X-ray Fractography Research Articles

Liquid metal embrittlement and deformation induced martensite: The case of 316 L austenitic steel LME by liquid eutectic gallium-indium

The liquid metal embrittlement sensitivity of a low nickel 316 L austenitic steel has been studied with eutectic gallium indium alloy. The embrittlement case is firmly established with this steel and studied by X-Ray fractography and EBSD. Brittle to ductile recoveries were observed via a dedicated parametric study (varying cross-head speed and temperature). The return to ductility with temperature is strongly correlated with a significant reduction in plastically induced α’ phase change suggesting it is a requirement for LME. This implies a strategy focused on limiting deformation induced martensite to design LME resistant austenitic steels at low temperature.

On the effect of Qnet on compressive residual stresses and ductile toughness of dissimilar HAZ in robotic GMAW joints between A572-50 and A36 steels

Different heat input values applied in robotic dissimilar welded joints of A36 carbon and A572-50 alloyed steels were evaluated by X-ray residual stresses, Vickers hardness, impact energy, microstructural analysis, and fractography. A welding process using pulsed metal arc for ten combinations involving welding current, arc voltage, welding speed, and power was performed by welding robot. Residual stress measurements in thickness direction at the HAZ within both steels indicated that five weldings achieved compressive stresses, resulting in the highest value (171 MPa) in the HAZ of A572 steel for joint number 3. Greater absorbed energy levels were achieved for the HAZ of A572 steel, followed by weld bead ER70S6 and the HAZ of A36 steel, which was linked to formation of a major amount of fine needles of acicular ferrite, giving the largest energy (160 J) for the HAZ of A572 steel of trial 31. Moreover, three joints showed ductile type failure with microhollow morphology of different sizes, including welding 3 within both kinds of dissimilar HAZ in A36 and A572 steels. Trial 3 was the best showing superficial compressive residual stresses within both kinds of HAZ, intermediate microhardness, and larger Charpy energy associated with acicular ferrite and ductile failure as a consequence of higher heat (0.615 kJ/mm). Welding 27 was better with complete compressive residual stresses in the HAZ of A36 steel, major absorbed energy, and fragile fracture by mechanism of transgranular cleavage within both types of HAZs.

X선 회절과 유한요소법을 이용한 터빈 블레이드의 파괴기구에 관한 연구

The failure analysis on fractured parts is divided into the qualitative method by naked eyes and metallurgical microscope etc. and the quantitative method by SEM and X-ray diffraction etc. X-ray fractography can be applied to contaminated surface as well as clean surface and gain the plastic deformation and the residual stress near the fractured surface. Turbine blade is subject to cyclic bending force by steam pressure and suffers fatigue damage according to the increasing operating time. Therefore, to clean up the fracture mechanism of torsion-mounted blade in nuclear plant, the fatigue and the X-ray diffraction test was performed on the 12%Cr steel for turbine blade and the fractured parts. The correlation of X-ray parameter and fracture mechanics parameter was determined, and then the load applied to actual broken turbine blade was predicted. Failure analysis was performed by contact stress analysis and Goodman diagram of torsion-mounted blade.

Ｘ線材料強度 高マンガンオーステナイト鋳鋼の疲労き裂進展挙動とＸ線フラクトグラフィ

Fatigue crack growth tests were carried out using a high manganese austenitic cast steel under constant amplitude loading. Average crystal grain sizes of the material are 200 micro-meters and 1000 micro-meters. For this material, threshold stress intensity factor range (ΔKth) is about 8MPa√m which is quite large as compared to the ΔKth of general structural steels. The crack growth rate is lower than the general structural steels especially in the lower ΔK region. The reasons of this behaviour are crack closure due to bridging and fretting oxide, decreasing of the stress concentration near the crack tip due to secondary crack and slip on crystal plane. X-ray fractography can be applied to the fatigue fracture surface of the material which has large grain by using oscillation of X-ray beam and in-plane oscillation on the fracture surface. The half-value breadth of the diffraction profile on the fracture surface increases with increase in the effective stress intensity factor range. The relationship between the half-value breadth and the effective stress intensity factor range was represented by a narrow band regardless of the stress ratio.Therefore, the effective stress intensity factor range can be estimated from this relation in fractured surface of actual components.

Ｘ線フラクトグラフィを用いたコネクティングロッド疲労破面の解析

Stress analysis by using fractography is already established technology as means for seeking cause of fracture and has been widely employed. In actually broken machine parts, however, sufficient analytical results may not always be obtained by the technique of fractography due to oxidation, stain or damage of the fracture surface. On the other hand, the fracture analysis method applying the X-ray diffraction method, that is, the X-ray fractography comes to be used as effective fracture surface analysis. In the X-ray diffraction method, the change in the values related to plastic deformation and residual stress near the fracture surface may be determined, and information of internal structure of material can be obtained.In the present study, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined, and application to actual broken machine parts was studied.

