Crack Growth Rate Tests Research Articles

The Influence of Bulk-Solution-Chemistry Conditions on Marine Corrosion Fatigue Crack Growth Rate

Abstract An exploratory study has been conducted to determine the influence of bulk-solution-chemistry conditions on corrosion fatigue crack growth rate in high strength alloys. Various solutions commonly employed in studies relating to marine corrosion were evaluated for their relative severity in crack growth rate tests. Related aspects involving aeration and applied cathodic potential were included. The results indicate that bulk-solution-chemistry conditions can influence measured values of corrosion fatigue crack growth rate by as much as a factor of three; however, the relative severity of various solutions can vary, depending on alloy composition.

Fatigue crack growth retardation behavior of in-100 at elevated temperature

In this investigation the effect of temperature on the fatigue crack growth retardation behavior of IN-100, a nickel base superalloy, when subjected to a single peak tensile overload cycle was examined. Baseline constant load amplitude fatigue crack growth rate ( da/ dN ) and single peak tensile overload testing was conducted at room temperature, 649 and 732°C in laboratory air. As a result of this investigation it was concluded that retardation of fatigue crack growth due to a single peak tensile overload cycle does occur in IN-100 at elevated temperatures. In general, the number of delay cycles decreased as temperature increased. The overload testing was conducted at two baseline stress intensity factor ( K max ) values. It was found that for a given amount of overload, the observed retardation was less for tests conducted at the higher value of baseline K max . A new parameter, the Crack Growth Rate Ratio (( da/ dN ) at K OL /( da/ dN ) at K max , was dev was found that the influence of test environment on the number of delay cycles resulting from a peak tensile overload could be correlated with the ratio of crack growth rate at the overload value of stress intensity to the crack growth rate at the baseline K max . The utility of the Crack Growth Rate Ratio as a potential tool for predicting the retardation behavior of a material when operating in a complex environment is discussed.

Analysis of cracked disk specimens

A Fredholm integral equation of the plane problem for an arbitrarily loaded disk with an arbitrarily located inner crack is obtained and its solution in the form of double series in power of two parameters is provided. A general formula to define stress intensity factors of central crack is given by which the stress intensity factors for some types of loading are derived and analysed. It is shown that disks loaded by centrifugal forces due to uniform rotation and compressed in the plane of the crack are particularly suitable in fracture toughness testing of brittle materials. It is found that for disks stretched by two forces applied at some distance from the crack the stress intensity factor remains constant in a large range of crack lengths. Therefore they are recommended to be used in subcritical crack growth rate testing. Suitable grips are developed and appropriate correction for their effect is made in the stress intensity factor formula. Recommendations for a choice of optimal dimension ratios for a disk specimen are given.

Effect of grain size and temperature on fatigue crack propagation in A533 B steel

Crack growth-rate tests were performed in a medium-strength pressure vessel steel, A533 B, which had been annealed to produce materials with widely varying prior austenite grain sizes. Testing was at two temperatures, normal room temperature and liquid nitrogen temperature, both on the lower shelf of the material's Charpy energy curve. Results show that both grain size and temperature influence quasibrittle crack growth, mainly through their effect on K Ic' . The threshold and power law region of the da/dN vs ΔK plot seem relatively uneffected while the upper limiting ΔK is shifted extensively. The data is presented and compared with that already published.

Fatigue Crack Growth Characteristics of A533 Grade B Class I Plate in an Environment of High-Temperature Primary Grade Nuclear Reactor Water

Fatigue crack growth rate tests conducted in primary grade reactor coolant at 550°F (288°C) on A533 Grade B Class 1 steel (HSST Plate 02) showed an increase in growth rates at a frequency of 1 cpm over previous results obtained at frequencies of 60 cpm and higher. This increase, the general character of the crack growth rate versus the ΔK curve, and the results from fractographic studies, all indicated that stress corrosion cracking might have occurred for this material and environment. However, a specimen loaded statically in a PWR environment showed no static load crack growth.

A crack-opening-displacement technique for crack length measurement in fatigue crack growth rate testing—development and evaluation

A crack-opening-displacement (COD) technique has been successfully employed to measure crack length in compact tension specimens for the determination of fatigue crack growth rate (FCGR). Details of the COD calibration and comparisons of COD-determined FCGR data with previously established trend lines for two high-strength steels are presented.

Variability in Fatigue Crack Growth Rate Testing

Abstract To provide the data necessary to develop a recommended practice for fatigue crack growth rate testing, an extensive interlaboratory (round robin) program was conducted and the variability and bias associated with the current state of the art of fatigue crack growth rate testing was determined. Fatigue crack growth rate data (expressed in terms of linear elastic fracture mechanics parameters) were generated for a 190-ksi (1310-MPa) yield strength 10 Ni-8Co-1Mo steel at 15 different laboratories with several test specimen geometries. The results were evaluated statistically and on the basis of a graphical comparison, and the variability and bias associated with both the experimental and analytical aspects of crack growth rate testing were determined. In general, the overall interlaboratory variability was found to be approximately 3 to 1 (on crack growth rate at a given stress intensity range). The intralaboratory variability was typically 2 to 1. No significant geometry or data processing bias was encountered. The results of this study show that the primary source of variability associated with fatigue crack growth rate testing is the experimental procedure used to obtain the raw test data (crack length versus elapsed cycles).

Strength level effects on fatigue crack growth and retardation

Constant amplitude and spectrum loading fatigue crack growth rate tests were performed on HP-9Ni-4Co-30C steel heat treated to three strength levels. It was concluded that the constant amplitude crack growth rate is dependent on the strength level of the material and independent of the toughness of the material. It is also shown that the fatigue crack growth retardation is greater for a material with low strength and high toughness. These findings are discussed in light of the Elber closure model and it is shown that the model predicts that both the constant amplitude fatigue crack growth data and the retardation data are controlled by the yield strength.

A Procedure for Verifying the Structural Integrity of an Existing Pressurized Wind Tunnel

This paper describes the application of material test, stress-fatigue-fracture mechanics analyses, nondestructive examinations and repairs to verify the structural integrity and the remaining cyclic life in a large pressurized wind tunnel (65,000 ft3) (1840 m3). The tunnel with pressures up to 135 psig (0.93 MPa) was constructed in 1940 and has been in service to the present date. The only record of a non-destructive examination conducted on the vessel prior to this evaluation was a hydrostatic test-pressure at 1 1/2 times the maximum working pressure. The material tests were performed on a sample of material (A-70 steel) cut from the tunnel shell. These tests included fracture toughness (R-curve, Kc) as determined from a compact tension specimen, crack growth rate (da/dn vs ΔK), Charpy V-notch, dynamic tear (from which the nil-ductility temperature was determined), and tensile and chemical tests. The results and applications are presented and discussed. Stress analyses include computer programs based on finite element and numerical integration techniques. Fatigue analyses incorporating a fatigue reduction or stress amplification factor to account for a small flaw existing in a weld are presented. Fracture mechanics analyses of the tunnel shell were performed for (1) the general membrane regions, (2) regions of high bending stress, and (3) areas at tunnel penetrations. The critical flaw sizes at each location are determined. The use of the “leak before break” criterion is discussed. The non-destructive examinations (radiograph, ultrasonic, sonic, and magnetic particle) to verify the assumptions of fatigue-fracture mechanics analyses and ASME Code applications are documented. Penetrations in the tunnel shell that were fatigue limited are shown “before” and “after” repair. The remaining cyclic life as obtained by the fatigue-fracture mechanics analyses and the operating envelope which resulted from these studies for metal temperature vs pressure was determined to be approximately 10 years.