INVESTIGATIONS ON FRACTURE TOUGHNESS OF WELDED SHIP STRUCTURES
The paper is concerned with fracture toughness of welded ship structures fabricated of micro-alloyed niobium contained steel (15GNb) and of low carbon steel (St41U5). Parent materials and weldments were tested by static and dynamic loads in temperature range of +20 to -60 deg C. Specimens with notches were used for crack opening displacement (COD) measure. By applying a number of cyclic loads before tests, the influence of fatigue process developement in local zone ahead of the notch tip, on fracture toughness of material and weld joint, has been studied. The chemical composition and mechanical properties of the steels are given. The main tests were performed with 3 series of specimens representing the welded joints of full thickness plates 36 and 21 mm. First of all a considerable difference of fracture toughness between parent material and weld zone for both of materials is worthy of remark. Decrease of the weld zone resistance to fracture was more pronounced for the Nb-steel, than for low carbon steel. For both of materials influence of fatigue process was evident, but changes observed for the Nb-steel were more obvious than in the case of low carbon steel. The reason for this was their metalurgical nature. In particular cases fatigue process caused important decrease of fracture toughness at low temperatures when at highest temperatures a noticeable increase of fracture toughness occured. Fractographic investigations showed that this behaviour is in reference to material susceptibility to lamellar decohesion, on reason of low coherent, non-metalic inclusions. Seperation of the layers diminish the constrain effect in plate thickness by tension, and this enabled increase of decohesion energy in result easier developement of large plastic deformation. By low temperatures more important influence have micro-cracks which occured in parent material between the separated layers, or in weld zone in result of high constraint caused by residual stresses.
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Technical University of Gdansk, PolandGdansk, Poland
- Kubera, S
- Publication Date: 1978
- Pagination: 19 p.
- Issue Number: 59
- TRT Terms: Cracking; Dislocation (Geology); Dynamic loads; Fatigue (Mechanics); Fracture properties; Joints (Engineering); Materials selection; Repeated loads; Strength of materials; Tearing; Weld strength; Weld tests; Welds
- Uncontrolled Terms: Welded joints
- Old TRIS Terms: Crack opening displacement; Materials evaluation
- Subject Areas: Marine Transportation; Materials;
- Accession Number: 00307503
- Record Type: Publication
- Files: TRIS
- Created Date: Feb 11 1980 12:00AM