# Enhancing the Accuracy of Advanced High Temperature Mechanical Testing through Thermography
## 3 Results
### Measurement Technique Comparisons
#### 3.2.2 Dynamic Temperature  
The previously described method of was applied dynamic thermal cycles in the form of a trapezoidal dwell waveform, more commonly described as a flight cycle in the gas turbine sector. Thermal waveforms were undertaken using both ICS and RLF heating sources over a 550-800 \({}^{\circ}\)C temperature range. Temperatures were monitored by spot welded, tie-on and non-contact thermocouples, as well as, a pyrometer at centre of the test piece gauge section. Typical responses from each of the techniques under RLF heating are shown in Figure 13.  
Figure 12: Isothermal stability of thermography control under RLF heating at 800 \({}^{\circ}\)C upon metallic specimen coated in HE23.  
The response from the spot-welded thermocouple closely follows that of the thermography area control, however the response from the tie-on thermocouple and pyrometer did not. The tie-on thermocouple overshoots and undershoots the temperature control target during the heating and cooling turning points. The pyrometer displayed a similar response to the tie-on thermocouple, albeit far less stable at lower temperatures. Clear interference between the wavelength of infra-red pyrometer and RLF is evident. As expected the non-contact thermocouple, shielded within a ceramic tube and not in contact with the specimen did not hit the minimum and maximum commanded temperatures. However, a repeatable waveform was achieved, this can be used to assess the long-term stability of specimen temperatures under thermography control and monitor highlight any potential temperature deviations and or drifting.  
A more detailed comparison of the temperature deviation between the thermography area control and monitoring spot welded TC during dynamic thermal cycling is given in Figure 14a. Typically thermocouples measure within \(\pm\)2 \({}^{\circ}\)C of the thermography area control for all tests during isothermal or constant temperature portions of the cycles. However, significant temperature differences up to 10 \({}^{\circ}\)C were found during heating and cooling turning points of the dynamic thermal cycles, Figure 14b,c. During the isothermal dwell stages of the waveform accuracy returned to within \(\pm\)2 \({}^{\circ}\)C.  
Figure 14: _Cont._  
Figure 13: Dynamic temperature response comparison utilising thermography area control, under RLF furnace heating upon a metallic HE23 coated specimen.  
A significant advantage of thermography is its ability to measure non-metallic materials during dynamic thermal cycling when thermocouples cannot be spot welded to the non-conductive ceramic material and the stability of a pyrometer is not accurate enough under RLF heating. As such a non-contact thermocouple was installed to capture a secondary measurement of long term peak cycle temperatures. Results of the peak cycle temperatures of both the thermography area control and the non-contact TC are given in Figure 15. Thermal testing ran for over 10,000 cycles, equivalent to 270 h. No drift in peak cycle temperatures was found in either the thermography area control or non-contact monitoring TC.