ASTM E756-05: Measuring the Damping Properties of Materials
What Is ASTM E756-05?
ASTM E756-05 is the standard test method for measuring the vibration damping properties of materials. It defines procedures for determining the loss factor (η) and Young’s modulus (E) of damping materials—typically viscoelastic polymers, elastomers, coatings, and composite laminates—as functions of temperature and frequency using a beam specimen test configuration.
Damping measurement per ASTM E756 is fundamental to the design of noise, vibration, and harshness (NVH) control systems across the automotive, aerospace, civil engineering, and consumer electronics industries.
Why Damping Property Measurement Matters
Structural vibration causes noise, fatigue, and discomfort in vehicles, buildings, machinery, and consumer products. Viscoelastic damping materials convert mechanical vibration energy into heat, attenuating resonant vibrations and reducing radiated noise. Designing effective damping treatments requires accurate material property data across the frequency and temperature range of service.
ASTM E756 provides a standardized, reproducible method for characterizing these properties—enabling material comparison, design modeling, and production quality control.
Test Configurations in ASTM E756
The test uses a thin beam specimen that is either:
Freely Suspended (Oberst Bar Method)
A free-free beam is suspended at its nodal points and excited by a non-contacting electromagnetic or acoustic driver. The beam’s resonant frequency and half-power bandwidth are measured at each resonant mode. From these measurements:
- Loss factor (η): η = Δf / fn (where Δf is the half-power bandwidth and fn is the resonant frequency)
- Young’s modulus (E): Calculated from the resonant frequency, specimen dimensions, and density
Constrained Layer Configuration
For testing constrained layer damping treatments (viscoelastic material sandwiched between two metal layers), the composite beam configuration is used. The effective properties of the damping layer are extracted by comparing the composite beam response to the bare beam response using analytical formulas.
Specimen Preparation
Standard test beams are made from a base metal (typically aluminum or steel, 20–25 mm wide, 200–300 mm long, 1–3 mm thick). The damping material is applied to one or both faces of the metal beam to create the test configuration. Specimen dimensions must be measured accurately (±0.01 mm) as they enter directly into the property calculations.
Temperature and Frequency Dependence
Viscoelastic damping materials are strongly temperature and frequency dependent. ASTM E756 specifies testing across a defined temperature range (typically −40°C to +80°C at 5°C steps) and using multiple beam lengths to cover multiple frequency decades (approximately 10 Hz to 10,000 Hz). Frequency-temperature superposition (time-temperature superposition) is then applied to construct master curves.
Outputs of ASTM E756 Testing
- Storage modulus (E’ or G’): Stiffness component of the material
- Loss modulus (E” or G”): Energy dissipation component
- Loss factor (η = E”/E’): Damping efficiency; values of 0.1–1.0+ are typical for viscoelastic damping materials
- Temperature and frequency maps: 3D or contour plots of loss factor vs. temperature and frequency
Applications
- Automotive body panels and floor systems (constrained layer damping treatments)
- Aerospace structural panels (honeycomb sandwich damping layers)
- Machine tool bases and structural elements (viscoelastic mounting pads)
- Electronic enclosures (damping coatings to reduce acoustic emission)
Why Choose Infinita Lab for ASTM E756 Damping Testing?
Infinita Lab offers ASTM E756-05 vibration damping property testing across its nationwide accredited laboratory network. Our specialists in dynamic mechanical analysis and vibration testing provide complete temperature-frequency characterization of damping materials for NVH material qualification and design support.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you. Request a Quote
Frequently Asked Questions (FAQs)
What is the loss factor and what value indicates good damping? The loss factor (η, also called loss tangent or tan δ) is the ratio of energy dissipated per cycle to energy stored per cycle. Values above 0.1 indicate useful damping; values of 0.3–1.0 are typical for high-performance viscoelastic damping materials. Steel and aluminum have loss factors of 0.001–0.01—very low damping.
How does ASTM E756 differ from DMA (Dynamic Mechanical Analysis)? DMA (ASTM E1640) applies forced oscillation to a specimen in a controlled fixture and measures modulus and loss factor directly as a function of temperature and frequency. ASTM E756 uses resonant beam vibration, which covers lower force amplitudes and can test larger material areas. DMA is better for small specimens and material development; ASTM E756 is more representative of structural application conditions.
Why is constrained layer damping more effective than free layer (extensional) damping? In a constrained layer treatment, the viscoelastic material is shear-deformed between the base structure and a stiff constraining layer during beam bending. Shear deformation is much more efficient at dissipating energy in viscoelastic materials than the extensional (tension-compression) deformation of a free layer treatment alone.
What is the effect of temperature on damping material performance? Most viscoelastic damping materials have a peak loss factor near their glass transition temperature (Tg). Below Tg, the material is glassy and stiff with low damping. Above Tg, it is rubbery with low damping but high compliance. The peak damping window may span only 20–30°C, making temperature range matching to the application critical in material selection.
Can ASTM E756 be used for liquid-applied damping coatings (LASD)? Yes. Liquid-applied spray damping materials are applied to the metal beam substrate, cured, and tested per ASTM E756. This is the standard method used by automotive OEMs to characterize and qualify LASD materials for body panel damping applications.
