應用貼紙格線與應變片互補理測應力－應變曲線

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Title:	應用貼紙格線與應變片互補理測應力－應變曲線
Authors:	陳文璟鍾傑仲陳正雄
Contributors:	機械系
Keywords:	拉伸試驗應力－應變曲線上降伏點貼紙格線影像處理軟體應變片應變貼紙格線量測之應變值應變片量測之應變值
Date:	2006-06
Issue Date:	2010-06-08 11:39:38 (UTC+8)
Abstract:	本實驗之應變量測結果驗證『降伏點伸長』現象中之Lüders bands蠕動學說；也確認在有上下降伏點之拉伸試驗，以應變片量測方法量測應變只適用至上降伏點止。本實驗也再度驗證應用貼紙格線與影像處理軟體之應變量測方法能精確地用來量測上降伏點之後的應力－應變曲線。在無上下降伏點之拉伸試驗，本實驗也確認應用貼紙格線與影像處理軟體所量測之應變值大於0.001 (0.1%或1000με)時，其精確度可以達±10%之內。針對應變片只能量測小應變，而貼紙格線只能量測大應變，而不能個別應用來量測完整之應力－應變曲線，本文先對格線應變量測法與應變片應變量測法所量測之應變精確度加以詳細分析，然後擬出應用貼紙格線與應變片互補量測應力－應變曲線之方法：(1)有上下降伏點時，採用應變片量測之應變值至上降伏點，接續以貼紙格線量測之應變值直至試片拉斷；(2)無上下降伏點時，採用應變片量測之應變值至0.2%偏斜線與應力－應變曲線之交點，接續以貼紙格線量測之應變值直至試片拉斷。 The results of strain measurements in this paper confirm the hypothesis of the propagation of Lüders bands across the gage length in the so called "yield point elongation." In this case, we find that the strain gages can accurately measure strains only up to the upper yield point in tensile test. The application of grid tab and image-handling software in strain measurement has been once again verified accurate and suitable for measuring the stress-strain curve in tensile test after the upper yield point. We also confirm that the accuracy of strains measured by using this method could be within±10%, if the measured strains are greater than 0.001 (0.1% or 1000με) in a tensile test without an upper yield point. Because the strain gages can measure only the small strains and the grid tabs can measure only the large strains, neither can stand along to be employed in the measurement of a whole stress-strain curve in tensile test. We first analyze the accuracy of the strains measured by using strain gages and those measured by using grid tabs and image-handling software, and propose the following complementary stress-strain curve measurements using a grid tab and a strain gage: (1) using the elastic strains measured by the strain gage up to the upper yield point, and followed by using the strains measured by the grid tab till the end of the test to construct a stress-strain curve when there is an upper yield point; and (2) using the strains measured by the strain gage up to the intersection point of the stress-strain curve by the 0.2% offset line, and followed by using the strains measured by the grid tab till the end of the test to construct a stress-strain curve when there is no upper yield point.
Relation:	華岡工程學報 20期 P.19-28
Appears in Collections:	[College of Engineering] Chinese Culture University Hwa Kang Journal of Engineering

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