Testing film puncture resistance

Figure 8,10 illustrates the general configuration for testing a film s puncture resistance. We can perform this test in a number of ways. The probe may be attached to the crosshead of a universal testing machine, similar to the one illustrated in Fig. 8.3. We drive the probe down through the film at a constant speed, while recording the force. Alternatively, we can perform an impact puncture test, in a similar fashion to impact plaque testing.

A free-falling dart method for polyethylene films is described in ASTM D1709. Unlike low-speed uniaxial tensile tests, the pendulum impact test measures the resistance of film to impact puncture, simulating high-speed end use application. Dart drop measures the energy lost by a moderate velocity blunt impact passing through... 

Puncture resistance of the thermoformed cavities can be characterized in two locations, bottom and comer. The cavity bottom is the center of the tray. The comer is the one opposite of the peel tab. To maintain consistent test geometry with flat film, the formed cavity is mounted and secured on mandrel. The mandrel is moimded on a fixture in such a way to present the outer smface of the comer perpendicular to the puncture probe. 

ISO 7765-2, Plastics film and sheeting - Determination of impact resistance by the free-falling dart method - Part 2 Instrumented puncture test, 1994. 

ISO 7765-2 1994. Plastics Film and Sheeting - Determination of Impact Resistance by the Free-Falling Dart Method - Part 2 Instrumented Puncture Test. 

ASTM D3420 Standard Test Method for Pendulum Impact Resistance of Plastic Film. Used to determine the resistance of film to impact-puncture penetration at ambient conditions. Also called Spencer Impact. 

In many film applications the product is subjected to puncture or impact loads. These types of loads are applied perpendicular to the plane of the film. Therefore, the stresses act biaxially (in both the machine and transverse directions simultaneously) and are not represented well by a uniaxial test. Impact resistance tests are designed to biaxially load the film to measure its energy absorbing capability. 

---