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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ratio of at least 5:1, as recommended by Brameshuber et al. (2016). However, the specimen length was smaller than the length recommended by the TRM tensile testing guidelines (ACI Committee 434 2011; Ascione et al. 2018; Brameshuber et al. 2016). 140mm was chosen as it allowed for the test equipment to achieve the target strain rates within the machine's capabilities. Subsequently, two aluminium tabs were epoxy bonded to either side of the gripping sections to distribute the gripping load evenly and prevent any specimen failure in the gripping area. Finally, the region of interest of every sample was coated with white and black spray paint to create a randomised speckle pattern in preparation for the DIC technique. All tests were performed after 28 days.

Fig.1.BTRM coupon specimen.

2.4. Test setup The quasi-static uniaxial tension tests were performed at Queen's University's Heavy Structures Lab using a 100kN capacity Zwick/Roell servohydraulic test system. Dynamic testing was carried out at the Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), Portugal, using a high-rate servohydraulic testing machine that can operate within the range of 1 - 1100mm/s with a load capacity of 20 kN. The machine loading rates for all the tests are listed in Table 1. Any specimen that failed outside the region of interest (in the tab locations) was deemed invalid and discarded (ACI Committee 434 2011). Displacement values were acquired via the Digital Image Correlation technique. Image acquisition equipment, sampling rate, DIC software, subset, step size and virtual gauge lengths for quasi-static and dynamic tests are summarised in Table 2.

Table 2:Image acquisition and analysis. Testing

Analysis

Specimens ID

Sampling rate (Hz)

Subset size

Step size

Virtual gauge lengths

Equipment

DIC Analysis

QS

LAVision 2D DIC system

10

DAVIS 10 GOM correlate

21

13

35

Photron SA3 high-speed camera; one halogen spotlight

6400

19

10

50

D

3. Results/Discussion 3.1. Effect of strain rate on Stress-strain response

Fig.2 presents the tensile stress-strain response of the BTRM composite subjected to different strain rates. Tensile stress was calculated by dividing the tensile force (F) by the cross-sectional area of the grid reinforcement (A GRID = 6.7mm x 3 x 0.039mm) (Brameshuber et al. 2016) and the cross-sectional area of the BTRM composites