Showing papers by "Alan J. Lesser published in 2005"

Effect of test conditions on the essential work of fracture in polyethylene terephthalate film

Abstract: The tear resistance of polyethylene terephthalate film is characterized by the essential work of fracture method in mode I as a function of test speed and temperature. Attempts to extrapolate tearing resistance found by the method of essential work to commercial slitting processes are discussed. Limitations of the essential work of fracture method with regards to specimen size are evaluated. Based on the findings modifications to the test protocol are suggested.

Structural Changes at Different Length Scales Caused by Mechanical Deformation of SEBS Triblock Copolymers

Abstract: A Kraton® poly (styrene-ethylene/butylene-styrene) (SEBS) Triblock copolymer, with hexagonally packed PS cylinders embedded within the Poly (ethylene/butylene) (E/B) matrix, has been studied using simultaneous small- and wide-angle X-ray diffraction (SAXD/WAXD) as a function of mechanical deformation. SAXD studies on unstrained samples not only show a series of concentric diffraction rings, that index as the successive orders of a two-dimensional hexagonal lattice of side a ≈ 30 nm, but also indicate the presence of a broader, more diffuse, diffraction ring of a different character centered at a spacing of 7.8 nm. At 65% strain, a four-point X-cross pattern develops and emerges from the {1010} diffraction ring for the unstrained sample. The fundamental spacing of the hexagonal lattice increases, and in addition the first evidence of discrete layer lines appears, orthogonal to the strain direction (SD). At higher strains, both the layer line spacing and the angle of the X-cross, relative to the SD, increase. These changes in layer line spacing as a function of strain provide additional insight into the extent of deformation imposed on the flexible matrix with shearing of PS cylinders layers relative to each other. Also, with increasing strain, the diffuse 7.8 nm diffraction signal transforms into a streak, parallel to the SD and centered on a reciprocal plane orthogonal to the SD. In the simultaneously recorded WAXD (4 nm-0.2 nm) patterns, an initial single diffraction ring observed at no strain, steadily transforms with strain into a symmetric pair of concentrated arcs centered on the equator. These X-ray diffraction results enable a delineation to be made between rotation and relative shear of layers of PS rods and the simultaneous strain-induced crystallization of the flexible matrix.