Thick Plate Specimens Research Articles

Laser cutting study of zirconium alloys for nuclear decommissioning

We conducted laser cutting studies on zirconium alloys, specifically Zircaloy-2 and Zr-2.5%Nb alloy, which are used as constituent materials in the nuclear fuel channel of a pressurized heavy water reactor. The study measured the maximum cutting speed, amount of secondary emissions, and aerosol characteristics for each material using 10 mm thick plate specimens. The cutting performance of the zirconium alloys was similar to each other. At a laser power of 1–5 kW, the maximum cutting speed ranged from 750 to 1900 mm/min, and the amount of secondary emissions per length ranged from 32 to 53 g/m. Compared to 304 L stainless steel, the maximum cutting speed was 1.7–1.9 times higher, and the amount of secondary emissions was about 60–70 % of that of stainless steel. Analyzing the physical properties of aerosols, both zirconium alloys generated larger particles with a count median aerodynamic diameter of 0.25 μm, which is approximately 15–17 % larger than that of 304 L stainless steel.

Correlation among Microstructure, Texture, and Properties along the Thickness Direction in As-Hot-Rolled and As-Solution-Quenched Al7055 Thick Plates

Both microstructure inhomogeneity and mechanical property diversity along the thickness direction in rolled thick aluminum plates have been considered to have a remarkable impact on the performance and properties of the products made from the plates. In this study, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) characterizations of microstructure and texture types along the thickness directions of Al7055 thick plate specimens prepared using two conditions, hot-rolling and solution-quenching, were performed. To examine the mechanical properties, uniaxial tensile tests were also carried out on specimens machined from both types of thick plates, using a layered strategy along the thickness direction. The results indicate that both the microstructure and mechanical properties are inhomogeneous under the two conditions. Furthermore, it is evident that there is a hereditary relationship between the mechanical properties of the two plates—areas with higher yield strength in the as-hot-rolled plate correspond to areas with the higher yield strength in the as-solution-quenched plate

Evaluation of damage and fracture of high Cr steel welds at elevated temperatures

High Cr ferritic steels have been used in the 600°C class ultra-super critical (USC) thermal power plants. More than a decade has passed from the application of high Cr steels to USC power plants in Japan, and type-IV creep damages in the welded components become concerns. In the present paper, long-term creep tests for the welded joints of the high Cr steels (Gr.91 and Gr.122 steels) were conducted. Microstructures and creep damages in the heat affected zone (HAZ) were investigated using the thick plate specimens. Remaining life assessment methods of high Cr steel welds were discussed based on the experimental results. Further, to assist the standardization of the testing method for creep crack growth in welded joints, we have conducted the round robin tests using the high Cr steels (Gr.91 and Gr.92 steels) and their welds as part of the VAMAS TWA31 collaboration.

The application of small overloads for fractography of small fatigue cracks initiated under constant-amplitude loading

Fatigue crack initiation and crack growth are relevant issues for various structures. Initially small fatigue cracks usually are a part-through crack. The growth rate is small and the initial crack growth life covers a significant part of the fatigue life. Prediction on crack growth of part-through cracks under constant-amplitude (CA) loading is still difficult. Experimental verification occurs by fractographic examination. It requires marker load cycles inserted between the CA cycles to delineate the shape of the crack front. In the present investigation it is proposed to adopt small overloads for this purpose. This can introduce crack growth delays. However, it may be insignificant for small OL’s and large blocks of the CA baseline cycles. Furthermore, OL’s should produce striations which are more easily detected in the electron microscope. These questions are the major topic of the present investigation. Crack growth tests are carried out on specimens of aerospace aluminium alloys with different marker load sequences. Crack fronts and crack growth rates of small part-through cracks at the edge of a tapered hole in a thick plate specimens are obtained. At the grain boundaries a chaotic crack surface is observed associated with different crystallographic orientations of the adjacent grains. The analysis of this issue has led to the conclusion that 2-dimensional models for crack extension in a load cycle along the entire crack front is unrealistic. It is a 3-dimensional phenomenon.

