PSI - Issue 54

Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 626–630

628

Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000

3

Table 1. LMD process parameters

Level -1

Level 0

Level 1

Laser power Scan speed Powder flow Track width

1150W

1300W

1450W

700mm / min

900mm / min

1100mm / min

9g / min

11g / min

13g / min

3mm

Transport gas flow

5 l / min 12 l / min

Inert gas flow Track overlap

50%

a)

b)

Fig. 1. Tensile testing setup, a) eletromechanical testing machine with lighting and image acquisition system b) specimen with random speckle pattern

20 Run Orders were manufactured, according to the DoE, and 3 specimens of each were tensile tested at displace ment rate of 1 mm / min. Strain was measured through digital image correlation (DIC). Specimens were painted with a white base-coat and random speckle pattern of black dots to enable full-field 2D strain measurement in the specimen. Fig. 1 a), shows the testing setup including the illumination required for uniform image acquisition, as well as the camera and optical setup for periodic time image acquisition for DIC. The specimens used, as exemplified in Fig. 1 b), are smaller than regular size ASTM E8M specimens, to ease their manufacturing, as well as enabling tensile testing with the same specimen design on di ff erent equipment at di ff erent strain-rates to study its e ff ect on the performance of these materials in future studies. Nevertheless the reduced size of the specimens will result in a size e ff ect on strain measurement with these specimens. Fig. 2 shows the evolution of the strain field on one of the specimens, namely a specimen of Run Order #7, measured through DIC. The strain field evolution and failure was consistent in all tested specimens of all process sets manufactured. All specimens showed a brittle failure and DIC measured strain field shows inconsistent strain evolution along the specimen, demonstrating significant anisotropy. The large deposition beads, with ≈ 1 mm width, and height of ≈ 0.28 mm, with close to 50 % overlap between beads, may have contributed to this anisotropy. Also some small porosity was found speckled throughout the specimen. This pores were at their largest 1.5 µ m in diameter. Besides the inconsistent strain field throughout the test, the free faces of the specimens also show this uneven deformation, as observed in Fig. 2 close to and after failure. The porosity observed in cross-section microscopy were stress concentrators and coincided with the regions with higher deformations which ultimate led to failure. A significant size e ff ect is observable given the relatively large size of the deposition beads and small dimensions of the specimens.