Fatigue crack growth rate of brazed joint

Fatigue crack propagates accompanying a small scale yielding at the crack tip. A fatigue crack growth rate in a filler metal between base metals of brazed joint depends probably on the degree of restraint of base metals to crack tip plastic deformation. The degree of restraint to crack tip plastic deformation by base metals depends on the thickness and the yield strength of filler metal in joint gap and stress intensity factor. Under a shear stress, crack tip plastic deformation is restrained by base metals when width of joint gap is smaller than a certain scale, and fatigue life of joint becomes longer. Under a tensile stress, base metals do not restrain a crack tip plastic deformation. Some experimental results of measuring fatigue crack growth rate in the filler metal of steel butt joint brazed with pure copper showed good agreement with the theoretical assumptions.