Gigacycle Fatigue Properties Research Articles

Effect of microstructure on gigacycle fatigue and crack growth behavior of X80 grade pipeline steels

The gigacycle fatigue properties and crack growth behavior of two X80 pipeline steels with different microstructures of acicular ferrite (AF) and dual-phase (DP) were investigated. The experimental results show that the S-N curves of the two steels exhibit continuous declines over 109 cycles without fatigue limits, with fatigue strengths of 428 ± 7 MPa and 363 ± 8 MPa respectively. Most fatigue cracks in the DP steel initiated from the surface, while the fatigue fracture of the AF steel was mainly initiated in the internal inclusions. The DP steel exhibited a higher fatigue crack growth (FCG) rate than the AF steel.

NIMS fatigue data sheet on gigacycle fatigue properties of A6061-T6 (Al-1.0Mg-0.6Si) aluminium alloy at high stress ratios

he new fatigue data sheet, No. 132, discloses gigacycle fatigue properties of the A6061-T6 aluminium alloys at high stress ratios. The fatigue tests were conducted mainly by the ultrasonic fatigue testing at 20 kHz, while conventional fatigue tests at 100 Hz were also conducted for comparison. The fatigue test results indicated that fatigue limits were obscure in the A6061-T6 alloys. Many specimens failed at over 107 cycles, developing internal fractures as well as surface fractures. On the other hand, fatigue failures at over 109 cycles were very rare, suggesting the presence of new fatigue limits in the gigacycle region. The differences in fatigue test results were negligible between the 20 kHz and 100 Hz tests, demonstrating that the 20 kHz tests were comparable to the conventional fatigue tests on this material. The fatigue strengths evaluated by the stress amplitude were decreased according to increase in the stress ratios, while the degradation of the fatigue strengths was not so serious. The fatigue strengths were higher than the modified Goodman lines, meaning that the stress ratio effects could be estimated by conventional ways.

Elevated-temperature gigacycle fatigue properties of nickel based superalloy: Grain related cracking mechanism and life prediction modelling

Fatigue properties of a nickel-based superalloy at 25 °C and 750 °C were studied under stress ratio R = −1 & 0.1 to identify crack nucleation and growth mechanisms. Results show that interior grain-related cracking is induced by microstructure in Goss or Copper grain. Moreover, owing to competition between temperature and vacuum effects, threshold values for small and long cracks, and the transition crack size, are all lower at elevated temperature. Finally, based on modeling of crack nucleation and growth, a fatigue life model with good prediction results is proposed. The crack nucleation consumes more than 90% of fatigue life.

Effect of hydrogen on gigacycle fatigue properties of SNCM439 steel used for storage cylinder in 70 MPa hydrogen station

Effect of hydrogen on gigacycle fatigue properties of SNCM439 steel used for storage cylinder in 70 MPa hydrogen station

Effects of MnS on Gigacycle Fatigue Properties of SCM440 Steel

Gigacycle fatigue tests were conducted on high-strength steels whose Mn and S contents were so high as to be close to upper limits of the JIS standard. Three types of materials were prepared with different working ratios. The fatigue strengths were in order of the working ratios, indicating that the high working ratios improved the fatigue strength. All specimens ended in internal fractures mostly originating from MnS. The MnS observed on the fracture surface was largely elongated in the cases of the materials with high wording ratios. ODAs (Optically Dark Areas) were then observed at around the center of the elongated MnS, meaning that small internal cracks were formed there. Although the shapes of the MnS were very complicated, the sizes were approximated by using ellipses which covered the whole MnS. When the MnS was largely elongated, the length l was cut off at four times of the width W, i.e., l = 4W, based on the results of Makino’s fracture mechanics analysis. The measured MnS sizes were applied to analysis by using a previously derived prediction, comparing the effects of MnS with those of oxides. As the result, it was suggested that the MnS was more harmful to the fatigue strength than the oxides. This was probably attributable to the properties of the MnS, while too large number of the MnS possibly reduced the fatigue strength.

10<sup>11</sup>-cycle Gigacycle Fatigue Properties of High-strength Steel

10<sup>11</sup>-cycle Gigacycle Fatigue Properties of High-strength Steel

Low- and giga-cycle fatigue properties of SUS329J3L duplex stainless steel.

Low- and giga-cycle fatigue properties of SUS329J3L duplex stainless steel.

Effect of stress ratio on gigacycle fatigue properties of SUS630 precipitation hardening stainless steel.

Effect of stress ratio on gigacycle fatigue properties of SUS630 precipitation hardening stainless steel.

