PSI - Issue 17

Pedro J. Sousa et al. / Procedia Structural Integrity 17 (2019) 835–842 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 u= φ X 4π sin λ α X

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4

( 1 )

v= φ Y 4π sin λ α Y ( 2 ) where λ is the wavelength and φ i and α i are the phase map and the incident beam angle relative to direction i . In the developed system, the w displacement (Z axis) is obtained from the phase map using the known displacement in the perpendicular X direction as: w= φ Z λ-u(1+cos α Z ) sin α Z 2π(1+cos α Z ) ( 3 ) 3. Thermal loading Between the two measurement stages, the specimen was heated with a heat gun controlled by an industrial temperature controller, which used a thermocouple attached to the backside of the PCB (Fig. 3) for feedback. The heat gun was positioned facing the back the specimen and pointed at its center.

Fig. 3. Configuration of the thermal loading system

Using a thermographic camera it was possible to define the necessary time for the specimen to reach a uniform stable temperature, Fig. 4, while programming the controller to a set point of 50°C. Thus, in order to ensure proper temperature distribution throughout the model, the control system was kept enabled for at least 3.5 minutes after reaching the controller’s target temperature, as measured on the thermocouple. The obtained temperature in the front of the specimen was approximately 40°C.

(a)

(b)

Fig. 4. Thermal analysis of the specimen. (a) Thermal image of the specimen after reaching a stable temperature. (b) Time evolution of the mean temperature in region 1 of (a). The heating system was disabled at approximately 210 s.