IIW Doc. XIII-1748-98

Introductory fatigue tests on welded joints in high strength steel and aluminum improved by various methods including ultrasonic impact treatment (UIT).

This paper summarizes fatigue test on high strength steel specimens in the as-welded condition and specimens treated by ultrasonic impact treatment, TIG dressing and a combination of TIG dressing and ultrasonic impact treatment. Single lap joint specimens in 6 mm aluminum plate material were tested in the as-welded, hammer peened, needle peened and ground condition.

Aluminum joints with longitudinal stiffeners in 8 mm plate were tested in the as-welded condition improved by ultrasonic impact treatment (UIT). Increases in fatigue strength at a life of 2 million cycles ranged from a negative influence for hammer peening of 6 mm aluminum lap joints to approximately 135 % for high strength steel specimens treated by TIG dressing plus UIT.

IIW Doc. XIII-2362-11

Overview of fatigue data for high frequency treated welded joints

This paper provides an overview of published experimental data on the fatigue strength of welded joints improved by high frequency treatment methods. In total, 387 data points from four specimen types are available. Most tests were performed using constant amplitude R=0.1 axial tension fatigue, but some data for other R-ratios, variable amplitude testing and bending fatigue are also reported. An S-N slope of m=5 gives a very good description of both individual data sets and of the composite data. Design curve recommendations for the four joint types and for the structural stress-based design curve are given. High frequency treated specimens generally follow the same trend as experimental data for hammer peened specimens, but the degree of improvement is better. Data for large structures, at stress ratios other than R=0.1 and for variable amplitude loading are still needed in order to update the IIW guideline for post-weld improvement. There is a general trend for increasing fatigue strength improvement as a function of steel yield strength but this influence needs further study in order to develop guidelines. Quality assurance measures for high frequency treatment methods must also be defined.

IIW Doc. XIII-2143-07

LIFE EXTENSION of CLASS F and CLASS F2 DETAILS USING ULTRASONIC PEENING

The application of fatigue life improvement techniques is gaining popularity in the last years. Classification Societies have been focusing more and more on these and the latest document dealing with it [1] presents recommendations for weld toe profiling by machining and grinding, weld toe grinding, TIG-dressing and hammer peening. The other important document in respect to execution of the improvement is the IIW Recommendations [2], which contains extensive reference data for various fatigue life improvements [3] and the quality assurance and control of their application.

Fatigue life improvement techniques can contribute to reduce maintenance cost by the avoidance of returning weld repairs. Furthermore life extension techniques are the only remedy when higher stress and/or fatigue cracks occur in a structure with many years remaining service life.

One other way to use the increased fatigue strength achieved during improvement is to increase the design stress for the structure. Higher design stresses mean either increased pay-load or extended life for retained design stresses for a specific structure.

IIW Doc. XIII-2316-10

Fatigue Life Extension Procedure by Ultrasonic Peening

The service life of metallic structures is limited by its structural integrity. Additionally the structural integrity is mainly governed by the fatigue resistance of critical weld details. Depending on the type of structure and the type of load these typical weld details could differ. Ultrasonic peening can improve the fatigue resistance of welded joints. Fatigue test results show a life extension of four times for high stress ranges and up to ten times for high cycle fatigue. For welded details which have already consumed half of their fatigue life ultrasonic peening treatment resets the clock to zero, as a minimum value.

Finite Element Analysis verified critical fatigue lives for some weld connections in the analyzed structures. The level of current stress ranges at these weld connections, taken as max principal stresses, were used to assess the potential life extension which could be achieved as well as to calculate the size of the area to be treated by ultrasonic peening.

Consequently ultrasonic peening treatment was applied to several steel structures on fatigue sensitive weld connections with the objective to extend their service life. The economical benefits due to reduced maintenance as a result of the ultrasonic peening treatment include.

Avoidance of long plan for recurring weld repairs 
Avoidance of long and unscheduled operational disruptions
Increased structural safety for the structure during its remaining service life

IIW Doc-1823-07/XIII-2151r4-07/XV-1254r4-07 Dec. 2008

Recommendations for Fatigue Design of Welded Joints and Components

This document has been prepared as a result of an initiative by Commissions XIII and XV of the International Institute of Welding (IIW). The task was transferred to the Joint Working Group XIII-XV, where it was discussed and drafted in the years 1990 to 1996 and then updated in the years 2002-2007. The main points of the update are: Revision of the chapter on structural hot spot stress, consideration of aluminium at the effective notch stress method, a new chapter on improvement techniques and a revision of the chapter on multiaxial loading.