Starting from an initial state with negligible stress, the evolution of the stress map calculated from large fluorescence maps (Fig. ) shows, the tensile stress field that develops around the crack tip as applied force increases (Fig. ). Tensile stresses are detected while the sample is still in the elastic domain, and well before the crack initiation. The stress field is asymmetric with the side at higher stress (left of the notch in Figure ) eventually fracturing with a crack initiating at about 70° of the notch plane for an applied force of 110 N. Before the crack can be observed at the surface of the sample, the area under tension remains constant and does not increase in size, only the value of the calculated stress increases with the loading force to exceed locally 300 MPa. While the crack extends, the tip of the uncracked ligament is subjected to important tensile stresses, with average values up to 250 MPa. The tensile nature of the stress field generated at the bottom of the notch is coherent with the SENB configuration At an applied force of 110 N, the first high-resolution image recorded (Fig. ) shows a stress accumulation pinned on a mechanical asperity along the crack (point 1). The force was increased to 114 N, and the sample was then maintained at a constant force for several hours. High-resolution maps display the evolution of the stress field, which highlight mechanical asperity effects during subcritical crack propagation. The crack first propagated towards a second mechanical asperity (point 2)