A design method of tensile triangles and low transformation temperature weld metal for reduction of stress concentration and residual stress of welded joints

Ultrasonic impact treatment (UIT), which is a type of peening method, is usually used as a post-weld treatment for mild steel in order to improve the fatigue strength of its welded joints. As there is insufficient fatigue data available on welded joints of austenitic stainless steel treated by UIT, the authors decide to conduct fatigue tests on butt welded joints of austenitic stainless steel treated by UIT. The results were compared with the fatigue lives of as-weld joints to investigate the effect of UIT on the fatigue lives of welded joints of austenitic stainless steel. The fatigue lives of butt welded joints treated by UIT were more than 1.5 times longer than those of as-weld joints. The following were considered as possible reasons for this improvement in fatigue life: change in residual stress near the weld toes, relaxation of stress concentration at the weld toes, and refinement of grains under the weld toes. The residual stress measured near the weld toes by using the X-ray diffraction method was transformed from tension to compression by the application of UIT. The stress concentration factors at the welded toes were reduced about 10% by the application of UIT.

Download Full-text

High-Cycle Fatigue Strength and Residual Stress in Welded Joints of Structural Steels

Elevated Temperature Design and Analysis, Nonlinear Analysis, and Plastic Components ◽

10.1115/pvp2004-2985 ◽

2004 ◽

Author(s):

Masahito Mochizuki ◽

Masao Toyoda

Keyword(s):

Residual Stress ◽

Phase Transformation ◽

Fatigue Strength ◽

Low Temperature ◽

Weld Metal ◽

Welded Joints ◽

Compressive Residual Stress ◽

High Cycle Fatigue ◽

Temperature Phase ◽

Cycle Fatigue

Improvement of high-cycle fatigue strength by reducing residual stress in welded joints is studied in this paper. 10% Nickel and 10% Chromium are involved in the developed welding material for producing the property of thermal shrinkage by martensitic phase transformation at a low temperature and for generating compressive residual stress during cooling process. A cruciform fillet-welded joint is used for the numerical simulation of the thermal elastic-plastic finite-element analysis with coupling phase transformation effect. Distribution of the computed residual stress agrees with the measuring values by strain gauge. Compressive residual stress mostly distributes in the weld metal for both longitudinal and transverse directions with weld line. Fatigue test is also performed in order to clarify the effect of the developed weld material on fatigue strength. Developed weld metal has much higher characteristics for high-cycle fatigue strength than a conventional one. Increase effect of fatigue strength is shown by the modified Goodman diagram when residual stress is treated as mean stress. Weld metal with the property of low-temperature phase transformation is effective to reduce residual stress and to improve fatigue strength.

Download Full-text

Prediction of fatigue limit improvement in needle peened welded joints containing crack-like defects

International Journal of Structural Integrity ◽

10.1108/ijsi-03-2017-0019 ◽

2018 ◽

Vol 9 (1) ◽

pp. 50-64 ◽

Cited By ~ 6

Author(s):

Ryutaro Fueki ◽

Koji Takahashi

Keyword(s):

Residual Stress ◽

Stainless Steel ◽

Stress Concentration ◽

Yield Stress ◽

Fatigue Limit ◽

Welded Joints ◽

Steel Structures ◽

Content Type ◽

Before And After ◽

Weld Toe

Purpose The purpose of this paper is to estimate the acceptable defect size amax after needle peening (NP) and predict the fatigue limit improvement through the use of NP for an austenitic stainless steel welded joint containing an artificial semi-circular slit on a weld toe. Design/methodology/approach Residual stress and hardness distribution were measured. Microstructures around the weld toe were observed to clarify the cause for the change in hardness after NP. Finite element method analysis was used to analyze the change in the stress concentration following NP. Fracture mechanics was used to evaluate amax after NP. The fatigue limits before and after NP were predicted by determining amax for several levels of stress amplitude. Findings The tensile residual stress induced at the surface of the weld toe prior to NP changed to a compressive residual stress after NP. The residual stress near the surface layer after NP exceeded the yield stress prior to NP due to the increase in yield stress as a result of work hardening as well as the generation of a deformation-induced martensitic structure. The stress concentration was reduced due to the shape improvement caused by NP. The estimation value of amax after NP and the prediction results of fatigue limits were in good agreement with the fatigue test results. Practical implications The proposed method is useful in improving the reliability of welded joints used in large steel structures, transportation equipments and industrial machines. Originality/value From an engineering perspective, it is essential to estimate amax and the fatigue limit of welded joints with crack-like defects. However, it is unclear as to whether it is possible to predict amax and the effects of NP on the fatigue limit for stainless steel welded joints.

Download Full-text

Factors That Affect the Fatigue Strength of Power Transmission Shafting and Their Impact on Design

Journal of Mechanisms Transmissions and Automation in Design ◽

10.1115/1.3260768 ◽

1986 ◽

Vol 108 (1) ◽

pp. 106-114 ◽

Cited By ~ 3

Author(s):

S. H. Loewenthal

Keyword(s):

Residual Stress ◽

Fatigue Strength ◽

Stress Concentration ◽

Power Transmission ◽

Design Method ◽

Surface Condition ◽

Operational Reliability ◽

Torsional Loading ◽

Variable Amplitude ◽

Limited Life

A long-standing objective in the design of power transmission shafting is to eliminate excess shaft material without compromising operational reliability. A shaft design method is presented which accounts for variable amplitude loading histories and their influence on limited life designs. The effects of combined bending and torsional loading are considered, along with a number of application factors known to influence the fatigue strength of shafting materials. Among the factors examined are surface condition, size, stress concentration, residual stress, and corrosion fatigue.

Download Full-text