PSI - Issue 17

C.A.R.P. Baptista et al. / Procedia Structural Integrity 17 (2019) 324–330 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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condition. Other six specimens were exposed to laser processing without coating treatment, with two distinct overlapping rates: 50% and 75%, from now denoted as LP50 and LP75 conditions.

Fig. 1. Microstructure of 2024-T3 alloy (etchant: Keller).

The experimental setup developed for the laser treatments is schematically shown in Figure 2. A Nd:YAG laser Quantel model Brilliant B, operating in the second harmonic (wavelength λ = 532 nm), with beam diameter ϕ = 8 mm and pulse duration  = 9 ns was employed. The laser beam was directed toward the specimen by using a 90  prism and a 500 mm focal distance lens. The pulse energy E p was measured with a thermopile sensor Ophir model 50A-PF-DIF-18 and found to be in the range 260-275 mJ. Upstream and downstream measurements indicated that the energy loss during the passage through the optical device was of the order of 10%. A sample holder was positioned on a 3 CNC axes plate with the vertical axis perpendicular to the sample surface. A continuous water flow with flow rate of 1.5 l/min was provided in order to create a water curtain on the test-pieces. After some preliminary tests and aiming to minimize the laser induced air breakdown caused by the high beam intensity in the focal distance, the laser beam was focused 20 mm under the specimens’ su rface, as indicated in Fig. 2, resulting in a spot size of D  800  m. Given the pulse energy ( E p ) and duration (  ), as well as the spot area ( A ), the power density P d was estimated from equation (1) to be 5.2 GW/cm 2 .

Fig. 2. Schematic view of the laser experimental setup.