Static Fracture Toughness Tests Research Articles

Performance of Sc-Y-ODS variant of Eurofer steel in stagnant PbLi at 600°C

This paper represents a part of the research of structural materials for fusion systems. The performance of a conventionally formed Eurofer-97 steel and its Sc-Y-ODS variant developed by our group was assessed in a stagnant liquid PbLi environment. The experiments were performed at 600°C for 500 and 1000 hours, and the subsequent microscopical investigation identified a solution-based attack as the dominant corrosion damage of both materials. The metal loss of the conventional Eurofer-97 steel was 66.2 µm after 1000 h exposure, corresponding to a rate of 580 µm/year. In contrast, the ODS Eurofer variant strengthened with various fine Sc-Y complex oxides showed a 70% lower corrosion damage, mainly owing to formation of a Sc-Y-rich Pb surface layer. To understand the degradation process in more detail, both materials were characterized before and after the PbLi exposure in terms of their microstructures and mechanical behavior including hardness, tensile, impact and static fracture toughness tests.

Microstructure and Failure Processes of Reactor Pressure Vessel Austenitic Cladding

This paper is dedicated to an experimental program focused on the evaluation of microstructure and failure mechanisms of WWER 440 type nuclear reactor pressure vessel cladding made from Sv 08Kh19N10G2B stainless steel. Static fracture toughness tests performed on standard precracked single edge bend specimens revealed extreme variations in fracture toughness values, J0.2. Fractured halves of test specimens were subject to detailed fractographic and metallographic analyses in order to identify the causes of this behavior and to determine the relationship between local microstructure, failure mode and fracture toughness. Results indicated that fracture toughness of the cladding was adversely affected by the brittle cracking of sigma particles which caused a considerable decrease in local ductile tearing resistance. Extreme variations in relative amounts of sigma phase, as well as the extreme overall structural heterogeneity of the cladding determined in individual specimens, provided a reasonable explanation for variations in fracture toughness values.

In vitro fracture resistance of molar teeth restored with a short fibre-reinforced composite material

ObjectivesThe purpose of this in vitro study was to evaluate the efficiency of a short fibre-reinforced composite (SFRC) material compared to conventional composites when restoring class II. MOD cavities in molar teeth with different layering techniques. MethodsOne hundred and thirty mandibular third molars were divided into 5 groups (n=26). Except for the control group (intact teeth), in all other groups MOD cavities were prepared. The cavities were restored by either conventional composite with horizontal and oblique layering or by SFRC with horizontal and oblique layering. The specimens were submitted to static fracture toughness test. Fracture thresholds and fracture patterns were evaluated. ResultsIn general, no statistically significant difference was found in fracture toughness between the study groups, except for horizontally layered conventional composite restorations, which turned out to be significantly weaker than controls. However, SFRC yielded noticeably higher fracture thresholds and only obliquely applied SFRC restorations exhibited favourable fracture patterns above chance level. ConclusionsThe application of SFRC did not lead to a statistically significant improvement of the fracture toughness of molar teeth with MOD cavities. Still, SFRC applied in oblique increments measurably reduces the chance of unrestorable fractures of molar teeth with class II MOD cavities. Clinical significanceThe restoration of severely weakened molar teeth with the use of SFRC combined with composite might have advantages over conventional composites alone. It was observed from the statistical data, that the application of SFRC with an oblique layering technique yielded not significantly but better fracture thresholds and more favourable fracture patterns than any other studied material/technique combination. Thus further investigations need to be carried out, to investigate the possible positive mechanical effects of SFRC. The application of the horizontal layering technique with conventional composite materials is inferior to the oblique technique and SFRC materials.

Determination of stretch zone width and height by powerful 3D SEM imaging technology

The focus of the present study is to demonstrate a new method to determine the stretch zone height and width using a fast and easy 3D imaging tool in the scanning electron microscope. The SEM MIRA3 XMU from TESCAN Company is equipped with a unique real-time 3D imaging technology. The paper compares 2D with 3D imaging (as anaglyph pictures) of several fracture surfaces after static fracture toughness tests on austenitic and ferritic steels as well as on cast iron showing more or less well pronounced stretch zones. The 3D images give a clear view of the fracture topography, which can hardly be achieved in 2D by tilting and looking from side positions. It is shown, how 3D reconstruction and length measurement is possible with dual image photogrammetry software allowing a precise determination both of the stretch zone width and height.

歯科用金合金の引張特性および静的破壊靭性に及ぼすミクロ組織の影響

Tensile tests and static fracture toughness tests were carried out on variously heat-treated type IV gold alloys. The effects of microstructures on tensile characteristics and static fracture toughness were discussed. The tensile strength of type IV gold alloy increases with increasing solutionizing temperature. Moreover, the tensile strength of type IV gold alloy increases with increasing ageing time when the solutionizing temperature is 1023 K. While the elongation of type IV gold alloy decreases with increasing solutionizing temperature. Static fracture toughness of type IV gold alloy increases with increasing solutionizing temperature. Static fracture toughness of type IV gold alloy of aged for 0.3 ks is the greatest, and that of aged for 1.8 ks is the smallest when the solutionizing temperature is 1023 K.

