Impact resistance or impact failure load of plastic films is defined as the weight of a hemispherical shaped dart, falling on the film held in a suitable clamp from a specified height, which causes failure of 50% of specimens tested.

The Dart Impact Tester for plastic films consists of a vacuum clamp of specified shape and size on which the specimen can be supported at its periphery in a horizontal plane, a dart with incremental weights, a vacuum pump with electric motor to provide the vacuum needed for holding the test specimen, and a clamping ring for holding thicker films during the test.

The dart used for striking the film under test has a hemispherical head of 38.1 mm diameter made of fiber reinforced bakelite and an aluminium shaft with mild steel tip for suspending it from an electromagnet. A set of annular shaped stainless steel weights is provided for changing the total mass of the dart for giving different impact energies. A foam padding is placed inside the clamp to avoid damage to the dart head if it passes through the test specimen.

The electromagnet for holding and releasing the dart is fixed on a bracket vertically above the centre of the clamp. An arrangement for fixing the bracket at three different locations to give the desired dropping heights is also provided.

The equipment is built on a rigid steel frame and is finished in shore blue matalic painting and bright chrome plating to give it a corrosion resistant finish.

Technical Specifications

Inside diameter of clamp	127 mm
Diameter of dart head	38.1 mm
Dimensions of dart shaft	6.4 mm diameter x 115 mm long with 12.7 mm long mild steel tip
Material of dard head	Fabric reinforced bakelite
Weight of dart with locking collar	50 g
Incremental weights	5 g - 5 of, 15 g - 24 of
Dropping heights	220 mm, 660 mm and 1524 mm
Related Standards
IS 2508 - 1984	Specifications for Low Density Polythelene Films
IS 10889 - 1984	Specification for High Density Polythylene Films
BS 2782 - 1970	Methods for Testing Plastics M ethod 306 F: Impact Resistance of Flexible Films by Falling Dart