TY - THES

T1 - Examination of J-Integral methods and their applicability to tough polypropylene materials

AU - Gosch, Anja

N1 - embargoed until null

PY - 2017

Y1 - 2017

N2 - To characterize the fracuture behaviour of a non linear elastic plastic material, it is common to describe the fracture process with the help of the crack resistance curve.The J-integral represents the difference in potential energy in a linear or nonlinear elastic material, with an infinitesimal difference in crack length. Applying the J-Integral to materials which show elastic plastic deformation behaviour requires some preconditions. Hence, several experimental methods exist to determine the crack resistance curve of said non-linear elastic plastic materials. In this study the focus is on the diffculties concerning the application of the load separation method to characterize commercial polymers. Therefore, three different types of polypropylene (PP-H, PP-R and PP-B) were tested. For the characterization of crack resistance the load separation method was used and compared to the more common multi-specimen method. The strong influence of the chosen elastic compliance correction to determine the plastic displacement was examined in detail, since it showed major influence to the load separation curve in the first region (at small plastic displacements/ ”unseparable region”) and the plateau region (almost constant values of the load separation parameter Spb/ blunting). In the last region (fracture propagation) all curves show nearly the same slope ms, regardless of chosen elastic compliance correction. This points toward a key role of the slope ms to indicate the crack advancement produced per unit of plastic displacement in a fracture process, as found in literature. For comparison multi-specimen tests according to ESIS TC 4 were performed and found to be in the same region as results from the load separation method, for the compliance correction chosen in this work. However, exact determination of crack advancement proved to be dicult, as expected.

AB - To characterize the fracuture behaviour of a non linear elastic plastic material, it is common to describe the fracture process with the help of the crack resistance curve.The J-integral represents the difference in potential energy in a linear or nonlinear elastic material, with an infinitesimal difference in crack length. Applying the J-Integral to materials which show elastic plastic deformation behaviour requires some preconditions. Hence, several experimental methods exist to determine the crack resistance curve of said non-linear elastic plastic materials. In this study the focus is on the diffculties concerning the application of the load separation method to characterize commercial polymers. Therefore, three different types of polypropylene (PP-H, PP-R and PP-B) were tested. For the characterization of crack resistance the load separation method was used and compared to the more common multi-specimen method. The strong influence of the chosen elastic compliance correction to determine the plastic displacement was examined in detail, since it showed major influence to the load separation curve in the first region (at small plastic displacements/ ”unseparable region”) and the plateau region (almost constant values of the load separation parameter Spb/ blunting). In the last region (fracture propagation) all curves show nearly the same slope ms, regardless of chosen elastic compliance correction. This points toward a key role of the slope ms to indicate the crack advancement produced per unit of plastic displacement in a fracture process, as found in literature. For comparison multi-specimen tests according to ESIS TC 4 were performed and found to be in the same region as results from the load separation method, for the compliance correction chosen in this work. However, exact determination of crack advancement proved to be dicult, as expected.

KW - J-Integral

KW - Polypropylene

KW - nicht-linear elastisch plastische Bruchmechanik

KW - j-integral

KW - load separation method

KW - multi-specimen method

KW - J-R-curve

KW - polypropylene

M3 - Master's Thesis

ER -