Limitations of elastic definitions in Al–Si–Mg cast alloys with enhanced plasticity: linear elastic fracture mechanics versus elastic–plastic fracture mechanics

Linear elastic fracture mechanics describes the fracture behavior of materials and components that respond elastically under loading. This approach is valuable and accurate for the continuum analysis of crack growth in brittle and high strength materials; however it introduces increasing inaccuracies for low-strength/high-ductility alloys (particularly low-carbon steels and light metal alloys). In the case of ductile alloys, different degrees of plastic deformation precede and accompany crack initiation and propagation, and a non-linear ductile fracture mechanics approach better characterizes the fatigue and fracture behavior under elastic–plastic conditions. To delineate plasticity effects in upper Region II and Region III of crack growth an analysis comparing linear elastic stress intensity factor ranges (Δ K el) with crack tip plasticity adjusted linear elastic stress intensity factor ranges (Δ K pl) is presented. To compute plasticity corrected stress intensity factor ranges (Δ K pl), a new relationship for plastic zone size determination was developed taking into account effects of plane-strain and plane-stress conditions (“ combo plastic zone”). In addition, for the upper part of the fatigue crack growth curve, elastic–plastic (cyclic J based) stress intensity factor ranges (Δ K J ) were computed from load–displacement records and compared to plasticity corrected stress intensity factor ranges (Δ K pl). A new cyclic J analysis was designed to compute elastic–plastic stress intensity factor ranges (Δ K J ) by determining cumulative plastic damage from load–displacement records captured in load-control ( K-control) fatigue crack growth tests. The cyclic J analysis provides the true fatigue crack growth behavior of the material. A methodology to evaluate the lower and upper bound fracture toughness of the material ( J IC and J max) directly from fatigue crack growth test data ( Δ K FT ( J IC ) and Δ K FT ( J max ) ) was developed and validated using static fracture toughness test results. The value of Δ K FT ( J IC ) (and implicitly J IC) is determined by comparing the plasticity corrected elastic fatigue crack growth curve with the elastic–plastic fatigue crack growth curve. A most relevant finding is that plasticity adjusted linear elastic stress intensity factor ranges (Δ K pl) are in remarkably good agreement with cyclic J analysis results (Δ K J ), and provide accurate plasticity corrections up to a Δ K corresponding to J IC (i.e. Δ K FT ( J IC ) ). Towards the end of the fatigue crack growth test (above Δ K FT ( J IC ) ) when plasticity is accompanied by significant tearing, the cyclic J analysis provides a more accurate way to capture the true behavior of the material and determine Δ K FT ( J max ) . A procedure to decouple and partition plasticity and tearing effects on crack growth rates is given. Three cast Al–Si–Mg alloys with different levels of ductility, provided by different Si contents and heat treatments (T61 and T4) are evaluated, and the effects of crack tip plasticity on fatigue crack growth are assessed. Fatigue crack growth tests were conducted at a constant stress ratio, R = 0.1, using compact tension specimens.

Effect of Microstructure on Tensile Properties and Static Fracture Toughness of Dental Gold Alloy

Tensile tests and static fracture toughness tests were conducted on dental type 4 gold alloys subjected to various heat treatments. The effects of microstructures on tensile characteristics and static fracture toughness are discussed.The tensile strength of dental type 4 gold alloy increases with the solutionizing temperature. Moreover, the tensile strength of dental type 4 gold alloy increases with aging time at a solutionizing temperature of 1023 K. On the other hand, dental type 4 gold alloy exhibits reduced elongation with an increase in the solutionizing temperature.Static fracture toughness of dental type 4 gold alloy increases with an increase in the solutionizing temperature. Static fracture toughness of dental type 4 gold alloy aged for 0.3 ks is the highest, and is the lowest when it is aged for 1.8 ks, with the solutionizing temperature at 1023 K.

Characteristics of unirradiated and 60 °C, 2.7 dpa irradiated Eurofer97

After the delivery of various product forms of Eurofer97, NRG has started a comprehensive characterisation effort. A laboratory-scale heat with the same specifications has been acquired as well. A 2.7 dpa irradiation has been carried out in the high flux reactor at Petten at reactor ambient temperature. Microstructural properties are investigated. Pre-irradiation as well as post-irradiation tensile, impact properties, and transition fracture toughness are determined. The microstructure of Eurofer97 is martensitic with ASTM 10.2 prior austenite grain size and few inclusions. Impact properties of the 25 mm plate are impaired: DBTT of −75 °C as opposed to −100 °C for the other forms. Tensile properties of Eurofer97 before and after irradiation are comparable to that of F82H under similar conditions. In impact tests, the Eurofer lab-scale heat outperforms F82H: the DBTT after irradiation is around −17 °C in stead of +35° for F82H-mod. Static fracture toughness tests show a larger shift in transition temperature than the impact tests.

