Polypropylene Copolymer versus Homopolymer Impact Resistance
Impact copolymers deliver superior notched and subzero impact resistance over homopolymers by incorporating a dispersed ethylene-propylene rubber phase.
Instrumented Drop Weight Impact
Meaning
Dynamic measurement of a material resistance to a falling striker provides a detailed profile of the force and energy during a puncture event. Using an instrumented drop weight impact test allows for the capture of real time data that simple pendulum tests cannot provide. The system records the entire strike from the first touch to the final failure of the plaque.
This analysis is restricted to rigid or semi rigid materials that can be held in a clamping fixture.
Data Acquisition
Integration of a load cell and an optical encoder into the striker assembly enables the recording of high speed events. Since the instrumented drop weight impact method generates a complete curve, engineers can see the exact moment when a crack initiates. These sensors must be calibrated frequently to maintain accuracy.
High frequency sampling ensures that no part of the impact is missed.
Fracture Analysis
Examination of the resulting graph identifies the peak force and the energy absorbed at different stages of deformation. While a standard test gives only the total energy, an instrumented drop weight impact distinguishes between the force needed to start a crack and the force needed to propagate it. Ductile materials show a broad curve with a long tail.
Brittle materials produce a sharp peak followed by a sudden drop.
Part Performance
Evaluation of finished components under realistic strike conditions helps validate the design of the tooling and the choice of resin. If a part fails an instrumented drop weight impact test, the data shows whether the failure was due to material choice or a structural weakness. Moulders use this information to optimize gate locations and wall thicknesses.
Testing protocols are adjusted to simulate the specific speeds and energies encountered in the field. Consistent results lead to safer products for the consumer.