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 Preliminary Evaluation of a Generation IV Liquid Metal Fast Reactor Due to Sloshing and Thermal Stress

The aim of this paper is a preliminary evaluation of the load bearing capability of a generation IV molten metal cooled reactor (LMFR), with reference, as an example, to the ELSY project in the event of a safe shutdown earthquake (SSE). Two relevant safety aspects were considered and analyzed by means finite element (FEM) codes: the fluid-structure interaction and the high thermal loads due to the residual heat levels of the possible high burnup fuel. The first issue depends on the presence of a liquid free surface that especially in seismic accident conditions, allows for fluid motion (“sloshing”) and may have a significant influence on the reactor structures stress levels. The second aspect deals with the irradiated core heat source thermal effects after the reactor shutdown. In order to evaluate the reactor and internal components structural response capability for both high temperature and hydrodynamic loads, appropriate 3-D models were set up. Moreover preliminary thermal analyses were carried out by means of MCNPX and Origen2.2 codes in order to determine the transient input decay power after shutdown. The obtained preliminary results allowed to individuate the structures mostly affected by the assumed loading conditions in order to make possible an upgrading of the design geometry, should any be necessary, for the considered reactor design. The mentioned activities was a part of a CE funded 6th FWP.

Opportunities for Permanent Corrosion Monitoring of Pipelines Using Guided Wave Tomography

Corrosion and erosion are two major degradation mechanisms of piping systems and pipelines that both lead to wall thickness loss. To ensure sufficient integrity levels of these assets NDE is currently conducted at time based intervals often associated with shut downs. However, both economical and social requirements are pushing the industry to higher levels of availability, reliability and safety of installations at minimum costs. Using permanent sensors that continuously monitor the wall thickness of assets over large areas allows improvement of the availability of installations at lower inspection costs. Because when inline data is continuously available the maintenance can be planned (just) in time at the most optimal moment. Therefore, the permanent sensors will save inspection costs and minimize unplanned maintenance. This can not be achieved with the current method of periodic inspections even when this is done risk based, because some corrosion processes behave unpredictable. This paper demonstrates a system which is able to monitor the wall thickness of pipe lines over large areas in an economical attractive way using a limited number of low-power ultrasonic transducers. The transducers excite specific guided wave modes with a phase velocity that strongly depends on the wall thickness. By applying tomographic inversion to the travel time of these wave modes along different paths, a wall thickness map with 100% coverage can be obtained. Experimental results on a 10″ steel pipe with a wall thickness (WT) of 8 mm show that this system is able to detect and size defects with a depth of 10% and diameter of 15 cm. The area covered in this case was the complete wall of a pipe with a length of 4 m. This paper further explains the advantages and the performance of this system. Furthermore, it will give an outlook of the possible applications.

On-Line Monitoring System for Main Steam Piping of Power Plants

An on-line life prediction system is developed for remote monitoring of material aging in a main steam piping system. The stress analysis of piping system is performed by using the finite element method. A sensor network is established in the monitoring system. The creep damage is evaluated from strain gages and a relationship is given based on a database between the damage and residual life. Web technologies are used for remote monitoring to predict the residual life for every part of the piping system. This system is useful for safety assessment procedures in thermal power plant, nuclear power plant and petrochemical industries.

Determination of the Plastic Collapse Load for Wire-Wound Pressure Vessels

This paper is focused on determining the plastic collapse load of vessels which consist of an inner cylinder prestressed by a surrounding winding. This winding consists of a wire helically wound edge-to-edge in pretension in a number of layers around the outside of the inner cylinder. As a consequence, compression stresses are introduced in the cylinder, and the fatigue life of the vessel can be greatly increased. The ASME code, Section VIII - Division 3, provides the analytical equations for the stress calculation in wire-wound vessels under linear-elastic conditions (ASME, 2007). However, to obtain the plastic collapse load of the vessel, finite element method should be used. In this way, the main aim of this paper is to present a numerical procedure for the FE simulation of wire-wound vessels. For this simulation, it must be taken into account that the wire winding is a continuous process where every new layer is coiled around all previous deformed layers. Hence, a layer-by-layer numerical procedure which takes into account this continuous process during winding has been developed. Some examples are given to demonstrate the applicability of the procedure. Once the numerical procedure was validated, it was used to obtain (i) the maximum circumferential stress after winding, (ii) the initial plastic load, and (iii) the plastic collapse load. To obtain the plastic collapse load, an elastic perfectly-plastic material behaviour has been considered. Finally, the numerical results obtained for the plastic collapse load were obtained as a function of several ratios over a wide range, which take into account the cylinder thickness, the wire-wound thickness, the wire-wound pretension and the yield limit of the material.