Coupled EFGM and F2LFEM for Fracture Analysis of Cracks

This paper presents a coupling technique for integrating the element–free Galerkin method (EFGM) with fractal two-level finite element method (F2LFEM) for analyzing homogeneous, isotropic, and two dimensional linear–elastic cracked structures subjected to mixed–mode (modes I and II) loading conditions. F2LFEM is adopted for discretization of domain close to the crack tip and EFGM is adopted in the rest of the domain. In the transition region interface elements are employed. The shape functions within interface elements which comprises both the element–free Galerkin and the finite element shape functions, satisfies the consistency condition thus ensuring convergence of the proposed method. The proposed method combines the best features of EFGM and F2LFEM, in the sense that no structured mesh or special enriched basis functions are necessary and no post–processing (employing any path independent integrals) is needed to determine fracture parameters such as stress–intensity factors (SIFs) and T–stress. The numerical results show that SIFs and T–stress obtained using the proposed method are in excellent agreement with the reference solutions for the structural and crack geometries considered in this study. Also a parametric study is carried out to examine the effects of the similarity ratio, and the number of transformation terms on the quality of the numerical solutions.

A Study of Developing Composite Material of Penetrated Diamond Particles Into Metal Plate

An explosive welding technique which uses underwater shock wave to weld thin aluminum plate has been studied and the technical advantages were reported. In this research, we propose a method to produce a composite material using an underwater shock wave generated by detonation of explosive. In the production process, a metal plate (flyer plate) accelerates to a high speed by the underwater shock wave, and collided with diamond particles and penetrated the metal plate. Diamonds were used as the particles and aluminum plates (A1050) as the flyer plates. Diamond has high hardness and excellent thermal conductivity, therefore diamond should provide improvement in the thermal conductivity of the composite material. From recovered sample, the multilayer joined surface including diamond particles was observed using an optical microscope. The production of the pipe of composite materials was attempted using this technique as the application. Details of the experimental methods and results are reported in this paper.

General Rule of Method for Measurement of Thickness and Crack Size by Electric Potential Drop Technique: Outline of the NDIS3426:2008

The Japanese Society for Non-Destructive Inspection (JSNDI) published general rule of method for measurement of thickness and crack size by Electric Potential Drop Technique as the Standard of JSNDI (NDIS3426) in January, 2008. NDIS3426 was established based on the researches for many years including the round robin tests conducted as the academic activities in JSNDI, and the previous technical guideline and standard ASTM E-647-05 ANNEX A6 and BS ISO 12108:2002 established for the measurement of fatigue crack growth in specimens. In this paper, the outline and the background of NDIS3426 was described. The electric potential drop technique is one of the promising methods to monitor or measure the thickness and crack size for the practical use in many industries. For the inspection of the surface deep fatigue crack in the steam turbine casing, the advanced crack depth indicator based on the potential drop technique has been applied. For the monitoring the creep damage accumulated in the seam-welded power piping, the commercialized tool based on the pulsed direct current potential drop technique has been used. For the pipe wall thinning measurement in the operating thermal power plant, the pulsed direct current potential drop technique was applied. This paper shows the present condition of the practical use and the future prospect of the potential drop technique.

Non-Linear Contact Analysis of an API Line Pipe Coupling

In this study, the finite element model of an API Line Pipe threaded pipe connection is presented. The non-linearities in material properties and contact behaviour are discussed. A series of modifications of the standard connection are simulated to gain a better understanding in the influence of geometrical and material parameters on the connection’s performance. Finally, test results obtained from a four-point bending fatigue experiment are presented and compared with numerical simulations.

