# Experiment and Modeling on Macro Fiber Composite Stress-Induced Actuation Function Degradation
## 2 Experiment Set Up and Procedures  
Actuation Function Degradation Characterization of Macro Fiber Composite (MFC) Actuator Undergoing Cyclic Load  
In order to quantitatively characterize the actuation function degradation behavior of an MFC actuator undergoing cyclic load, an experimental test procedure is established to measure the actuation function degradation degree of the MFC actuator at different cyclic loads.  
The MFC actuator is a type of flexible patch actuator, and it is not convenient to directly apply cyclic load on the actuator to implement the measurement of its actuation function degradation. In order to carry out the measurement of the MFC actuator undergoing cyclic load, this MFC actuator needs to be made into an MFC piezoelectric beam specimen. Resonant displacement amplitude of the MFC piezoelectric beam actuated by the attached MFC actuator will be measured and used to characterize the actuation function of the MFC actuator.  
The relative decrease percentage of measured resonant displacement amplitudes will be used to indicate the actuation function degradation degree of the MFC actuator. Degradation degree versus the cycles of cyclic load will provide a group of degradation data. The fitting curve of these data can be used to exhibit the actuation function degradation tendency of the MFC actuator undergoing cyclic load. To get these relative decrease percentages of displacement amplitudes, the resonant amplitude of an MFC piezoelectric beam actuated by the intact MFC actuator needs to be measured first of all, and this value is then denoted as \(A_{0}\). A shaker is used to impose cyclic load on the MFC actuator. When the cycles of cyclic load \(N\) reaches a certain number, the cyclic load is paused for an actuation function test. The resonant displacement amplitude in the free end of the beam actuated by MFC is measured under the same driving condition as for the intact MFC, which is denoted by \(A_{t}\)\((\sigma,N)\), in which \(\sigma\) is the stress amplitude of the cyclic load and \(N\) represents the cyclic loading cycles. The actuation function degradation degree of our MFC actuator can be characterized by the actuation function index \(A\)\((\sigma,N)\), which is defined as  
\[A(\sigma,N)=\frac{A_{t}(\sigma,N)}{A_{0}}\times 100\% \tag{1}\]  
where \(A_{0}\) is the measured resonant displacement amplitude in the free end of the MFC piezoelectric beam actuated by the intact MFC actuator. \(A_{t}\)\((\sigma,N)\) is the free end resonant displacement amplitude of the MFC piezoelectric beam actuated by MFC actuator, which can be measured right after \(N\) cycles of cyclic load with stress amplitude \(\sigma\) has been imposed on the MFC actuator.  
For an intact MFC actuator the actuation function index \(A\) (0,0) = 100%. When \(A\%\) is less than 100% it means that the actuation function degradation of the MFC actuator occurs. In other words, the actuation function of the MFC actuator degenerates to \(A\%\) of its intact level.  
In the calculation of this actuation function index \(A\)\((\sigma,N)\), it should be ensured that the used two resonant displacement amplitudes are comparable, which means the corresponding driving conditions and boundary conditions of the beam for the measurement of the two resonant displacement amplitudes must be the same. Hence for the measurements of the two resonant amplitudes \(A_{t}\)\((\sigma,N)\) and \(A_{0}\), the amplitude and the frequency of the driving voltage for the MFC actuator both need to remain consistent, where the frequency should be confirmed as the first bending mode natural frequency of the MFC piezoelectric beam under the corresponding boundary conditions.