Low Cycle Fatigue Crack Propagation Research Articles

912 Ti-6Al-4V 合金の高温低サイクル疲労き裂発生・伝ぱ挙動に及ぼす負荷ひずみ波形の影響

912 Ti-6Al-4V 合金の高温低サイクル疲労き裂発生・伝ぱ挙動に及ぼす負荷ひずみ波形の影響

Low Cycle Fatigue Crack Growth Analysis for the Piping with a Surface Crack(Student Poster Session)

In this paper an analytical model, based upon the line spring model installed in ABAQUS, has been proposed in order to simulate the low cycle fatigue crack propagation. And a series of computer simulations have been carried out in order to investigate the experimental behaviors of the degraded pipes. It has been shown that the leak behavior of circumferentially cracked piping can be simulated well by the proposed method.

Various processes for in situ formation of aluminium-aluminium nitride : Y.Takeda et al. (Sumitomo Electric Industries, Koyakita, Japan.)

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

A numerical simulation of fatigue growth of multiple surface initially semicircular defects under tension : Smith, R.A. and Lin, X.B. Int. J. Pressure Vessels Piping (1995) 62 (3), 281–289

The titanium grade 2 is currently used in high-pressure heat exchanges, piping systems in sea water desalination plants, offshore technology and chemical plants. In many of the applications fatigue and/or creep loading conditions occur. In this paper are presented the results of the mechanical behaviour, low cycle fatigue parameters and fatigue crack propagation at room temperature and at 400°C. The influence of temperature, frequency and the shape of wave loading was studied. The creep behaviour was also studied. Curves of the strain and the stress against the time were obtained to 400°C and 500°C. Also the Larson-Miller parameter was determined. Tests to the creep crack propagation study were carried out. Crack propagation in the creep tests conditions used was not verified.

Studies on Relation between Low Cycle Fatigue Strength and Fatigue Crack Propagation Rate in Structural Materials.

The estimation of fatigue crack propagation rate in structural materials and the clarification of crack propagation mechanism are extremely important. In this study, a low cycle fatigue test and a fatigue crack propagation test were carried out. Then the relation between the low cycle fatigue strength and the fatigue crack propagation rate was investigated, and the factors affecting the fatigue crack propagation rate were clarified on the basis of a damage accumulation model. Consequently it was found that Young's modulus E, the fracture ductility ef and the yield strain eN considerably affected the fatigue crack propagation rate da/dN, and the following equation involving the effective stress intensity factor range ΔKeff was proposed in order to consider the effect of material properties on the fatigue crack propagation rate. da/dN=506(ΔKeff/E)2.79/(ef√(ey))

Fatigue and creep in titanium grade 2

The titanium grade 2 is currently used in high-pressure heat exchanges, piping systems in sea water desalination plants, offshore technology and chemical plants. In many of the applications fatigue and/or creep loading conditions occur. In this paper are presented the results of the mechanical behaviour, low cycle fatigue parameters and fatigue crack propagation at room temperature and at 400°C. The influence of temperature, frequency and the shape of wave loading was studied. The creep behaviour was also studied. Curves of the strain and the stress against the time were obtained to 400°C and 500°C. Also the Larson-Miller parameter was determined. Tests to the creep crack propagation study were carried out. Crack propagation in the creep tests conditions used was not verified.

Effect of interstitial content on high- temperature fatigue crack propagation and low- cycle fatigue of alloy 720

Alloy 720 is a high-strength cast and wrought turbine disc alloy currently in use for temperatures up to about 650 °C in Allison’s T800, T406, GMA 2100, and GMA 3007 engines. In the original composition in-tended for use as turbine blades, large carbide and boride stringers formed and acted as preferred crack initiators. Stringering was attributed to relatively higher boron and carbon levels. These interstitials are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the total life approach in the design of turbine discs necessitates better understanding of the interactive fatigue crack propagation and low-cycle fatigue behavior at high temperatures. The objective of this study was to improve the damage tolerance of Alloy 720 by systematically modifying boron and carbon levels in the master melt, without altering the low-cy-cle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modifica-tion. The fatigue crack propagation rate was reduced by a concurrent reduction of both carbon and bo-ron levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings.

