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EURAXESS

MSCA-COFUND-CLEAR-Doc-PhD Position #CD22-20 Increase in service life by finishing welded joints: application to metal structures in service

13/10/2022

Job Information

Organisation/Company
Université Gustave Eiffel
Department
MAST-SMC
Research Field
Engineering
Engineering » Civil engineering
Researcher Profile
First Stage Researcher (R1)
Country
France
Application Deadline
Type of Contract
Temporary
Job Status
Full-time
Hours Per Week
35
Is the job funded through the EU Research Framework Programme?
H2020 / Marie Skłodowska-Curie Actions COFUND
Marie Curie Grant Agreement Number
101034248
Is the Job related to staff position within a Research Infrastructure?
No

Offer Description

The thesis is particularly interested in the durability of metal structures assembled by welding that have undergone or not finishing operations. These structures can be onshore (metal bridges, wind turbines, etc.) or offshore (platforms, wind turbines, ships, etc.).

Previous work on the study of fatigue in welded high yield strength steel (HYS) assemblies in offshore structures has led to the development of experimental methods to study the influence of certain finishing processes (typically stress blasting) on the fatigue life of welded joints. The results available in the literature show, for a load ratio R=0.1, that the cracking kinetics are influenced by the residual stress field resulting from the welding operation. Interpretation of the results was made possible after existing residual stress measurements in the welded joint.

An improved welding procedure has been proposed for corner welds in HYS welded assemblies. This procedure, which provides practically, geometric and metallurgical advantages, minimises global and local stress concentrations and reduces residual stress due to the welding operation, in the vicinity of the weld bead foot. The endurance tests on welded joints showed a very good resistance to fatigue, especially in the field of large numbers of cycles, attributed to a significant gain in crack initiation time.

Prestressing shot peening has been studied as a ""global"" finishing treatment to improve the fatigue life of welded joints. The choice of technological parameters (ALMEN intensity, shot size...) is based on a preliminary study of the stresses introduced by different shot peening parameters: stress intensity and depth affected. In addition, a small enough shot size must be provided to treat all drawstring foot defects. The fatigue results showed a significant improvement in the fatigue performance of shot welded joints, particularly in the area of long service lives.

This experimental work, although very interesting, is limited to welding and initial finishing of HYS steels and this for a single loading ratio.

This thesis is intended to complement this work and extend it to conventional steels for all types of loading by the use of numerical tools capable of simulating and predicting on the one hand the thermomechanical behaviour from the welding phase to the cooling (source of generation of residual stresses) and on the other hand the blasting processes.

This thesis project thus consists in quantifying the beneficial effect of two methods of post-treatment of the weld and building a base of exploitable results during a dimensioning / calculation/ verification of fatigue. He is interested in both new structures (i.e. before commissioning), welded and finished, as well as structures already in service and undergoing fatigue ageing.

To meet this general objective, numerical and experimental work will be carried out. The definition of the welding and finishing procedure will be carried out based on the recommendations of the international welding institute, the know-how developed at the SMC laboratory and the feedback of our industrial partner SONATS Europe Technologies (for US hammering).

To meet these objectives, several scientific questions must be answered:

 Construction of a multiphysical FEM welding model. The law of multiphase behavior will be introduced into the model either through a subroutine or through a UMT.

 Integration of behavioural laws adapted for each method of completion. In the case of hammering, the chosen laws of behaviour must be able to follow the mechanical state of the structure under repeated impacts. The choice of the type of work hardening of the material (kinematic and/or isotropic) is thus a key step for the modelling of hammering. In the case of TIG remelting, the proposed multi-phase behaviour law for welding will be reused.

 Evaluation of residual stresses present in the volume before completion. Experimentally, an X-ray diffraction (DRX) analysis will be conducted on our test pieces to describe their residual stress state and validate the proposed numerical models.

 Quantitative evaluation of the beneficial effect of completion methods, as well as an understanding of the relationship between the effects of completion (Stress Introduction/Geometry Modification) and post-treatment life.

