# Monotonic and Fatigue Properties of Steel Material Manufactured by Wire Arc Additive Manufacturing
## 2 Specim Materials and Experiments
### Conducted Measurements and Experiments  
In the following text, the procedures used for the different tests and measurements are listed and described briefly. To gain insight into the residual stress state in the WAAM material, measurements were made using the hole-drilling strain gauge method. To apply the necessary strain gauge rosettes, 2 to 3 mm of the rough weld surface had to be removed by milling. The strain gauge rosettes used were of type  
Figure 2: Technical drafts of tensile specimens with essential dimensions: (**a**) fatigue specimen, (**b**) specimen for tensile tests at room temperature, (**c**) specimen for tensile tests at elevated temperatures, (**d**) specimen for deformation measurements with digital image correlation. HBM 1-RY61-1.5/120K and the hole diameter was 1.8 mm. The strain was measured over a hole depth of 0.72 mm, and the residual stress was evaluated using the procedure described in ASTM Standard E837 [13]. In accordance with Vickers, the micro hardness HV 0.2 was measured every 0.3 mm along path B in agreement with ISO Standard 6507-1 [14]. The small test load for the Vickers hardness test was chosen to acquire a detailed hardness profile and to be able to determine different zones within the welded material. In addition, micrographs were prepared by polishing and nital etching the extracted material. While the monotonic properties at room temperature were determined by tensile tests according to ISO Standard 6892-1 [15], the tests at elevated temperatures, namely at 150 and 300 \({}^{\circ}\)C, were conducted in accordance with ISO 6892-2 [12]. Both types of tests are conducted on testing machines for tensile testing of type Z100 in combination with control software testXpert, both from Zwick GmbH & Co. KG (Ulm, Germany). The testing machine used for the tests at elevated temperatures is equipped with a heating chamber, also from Zwick. First, all tensile specimens to be tested were placed in an external oven (power: 5 kW, maximum temperature: 850 \({}^{\circ}\)C) for a sufficient dwell time to heat the specimens to the core. Successively, the samples were removed from the oven and clamped in the testing machine surrounded by the pre-heated chamber. After the chamber had been closed around the specimen, the test started. While the tests at room temperature could be conducted using a clip-on extensometer, such a sensor was not available for the testing machine for elevated temperatures. Hence, the crosshead movement was used to calculate the necessary strain for the evaluation of the yield strength Rp0.2 and elongation at rupture A. Due to the inaccuracies associated with the use of the crosshead movement the elongation at rupture was crosschecked with measurements on the broken specimens. While fatigue testing and tensile testing at room temperature was conducted on specimens from both extraction directions, tensile properties at elevated temperature were only determined for the crosswise extraction direction due to limited available material. To describe the cyclic fatigue and deformation behavior, the cyclic properties were determined. The cyclic properties \(\sigma^{\prime}{}_{t}\), b, \(\epsilon^{\prime}{}_{t}\), and c together with the elastic modulus E are used to describe the strain-life curve in accordance with [PERSON] and Manson, [16; 17], Equation (1):  
\[\varepsilon_{\text{a}}\text{= }\varepsilon_{\text{a,el}}\text{+}\varepsilon_{ \text{a,pl}}\text{= }\frac{\sigma^{\prime}{}_{t}}{\text{E}}\text{(2N)}^{\text{b}}\text{+} \epsilon^{\prime}{}_{t}\text{(2N)}^{\text{c}} \tag{1}\]  
The strain-life curve contains the dependency between a constant strain amplitude \(\varepsilon_{\text{a}}\) and the achieved fatigue life in number of cycles until crack initiation N, Figure 3a. Both parts of this equation, the one describing the elastic part of the strain amplitude and the one describing the plastic part, appear as a straight line on a log-log scale. The lines intercept the values \(\frac{\sigma^{\prime}{}_{t}}{\text{E}}\) and \(\epsilon^{\prime}{}_{t}\) at N = 0.5.