Ｘ線材料強度 シンクロトロン放射光を用いた複合材料のＸ線応力測定

We used X-ray diffraction method using Synchrotron radiation (SR) for solving residual stress in composite material. Diffraction planes with arbitrary diffraction angle were measured. Moreover, there is a characteristic that the different diffraction planes at same 2θ angle were obtained using SR with different wave length. In this study, effects of penetration depth on an X-ray parameter of the composite material were examined. First of all, the X-ray elastic constant of the single-phase body (PXEC) was measured for the evaluation of the phase stress. Next, the elastic deformation behavior of phase stress in the matrix phase was evaluated, and the influence of the second phase particle was investigated. Residual phase stress of each phase in the fracture surface is measured as an application example for the X-ray Fractography. The relation between the stress intensity factor and TiN volume fraction was examined.Trying to fracture toughness test in composite material, we discussed influence of fracture toughness value on residual stress. Deformation behavior of softer matrix phase was controlled by hard second phase particle under macroscopic tensile stress. It was found that residual stresses in the fracture surface were relaxed on the surface.Furthermore, there is the correlation between the stress intensity factor at the fracture and the phase stress in the matrix phase.

疲労 回転曲げ疲労破面のＸ線フラクトグラフィ （第２報） 疲労破面の残留主応力とき裂進展方向

X-ray fractography is a technique for analyzing the cause of fractures through the information obtained by irradiating X-ray on the fractured surface. The residual stresses or full widths at half maximums are usually used as the information. This technique is a useful tool for fractrure analysis, since the quantitative loading condition etc. can be estimated. X-ray fractography is used in various countries alongside the electron-microscope fractography. In the previous paper, X-ray fractography has been applied to actual size four “Shinkansen (bullet train)” axles tested at the railway Technology Research Institute. The axles are about 200mm in diameters, induction hardened 0.38% carbon steel with semi-elliptical artificial flaw. X-ray stress measurements were carried out on the fractured surface along the line from the bottom of the artificial flaws to the axle center at intervals of 5mm. All the results showed that the residual stress on the fractured surface were tensile at the initial crack propagation region, increased to tensile maximums, decreased into compression reaching at the compressive maximums then went up toward zero stress near the final fractured surface.This paper describes the procedure estimating the crack propagation direction through rosette analyses of residual stresses. A CCT specimen, which was tested under similar stress condition as test axles, was analyzed and found out that crack propagation directions are coincide with the directions of residual principal stresses. This relationship was utilized in rosette analyses on fractured surface of a test axle, and crack propagation lines were estimated and also the crack closure behavior was discussed.

Ｔｉ‐６Ａｌ‐４Ｖ合金の疲労破面におけるＸ線フラクトグラフィ

Fatigue tests were carried out with Ti-6Al-4V alloy CT specimens after three kinds of the heat treatments, namely, 1) solution at 1223K, aging at 813K(STA), 2) annealing at 1123K(AN850) and 3) annealing at 1373K(±β-AN). X-ray fractography, which is a technique to estimate applied stress conditions when a fracture occurs and to be used for analysing a mechanism of fracture, was applied on the fatigue fractured surface. Distributions of residual stress and half-value breadth were measured on the fractured surface along the crack propagation direction as a function of a stress intensity factor. It was found that the residual stress on the fatigue fractured surface had a peak value when maximum stress intensity factor was nearly equal to 25MPa√m. The strain induced transformation was confirmed on the fatigue fractured surface from X-ray diffraction profile pattern. Depth of monotonous plastic zone size was estimated from the distribution of the residual stress beneath fractured surface. Depth of monotonous plastic zone size ωy was expressed by following equation; ωy=α(Kmax/σy)2, where the values of α were 0.17 for STA and 0.13 for AN850. By using X-ray fractography technique on fatigue fractured surfaces of Ti-6Al-4V alloy, a value of maximum stress intensity factor Kmax where the residual stress reach maximum value can be predicted.

Ｆｅ‐Ｃｒ鋼／ＴｉＮ系焼結複合材料のＸ線フラクトグラフィ的研究

Residual stress generating in each component phase is formed due to the disturbance strain by interaction between the composition phases as for Fe-Cr steel/TiN system composite prepared by powder metallurgy (P/M). We can obtain macro- and microstresses by using X-ray stress measurement method. And X-ray fractography technique was advanced in the field of the fracture analysis. In this study, we tried to fracture toughness test by using three points bending test pieces which have a different notch radius. Effects of notch radius on stress intensity factor when the crack arisen were discussed. Distributions of residual stress and plastic zone depths near fracture surface were evaluated. Experiment results obtained were approved to the equation of the fracture mechanics.

