Relationship between Crack Velocity and Fracture Surface Marks in a Sheet Specimen of UP and PMMA : Results of the Large Size Specimen Having a Central Crack

We have reported that both-ends-closed marks (BECM) like an ellipse and one-end-opened marks (OEOM) like a parabola or a hyperbola are observed in a fracture surface of unsaturated polyester (UP) resin. The total number of them and the competition of their densities in a specimen change with fracture strength, crack velocity and a primary crack length introduced. We have also reported that fracture surface marks observed in a polymethyl methacryate (PMMA) specimen are mostly one-end-opened marks and the total number in a specimen is controlled by fracture strength, crack velocity and a primary crack length introduced. Here, we compared the both results in UP and PMMA where the specimen design and dimensions are exactly same. In both cases the cracks are shown to propagate in three different conditions of a constant stress, a mixed and a constant strain and fracture strength decreases with an increase of the central primary crack length. It is discussed if the number of marks are mainly controlled by fracture strength of a specimen or by the mean crack velocity of it.