scholarly journals Influence of Weld-Porosity Defects on Fatigue Strength of AH36 Butt Joints Used in Ship Structures

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 444
Author(s):  
Vincenzo Crupi ◽  
Gabriella Epasto ◽  
Eugenio Guglielmino ◽  
Alberto Marinò
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Stress Ratio ◽  
Infrared Camera ◽  
Experimental Tests ◽  
Fatigue Tests ◽  
Butt Joints ◽  
Ship Structures ◽  
Weld Porosity ◽  
Porosity Defects

Experimental tests were carried out to assess the fatigue strength of four types of welded joints, made of AH36 steel and used for ship structures. The joints differ for the presence of weld defects and for the thickness value. Fatigue tests were carried out applying axial cyclic loads at a frequency of 20 Hz and at a stress ratio R = 0.5. The temperature e increment of the specimen surface was detected during the load application by means of an infrared camera. The analysis of the thermographic images allowed the assessment of both the fatigue strength of the welded joints, applying the rapid thermographic method, and the S-N curve by the energy approach. Moreover, 3D computed tomography was used for the analysis of the defective welded joints.

Differences in Fatigue Strength Between Arc and Laser Hybrid Welded Joints

2008 ◽  
Vol 24 (03) ◽  
pp. 139-146
Author(s):  
H. Remes ◽  
P. Varsta
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Tests ◽  
Notch Depth ◽  
Butt Joints ◽  
Fatigue Design ◽  
Notch Stress ◽  
Notch Geometry ◽  
Laser Hybrid ◽  
Fatigue Endurance

This paper presents the results of fatigue tests, including tests of laser hybrid and arc welded butt joints, for two plate thicknesses, 6 and 12 mm. Pure laser welded joints were also tested. The S-N curves based on nominal stresses for the different welded joints are presented. The results were further analyzed using the notch stress approach, where the fatigue notch factors were determined from the measured geometries of the welded joints. Unexpected differences in the S-N curves based on the notch stresses were found between the laser hybrid and arc welded joints and between the laser hybrid and pure laser welded joints. The reasons for this difference were studied with the help of extensive measurements of weld notch geometries. Significant differences in the geometries were observed. Taking into account the notch geometry and the notch depth, the notch stress approach partially explains the differences between the fatigue endurance limits of the laser hybrid and arc welded joints. The applicability of the notch stress approach to the fatigue design of laser hybrid welded joints is also discussed.

scholarly journals Effect of micro-notches on fatigue strength of electrodeposited nanocrystalline nickel thin films

2018 ◽  
Vol 165 ◽  
pp. 04011
Author(s):  
Keisuke Tanaka ◽  
Yuta Murase ◽  
Hirohisa Kimachi
Keyword(s):  
Thin Films ◽  
Fatigue Strength ◽  
Fatigue Limit ◽  
Stress Ratio ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Fine Grained ◽  
Nickel Thin Films ◽  
Nano Crystalline ◽  
Fictitious Crack

The effect of micro-notches on the fatigue strength of nickel thin films was studied. Two types of thin films with 10 μm thickness were produced by electrodeposition using sulfamate solution without and with brightener: ultra-fine grained film (UFG) with the grain size of 384 nm and nano-crystalline grained film (NCG) with that of 17 nm. Micro-sized notches introduced by FIB had the width of 2 μm and various depths from 8 to 150μm. Fatigue tests were conducted under the stress ratio of 0.1. The fatigue strength decreased with increasing depth of notches. NCG had much higher strength than UFG compared at the same notch depth. Notches as small as 8μm did reduce the fatigue strength of both UFG and NCG. The fatigue limit was controlled by the initiation of cracks and no non-propagating crack was observed in specimens fatigued below the fatigue limit. A model of fictitious crack successfully predicted the reduction of the fatigue limit due to micro-notches. The characteristic crack length of NCG was much smaller than the UFG, while the fatigue strength of defect-free NCG was larger than that of UFG. SEM observation of fracture surfaces was conducted to reveal micromechanisms of fatigue crack initiation.

Influence of backing materials towards the fatigue strength of butt-welded joints

2011 ◽  
Vol 225 (8) ◽  
pp. 1798-1807 ◽  
Author(s):  
M H Kim ◽  
H J Kim ◽  
J H Han ◽  
J M Lee ◽  
Y D Kim ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Tests ◽  
Experimental Results ◽  
Finite Element Analyses ◽  
Cold Metal Transfer ◽  
Notch Stress ◽  
Effective Notch Stress ◽  
Cold Metal

The purpose of this study is to investigate the fatigue strength of butt-welded joints with special attention paid to employing different kinds of backing plates. The effect of the under-matched weld was also considered. Four different cases of backing scenarios for butt-welded specimens such as steel backing, ceramic backing, CMT (no backing by cold metal transfer) and UM (under-matched welded specimen) were investigated. A series of fatigue tests was performed to compare the fatigue strength of butt-welded joints with respect to different backing scenarios. Effective notch stress was used for the interpretation of fatigue strength of butt-welded specimens with backing plates based on finite element analyses for calculating fatigue notch factors. When results were presented from the effective notch stress, all backing scenarios considered in this study exhibited the fatigue strengths corresponding to the FAT 225 curve. From the experimental results of this study, it was determined that the fatigue strengths of butt-welded joints were found to be in the order of CMT, ceramic backing, UM, and steel backing. No significant decrease in fatigue strength, however, was observed when backing plates were steel backing and ceramic backing types.

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.

