Shinji Sakata

Strain Analysis in Fine Al Interconnections by X-Ray Diffraction Spectrometry Using Micro X-Ray Beam

An energy dispersive diffraction X-ray spectrometer with a sub-micron X-ray beam is developed to analyze crystalline structures in micro-regions of ULSIs. It is used to analyze strain in fine Al interconnections. The strain (e) in lines with Al single-layer structures showed a dependence on the line width (W)=e-0.8 at W below 1.5 µ m. The origin of these strains is mainly intrinsic stress in Al films and thermal stress caused by differences in the coefficients of thermal expansion between Al and Si. Introducing barrier metals reduces the dependence of strain in an Al layer on the line width.

Residual stresses in girth butt welded pipes and treatments to modify these

Abstract A number of Type 304 stainless steel pipes are used in the primary cooling systems of nuclear plants. Intergranular stress corrosion cracks (IGSCC) were found at some welded joints in these piping systems due to very high tensile residual stress, sensitization of the material due to welding, and corrosive environment, all occurring simultaneously. Investigations have shown that at least one of the above factors must be eliminated to prevent IGSCC. This report describes experimental results on the temperature variations during pipe welding by conventional techniques and by the heat sink welding (HSW) technique. The mechanism of residual stress generation due to welding is also discussed. The pipe used in these experiments was 4B Sch80 Type 304 stainless steel. It was found that the temperature distribution through the thickness of the pipes was almost uniform for the conventional welding technique, but had a very sharp gradient for HSW. In the pipe axial direction, the temperatures varied sharply for both welding techniques. This implies that the sensitization of metal due to HSW is lighter than that of conventional welding and that the residual stress on the inside surface of the heat sink welded pipe is compressive. The induction heating stress improvement (IHSI) method has been investigated analytically and experimentally. In the IHSI method, a pipe is heated with an induction coil while cold water is pumped through it. This causes a temperature gradient throughout the pipe wall which generates high thermal stresses. This, in turn, generates compressive stresses on the inner surface of the pipe. This method is designed to eliminate tensile residual stresses near the weld heat affected zone on the inner surface. Temperature analysis and subsequent thermoelastic-plastic analysis show that tensile weld residual stresses at a joint were changed into compressive stresses on the inner surface of a pipe. It was confirmed experimentally that these stresses suppressed fatigue crack propagation in the heat affected zone (HAZ) of a welded pipe. Therefore, the IHSI method is effective not only in preventing crack initiation but also in suppressing crack propagation. As for the relaxation of residual stresses, no significant relaxation was measured when external loads were applied at as much as 80% of the yield strength in the experiments.

A two-dimensional thermal oxidation simulator using visco-elastic stress analysis

A two-dimensional thermal oxidation process simulation program, OXSIM2D, has been developed, taking into account viscoelastic material properties. Novel models for oxidation, stress dependency, and the white ribbon effect are introduced. The proposed approach can be used to analyze SiO/sub x/ growth on Si surfaces and the change in stress in the total structure, including the Si substrate. Simulation results showed good agreement with experiments for both a LOCOS and a shallow trench structure.<<ETX>>

Leakage and breakage estimation based on a net-stress approach for stainless steel pipes with circumferential cracks

Abstract Coolant leakage and breakage external loads for stainless steel pipes with circumferentially part-through cracks are predicted by the mechanical properties of pipe materials. In addition, the predicted loads at leaks and breaks are compared with other net-stress approaches. The plastic limit load criterion, a traditional and convenient method, is found to give an overly conservative estimation for shallow cracks and to be nonconservative for 60–80% wall-thickness cracks.