Elastoplastic characterization and damage predictions under evolving local triaxiality: axysimmetric and thick plate specimens

Ductile failure is a phenomenon involving large plastic strains, thus any method for predicting fracture of mechanical components needs to be supported by a reliable procedure for the material stress–strain characterization, whose accuracy is an essential prerequisite for allowing any damage model to deliver accurate predictions. Sometimes the true stress–true strain curves from smooth tensile specimens are used in the literature for identifying a metal despite their low accuracy at the post-necking deformation levels, but usually the experimental true stress is corrected by the Bridgman factor for the necking effect. Two mathematical models, of the stress–strain characterization in the elastoplastic post-necking phase and of the ductile failure prediction, are used in this paper for a FE 370 carbon steel. The stress–strain data accounting for the necking-induced triaxiality and the critical value of a damage indicator based on the cumulated stress triaxiality are obtained by applying the model called MLR and the Bao–Wierzbicki model, respectively, to experimental data from tensile tests on smooth and notched specimens. Then, the acquired data are used to simulate the material behavior with reference to two series of differently notched plate specimens. Simulated behavior is then compared with experiments for evaluating the achieved degree of accuracy.

Thermal fatigue crack propagation behaviour of F82H ferritic steel

This paper presents an issue obtained from thermal fatigue research, which attempts to examine the fusion reactor first wall by fracture mechanics. The research is organised with two different approaches: 1. Studies of the thermal fatigue crack propagation behaviour on notched 5-mm thick plate specimens of ferritic steel F82H (9Cr-1W), compared with 9Cr-1Mo ferritic steel and type 316 stainless steel; 2. Numerical simulations of the stress field caused by thermal loads including fracture mechanics. It is concluded that the stress intensity factor Δ K I is substantial for crack growth while cyclic thermal loading.

Transverse and torsional complex vibration systems for ultrasonic seam welding of metal plates

Transverse and torsional complex vibration systems for ultrasonic seam welding of metal plate specimens, using a 27 kHz complex vibration disk welding tip vibrating in transverse and torsional vibration modes, were studied. Using a complex vibration welding system with a welding tip vibrating in elliptical or circular locus, thick plate specimens can be welded with a more uniform and larger area compared to a conventional ultrasonic welding system. The disk welding tip vibrates in an elliptical or circular locus. The complex vibration system can continuously weld multiple parts of metal plate specimens such as heat sinks with a large number of fins.

Ultrasonic Seam Welding System Using a Complex Vibration Circular Disk in Transverse and Torsional Vibrations

Ultrasonic seam welding of metal plate specimens using a 28 kHz complex vibration disk welding tip vibrating in transverse and torsional vibration modes is studied. Conventional ultrasonic seam welding equipment using one-dimensional vibration locus can only join metal foil or very thin plate specimens and not join thick metal plate specimens. Using a complex vibration welding system with a welding tip vibrating in elliptical or circular locus, thick plate specimens can be welded with a more uniform and larger area weldment compared to a conventional ultrasonic welding system. An ultrasonic seam welding system consists of a complex vibration disk welding tip which is driven by a longitudinal vibration system through a longitudinal-torsional vibration converter. The disk welding tip vibrates in elliptical locus. Aluminum plate specimens 0.3 mm and 3.0 mm in thickness were successfully joined with such weld strengths that the specimens were broken at the plate parts adjacent to the welded area under tensile strength test. Aluminum plates 50 mm in width were successfully joined by the ultrasonic seam welding system.

