Abstract
The testing methods of characterizing the impact behavior of film materials can be classified into two types; the uniaxial tensile impact tests and those multiaxial. The former are of theoretical interest on account of their analytical simplicity, but are often open to question regarding their practical use. The conventional standard tests which fall on the latter category, on the other hand, are widely used because of their good correspondence to the actual impact situations encountered, yet very few results of their analytical studies have so far been announced.
In this paper the authors report a newly designed impact test of more practical significance, and propose some approaches to the analysis of the experimental data.
The feature of this apparatus is that the films are tested by allowing a membrance-shaped specimen attached to the ram to fall on the semispherically edged mandrel, and thereby to be pierced and fractured, and that the load-deflection curves can be provided by the synchroscope through the load-cell connected to the mandrel.
In an attempt to determine the impact characteristics from the diagrams obtained, the authors set up two approximate expressions for the stresses from the different standpoints, by which the ultimate impact strengths were calculated; one deduced from the deflection pattern and the other on the analogy of the thin plate with large deflection problem in the theory of elasticity.
The static penetration tests with the same jig and the static tensile tests on an Instron type tester were also conducted to compare the applicability of the two equations above mentioned.
The results show that, for the film materials such as polyethylene and polypropylene which show large ultimate elongation, the stress equation based on the scheme provides a good basis for the analysis, while to polystylene and cellophane which exhibit only little elongation at break, the stress equation based on the elastic membrane analogy can be applied more successfully.
