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  • 學位論文

聚酯加勁格網於不同溫度環境下應力應變行為之探討

The Stress and Strain Behavior of a Polyester Geogrid under Different Temperature Conditions

指導教授 : 謝啟萬

摘要


地工合成材屬於高分子聚合物,容易受到溫度、水化、化學效應及紫外線等因素之影響,地工加勁格網為地工合成材料之ㄧ種,其應用於大地工程上已行之多年,且應用之區域包含寒帶、溫帶、熱帶及沙漠地區等。由於且目前地工加勁格網之特性仍集中於標準環境中,為暸解聚酯加勁地工格網於各種不同溫度環境下之應力應變行為,因而進行短期抗張強度試驗與潛變試驗。 本研究採用台灣地區生產之聚酯加勁地工格網,其標稱強度為100kN/m × 100kN/m,試驗前先進行地工格網之基本物理性質(包含開孔率、每米肋條數、肋條寬度等),以了解地工格網之形式。研究係採用ASTM D6637進行地工格網於不同環境溫度(0℃~80℃)下之抗張特性試驗,暸解溫度對於地工加勁格網之影響性,以及ASTM D5262進行10℃、20℃、40℃之傳統1000小時潛變試驗,以了解溫度對於長期應變之影響性,且為瞭解階段式恆溫加速潛變試驗(ASTM D6992)於聚酯地工加勁格網之適用性,探討試驗最終溫度與斷裂時間之關係。 由研究結果顯示,地工加勁格網於環境溫度0℃~70℃中,其強度成線性遞減,遞減率大約 -0.25%/℃,而當溫度環境70℃~80℃之間時,其遞減斜率大約為-1.26%/℃;在此溫度環境抗拉試驗中,極限延伸率大約介於10%~11%之間,並沒有明顯之變化,因此推估,此聚酯加勁格網之玻璃轉化溫度(Tg)介於70℃到80℃之間。 傳統長期潛變試驗發現,若以同樣百分比之荷載、不同環境溫度狀況下其應力應變斜率會呈現一致;其10℃、20℃與40℃之初始延伸率分別為6.71%、7.04%與7.83%,但潛變模數分別為1191 kN/m、1088 kN/m與932 kN/m;而此情況下之1~1000小時之潛變增量大約為0.6%。 若以相同荷重(40℃之65%UTS)75.00kN/m、不同溫度狀況下,其應變斜率與初始延伸率皆會不同,別為10℃、20℃與40℃為初始延伸率分6.56%、6.96%與7.83%,其斜率大約為0.044 ℃/ log (t,hour)~0.065 ℃/ log (t,hour)之間,且其潛變模數分別為1123 kN/m、1038 kN/m與932 kN/m;而此情況下之1~1000小時之潛變增量介於0.33%~0.67%之間,且溫度上升10℃時,其初始延伸率增加約0.4%。 在傳統潛變破壞試驗中發現,當溫度環境升高,其延伸率增加,折減係數也相對提升,因此斜率由10℃之-2.080 %UTS / log (t,hour)增加到40℃為-2.593 %UTS / log (t,hour),由此得知,溫度會造成潛變破壞時間提前。加速潛變部分發現,若以極限荷重70% UTS(8.09kN)來觀察,當溫度高於65℃時,試片斷裂延時均小於10800秒之溫階延時,由此可知,試驗荷載與最終溫度均為SIM加速潛變試驗之重要因素。

並列摘要


Geosynthetic is an environment and temperature sensitive material. It has been widely used in cold, warm, tropical, and arid areas. The major international test standards for the mechanical properties of geosynthetic are prepared in the 20C standard condition. Therefore, the objective of this study is to investigate the tensile and creep behavior of a polyester geogrid at different temperature conditions. A nominal tensile strength of 100 kN/m by 100 kN/m produced by a local manufacturer was used in the study. The tensile strength of the geogrid was tested according to ASTM D6637 standard test method under different temperatures varying from 0C to 80C. 1000-hour ASTM D5262 conventional creep tests at temperatures of 10C, 20C, and 40C were performed. The maximum step temperature for the accelerated creep test according to ASTM D6992 test standard was also investigated. The results of the tests indicated that the tensile strength of the test geogrid decreased as the test temperature increased. The strength decreasing rate was -0.25% per degree of Celsius up to 70C. However, the tensile strength decreasing rate was -1.26% per degree of Celsius as temperature changing from 70C to 80C. It is believe that the glass transition temperature of the polyester yarn is within the range of 70C to 80C for the test geogrid and the phenomenon of glass formation might have some effects on the engineering behavior of the test geogrid. The elongation at break was about 11% for the tested conditions varied from 0C to 80C. The creep strain rate also increased as the test temperature increased. Temperature and tensile creep load would affect the initial creep strain and creep strain rate of the conventional tensile creep test. Under same creep tensile load or same percentile of UTS tensile load, the initial creep strain increased as increasing the test temperature. However, the creep modulus decreased as the test temperature increased. The creep strain rate varied from 0.044 C/log(t,hour) to 0.065 C/log(t,hour) for the temperature condition changing from 10C to 40C. The results of the accelerated creep tests indicated that the required rupture time linearly decreased as creep load increased on a log time scale. The decreasing rate on rupture time increased as the test temperature increased. Since test sample would break for the time less than 10800 second as the test temperature at 70C and creep tensile load of 70% UTS, it is recommended that the maximum step temperature for accelerated creep SIM test should not be exceeded to the glass transition temperature of the PET yarn.

參考文獻


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被引用紀錄


焙富莊(2011)。聚酯纖維於製程烘烤溫度與張應力作用下抗張潛變行為〔碩士論文,國立屏東科技大學〕。華藝線上圖書館。https://doi.org/10.6346%2fNPUST.2011.00244

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