# Prediction of the Tensile Load of Drilled CFRP by Artificial Neural Network
## 2 Materials and Methods
### Experimental Measurement  
The drilling of CFRP was done on Brother SPEEDIO S500x1 CNC (Brother, Rosengarten, Germany). The drill bit type, feed rate and spindle speed have been selected for the drilling parameters. The drilling setup is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c} \hline
**Properties.** & **Fiber** & **Resin** \\ \hline Type & Carbon & Polyester \\ Volume Rate (\%) & 55 & 45 \\ Tensile Strength (Mpa) & 66.47 \\ Number of Layers & 11 \\ Ply Thickness (mm) & 0.545 \\ Fiber Orientation & (+45/\(-\)45) \\ \hline \end{tabular}
\end{table}
Table 1: The features of composites.  
Figure 1: Flow chart of experimental setup.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Properties** & **High Speed Steel** & **Brad Spur** & **Tungsten Carbide** \\ \hline Drill Bit Type & Twist & Twist & Twist \\ Point Angle (\({}^{\circ}\)) & 118 & - & 140 \\ Helix Angle (\({}^{\circ}\)) & 30 & 30 & 30 \\ Material & High Speed Steel & Tungsten Carbide \\ \hline \end{tabular}
\end{table}
Table 2: The properties of drill bits.  
The drilling operations were performed with 3 different drill bits that have 6 mm of diameter, 3 different feed rates and 3 different spindle speeds. The drilling parameters are given Table 3.  
The thrust force was measured using Kistler 9257B triaxial force sensor load cell connected to a multichannel amplifier. The thrust force data was recorded by Kistler DynoWare software. The typical thrust force graph is given Figure 3. At the first stage, the cutting edge of the drill bit touches the CFRP and the force increases from zero. At the second stage, the cutting edge of drill bit begins to penetrate the CFRP. This state causes the increase in thrust force rapidly and removes the chip from the material. At the third stage, the length of the cutting edge of drill bit penetrates the materials. It continues until the cutting edge exit through to the bottom of the material. Cutting force decreases slightly during this time. At the fourth stage, cutting edge of the drill bit exits through to the bottom side of the material. This state thrust force decrease in rapidly. At the last stage, drilling operation finishes and thrust force decreases to zero.  
The surface quality of CFRP was measured by Time Surf Tr200 (160 \(\upmu\)) hand-held tester with cut off the length of 0.25 mm. Four selected measurement points were 0\({}^{\circ}\), 90\({}^{\circ}\), 270\({}^{\circ}\) and 360\({}^{\circ}\). For each position, 3 measurements were taken around the drilled hole. The average surface roughness is calculated as the average of all points values. The surface roughness profile of CFRP drilled with Brad Spur drill bit at 5000 rpm and at 0.05 mm/rev is shown Figure 4.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Level** & **Feed Rate(mm/rev)** & **Spindle Speed (rev/min)** \\ \hline
1 & 0.05 & 1000 \\
2 & 0.10 & 3000 \\
3 & 0.15 & 5000 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Drilling parameters.  
Figure 3: Typical thrust force graphic.  
Figure 2: The drilling setup.  
The delamination factor of top and bottom of drilled specimens were measured with the Medpro Microscopy-MM800 TRF (Goodbrother, Ningbo, China). The delamination factor is formulated as in in Figure 5 (where D\({}_{\text{max}}\) is diameter of maximum damaged area of drilled hole and D is diameter of hole) [20; 21; 22; 23].  
The tensile tests were carried out on Shimadzu Autograph AG-X under displacement at 1 mm/min. The experimental study consists of 3 steps. In the first step, drilling operations were carried out. In the second step, thrust force, delamination and surface roughness were measured. In the final step, tensile tests were carried out.