Damping Steel Plate Testing

Damping steel plate inspection mainly conducts scientific testing and analysis on the damping performance, mechanical properties, interlayer bonding strength, environmental resistance and physical and chemical characteristics, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Damping performance: This is the most core testing item of the damping steel plate, mainly evaluating its ability to convert the vibration mechanical energy into the heat energy and dissipate it. It is usually quantified by measuring the loss factor (η) or damping ratio. The larger the loss factor, the more excellent the vibration and noise reduction performance of the material. The test results directly affect its application effects of suppressing the structural resonance and noise in the fields such as the automobiles, household appliances and buildings.

Mechanical properties: Although the vibration reduction is the main function, the damping steel plate still needs to have the basic mechanical strength as a structural part. The routine testing includes the yield strength, tensile strength, elongation and hardness. These indicators ensure that the material will not produce the plastic deformation or fracture when bearing the loads, meeting the comprehensive requirements of the specific structural applications for the stiffness and load-bearing capacity.

Interlayer bonding strength: For the constrained damping steel plates (i.e. the composite damping steel plates), the bonding states between the constraint layers (usually the thin steel plates) and the middle viscoelastic damping layers need to be emphatically tested. The peel testing or tensile shear testing is usually adopted to evaluate the interlayer adhesion. The insufficient bonding strength will cause the debonding between the damping layer and constraint layer, making the damping performance drop sharply.

Environmental resistance: Evaluates the performance stability of the damping steel plate under the different environments. Mainly including the high and low temperature cycling testing, damp heat aging testing and salt spray corrosion testing. The purpose is to simulate the actual service environments and verify whether its damping performance and mechanical properties significantly decay with the factors such as the time, temperature and humidity.

Physical and chemical characteristics: Including the testing of the densities, thickness uniformities, surface roughnesses of the steel plate substrates and damping coatings, and the coating composition analyses (such as the Fourier transform infrared spectroscopy FT-IR). These characteristics directly affect the processing performance (such as the stamping and welding), painting performance and the final damping effectiveness and service life of the material.

Testing Scope

Free damping steel plates: The testing objects are the single-layer steel plates with the viscoelastic damping materials directly coated or pasted on the surfaces. The testing emphasis is on the loss factor of the damping coating itself, the adhesion strength with the base plate, and the damping performance change curves at the different frequencies and temperatures (i.e. the temperature-frequency spectra), evaluating its vibration reduction effects in the wide frequency band.

Constrained damping steel plates: The testing objects are the typical "steel-damping layer-steel" sandwich composite structures. In addition to the properties of the various layer materials, the testing scope more emphasizes the composite loss factors of the overall structures, interlayer shear properties, and the constraint effects of the constraint layers on the damping layers. The vibration reduction performance of this type of materials is usually better than that of the free damping structures.

Special damping steel plates: Including the high-temperature damping steel plates (used in the environments such as around the engines) and composite damping steel plates with the electromagnetic shielding functions. The testing scope needs to be expanded according to their special functions, for example, adding the special tests such as the damping performance retention rates at the high temperatures and electromagnetic shielding effectiveness (SE).

Different specifications and application fields: The testing covers the damping steel plates of the different thicknesses (such as from 0.5 mm to 3.0 mm) and different widths. The application-oriented testing scope includes the performance simulation testing under the specific working conditions such as the automobile body panels, engine hoods, household appliance housings (washing machines and air conditioners), building floor slabs and industrial equipment casings.

Raw materials and production process: The testing scope extends upstream to the chemical compositions and metallographic structures of the steel plate substrates, as well as the viscosities, solid contents and storage stabilities of the damping coatings. The production process testing includes the monitoring of the coating uniformity, curing temperatures and times, ensuring the consistent quality between the product batches.