Different Methods for Fatigue Assessment of T Welded Joints Used in Ship Structures

2007 ◽  
Vol 51 (02) ◽  
pp. 150-159 ◽  
Author(s):  
V. Crupi ◽  
E. Guglielmino ◽  
A. Risitano ◽  
D. Taylor
Keyword(s):  
Welded Joints ◽  
Fatigue Behavior ◽  
Experimental Tests ◽  
Ship Structures ◽  
Element Analysis ◽  
Fatigue Assessment ◽  
Endurance Limits ◽  
Thermographic Analysis ◽  
Using Data ◽  
Cycle Endurance

The aim of this work is the prediction of high-cycle fatigue behavior in welded joints, which represent regions of weakness in the ship structures. The traditional methods for fatigue assessment of welded joints have some limitations. Some new methods were recently developed by Taylor: the crack modeling method (CMM) and the theory of critical distances methods (TCD). Experimental tests were carried out to define the high-cycle endurance limits of aluminum T-shaped welded joints. Using data obtained from finite element analysis (FEA), the fatigue strength was evaluated according to the CMM and the TCD. Thermographic analysis was also carried out during the experimental tests to assess the high-cycle endurance limits of the welds by means of the Risitano method (RM). The previous methods were also applied to a specific case, fatigue in T joints containing a drilled hole at different angles, which allowed us to study a typical industrial design problem involving two different features. Good predictions were achieved using all the methods.

Effect of preload and stress ratio on fatigue strength of welded joints improved by ultrasonic impact treatment

2012 ◽  
Vol 57 (2) ◽  
pp. 235-241 ◽  
Author(s):  
T. Okawa ◽  
H. Shimanuki ◽  
Y. Funatsu ◽  
T. Nose ◽  
Y. Sumi
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Stress Ratio ◽  
Ultrasonic Impact Treatment

Analytical Study on Fatigue Strength Reduction Factor of Small-Diameter Socket-Welded Pipe Joints

1998 ◽  
Vol 120 (2) ◽  
pp. 157-163 ◽  
Author(s):  
M. Higuchi ◽  
A. Nakagawa ◽  
K. Iida ◽  
M. Hayashi ◽  
T. Yamauchi ◽  
...  
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Small Diameter ◽  
Large Change ◽  
Fatigue Tests ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Welded Pipe

Four-point bending and rotating bending fatigue tests were conducted on socket-welded joints made of carbon, stainless, and Cr-Mo steels for clarification of the effects of diameter, welding pass sequence and post-weld heat treatment (PWHT) on fatigue strength. The results were evaluated quantitatively. Fatigue strength of socket-welded joints was found to strongly depend on weld pass sequences in fillet welds, this being possibly due to large change in residual stress distribution at roots and toes. The effects of residual stress were thus examined quantitatively by comparison of fatigue strength of PWHT stress-free specimens with that of as-welded specimens. By the modified Goodman’s method, the lowest S-N curve corresponding to maximum tensile residual stress and the highest S-N curve corresponding to maximum compression residual stress were obtained for different steels and diameters. Conventional S-N data of socket-welded joints were situated between these two limiting curves. Based on the lowest curve, fatigue strength reduction factors of socket-welded joints were proposed.

Fatigue Strength Assessment for High Strength Steel Welded Joints

2010 ◽  
Author(s):  
Ho Jung Kim ◽  
Sung Won Kang ◽  
Jae Myung Lee ◽  
Myung Hyun Kim
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
High Strength Steel ◽  
Fatigue Behavior ◽  
High Strength ◽  
Fatigue Tests ◽  
Cold Metal Transfer ◽  
Strength Assessment ◽  
Back Plate ◽  
Cold Metal

The aim of the present paper is to investigate and to compare the fatigue characteristics of butt welded joints made of high strength steel with tensile strength 700MPa. The influence of different back plate materials and the groove shapes of copper backing are investigated. Various backing methods have been used in the steel construction industries, but steel backing, which is the most frequently used, sometimes is not capable of providing sufficient fatigue strengths for welded joint, particularly for high strength steel. Therefore, alternative backing methods have been investigated in order to improve the fatigue strength by employing ceramic backing, CMT (Cold Metal Transfer) [1] and copper backing. The main objective of the work is to estimate the fatigue test results for improving fatigue strength by comparing different backing materials and groove shapes. A series of fatigue tests with different types of backings has been carried out to obtain the fatigue life of butt welded joints. It was observed that the fatigue behavior of welded joints can be substantially improved by changing back bead shapes. The result has shown that the back bead shape of copper backing is better than others except for that of CMT, accompanied by improved fatigue strength.

scholarly journals Fatigue improvement of aluminium welds by means of deep rolling and diamond burnishing

2021 ◽  
Author(s):  
Jan Schubnell ◽  
Majid Farajian
Keyword(s):  
Fatigue Strength ◽  
Treatment Process ◽  
Potential Method ◽  
Fatigue Tests ◽  
Deep Rolling ◽  
Butt Joints ◽  
Diamond Burnishing ◽  
Life Improvement ◽  
Stress States ◽  
Mechanical Surface

AbstractDeep rolling is an industrially widely established mechanical surface treatment process for the modification of roughness and fatigue resistance. However, the process has not been considered as a potential method for the mechanical post welded treatment of welded joints yet. Even, the potential of deep rolling for increasing the fatigue strength is comparably well-known in the case of non-welded components. Therefore, the effect of deep rolling (hydrostatic mounted tool) and diamond burnishing (mechanical mounted tool) to increase the fatigue strength of butt joints was approved in this work for aluminium alloy AlMg4,5Mn0,7 (EN AW 5083). For this purpose, fatigue tests under full tensile loading were performed in as-welded and deep rolled, burnished and ultrasonic impact treated conditions. Different residual stress states as well as work hardening states are determined in deep rolled and burnished condition. However, similar and significant fatigue life improvement was determined for both processes.

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