Stable crack propagation in steel at 1173 K: Experimental investigation and simulation using 3D cohesive elements in large-displacements

N Tardif,A Combescure,M Coret,P Matheron

doi:10.1016/j.engfracmech.2009.12.015

N Tardif, A Combescure + Show 2 more

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This paper deals with the numerical simulation of a stable crack propagation experiment at 1173 K in a 16MND5 steel. At this temperature, the material is viscoplastic. A cohesive zone model is formulated in order to simulate the rupture of a CT specimen. A large displacement 3D cohesive element with eight nodes is implemented in the finite element code ABAQUS. The associated traction–separation law is of Tvergaard and Hutchinson type, in which an hardening slope has been added. This hardening simulates the material strengthening associated to the increasing strain rate in front of the crack tip when crack tip starts to propagate. We show that in this case the form of the cohesive law has great impact on the simulated propagation velocity.

Highlights

In the event of a serious accident on a pressurized water reactor (PWR) involving fusion of the fuel core and internal structural elements, the bottom head is subjected to significant thermal and mechanical solicitations
The crack is modeled using cohesive elements. The specificity of such an analysis lies in the viscoplastic nature of the material and the large strains induced by the temperature of the test
These specificities are taken into account in the cohesive elements at different stages

Summary

Introduction

In the event of a serious accident on a pressurized water reactor (PWR) involving fusion of the fuel core and internal structural elements, the bottom head is subjected to significant thermal and mechanical solicitations. The crack’s initiation and propagation are modeled using cohesive surface elements under large-displacement and large-strain assumptions. Chen et al [27], showed in an analysis of the tearing of CT specimens that a plane strain simulation is unable to reproduce the triaxiality state at the crack’s tip which can be obtained near the middle section of the 3D model using an identical traction–separation law.

The material and test setup

Principle of virtual work under large-displacements

F Á DuÃds

The traction–separation law

Mesh and boundary conditions

The calculation procedure

The constitutive relation of the bulk

Constitutive law of the interface

Comparison with the test results

Dependence of the traction–separation law on the triaxiality rate

Dependence on the form of the traction–separation law

Influence on the global behavior of the specimen