Interaction between weld residual stresses and warm pre-stressing

Background

The “Warm Pre-stressing” (WPS) effect is the seen increase of the apparent brittle fracture toughness for a component pre-loaded at a temperature corresponding to the dutcile upper shelf region and then cooled to the brittle lower shelf region of the material fracture toughness transition curve.

The WPS effect can be attributed to three main mechanisms. These mechanisms have different impact, depending on the load path and pre-load level. All the mechanisms are related to plastic straining at pre-load. The engineering method used today do not consider constraint and do not consider all the mechanics behind WPS.

Furthermore, the interactions between a prior residual stress field and the WPS effect is something that has not been widely studied. It is important to study the interaction between a prior residual stress field and the WPS effect since defects are mainly found in welds where weld residual stresses are present.

The proposed master thesis will be a numerical pre-study to an experimental program that aims to investigate the interaction between residual stresses and the WPS effect. In the numerical work the interaction between a prior residual stress field and the compressive residual stresses that are due to the WPS effect will be studied.

Goal

The goal with the master thesis is to answer the question: Can we expect a WPS effect for a cracked component with a prior tensile residual stress field if we only consider the compressive residual stresses as the main mechanism behind the WPS effect.

Assignment description

The interaction between a prior residual stress field and the compressive residual stresses that are due to the WPS effect will be studied. This is done by a study of the near tip stress field using FE-analyses.

Education level: Masters degree
Estimated time: 20 weeks
Start date: According to agreement however not before spring 2019
Location:  Stockholm
Contact person: Tobias Bolinder, tobias.bolinder@kiwa.com 
Application: is sent to tobias.bolinder@kiwa.com with attached grades and CV.