Abstract. Stress-strain tests at constant strain rate were carried out with an Instron TM tester to evaluate the effects of single-edge razor notches and orientation on the ultimate mechanical properties of a LDPE blown film. Introduction of small notches of a length c₀ = 0.l - 1.0 mm reduces the strain-at-break dramatically, and reverses the order of ε_b values in the machine and cross direction. Such a behaviour qualitatively resembles that observed in the creep rupture experiment, and has also been explained by assuming that the film contains a system of intrinsic flaws of elongated shape aligned along the machine direction of the film and interfering with the propagating main crack. Irradiation of the film with UV light induces anisotropic embrittlement, remarkably similar to the effect of the macroscopic notch. An anomalous maximum observed with notched specimens on the time-to-break vs stress curve in the creep rupture experiment has no analogy in the tests at constant strain rate since in this latter case the experimental time scale is determined by an independently variable strain rate, and the stress-lime relationship is therefore necessarily expressed as an one-to-one mapping.

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