回転曲げ疲労破面のＸ線フラクトグラフィ

X-ray fractography is a technique for estimating the loading conditions at fractures from the information obtained by X-ray stress analysis on fatigue fractured surfaces. This technique was applied to a rotating bending fatigue fractured surface. The specimens were actual size “Shinkansen (Bullet train)” axles bench tested at the Railway Technology Research Institute.The axles are 209 or 210mm in diameter, induction hardened 0.38% carbon steel (JIS S38C) with semi-elliptical artificial flaws. Fatigue fracture was caused mainly by rotating bending stress, and the effect of torsional stress was very slight. The residual stress at the fatigue fractured surface was tensile at the initial crack propagation region, increased to a tensile maximum value, then decreased to a compressive maximum value and increased again toward zero near the final fractured area.The results were compared to the residual stress distribution on fatigue fractured surfaces of CCT specimens under a tension-compression fatigue load of stress ratio R=-1. The general tendencies of residual stress distributions on both fatigue fractured surfaces agree well qualitatively.

X-ray fractography on fatigue fracture surface formed by crack propagation in initial tensile residual stress field : Akita, K., Inoue, T., Takahashi, S., Misawa, H. and Kodama, S. Journal of the Society of Materials Science, Japan (1996) 45, 746–751

X-ray fractography on fatigue fracture surface formed by crack propagation in initial tensile residual stress field : Akita, K., Inoue, T., Takahashi, S., Misawa, H. and Kodama, S. Journal of the Society of Materials Science, Japan (1996) 45, 746–751

Duplex stainless steel fracture surface analysis using x-ray fractography

The fatigue fracture surface of a duplex stainless steel was analyzed using x- ray fractography. A lower than average austenite content was observed at the fracture surface due to the transformation of austenite into deformation- induced martensite. The influence of fatigue cycling on the transformation was confined to a depth of about 30 μm below the fracture surface. X- ray analyses of both the ferrite- martensite and the austenite phases indicated residual stresses (σr) increasing with depth from the fracture surface and reaching a maximum some tens of microns below the fracture surface. The lower σr observed at the fracture surface has been attributed to the stress relaxation effects caused by the new fracture surfaces created in the crack growth process. The observed decrease in full width at half maximum (FWHM) in the ferrite- martensite phase was presumed to be due to the dynamic recovery effect that was likely to occur within the material close to the crack tip as a consequence of fatigue cycling.

X-ray Fractography on Fatigue Fractured Surface of Solution and Aging Treated Ti-6Al-4V Alloy.

Fatigue tests were carried out under two kinds of stress ratios in constant amplitude loading of Ti-6Al-4V alloy after heat treatment of solution at 1223K and aging at 813 K (STA). Retardation behavior of fatigue crack propagation was observed. It is considered that this retardation is caused a stress relieving at front of crack tip by growth of secondary cracks. X-ray fractography, which is a technique to estimate the stress conditions and to be used for analysing a mechanisms when a fracture of structures occurs, is applied on fractured surface. Distributions of residual stress and halfvalue breadth by X-ray technique on the fractured surface along the crack propagation direction as a function of a stress intensity factor. It was found that the residual stress on the fatigue fractured surface had a peak value when maximum stress intensity factor was nearly equal to 25MPa√(m). Strain induced transformation was observed on the fatigue fractured surface from X-ray diffraction pattern. The half-value breadth on fractured surfaces increased with increasing maximum stress intensity factors. Depth of monotonous plastic zone size was estimated from a change of the distribution of the residual stress in direction of depth near fractured surface. Depth of monotonous plastic zone size ωy was expressed by following equation ; ωy=a(Kmax/σy)2, where the value of a was 0.17. By using X-ray fractography, maximum stress intensity factor Kmax in fatigue crack propagation of Ti-6Al-4V alloy can be predicted.

Ｘ線材料強度 高マンガンオーステナイト鋼の疲労破面におけるＸ線フラクトグラフィ

Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese Mn-Cr steel. X-ray fractography was applied on the fatigue fractured surface to investigate the relationship between stress intensity factor and residual stress or half-value breadth of the X-ray diffraction profile. The fatigue crack propagation rate of this non-magnetic Mn-Cr steel had the same tendency as in the ordinary structural ferritic steels. The relationship between stress intensity factor and the residual stress or half-value breadth of the steel was almost the same as that of the ferritic cyclic work hardening steels. No stress induced transformation was observed on the fracture surface, but the residual stress on the fractured surface was compressive in the high stress intensity factors range, which is typical in the cyclic work hardening steels. The half-value breadth on the fractured surface increased with increasing effective stress intensity factor range. The relationship between the half-value breadth and stress intensity factor range was represented by a linear line regardless of the stress ratio. Therefore, the acting stress intensity factor range at the time of fracture can be estimated from the half-value breadth. The depth of monotonic plastic zone was estimated from the distribution of half-value breadth beneath the fractured surface. The relationship between the maximum stress intensity factor and half-value breadth was expressed by the equation ωm=α(Kmax/σy)2, where the value of α was 0.025. This is about one sixth of the value for ferritic steels, and the fact shows the severe work hardening occuring in the plastic zone in this manganese steel.

