# Resonant Fatigue Tests on Drill Pipe Connections with Different Geometries and Sizes
## 3 Results
The FE analysis presented in Figure 12 clearly shows that the presence of the hole was, therefore, not detrimental to the fatigue strength of the Wired Connection samples. In Figure 10, which compares all the results with previous tests, it is shown that the samples belonging to the Wired Connection type and those of the Connection with 6-5/8\(\times\)0.750\" pipe body (both Z140 and UD165), together with the samples referred to the previous tests of ref. [43], follow a common trend of fatigue failure. On the other hand, the samples of the connection type with 5-1/2\(\times\)0.415\" pipe body showed a noticeably higher fatigue strength than the common trend of the other specimens. Moreover, the samples belonging to the category Pipe specimens 6-5/8\(\times\)0.750\" failed at a number of cycles higher than that of the samples of the connection with the same size pipe body. This is coherent with the fact that the connection specimens experienced failures at the threaded zone, which is indeed the weakest link of the entire specimen structure. An additional detrimental effect on the fatigue strength of the former samples, discussed by [PERSON] et al. in ref. [43], was provided by the corrosion, whereas it apparently less influenced the fatigue strength of the present Pipe specimens 6-5/8\(\times\)0.750\". It is important to highlight that the values of the imposed stress amplitude on the Connection with 5-1/2\(\times\)0.415\" pipe body reported in Table 1 are referred to the upset region, whereas those reported in Figure 10 are referred to the pipe body. The rescale factor between these two values was obtained by considering the modal distribution of the bending moment and the different sections of the two zones. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen Type** & **Specimen ID** & \begin{tabular}{c} **Imposed Stress** \\ **Amplitude \(\sigma_{\mathbf{a}}\) (MPa)** \\ \end{tabular} & \begin{tabular}{c} **Number of Cycles** \\ **to Failure, \(N_{\mathrm{f}}\)** \\ \end{tabular} & \begin{tabular}{c} **Location of Crack** \\ **Initiation Point** \\ \end{tabular} \\ \hline \multirow{4}{*}{Connection with 5-1/2” pipe body} & RU W0581-1 & 187.3 & \(279.7\times 10^{3}\) & \\  & RU W0581-2 & 191.5 & \(291.0\times 10^{3}\) & FET of the \\  & LU W0579-1 & 194.6 & \(247.3\times 10^{3}\) & Pin side \\  & LU W0582-1 & 187.1 & \(310.0\times 10^{3}\) & \\ \hline \multirow{4}{*}{Wired Connection with 5” pipe body} & A51136 & 202.2 & \(135.9\times 10^{3}\) & \\  & A51155 & 201.9 & \(218.7\times 10^{3}\) & \\ \cline{1-1}  & A51168 & 194.9 & \(214.7\times 10^{3}\) & \\ \cline{1-1}  & A51167 & 244.6 & \(439.0\times 10^{3}\) & \\ \cline{1-1}  & A51140 & 242.8 & \(272.5\times 10^{3}\) & \\ \cline{1-1}  & A51119 & 191.7 & \(220.9\times 10^{3}\) & \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Connection with 6-5/8” pipe body \\ \end{tabular} } & Z140-14012 & 270 & \(47.9\times 10^{3}\) & \\  & Z140-14030 & 270 & \(116.3\times 10^{3}\) & \\ \cline{1-1}  & Z140-14041 & 270 & \(99.2\times 10^{3}\) & \\ \cline{1-1}  & Z140-14076 & 270 & \(116.9\times 10^{3}\) & \\ \cline{1-1}  & Z140-14099 & 270 & \(110.5\times 10^{3}\) & FET of the \\ \cline{1-1}  & Z140-14110 & 270 & \(116.5\times 10^{3}\) & Pin side \\ \cline{1-1}  & UD165-9250 & 270 & \(922.0\times 10^{3}\) & \\ \cline{1-1}  & UD165-49267 & 270 & \(107.5\times 10^{3}\) & \\ \cline{1-1}  & UD165-49218 & 270 & \(109.5\times 10^{3}\) & \\ \cline{1-1}  & UD165-49221 & 270 & \(136.7\times 10^{3}\) & \\ \cline{1-1}  & UD165-9257 & 270 & \(96.7\times 10^{3}\) & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Pipe specimens \\ 6-5/8” \\ \end{tabular} } & UD165-49267 & 270 & \(256.5\times 10^{3}\) & \\ \cline{1-1}  & Z140-14076 & 270 & \(238.5\times 10^{3}\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Fatigue strength amplitude and number of cycles to failure for each sample of the four specimens types.