# Towards reliable elastic characterization of glass bead reinforced thermoplastic composites using impulse excitation and conventional testing

## TL;DR

This paper compares impulse excitation with other methods to determine the elastic properties of thermoplastic composites reinforced with glass beads, showing that impulse excitation is a fast and accurate non-destructive method.

## Contribution

The study demonstrates that impulse excitation is a reliable and efficient method for characterizing elastic properties of glass bead-reinforced thermoplastic composites.

## Key findings

- Impulse excitation technique (IET) provided elastic constants comparable to tensile testing, DMA, and OT.
- IET showed higher longitudinal moduli explained by frequency differences and microstructural anisotropy.
- IET is a faster, non-destructive method suitable for structural design of thermoplastic composites.

## Abstract

Reliable determination of elastic properties is essential for the structural use of polymer composites in engineering applications. This work aims to evaluate the impulse excitation technique (IET) as a method for determining elastic constants of glass bead‑reinforced polyamide 66 (PA66) and polybutylene terephthalate (PBT), and to compare its performance to tensile testing (TT), dynamic mechanical analysis (DMA), and oscillatory torsion (OT). Commercial PA66 and PBT grades with 0–40 wt% glass beads were injection‑molded and annealed; the addition of glass beads increased Young’s moduli by 60–70% for PA66 and 40–60% for PBT compared to the neat matrices, depending on filler content. IET, supported by finite element analysis, provided dynamic flexural and longitudinal moduli, shear modulus, and Poisson’s ratio which were comparable to those obtained from TT, DMA and OT. In the linear elastic regime IET data differed within the standard deviations of TT, DMA and OT. The moduli determined by flexural excitation using IET and DMA agreed within experimental uncertainty only above an amplitude threshold of approximately 110 μm, while Young’s moduli from TT and IET showed good agreement, though TT exhibited greater variability. Consistent trends were also found for shear modulus and Poisson’s ratio. The higher longitudinal moduli (4 to 8% for PA66 and 2 to 4% for PBT) measured by IET are explained by higher frequencies (3 to 4 orders of magnitude) and cross-sectional microstructural anisotropy and crystallinity differences confirmed by microscopy and calorimetry. The results demonstrate that IET is a much faster, non‑destructive and accurate method for obtaining elastic constants of thermoplastic composites particularly suited for the design and dimensioning of load‑bearing structural components.

The online version contains supplementary material available at 10.1038/s41598-026-36346-z.