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T rue stress logarithm ic strain curves test of pipeline steels using 3D digital image correlation

L. Z. KONG1,* , J. SHUAI1, Y. ZHOU2, K. HUANG2, G. J. YU3

Affiliation

  1. College of Mechanical and Transportation Engineering, China University of Petroleum Bejing, Beijing 102249, China
  2. Department of Oil and Natural Gas Engineering , Southwest Petroleum University, Chengdu 610500 , China
  3. Merchant Marine College, Shanghai Maritime Uni versity, Shanghai 201306, China

Abstract

True stress logarithmic strain curves of two pipeline steels, API 5L X65 and X90, using the 3D DIC (digital image correlation) technique were tested. T hree methods to obtain the true stress were studied Method I is based on the displacements of the front and lateral face s of the specimen. Method II , which is based on the longitudinal logarithm ic strain, was verified by method I The results of m ethod II revealed to be smoother and more stable. Method III, which is based on the transvers e logarithm ic strain, was shown to be invalid after the onset of necking. Six points located in longitudinal and transverse directions of the specimen were studied and the results showed that points’ location had little effect on tru e stress logarithmic strain curves if the points were on the line of fracture. The material properties of API 5L X65 were compared with those of API 5L X90. API 5L X65 has a higher value of ultimate stress and API 5L X90 has a higher value of ultimate loga rithm strain. Comparisons for the yield stress and nominal elongation were also made..

Keywords

True stress, Logarithmic strain, Pipeline steel, API 5L X90, Digital Image Correlation.

Citation

L. Z. KONG, J. SHUAI, Y. ZHOU, K. HUANG, G. J. YU, T rue stress logarithm ic strain curves test of pipeline steels using 3D digital image correlation, Optoelectronics and Advanced Materials - Rapid Communications, 9, 11-12, November-December 2015, pp.1380-1388 (2015).

Submitted at: Sept. 12, 2015

Accepted at: Oct. 28, 2015