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FE Issues Related To Creep And Viscoelasticity

A summary report of the FENet Durability and Life Extension (DLE) workshop in Majorca, Spain, 25th - 26th March 2004.

Prof Adib BeckerBy Prof. Adib Becker, University of Nottingham, UK

Introduction

Under the FENET technology theme of Durability and Life Extension (DLE), 6 workshops have been launched to date:

  • First DLE Workshop: “Industrial Views on Durability and Life Extension Issues” (13 November 2001, Wiesbaden, Germany)
  • Second DLE Workshop: “Finite Element Simulation of Contact Problems” (27-28 February 2002, Copenhagen, Denmark)
  • Third DLE Workshop: “FE issues related to Structural Integrity-Fracture, Fatigue, and Creep” (13-14 June 2002, Zurich, Switzerland)
  • Fourth DLE Workshop: “Finite element simulation of fracture and crack growth” (11-12 September 2002, Trieste, Italy)
  • Fifth DLE Workshop: “Finite Element Simulation of Welds and Joints” (27-28 February 2003, Barcelona, Spain)
  • Sixth FENET-DLE Workshop: “Modelling Fatigue of Metals” (9-10 October 2003, Noordwijk, The Netherlands)

Discussions in previous DLE workshops have identified the analysis of creep and viscoelasticity as an important issue across many industry sectors, and have highlighted several difficulties in modelling the reallife behaviour of components operating under elevated temperatures. This DLE workshop aimed to provide a forum for discussion of the issues relevant to the FE analysis of creep and viscoelasticity.

 

Workshop Objectives

The main objectives of this workshop were:

  • To provide an overview of the current state of FE technology in applications related to creep, viscoelasticity and high temperature applications
  • To identify current limitations and difficulties in modelling real-life creep behaviour
  • To provide a forum for discussion of “Guidelines” and “Best Practice” on using FE in creep and high temperature applications
  • To present current techniques for modelling creep damage, crack growth and creep life estimation

 

List of Presentations

A total of 5 technical presentations were delivered in this workshop. Presenters represented university research groups, industry and FE software vendors.

The following is a list of the technical presentations:

FENET-DLE Workshops - Introduction and Objectives
Prof. Adib Becker, University of Nottingham, UK

Development of a New Material Model for Polymer- Bonded Materials – An Overview
Dr G.S. Kalsi, AWE, Aldermaston, UK

Modelling Creep of Lead in Water Pipe Joints
Malcolm Toft, Advanced Engineering Solutions Ltd, UK

Creep Simulations with ABAQUS: Super Plastic Forming
Jose L. San-Vicente, PRINCIPIA, Spain

FE Analysis of Creep of welds - Challenges and Difficulties
Prof. Adib Becker, University of Nottingham, UK

 

Analysis of Workshop

The workshop was chaired by Professor Adib Becker (University of Nottingham, UK). The main topics covered in this workshop included the following:

  • Modelling viscoelastic polymer- bonded materials
  • Creep stress relaxation and healing effects
  • Creep of lead pipes at low temperatures
  • Modelling creep associated with superplastic forming of aerospace components
  • Robustness of FE software in modelling high temperature manufacturing processes
  • Difficulties in generating creep material properties
  • FE modelling
  • Incorporating creep continuum damage in FE software
  • Benchmarks for creep damage modelling
  • Creep-fatigue interaction

Discussions were invited after each presentation, with a final open discussion session held after the last presentation. The workshop raised many issues related to creep of metals and polymers and stimulated a number of discussions on the current state and limitations of commercial FE software.

 

Concluding Remarks

  • Reliable creep material properties are not easy to obtain
  • The creep material properties of narrow Heat-Affected Zones in welds are particularly difficult to obtain in laboratory tests.
  • Effects of ageing/degradation of the material are difficult to measure
  • To predict creep failure, it is important to understand the creep failure mechanisms of the material
  • User-subroutines are often needed to model creep material laws
  • Creep constants are often very small, e.g. of the order 10-40
  • Creep continuum damage is not easily incorporated in commercial FE codes
  • FE benchmarks for creep continuum damage mechanics are useful in assessing the accuracy of FE software.