PSI - Issue 42

Goran Vizentin et al. / Procedia Structural Integrity 42 (2022) 793–798 Vizentin/ Structural Integrity Procedia 00 (2019) 000 – 000

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specimens tested. Modified S-N curves that can be used for the prediction can be obtained by combining equations (1) and (2) into:



 

  

B t e

A

( ) N

(3)

log

 = 



max

3. Results and discussion Equation (3) can be used to plot S-N curves that can be used to predict the deterioration of the ultimate tensile strength of glass/polyester composites exposed to the real marine environment in real time. The necessary coefficients for the equation that have been obtained during the research presented here are shown in Table 1.

Table 1. Regression model data.

Fiber layout configuration

Coefficient A

Coefficient B

R 2 value

UD0°

165,50 153,37 143,51

-0,0349 -0,0252 -0,0162

0,7079 0,6557 0,6540

(0/90)s

(0/45/90)s

The predicted change of the ultimate strength in dependence to the number of cycles is shown only for the (0/45/90)s fiber layout configuration as the most commonly used one in marine structures is shown in Figure 2.

150

0 mths

12 mths

24 mths

100

36 mths

 ŵĂdž ΀DWĂ΁

48 mths

50

60 mths

0

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 1.E+10 1.E+12 1.E+14

N , number of cycles

Fig 2. Predicted S – N curve change, (0/45/90)s polyester/glass composite.

For clearer representation of the environmentally influenced reduction of the expected number of lifecycles, the above used equations can be normalized by setting the  and  parameters to single values. By doing so, the life cycle reduction in dependence of the percentage of the ultimate tensile strength that a marine structure can be expected to endure during its operational life can be illustrated as shown in Figure 3.