13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table 1. — Experimental conditions Laser energy Water temperature Water layer thickness (a)-1 10 – 100 mJ 20 °C - (a)-2 100 mJ 15 - 50 °C - (b) 60 mJ 20 °C 1 – 10 mm 2.2 Optical observation by high speed camera High speed cameras (Phantom Miro LC310 producted by Vision Research® Inc. and HyperVision HPV-2A producted by SHIMADZU CORPORATION) were used to observe the phenomenon during laser shock peening in experiment set-up as shown in Fig.2. The camera was set to observe the sample from an oblique direction. The phenomenon was recorded using lighting from opposite side of high speed camera. At the same time, fluctuation in water near sample surface was mainly also recorded by Phantom Miro LC310 with the sampling rate of 120,000 fps and pixels of 128 × 128. 2.3 AE measurement An AE sensor (Pico, Physical Acoustics Corp.) was attached on the back side of the sample as shown in Fig. 1(a). Elastic waves associated with laser irradiation were recorded by Continuous Wave Memory (CWM) system, which is developed by our research group [3]. This system provides a capability to memorize all waveforms continuously at the sampling rate of 10 MHz. Waterproof paste was used to cover cables. 2.4 AE inverse analysis Impact forces generated from laser irradiation were evaluated by an inverse analysis of AE waveform [1]. Detected AE waveform can be represented by V(t)=S(t)*G(t)*I(t) where V(t), S(t), G(t) and I(t) are detected waveform, response function of sensor, Green’s function of media and source function of impact force, respectively. S(t) and G(t) could be obtained from a simulation of AE waveform by finite element method and experimental of sharp pencil lead breaking and then I(t) Camera Laser Light Figure 2. Top view of camera setting in Fig. 1(a)
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