Overload effect on the fatigue crack propagation in large‐scale tubular joints

Abstract

This paper examines the overloading effect on the fatigue crack propagations monitored in a large‐scale tubular X‐joint specimen under two separate cyclic tests. The first cyclic test applies a constant‐amplitude brace in‐plane bending to the joint, with a single cycle of 150% overload before the crack depth reaches the mid‐thickness of the chord. The second fatigue test applies two batches of cyclic loads, with the amplitude of the second batch at 66% of the former. The X‐joint specimen experiences a 150% overload cycle during the first batch of loading, followed by the second batch after it has recovered from the overload effect. The experimental results reveal that deep surface cracks experience more significant overload retardation than does a shallow fatigue crack. The Paris law estimation indicates that the single overload cycle applied in the first specimen leads to a 7% increase in the fatigue life of the X‐joint.

Fatigue crack propagation for Q345qD bridge steel and its butt welds at low temperatures

“…1 The safety of such infrastructures has posed a critical concern for countries residing in the cold region. [8][9][10][11][12] However, the Paris material constants used in estimating the fatigue life in these design codes derive primarily from the experimental database recorded at the room temperature. 2,3 A number of design procedures [4][5][6][7] have evolved for the fatigue prone structural details, based on a Paris type crack propagation rule, to assess the fatigue performance of steel bridges and Nomenclature: a, = crack length; a 0 , = initial crack length at the end of fatigue pre-cracking; A, = percentage of elongation at fracture; B, = thickness of the compact tension, C(T), specimen; C, = Paris-law coefficient; C 0 , = coefficient of stress intensity factor gradient method; E, = elastic modulus; f y , = yield strength; f u , = ultimate tensile strength; K I , = stress intensity factor; ΔK I , = stress intensity factor range; ΔK th , = fatigue crack propagation threshold; m, = exponent of the Paris-law; N, = number of loading cycles; P max , = maximum load; ΔP, = applied cyclic load range; R, = stress ratio; R 2 , = correlation coefficient; T, = temperature; T 27J , = fracture ductile-to-brittle transition temperature at which the Charpy impact energy is 27 J; T SA , = fracture ductile-to-brittle transition temperature at which the percent shear area of fracture surface in a Charpy specimen is 50%; T t , = fracture ductile-tobrittle transition temperature based on Boltzmann function; W, = width of compact tension, C(T), specimen; Z, = percentage of area reduction other welded steel structures.…”

“…2,3 A number of design procedures [4][5][6][7] have evolved for the fatigue prone structural details, based on a Paris type crack propagation rule, to assess the fatigue performance of steel bridges and Nomenclature: a, = crack length; a 0 , = initial crack length at the end of fatigue pre-cracking; A, = percentage of elongation at fracture; B, = thickness of the compact tension, C(T), specimen; C, = Paris-law coefficient; C 0 , = coefficient of stress intensity factor gradient method; E, = elastic modulus; f y , = yield strength; f u , = ultimate tensile strength; K I , = stress intensity factor; ΔK I , = stress intensity factor range; ΔK th , = fatigue crack propagation threshold; m, = exponent of the Paris-law; N, = number of loading cycles; P max , = maximum load; ΔP, = applied cyclic load range; R, = stress ratio; R 2 , = correlation coefficient; T, = temperature; T 27J , = fracture ductile-to-brittle transition temperature at which the Charpy impact energy is 27 J; T SA , = fracture ductile-to-brittle transition temperature at which the percent shear area of fracture surface in a Charpy specimen is 50%; T t , = fracture ductile-tobrittle transition temperature based on Boltzmann function; W, = width of compact tension, C(T), specimen; Z, = percentage of area reduction other welded steel structures. [8][9][10][11][12] However, the Paris material constants used in estimating the fatigue life in these design codes derive primarily from the experimental database recorded at the room temperature. Their validity of these parameters at a low ambient temperature requires further validation for enhanced fatigue assessment of welded components in steel bridges.…”