Effects of tensile and compressive stresses on damage evolution law of nuclear graphite

Nuclear graphite, a quasi-brittle material containing microdefects, is essential for constructing the neutron moderators, reflectors, and cores in very-high-temperature gas-cooled reactors. Such reactors are prone to damage during loading, resulting in the failure of nuclear graphite materials or structures and possibly affecting the integrity of the entire core structure. Therefore, the damage evolution law of nuclear graphite should be studied while assessing the safety of the core. In addition, considering the different mechanical characteristics of quasi-brittle materials under tensile and compressive stresses as well as the complex stress states of quasi-brittle nuclear graphite structures in the core, the effects of stress states on the damage evolution law of nuclear graphite should be unveiled. These aspects are difficult to evaluate owing to the complexity of damage characterisation and measurement throughout the test loading of nuclear graphite under different stress states. Therefore, we propose damage measurement tests of nuclear graphite under unidirectional tensile and compressive stress states based on digital image correlation to obtain damage evolution laws under different stress states. By analysing the effects of different stress states on the damage evolution laws of nuclear graphite, we found that the damage properties under unidirectional tensile and compressive stresses show variations and that damage more likely occurs under tensile stress.