Direct measurement of reactor pressure vessel steels fracture toughness: Master Curve concept and instrumented Charpy-V test

One of the key issues concerning the structural integrity of reactor pressure vessel is the effect of neutron irradiation on the material fracture toughness. At present, this is achieved indirectly by means of correlation between Charpy and fracture toughness due to neutron irradiation. The uncertainties associated with this indirect determination have increased the need for a direct measurement of the fracture toughness. Taking into account that the surveillance capsules include Charpy-V specimens, recent investigations are focused on the determination of the fracture toughness using this type of geometry. This paper presents two different ways to obtain fracture toughness from Charpy-V specimens: instrumented Charpy-V tests and static fracture toughness tests (three-point bend) applying the “Master Curve” concept. The two methodologies are applied to reactor pressure vessel steels in the unirradiated condition.

FRACTURE TOUGNESS EVALUATION IN PARTICULATE REINFORCED ALUMINUM ALLOY COMPOSITE

SiC-particulate-reinforced aluminum alloy (SiC{sub p}/Al) composites have received considerable attention in the automobile and aerospace industries, owing to their advantages of light weight and high rigidity. Although numerous papers concerning mechanical properties of SiC{sub p}/Al composites have been reported, there are many problems on exact evaluation of their static and dynamic fracture toughness which are important for their use in structural components. In this study, dynamic and static fracture toughness tests are carried out on SiC{sub p}/Al composite. The evaluation method of fracture toughness based on J-integral and the relationship between the evaluation procedure of fracture toughness and the fracture process are discussed.

IMPACT FRACTURE TOUGHNESS TEST OF CERAMIC REINFORCED METALS

Impact frature toughness tests are performed at room temperature and 200°C by using the one-point-bending impact system. Young's modulus and Poisson's ratio of the tested materials are measured at each test temperature to determine the stress intensity factor accurately. Yield stress of the tested materials is measured to calculate the stress intensity factor with plastic zone correction. Also static fracture toughness tests are performed to compare the dynamic with static fracture toughness data. It is found that the impact fracture toughness of the tested materials decreases with increasing test temperature and, furthermore, that the fracture toughness increases with increasing loading rate.

球状黒鉛鋳鉄材の衝撃特性のＸ線フラクトグラフィ的研究

Austempered Ductile Iron (ADI) is being used in highly stressed components, particularly in the automotive industry. It therefore becomes essential to understand the factors influencing the ductile and fatigue properties of this material.In the present paper, to obtain basic data of ADI, dynamic fracture toughness test and static fracture toughness test were conducted. And then X-ray fractographic technique was applied on the fracture surface made by these fracture toughness tests. The plastic zone size was determined from the distribution of the half value and residual stress near the fracture surface. These data obtained in the laboratory tests were used to estimate the dynamic fracture toughness parameter KId at actual fracture of machine parts.

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.

Evaluation of static and dynamic fracture toughness in ceramics

In the present study, static fracture toughness of ceramics is evaluated by a three point bending test using a precracked specimen. The obtained results are compared with the ones obtained by conventional static fracture toughness testing methods. Moreover, dynamic fracture toughness of ceramics is evaluated by the impact response curve method using a strain gage attached onto the specimen in an instrumented Charpy impact test. Furthermore, an influence of notch root radius on the fracture toughness is examined experimentally and theoretically. As a result, it has been shown that a static fracture toughness test using the precracked specimen evaluates a lower bound of static fracture toughness in comparison with one obtained from the traditional test method. Dynamic fracture toughness K d in partially stabilized zirconia has been observed to increase with loading rate . K. On the other hand, K d in Si 3N 4 has decreased once and then increased with increase of . K. This phenomenon suggests an existence of minimum K d value in Si 3N 4 at a certain . K level. It has also been shown that fracture toughness depends on notch root radius, and the variation of fracture toughness with notch root radius follows the theoretical formula presented by Williams.

部分安定化ジルコニアおよび窒化けい素セラミックスにおける破壊靭性測定と負荷速度の影響

Although there are many researches on static fracture toughness tests of ceramics in the literature, the testing method has not yet been standardized. On the other hand, only a few reports dealt with dynamic fracture toughness tests of ceramics have been observed. Moreover, it becomes a problem that conventional methods of static fracture toughness testing have been applied mainly to specimens without precracking. Therefore, the values of static fracture toughness obtained by the methods are lacking in reliability. Moreower, it is very difficult to measure the real fracture load in the dynamic fracture toughness test because of a remarkable inertial loading effect.In the present study, static fracture toughness of ceramics was measured by a three-point bending test using precracked specimens. The results were compared with those obtained by the conventional methods. Moreover, the dynamic fracture toughness of ceramics was measured by the impact response curve method using a strain gage attached to the specimen in the instrumented Charpy impact test.As a result, it has been shown that the static fracture toughness test using precracked specimens can evaluate the lower limits of static fracture toughness in contrast with the conventional methods. Dynamic fracture toughness Kd in partially stabilized zirconia has been observed to increase monotonously with loading rate \dotK, while Kd in Si3N4 decreases at first and then increases with increase of \dotK. This phenomenon suggests the existence of a minimum Kd value in ceramics. It has also been made clear that a rather good correlation exists between Kd and the total absorbed energy Et of the unnotched impact test specimen when the latter value is corrected by the fracture unit distance.