Delayed Fracture Test Research Articles

The committee report on the results of a preliminary investigation to standardize delayed fracture tests for springs

The committee report on the results of a preliminary investigation to standardize delayed fracture tests for springs

The delayed fracture test for viscoelastic elastomers

In a recent contribution, Shrimali and Lopez-Pamies (Extreme Mech Lett 58, 101944, 2023a) have shown that the Griffith criticality condition that governs crack growth in viscoelastic elastomers can be reduced—from its ordinary form involving a historically elusive loading-history-dependent critical tearing energy $$T_c$$ —to a fundamental form that involves exclusively the intrinsic fracture energy $$G_c$$ of the elastomer. The purpose of this paper is to make use of this fundamental form to explain one of the most telltale fracture tests for viscoelastic elastomers, the so-called delayed fracture test.

Structure Formation of Butt Joints Made of Aluminum Alloys to Ensure the Quality of Mechanical Engineering Products

The article discusses the problems of ensuring high-quality formation and normative properties of butt joints of the 1560M and 1980T1 (AMg6 and B48) aluminum alloys as applied to engineering. A method is proposed for joining materials by means of EBW using an electron beam sweep. Homogeneous and dissimilar joints have been investigated, heat treatment of joint from the 1980T1 alloy and a dissimilar joint from the 1560M + 1980T1 alloys is recommended. The paper also presents the results of mechanical properties testing, the corrosion resistance and the delayed fracture tests. A welding technology that makes it possible to obtain high-quality butt-welded joints from aluminum alloys in thicknesses up to 40 mm has been developed and implemented.

Effect of the Segregation of Embrittling Impurities on the Local Strength of Grain Boundaries in a Martensitic Steel

The finite element method and the results of delayed fracture tests of Charpy specimens are used to determine the local strength of grain boundaries in 18Kh2N4VA steel at various contents of phosphorus, antimony, and tin impurities. The embrittlement of grain boundaries is attributed to the adsorption enrichment of grain boundaries in impurities in initial austenite, which leads to weakening of the intergranular cohesion. Phosphorus is found to have the highest susceptibility to intergranular segregation: during the same heat treatment, its grain-boundary concentration is higher than that in steel with antimony or tin. However, the segregation of antimony is more dangerous than the segregation of phosphorus, since, at its lower intergranular concentration, the local strength of grains of quenched steel decreases as in the case of phosphorus segregation.

キャビテーションピーニングによるクロムモリブデン鋼製ボルトの遅れ破壊耐性の向上

In order to demonstrate the effect of cavitation peening on crack initiation stage of hydrogen-charged materials with the objective of industrial application, and suppression of the delayed fracture of bolt, the delayed fracture test was conducted under constant load after hydrogen charging. The obtained results show that fracture surface at an origination of the delayed fracture took on intergranular fracture, and fracture occurred in a moment after crack initiate from stress concentration portion such as root of thread potion and incomplete thread. That is to say, evaluation of crack initiation stage of hydrogen-charged materials can be achieved by the delayed fracture test. Threshold stress σth of the delayed fracture was increased by cavitation peening and kept on increasing with processing time of cavitation peening. σth increased from 327 ± 22 MPa to 505 ± 42 MPa due to cavitation peening with tp = 6 s/mm. This effect was caused by introduction of compressive residual stress at root of thread potion, where subject to be fracture origin.

HYDROGEN INDUCED DELAYED FRACTURE BEHAVIOR OF A LOW-CARBON Mn-B TYPE ULTRA-HIGH STRENGTH STEEL SHEET AFTER HOT STAMPING

In consideration of the light weight and the impact safety of cars, in recent years, hot stamping has been increasingly applied to the manufacture of car parts, which has driven forward the increasing use of ultra-high strength steel sheet in the automobile industry. However, when the tensile strength of steel is more than about 1200 MPa, the steel sheet is very susceptible to hydrogen induced delayed fracture. Up to now, some research has been carried out on delayed fracture behavior of both high strength and ultra-high strength steel sheet. However, the delayed fracture behavior of a low-carbon Mn-B type steel sheet widely used for hot stamping has not been paid enough attention and fully studied. There are also a scarcity of reports on hydrogen induced delayed fracture behavior of this steel sheet after hot stamping. With the development of the hot stamping, the evaluation of delayed fracture behavior of ultra-high strength steel sheet for hot stamping, especially the delayed fracture behavior of steel sheet after hot stamping has become very urgent. For these reasons, hydrogen induced delayed fracture behavior of a low-carbon Mn-B type ultra-high strength hot stamping steel sheet at both the hot stamped status and the common quenched and tempered status was studied by means of constant load delayed fracture test and hydrogen thermal desorption spectrometry (TDS) analysis. The results show that both the critical delayed fracture stressc and delayed fracture life of

Effect of Vanadium on Delayed Fracture Resistance of High Strength Pre-Stressed Concrete Steel Bar

The delayed fracture resistance of pre-stressed concrete (PC) steel bar with different vanadium contents was investigated by using tensile sustained load delayed fracture test and optical microscope. The experimental results show that delayed fracture resistance of vanadium containing steels is higher than that of conventional steel 30MnSi at the same strength level and it increases with the increase of vanadium content. The improvement is resulted mainly from the irreversible traps for hydrogen and the prior austenite grain size refinement by vanadium carbide particles.

