تحليل تجربي رفتار رچتينگ لوله پلي استال تحت بارگذاري متناوب تك محوره و فشار داخلي

An Experimental Study on Ratcheting Behavior of Polyacetal Tube Under Uniaxial Ioading and Internal Pressure

در اين مقاله آزمايش هايي تجربي به منظور تحليل رفتار رچتينگ ماده پلي استال تحت بارگذاري متناوب تك محوره و فشار داخلي طراحي و انجام شد. آزمايش هاي تجربي در اين تحقيق به وسيله يك دستگاه پيشرفته سروهيدروليكي انجام شده و اثر دامنه تنش، تنش ميانگين و فشار داخلي بر كرنش رچتينگ و رفتار نرم شوندگي يك لوله از جنس پلي استال بررسي شد. يك عامل سخت شوندگي مناسب معرفي شد و نسبت عمر خستگي ماده پلي استال با آن مورد بررسي قرار گرفت. در يك سيكل بارگذاري معين براي نمونه اي كه عامل سخت شوندگي آن بزرگتر باشد، عمر خستگي كمتري مشاهده شد. نرم شوندگي ماده با افزايش تعداد سيكل بارگذاري بيشتر مي شود. نتايج نشان مي دهند نمونه اي كه مقدار كرنش رچتينگ بيشتري دارد، عمر خستگي كمتري دارد.

In this study, the experimental tests are designed and carried out to analyze the behavior of polyacetal ratcheting under both uniaxial loading and internal pressure. Experimental tests are performed by an accurate servo-hydraulic machine, Instron 8802. Three group tests were presented in which two of the stress amplitude, mean stress or internal pressure was constant to observe the effect of another factor. The effect of stress amplitude, mean stress and internal pressure on ratcheting strain and softening behavior of the polyacetal tube are investigated. Graphs of ratcheting strain, ratcheting strain range, hysteresis loops of group tests were drawn. By using these graphs, some results such as softening behavior obtained. A suitable hardening factor was presented and its relation with the polyacetal fatigue life was examined. In a specific loading cycle for the specimen, whose hardening factor is more than the others, a lower fatigue life predicted. Softening behavior of the material, increases with increasing the loading cycles. The results show that the specimen with the high ratcheting strain value has lower fatigue life.