High-rate J-testing of toughened polyamide 6/6: Applicability of the load separation criterion and the normalization method

This paper examines the applicability of the load separation criterion and the normalization method in determining JR curve of a toughened polyamide 6/6 at high loading rates (1 m/s). The analysis of procedure problems associated to this high experimental rate is performed. The results obtained using the normalization method are then compared with those measured via multi-specimen testing procedures proposed by ESIS (Technical Committee 4). The results show that, unlike low loading rate tests, the presence of the oscillations in the load vs displacement traces, due to the inertial effects produced during the impact, complicate considerably the elaboration of the data, with particular reference to the identification of the separable blunting region. The comparison of JIc values obtained according to the different procedures examined indicates that the values of JIc = J0.2 (taken at 0.2 mm crack growth) are in good agreement, whereas consistent differences among the values of JIc = J-blunting (taken at the blunting line) are observed

DSC analysis of post-yield deformed PBT. Effects of thermal history

The effect of the deformation temperature on the energy stored in post-yield deformed poly(butylene terephthalate) PBT, was studied by means of DSC tests. Deformed specimens were rapidly cooled after unloading, in order to avoid the energy relaxation processes occurring before the DSC measurements. Cooling revealed to have a significant contribution on the whole stored energy, as shown by DSC tests conducted on undeformed PBT specimens conditioned at various temperatures. This work is aimed at separating the effects due to cooling and those ascribed to deformation on the energy storage and release processes, permitting to better understand previous findings on post-yield compressed PBT

Mechanical and structural characterization of POSS-modified polyamide 6

This work investigated the mechanical behavior of POSS-modified polyamide 6 (PA6), containing PA6 chains terminated at one end with aminopropyl-heptaisobutyl POSS. Three systems with different POSS contents (5.4, 10.8, and 16.2 wt %), each characterized by a specific molecular mass, and the corresponding PA6 neat polymers were examined. The materials were first subjected to morphological and calorimetric analysis by wide-angle X-ray diffraction and differential scanning calorimetry, respectively. Tensile tests, performed on the samples in wet conditions, showed that stiffness, strength, and ductility were appreciably modified by the presence of POSS in the polymeric chains. The relationships among these effects and the microstructural characteristics of the systems also were analyzed

On the determination of the point of fracture initiation by the load separation criterion in J-testing of ductile polymers

The application of an experimental approach based on the load separation criterion for the determination of the point of fracture initiation in a fracture test on a ductile polymer was critically examined. To this aim, the fracture process outlined by the application of this method was related to that described by the visual analysis of the fracture surfaces obtained in fracture tests on nominally identical specimens, in which different levels of crack extension were produced. The material examined was an acrylonitrile-butadiene-styrene (ABS) resin, and the fracture tests were performed at low loading rate on single-edge notched in bending specimens. The results demonstrated that this load separation criterion based methodology is a promising approach for the determination of the point of fracture initiation, and for material fracture resistance, JIc, evaluation. The method also has experimental simplicity and a high degree of repeatability