Fatigue Crack Growth Characteristics Research Articles

Evaluation of Fatigue Crack Growth Characteristics of Sensitized Duplex Stainless Steel

Evaluation of Fatigue Crack Growth Characteristics of Sensitized Duplex Stainless Steel

S031012 鉄鋼材料の低サイクル疲労における表面および内部の疲労損傷([S03101]低サイクル疲労とその応用(1))

In this study, low cycle fatigue tests were conducted for low ally steel, SFVQ1A, austenitic stainless steel, SUS316NG, and carbon steel, STS410, in order to investigate internal fatigue crack growth characteristics. The tests were conducted under repeated two-step variable amplitude strain condition to appear beach marks of cracks on the fracture surface. In addition to these tests, tests with surface removal were also conducted to suppress surface fatigue cracks by polishing the specimen surface during the fatigue tests. Cracks initiated from internal inclusion and those fatigue life were slightly larger under surface removal test for SFVQ1A and SUS316NG compared to those under no surface removal tests. STS410 specimen under surface removal test was not broken until its specimen diameter became too small. There was an internal crack observed on the section of the specimen cut longitudinally. Internal crack growth rate calculated from beach marks for SFVQ1A and SUS316NG was similar to that of surface cracks.

OS12-4-4 Fatigue Crack Growth Characteristics of Epoxy Resin Reinforced by Silica Particles at Ambient Temperature and Elevated Temperatures

OS12-4-4 Fatigue Crack Growth Characteristics of Epoxy Resin Reinforced by Silica Particles at Ambient Temperature and Elevated Temperatures

Microstructurally small fatigue crack growth in thin, aluminum-alloy, pressure vessel liner

Motivation to decrease weight and cost of composite-overwrapped pressure vessels used in space exploration leads to designs that challenge the current qualification standards and methods for predicting fatigue life of the structures. Namely, as thickness of the metallic, overwrapped liners is reduced (potentially to tens of grains through-thickness), plastic deformation extends to the liner bounds, and linear elastic fracture parameters become invalid for fatigue crack growth characterization. In this case, fatigue crack growth is likely governed by microstructural features of the material. Life predictions should ultimately reflect this microstructural dependence. In this work, we design a study that involves both experimental and computational modeling aspects to gain three-dimensional perspective of the microstructural features influencing fatigue crack growth in a thin aluminum alloy reminiscent of a metallic liner material. High-energy X-ray diffraction microscopy is explored as a method for characterizing microstructural morphology, including crystallographic orientations, in a volume of material containing a microstructurally small fatigue crack. Initial work involves a feasibility study of the material form (rolled sheet versus actual liner material) to be used in the proposed experimental study. An outlook on future work of the study is provided.

LNG 저장탱크용 9% Ni강 용접부의 저온피로균열진전 특성

The fatigue crack growth characteristics of base metal and weld joint of 9% Ni steel for LNG storage tank was carried out using CT specimen at room temperature and <TEX>$-162^{\circ}C$</TEX>. Fatigue crack growth rate of base and weld metals at RT and <TEX>$-162^{\circ}C$</TEX> was coincided with a single line independent of the change of stress ratio and temperature. In the region of lower stress intensity factor range, fatigue crack growth rate at <TEX>$-162^{\circ}C$</TEX> was slower than that at RT, and the slop of fatigue crack growth rate at <TEX>$-162^{\circ}C$</TEX> increased sharply with propagating of fatigue crack, fatigue crack growth rate at RT and <TEX>$-162^{\circ}C$</TEX> was intersected near the region of <TEX>$2{\times}10-4\;mm$</TEX>/cycle, and after the intersection region, fatigue crack growth rate at <TEX>$-162^{\circ}C$</TEX> was faster than that at RT. The micro-fracture mechanism using SEM shows the ductile striation in the stable crack growth region. Also the defects of weld specimen after fatigue testing were detected using the A scan of ultrasonic apparatus.

Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures

Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25 mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range (Δ K) of 14–38 MPa√m, exhibited stage II crack growth in Paris’ regime with nearly same slopes of crack growth per cycle versus Δ K plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the Δ K range of 14–24 MPa√m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (1 1 1) plane. The fracture toughness values ( J 0.2) for LRMed Inconel 625 specimens were found to be in the range of about 200–255 kJ/m 2. The LRMed specimens exhibited stable crack growth during the J-integral test.

