PSI - Issue 44

Rebecca Fugger et al. / Procedia Structural Integrity 44 (2023) 2166–2173 Author name / Structural Integrity Procedia 00 (2022) 000–000

2169

4

under displacement control at 1.0mm/min rate for textile-only specimens and 0.5mm/min for lime-only and composite specimens, using a universal Material Testing System (MTS) load frame with 100kN capacity. As far as the frame is concerned, it is composed by four steel plates measuring 300mmx50mmx15mm to be positioned staggered around the specimen in order to confine it. Four hinges are then placed in the corners formed by the plates allowing for rotation. Moreover, to avoid the sliding of the textile from the frame, four steel plates, measuring 198.5mmx50mmx15mm and specifically shaped to not touch the hinges, are bolted to the plates that round the specimen. In order to perform DIC, black and white pictures were taken at 5s time interval by a digital camera placed on a stiff frame at 1.00m from the specimen. Pictures had 6016x4016 pixels, corresponding to a pixel size of 0.147mm. As also explained by Blaber et al. (2015), image correlation provided, for each picture, the vertical and horizontal displacement and vertical strains of the entire specimen, with respect to the first picture, taken before starting the test. Fig. 3 shows a big picture of the experimental set-up comprising the camera used for DIC.

Fig. 3 - Experimental set-up for (a) bare textile; (b) mortar and composite specimens and (c) position of the camera for DIC.

3. Main outcomes Table 1 collects, in addition to the specimen type and test code, the main results of the individual tests, namely the average values of the maximum shear stress (τ max ), the corresponding shear deformation (γ(τ max )), the shear modulus (G) and the maximum shear load per unit width (τ* max ). The results of direct shear tests are calculated according to the instruction of ASTM E519-07 (2007) guideline: 0.707 P

 

(1)

A

n

V H g 0.707 P w   





(2)

  

(3)

Where A n is the net area of the specimen calculated as the product of the width w of the specimen (200 mm for all specimens) for the thickness (10mm for the mortar and for the composite specimen and 0.064mm for the textile), P is the applied load recorded by the testing machine, ΔV and ΔH are the vertical extension and the horizontal shortening of the specimen respectively, evaluated by DIC analysis, and g is the gage length (about 300 mm for the textile and