Falling dart impact strength testing

Other impact strength tests that use gravity are the Gardner impact and Falling Dart tests. These are described in the following standards ... 

Methods employed to determine the impact resistance of plastics include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either with the specimen notched or unnotched). The tensile impact test has a bar loaded in tension and the striking force tends to elongate the bar (Chapter 5, Impact Strength). 

Impact Resistance of Plastic Film by the Free-Falling Dart Method. Primary Film Test Method ASTM D1709 Additional Test Method ISO 7765-1. A weighted dart is dropped from a standard height onto a taut sample. Depending upon the expected impact strength of the test sample, either method A or method B is chosen. The method defines the dart size and the drop height for the dart. Test method A specifies a dart with a 38 mm diameter dropped from 0.66 m. Test method B specifies a dart with a 51 mm diameter dropped from 1.5 m. 

Fig. 1.31. The energy required for rupture and the impact strength (as measured by the falling-dart test) shown as functions of composition for bimodal PDMS networks in the vicinity of room temperature [129].

A problem associated with impact strength determination is that standard methods in use (notched Izod, falling weight, and dart impact tests) often have poor correlation. It would be of interest to develop DMA procedures to simulate field service impact situations. 

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