PSI - Issue 47

Andreal Muhammad Naufal et al. / Procedia Structural Integrity 47 (2023) 133–141 Naufal et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2.1. Honeycomb material Nomex honeycomb is a bionic honeycomb core material made of poly (m-phenylene isophthalamide) fiber paper. Nomex honeycomb has many advantages including, high strength, rigid, high corrosion resistance, fire resistance, good environmental resistance, material that is resistant to vibration, and a resilient material (Xie et al., 2020). Because of this, the honeycomb Nomex material was chosen as the core of the CWP OTEC constituent material. The dimensions of the honeycomb Nomex used are 4.5 mm thick these dimensions are obtained from the scaling of sandwich core material used by Lockheed Martin (Miller et al., 2012). Details of honeycomb cell sizes can be seen in Figure 2. Material properties of honeycomb are needed for modeling on ABAQUS, for that the authors consider the material properties of Nomex honeycomb which is presented in Table 1. These material properties are sourced in a paper written by Roy et al. (2014).

Figure 2. Nomex honeycomb cell dimensions (in mm).

Table 1. Material properties of the nomex honeycomb. ρ (g/cm 3 ) E 1 (MPa) E 2 (MPa) E 3 (MPa)

N 1 (-)

N 2 (-)

N 3 (-)

G 1 (MPa)

G 2 (MPa)

G 3 (MPa)

0.64

5200

4400

4400

0.24

0.24

0.24

1400

1400

1400

2.2. Bidirectional carbon fiber Carbon fiber is a material with a very large ratio of strength and weight (Sharma et al., 2014) for this reason, the author chose carbon fiber as a material for facing sandwich CWP OTEC. With a lightweight and strong material, it is expected that the pipe can be made as light as possible with strength that can withstand the desired hydrostatic pressure. Table 2. The following shows the material properties of carbon fiber.

Table 2. Material properties of the carbon fiber. ρ (g/cm 3 ) E 1 (MPa)

E 2 (MPa) 112000

N 1 (-) 0.3

G 12 (MPa) 4500

G 23 (MPa) 4500

G 31 (MPa) 3000

1.58

112000

Material properties are collected from previously existing papers, for the above properties are collected from papers made by Isbilir et al. (2012). In the original paper, the properties are unidirectional carbon fiber. In this paper, the author assumes the strength of E 1 = E 2 for the bidirectional properties of carbon fiber. The facing part of the sandwich material consists of 3 layers with an orientation of 0-45-0 to obtain a good spread of tensile. 3. Testing Method The material is tested using three-point bending with the ASTM D7264 procedure, which is the standard procedure for testing composite materials. Figure 3, it is explained the schematic of testing. The material is placed on a jig with a length of L with a load point right in the middle of the jig (ASTM, 2007). Material dimensions made to meet the test standards of ASTM D7264 are recommended in specimen procedures to be at least 20% longer than the