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Journal ArticleDOI

Development of non-iterative self correcting solution (nonss) method for the viscoplastic analysis with the chaboche model

30 Oct 1998-International Journal for Numerical Methods in Engineering (Wiley)-Vol. 43, Iss: 4, pp 621-654

AboutThis article is published in International Journal for Numerical Methods in Engineering.The article was published on 1998-10-30. It has received 7 citation(s) till now. The article focuses on the topic(s): Tangent stiffness matrix & Viscoplasticity.

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Citations
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Journal ArticleDOI
Abstract: In a postulated severe core damage accident in a PHWR, multiple failures of core cooling systems may lead to the collapse of pressure tubes and calandria tubes, which may ultimately relocate inside the calandria vessel forming a terminal debris bed. The debris bed, which may reach high temperatures due to the decay heat, is cooled by the moderator in the calandria. With time, the moderator is evaporated and after some time, a hot dry debris bed is formed. The debris bed transfers heat to the calandria vault water which acts as the ultimate heat sink. However, the questions remain: how long would the vault water be an ultimate heat sink, and what would be the failure mode of the calandria vessel if the heat sink capability of the reactor vault water is lost? In the present study, a numerical analysis is performed to evaluate the thermal loads and the stresses in the calandria vessel following the above accident scenario. The heat transfer from the molten corium pool to the surrounding is assumed to be by a combination of radiation, conduction, and convection from the calandria vessel wall to the vault water. From the temperature distribution in the vessel wall, the transient thermal loads have been evaluated. The strain rate and the vessel failure have been evaluated for the above scenario.

13 citations

Journal ArticleDOI
Abstract: The so called ‘in-vessel retention (IVR)’ is regarded as a severe accident (SA) mitigation strategy, which is widely used in most of advanced nuclear power plants. The effectiveness of IVR strategy is to employ the external water flooding to cool the reactor pressure vessel (RPV). The RPV integrity has to be maintained within a required period during the IVR period. The degraded melting core is assumed to be arrested in the lower head (LH) to form the melting pool that is bounded by upper, side and lower crusts. Consequently, the existence of the crust layer greatly affects the RPV structural behavior as well as failure process. In order to disclose this influence caused by the crust layer, a detailed investigation is conducted by using numerical simulation on the two RPVs with and without crust layer respectively. Taking the RPV without crust layer as a basis for the comparison, the present study assesses the likelihood and potential failure location, time and mode of the LH under the loadings of the critical heat flux (CHF) and slight internal pressure. Due to the high temperature melt on the inside and nucleate boiling on the outside, the RPV integrity is found to be compromised by melt-through, creep, elasticity, plasticity as well as thermal expansion. Through in-depth investigation, it is found that the creep and plasticity are of vital importance to the final structural failure, and the introduction of crust layer results in a significant change on field parameters in terms of temperature, deformation, stress(strain), triaxiality factor and total damage.

6 citations

Book ChapterDOI
01 Jan 2010
Abstract: This chapter gives an overview of life management issues of sodium cooled fast neutron spectrum reactors (SFRs). The topics covered in this chapter include robust design and validation, design by analysis philosophy, materials selection, manufacturing processes, state-of-the-art operation and maintenance strategies, meticulous in-service inspection, materials behaviour and ageing management, human resources and knowledge and asset management. The present state-of-the-art of PLiM practices for SFRs is reviewed and future trends in life assessment procedures and R&D required for further enhancing the safety and reliability of SFRs are highlighted.

4 citations

Journal ArticleDOI
Abstract: Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects The complexity and interaction of such factors must be considered in suitable way in the mechanical behavior modeling using the appropriate material behavior laws The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with these critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model That is the aim of this paper with application to a tin based solder token as the test material

3 citations

Proceedings ArticleDOI
26 Apr 2010
Abstract: Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behaviour modelling using the appropriate material behaviour laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with this critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material.

2 citations


Cites background from "Development of non-iterative self c..."

  • ...[5] Chaboche [6] are "painfully" implemented in the FE codes by suitable integration algorithms....

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References
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Journal ArticleDOI
Abstract: A one step forward gradient time integration scheme is developed which leads to a tangent stiffness type method for rate dependent solids. Within the context of small strain theory numerical examples are presented showing application of the method to material behaviors ranging from elasticnonlinearly viscous to nearly rate independent. The adaptability of this rate dependent tangent modulus method to complex constitutive relations and to finite deformation analyses is also illustrated.

632 citations

Journal ArticleDOI
Abstract: Robinson's viscoplastic model, a representative of the so-called overstress models, is integrated by use of the generalized midpoint rule. The solution of the non-linear system of algebraic equations arising from time discretization of the constitutive equations is determined using a projection method in combination with Newton's method. Consistent tangent moduli are calculated and the quadratic convergence of the global Newton equilibrium iteration is shown. The time increment size is controlled by the convergence behaviour of the equilibrium iteration and the accuracy of the numerical integration. Various numerical examples are considered to demonstrate the efficiency of the methods.

36 citations

Journal ArticleDOI
Abstract: A unified numerical method to integrate stiff time-dependent constitutive equations has been developed. This method is a stable, non-iterative and self-correcting solution procedure which works successfully over a wide range in strain rate sensitivity. Time steps are automatically controlled during integration to achieve a user-specified accuracy. This method is implemented in the program package NONSS whose dual purpose is examination of the behaviour of unified constitutive models by themselves (‘one-element behaviour’) as well as providing a computationally efficient subroutine for utilizing such models with existing finite element programs for non-linear structural and metal forming analyses. This paper first reviews the relation between the numerical characteristic of constitutive equations and the choice of integration methods. Then the paper presents the derivation of the governing basic equations in the new method, and also derives a special algorithm which permits large integration steps within the negative strain rate sensitivity (‘serrated yielding’) regime. Examples of the program's performance are given, including plasticity at high and low temperatures, cyclic deformation and multiaxial straining.

26 citations

Journal ArticleDOI
Abstract: A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

20 citations