ABSTRACT
With the scientific advances of the last few decades in the field of material mechanics, it has been realized that the classical concept of strength, understood as force per unit surface causing fracture, is in need of revision, especially in cases where particularly large or particularly small structures are involved. That is, the strength of the material must be compared against another characteristic, the toughness of the material, to define, via the dimension of the structure, the ductility or the brittleness of the structure itself. Two intrinsic characteristics of the material, plus a geometrical characteristic of the structure, are, in fact, the minimum basis for being able to predict the type of structural response. The fracture energy, GIC, is one of the parameters capable of measuring the toughness of the material. Through it, we will describe how the structural response to uniaxial tension varies as GIC and/or the length of a bar longitudinally subjected to tension varies. In that case, a tendency emerges toward ductile behavior in the case of short lengths of the bar and, on the other hand, a tendency toward brittle behavior (snap-back) in the case of greater bar lengths. This tendency will also be encountered in the case of two-and three-dimensional solids, in such a way as to associate ductile behavior with relatively small solids, and brittle behavior with relatively large solids. Just as in structures acted on prevalently by a compressive force (Figure 7.11), there is a transition from plastic collapse to buckling instability as slenderness increases, so in structures acted on prevalently by a tensile force, there is a transition from plastic collapse to brittle fracture as the size scale increases.
