## 2 Material and Equipment
### Testing Equipment and Experimental Techniques  
All of the tests were performed on a MTS (Eden Prairie, MN, USA) servo-hydraulic test bench with a load cell of 100 kN capacity. The material was stored at ambient conditions and the tests were conducted at room temperature and humidity. The quasi-static tests were performed in a displacement control with a rate of 1 mm/min. Both continuous and interrupted static tests were performed; firstly, to obtain all of the mechanical material properties, and secondly, to perform damage monitoring using in situ microscopy. At least three repetitions for each test case were performed, in order to have statistically acceptable results.  
In Figure 2, the total experimental set-up is presented. For the optical analysis, a Leica Microsystems (Wetzlar, Germany) MZ125 stereomicroscope with 8-100\(\times\) magnification and 375 line-pairs/mm resolution was mounted on the test bench so as to monitor the free edge of the specimen and to perform through-thickness damage observations. The microscope was mounted in such a way that movements along the specimen axis were possible, allowing for damage monitoring over a total length of 70 mm along the gauge length of the specimen. The static tests were interrupted at regular steps and images were captured while keeping the specimen mounted and without unloading it. During all of these intervals, images with different magnifications were manually captured. Prior to testing, the sides of the specimens were polished using SiC grit papers of descending particle size (from 46 \(\upmu\)m down to 5 \(\upmu\)m) so as to remove possible edge fracture initiation points, and to improve the microscopy analysis.  
An eight-channel DiSP system by Mistras Group (Princeton Junction, NJ, USA USA) was used for monitoring the acoustic activity. Two piezoelectric transducers (Pico) with a broadband response and peak frequency at 450 kHz were mounted on the front side of the specimen. Vaseline was applied for the acoustic coupling and duct tape was used to guarantee a stable placement of the sensors on the specimen. The signals were pre-amplified by 40 dB and a 35 dB threshold was applied in order to filter out the noise of the mechanical system. In order to take into account only signals related to the  
Figure 2: Experimental set-up. DIC—digital image correlation; AE—acoustic emission.  
specific damage incidents during the test, linear localization algorithms were performed by taking into account the wave velocity and the attenuation effect, both measured by performing pencil lead breaks prior to testing. Through the post-processing of the AE data, the overall AE activity was analyzed.  
The deflection during testing was measured using a 50 mm MTS extensometer, and last but not least, a DIC system, VIC-3D by Correlated Solutions (Columbia, SC, USA), was used in order to obtain the full-field strain maps on the surface of the specimen. A black/white speckle pattern was applied on the specimen using aerosol paint. A pair of 5 MP Stingray cameras and 23 mm focal length lenses were used. The strain calculation was obtained through the triangulation of the two cameras. Through the DIC software and the post-processing tools, the strains (longitudinal, transverse, and shear) developed on the surface of the specimen were obtained. In order to achieve this, the change in the average grey scale intensity of the specific collections of pixels, called subsets, between the reference and the deformed images was tracked in the DIC software. The middle point of any subset on the correlated area corresponds to one data point. By taking into account the subset size and the step size (defined as the spacing of the data points analyzed during correlation), an average map of the strains and other parameters was obtained. For the DIC analysis, a subset of 21 by 21 pixels was used and a step of seven pixels both in the vertical and in the horizontal direction was applied. Images were captured every one second.