Restraint of fatigue crack propagation by wedge effect of fine particles

Restraint of fatigue crack propagation by wedge effect of some fine particles was examined on a JIS A 5083P-O Al-Mg alloy.For a fatigue test, a 5 mm thick plate specimen with a central EDM notch was used. As the fine particles to be wedged into fatigue cracks, three kinds of particles were prepared, namely, magnetic particles and two kinds of alumina particles of which the mean particle sizes were 47.3μm and 15.2μm. Before the fatigue tests, particles of each kind were suspended in an oil, and the suspension was spread on the specimen surface covering the notch part. Fatigue tests were performed by a servohydraulic type fatigue tester with a test frequency of 2 Hz and a load ratio of R=0.First a control fatigue test was done by spreading only the oil on the specimen surface, and it was proved that the wedge effect of the oil itself is negligible. The alumina particles of large size were also not effective to restrain the crack propagation, because the suspension is difficult to be made due to the large particle size and the particles cannot be sent to the crack tip properly.On the other hand, both of the magnetic particles and the alumina particles of small size had evident effects to restrain the crack propagation, especially in the case of the alumina particles the failure lives were extended by the range from 4×105 to 7×105 cycles. From some crack propagation plots, it was found that the restraint of crack propagation by the particles occurs mainly in the very early stage of crack propagation and the restraint effects become weak when the fatigue crack length exceeds approximately 3 mm.After the fatigue tests, some macro- and microfractographic analyses were performed using a CCD microscope, a SEM and an EPMA, in order to examine the mechanism of fatigue crack restraint by the wedge effects of the fine particles. From those analyses, it was reasoned that the fine alumina particles wedged into a fatigue crack are subjected to cyclic pressures from the crack surfaces, crushed up into finer particles, and then form a kind of alumina coating (in the vicinity of the notch root) which prevents the free crack closure as a wedge.

多重歯翼溝の解析的クリープ破断寿命予測

An analytical prediction method of brittle and ductile creep rupture lives was proposed for 1CrMoV steel multiple-lug rotor steeples which have a tendency of degradation in creep ductility after long-term service. Rupture time was evaluated as a sum of crack initiation life and crack growth life with consideration of creep ductility and load-carrying factors of multiple-lugs in the steady creep state.This method was experimentally verified by creep rupture tests of notched thick plate specimens and interrupted creep tests and microstructure observation of notched thick plate specimens and blade-root and rotor-steeple models at 600°C. Two kinds of 1CrMoV steel in creep ductility were tested. The main conclusions are as follows.1) An estimation method of load-carrying factors of multiple-lugs in the steady creep state was proposed and a uniforming tendency of load-carrying factors was recognized in the present models.2) An estimation method of creep stress at the lug root with consideration of the stress-dependent creep strain rate was proposed for damage analysis and its validity was verified.3) Creep rupture life of 1CrMoV rotor steeples can be evaluated in a practically reasonable accuracy as a sum of creep crack initiation life and creep crack growth life with consideration of creep ductility and load carrying factors of multiple-lugs in the steady creep state.

On the acoustic determination of the elastic moduli of anisotropic solids and acoustic conditions for the existence of symmetry planes

The 21 elastic moduli of a homogeneous anisotropic solid can be determined from the second‐order acoustical tensors associated with wave motion in six phase directions. The acoustical tensor can be calculated from the three phase speeds and displacement polarizations for a given phase direction. The six directions may be quite arbitrary as long as they cannot be contained in less than three distinct planes through the origin and do not all lie on the curves formed by the intersection of the unit sphere with an elliptical cone. It is shown, for example, how the general procedure can be used to find the elastic moduli for a thick plate specimen, for which acoustic access is limited to inspection from the two parallel faces. Acoustic conditions that are both necessary and sufficient, that a solid possess a plane of material symmetry, will also be discussed. [Work supported by NSF.]

Techniques for the Determination of Complete Polefigures Using Composite Specimens

A simple, accurate and flexible method is described for the preparation of composite samples from metal sheets. The basic technique can be adapted to conserve material or for the measurement of thick plate specimens. Any combination of the four possible quadrants of the polefigure can be determined singly or combined. In its routine application the technique is ideally suited to the measurement of three complete polefigures for the determination of orientation distribution functions. In particular, the through thickness integration, sheet area sampling and applicability to large grained materials make it suitable for the measurement of texture for comparison with bulk physical properties. Complete instructions are given for the application of the technique in practice.