Fatigue Crack Growth Behaviors at the Toe of Fillet Welded Joints under Plane Bending Load

Study on Bending Fatigue of Fillet Welded Joints of Mild Steel (1st. Report)

Abstract

In order to study on fatigue crack growth characteristics at the toe of fillet welded joints, simple plate type specimens with fillet welded gussets were tested under load controlled conditions by T- and 4-point-bending. Fatigue crack growth tests on edge-notched and planer surface notched specimens were also carried out under plane bending load.
The results are summarized as follows:
(1). Fatigue crack growth behaviors along the weld toe lines were affected by bending stress range, Δσ_b and stress concentration factor at the weld toe, K_t, but to depth direction not so much affected by the variation of Δσ_b.
(2). The average crack growth rates along the weld toes in earlier stage of life may be expressed as,
d(2b)/dN=C(K_t⋅Δσ_b⋅f₁(R))^m
here, f₁(R): Coefficients of stress ratio R, 1.0 for R=0 and 0.614 for R=-1; C, m: Material constants.
The values of f₁(R), C and m to be used were derived from the test results of surface notched specimens.
(3). The crack growth rates to depth direction may be expressed. as,
da/dN=C⋅f(R)⋅(ΔK)^m
here, f(R): Coefficients of stress ratio R, 1.0 for R=0 and 0.5 for R=-1.
ΔK: Range of stress intensity factor in a plate with edge crack under uniform bending.
C, m: Material constants derived from the test results of edge notched specimens.