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Overview of Fatigue Data for High Frequency Mechanical Impact Treated Welded Joints


paper provides an overview of published experimental data on the fatigue strength of welded joints by high frequency mechanical impact (HFMI) treatment methods, In total, 414 data points from four specimen types are available,tests were performed using constant amplitude R = 0.1 axial tension fatigue, but some data for other R rations, 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. HFMI 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 HFMI treatment methods must also be defined.

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Statistical intercept


Statistical slope


Estimate of the intercept


Estimate of the slope

Ci :

Fatigue capacity of specimen i

C50% :

Computed mean fatigue capacity of test series

C97.7% :

Characteristic fatigue capacity of the test serjes

fy :

Yield strength

fu :

Ultimate tensile strength


Characteristic fatigue class in MPa at 2 × 106 cycles to failure Characteristic fatigue class in MPa based on 97.7 % survival

FAT97.7% :

probability at 2 × 106 cycles to failure at 75 % level of confidence


Number of test specimens in a data set

kR :

Stress ratio correction factor

khs :

Structural hot-spot stress concentration factor


Slope of the S-N curve


Number of fatigue cycles

Nf :

Cycles to failure

Ni :

The number of cycles to failure of specimen i

Pf :

Probability of failure


Stress ratio

ΔSi :

Stress range of specimen i

Seq :

Equivalent constant amplitude stress range

SnA5 :

Nominal stress amplitude at 5 % failure probabilities

SnA95 :

Nominal stress amplitude at 95 % failure probabilities

Tσ :

Scatter range in stress

tp :

Student distribution

Xi :

log Ni

Yi :

log ΔSi

\( \bar X \) :

Average of log Ni

\( \bar Y \) :

Average of log ASi


Estimate of log ASi


Standard deviation

\( \hat \sigma _{\rm N} \) :

Estimate of the normal distribution variance


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Correspondence to Halid Can Yildirim.

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Yildirim, H.C., Marquis, G.B. Overview of Fatigue Data for High Frequency Mechanical Impact Treated Welded Joints. Weld World 56, 82–96 (2012).

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IIW-Thesaurus keywords

  • Fatigue improvement
  • High strength steels
  • Impact toughness
  • Weld toes