Characterizing the Spring and Damping Properties of Materials, Devices, and Systems
To understand how a material or system (group of materials/devices interacting) will perform in a certain application, characterization tests must be performed to ensure the performance meets the design specifications. Most systems are dynamic (not static or completely rigid) and experience shock and or vibration inputs. Systems can be represented as a mass, spring, or a damper (dashpot). A good example is a vehicle, where many of the components are in motion. The vehicle body is the mass, and the suspension system consists of the the spring and damper. A damper or shock absorber is a device that dissipates energy (usually as heat). In a suspension system, the damper controls the rate at which the spring stores and releases energy. Careful consideration must be put into suspension system design to ensure the spring and damping rates are tuned for the mass and the typical system inputs. Elastomeric materials such as rubber also have damping capabilities, and as such are used as mounts, padding, and even bridge bearings. Advanced Materials and Devices (AMAD) specializes in the design and characterization of materials and systems.
The spring and damping rate of a flexible material can be characterized to determine how this material will perform in a system. To determine a material’s spring rate, a force-displacement plot can be created. AMAD uses an MTS Insight Universal Test System for tension, compression and shear testing to plot the force-displacement curve of a material to determine the spring rate, k. This machine, as shown in Figure 1, is also used for mechanical testing to determine tensile and shear strength of materials, flexible or rigid.
Shock Testing and vibration testing can be done to ensure systems and devices can withstand high levels of acceleration and frequency without failure, and to characterize a system’s response to a shock or vibration input. Our LDS V850-440-T Shaker is used to apply a shock or vibration input into system/device. Measuring the transmitted acceleration during a frequency sweep vibration test, will determine the system’s natural frequency. Measuring the acceleration decay after a shock input will determine the material/systems damping rate. A typical test setup to characterize a flexible material with shock testing and vibration testing is shown in Figure 2.
AMAD also performs device and system characterization with a MTS 852 damper test machine. As the name implies, this machine is ideal for damper performance and durability testing. This test machine uses servo hydraulic valves which allows us to perform loading profiles such as sine on sine, ramp on ramp, and random road profiles. This is well suited for position dependent dampers as we can measure the damping rate for every range in the dampers displacement. This equipment is not limited to only dampers, or shock absorbers, as flexible materials can also be characterized with this machine. Figure 3 displays a flexible material being tested with our MTS 852 damper test machine to characterize the spring and damping rate. The slope of the force – velocity curve produced from this test is the materials damping rate. The slope of the force – displacement curve produced from this test is the materials spring rate.
For more information on shock testing, vibration testing, and material characterization testing, check out our website or blog series. If you are interested in having your material, device, or system characterized for its performance and ruggedness, contact us for more information about what we can offer.