Viscoelastic Characterization
International standards specify the methods for determining the dynamic mechanical properties of plastics under non resonant vibrations. The application of iso 6721 involves subjecting a specimen to a sinusoidal stress or strain to measure its storage and loss moduli. It provides a consistent methodology for comparing the damping characteristics of different polymer grades.
Test Configuration
Mechanical oscillators apply small deformations to ensure that the material remains within its linear viscoelastic region. Different parts of iso 6721 cover various loading modes including bending, tension, shear, or torsion. The selection of the frequency range is critical for identifying the glass transition temperature.
Environmental Control
Temperature sweeps across a broad range reveal the thermal stability and phase transitions of the material. According to iso 6721, the heating rate must be slow enough to ensure thermal equilibrium throughout the cross section of the sample. Thermocouples placed near the specimen verify that the actual temperature matches the programmed setpoint.
This verification prevents errors caused by thermal lag in thick samples.
Reporting Requirement
Final test reports must include sample dimensions and preconditioning history. The iso 6721 document mandates these details to ensure that comparisons between laboratories remain valid. Output data supports the qualification of materials for vibration damping.