Some studies on the influence of stress ratio and test temperature on X-ray fractography observations in C45 steel specimens

This paper deals with additional “X-ray fractography” observations made on C45 steel, subsequent to the earlier work [K. Rajanna, B. Pathiraj and B. H. Kolster, Fatigue fracture surface analysis in C45 steel specimens using X-ray fractography. Engng Fracture Mech. 39, 147–157 (1991)]. Fatigue crack: growth tests were carried out at 20°C on CT samples prepared from this steel using different stress ratios (0.1 R, 0.5 R and 0.7 R). Tests were also carried out at different temperatures (−20°C, 20°C and 115°C) using a stress ratio of 0.1. The fractured surfaces were analysed for their residual stress state. The influence of the test conditions on the residual stresses developed is discussed.

X-ray fractography studies on austenitic stainless steels

In this investigation, the fracture surfaces of SS 304 and SS 316 austenitic steels were analysed using the X-ray fractography technique. In both cases, a decrease in the austenite content was observed at the fracture surface as a result of deformation induced martensite, indicating a linear relation with K max within the stable crack growth region. The presence of this martensite was found to be confined to a very thin layer close to the fracture surface. The magnitudes of the residual stress ( σ r) as well as the profile breadth ( B) as a function of K max in martensite were found to be higher than in austenite, with greater differences in SS 304 than in SS 316. In both the steels a gradual decrease of σ r with depth below the fracture surface was noticed. While a gradual decrease of B was noticed in SS 304, a shallow minimum was noticed at a depth of about 100 μm in SS 316.

X-Ray Fractography on Fatigue Fracture Surfaces of Mg-9mass%Al-1mass%Zn Alloy

X-ray diffraction observation of fracture surfaces provides fracture analysis with useful information on the mechanisms and mechanical conditions of fracturing. This method is called ” X-ray fractography “ and has been developed especially in Japan as a new engineering tool for fracture analysis.In the present paper, X-ray fractography is applied to fatigue fracture surfaces of AZ91 magnesium alloy which are used for machine parts. The X-ray stress constant, H,was first determined. The fatigue tests were conducted by using compact tension ( CT ) specimens of AZ91 magnesium alloy. The residual stress was measured on and beneath the fatigue fracture surface. The depth of the plastic zone left on the fatigue fracture surface was evaluated from the residual stress distribution. The results are discussed on the basis of fracture mechanics.

X-Ray Quantitative Analysis of Transformed Martensite in Austentic Stainless Steel

Austenitic stainless steel has large toughness and high corrosion resistance compared to other alloy steels. The austenite near the fracture surface will be transformed to the martensite when it is fractured. In the present study, X-ray fractography is applied to a fatigue fracture surface of austenitic stainless steel. The fatigue tests were carried out on compact tension ( CT ) type specimens. The volume fraction of transformed martensite was quantitatively evaluated on fatigue fracture surfaces by the X-ray method. The plastic strain on the fracture surface was estimated by measuring the line broadening of X-ray diffraction profiles. The size of plastic zone left on the fatigue fracture surface was determined from the distribution of the line broadening

Non-destructive evaluation for in-service material degradation of CrMo steel by X-ray fractography : Journal of JSNDI, vol. 42, no. 7 (July 1993) p. 464 Higashi, Koji; Matsui, Kazuyuki; Nokata, Fumio; Hirose, Yukio

Non-destructive evaluation for in-service material degradation of CrMo steel by X-ray fractography : Journal of JSNDI, vol. 42, no. 7 (July 1993) p. 464 Higashi, Koji; Matsui, Kazuyuki; Nokata, Fumio; Hirose, Yukio

X-ray Fractography on Fatigue Fractured Surface of Austenitic Stainless Steel

X-ray diffraction observation of the material internal structure beneath fracture surfaces provide fracture analysis with useful information to investigate the conditions and mechanisms of fracture. X-ray fractography is a generic name given to this technique.In the present study, X-ray fractography was applied to fatigue fracture surfaces of austenitic stainless steel (AISI 304) which consisted of solution treatment. The fatigue tests were carried out on compact tension (CT) specimens. The plastic strain on the fracture surface was estimated from measuring the line broadening of X-ray diffraction profiles. The line broadening of X-ray diffraction profiles was measured on and beneath fatigue fracture surfaces. The depth of the plastic zone left on fracture surfaces was evaluated from the line broadening. The results are discussed on the basis of fracture mechanics.