Energy release rate of beam-type fracture specimens with hygrothermal influence

Three interface joint models for calculating energy release rate are extended to include hygrothermal effect with consideration of uniform or nonuniform changes of temperature or moisture through layer thickness in a cracked bilayer beam system using both J-integral and correction methods. The method of J-integral leads to a general expression of total energy release rate in terms of the crack-tip moments and forces, while the correction method gives explicit formulas of total energy release rate with inclusion of a separate energy release rate term subjected to only mechanical loads. Several bilayer beam fracture specimens subjected to transverse load or equivalent bending moment and thermal load are considered to validate accuracy of two methods in connection with three interface joint models, and the results show that the flexible joint model produces the best predictions for all the specimens. A parameter study is conducted to evaluate influences of thickness ratio, modulus ratio of upper and lower layers, change of temperature, and temperature gradient on the energy release rate. All the factors show a pronounced influence on the energy release rate, and a special attention is paid to evaluate effect of temperature change and temperature gradient on the energy release rate of bilayer beams. The moisture change and its gradient have the same effect and formulations on the energy release rate of bilayer beams as those of temperature, and the moisture portion of derivations and its effect are thus not given in detail.