マルテンサイト系ステンレス鋼の応力腐食割れおよび腐食疲労き裂進展特性の評価

マルテンサイト系ステンレス鋼の応力腐食割れおよび腐食疲労き裂進展特性の評価

Local strains and mesoscopic mechanisms of crack growth in 25Kh1M1F steel

Fatigue crack growth characterization requires non-homogeneous strain field measurements, the use of specific tech- niques is necessary. In this paper, the efficiency of the automated grid method for measuring in-plane displacements in the presence of high strain gradient is discussed. Vectors fields of displacement and strain gradient near crack tip have been stud- ied: macrostrain localization, mesostrain concentration at a crack tip in a 25Kh1M1F steel, and micromechanisms of fracture on a crack front.

Near-threshold fatigue crack growth in bulk metallic glass composites

A major drawback in using bulk metallic glasses (BMGs) as structural materials is their extremely poor fatigue performance. One way to alleviate this problem is through the composite route, in which second phases are introduced into the glass to arrest crack growth. In this paper, the fatigue crack growth behavior of in situ reinforced BMGs with crystalline dendrites, which are tailored to impart significant ductility and toughness to the BMG, was investigated. Three composites, all with equal volume fraction of dendrite phases, were examined to assess the influence of chemical composition on the near-threshold fatigue crack growth characteristics. While the ductility is enhanced at the cost of yield strength vis-à-vis that of the fully amorphous BMG, the threshold stress intensity factor range for fatigue crack initiation in composites was found to be enhanced by more than 100%. Crack blunting and trapping by the dendritic phases and constraining of the shear bands within the interdendritic regions are the micromechanisms responsible for this enhanced fatigue crack growth resistance.

Predicting the influence of overload and loading mode on fatigue crack growth: A numerical approach using irreversible cohesive elements

This paper describes an irreversible cohesive zone model to simulate fatigue crack growth. The model includes a three-dimensional (3-D) cohesive law that follows a distinct loading/unloading path and a damage evolution mechanism that reflects a gradual degradation of cohesive properties of the material under the influence of cyclic loading. To overcome convergence difficulties arising from nonlinearity of the cohesive zone model, the stabilization technique and the viscous regularization of the constitutive law are employed. For high-cycle fatigue applications, a damage extrapolation scheme is adopted to reduce computational cost. The irreversible cohesive zone model is implemented in the finite element software ABAQUS through a user defined subroutine and is used to predict fatigue crack growth in a compact-tension-shear (CTS) specimen with an emphasis on the extrinsic influence of overload for different loading modes. The numerical results show good agreement with experimental records documented in the open literature and capture the essential features of fatigue crack growth for various loading conditions. This indicates that the irreversible cohesive zone model can serve both as an accurate and efficient tool for the prediction of fatigue crack growth.

Feasibility analysis for monitoring fatigue crack in hydraulic turbine blades using acoustic emission technique

In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.

Computed Dependence of Rubber'S Fatigue Behavior on Strain Crystallization

Abstract This work explores the consequences of strain crystallization on rubber's fatigue crack nucleation behavior over an extensive space of operating conditions, including tension and compression loading states, and relaxing and non-relaxing cycles. The study considers, via computation, how the nonlinear elastic stress-strain behavior, the fatigue crack growth characteristics, and the damage accumulation law combine to produce the Haigh diagram and the Cadwell diagram. Four hypothetical materials are studied, which differ in their crystallization and associated fatigue crack growth behavior. The calculations demonstrate that a relatively simple idealization can credibly predict the unique shape and sensitivities of observed fatigue behavior over a wide range of conditions. They also clarify how features of the Haigh and Cadwell diagrams are linked to the occurrence of crystallization and to parameters such as the power-law slope and the fatigue threshold.

