PSI - Issue 17

Ana Isabel Marques et al. / Procedia Structural Integrity 17 (2019) 1002–1009 Author name / Structural Integrity Procedia 00 (2019) 000–000

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to the specimen between these sections, on opposite faces, as the cyclic compression test is taking place, and compensate some of the geometric and volumetric defects of the specimen.

Fig. 2. Instrumented test specimen for a static E test.

The static E tests were carried out on a mechanical test machine (ETI – HM-S/CPC from PROETI) using displacement control for the compressive loading cycles, with an experimentally determined loading speed of 0.375 mm/min. The resulting load was measured using a piezoelectric load cell mounted in the test machine and recorded, together with the data from the displacement transducers, at 2 Hz. The following methodology describes the proposed experimental methodology developed to determine static E for coating mortar specimens: 1. Place the instrumented specimen in the loading device. Move the specimen to the center of the lower plate, with the dedicated spherical plain bearing on top of it. Remove the spacing bars from the measuring device; 2. Apply a small load on the specimen (500 N was used as threshold value). This guarantees that any major gaps between the plates and the specimen are closed; 3. Perform one cyclic compression test on the specimen up to 0.33 of its σ c , to make sure that any internal voids and gaps are closed for the rest of the test; 4. Gauge if flexion was applied on the specimen during the initial cycle, by comparing the data obtained from the two displacement transducers (Fig. 3, left). Differences between both displacement transducers can’t be higher than 25% of applied peak displacement; 5. Without fully unloading the specimen, start another cyclic compression test comprising three loading cycles, again up to 0.33 of the specimen’s σ c . This is the main part of the experimental methodology and provides the data to calculate the specimen’s E value (Fig. 3, right).

Fig. 3. Static E test results example: (left) displacement-time data from the two displacement transducers; (right) average stress-strain curve.