Influence of Oxidation on Low-Cycle Fatigue Crack Initiation and Propagation at High Temperature.

The initiation and propagation behavior of small cracks of SUS 316 stainless steels under low-cycle fatigue loading at 700°C have been studied with a special emphasis on the role of oxidation both in the surface and subsurface. Intergranular cracking in air is due to preferential oxidation attack on the grain boundaries, while in vacuum the most frequent mode of cracking is transgranular. Also, coalescence of cracks in the surface plays an important role in the early stage of crack propagation both in air and vacuum, i. e., irrespective of the oxidation attack. Consequetly, the difference between fatigue life in air and that in vacuum could not be associated with the preferential intergranular cracking in the surface but with the relatively high rate of crack propagation in the depth direction in air compared with that in vacuum.

Explicit cyclic [formula omitted] expressions for low-cycle fatigue modeling of plane stress crack problems

Low-cycle fatigue crack propagation has been modeled successfully by an equation employing the cyclic J- integral , ΔJ. The use of this equation in practice is hindered by the difficulty of calculating ΔJ. A load-deflection hysteresis diagram must be obtained to estimate its value for several points on the crack growth curve. Several approximations have been presented to estimate the J- integral for monotonic crack growth, of which the work of Shih and Hutchinson seems to be the most promising. In their work they present fully plastic estimates of the J- integral , which they fit to full numerical calculations obtained using the finite element method. In this paper, the fully plastic estimates of the J- integral given by Shih and Hutchinson for Ramberg-Osgood type materials in plane stress conditions are extended to arrive at an equation for calculating the J- integral range, ΔJ. The estimates are fitted to experimentally obtained values of ΔJ and a correction term is found. The new estimates are used to correlate low-cycle fatigue crack growth rates. The results indicate that the estimates are quite accurate and provide a relatively easy method for estimating ΔJ. Also, the values calculated using this method correlate with low-cycle fatigue crack growth data quite well, and thus provide a tool for low-cycle fatigue modeling. In addition, the whole procedure employing ΔJ lends itself to high-cycle fatigue problems where ΔJ reduces to the stress intensity factor, ΔK, used for high-cycle fatigue.

Developments in sintered stainless steel

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

Low-temperature fatigue of 316L and 316LN austenitic stainless steels

This article is concerned with the cyclic properties of 316L-type austenitic stainless at 300 and 77 K. The role of nitrogen alloying and of the temperature decrease is examined during low-cycle fatigue (LCF) and fatigue crack propagation. Fatigue resistance is enhanced by the addition of nitrogen in steel at both test temperatures. The results are discussed on the basis of micro-structural observations. Planar slip of dislocations is found in the nitrogen-containing steel and is favored by a decrease in test temperature. To some extent, the influence of interstitial nitrogen on the fatigue properties is related to its role in stabilizing austenite observed during cooling as well as during straining.

On the role of environment on the fatigue behavior of two aluminum-lithium alloys

In this paper the low cycle fatigue and fatigue crack propagation behavior of Al-3Li-1.25Mn and Al-4.5Cu-l.21Li-0.51Mn alloys in the peak-aged condition is examined as a function of environment. It is observed that nature of the environment has no influence on the low cycle fatigue lives of the two alloys over the range of strain amplitudes investigated and little to no influence on fatigue crack propagation characteristics. The presence of shearable precipitates in the two alloys results in a local decrease in resistance to dislocation movement leading to progressive loss of ordering contributions to hardening and slip concentration. The slip concentration coupled with the exacerbating effect of precipitate-free zones promotes strain localization with concomitant stress incompatibility effects at the grain boundary. Embrittlement at the grain boundary is promoted by the applied stress and plays an important role in accelerating crack initiation and subsequent crack propagation. The apparent lack of an environmental effect on fatigue life is ascribed to the complex interaction of several mechanisms involving intrinsic microstructural features, embrittling effect of the environment, chemical reactions, dislocation-microstructure interactions and matrix-slip characteristics.

