ЭКСПЕРИМЕНТАЛЬНАЯ И РАСЧЕТНАЯ ОЦЕНКА КРАТКОВРЕМЕННОЙ ПРОЧНОСТИ ОБРАЗЦОВ ИЗ ПЛАСТИЧНОГО МАТЕРИАЛА С U- И V-ОБРАЗНЫМИ ОСТРЫМИ НАДРЕЗАМИ

Abstract

In this work, the experimental and calculation studies of the short-time strength of tensile rods made of a plastic material with U- and V-shape sharp notches were made. Thermoplastic-acryl-butadiene-styrene (ABS) was chosen as the model material. Samples with a diameter of about 5 mm were obtained on a single-screw extruder by melting granules. In the first part of the paper, the dependence of the mechanical properties of ABS in a wide range of quasi-static strain rates (0.02 ... 10 min-1) was studied. With these conditions, under single-step loading, this material can be considered as an elastoplastic one with an elastic modulus of 2200 MPa, with the yield strength of about 41 MPa and independent of the given strain rates with an error of less than 5 %. For the tested smooth samples, the residual longitudinal strain at rupture was 15 ... 25 %, the residual decreasing of a cross-section (necking) was 30 ... 50 %. The next group of samples had U-notches with a radius of 1.6 mm. The angle of sharp V-notches was 60°. The depth of the single-sided notches was varied in the range of 0 ... 3.5 mm. It is obtained that the ultimate load held by the samples with V-notches exceeds the corresponding load of the samples with U-notches of the same depth due to a greater constraint of the plastic strains in a notch zone. Notches up to 1 mm depth practically do not reduce the ultimate load of the samples. In the second part of the work, with the help of the FEM, the elastic-plastic deformation and fracture kinetics were calculated using a non-local approach, an explicit integration scheme in the ANSYS Workbench package. The calculations showed that the ultimate load is determined only by the yield strength of the material and the configuration of the notch. Rupture of samples (in ANSYS this is the technology of removing critically deformed finite elements) occurred at lower loads, depending on the plasticity resource of the material and the configuration of the notch. The calculated values of the ultimate and rupture loads are in a good agreement with the experimental data. The technique can be recommended for evaluating the strength of complex shape samples of plastic materials with arbitrary stress concentrators.