Constant-load delayed fracture test of atmospherically corroded high strength steels

Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that delayed fracture occurs when the hydrogen content from the environment, H E, exceeds the critical hydrogen content for delayed fracture, H C. During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H E of the fractured specimens was higher than H C, and H E of the specimens not fractured was lower than H C. This result confirms that the balance between H C and H E determines the occurrence of delayed fracture and that hydrogen-content-based evaluation of susceptibility to delayed fracture is reasonable. To certify the increase of H E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.

Hydrogen Embrittlement of a Manganese–aluminum High-strength Bainitic Steel for Railway Crossings

The hydrogen embrittlement characteristics of a Mn–Al bainitic steel for railway crossings were studied by means of the slow strain rate test (SSRT), the delayed fracture test and X-ray diffraction (XRD) analysis. The binding energies and hydrogen diffusion barriers of an iron unit cell were tested separately with Al, Si and H, and were evaluated by the first principle calculation. The results showed that the hydrogen embrittlement decreased greatly with increased Al content. Microstructure examinations indicated that the content of retained austenite increased with increased Al content, which was as irreversible hydrogen traps and was not sensitive to hydrogen embrittlement. It is found that the characteristics of hydrogen embrittlement identified by SSRT and the delayed fracture test were different. From the first principle calculation, the binding energy of the iron lattice containing aluminum decreased less as compared to those of the cell containing silicon, but the diffusion barriers increased significantly.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium-carbon high strength spring steel containing different amounts of boron (0.000 5%, 0.001 6%) was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron content from 0.000 5 % to 0.001 6 %. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350 °C, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initiation area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 (C, B) phase.

2134 電場下における圧電セラミックスの三点曲げによる遅れ破壊挙動(S12-2 圧電材料,S12 先端材料システムの強度・機能評価とメゾメカニックス)

This paper investigates experimentally and analytically the delayed fracture in lead zirconate titanate (PZT) ceramics under electromechanical loading. Delayed fracture tests were conducted on single-edge precracked-beam specimens, and time-to-failure and fracture load under different DC electric fields were obtained. Possible mechanisms for delayed fracture were also discussed by scanning electron microscope (SEM) examination of the fracture surface of the PZT ceramics. Further, a nonlinear finite element analysis was employed to calculate the energy release rate for the permeable, impermeable and open crack models, and the effects of applied DC electric fields and localized polarization switching on the energy release rate are examined.

307 水素スタンド構成金属材料の評価(技術OS 水素,技術OS1 水素利用技術における材料強度上の問題3)

Hydrogen" entrusted by New Energy and Industrial Technology Development Organization (NEDO), special material testing equipment with heavy walled pressure vessel under 45MPa gaseous hydrogen is facilitated. Tensile properties, strain controlled, low-cycle and high-cycle fatigue and fatigue crack growth tests on CrMo steel (SCM435 (JIS G 4105)) which will be applied for the storage gas cylinders in Japanese hydrogen fuel stations are investigated. The results of the tensile tests under 45MPa ultra high purity hydrogen gas (O2<1ppm) at room temperature shows that there are no difference in yield and maximum tensile strength with those tested in air. However, the reduced ductilities with brittle fracture surface were observed which indicates the occurrence of hydrogen environment embrittlement. It was also found by tensile tests that the embrittling origin is not only caused by machined traces on surface but also by the non-metallic inclusions dispersed on surface. Further discussions on surface treatment effects will be presented. In low cycle fatigue tests, considerable reductions in cycles to failure in 45MPa ultra high purity hydrogen gas were observed. However, there are tendencies that the effect of hydrogen environment embrittlement becomes not so significant as the plastic strain range decreases. It was demonstrated that there was no effect of hydrogen on fatigue limit and this implies that CrMo gas cylinders can be operated in limited fatigue safe condition. Another series of hydrogen test results, temperature effect, fatigue crack growth rate, delayed fracture test using wedge opening loaded specimens, and fatigue test of CrMo gas cylinders under repeated internal pressure with artificial crack will be presented.

Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions.

Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride.

