PSI - Issue 37

P.N.B. Reis et al. / Procedia Structural Integrity 37 (2022) 934–940 P.N.B. Reis et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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of the tests performed for the other loading modes. It is possible to observe a consistent behaviour and without significant dispersion, which justifies the low scattering that will be observed. Figure 3 plots the average load versus time obtained for a fixed displacement correspondent to 40% of the yield stress, where P is the load at any given moment of the test and P 0 is the initial load. The creep behaviour is also shown (Fig.3b), where the displacement is the value obtained at any instant of the test (D) divided by its initial value (D 0 ).

8 10 12 14 16 18 20

3.5

a)

3.1

2.7

2.3

Bending load [N]

1.9

b)

Bending displacement [mm]

1.5

0

50

100

150

200

0

50

100

150

200

Time [min]

Time [min]

Fig. 2. Repeatability of the curves for 40% of the maximum bending stress for: a) Stress relaxation; b) Creep.

0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Bending mode Compression mode Tensile mode

P/P 0 [-]

D/D 0 [-]

Bending mode Compression mode Tensile mode

a)

b)

0

50

100

150

200

0

50

100

150

200

Time [min]

Time [min]

Fig. 3. For different loading modes: a) Stress relaxation curves; b) Creep curves.

From Fig. 3a, it is noticed that the load decreases with time for all loading modes, but this tendency becomes more pronounced for the tensile mode. For example, compared to the bending mode, the loading mode that presented the lowest stress relaxation, the compressive mode presents a stress relaxation 18% higher and 25.4% for the tensile mode. This behaviour can be explained by physical and/or chemical phenomena, where, in the first case, molecular rearrangements that require little formation or rupture of primary bonds explain the observed decrease, while from a chemical point of view it is justified by the chain scission, crosslink scission or cross-link formation. Any decohesion that may occur between the printed interface layers or the air gaps between adjacent printed layers can also contribute for the observed decrease. In terms of creep (Fig. 3b), all curves present an instantaneous displacement, followed by