Stress intensity factors for cracked homogeneous and composite multi-channel beams

The homogeneous and composite multi-channel beams are a typical three-dimensional infinite boundary problem. For the cracks in such structures, a very simple method to determine the stress intensity factors has been proposed by using a new concept of the crack surface widening energy release rate and the principle of virtual work. This kind of the energy release rate can be defined by the curved surface integral and the work done by the external loads. From the present discussions a series of the stress intensity factors are derived for the channel and multi-channel beams. Additionally, the stress intensity factor for the cracked T beam can be evolved from the present results for multi-channel beams.