DC Electrical Potential Method Research Articles

Determination of Mode of Damage During Creep-Fatigue Interaction

A technique has been developed using the reversing dc electrical potential method to determine the mode of damage taking place during creep-fatigue interaction. It is observed that the hysteresis loop created by plotting the stress verses electrical potential gives a clear indication whether the damage in process is creep dominated or fatigue-dominated. During the fatigue-dominated damage process the hysteresis loop of stress verses electrical potential changes the shape whereas during the creep-dominated damage process the hysteresis loop of stress verses electrical potential does not change the shape but moves in the direction of higher electrical potential values. These changes are observed well before any indication seen on the conventional hysteresis loop of stress verses strain. This identification of the damage mode is observed well before failure occurs. The conclusion has been confirmed through fractographs. Hence it can be said that this technique eliminates the need for fractographs when determining the mode of damage during creep-fatigue interaction.

Reliability Engineering Approach to Fatigue Crack Growth Rate Under Random Loading Using DC Eletrical Potential Method

Automatic fatigue crack length measuring system using DC electrical potential method and the system control program for automatic fatigue testing under random load condition were made in this study. And using these system and control program, fatigue tests were executed under constant and random load condition. As the result, the propagation of crack in random loading can be represented Paris equaiton and log normal probability function. But constant and random load test show different crack propagation properties.

Reliability engineering approach to fatigue crack growth rate in high strength steel HT60 by DC electrical potential method : 49991 Matsumura, T.; Takamatsu, T.; Ichikawa, M.; Konno, T.; Nishijima, S. Journal of the Society of Materials Science, Japan, Vol. 41, No. 464, pp. 637–642 (May 1992)

Reliability engineering approach to fatigue crack growth rate in high strength steel HT60 by DC electrical potential method : 49991 Matsumura, T.; Takamatsu, T.; Ichikawa, M.; Konno, T.; Nishijima, S. Journal of the Society of Materials Science, Japan, Vol. 41, No. 464, pp. 637–642 (May 1992)

Reliability engineering approach to fatigue crack growth rate using DC electrical potential method (development of DC electrical potential system and preliminary experiments) : 39506 Ichikawa, M.; Akita, A.; Takamatsu, T.; Matsumura, T.; Sato, M.; Nishijima, S. Journal of the Society of Materials Science, Japan, Vol. 37, No. 420, pp. 28–34 (Sep. 1988)

Reliability engineering approach to fatigue crack growth rate using DC electrical potential method (development of DC electrical potential system and preliminary experiments) : 39506 Ichikawa, M.; Akita, A.; Takamatsu, T.; Matsumura, T.; Sato, M.; Nishijima, S. Journal of the Society of Materials Science, Japan, Vol. 37, No. 420, pp. 28–34 (Sep. 1988)

Reliability engineering approach to fatigue crack growth rate in high strenght steel HT60 by dc electrical potential method: Matsumara, T. Takamatsu, T., Ichikawa, M., Konno, T. and Nishijima, S. J. Soc. Mater. Sci. Jpn May 1992 41, (464), 637–642 (in Japanese)

Reliability engineering approach to fatigue crack growth rate in high strenght steel HT60 by dc electrical potential method: Matsumara, T. Takamatsu, T., Ichikawa, M., Konno, T. and Nishijima, S. J. Soc. Mater. Sci. Jpn May 1992 41, (464), 637–642 (in Japanese)

Statistical experiment of fatigue crack growth rate using DC electrical potential method and examination of stochastic models (2024-T3 aluminium alloy): Ichikawa, M., Takamatsu, T., Matsumura, T., Suzuki, N. and Nishijima, S. J. Soc. Mater. Sci., Japan Mar. 1991 40, (450), 283–288 ( in Japanese)

Statistical experiment of fatigue crack growth rate using DC electrical potential method and examination of stochastic models (2024-T3 aluminium alloy): Ichikawa, M., Takamatsu, T., Matsumura, T., Suzuki, N. and Nishijima, S. J. Soc. Mater. Sci., Japan Mar. 1991 40, (450), 283–288 ( in Japanese)

