PSI - Issue 18
Abdeljalil Jikal et al. / Procedia Structural Integrity 18 (2019) 731–741 Abdeljalil JIKAL et al./ Structural Integrity Procedia 00 (2019) 000–000
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In order to correct this discrepancy, the formula (3) is corrected by a new coefficient that represents the ratio between the maximum force max F and the force at break r F .Then, the approximate corrected equation of Faupel is given by:
D
2
y
t
(6)
F
S
2
ln
.
y
n D
3
u
f
f
Where
F
max r F
Afterwards, the corrected forces obtained by the Eq. (6) are represented as shown in Fig.4.
Fig. 4. Evolution of theoretically corrected force and experimental force of damaged strands as a function of the life fraction.
4.3. Static damage The corrected theoretical damage model is obtained by combining the static damage, based on the breaking forces, to the corrected breaking force formula of Faupel for different life fractions. Therefore, we obtain the ultimate force u F , the ultimate residual forces ur F and the applied force F , which corresponds to the life fraction just before breaking a F . Then, these forces were integrated in the static damage Eq. (4), to obtain the corrected model. Finally, we represent the theoretical and the experimental damage in comparison as a function of life fraction of strand as shown in Fig. 5. The damage evolution is monitored for different levels of degradation, from the virgin strand up to the last strand immersed in H � SO � solution. The increase in damage means that the strength of specimens is lost during the static tensile test. This loss becomes more significant as the immersion time increases. According to Fig. 8, three stages of damage evolution can be distinguished: Stage I is the initiation of the strand failure for the life fraction between � � ���� ���� of damage to the strand, the damage is slowly increasing. Stage II reached for the life fraction between � ����� ���� . In this phase, the damage is progressive and predictive maintenance is essential to industrial user. Stage III, which is characterized by a critical life fraction � � ��� of damage to the strand, which corresponds to twenty-four hours of immersion in the acid solution. After that, the progressive damage is suddenly accelerated and the strand break can be brutal for low level of load.
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