To begin this thesis, a bibliographical review must be conducted in order to assimilate all the basic notions that will be developed throughout our study. It is necessary to have a good knowledge of the finishing methods studied, of the fatigue aspects of a welded assembly and of the main conclusions of the literature studies on the improvement of the fatigue performance of welded assemblies. Then, the project will be organized according to the sub objectives to be achieved over the three years of the thesis according to a schedule

 Characterization of the mechanical state of a T-welded structure: integration of a thermomechanical and metallurgical law behaviour taking into account all the mechanisms at the origin of residual welding stresses, in the case of S355 steel;

 Choice of the completion method and translation of the process parameters into input data for the simulations;

 Construction and validation of the numerical model proposed. It will be capable to predict the residual stresses of a completed welded structure;

 Experimental and numerical evaluation of the fatigue life of completed assemblies before and after surface treatment: monitoring of stress relaxation/stabilization mechanisms;

 Recommendations for the implementation of completion on new and existing structures.

The thesis will take place at the SMC-Lab at the Gustave Eiffel University in France. This laboratory has strong skills on the subject, with an experienced coaching team and experimental means adapted to the theme of the thesis subject (instrumentation, mechanical test equipment, welding and finishing skills, modelling equipment). This project will thus enable the doctoral student to acquire knowledge in the field of structures and structures essential to the energy transition, to contribute to the sobriety of resources by aiming to increase the life of structures. The candidate will develop numerical skills and conduct laboratory tests.

Requirements

Research Field
Engineering
Education Level
Bachelor Degree or equivalent
Skills/Qualifications
  • At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree.
  • At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate.
Languages
FRENCH
Level
Basic
Languages
ENGLISH
Level
Good

Additional Information

Benefits
  • High-quality doctoral training rewarded by a PhD degree, delivered by Université Gustave Eiffel
  • Access to cutting-edge infrastructures for research & innovation
  • Appointment for a period of 36 months based on a salary of 2 700 € (gross salary per month)
  • Job contract under the French labour legislation in force, respecting health and safety, and social security: 35 hours per week contract, 25 days of annual leave per year
  • International mobility will be mandatory
  • An international environment supported by the adherence to the European Charter & Code
  • Access to dedicated CLEAR-Doc trainings with a strong interdisciplinary focus, together with a Career development Plan

 

Eligibility criteria

Applicants must fulfil the following eligibility criteria :

  • At the time of the deadline, applicants must be in possession or finalizing their Master’s degree or equivalent/postgraduate degree
  • At the time of recruitment, applicants must be in possession of their Master’s degree or equivalent/postgraduate degree which would formally entitle to embark on a doctorate
  • At the time of the deadline, applicants must be in the first four years (full-time equivalent research experience) of their research career (career breaks excluded) and not yet been awarded a doctoral degree. Career breaks refer to periods of time where the candidate was not active in research, regardless of his/her employment status (sick leave, maternity leave etc). Short stays such as holidays and/or compulsory national service are not taken into account
  • At the time of the deadline, applicants must fulfil the transnational mobility rule: incoming applicants must not have resided or carried out their main activity (work, studies, etc.) in France for more than 12 months in the 3 previous years
  • One application per call per year is allowed
  • Applicants must be available full-time to start the programme on schedule (November 1st 2023)
  • Application rules are enforced by the French doctoral system which specifies a standard duration of 3 years for a full-time PhD together with the MSCA standards and the OTM-R European rules as follows
  • Citizens of any nationality may apply to the programme
  • There is no age limit
Selection process
Additional comments
  • The first step before applying is contacting the PhD supervisor. You will not be able to apply without an acceptation letter from the PhD supervisor.
  • International mobility : please contact your PhD supervisor for any detail regarding the international mobility.
  • Please contact the PhD supervisor for any additional detail on job offer
  • There are no restrictions concerning the age, gender or nationality of the candidates Applicants with career breaks or variations in the chronological sequence of their career, with mobility experience or with interdisciplinary background or private sector experience are welcome to apply
  • Support service is available during every step of the application process by email: clear-doc@univ-eiffel.fr
Website for additional job details

Work Location(s)

Number of offers available
1
Company/Institute
Université Gustave Eiffel
Country
France
City
Bouguenais
Postal Code
44340
Street
Allée des Ponts et Chaussées
Geofield

Contact

City
Marne-La-Vallée
Website
Street
5, Boulevard Descartes
Postal Code
77454
E-Mail
lamine.dieng@univ-eiffel.fr