PSI - Issue 19

Masahiro Takanashi et al. / Procedia Structural Integrity 19 (2019) 275–283 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Experimental procedures

2.1. Test specimens

Two types of materials were employed in this study: a 100-mm-thick rolled plate of normalized carbon steel for machine structural use, namely JIS S45C (Carbon content 0.45%), and a 161-mm-thick rolled plate of quench and tempered low-alloy steel for pressure vessels, namely JIS SQV2A. The low-alloy steel was quenched at 880 °C for 310 min and tempered at 615 °C for 45 h. The mechanical properties obtained from tensile tests are listed in Table 1. The plate specimen was subjected to a fatigue test. As shown in Fig. 1, the test specimen was 1000 mm long, 150 mm wide, and 90 mm thick. A shallow dull notch was installed in the center of the specimen to limit the crack initiation site. The notch surface was machined to Ra 3.2 μm and finished with sandpapers #200, #400, #600, #800, and #1000 sequentially, in a similar manner to that followed for a small-sized specimen. The stress distribution in the vicinity of the notch root determined via the finite element analysis was reported in the previous study (Takanashi et al., 2018). The stress concentration factor due to the notch was 1.27.

Table 1. Mechanical properties. Material

0.2% proof stress (MPa)

Ult. tensile strength (MPa)

Elongation (%)

Reduction of area (%)

S45C

487 448

637 597

24 26

68 77

SQV2A

Fig. 1. Configuration of large-scale specimen (unit : mm).

2.2. Testing methods

A fatigue test was conducted using an electrohydraulic servo control fatigue testing machine (capacity: 2 MN). The loading method was four-point bending with an inner span of 300 mm and an outer span of 800 mm. Before the fatigue test, the enforced displacement was statically applied to the specimen, and the relation between the actuator displacement and the longitudinal strain at the notch root measured using a strain gauge of 1 mm gauge length was obtained. Based on this relation, the fatigue test was performed with the actuator displacement controlled. During the fatigue test, the testing machine was periodically stopped to allow the surface crack to be observed. The strain gauges were peeled off and replica observations were performed. Before restarting the fatigue test, the strain gauges were reinstalled. Once visible cracks were detected, a beach mark was introduced to measure the crack depth. For more detailed testing procedures, refer to the previous study (Takanashi et al., 2018).