# Monotonic and Fatigue Properties of Steel Material Manufactured by Wire Arc Additive Manufacturing
## 3 Results
### Monotonic and Fatigue Properties
#### 3.3.1 Monotonic Tensile Properties  
The stress-strain curves of the monotonic tensile tests at room temperature for both the different interlayer temperatures as well as the extraction directions are shown in Figure 7. The corresponding average material properties determined are listed in Table 2. Table 2 also contains the standard deviations for these properties. However, it shall be pointed out that the given standard deviations are only based on four properties each, which limits the validity of this value. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Interlayer** & **Extraction** & **Tensile Strength** & \multicolumn{2}{c}{**Upper Yield**} & \multicolumn{2}{c}{**Elongation at**} \\
**Temp/\({}^{\circ}\)C** & **Direction** & \multicolumn{2}{c}{**R\({}_{\text{m}}\)/MPa**} & \multicolumn{2}{c}{**Strength R\({}_{\text{eH}}\)/MPa**} & \multicolumn{2}{c}{**Rupture A**} \\ \hline
150 & lengthwise & 539 & (1.9) & 377 & (2.5) & 29.3\% & (3.0\%) \\
150 & crosswise & 539 & (14.7) & 376 & (11.0) & 27.9\% & (2.4\%) \\
300 & lengthwise & 536 & (3.3) & 319 & (16.7) & 34.3\% & (1.3\%) \\
300 & crosswise & 531 & (1.2) & 325 & (19.2) & 27.6\% & (1.9\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average and standard deviation (values in brackets) of monotonic properties at room temperature. Figure 7: Stress–strain curves (engineering stresses and strains) from monotonic tensile tests at room temperature for interlayer temperature of 150 \({}^{\circ}\)C for lengthwise (**a**) and crosswise (**b**) extraction direction and for interlayer temperature of 300 \({}^{\circ}\)C for lengthwise (**c**) and crosswise (**d**) extraction direction. The tensile tests at room temperature contain two influences: the direction in which the samples are extracted and the interlayer temperature with which the material was manufactured. For this reason, the results will be compared below, one after the other, with regard to these two influences. First, the direction in which the tensile specimens were extracted is considered in relation to the manufacturing direction. The monotonic strength, yield strength, and tensile strength do not show pronounced differences. The average elongation at rupture is noticeably larger for the interlayer temperature of 300 \({}^{\circ}\)C lengthwise to the manufacturing direction compared to in the crosswise direction. By comparing the test results for the two different interlayer temperatures with each other, the following results are found: there is a significant difference in the strength properties only found for the yield strength, which can be related to less free interstitial carbon atoms present for a higher interlayer temperature, due to the larger amount of perlite. For the interlayer temperature of 150 \({}^{\circ}\)C, it is higher by about a factor of 1.15 than that at 300 \({}^{\circ}\)C. The tensile strength, however, does not show any discernible difference. It is about 536 MPa for all directions and interlayer temperatures. In addition, tensile tests were conducted at elevated temperatures of 150 and 300 \({}^{\circ}\)C mainly to determine the yield strength at different temperatures for an assessment of the measured local residual stresses. Due to limited available WAAM material, tests at elevated temperatures were only conducted for specimens extracted in crosswise direction. These tests were done on another testing machine with a different clamping mechanism than the tests done at room temperature mentioned above. Therefore, a larger specimen diameter is used. To allow the results to be compared between the different testing conditions, tests at room temperature were also conducted at the testing machine for elevated temperatures. Since a clip-on extensometer was not available, the crosshead movement was used to calculate the necessary strains. Therefore, the elastic part of the stress-strain curves shown is spoiled for realistic elastic moduli, because the crosshead movement also contains the elastic deformation of the testing machine itself.