PSI - Issue 44

Annalisa Franco et al. / Procedia Structural Integrity 44 (2023) 2246–2253 Author name / Structural Integrity Procedia 00 (2022) 000–000

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3

Tab. 1. Properties of the mesh and of the fibre.

P ROPERTY

U NITS

S YSTEM “F”

S YSTEM “G”

MESH PROPERTIES

Weft (flat threads)

Warp (twisted threads)

Weft (circular threads)

Warp (twisted threads)

Mesh size (weft x warp) Mesh opening (weft x warp) Measured area of single bar Width x thickness or diameter of single bar

mm mm mm 2 mm n/m g/m 2

66 x 66 62 x 59

99 x 99 96 x 96

12,30

7,66

7,37

7,04

7,0 x 2,5

3,0 x 3,0

3

3

Bars for each side Mass per surface unit FIBRE PROPERTIES Fibre type

15

15

10

10

420

250

Alkali Resistant (AR) glass

-

Glass 2,65 2400

2,68 600

Fibre density

g/cm 3

Yarn linear density

tex

The experimental campaign was mainly focused on the behaviour of dry glass yarns and the warp direction of grids. Tensile resistance of dry yarns has been assessed by using an Instron Universal Testing Machine (UTM) with a maximum load of 10 kN, as shown in Fig. 2. Yarns were fixed between flat rubber clamps using a pressure of about 5 bars, without using any specific tabs. General reference standard used for the test was ISO 3341 (ISO 3341, 2000). Tests were performed using a gauge length of 500 mm and a pre-tension of 5 mN/tex. The crosshead speeds of 2 mm/min and 200 mm/min were considered for the tests. The 200 mm/min is the value suggested by ISO 3341, while the 2 mm/min is the one indicated for FRP grids according to EAD 340392-00-0104 (EAD 340392-00-0104:11-2018, 2020). Only for the system “F” tests were conducted also at an intermediate speed of 50 mm/min, because tests at 200 mm/min on the FRP grid lately showed that rupture always occurred at the epoxy tab. A deeper investigation is needed on this aspect. Five specimens of length 600 mm were therefore prepared for each system and for each testing configuration. The summary of tested specimens is reported in Tab. 2. Specimens were denoted with the general notation “F(G)_Y(W)_2(50, 200)_ n ”, where the first letter indicates the type of system (F or G), the second letter the element tested (Yarn or Warp) and the third number denotes the displacement rate (2, 50 or 200 mm/min). Lastly, n is the progressive number of tested specimen.

(a)

(b)

Fig. 2. Tensile test of dry glass yarns: (a) tensile test setup; (b) detail of specimen during testing.