Hisashi Serizawa

IFMIF: overview of the validation activities

The Engineering Validation and Engineering Design Activities (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF), an international collaboration under the Broader Approach Agreement between Japan Government and EURATOM, aims at allowing a rapid construction phase of IFMIF in due time with an understanding of the cost involved. The three main facilities of IFMIF (1) the Accelerator Facility, (2) the Target Facility and (3) the Test Facility are the subject of validation activities that include the construction of either full scale prototypes or smartly devised scaled down facilities that will allow a straightforward extrapolation to IFMIF needs. By July 2013, the engineering design activities of IFMIF matured with the delivery of an Intermediate IFMIF Engineering Design Report (IIEDR) supported by experimental results. The installation of a Linac of 1.125 MW (125 mA and 9 MeV) of deuterons started in March 2013 in Rokkasho (Japan). The worlds largest liquid Li test loop is running in Oarai (Japan) with an ambitious experimental programme for the years ahead. A full scale high flux test module that will house ~1000 small specimens developed jointly in Europe and Japan for the Fusion programme has been constructed by KIT (Karlsruhe) together with its He gas cooling loop. A full scale medium flux test module to carry out on-line creep measurement has been validated by CRPP (Villigen).

Actual application of FEM to analysis of large scale mechanical problems in welding

Abstract The finite element method is a powerful tool for predicting welding distortion. However, the mechanical phenomena are strongly non-linear and transient and thus, thermo–elastic–plastic finite element analyses of the phenomena require very long computational time. To overcome this problem, an interactive substructure method was developed as an approach to reduce the computational time in three-dimensional analyses. In this paper, in order to confirm calculation efficiency for a large scale problem, a pipe model with 538 200 degrees of freedom was computed. Furthermore, the residual distortion in an engine component was computed and the applicability of the calculation for problems in welding practices was demonstrated.

Temperature dependence of internal friction and elastic modulus of SiC/SiC composites

Although SiC/SiC composites are expected to be used as advanced composite materials due to their superiorities in strength-to-weight and stiffness-to-weight ratios, there have been few reports on the internal friction of SiC-based composite materials. In this study, PIP, HP and CVI methods were employed as fabrication processes of SiC-based composites. In the case of the composite produced by the CVI process, by controlling the conditions of manufacturing and thermal annealing, a stable peak of internal friction due to the grain boundary relaxation was obtained at about 1200 K. It was found that this peak was affected not by the property of the fiber but the microstructure of the matrix and the temperature of the peak moved to the lower side after heat treatment at 1773 K. Also, it is expected that SiC/SiC composites may have a greater high-damping property by crystallizing the matrix.

Welding distortion investigation in fillet welded joint and structure based on iterative substructure method

Abstract In this paper, prediction and controlling angular distortion in fillet welded joint and structure were investigated. First, two methods to reduce angular distortion in fillet welded joint were investigated by experimental and numerical analysis. One was to apply a constant external force in-process and the other was rigid clamping. In numerical analysis, a new in-house finite element code has been developed based on the idea of iterative substructure method (ISM) to calculate welding distortion in rational time. During experimental analysis, the constant external force was designed and applied in-process to reduce angular distortion of fillet welded joint. The results showed that the distortion can be efficiently predicted by ISM, which were in good agreement with the experimental ones. Applying constant external force in process was a more effective method to reduce distortion than using rigid clamping. In addition, with a constant load distance from weld bead, the locations of the applied constant external force and rigid clamping along the longitudinal direction (welding direction) have little influence on the magnitude of welding angular distortion. Finally, the angular distortion of a large fillet welded structure was predicted with ISM and also controlled with applying a constant external force based on the simulation results of the fillet welded joint.

Parametric studies of welding distortion in fillet welded structure based on FEA using iterative substructure method

Abstract Using an in house finite element (FE) code developed based on the idea of iterative substructure method (ISM), this paper presents a numerical study to evaluate the effects of welding sequence, fixture condition and prestrain on the residual welding distortion in a fillet welded structure. The results show that welding sequence has appreciable influence on residual distortion, appropriate fixture can greatly reduce angular distortion in the workpiece and application of prestrain can significantly reduce the residual distortion. Taking advantage of the high efficiency of ISM, the optimum scheme of prestrain has been numerically predicted within practical time based on a systematic investigation.