直流電位差法による疲労き裂伝ぱ速度の信頼性工学的研究 （第３報） 直流電位差法による高張力鋼ＨＴ６０の疲労き裂伝ぱ速度の信頼性工学的研究

Fatigue crack growth tests under tension-tension loading were performed on center-notched specimens of a high strength steel HT60, and the statistical property of fatigue crack growth rate da/dN was studied by testing 36 specimens under the same condition. The fatigue crack length was measured automatically using the DC electrical potential method and a microcomputer. The experimental data were analyzed from the viewpoint of the composite variability model of the fatigue crack growth rate which had been proposed by the present authors. The model parameters were estimated by a new method proposed in this paper as well as by the one proposed previously. The result of data analysis was compared with the previous result of 2024-T3 Al alloy. When expressing C in the Paris equation da/dN=C(ΔK)m as C=C*gl where g and l correspond to inter-specimen variability and intra-specimen variability of C respectively, the coefficients of variation of g and l for HT60 were approximately of the same magnitude as those for 2024-T3 Al alloy. On the other hand, the correlation distance for intra-specimen variability was smaller for HT60 than for 2024-T3 Al alloy. When a straight line log(da/dN)=logCs+mslog(ΔK) was fitted to the data of each specimen, ms and logCs of each specimen followed normal distributions approximately and strong negative correlation was found between ms and logCs. This property was quite similar to that for 2024-T3 Al alloy.

直流電位差法による疲労き裂伝ぱ速度の信頼性工学的研究（第２報） 直流電位差法による疲労き裂伝ぱ速度の統計的実験と確率モデルの検討

By using the fatigue crack growth test system developed in the previous study, statistical data of fatigue crack growth rate da/dN in 2024-T3 aluminum alloy were obtained. Eighteen specimens were tested. In the test system used, the crack length was measured using the DC electrical potential method and precise load control was made using a microcomputer. Thus, scatter in testing conditions and labor needed were decreased as compared with the previous test by the present authors in which the crack length was measured using a travelling microscope. From analyses of the experimental data, the coefficient of variation, ηΔN, of the number of stress cycles for crack growth from a given value of a to a+Δa (Δa=0.1mm) was found to be nearly constant independent of a. This implies that m in Paris' law da/dN=C(ΔK)m can be regarded to be deterministic in the present data. Then, the composite variability model as a stochastic model of da/dN proposed previously by the present authors was examined using the present data. In this model, C is treated as a random variable involving the inter-specimen variability and the intra-specimen variability, whereas m is treated as deterministic. From comparison of the model with the data, the inter-specimen variability was found to be considerably smaller in the present data than in the previous data. This seems to be due to the decrease of scatter in testing conditions. Furthermore, the correlation distance δ of the intra-specimen variability of C was found to be much smaller in the present data than in the previous data. The value of δ estimated from the present data was of the order of a grain size. This suggests that the intra-specimen variability of C occurs from grain to grain.

Reliability engineering approach to fatigue crack growth rate using DC electrical potential method (development of DC electrical potential system and preliminary experiments): Ichihawa, M., Akita, S. and Takamatsu, T. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1010–1017 (in Japanese)

Increased evidence suggests that apart from patients with increased albumin excretion and decreased glomerular filtration rate (GFR); there are also patients with type 2 diabetes with decreased GFR but without albuminuria. The exact pathophysiologic mechanisms regarding these clinical conditions are not known. We suggest that different blood pressure (BP) levels may be one the factors for these different clinical conditions. However, before labeling BP as a causative factor; one must show whether BP levels are different in these patients. Thus the current study was performed to analyze the relationship between creatinine clearance, microalbuminuria and circadian blood pressure levels in newly diagnosed essential hypertensive and type 2 diabetic patients.Medical history, physical examination, laboratory analysis and ambulatory blood pressure measurements (ABPMs) were analyzed. 24-h urine specimens were collected to measure creatinine clearance and albumin excretionIn total 216 patients were included which were divided into 4 groups: group 1 composed of 90 patients with normal GFR and without microalbuminuria (MA), group 2 composed of 50 patients with normal GFR and with MA, group 3 composed of 36 patients with decreased GFR and without MA and group 4 composed of 40 patients with both decreased GFR and MA. The ratio of dippers vs. non dippers was not different between group 1, group 2 and group 3 patients. However ratio of dippers was higher in group 1 when compared to group 4 (P: 0.003) and group 4 patients have an odds of 7.678 (CI: 1.657–35.576, P: 0.009) for non-dapping status when compared to patients in group 1.In conclusion, ABPM measurements were highest in patients with both decreased GFR and MA, whereas they are lowest in patients with normal GFR and normal UAE.

Toughness and microstructural factors of Ti6Al4V alloy

The instrumented Charpy impact test, the dynamic fracture toughness test and the static fracture toughness test using the DC electrical potential method were carried out on Ti6Al4V alloys. Ti6Al4V alloys with various microstructures were used to investigate the relation between microstructural factors, including fractographic measurements, and various toughness criteria, i.e. Charpy absorbed energies (E t, total absorbed energy; E i, apparent crack initiation energy; E p, apparent crack propagation energy); dynamic fracture toughness J d; static fracture toughness (J Ic (EPM), by DC electrical potential method or K Q); static fracture propagation resistance curve (J R curve); and static tearing modulus T mat. The toughness of the Ti6Al4V alloy as evaluated by the Charpy test was different from that given by the dynamic toughness test mainly because the microstructural unit which controlled the fracture was different in the different tests. The toughness evaluated by means of the J R curve or T mat does not always coincide with that given by J Ic (EPM). Therefore it is necessary to use an appropriate toughness criterion that corresponds to the method of design. It was found that the microstructure had a greater influence on T mat than on J Ic (EPM). In addition, the relationships between microstructural factors (i.e. the areal fraction of the primary α phase, the mean free path in the primary α, the depth of dimples, the prior β grain size) and the various toughness criteria mentioned above must be clearly defined.