Development of Alternate Methods for Establishing Design Margins for ASME Section VIII Division 3: Part 2

The design margin against collapse for Division 3 is based on Nadal’s equation. For high strength material this method is adequate. However for material with a lower ratio of Sy/Su this method has additional margin from yielding through the thickness to final collapse or burst. The experimental burst test results for closed-end cylinder show the excessive margin for these materials as stated in former paper. Therefore the development of alternate methods for establishing design margin for all materials is desirable. The design margin of 1.5 in equation for open-end cylindrical shell and spherical shell in current code is different from that of 1.732 for closed-end cylindrical shell. The design margin of elastic-plastic analysis is 1.732. Therefore the consistent design margins of equations and elastic-plastic analysis for open-end cylindrical shells and spherical shells are also desirable. In this paper new equations for design pressure of cylindrical shell and spherical shell are proposed by investigation of burst test results and case studies of various methods.

Non Destructive Examination of Helium Implanted Fe-Cr Model Alloys

The helium implantation has been successfully used for the obtaining of radiation damage in different Fe-Cr ferritic/martensitic steels. Implanted doses within the range 6.24×1017 – 3.12×1018 cm−2 corresponding to local damage up to 90 DPA (Displacement per Atom) were acquired in a thin (<1 μm) region. For observing the dependence of vacancy-type defects on the load and the chromium content, positron annihilation lifetime spectroscopy (PALS) has been used. Experiments showed that chromium had a significant effect on the radiation treated microstructures of the materials. In particular, chromium influences the size and density of the implantation induced defects and specific Cr content should prevent the formation of vacancy clusters.

A Study on Safer Operation of Impulsively Loaded Vessels

ASME published Code Case 2564 [1] in January 2008 on impulsively loaded vessels, which is the first design guidance of this kind worldwide. The authors participated in the Task Group of Sec. VIII, Div. 3 [2] and were also intimately engaged in development, design and operation of detonation chambers DAVINCH®. DAVINCH® is an acronym for Detonation of Ammunition in Vacuum INtegrated CHamber, utilized for destruction of old non-stockpile chemical weapons, which were recovered from underground and sea in several areas of Japan, China, and Belgium. The quantity destroyed to-date has reached as high as 4,500 items. Figure 1, and 2 show the installations of DV65 at Port Kanda, Japan and DV50 at Poelkapelle, Belgium, with maximum capacity of 65kg and 50 kg TNT-equivalent respectively.

Effect of Softening on Tensile Strength Limit in Girth-Welded Pipe Joints

This paper discusses the ultimate tensile strength of girth-welded pipe joints with one or more soft interlayers, as determined by theoretical approaches and FE analysis. In FE analysis, the soft interlayer is assigned to be either the weld metal or heat-affected zone (HAZ). Based on the results of the FE analysis, an evaluation formula is proposed for the ultimate tensile strength of a welded joint including the soft interlayer.

Modelling of Prestrain Effects on Fracture Using Local Approach Methods

The effects of load history on component fracture behaviour have been studied at length in terms of the generation and resulting influence of residual stresses. Despite this, the effect of plastic strain history, separate from the generation of residual stresses, is still not clearly defined. This work presents an investigation into the effect of accumulated strain on subsequent fracture behaviour. The effects of load history on low temperature cleavage fracture are modelled by means of a number of local approach methods, accounting for variations in stress and strain throughout the component’s load history. Prior strain was found to reduce the mean fracture load of 20mm thick CT specimens, irrespective of the level of room temperature strain applied. Local approach methods, calibrated to low and high constraint fracture data, were able to correctly predict a reduction in fracture load, although the exact magnitude of the reduced loads were not always correctly resolved. Further experimental data and further work on model formulation is needed to confirm the conclusions drawn here.

Ductile Failure Simulation of Tensile Plates With Multiple Through-Wall Cracks

This paper proposes a simple numerical method to simulate plastic behaviours of tensile plates with twin through-wall cracks. The method is based on finite element analysis with a simple damage theory. To validate the proposed method, simulated results are compared with experimental data performed by Japanese researchers. Despite its simplicity, the proposed method well predicts plastic behaviours of tensile plates with twin cracks, including crack coalescence. Predicted maximum loads are overall lower than experimentally-measured ones.