Ways to Express the Formula of Viscoelastic Damping Materials

There are four ways to present the formula of viscoelastic damping materials, usually in the form of a proportion table.

(1) Basic formula form. It's expressed with the main polymer in the formula as 100 parts by mass (if several polymers are used together or blended, their total amount is 100), and other additives are expressed in relative parts by mass. This basic formula form is often used in the design, research and testing of damping material formulas.

(2) Mass percentage formula form. The total mass of all components in the formula is 100, and the percentage of each component represents the amount of that component. The mass percentage formula is the most reasonable way of expression and is convenient for cost calculation.

(3) Volume percentage formula form. It's a formula form expressed by volume. All components in the formula should be converted into volume, the sum of the total volume is 100, and the percentage of the volume occupied by each component is the amount of that component. When it's necessary to calculate the cost based on the volume of the rubber compound, the volume percentage formula can be chosen. It's relatively rarely used in the research and production of viscoelastic damping materials.

(4) Production formula form. According to the specifications of production equipment or processing capacity, the mass formula used in actual production is calculated from the basic formula, expressed by the actual feeding amount of each component, usually in kilograms.

Each component in the formula should have detailed technical information such as a clear and specific name, specification model or brand, origin, quality standard, dosage, as well as production process conditions and main properties. Test formulas should be numbered, and production formulas should have codes, which is helpful for comparison or reference. The number, code or symbol should reflect as much key information of the formula as possible.

Now let's take a brief look at the MRC-OG4 damping material used in U.S. submarines as an example.The specific formula is listed in Table 1-1.

Table 1-1 Formula of MRC-OG4 damping material

When using MRC-OC4, you glue it to the steel plates of the ship's hull with epoxy adhesive. The amount of adhesive applied is 4.5 pounds per square foot (that's about 22.1 kg per square meter).

If you stick a 14.5mm thick damping layer (so the thickness ratio is 1.5) onto a 9.5mm thick steel plate, it'll show a critical damping of more than 3% to 5% when the frequency is between 100Hz and 6000Hz, and the working temperature is from 0℃ to 49℃. It can self-extinguish, resist JP-4 jet fuel, seawater, and impact too. At around 23℃ and 1000Hz, the best critical damping can reach about 10%. It also has pretty good damping performance at low frequencies, like around 100Hz.

This material can also be used as a constrained damping material. The constraining layer is an aluminum plate, with a thickness ranging from 1/8 inch to 5/4 inches (roughly 3mm to 31mm), and the damping layer is between 1/16 inch and 1 inch (about 1.6mm to 25mm), with a mass ratio of 25%.

When the damping layer is 1/16 inch thick (about 1.6mm), it's a perforated type. The holes are square, 1/4 inch (around 6.25mm) in size, and the distance between holes is also 1/4 inch (about 6.25mm). The perforated one actually has better damping than the solid one.

This constrained damping material is fixed to the metal base plate with bolts and nuts. The bolts are 1/2 inch in diameter (12.5mm), welded onto the metal base plate, and spaced 12 inches (30cm) apart. You can also glue it to the metal base plate using Chemlok 301 epoxy adhesive, and then add bolts to reinforce it after gluing.