有限要素解析を採用した引裂き試験法による破壊靭性値の評価

A rather good correlation between fracture properties obtained from tear test fracture toughness value JIC has already been reported in the previous study. A method of estimating fracture toughness parameters directly from the tear test is studied and presented in this study with a help of the finite element analysis. Tear test is carried out using specimen with a deep notch ratio of a/W=0.3 which is recommended from the result of finite element analysis, while its other geometry is held same as that of the standard tear test one. In such test, load-load line deflection curve and crack initiation point are recorded. Then, the fracture toughness JIC can be successfully evaluated by putting the area under the load-deflection curve up to the crack initiation point into the Rice's simple J integral estimation formula. Crack initiation point can be experimentally detected by the DC electrical potential method or the compliance changing rate method developed by the authors. It is also shown that crack initiation point may be also detected by the maximum load if side grooves are added to the specimen. Moreover, it is verified that crack extension resistance, i.e., tearing modulus Tmat, from the tear test coincides with that obtained from the test of CT specimen.

Fatigue crack initiation at notches in SA 333 piping steel

AbstractIn this paper are reported two recent investigations into crack initiation at notch roots using techniques developed for remote monitoring of crack growth in high–temperature water environments. In the first, a notched compact–type specimen of a carbon steel, SA 333 Gr. 6, was monitored for crack initiation (defined as a 0·076 mm crack at the notch root) in a variety of water chemistries and testing conditions. The mechanical conditions at the notch root have been analysed using the Neuber–notch method, enabling a direct comparison to be made with the strain–controlled fatigue data curves used for a smooth specimen in the ASME Boiler and Pressure Vessel Code, Section III. In the second investigation a different method was considered for monitoring crack initiation. A modification of the electrical–potential technique, called the reversing dc electrical potential method, was used to obtain quantitative information on the initiation and early growth of small surface cracks in notched bars of a high–...

Evaluation of neutron irradiation embrittlement of heavy section nuclear reactor pressure vessel steels in terms of elastic-plastic fracture toughness

The fracture toughness degradation due to neutron irradiation was examined for the evaluation of the structural integrity of a nuclear reactor pressure vessel using four kinds of currently used heavy section manganese-molybdenum-nickel low alloy steels, which included the welded joint as well as the base metal. Neutron irradiation was conducted up to 2to 7×10 19 n/cm 2 > 1 MeV at 290°C in JMTR, and the embrittlement was mainly evaluated by the Charpy and fracture toughness tests using small three point bend specimens. From the results, the following can be pointed out: 1. (1) The elevations of the transition temperature of steels used, which are evaluated by 41 J of the Charpy absorbed energy, are within 50°C, and a quite high resistance against neutron irradiation embrittlement is observed. 2. (2) The J IC fracture toughness and J - R curve of irradiated materials as well as unirradiated ones are successfully determined by a dc electrical potential method using a single specimen. 3. (3) At the transition region, the increase of transition temperature (ΔRT NDT) at the 41 J level of the Charpy impact test is nearly equal to the shift at the 100 MPa m 1 2 level of the fracture toughness test.

球状黒鉛鋳鉄の切欠き付ＣＴ試験片の破壊じん性

The fracture toughness tests of ductile cast iron (JIS FCD 60) were conducted at room temperature by using compact tension specimens with blunt-notches. The method to determine the point of crack extension was established and the effect of notch-tip radius on the fracture toughness Ki was investigated. The main results obtained are summarized as follows:(1) The DC electrical potential method can be applied to detect the point of crack extension in blunt-notched CT specimens of ductile cast iron, which is almost identical to that determined by the R-curve method. Acoustic emissions became severe before the crack extension point was detected by the electrical potential method.(2) The relation between Ki and notch-tip radius ρ can be divided into three regions: region I where ρ is smaller than the radius of spheroidal graphite ρG(30μm), region II where ρ is above ρG and below 2mm, and region III where ρ is larger than 2mm. Ki was constant in regions I and III, while it increased linearly with √ρ in region II. The plastic strain εf on the fracture surface estimated by X-rays showed a similar trend in its variation with ρ. In region II, εf became larger with increasing Ki/√ρσY.