# Withstanding Capacity of Machine Guards: Evaluation and Validation by 3D Scanners
## 2 Materials and Methods
### Impact Tests  
Impact tests were performed using the standardized test rig schematized in Figure 2. The test rig comprises the following components: compressed air gun, compressed air tank, and a clamping and support frame with a test panel. To highlight the impact mechanism and measure the impact and residual velocities as requested by the R&I regression technique, the high-speed camera Phantom V710 (Vision Research, Ametek, Wayne, NJ, USA) was employed. Tests were performed at a 10,000 fps frame rate and a resolution of 912 \(\times\) 304 pixels. The camera was calibrated before the tests. Standard projectiles were used, whose shape and dimensions are shown in Figure 3 and Table 1.  
Figure 1: [PERSON] and Ipson curve. The steel projectile presented the following mechanical properties [6]:  
* Tensile strength: 560 N\(\cdot\)mm\({}^{-2}\)\(\leq\)\(R_{m}\)\(\leq\) 690 N\(\cdot\)mm\({}^{-2}\)
* Yield strength \(\leq\)\(R_{0,2}\)\(\geq\) 330 N\(\cdot\)mm\({}^{-2}\)
* Elongation at rupture: \(A\) = 20%
* Hardened to a minimum of 56 HRC over a depth of at least 0.5 mmTest polycarbonate panels were clamped on all four sides and supported by a steel rigid frame device properly designed to mount the two different panel sizes (Figure 4A). The constraints are adjustable to mount panels of different thicknesses. Furthermore, the clamping device does not come loose during the impact and the window b ensures that the impact area is fully visible by the camera during the test (Figure 4B). The clamping and support system has a modular structure which allows a quick exchange of the plate sizes. The steel support guarantees a sufficient rigidity during the impact. The clamping frame for standard panels consists of two modules with an open window of 450 \(\times\) 450 mm, with 25 mm of side overlapping, as prescribed by the standards (Figure 5A). The clamping device is provided by knob screws to allow a simple and fast installation without screwdrivers. The sample guard can be positioned between the two frames and tightened. A specific module allows to clamp the non-standardized plate sizes (300 \(\times\) 300 mm, with an open window of 250 \(\times\) 250 mm and a side overlapping of 25 mm, as prescribed by the standards). A 500 \(\times\) 500 mm steel plate is placed inside the main frame instead of the standard size plate. The test plate is clamped by a second steel element screwed with four manual knob screws. This clamping and support device guarantees a homogeneity of the clamping forces along the edges (Figure 5B). The standardized tests imply a perfect perpendicular impact. Test panels were initially located at 71 cm from the gun barrel, but projectiles rotated and did not impact the test panels with a perpendicular direction. In this paper, shot tests with an impact angle lower than 5 degrees from the perpendicularity were considered as valid. The actual impact angle was measured by the high-speed camera. After some tests, the optimized distance to achieve perpendicularity of the impact was found and fixed at 41 cm. The system was initially calibrated performing the so-called \"free shooting\" (tests at different constant speeds without the test panel installed). Figure 4: (**A**) Clamping and support system: (a) clamping device, (b) window for camera view. (**B**) Camera framing. In standardized tests, after a single shot with an impact velocity close to the maximum working velocity of the machine, damages on the panels after the impact are evaluated and classified according to the following list [6]:  
1. Crushing/bulging (permanent deformation without cracks)
2. Incipient fracture (visible only on one surface of the panel)
3. Through-hole fracture (visible on both sides of the panel)
4. Penetration
5. Clamping frame loose
6. Test panel loose  
The standardized test for the guard vision panel is considered to have failed if the projectile opens a crack through the entire thickness of the panel. Thus, the withstanding capability test is \"passed\" only in the cases (a) and (b).