# Detection of Impact Damage on PVA-ECC Beam Using Infrared Thermography
## 3 Experimental Setup and Procedure
### Experimental Setup  
The experimental setup basically includes a PVA-ECC beam, an infrared camera and a halogen lamp for thermal stimulation, as shown in Figure 2. The camera and lamp are positioned and fixed on the same side to perform measurements in reflection mode. The thermal wave, which delivered to the specimen surface, propagates inside the specimen and gets reflected when it reaches crack or defects [56]. The reflected thermal wave will then be captured by the infrared camera (E60, FLIR Systems, Wilsonville, OR, USA).  
The PVA-ECC beam was fabricated in the Smart Material and Structure Laboratory, University of Houston (Houston, TX, USA). The size of the beam specimen was 100 \(\times\) 100 \(\times\) 400 mm\({}^{3}\) and its quantitative composition was given in Table 1. The properties of PVA fibers were listed in Table 2. The specimen was fixed in an L-shaped fixture, which was used to prevent horizontal movement during the impact test. Thereby, the location of each impact was limited at the top of the upper surface of the specimen. The L-shaped fixture was welded on a metal base, which was fixed to the  
Figure 1: Schematic diagram of infrared thermography detection.  
Figure 2: Impact experimental setup (**a**) test setup; (**b**) data acquisition system. (PVC: polyvinyl chloride; PVA-ECC: polyvinyl alcohol fiber reinforced engineering cementitious composite).  
ground in all directions. The drop weight is a spherical ball with a diameter of 90 mm. Its mass is 2.7 kg. The specimen was subjected to impact tests, with the drop weight falling from 1 m high. After each drop weight impact, the halogen lamp heats the side surface of the specimen to increase the temperature. In the meantime, the temperature of the side face was monitored with an infrared camera in order to visualize impact-induced thermal signatures. The impact test was repeated until a clear crack appeared on the beam due to the impact-induced damage. The total number of impact events in this study was nine.  
Thermal stimulation was applied using a halogen lamp with a power of 250 W. The lamp was turned on for 20 s to heat the specimen. After the lamp was turned off, the temperature decay was also recorded for another 20 s, making a total duration of 40 s. Both the temperature increase and decay periods were of interest. Thermal graphs were acquired using the ThermaCam FLIR E60 (FLIR Systems, Wilsonville, OR, USA), which is an uncooled focal plane array camera. The thermal sensitivity is <0.05\({}^{\circ}\)C at 30 \({}^{\circ}\)C and the frame rate is 60 Hz. It works in the far 7.5-13 \(\upmu\)m band and has spatial resolution 320 \(\times\) 240 pixels for a full frame.  
Infrared images acquired from active thermography tests are greatly affected by the non-uniform properties of the material surface being inspected, and also by the uneven heat generated by the thermal stimulus [48]. Thus, it is necessary to subtract the background from the image before further processing. The FLIR Tools + software (6.4.18039.1003) was used, which allows manipulating of the infrared camera, handling of thermal images, visualization and processing of thermal images.