ên13th International Conferenceon Fracture June 16–21, 2013,Beijing, China -9- properly. So, it follows that the principal stresses S1 and S2 have almost the same values SY and SX, respectively. 6.3Performance of the mortar layer on the fatigue Given that the thermal shock is a transient phenomenon, which produces variation in the stress state along time, one can understand the difference between the final state and the initial state of stresses as the alternated loads that affect the structure. Then it is appropriate to evaluate the performance of the structure (specifically the adhesive mortar) as fatigue, determining how many cycles of alternating stresses (S) are necessary to the rupture. In this paper, only the performance of the layer of adhesive mortar is evaluated. For this, Equations 12 and 13 are used, which displays the linearized equation of SN curve (or Wöhler curve) for the adhesive mortar, obtained under test. The critical situations, where the highest stresses occurred, in the mortar, were on top of layer (grout interface) to the stresses S2, and at the base of the layer (plaster interface) to stress S1, both in section BB’ section. ܵ ൌ 9,5771 െ 0,7523 logሺܰ ሻ, ܰ൏1,1ൈ10 (12) ܵ ൌ ߪ ோ ൌ5,06 , ܽܲܯ ܰ1,1ൈ10 (13) Table 3 – Calculation of alternatedstress CASE1 (CLEAR CERAMIC) PRINCIPAL STRESSES (MPa) ALTERNATED STRESSES(MPa) during shock 120 min S = S (120 min) ‐ S (Shock) S1 ‐0,27579 ‐0,06181 ‐0,06181 – (‐0,27579) = 0,21398 S2 ‐2,16630 ‐0,55252 ‐0,55252 – (‐2,16630) = 1,61378 CASE2 (DARKCERAMIC) PRINCIPAL STRESSES (MPa) ALTERNATED STRESSES(MPa) during shock 120 min S = S (120 min) ‐ S (Shock) S1 ‐0,47798 ‐0,12571 ‐0,12571 – (‐0,47798) = 0,35227 S2 ‐3,75780 ‐1,10190 ‐1,10190 – (‐3,75780) = 2,65590 So for both cases, there is no risk of fatigue failure in any of the directions of principal stress, because the variation of both principal stresses ΔS1 and ΔS2 is smaller than the threshold fatigue resistance ( ߪ ோ=5,06 MPa). 7. Final Thoughts The methodology consisted of three phases: characterization tests of the behavior of the adhesive mortar when subjected to cyclic loading; the conception of an analytical equation to explain the temperature distribution inside the coating structure, in responseto the incidence of heat loss shock;
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