Computational analysis of creep fracture deformation in SiC/SiC composites

Creep fracture deformation in SiC/SiC composites was analyzed using a new computer simulation method with time-dependent interface elements. The simulation method was used to describe the crack growth deformation in SiC/SiC composite under four-point bending of single-edge-notched beam bend-bars. Two methods were used to simulate the crack growth due to fiber creep. In one method, the creep property was introduced into the interface elements by the general method of FEM analysis. In the second method, a new technique making the best use of the potential function was used. The stage-II steady-state creep deformation was simulated by both methods, and the stage-III crack growth and the transition from stage-II to stage-III could be simulated by only the new method. Additionally, the stage-I was simulated by the new method. The new method has the potential to completely simulate creep fracture deformation in SiC/SiC composite due to fiber creep.

Numerical analysis of deformation in multi-pass circumferential TIG welding with narrow gap

As one of the practical issues for narrow gap tungsten inert gas welding, the mechanism of gap width shrinkage in multi-pass circumferential butt welding of thick-walled pipes was examined experimentally and numerically. The experimental result using 600-mm outer diameter pipes with 200-mm wall thickness revealed that the shrinkage of gap at the beginning of the welding process of 174 pass welding for 73 layers would be independent of the groove shape. Also, from the results of the thermal elastic–plastic finite element analyses, it was found that a 2D axisymmetric model was inadequate in predicting the initial shrinkage of gap width. Moreover, the computational results indicate that the shrinkage of gap width could be estimated quantitatively using a 3D model of whole pipe and defining the appropriate heat input area, while the results of the 3D partial model of pipe with small degree was insufficient to predict the initial shrinkage precisely.

NUMERICAL PREDICTION OF WELDING HOT CRACKING USING THREE-DIMENSIONAL FEM WITH TEMPERATURE DEPENDENT INTERFACE ELEMENT

The Finite Element Method (FEM) is a powerful tool to predict welding residual stresses and distortions. However, it is impossible to analyse the hot cracking with a simple thermal-elastic-plastic FEM code, since the conventional FEM models only volumetric behaviour. Based on the interface element proposed for the cracking propagation problem, a three-dimensional FEM with a temperature dependent interface element has been developed. The proposed method is applied to the analysis of the pear-shaped bead cracking under narrow gap welding as one example of hot cracking in welding. Both the pear-shaped bead cracking and the surface cracking along the welding line can be simulated using the proposed method. Also, it is found that the heat input, the groove width, and the constraint under the solidification are the essential causes of the pear-shaped bead cracking.

Evaluation of Fracture Behavior of Ceramic Composite Joints by Using a New Interface Potential

In order to examine mode-I & II type fracture behavior of ceramic joints, the interface element was proposed as a simple model which represents the mechanism of failure in an explicit manner. It was applied to the analyses of four point bending test and asymmetrical four point bending test for SiC/SiC composite specimen joined by ARCJoinTTM. By using a new type interface potential, which is a coupled function of opening and shear deformations, both the bending and asymmetrical bending tests were simulated. From comparison with experiments, surface energy at the interface between the joint and composite was estimated to be about 30 N/m regardless of the fracture mode. Also, from the comparison between the predicted strength and the experiments for the tensile test of lap joint of SiC/SiC composites, it was found that the proposed method was considered to have a great potential as a tool to study the failure problems whose fracture type was a mixture of mode-I & II.

Fast Computational Residual Stress Analysis for Welded Pipe Joint Based on Iterative Substructure Method

An efficient and reliable method for welding residual stress analysis is reported in this paper. The analysis method to calculate the residual stress using the iterative substructure method was developed and compared with a conventional one using a commercial finite element analysis code; comparisons were made for the analysis accuracy and the computational speed of the residual stress in a welded pipe joint. The residual stress distributions obtained by the both methods agreed well with each other. Moreover, it was clarified that the developed method could calculate the residual stress in a shorter computing time and could calculate the residual stress distribution much faster with nearly the same accuracy as the conventional method when the size of the welding structure was large.Copyright