PSI - Issue 64

Amrita Milling et al. / Procedia Structural Integrity 64 (2024) 1009–1016 Milling/ Structural Integrity Procedia 00 (2024) 000 – 000

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technique. BTRM quasi-static tests were also performed for strain rate comparison using a Zwick/Roell conventional servohydraulic test system.

Nomenclature A GRID Cross-sectional area of grid A BTRM Cross-sectional area of composite D Dynamic ̇ Strain rate F Tensile force QS Quasi-static

2. Experimental Methodology 2.1. Testing programme

Fourteen BTRM samples were tested in this study: four at quasi-static and ten at intermediate strain rates, as shown in Table 1. Specimens were named 'QS' and 'D' for quasi-static and dynamic specimens, and the number segment of the ID represents the actual strain rates determined from strain-time plots.

Table 1: Specimen ID and loading rates. Machine Loading rate [mm/s]

Strain rate [1/s]

Specimen ID QS-0.0069/s QS-0.0086/s QS-0.0094/s QS-0.0100/s

0.005 < ̇ ≤ 0.01

1/300

0.5 < ̇ ≤ 1 6< ̇ ≤10 ̇ ≈2

D-0.59/s D-0.65/s D-0.72/s D-0.95/s D-2.22/s D-2.28/s D-2.41/s D-6.17/s D-7.84/s D-9.04/s

50

250

500

2.2. Materials The BTRM composites were made using the MAPEI ® brand Planitop HDM maxi mortar and an alkali-resistant basalt fibre grid. The matrix is made of polymer cement, short glass fibres, and special admixtures and has a maximum aggregate size of 1mm. The flexural and compressive strength after 28 days was 6.4 MPa (COV 9%) and 37.4 MPa (COV 5.88%), respectively, as determined by EN 196-1:2005 (British Standards Institution 2019). The grid is bidirectional with a 6.7mm x 6.7mm centre-to-centre cell size. According to the manufacturer's data, it has an equivalent dry thickness, fibre density, tensile capacity and elastic modulus of 0.039mm, 2.75 g/cm 3 , 60 kN/m, and 89 GPa, respectively.

2.3. Specimen preparation

A BTRM slab measuring 500mm x 140mm x 8mm was cast in a fabricated mould using the wet layup technique. The composite material was strengthened by incorporating a single layer of the grid material over the whole length of the specimen and two layers of the grid material in the gripping areas, as illustrated in Fig.1. Following the curing process, coupon specimens of 140mm x 25mm x 8mm were cut using a ban saw. The specimen had a length-to-width