耐熱鋳鋼のクリープ・疲労特性におよぼす組織と力学因子について

Low cycle fatigue (LCF) and fatigue crack propagation (FCP) tests under creep conditions were carried out on HK40, HP, and their modified alloys containing a small amount of Zr, Nb, and/or Ti. The failure mechanism was established based on the microscopic observations by the scanning and transmission electron microscopies. Also, the mechanical factors affecting the LCF life were discussed, considering the crack propagation law. The main results obtained are as follows;(1) The addition of Nb, Ti and/or Zr improves the LCF life and the FCP resistance under creep conditions. In particular, the effect of Zr is marked.(2) Cracks propagate along the intensive sub-boundaries, on which coarse M23C6 carbides precipitate during the LCF test.(3) Zirconium, Nb and Ti form fine and dispersed secondary carbides (MC) in the matrix of material. These fine carbides lead to a uniform dislocation structure without intensive sub-boundaries and then result in the dispersed precipitation of coarse M23C6 carbides. Accordingly, the addition of these elements improves LCF and FCP properties.(4) From a mechanical viewpoint, the LCF life can be determined by the fatigue and creep crack propagation laws and the strain energy densities which are obtainable based on J-integral analysis on a cracked body.

Initial fatigue crack growth behaviour in a notched component: V. Assessment of initial defect in respect to fatigue life of a notched component: Horikawa, K. and Cho, S.-M. Trans. JWRI 1988 17, (2), 433–440

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

Low cycle fatigue crack propagation and fractography of a SUS 304 stainless steel at elevated temperature: Koterazwa, R. and Nosho, T. J. Soc. Mater. Sci. Jpn. Sept. 1988 37, (420), 1090–1096 (in Japanese)

The present paper proposes a novel approach to the identification of the mechanical properties of individual component layers of a bimetallic sheet. In this approach, a set of material parameters in a constitutive model of cyclic elasto-plasticity are identified for the two layers of the sheet simultaneously by minimizing the difference between the experimental results and the corresponding results of numerical simulation. This method has an advantage of using the experimental data (tensile load vs strain curve in the uniaxial tension test and the bending moment vs curvature diagram in the cyclic bending test) for a whole bimetallic sheet but not for individual component layers. An optimization technique based on the iterative multipoint approximation concept is used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification, and the verification of this approach using two types of constitutive models (the Chaboche-Rousselier and the Prager models) for an aluminum clad stainless steel sheet.

Low-Cycle Fatigue Analysis of Notched Members

Abstract Low-cycle fatigue crack initiation and propagation lives of notched members are investigated. By relating Nci(ΔJ/ψρ)β = Cn to the Coffin-Manson equation and correlating to test results, β and Cn are found to be functions of several parameters: cyclic stress-strain constants, geometry of notch (depth and curvature), and stress ratio. (ΔJ/σ′y) is chosen as a parameter for crack propagation in notched members. Fatigue crack initiation and propagation tests were conducted on notched plate specimens of different notch radii and stress ratios. Crack initiation life, crack propagation life, and total fatigue life are compared with the calculations. There are good correlations between the test results and the calculations.

