微型平板試片之高峰負載減速現象

Abstract

傳統疲勞實驗使用大型的材料試驗機以及標準試片，使得進行一次實驗必須花費較多的成本與時間。利用微型平板試片進行疲勞試驗，比標準試片節省材料與製作成本，改採取微型疲勞試驗機來取代大型材料試驗機，更能藉著其高拉伸頻率來縮短疲勞試驗的時間。 本文以AISI 4340合金鋼和304不鏽鋼為實驗材料，研究微型疲勞試驗機以及微型平板試片應用於觀察高峰負載減速現象之可行性。實驗中，將AISI 4340合金鋼以及304不鏽鋼兩種材料製成微型平板試片，進行高峰負載疲勞實驗，並比較微型平板試片與標準疲勞試片所反映出數據結果之異同。 實驗結果說明微型平板試片於高峰負載後可以發現明顯之減速現象以及減速區，兩種材料減速模式皆和標準疲勞試片之實驗結果相同。配合裂縫封閉之量測，能有效估算其高峰負載施加前之裂縫生長速度。

Conventional fatigue test was conducted by MTS (material test system) with standard CT specimens, it would be time and cost consuming. Using miniature specimens could save material and cost ,and the high working frequency of miniature fatigue test system could save much time during fatigue testing. The experiment materials of this study were AISI 4340 steel alloy, and 304 stainless steel. We prepared miniature fatigue specimens to observe the phenomenon of fatigue crack propagation following an tensile overload. Finally, we discussed the usage and practicability of miniature fatigue specimen testing by comparing the results between standard CT specimens and miniature specimens. After experiments, we can find out the overload retardation phenomenon obviously and retardation modes of the two experiment materials are the same with the results of standard CT specimens. We can also predict the fatigue crack growth rate effectively before applying overload by considering the crack closure.