The RVE is here defined as the smallest material volume whose failure suffices to make the whole structure fail. From experience, the structure is sufficiently larger than one RVE if the equivalent number N e q of RVEs in the structure is larger than about 10 4 ; N e q = ( D / l 0 ) n d Ψ Ψ = number of RVEs giving the same P f if the stress field is homogeneous (always N e q < N , and usually N e q ≪ ≪ N ). For most normal-scale applications to metals and fine-grained ceramics, except for micrometer scale devices, the size is large enough for the Weibull theory to apply (but not for coarse-grained materials such as concrete).