Numerical and Experimental Results on Charpy Tests for Blends Polypropylene + Polyamide + Ethylene Propylene Diene Monomer (PP + PA + EPDM)

Abstract

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP + PA6 + EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s and its mass of 3.219 kg and these data were also introduced in the finite element model. The proposed model takes into account the system of four balls, including support and the ring of fixing the three balls and it has a finer discretization of the impact area to highlight the mechanisms of failure and their development in time. The constitutive models for four materials (polypropylene with 1% Kritilen, two blends PP + PA6 + EPDM and a blend PA6 + EPDM) were derived from tensile tests. Running simulations for each constitutive model of material makes possible to differentiate the destruction mechanisms according to the material introduced in the simulation, including the initiation and the development of the crack(s), based on equivalent plastic strain at break (EPS) for each material. The validation of the model and the simulation results were done qualitatively, analyzing the shape of broken surfaces and comparing them to SEM images and quantitatively by comparing the impact duration, energy absorbed by the sample, the value of maximum force during impact. The duration of the destruction of the specimen is longer than the actual one, explainable by the fact that the material model does not take into account the influence of the material deformation speed in Charpy test, the model being designed with the help of tests done at 0.016 m/s (1000 mm/min) (maximum strain rate for the tensile tests). Experimental results are encouraging for recommending the blends 20% PP + 42% PA6 + 28% EPDM and 60% PA6 + 40% EPDM as materials for impact protection at low velocity (1 m/s). Simulation results are closer to the experimental ones for the more brittle tested materials (with less content of PA6 and EPDM) and more distanced for the more ductile materials (with higher content of PA6 and EPDM).

Mechanical Characterization of Two Blends PP+PA6+EPDM. Part 2. Results of Tensile Tests

“…To reduce the sensitivity of polyamide to crack initiation and its development on low velocity impact, the polymer is mixed with 10-25% elastomer (including EDPM that was used for these two original recipes) [50].…”

“…The first two materials have brittle fractures, with fractured, rough surfaces and the other two have visible necking and local material yielding. The aspect of material failure was also kept for Charpy tests [50], brittle for materials PP and H and ductile for materials G and PA6.…”

“…10 mm/min 250 mm/min 1000 mm/min order for all rates (250...1000 mm/min): H, PP, PA6, G. Material G, as developed in [26], [60], [50] have promising results as moderate impact-resistant material. The tensile strength at break shows a tendency to increase the average values with the increase of polyamide concentration, but yet simple polyamide has the highest average values of the tensile strength at break.…”