Fatigue Crack Growth Rate of Brazed Joint

Abstract

It is well known that fatigue crack propergates accompanying a small scale yielding at the crack tip. In filler metal between base metals of brazed joint, fatigue crack growth rate depends possively on the degree of restraint of crack tip plastic deformation by base metals, because the width of crack tip plastic deformation zone is nearly the same with the width of joint gap and crack tip plastic deformation can be restrained by base metals.
The theoretical discussions on correlation of crack tip plastic deformation and base metals revealed;
1) The degree of restraint of crack tip plastic deformation by base metals depends on yield strength of filler metal in joint gap, stress intencity factor and joint gap.
2) Under shear stress, crack tip deformation is restrained when joint gap is smaller than a certain scale, and fatigue life of joint becomes longer.
3) Under tensile stress, base metals do not restrain a crack tip plastic deformation, and fatigue crack growth rate depends on stress concentration factor range which becomes greater with the width of joint gap.
Some experiments on fatigue crack propergation rate in copper filler metal of steel butt joint showed good agreement with the theoretical assumptions.