Reflections on ‘The effect of elevated temperature and environment on the fatigue crack growth characteristics of Ti‐6Al‐2Sn‐4Zr‐2Mo‐0.1Si’ by J. A. Ruppen and A. J. McEvily, FFEMS, Vol 2, Issue 1, 1979, pp. 63–72

A principal finding of the study was that at 538 °C fatigue crack growth tests in air and in vacuum showed that oxidation rather than creep was more important in affecting the fatigue crack growth rate in the range of test frequencies from 1 to 30 Hz. Similar results have also been found for steel, as shown in Fig. 1. Effect of testing conditions on the fatigue crack growth behaviour of a 9Cr-2Mo steel.1 Figure 2 shows long crack growth behaviour as a function of Eq. (2) and R value. The transition in growth behaviour occurs where the plastic zone size is about equal to the grain size of the α-phase, 10 μm. The rate of fatigue crack growth in Ti-6Al-4V as a function of (ΔKeff−ΔKeffth)2, modified for static modes of separation which occur at the highest value of the parameter. A comparison of experimental and predicted values of the fatigue strength, σw, as a function of the initial flaw size, a0.4 Note that the smallest flaw is but 15 μm in length. After some 60 year of intense research by many investigators, it is beginning to look as though we can deal with fatigue crack propagation on a quantitative basis, based upon the understanding of the basic mechanisms involved.

Evaluations of Fatigue Crack Growth Characteristics of Sintered and Thermal-Sprayed WC-Co Materials

Fatigue crack growth characteristics were investigated for sintered and thermal-sprayed tungsten carbide with cobalt (WC-Co) cermets. Acoustic emission (AE) techniques were applied to study the crack growth mechanism. The materials used were two types of sintered WC-Co materials, commercially available as G5 and KD20 with the WC grain sizes of 1.0∼8.0μm and 0.5∼1.5μm, respectively, and 7mm thick sprayed layer with the WC grain size of 0.5∼1.5μm. The Co content (mass %) of these materials were 12∼13%. Compact type (CT) specimens were employed for fracture mechanics experiments in accordance with ASTM E647-95a. AE source wave analysis enabled us to estimate the crack volume dynamically developed near the crack tip. The fatigue crack growth rate, da/dN, depended on the WC grain size as well as the stress ratio for the sintered materials, and it was accelerated in sprayed material because of the existence of micro-pores. When these da/dN were compared with structural steels and aluminum alloy as a function of effective stress intensity factor, ΔKeff, normalized by Young's modulus, E, they were much higher than those of the structural materials. This behavior was due to the brittle inter-granular (IG) fracture of WC particle, whose contributions were estimated by AE analysis and fracture surface observations. AE source wave analysis revealed that fracture volume of the IG fracture corresponded to the WC grain size and thus the IG fracture assumed to occur at the individual WC particles. The results of maximum stress intensity factor, Kmax, constant, ΔK decreasing tests suggested that the frequency of the IG fracture of the WC particle was controlled by Kmax. In the threshold region, the contribution of the IG fracture decreased and the threshold value of ΔKeff tended to be constant for sintered materials, while it was lower for sprayed material due to the micro-pores.

OS0739 SUS304鋼の高温多軸疲労き裂進展の定量的評価(構造用材料の疲労挙動と寿命評価,オーガナイズドセッション)

Fatigue crack growth tests under multiaxial loading condition were conducted at elevated temperature. Cyclic tension and torsion was applied to the thin-walled cylindrical specimens of SUS 304 stainless steeL By using DC electrical potential drop (PD) method, fatigue crack growth under multiaxial loading condition was evaluated. Under multiaxial loading condition, two types of fatigue crack growth were observed; "tensile type" crack, which propagates along the direction perpendicular to the maximum principal stress, σ1 and "shear type" crack, which propagates along the diiection of maximum shear stress, τ_<max> The type of the crack observed for a test depends on the value of △τ/△σ and shape of the initial notch Broadly speaking, the tensile type crack growth was observed under the conditions of △τ/△σ≦0.22 and △τ/△σ≧2.l6, whereas the shear type crack growth or mixture of the both growth type were observed under the intermediate condition of △τ/△σr. Using the crack length projected to the direction of τ_<max>, shear type fatigue crack growth was quantified. From these results, the characteristics of shear type fatigue crack growth were discussed.

