PSI - Issue 25

P. Santos et al. / Procedia Structural Integrity 25 (2020) 370–377 P. Santos./ Structural Integrity Procedia 00 (2019) 000–000

375

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Fig. 5 compares the theoretical data with the experimental results for 2xhybrid laminates, and the final bands represent the maximum and minimum values obtained. Table 3 summarizes all parameters of the KWW model and respective error relatively to the experimental results, while Table 4 summarizes the Findley parameters and respective errors. The maximum errors obtained with the KWW model and Findley model are 0.43% and 0.17%, respectively, which evidences the good accuracy obtained with these models.

52

1,1

Experimental average curve Findley model

Experimental average curve KWW model

50

1,0

48

0,9

46

Displacement [mm]

Flexural stress [MPa]

0,8

44

0

50

100

150

200

0

50

100

150

200

Time [min]

Time [min]

a)

b) Fig. 5 a) Stress relaxation for 2× hybrid laminate, comparison between experimental average curve and theoretical curve obtained with the KWW model for bending stress of 50 MPa; b) Creep curves for 2× hybrid laminate, comparison between experimental average curve and theoretical curve obtained with the Findley model for bending stress of 50 MPa.

Table 3. Parameters of the KWW model for stress relaxation for 2× hybrid laminate.

Bending stress after 3 hours [MPa]

Initial bending stress [MPa]





Experimental value  KWW value  Error [%] 

50

0.230 6.435×10 6

45.91

45.8

0.24

118

0.236 1.879×10 6

105.8

105.4

0.30

0.241 1.376×10 6 158.3

157.6

0.43

177

Table 4. Parameters of the Findley’s law model for creep.

Bending stress after 3 hours [MPa]

A

n

Initial bending Stress [MPa]

 

Experimental value  Findley value  Error [%] 

50

0.408 0.426 0.0205 0.93

0.92

0.16

118

0.830 1.176 0.0249 2.32

2.31

0.17

177

0.862 1.899 0.0243 3.25

3.24

0.13