ＳＵＳ３０４鋼の高温低サイクル疲労き裂伝ぱとフラクトグラフィ

High temperature low-cycle fatigue crack propagation behaviour of SUS 304 stainless steel under typical four types of reversed loading patterns (P-P, P-C, C-P and C-C type) was investigated, and the results were discussed in the light of fracture mechanics and electron fractography. The stress intensity factor range ΔK failed to describe the crack propagation behaviour adequately. In the case of loading with tension hold (i.e. C-P and C-C type), the crack propagation rate was successfully correlated with the modified J-integral J and agreed with the static creep crack propagation rate. The crack propagation rate for all of the four types of loading was successfully correlated in terms of the cyclic J-integral range ΔJ, and it was unnecessary to separate ΔJ into ΔJf and ΔJc. The crack propagation rate for the types of loading without tension hold or with short tension hold time (i.e. P-P and P-C type, and C-P and C-C type with comparatively short tension hold time) was successfully correlated with ΔJf, and that long tension hold time (i.e. C-P and C-C type with comparatively long tension hold time) was successfully correlated with ΔJc. The fracture surfaces of the case where the crack propagation rate was correlated with ΔJf were predominantly transgranular fatigue type, that is, fracture morphology and correlating fracture mechanics parameter (ΔJf) were of the same type (fatigue type). On the other hand, those of the case where crack propagation rate was correlated with ΔJc were transgranular fatigue type or intergranular creep type or mixed type depending on the condition, that is, fracture morphology and correlating fracture mechanics parameter (ΔJc) were of different type in some cases.There was no significant effect of creep-fatigue interaction on the crack propagation under the combined creep and fatigue conditions, and crack propagation may be assessed by a simple summation of fatigue component and creep component.

熱間鍛造用型鋼の高温破面解析

In order to investigate the high temperature fracture behavior of hot forging die steel, low cycle fatigue life and crack propagation tests of SKD62 were carried out. The effects of testing temperature, hardness of base metal and surface hardening treatments such as ion nitriding, tuftriding and sul-surf treatment on low cycle fatigue strength and crack propagation rate were investigated.Decrease of low cycle fatigue strength and increase of crack propagation rate were comparatively prominent at 450°C. Increase of hardness of base metal was most effective to improve the low cycle fatigue strength of SKD62 due to delay of crack initiation. Among various surface treatments, ion nitriding was most effective to improve the low cycle fatigue strength of SKD62.Striation was predominant in the fracture surfaces of all low cycle fatigue tested specimens in this experiments.Thermal fatigue crack initiation and propagation tests were also conducted by heating specimens up to 1000°C by use of a laboratory made thermal fatigue testing machine. By lowering the temperature difference between heating and cooling, crack initiation life was increased and crack propagation rate was decelerated. Striation like pattern appeared remarkably on the thermal fatigue fracture surface. The same type of fracture surface was observed on the thermal fatigue failed fracture surface of hot forging die.

The effect of strain rate on the monotonic and cyclic properties of β-TiV alloys

The effects of strain rate and test environment on the low cycle fatigue and fatigue crack propagation behavior of three TiV alloys having different deformation mechanisms were studied. The strain rate affected both the cyclic stress strain response and the fracture mode. The details of the effect depended on deformation characteristics, with the sensitivity to changes in strain rate increasing with increasing planarity of slip. All alloys exhibited longer fatigue lives at the higher strain rate. This effect was related to changes in cyclic hardening behavior and in some cases changes in fracture mode. The fatigue crack propagation resistance was also greater at the higher test frequency, with the effect being most pronounced in the vacuum environment for the higher vanadium content alloy. The results can be explained by the influence of vanadium content on the strength and deformation characteristics.

Effects of processing and microstructure on the fatigue behaviour of the nickel-base superalloy René 95

Forms of the nickel-base superalloy René 95 produced by three processing methods were evaluated in tensile, low cycle fatigue and fatigue crack propagation tests at 540 and 650°C. Two powder-metallurgy (PM) forms, hot-isostatically-pressed and extruded-and-forged, and a conventionaslly cast-of-wrought form were all given the same heat treatment. The extruded-and-forged form showed superior fatigue life in low strain range tests though the two PM forms exhibited nearly identical mechanical behaviour in all other respects. Further, this life difference could not be explained by significant differences in the types, sizes or shapes of the defects initiating failure. The cast-and-wroght René 95, however, had lower strenght, ductility and fatigue life, but higher fatigue crack propagation resistance because of a larger grain size. It did not exhibit the environmentally-assisted intergranular mode of propagation which occurs in PM René 95 and other fine-grained superalloys at these test temperatures and frequencies.