In situ observation of microscopic damage and crack initiation mechanisms in a filled EPDM

The paper presents a precise 3D quantification of damage evolution and eventual crack initiation due to metallic oxide particles and filler agglomerates in a peroxide crosslinked filled EPDM during uniaxial solicitation, thanks to synchrotron radiation X-ray Tomography. An in-situ tensile study using this technique reveals polymer debonding at the poles of all metallic oxide particles upon stretching. The cavities caused by this decohesion do not lead to crack initiation since they grow parallel to the applied stress direction. Conversely, crack always initiates from carbon black agglomerates (CBaggl). The crack initiation mechanism is a three step process that begins with the nucleation of cavities inside the CBaggl upon stretching. This is followed by the growth of these cavities which brings about the fracture of the agglomerates. Finally, this fracture can lead to the creation of a matrix crack at the origin of the material rupture. It is also confirmed that CBaggl that initiate the critical crack in the material are the biggest sized CBaggl and are located close to the edges of the sample.