PSI - Issue 64

Henrik Becks et al. / Procedia Structural Integrity 64 (2024) 1279–1286 Henrik Becks / Structural Integrity Procedia 00 (2019) 000 – 000

1282

4

splitting tensile strength were determined to be 36 MPa, 28,437 MPa, and 2.9 MPa, respectively. These material samples were cast in non-metallic forms, cured in the formwork alongside the uniaxial tensile tests for one day, and then stored under controlled conditions until testing.

a) geometry

b) FOS layout

c) test setup

20

top view:

100

steel clamp

I

side view:

30 – 50 cm

I

section I-I without reinforcement:

section I-I with reinforcement:

2.5

4

6 mm rebar

12

12

[cm]

Figure 2. a) Specimen geometry, b) FOS layout, and c) fully ensembled test setup.

3.2. Instrumentation To test the newly developed 2D-FOS concept, the preliminary experiments initially focus on a single axis of the three-axis fiber network layout. This allows for the investigation of crucial influencing factors such as the adhesive, fiber type, and primer. Since one of the primary advantages of FOS is its capability to offer quasi-continuous strain measurement across a long measuring length, the measuring fiber was consistently adhered to the concrete surface using a two-component epoxy adhesive. The FOS system employed was the ODiSI 6108 system from Luna Innovations Incorporated , featuring a minimum measurement point distance of 0.65 mm. In recent years, a wide range of fiber types have become available on the market. The main distinguishing factor among them is the coating, which significantly impacts the measurable strain, i.e., the local resolution. To identify the most suitable fiber coating for 2D-FOS, tests were conducted on two commonly used fiber types in a preliminary testing campaign (Becks, Baktheer et al., 2023; Becks, Brockmann et al., 2023). The investigations revealed that – under compressive loading – acrylate-coated fibers yield significantly smoother (less scatter) and more stable (fewer missing data points) recording results compared to polyimide-coated fibers. Assuming that this fundamental behavior can also be applied to tensile loading, an acrylate-coated fiber was initially selected for the presented experiments. To measure the strain across the width of the specimen and additionally determine the strain profile along the longitudinal beam axis, only a single measuring fiber was utilized. This fiber was arranged in a meandering pattern with a spacing of 2.4 cm (Figure 2b). This approach reduces costs and simplifies production, handling, and evaluation compared to using multiple measuring fibers.

3.3. Test types and procedure

For a systematic investigation of measurement reliability and accuracy before and after crack formation, three basic types of experiments were examined: (1) Unreinforced specimens under monotonic loading; (2) Reinforced