1993 Volume 42 Issue 475 Pages 384-390
The effects of frequency and temperature on the delamination crack growth under cyclic loading were investigated with unidirectional CF/epoxy laminates. Tests were conducted at room temperature, 50°C, and 80°C in air with double cantilever beam (DCB) specimens.
At room temperature, the growth rate in terms of number of cycles, da/dN, was given by a power function of the stress intensity range, ΔK, when da/dN was larger than 5×10-9(m/cycle). The relation was almost independent of the loading frequency.
At 50°C and 80°C, the growth rate in terms of number of cycles, da/dN, was given by a power function of the stress intensity range, ΔK, when da/dN was larger than 5×10-11(m/cycle). When compared at the same value of ΔK, the growth rate, da/dN, was higher for higher temperature and for lower frequency. However, the growth rate expressed in terms of time, da/dt, was found to be controlled by the maximum stress intensity factor, Kmax, independent of the loading frequency at the same temperature, i.e., the delamination crack was considered to have grown by time dependent mechanisms under cyclic loading.
The da/dt-Kmax relation also depended on temperature. For higher temperature, the growth rate, da/dt, was higher at the same value of Kmax.