Distance Learning's Sample Lesson - page 7
10-D Force Measurements
Back in Lesson 7 we mentioned force sensors and we will encounter them again in Lesson 19 on sinusoidal vibration testing of satellites. Also in Lesson 31 on modal testing. Whereas displacement and velocity pickups as well as accelerometers are mounted on structures, force sensors are mounted between structures, as shown in Figure 10-8 (Strain gage force sensors are often called load cells).
Only when you are calibrating a force sensor will the driven structure be an inert mass.
Practical measurements of applied driving force combined with measurements of resulting acceleration (at various locations on the driven structure) enable us to determine the resonant spring-mass characteristics of the driven structure.
Figure 10-8 Application of Force Sensor
Figure 10-9 Modal Hammer
A modal hammer can be used for shock exciting all of a structure’s resonances.
Figure 10-10 Modal Hammer in Action
The "structure" in Figure 10-10 will become the rib cage of a dummy to be used in automotive crash testing. The hammer wielder is trying to verify that rib cage natural frequencies match those of human subjects.
The light graph in Figure 10-11 came from sensors on an aluminum honeycomb panel. The dark graph shows the improvement (lowering of peaks) achieved by adding damping tape to the panel. Figure 10-12 shows a practical application of damping tape.
Figure 10-11 Effect of Adding Damping to Aluminum Honeycomb Panel
Figure 10-12 Aircraft Engine Application
Figure 10-13 Disk Brake Assembly
Cut away to show brake pad. Dampers reduce brake "squeal".
