Figure 6:

Example load waveforms showing degrees of fidelity between the software-programmed, command waveforms and the load cell-measured waveforms for (A) triangle waveform³⁸, (B) trapezoidal waveform, and (C) haversine and triangle waveforms⁶⁶. These waveforms were commanded on different mechanical systems: (A) TA Instruments Electroforce TestBench, (B) TA Instruments Electroforce 3100, (C) Instron ElectroPuls E1000. In (A), the small ‘recovery’ spike needed to achieve the correct command pre-load results in a short delay of the signal and a load frequency of 3.75Hz, as opposed to the intended 4Hz. Some custom devices do not exhibit this spike when conducting triangle waveforms52.