Meaning
Speed at which an acoustic wave travels through a polymer material. Sound velocity depends on the density and the elastic modulus of the resin, making it a useful tool for non-destructive testing and material characterization. Measuring the time an ultrasonic pulse takes to move through a known thickness allows for the calculation of the physical state of the internal polymer structure.
Defect Detection
Changes in the speed of the wave can reveal internal flaws such as voids or delaminations. In a consistent part, the sound velocity remains stable across the geometry. A sudden drop often indicates a region of low density or a fracture that would be invisible to a visual inspection.
Crystal Correlation
Velocity of the sound wave is influenced by the internal structure of the polymer. Semi-crystalline resins like polypropylene show variations in sound velocity based on the size and distribution of spherulites. This relationship allows for the estimation of the crystalline content without destroying the sample.
Wall Thickness
Ultrasonic gauges use this property to measure the thickness of parts where only one side is accessible. By knowing the sound velocity for the specific resin, the device calculates the distance to the back wall based on the reflection time.
