T
his paper examines t
he mode-mixity of stress-intensity factors for surface cracks located near weld toes of t
he crown point at t
he toe of t
he tension brace in circular
hollow section K-joints under different c
hord/brace end constraints. T
he remote loading applies a uniform stress at t
he end of t
he brace along its axis. T
he 3-D finite element models employ mes
h-tieing between a topologically continuous, global mes
h and a separate, local crack-front mes
h. T
he linear-elastic analyses compute t
he mixed-mode stress-intensity factors along t
he crack front using an interaction-integral approac
h. T
he analyses for t
hree different crack locations along t
he brace–c
hord intersection demonstrate t
hat t
he critical location for t
he surface flaw lies at t
he crown point of t
he brace toe. T
he numerical investigation of six different boundary conditions indicate t
hat t
he unbalanced loading conditions cause significant bending stresses in t
he c
hord and generate a considerably larger mode I stress-intensity factor t
han found for t
he balanced loading case. T
he mixed-mode stress-intensity factors indicate t
hat t
he crack front experiences predominantly mode I loading, wit
h KIII → 0 near t
he deepest point on t
he front (
= π/2). T
he non-dimensional, mode I crack driving force, described by
, reaches a maximum value at the deepest point of the crack for the crack aspect ratio a/c = 0.25 considered here. The mode-mixity angle, ψ = tan−1(KII/KI), at = π/2 is compared for a range of practical K-joint configurations. The present study demonstrates that the mode-mixity angle ψ becomes significantly larger in the balanced loading conditions than in the unbalanced loading condition. Values of the non-dimensional stress-intensity factors ( and ), however, decrease for the balanced loading condition. Variations in the brace-to-chord diameter ratio (β) and chord radius to wall thickness ratio (γ) generate significant changes in the mode mixity. Thin-walled joints (γ = 20) generally experience a larger crack driving force with a higher mode-mixity angle.