Guide
What is Impulse Excitation Technique (IET)?
A complete guide to the non-destructive method for measuring elastic properties of materials.
What is IET?
Impulse Excitation Technique (IET) is a non-destructive testing method that determines the elastic properties of materials by measuring their natural resonance frequencies.
When you tap a material, it vibrates at specific frequencies determined by its stiffness, density, and geometry. By measuring these frequencies precisely, you can calculate:
- Young’s modulus (E) — stiffness in tension/compression
- Shear modulus (G) — stiffness in shear
- Poisson’s ratio (ν) — lateral contraction ratio
- Damping — internal friction, energy dissipation
The technique has been standardized since the 1990s (ASTM E1876) and is used globally in research, quality control, and materials development.
How It Works
Excitation
A small impulse (tap) excites the sample, causing it to vibrate at its natural frequencies
Detection
A microphone or piezoelectric sensor captures the acoustic response
Analysis
Signal processing extracts resonance frequencies and damping values
The sample is supported at its nodal points (where vibration amplitude is zero) to allow free vibration. Different support positions excite different vibration modes:
- Flexural mode — Support at nodes, tap at antinode center → Young’s modulus
- Torsional mode — Support at center, tap at corner → Shear modulus
What It Measures
Young's Modulus (E)
Measure of stiffness — resistance to elastic deformation under tension or compression. Calculated from the fundamental flexural resonance frequency.
Typical range: 1 GPa (polymers) to 400+ GPa (ceramics)
Shear Modulus (G)
Resistance to shear deformation. Calculated from the fundamental torsional resonance frequency.
Related to E by Poisson's ratio: G = E / 2(1+ν)
Poisson's Ratio (ν)
Ratio of lateral strain to axial strain. Calculated from E and G — no separate test needed.
Typical range: 0.2 (ceramics) to 0.5 (rubber)
Damping (Q⁻¹)
Internal friction — energy dissipation during vibration. Sensitive to defects, microstructure, and temperature.
Key indicator for defect detection in QC applications
Standards
IET is standardized by ASTM International:
- ASTM E1876 — Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio by Impulse Excitation of Vibration
- ASTM C1259 — Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio for Advanced Ceramics
- ASTM C215 — Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of Concrete Specimens
- ASTM E3397 — Non-Destructive Defect Detection Using Resonant Ultrasound Spectroscopy
Applications
Research & Development
- New material development
- Process optimization
- Temperature-dependent properties
- Aging and degradation studies
Quality Control
- Incoming material inspection
- 100% production testing
- GO/NOGO sorting
- Process consistency monitoring
Industries
- Aerospace
- Automotive
- Ceramics
- Additive manufacturing
Materials
- Metals and alloys
- Ceramics and glass
- Composites
- Polymers
Advantages of IET
Non-Destructive
Test finished parts without damage
Fast
Results in seconds, 1000+ parts/hour automated
Accurate
Typically ±1% for modulus values
High Temperature
Measure up to 1600°C with specialized equipment
Simple Sample Prep
Standard geometries, minimal preparation
Standardized
ASTM standards ensure reproducibility
Ready to Get Started?
Contact us to discuss your requirements and see how IET can help.