Nuclear graphite, usually used as a moderator in the reactor core, is a typical quasi-brittle material. It is multi-phase, aggregated and porous. During service, neutron irradiation and radiolytic oxidation causes weight loss and increased porosity. Virgin and irradiated, graphite have a non-linear stress-strain response because of distributed damage and damage accumulation prior to rupture. There is no evidence that these graphites can be plastically deformed. Hence, changes in compliance, together with any deviation from an initial linear load-displacement curve are attributed to micro-cracking This proposal use a model graphite to (i) examine the change of lattice strain with externally applied load in a high porosity quasi-brittle material and (ii) extend the understanding of quasi-brittle fracture and structural instability combined with the previous neutron diffraction results.