Testing Methods

Cantilever beam resonance method: This is the classical method of measuring the loss factor of the material. The strip specimen is fixed at one end to form a cantilever beam, and through the excitation, it resonates at the fundamental frequency or a certain order frequency, and the resonance frequency and half-power bandwidth are measured, thereby calculating the loss factor. This method has the relatively simple equipment, and is suitable for the fast and accurate comparison and evaluation of the material damping properties in the laboratory.

Dynamic mechanical analysis (DMA): A precise method that applies the small amplitude oscillating forces to the specimen under the programmed temperature control, measuring its storage modulus, loss modulus and loss factor. The DMA can provide the complete spectra of the material damping properties changing with the temperature and frequency, and is the core means of studying the glass transition temperature (Tg) and temperature-frequency characteristics of the damping materials. The results are precise but the equipment is expensive.

Acoustic impedance tube method: Mainly used to evaluate the sound insulation and sound absorption properties of the damping steel plates. The specimen is placed in the impedance tube, and the incident and reflected sound pressures of the sound waves in the tube are measured with the microphones, calculating the acoustic impedance, sound absorption coefficient and sound insulation of the material. This method is directly related to the noise control application effects of the material.

Vibration decay method: Through the impact excitation or initial displacement, the specimen (such as the plate) is made to produce the free vibration, and the curves of the amplitude decaying with the time are recorded. The damping ratio of the material can be calculated by using the logarithmic decrement rate. This method is closer to the vibration decay process under the actual working conditions, and is commonly used to evaluate the damping effects at the component level.

Peel and shear testing: For the composite damping steel plates, the standardized peel testing (such as the 180° peel) and tensile shear testing are adopted to quantitatively evaluate the interlayer bonding strength. A universal material testing machine is used, and the loading is carried out at the rates specified in the relevant standards (such as ASTM D903 and ASTM D1002), recording the peel forces or shear forces until the failures.

Testing Standards

Domestic Standards:

1. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

3. GB/T 232-2010, Metallic materials — Bend test method

4. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

5. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

International Standards:

1. ASTM D903, Standard test method for peel or stripping strength of adhesive bonds

2. ASTM D1002, Standard test method for apparent shear strength of single-lap-joint adhesively bonded metal specimens by tension loading (metal-to-metal)

3. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

4. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Dynamic mechanical analyser (DMA): The core equipment, used to precisely measure the dynamic mechanical properties of the material in the wide temperature and frequency ranges. Through the precise displacement sensors and force sensors, the instrument works in the various modes such as the tensile, bending and shear, and directly outputs the key parameter curves such as the storage modulus, loss modulus and loss factor (tan δ). It is the key tool of the material research and development and quality control.

Vibration testing system: Usually composed of the exciters (or impact hammers), acceleration sensors, charge amplifiers and dynamic signal analysers. Used to implement the tests such as the cantilever beam resonance method and vibration decay method. The system can acquire the frequency response functions (FRF) of the specimens, analyse their natural frequencies, mode shapes and damping characteristics, and is suitable for the specimens of the different sizes and boundary conditions.

Universal material testing machine: Used to carry out all the static mechanical property tests (tensile, compression and bending) and the interlayer bonding strength tests (peel and shear). The equipment is equipped with the high-precision load cells and displacement extensometers, can control the loading rates according to the standards, and precisely obtain the stress-strain curves and bonding strength data of the material.

Acoustic impedance tube system: Composed of the rigid circular tubes of the different diameters (covering the different frequency ranges), sound sources (loudspeakers), multiple precision microphones, data acquisition devices and analysis software. It is used to measure the sound absorption coefficients and sound insulation of the materials under the normal incidence sound wave conditions, evaluating their acoustic properties. It is an important testing equipment of the noise control applications.

Environmental test chamber: Including the high and low temperature test chambers, constant temperature and humidity test chambers and salt spray test chambers. Used to simulate the various harsh environments that the damping steel plates may face. The specimens are treated for a certain period under the specific environmental conditions (such as the -40 ℃ to 120 ℃ cycles, 95% RH damp heat and 5% NaCl salt spray), and then the performance retention rates are tested, evaluating their durability and reliability.