Delayed fracture of beta titanium orthodontic wire in fluoride aqueous solutions

Hydrogen embrittlement of a beta titanium orthodontic wire has been examined by means of a delayed-fracture test in acid and neutral fluoride aqueous solutions and hydrogen thermal desorption analysis. The time to fracture increased with decreasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions. The fracture mode changed from ductile to brittle when the applied stress was lower than 500 MPa in 2.0% APF solution. On the other hand, the delayed fracture did not occur within 1000 h in neutral NaF solutions, although general corrosion was also observed similar to that in APF solutions. Hydrogen desorption of the delayed-fracture-tested specimens was observed with a peak at approximately 500°C. The amount of absorbed hydrogen was 5000–6500 mass ppm under an applied stress in 2.0% APF solution for 24 h. It is concluded that the immersion in fluoride solutions leads to the degradation of the mechanical properties and fracture of beta titanium alloy associated with hydrogen absorption.

Atomic force microscopy of induction- and furnace-heating-tempered prestressed steels with different delayed fracture properties

Quantitative microstructure analyses by atomic force microscope and delayed fracture tests were performed for two types of prestressed steel with a tensile strength of 1470 MPa; an induction-heated-tempered specimen, and a furnace-heated-tempered specimen. Size distributions of cementite particles were measured to characterize the relationship between microstructures and delayed fracture properties.

Susceptibility to delayed fracture of Ni–Ti superelastic alloy

The susceptibility of Ni–Ti superelastic alloys to hydrogen embrittlement has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. It was found that the time to fracture was drastically reduced when the applied stress exceeded the critical stress for martensite transformation. In the applied stress range lower than the critical stress, the time to fracture lessened in the order of instability of the alloys to undergo reversible martensite transformation. Hydrogen thermal desorption of specimens subjected to delayed-fracture test is classified into two types according to the applied stress level. The amount of desorbed hydrogen was markedly increased when the applied stress was higher than the critical stress. It was concluded that Ni–Ti superelastic alloys transformed to martensite are sensitive to environmental conditions accompanying accelerated hydrogen embrittlement.

Hydrogen thermal desorption relevant to delayed-fracture susceptibility of high-strength steels

The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorptionrate peak around 50 °C to 200 °C increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

超高強度ボルトの遅れ破壊に関する実験的研究 : その1 鋼種と形状の観点から

Accelerated delayed fracture tests were carried out on the subject of the ultra high strength bolts in number of 1480. Experimental parameters were 8 kinds of metal materials and 6 kinds of strength level as well as shape of thread. Each test bolt was inserted into the test cylinder and loaded. The cylinder was coated by epoxy resin to eliminate corrosion, further it has load cell function putting the wire strain gages on both sides. The loaded assemblies were exposed to alternate immersion cycle in sulfuric acid solution accomplished by subjecting the specimens to the solution for period of 10 minutes per hour, followed by drying in air for a period of 50 minutes. We got conclusions as follows, the development of cracks or failures of bolts were caused mainly by tempering temperature, which was able to be related to carbon equivalent value of bolts material. On the other hand, the effect of shape of thread and bolts strength level accordance with the quality of the material and tempering temperature, themselves were of secondary importance.

Observation of Trapping Sites of Hydrogen and Deuterium in High-Strength Steels by Using Secondary Ion Mass Spectrometry

Hydrogen and deuterium trapping sites in high-strength steels have been observed by secondary ion mass spectrometry (SIMS). High-strength steels with 1400 MPa tensile strength are stressed and dipped in D2O and 20% NH4SCN solution at 323 K to occlude hydrogen and deuterium. Depth profiles by SIMS show the presence of deuterium, which indicates hydrogen trapping sites occluded during the delayed fracture test. Secondary ion image analysis by SIMS has made it possible to observe hydrogen and deuterium trapping sites in high-strength steels. Hydrogen tends to accumulate at grain boundaries, in segregation bands, and on inclusions. Line scans by SIMS have shown that the accumulation ratios of hydrogen for the grain boundaries, segregation bands of P and inclusions are 7.8, 5.0 and 11.0 times higher than that in the matrix, respectively. Hydrogen trapping sites at the grain boundaries can be observed by measuring within 24 h after the delayed fracture test.

耐遅れ破壊特性に優れたSi及びSi,Ca複合添加高強度鋼の水素吸蔵特性

Medium carbon steels added 2.0% Si or 1.5% Si-30ppm Ca with 1400N/mm2 tensile strength show high resistance to delayed fracture. It is important to clarify the hydrogen occlusion behavior to delayed fracture of steels with high resistance to delayed fracture. The hydrogen diffusion coefficient and hydrogen content were measured by electrochemical permeation technique, and hydrogen evolution content after accelerated delayed fracture test was directly measured by hydrogen thermal analysis. It is found that high resistance to delayed fracture of 2.0% Si steel is due to the high hydrogen content needed for fracture, in spite of its high hydrogen occlusion rate. Also the high resistance to delayed fracture of 1.5% Si-30ppm Ca steel is found to be due to the low hydrogen occlusion rate and the low hydrogen content needed for fracture.