Correlation between fatigue crack growth rate and striation spacing in XZM

1990 ◽  
Vol 48 (4) ◽  
pp. 834-835
Author(s):  
Scott M. DeTurk ◽  
Roy J. Cunningham
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Surface ◽  
Crack Growth ◽  
Fatigue Fracture ◽  
Growth Rates ◽  
Load Cycle ◽  
Fatigue Fracture Surface ◽  
Metallic Component ◽  
The Relationship

Much information can be learned from the fracture surface of a metallic component. At a microscopic level, the relationship between a fatigue fracture surface and the rate at which the crack propagated through the material is of particular interest. At certain growth rates, a fatigue fracture surface is comprised of striations which are the results of a cyclical loading being applied to a component. When evaluating a fatigue fracture surface to determine crack growth rates, a Transmission Electron Microscope (TEM) is employed to observe the striations. However, the following question arises, “Does one fatigue striation equal one load cycle”? In previously published literature, the relationship of one striation being equal to one load cycle has been confirmed for various aluminum alloys. The test data presented herein is for steel, i.e., a High Hot Hardness (HHH) gear material utilized in helicopter transmissions. The correlation of one striation being equal to one load cycle was obtained and documented during a fatigue crack growth test of X2M gear steel. A prime use of this data would be in the evaluation of a fatigue fracture surface to determine the initiation time and propagation rate for a service related failure.

The Influence of Metallurgical and Mechanical Pre-Damage on Creep-Crack and Fatigue-Crack Growth Rates of CrMoV Steel

2004 ◽  
Author(s):  
Masaru Sekihara ◽  
Shigeo Sakurai
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Creep Crack Growth ◽  
Creep Crack ◽  
The Relationship ◽  
Crack Growth Rates

The effects of mechanical degradation on the creep- and fatigue-crack growth rates in power plants operated long-term were studied. Creep-crack growth tests and fatigue-crack growth tests were performed using creep-pre-strained and repetitive-strained CrMoV rotor-steel specimens. It was found that the creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were larger than those of virgin specimens under constant load. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep void induced specimens was increased five times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fell in a narrow scatter band in the relationship between C* and da/dt. The effect of long-term operating degradation appeared on the creep- and fatigue-damage under the Slow-Fast waveform. Also the crack density was larger in the damaged specimens compared with the virgin specimens. Other results showed that the fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were larger than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in a specimen with approximately 10%-creep was increased 20 times. Moreover da/dN in fatigue-pre-damaged specimens was accelerated 10 times. However, the results of the strain-controlled crack growth test fell in a narrow scatter band in the relationship between J integral range ΔJ and da/dN. These results suggest that the creep remaining lives and fatigue remaining lives of mechanically damaged CrMoV steel can be estimated using the C* & ΔJ values considering the creep rate and the deformation rate of the pre-damaged materials and the da/dt and da/dN values of the virgin material.

scholarly journals Measurement of Fatigue Crack Growth Relationships in Hydrogen Gas for Pressure Swing Adsorber Vessel Steels

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Brian P. Somerday ◽  
Monica Barney
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Load Cycle ◽  
Hydrogen Gas ◽  
Stress Intensity Factor Range ◽  
Cycle Frequency ◽  
Pressure Swing ◽  
Crack Growth Rates

Hydrogen-assisted fatigue crack growth rates (da/dN) were measured for SA516 Grade 70 steel as a function of stress-intensity factor range (ΔK) and load-cycle frequency to provide life-prediction data relevant to pressure swing adsorber (PSA) vessels. For ΔK values up to 18.5 MPa m1/2, the baseline da/dN versus ΔK relationship measured at 1 Hz in 2.8 MPa hydrogen gas represents an upper bound with respect to crack growth rates measured at lower frequency. However, at higher ΔK values, baseline da/dN data must be corrected to account for modestly higher crack growth rates at the lower frequencies relevant to PSA vessel operation.

Fatigue-Crack Propagation in Steels of Various Yield Strengths

1971 ◽  
Vol 93 (4) ◽  
pp. 1190-1196 ◽  
Author(s):  
J. M. Barsom
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Structural Steels ◽  
Martensitic Steels ◽  
The Relationship ◽  
Crack Growth Rates

The useful life of highly constrained welded structures subjected to cyclic loads often depends on the crack-propagation behavior of the material. Thus, to predict the service life of many structures and to establish safe inspection intervals, an understanding of the rate of fatigue-crack propagation in steel is required. Accordingly, an investigation was conducted to determine the fatigue-crack-growth rates in structural steels ranging in yield strength from 36 to 191 ksi; for this study, wedge-opening-loading (WOL) specimens were used. The tests were conducted at room temperature in an air environment, and the results were compared with published fatigue-crack-growth data for steels having similar yield strengths. The results showed that the primary factor affecting fatigue-crack-growth rates in structural steels is the applied stress-intensity-factor range, ΔKI, and that conservative estimates of fatigue-crack growth per cycle of loading, da/dN, for martensitic steels are obtained from the relationship dadN=0.66×10−8(ΔKI)2.25 where a is in inches and ΔKI is in ksi in. Similarly, the data showed that conservative estimates of da/dN for ferrite-pearlite steels are obtained from the relationship dadN=3.6×10−10(ΔKI)3 As indicated in these equations, the fatigue-crack-growth rates were higher for martensitic steels than for ferrite-pearlite steels. The data also showed that the fatigue-crack growth per cycle accelerated for all the steels, and that this transition from the above relationships to increased rates occurred when the crack-opening-displacement range, Δδ, which is a measure of the strain range at the crack tip, reaches a critical value. The fatigue-rate transition in martensitic steels occurred when Δδ was about 1.6 × 10−3 in. However, the fatigue-rate transition in ferrite-pearlite steels occurred at a Δδ value slightly higher than 1.6 × 10−3 in. A model based on micro structural considerations is presented, which accounts for these differences in the fatigue-crack-growth behavior between martensitic and ferrite-pearlite steels.

scholarly journals Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 475
Author(s):  
Lukáš Trávníček ◽  
Ivo Kuběna ◽  
Veronika Mazánová ◽  
Tomáš Vojtek ◽  
Jaroslav Polák ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Rates ◽  
Large Scale ◽  
J Integral ◽  
Scale Yielding ◽  
Residual Fatigue ◽  
Crack Growth Rates

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanicro 25 and 304L. Despite their coarse microstructure and very different cyclic stress–strain response, the employed continuum mechanics models were found to give satisfactory results. Finite element modeling was used to determine the J-integrals and to simulate the evolution of crack front shapes, which corresponded to the real cracks observed on the fracture surfaces of the specimens. Residual fatigue lives estimated by these models were in good agreement with the number of cycles to failure of individual test specimens strained at various total strain amplitudes. Moreover, the crack growth rates of both investigated materials fell onto the same curve that was previously obtained for other steels with different properties. Such a “master curve” was achieved using the plastic part of J-integral and it has the potential of being an advantageous tool to model the fatigue crack propagation under large-scale yielding regime without a need of any additional experimental data.

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