A review of fatigue strength improvement methods

1985 ◽  
Vol 12 (1) ◽  
pp. 166-183 ◽  
Author(s):  
Ian F.C. Smith ◽  
Manfred A. Hirt
Keyword(s):  
Quality Control ◽  
Finite Element ◽  
Fatigue Strength ◽  
Structural Steel ◽  
Welded Joints ◽  
Three Dimensional ◽  
High Strength Steels ◽  
High Strength ◽  
High Yield ◽  
Element Analysis

Improving the fatigue strength of welded joints may be economically interesting in many situations, especially in those cases where high-strength steels are used. However, widespread use of a method is, in many cases, restricted by a lack of knowledge of its reliability. Previous work has focused only on the effectiveness of improvement methods to increase fatigue strength; cost studies and quality control instructions are rarely given.In this report, several methods for structural steel are summarized. A review of existing test results shows that improved connections made from a high yield strength steel reveal a higher percentage improvement than mild steel connections using the same improvement method. In addition, improved joints may be sensitive to the applied stress ratio. Finally, the most efficient method depends on the type of welded joint.Residual stress methods have relatively inexpensive application costs whereas some grinding methods are very costly. Quality control depends upon fabrication, loading, and environmental conditions. Examination of four types of fillet-welded joints has identified several methods that require further research. A three-dimensional finite element study of these joints predicts that at crack locations, under service loading, a very small plastic zone is formed. Therefore, residual stress methods may remain effective under variable-amplitude load conditions. Key words: structural steel, welded joints, fatigue, improvement methods, fillet welds, finite element analysis.

Finite Element Analysis of Residual Stresses on Butt Welded Joints

2006 ◽  
Author(s):  
Enrico Armentani ◽  
Renato Esposito ◽  
Raffaele Sepe
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Fusion Zone ◽  
Welded Joints ◽  
High Strength Steels ◽  
High Strength ◽  
Heat Of Fusion ◽  
Temperature Dependent ◽  
Element Analysis ◽  
Welding Processes

Localized heating during welding, followed by rapid cooling, usually generates residual stresses in the weld and in the base metal. Residual stresses in welding processes give significant problems in the accurate manufacture of structures because those stresses heavily induce the formation of cracks in the fusion zone in high strength steels. Therefore, estimating the magnitude and distribution of welding residual stresses and characterizing the effects of certain welding conditions on the residual stresses are deemed necessary. In this work, residual stresses and distortions on butt welded joints are numerically evaluated by means of finite element method. The FE analysis allows to highlight and evaluate the stress field and his gradient around the fusion zone of welded joints, higher than any other located in the surrounding area. Temperature-dependent material properties, welding velocity, external mechanism constraints, technique of ‘element birth and death’ and latent heat of fusion are also taken into account. Some numerical results are compared with experimental data showing a very good correlation.

Influence of Strength Level of Steels on Fatigue Strength and Fracture Morphology of Spot Welded Joints

2011 ◽  
Vol 462-463 ◽  
pp. 94-99
Author(s):  
Keiichiro Tohgo ◽  
Tomoya Ohguma ◽  
Yoshinobu Shimamura ◽  
Yoshifumi Ojima
Keyword(s):  
Finite Element ◽  
Fatigue Strength ◽  
Mild Steel ◽  
Welded Joints ◽  
High Strength ◽  
Fracture Morphology ◽  
Fatigue Tests ◽  
Finite Element Analyses ◽  
Ultra High Strength Steel ◽  
Spot Welded

In this paper, fatigue tests and finite element analyses are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) in order to investigate the influence of strength level of base steels on fatigue strength and fracture morphology of spot welded joints. From the fatigue tests the following results are obtained: (1) Fatigue limit of spot welded joints is almost the same in both steels. (2) Fatigue fracture morphology of spot welded joints depends on the load level in the ultra-high strength steel, but not in the mild steel. From discussion based on the finite element analyses the following results are obtained: (3) The fatigue limit of spot welded joints can be predicted by stress intensity factors for a nugget edge, fracture criterion for a mixed mode crack and threshold value for fatigue crack growth in base steel. (4) Plastic deformation around a nugget in spot welded joints strongly affects the fatigue fracture morphology.

