Fracture mechanisms and failure modes in biocomposites and bionanocomposites

There are various mechanisms that can be responsible for material fracture which can ultimately lead to failure and there are different modes of failure. More often, the quantification of the dominating failure mode and the attendant prevailing fracture mechanism is an arduous task, even though this is of significant importance for the purposes of design. The deformation of a material can lead to any of three fracture mechanisms, which include: (a) elastic, leading to linear-elastic fracture mechanisms, (b) plastic, leading to elastic-plastic fracture mechanisms and (c) viscoelastic/visco-plastic, leading to creep fracture mechanisms. Failure behaviour of a material can be of three types, viz. (i) ductile, which can lead to either shear or dimple fracture, (ii) brittle which can lead to a cleavage fracture or a rupture and (iii) creep, which can lead to a creepfracture or normal/shear fracture. For fracture to occur, there must be some sort of material loading. Loading can be in the form of: (1) cyclic, leading to fatigue fracture, (2) static, leading to forced fracture, (3) dynamic, leading to fast fracture and (4) chemical, leading to stress corrosion cracking or fatigue corrosion cracking. These mechanisms and the different modes of fracture shall be discussed, in particular, for biocomposites and bionanocomposites, as these parameters (type of fracture mechanism, type of failure and type of loading) and, of course, the design protocols collectively determine the eventual performance of any material.