Stress‐Strength Reliability Analysis with Extreme Values based on q‐Exponential Distribution

When dealing with practical problems of stress–strength reliability, one can work with fatigue life data and make use of the well‐known relation between stress and cycles until failure. For some materials, this kind of data can involve extremely large values. In this context, this paper discusses the problem of estimating the reliability index R = P(Y < X) for stress–strength reliability, where stress Y and strength X are independent q‐exponential random variables. This choice is based on the q‐exponential distribution's capability to model data with extremely large values. We develop the maximum likelihood estimator for the index R and analyze its behavior by means of simulated experiments. Moreover, confidence intervals are developed based on parametric and nonparametric bootstrap. The proposed approach is applied to two case studies involving experimental data: The first one is related to the analysis of high‐cycle fatigue of ductile cast iron, whereas the second one evaluates the specimen size effects on gigacycle fatigue properties of high‐strength steel. The adequacy of the q‐exponential distribution for both case studies and the point and interval estimates based on maximum likelihood estimator of the index R are provided. A comparison between the q‐exponential and both Weibull and exponential distributions shows that the q‐exponential distribution presents better results for fitting both stress and strength experimental data as well as for the estimated R index. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of Temperature and Loading Frequency on the Fatigue Behavior of Ti-17

A high-temperature ultrasonic fatigue testing system was developed to evaluate the gigacycle fatigue properties of Ti-17. Ultrasonic (20 kHz) fatigue tests were performed at room temperature, 200°C and 350°C, respectively. The dynamic Young’s modulus and fatigue endurance limit decrease with increasing temperature linearly. Rotating bending (50 Hz) tests were performed to evaluate the influence of loading frequency at room temperature, 200°C and 350°C, respectively. There is an obviously loading frequency effect at elevated temperature, although no loading frequency effect at room temperature.

GS0204-256 アルミニウム合金A5083P-Oのギガサイクル疲労特性

GS0204-256 アルミニウム合金A5083P-Oのギガサイクル疲労特性

High-Temperature Ultrasonic Fatigue Testing at 1000°C

A high-temperature ultrasonic fatigue testing system was developed to evaluate the gigacycle fatigue properties of single-crystal superalloys used in aircraft engine turbine blades. In this development, a commercial ultrasonic fatigue testing machine was considerably modified to achieve high-temperature fatigue testing. The developed system took account of temperature dependency of Youngs modulus, and also had a function to evaluate the Youngs modulus. In order to protect the testing system from the heat of a specimen, straight and round rods were inserted between the testing system and the specimen. Other modifications achieved accurate control of temperature, edge displacement and resonance frequency, which were necessary for accurate control of stress amplitude. The testing system was first applied to a heat-resistant steel at 650 °C to check its accuracy, and next to SC superalloy samples at 1000 °C. In the conventional fatigue tests on the heat-resistant steel, the results were coincident in a frequency range from 1 Hz to 800 Hz, suggesting that comparable results would be obtained in ultrasonic fatigue testing at 20 kHz. In case of the SC superalloy samples, conventional fatigue tests were conducted at only 10 Hz, so the frequency effects were not clarified. In both cases, ultrasonic fatigue testing showed good agreement with conventional fatigue testing. The accuracy of the developed system is therefore high, even at 1000 °C. In these results, the SC superalloys showed no fatigue limit, indicating gigacycle fatigue tests to be necessary.

On specimen design for size effect evaluation in ultrasonic gigacycle fatigue testing

ABSTRACTLiterature datasets showed that gigacycle fatigue properties of materials may be affected by the specimen risk‐volume, i.e., the part of the specimen subjected to applied stress amplitudes above a prescribed percentage of the maximum applied stress amplitude. The paper proposes a Gaussian specimen shape able to attain large risk‐volumes for gigacycle fatigue tests, together with a general procedure for its design: wave propagation equations are analytically solved in order to obtain a specimen shape characterised by a uniform stress distribution on an extended length and, as a consequence, by a larger risk‐volume. The uniformity of the stress distribution in the Gaussian specimen is numerically verified through a finite element analysis and experimentally validated by means of strain gauge measurements.