scholarly journals Finite Element Analysis of Springback of High-Strength Metal SCGA1180DUB While U-Channeling, According to Wall Angle and Die Radius

2021 ◽  
Author(s):  
Samet Karabulut ◽  
İsmail Esen
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Sheet Thickness ◽  
High Strength ◽  
Sheet Forming ◽  
High Yield ◽  
Process Conditions ◽  
Wall Angle ◽  
Element Analysis ◽  
Multi Phase

Abstract Springback is a problem as important as tearing or thinning, while forming high-strength sheets. Springback is an undesirable situation and it is the form difference between the desired form of a part in theory and the form obtained due to mechanical characteristics and process inputs of the material after die forming. It affects operations in shearing, punching or bending dies in subsequent operations in forming die sets. If the part is not within the desired tolerance range, it creates problems during assembly. In order for cost effective production plans for automotive parts to be made, suitable sheet forming simulations are needed. Waste of time and failures during die construction are minimized by defining accurate parameters by finite element analyses and minimizing periods of trial-and-error. In this study, the material SCGA1180DUB in sheet thickness of 0.8 mm from multi-phase steel sheet group was U-channeled, using Autoform sheet forming analysis program, according to appropriate process conditions having wall angles of 7°,10°,12° and die radius values of R3, R5, R8 and the springback values were estimated. The results obtained were compared through the finite element program and suitable wall angle and die radius values for the material SCGA1180DUB for forming advanced high-strength sheets were determined. As the die radii increased at the same wall angles, the amount of spring back increased significantly. In particular, due to high yield and tensile strength of multi-phase high strength sheet, springback values were observed to be high. Negative springbacks were observed in the roof of the part. In the same die radii, under the same process conditions, as wall angles increase, springback values decreased. In the literature, it is interesting that there are few studies regarding forming, springback of high-strength sheets SCGA1180DUB. This study will contribute to the literature. Autoform program was used for Finite Element Analysis.

Testing and Modeling of Roll Levelling Process

2014 ◽  
Vol 611-612 ◽  
pp. 1753-1762 ◽  
Author(s):  
Elena Silvestre ◽  
Eneko Sáenz de Argandoña ◽  
Lander Galdos ◽  
Joseba Mendiguren
Keyword(s):  
Finite Element ◽  
High Strength Steels ◽  
Beam Theory ◽  
High Strength ◽  
Theoretical Models ◽  
Element Model ◽  
Forming Process ◽  
Element Analysis ◽  
Design Engineers ◽  
Ultra High Strength Steels

Roll levelling is a forming process used to remove the residual stresses and imperfections of metal strips by means of plastic deformations. During the process the metal fibres are subjected to cyclic tension-compression deformations leading to achieve flat product. The process is especially important to avoid final geometrical errors when coils are cold formed or when thick plates are cut by laser. In the last years, and due to the appearance of high strength materials such as Ultra High Strength Steels, machine design engineers are demanding a reliable tool for the dimensioning of the levelling facilities. In response to this demand, Finite Element Analysis and Analytical methods are becoming an important technique able to lead engineers towards facilities optimization through a deeper understanding of the process. Aiming to this study two different models have been developed to analyze the roll levelling operations: an analytical model and a finite element model. The FE-analysis was done using 2D-modelling assuming plane strain conditions. Differing settings, leveller configuration and materials were investigated. The one-dimensional analytical levelling model is based on classical beam theory to calculate the induced strain distribution through the strip, and hence the evolving elastic/plastic stress distribution. Both models provide a useful guide to process-sensitivities and are able to identify causes of poor leveller performance. The theoretical models have been verified by a levelling experimental prototype with 13 rolls at laboratory.

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