Analytical modeling of fatigue crack propagation in metals coupled with elasto-plastic deformation

In the present investigation, the Gmax criterion, which is based on the elastic strain energy principle, is extended to study the fatigue crack growth characteristics of mixed mode cracks. A modification has been made to this criterion to implement the plastic strain energy and, hence, a new elasto-plastic energy-based model is presented. Subsequently, the proposed model is employed to predict fatigue crack growth in rectangular steel plates under complex stress states. The results obtained using the elasto-plastic energy model proposed are compared with those obtained using the commonly used Paris law and our experimental data.

Influence of foreign object damage on fatigue crack growth of gas turbine aerofoils under complex loading conditions

ABSTRACTForeign object damage (FOD) has been identified as one of the main life limiting factors for aeroengine blades, with the leading edge of aerofoils particularly susceptible. In this work, a generic edge ‘aerofoil’ geometry was utilized in a study of early fatigue crack growth behaviour due to FOD under low cycle fatigue (LCF), high cycle fatigue (HCF) and combined LCF and HCF loading conditions. Residual stresses due to FOD were analyzed using the finite element method. The longitudinal residual stress component along the crack path was introduced as a nodal temperature distribution, and used in the correction of the stress intensity factor range. The crack growth was monitored using a nanodirect current potential drop (DCPD) system and crack growth rates were correlated with the corrected stress intensity factor considering the residual stresses. The results were discussed with regard to the role of residual stresses in the characterization of fatigue crack growth. Small crack growth behaviour in FODed specimens was revealed only after the residual stresses were taken into account in the calculation of the stress intensity factor, a feature common to LCF, HCF and combined LCF + HCF loading conditions.

A Study on Fatigue Crack Propagation Properties Using the X-Ray Diffraction Method

This study evaluated fatigue crack growth characteristics, Besides consider compressive residual stress effect and verified the most suitable shot peening velocity. Fatigue crack growth delay effect was compressive residual stress, but over peening did action projecting velocity that accelerate fatigue crack growth rate. X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface. Fracture mechanics parameters could be estimated by the measurement of X-ray parameters, and the fractography observation was performed using a scanning electron microscope (SEM) for fatigue fracture surface. As the shot peening velocity increases, striation width increased. The changes in X-ray material parameters described above are directly related to the process of fatigue until the initiation of fatigue crack and X-ray diffraction pattern is thought that failure prediction with stress distribution is possible.

1036 軸受鋼のモードI疲労き裂進展挙動に及ぼす熱処理と異方性の影響(J12-1 金属材料の疲労特性と破壊機構(1) 疲労き裂進展,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

1036 軸受鋼のモードI疲労き裂進展挙動に及ぼす熱処理と異方性の影響(J12-1 金属材料の疲労特性と破壊機構(1) 疲労き裂進展,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Fatigue Crack Growth Characteristics and Effects of Testing Frequency on Fatigue Crack Growth Rate in a Hydrogen Gas Environment in a Few Alloys

In order to investigate the hydrogen effect on fatigue crack growth (FCG) behavior in a few kinds of practical alloys; austenitic stainless steels (solution-treated metastable type 304 and stable type 316L), an aluminum alloy (age-hardened 6061) and a low carbon steel (annealed 0.13%C-Fe), FCG tests were carried out in hydrogen gas and in nitrogen gas. The FCG rates of these materials are enhanced by hydrogen, though the acceleration degrees are different. A crack grows across grains by slip-off in 316L stainless steel and in age-hardened 6061 aluminum alloys even in hydrogen. Faceted area increases in 304 stainless steel and in low carbon steel in hydrogen. In 304 stainless steel, the ratio of facets to the entire fracture surface was not so large. Thus, the FCG rate is not significantly affected through the facets in 304 stainless steel. In low carbon steel, facets were increased considerably, though a crack grows step by step or after a large number of loading cycles even along grain boundaries. Anyhow hydrogen enhances the FCG rate of these materials through the influence on slip behavior. Based on above-mentioned results, the effect of loading frequency on FCG rate in hydrogen of the age-hardened 6061 aluminum alloy was also investigated. The FCG rate increases as the testing frequency decreases, though the FCG rate in hydrogen shows the tendency to saturate.