Investigation of the Flow Field in a Multistage Pump by Using LES

Unsteady numerical calculation of an entire multistage pump was performed by using a large eddy simulation (LES) at the design flow rate to investigate the flow field in the pump in detail and to evaluate the accuracy of LES by comparing the results with an experimental and a conventional CFD result based on a Reynolds-averaged Navier-Stokes (RANS) equation. We investigated a four-stage centrifugal pump consisting of a suction bend, impellers, vaned diffusers, return channels, and a discharge volute. The interaction between the impeller and the stator was taken into account by using a moving overset grid in LES calculations, and the flow field in the inlet portion of each hydraulic part was investigated using the calculated result. In the experimental investigation, velocity distributions and pressure fluctuation were measured at several points by using a scaled model pump. RANS calculation was performed with respect to a single-stage pump composed of the first-stage component of the four-stage pump. We found that the hydraulic design of the four-stage pump is satisfactory and that LES was a very effective design tool for investigating the flow field in detail including the unsteadiness in the hydraulic passageway of the multistage pump.Copyright

Applications of a Micro X-Ray Spectrometer and a Computer Simulator for Stress Analyses in Al Interconnections

An energy-dispersive X-ray diffraction spectrometer with a 5.7 µm X-ray probe and a computer stress simulator are complementarily used with each other for strain analyses in aluminum interconnections for ULSIs. They clarify that the strains in Al layers remarkably increase in proportion to W-0.6~W-1 (W: linewidth) when their widths are narrowed to below approximately 3 µm. This phenomenon is caused by forces (thermal stresses) which act upon the side walls of Al layers.

Analysis of Ductile Fracture Behavior of Type 304 Stainless Steel

This report describes the plastic deformation behavior of notched plates of type 304 stainless steel and the ductile fracture criteria for such plates. Elastic-plastic finite element analyses were carried out to determine the relation between crack opening displacement and applied load. The results of the analyses agreed rather well with those obtained in experiments over a relatively small strain, but there were large differences were apparent between the calculated and experimental values in the large strain in which cracks initiate around notches. A simple equation was proposed to predict the load at the onset of penetration of the part-through notched plates.

Elasto-plastic analysis of pipe with internal circumferential crack in bending

Abstract An elasto-plastic analysis program using the finite element method and a J- integral post-processor are developed. Program accuracy is examined using test problems of a single-edge notched specimen and a plate with a part-through wall crack. This program solves the Battelle/NRC finite element analysis round-robin problem of elasto-plastic analysis of a pipe with an internal circumferential crack in bending. Also, through this problem, the effect of the finite element mesh on the J- integral values is investigated.

Elastic-plastic analysis of pipe with internal circumferential crack in bending.

An elastic-plastic analysis program using the finite element method and a J-integral post-processor using the virtual crack extension method are developed. The program accuracy is examined by two test problems: a plate with a hole in tension and a single -edge notched specimen in bending. This program solves the Battelle/NRC finite element analysis round-robin problem regarding an elastic-plastic analysis of a pipe with an internal circumferential crack in bending. An investigation is made into the effect of the finite element mesh on the results of the elastic-plastic analysis. It is found that a finer mesh gives greater J-integral and COD values, while the mesh does not affect the load-load point displacement curve.

The development of a high-speed structural-analysis program, SIMUS

Abstract By putting supercomputers to use, there is a possibility of solving large-scale structural problems by the finite-element method at high computing speeds. The authors have developed a high-speed structural-analysis program, SIMUS, by applying algorithms suitable for supercomputers that have vector processors. To obtain a high processing speed by using vector processors, it is necessary to make the ratio of operation time in DO-loops to total execution time larger. It is therefore necessary to enhance the vectorized ratio. SIMUS has three characteristics for high-speed processing: 1. (1) the vectorized ratio and DO-loop ratio are enhanced; 2. (2) the number of repetitions in DO-loops is enlarged; 3. (3) plural calculators are used in parallel. As a result of applying four examples of linear-elastic stress analysis using this program, a vectorized ratio of 99% and a processing speed ratio in CPU time (scalar CPU/vector CPU) of 29 times are obtained for very large-scale problems, for example, over 10 4 D.O.F.