of the C* parameter. A 12CrWCoB turbine rotor steel has been tested using circumferential notched round bar specimens with different multi-axiality. Circumferential notched round bar specimens show increased brittle creep crack growth behaviour due to the multi-axial stress condition. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multi-axial conditions.

Sign in / Sign up

Export Citation Format

Share Document