INFLUENCE OF STRESS RELIEVING BY VIBRATION AS COMPARED TO POSTWELD HEAT TREATMENT ON THE FATIGUE BEHAVIOUR OF REPAIRED WELDS.

Información del proyecto

Identificador del acuerdo de subvención: 7210-KD-118

Proyecto cerrado

Fecha de inicio 1 Julio 1985

Fecha de finalización 31 Diciembre 1989

Financiado con arreglo a

• Medium-term orientation (ECSC) "steel research in relation to the General Objectives for Steel", 1981-1985

Coste total

Sin datos

Aportación de la UE

Sin datos

Coordinado por

FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG E.V.*
Germany

Objetivo

THE HIGH STRENGTH LOW ALLOY STEELS ARE INCREASINGLY USED FOR CONTRUCTIONAL STEELWORK, OFFSHORE INDUSTRY AND FOR HEAVY MACHINE INDUSTRY ETC.
THESE STEELS HAVE EXCELLENT WELDABILITY CHARACTERISTICS IF THE RIGHT PRECAUTIONS ARE TAKEN INTO ACCOUNT. AS A PRECAUTION SAFEGUARDING AGAINST BRITTLE FRACTURE WELDMENTS IN THESE STEELS ARE OFTEN STRESS RELIEVED.
THE MOST COMMON METHOD FOR RELIEVING THE RESIDUAL STRESSES IS POST WELD HEAT TREATMENT (PWHT). THE BENEFICIAL INFLUENCE OF PWHT ON FATIGUE SHOULD NOT BE NEGLECTED, BECAUSE A SIGNIFICANT IMPROVEMENT IN FATIGUE ENDURANCE HAS BEEN OBSERVED AT R = -1.
BY FAR THE MOST EXPERIENCE EXISTS WITH PWHT AND THIS METHOD IS, WHENEVER APPLICABLE, WIDELY APPLIED IN PRACTICE.
HOWEVER, A NEED EXISTS FOR A GOOD ALTERNATIVE BECAUSE PWHT HAS SOME SIGNIFICANT DISADVANTAGES:
- HIGH COSTS,
- IMPORTANT METALLURGICAL CONSEQUENCES FOR THE PLATE MATERIAL, THE HAZ AND WELDMETAL PROPERTIES,
- LACK OF DIMENSIONAL STABILITY.
- PWHT IS NOT ALWAYS APPLICABLE.
A VIBRATION STRESS RELIEF (VSR) MAY BE A SUCCESSFUL ALTERNATIVE. THIS METHOD CONSISTS IN THE EXCITATION OF DEFINITE VALUE BY MEANS OF A MECHANICAL VIBRATION WITH A RESONANCE FREQUENCY.
THESE VIBRATIONS ARE GRADUALLY DECREASED AT CRITICAL PLACES WITH A HIGH STRESS LEVEL. INDUCED LATTICE VIBRATIONS ALLOWS THE DISLOCATIONS TO REARRANGE AND THE ATOMS TO MIGRATE ON A SMALL SCALE, SO THE MICROSTRESSES ARE REDUCED TO A STABLE LEVEL.
THE RELIEF OF STRESSES SEEMS TO BE VERY EFFECTIVE AT RESONANCE FREQUENCIES (100 HZ) AND TAKES ABOUT 10-60 MINUTES.
SIGNIFICANT ADVANTAGES ARE:
- REDUCTION OF CAPITAL OUTLAYS,
- DECREASE OF LABOUR CONSUMPTION,
- LESS POWER CONSUMPTION,
- ABSENCE OF SCALE ETC.,
- NO DETERIORATION OF THE TOUGHNESS PROPERTIES,
- ALSO APPLICABLE TO JOINTS IN DISSIMILAR METALS,
- INDEPENDENT OF DIMENSIONS.

THE USERS OF STEELWORKS ARE INCREASINGLY INTERESTED AND CONFRONTED WITH VRS METHODS-PRODUCTS INSTEAD OF PWHT.
HOWEVER THERE IS DOUBT ABOUT THE RELIABILITY. THERE ARE INDICATIONS THAT THIS TECHNIQUE IS NOT EFFECTIVE ENOUGH IN REDUCING RESIDUAL STRESSES, AND THAT MICROSCOPIC FLAW INITIATION MAY OCCUR.
A RESEARCH PROGRAMME IS PROPOSED TO COMPARE VSR AND PWHT. FURTHERMORE THE INFLUENCE OF REPAIR-WELDING ON THE FITNESS FOR PURPOSE (FATIGUE PROPERTIES) WILL BE INVESTIGATED.
THIS STRONGLY GROWING INTEREST FOR REPAIR WELDING OF CONSTRUCTIONS IS CONNECTED AMONG OTHER THINGS WITH THE FOLLOWING FACTORS:
- THE RISKS AND ECONOMICAL CONSEQUENCES LINKED WITH THE BREAK-DOWN OF A CONSTRUCTION ARE VERY LARGE. FOR THAT REASON INCREASINGLY STRONGER REQUIREMENTS ARE STIPULATED FOR STEEL STRUCTURES (FOR EXAMPLE FREQUENT INSPECTION WITH SOPHISTICATED NON-DESTRUCTIVE INSPECTION METHODS) RESULTING IN AN INCREASING NECESSITY FOR REPAIRING.
- THE ECONOMICAL LIFE OF ANY CONSTRUCTIONS IS INCREASED DURING THE LAST DECADE.
- THE IN-SERVICE CONDITIONS HAVE OFTEN BECOME MORE SEVERE (OFF-SHORE STRUCTURES, HEAVY MACHINE INDUSTRY).
FROM A PRACTICAL POINT OF VIEW REPAIRING HAS TO BE DONE UNDER DIFFICULT CIRCUMSTANCES (HIGH RESTRAINT, WELDING PERFORMANCE, ETC.) WITH THE RESULT THAT STRESS RELIEVING TREAMENTS ARE DESIRABLE TO IMPROVE THE PROPERTIES OF THE REPAIRWELDS AND TO ENHANCE THE FITNESS FOR PURPOSE.
HOWEVER POSTWELD HEAT TREATMENT IS NOT ALWAYS POSSIBLE. FOR EXAMPLE FOR REPAIRED WELDED COWPERS VSR IS THE ONLY POSSIBILITY TO RELIEVE RESIDUAL STRESSES. VSR IS ALSO INCREASINGLY BEING USED FOR MACHINED COMPONENTS IN HEAVY APPARATUS INDUSTRY.
SO FAR, ONLY ON A LIMITED SCALE, LESS SYSTEMATIC RESEARCH OF REPAIRED CONSTRUCTIONS HAS BEEN CARRIED OUT. FOR REASONS OF AN INCREASED APPLICATION AND OF ADVANTAGES OF THE RELIABILITY IT IS PROPOSED TO CARRY OUT THE RESEARCH ON REPAIRED WELDS.

Ámbito científico (EuroSciVoc)

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Programa(s)

• ECSC-STEELRES 6C - Medium-term orientation (ECSC) "steel research in relation to the General Objectives for Steel", 1981-1985

Tema(s)

Datos no disponibles

Convocatoria de propuestas

Datos no disponibles

Régimen de financiación

Datos no disponibles

Coordinador

FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG E.V.*

• Aportación de la UE: Sin datos
• Dirección: Bartningstrasse 47 ; 64289 DARMSTADT ; Alemania
• Coste total: Sin datos

Participantes (1)

NIL

Países Bajos

• Aportación de la UE: Sin datos
• Dirección: DELFT
• Coste total: Sin datos