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Tool mark identification relies on the premise that microscopic imperfections on a tool's working surface are sufficiently unique and faithfully transferred to enable a one-to-one association between a tool and the tool marks it creates. This paper presents a study undertaken to assess the validity of this premise. As part of this study sets of striated tool marks were created under different conditions and on different media. The topography of these tool marks was acquired and the degree of similarity between them was quantified using well-defined metrics. An analysis of the resulting matching and nonmatching similarity distributions shows nearly error-free identification under most conditions. These results provide substantial support for the validity of the premise of tool mark identification. Because the approach taken in this study relies on a quantifiable similarity metric, the results have greater repeatability and objectivity than those obtained using less precise measures of similarity.

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SynopsisStudies on impact and tensile properties of binary blend of PP and ABS and ternary blend of PP, ABS, and LDPE are presented. Variation of impact strength and the fracture surface morphology with blend composition is examined and interpreted. Tensile behavior in the yield region is studied and the trends of variation of work of yield and impact strength are compared to ascertain the predominent mechanism of impact toughening in these binary and ternary blends. An analysis of yield-stress data in terms of theoretical models is presented to reveal the differences in these binary and ternary blends, attributable to the role of LDPE component in the ternary blend. INTRODUCTIONStudies on blends of polypropylene (PP) with acrylonitrile-butadienestyrene terpolymer (ABS) are mostly confined to patents and quite rarely to the published literature. The paper by Markin and Williams' is apparently a pioneering one on PP/ABS blend. We have carried out studies on PP/ABS binary blend and a corresponding ternary blend with LDPE (low-density polyethylene) as the third component. In the first part2 of this work, we reported rheological properties in molten state of these binary and ternary blends.In this second part of the work, we present studies on impact and tensile properties of the same binary and ternary blends of PP, ABS and LDPE. Variations of impact strength as function of blend composition, mode of fracture by scanning electron microscopy, and tensile yield behavior as a function of blend composition are studied, and the results are analyzed and interpreted to explain the role of structure and morphology in the properties. EXPERIMENTAL Mat4?rialSCommercial injection molding grade polymers, PP (Koylene-M3030, melt flow index 3.0) and LDPE (Indothene-22FA 002, melt flow index 0. Blend PreparationBlends were prepared by melt mixing in Betol BM-1820 single screw extruder keeping 205,210, and 215OC as temperatures of the three zones and 40 rpm screw speed. For the case of the ternary blends, blending was done in two steps: (i) a 50:50 blend of ABS and LDPE was prepared and granulated; (ii) this ABS/LDPE blend was then mixed with PP in varying proportions to obtain the ternary blend PP/(ABS/LDPE). MeasurementsIzod impact strength of notched samples was measured in accordance with ASTM D 256 test procedure, on a FIE (Model IT-0.42) impact tester. Injection-molded specimens of dimensions 5 X 1.1 X 0.6 cm with triangular notch of 45O angle and 3 mm depth were used. Ten samples for each composition of the blend were tested.Tensile tests were carried out on an Instron universal testing machine (Model 1121) using dumbbell-shaped injection-molded specimens in accordance with ASTM D 638. Testing was done at a crosshead separation speed of 20 mm/min for an initial gauge length of 50 mm. At least five samples for each composition were tested.Electron micrographs of impact fractured surfaces were recorded on a Cambridge Instruments (Model S4-10) scanning electron microscope. RESULTS AND DISCUSSION Impact Properties Binary BkndNot...