Gigacycle fatigue properties of Ti–6Al–4V alloy under tensile mean stress

The mean stress effects on the gigacycle fatigue properties of three heats of Ti–6Al–4V alloy were investigated by means of ultrasonic and electromagnetic resonance fatigue tests. All heats developed internal fractures under mean stress conditions of R≥0 with negligible frequency effects. The origins of the internal fractures proved not to be inclusions, but clusters of facets. Cross-sectional observations of the internal fractured specimen revealed the facets to have formed in the α-phase in an inclined direction. The gigacycle fatigue strength of the Ti–6Al–4V alloy at R=−1 matched that of quenched and tempered steel, while that under R=0 was clearly lower. Ti–6Al–4V alloy is more prone to internal fracturing under tensile mean stress conditions, resulting in reduced fatigue strength. Its gigacycle fatigue strengths are thus below the modified Goodman line at around R=0. This trend is very dangerous, since the modified Goodman line generally gives predictions with a good margin of safety.

Evaluation of gigacycle fatigue limit and life of high-strength steel with interior inclusion-induced failure

The gigacycle fatigue properties with the interior inclusion-induced failure for three kinds of high-strength steels are investigated in this study. Fatigue strength of these steels in the gigacycle regime is highly related to the sizes of inclusions that are present in the effective damage zone under loading condition. The induced stress concentration at the inclusion–matrix interface plays a key role in the small crack growth process within fine granular area, but has little effect on the macroscopic crack growth outside the fine granular area. Considering the effect of stress gradient around the inclusion, new models were developed to evaluate the values of stress intensity factor at the front of the fine granular area and the fish-eye. A nearly constant stress intensity factor value of 4.5[Formula: see text] for the fine granular area can be regarded as the threshold value controlling interior macroscopic crack growth. A method from the viewpoint of small crack growth was proposed to evaluate the fatigue limit/life of high-strength steel with the interior inclusion-induced failure in the gigacycle regime, which reveals the influences of loading condition, inclusion size, and specimen size. In life prediction, this method is mainly based on the relationship between the fine granular area size and the fatigue life. Because of the maximum inclusion sizes used, the partially predicted results may be somewhat conservative, but they are more satisfied with the requirement of safety design.

OS1002 水素ステーション蓄圧器用SNCM439鋼のギガサイクル疲労特性に及ぼす水素の影響

OS1002 水素ステーション蓄圧器用SNCM439鋼のギガサイクル疲労特性に及ぼす水素の影響

Gigacycle Fatigue Properties of Double-Melted SCM440 Steel and Size Effects

Gigacycle Fatigue Properties of Double-Melted SCM440 Steel and Size Effects

Gaussian Specimens for Gigacycle Fatigue Tests: Damping Effects

Experimental tests investigating the gigacycle fatigue properties of materials are commonly performed with ultrasonic testing procedures, which allow for a significant reduction of testing time but induce a significant temperature increment in specimens. In order to evaluate the significance of size effects on the fatigue strength of materials, the Authors recently proposed to adopt Gaussian specimens for gigacycle tests. Fatigue specimens were designed without taking into account the hysteretic damping and its effects both on the stress distribution and on the heat power dissipation. However, in order to evaluate the temperature increment and the feasibility of ultrasonic fatigue tests with Gaussian specimens, the total dissipated heat power as well as the distribution of the dissipated heat power density along the specimen must be taken into account.The present paper proposes an analytical model validated through a finite element analysis, which permits to evaluate the effects of the hysteretic damping on the stress distribution, on the dissipated heat power density distribution and on the total dissipated heat power in Gaussian specimens.

Evaluation of Threshold Condition of Interior Annular Crack Growth in Gigacycle Regime

Gigacycle fatigue properties with interior-induced failure of three high strength steels under different loading conditions were investigated, and an experimental-theoretical method is proposed to quantitatively evaluate the threshold condition of interior crack growth. The entire growth process consists of small crack growth within fine granular area (FGA), stable long crack growth outside of FGA within fish-eye and unstable crack growth outside of fish-eye. Based on the comparison between evaluated and experimental results, the validity of method is verified.

Comparison between dog-bone and Gaussian specimens for size effect evaluation in gigacycle fatigue

Gigacycle fatigue properties of materials are strongly affected by the specimen risk volume (volume of material subjected to a stress amplitude larger than the 90% of the maximum stress). Gigacycle fatigue tests, performed with ultrasonic fatigue testing machines, are commonly carried out by using hourglass shaped specimens with a small risk volume. The adoption of traditional dog-bone specimens allows for increasing the risk volume, even if the increment is quite limited. In order to obtain larger risk volumes, a new specimen shape is proposed (Gaussian specimen). The dog-bone and the Gaussian specimens are compared through Finite Element Analyses and the numerical results are validated experimentally by means of strain gages measurements. The range of applicability of the two different specimens in terms of available risk volume and stress concentration effects due to the cross section variation is determined.