It is now well established that for non-associated materials such as granular geomaterials, a broad domain exists, strictly within the plastic limit, where failure can occur. Considering that failure corresponds to a brutal increase in kinetic energy with no change in the loading parameters, the vanishing of the second-order work , defined on the macroscopic scale from tensorial variables, is shown to play a fundamental role in detecting the occurrence of mechanisms. Then, we enlarge the debate by addressing this question from a micro-mechanical point of view. By considering that each contact between adjoining particles can be regarded as the fundamental constitutive unit of a grain assembly, the standard macroscopic second-order work defined from tensorial variables was established to coincide with the sum of the microscopic second-order works defined on each contact with respect to a suitable frame. The microscopic second-order work can be computed at each contact from discrete variables such as both incremental relative displacement and contact force. The microscopic critical conditions, that govern the vanishing of the microscopic second-order work, are finally derived. These conditions embed the influence of the microstructure of the material, and provide some important information about how the microstructure evolves over failure mechanisms.