Effect of Ultrasonic Impact Treatment on Welded Details under Cyclic Loading Conditions
Author
Laursen, Martin Riskjær
Term
4. term
Education
Publication year
2018
Submitted on
2018-08-01
Abstract
This thesis examines how Ultrasonic Impact Treatment (UIT) influences the fatigue life of welded T-joints under cyclic loading. A continuously running numerical model of the impact process is developed in LS-DYNA, differing from earlier restart-based approaches by reducing computation time. The model is qualitatively validated against published residual stress distributions and geometry changes after treatment. A parameter study explores material and process effects: representing material hardening via the tangent modulus has a limited impact, while the tool path angle shows a stronger influence. Fatigue life is estimated using the notch stress approach, comparing the stress range computed from the UIT-treated model with an as-welded reference within the same detail category (using FAT200 as baseline). The analysis indicates a life improvement factor of about 4.4, which is lower than values suggested in common standards. The study also considers loading and relaxation through a four-point bending simulation. Overall, the work suggests that a faster, continuous process model can support assessing UIT effects, while further calibration is needed to reconcile predictions with standard expectations.
Dette speciale undersøger, hvordan Ultrasonic Impact Treatment (UIT) påvirker udmattelseslevetiden for svejsede T-samlinger under cyklisk belastning. Der udvikles en kontinuerligt kørende numerisk model af selve slagprocessen i LS-DYNA, som adskiller sig fra tidligere genstart-baserede modeller ved at reducere beregningstiden. Modellen er kvalitativt valideret mod publicerede restspændingsprofiler og geometriske ændringer efter behandling. Et parameterstudie vurderer både materiale- og procesindflydelser: materialets hærdningsrepræsentation via tangentmodulet havde begrænset effekt, mens arbejdsgangens vinkel viste større betydning. For at estimere levetidsforbedringer anvendes notch stress-tilgangen, hvor den beregnede spændingsvidde fra den UIT-behandlede model sammenlignes med en as-welded reference inden for samme detailkategori (med FAT200 som grundlag). Resultatet indikerer en levetidsforbedringsfaktor på cirka 4,4, hvilket er lavere end værdier angivet i gængse standarder. Specialet diskuterer desuden belastnings- og relaxationsforhold via en firepunktsbøjningssimulering. Samlet peger arbejdet på, at en hurtigere, kontinuerlig procesmodel kan understøtte vurdering af UIT’s effekt, men at yderligere kalibrering er nødvendig for at harmonere med standardernes forventninger.
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