Bending Stress Determination in a Pipe Test Bench Using DSPI Combined with Instrumented Indentation

摘要

This paper presents the application of a modular device based on digital speckle pattern interferometry (DSPI) combined with an instrumented indenter, in order to determine bending loads in a reference pipe bench. The system is divided into two modules, the interferometric and the indentation module, which are interchanged during the measurements using a kinematic universal base. Presently there is no documented method that allows to relate the displacement field generated around an indentation with the stress field present inside the indented material. This paper proposes a numerical method to compute stresses in pipes under a bending load from a set of measured radial in-plane displacement fields. This methodology is based on measurements where known stresses are used as a reference. Proportionality constants are used to compute stresses. The performance of the methodology was evaluated by using a test bending stress bench consisting of two 12-m pipes placed horizontally and with a well-known bending moment. Stresses were evaluated as a set of eight points angularly equidistant in eight cross-sections. After that, bending moments and stresses were computed and subsequently compared with the reference values. Good agreement was found between the computed bending stress using strain gauges and load cells, and the proposed method.