Investigation of strain measurements in (curved) wide plate specimens using digital image correlation and finite element analysis

Abstract

Some pipelines face global plastic straining due to the nature of their installation process or harsh environmental conditions during operation. The ability of the girth welds to withstand these plastic strains is often evaluated on the basis of wide plate tests. Key for the validity of these tests is a representative measurement of remote strain, mostly obtained by linear variable differential transformers and/or strain gauges. The outcome of the remote strain measurement depends on the specimen geometry and the position of these sensors. In an attempt to investigate a specific geometric design of wide plate specimens and to find appropriate remote strain sensor positions, the authors have performed a series of tension tests on medium-sized wide plate specimens, supported by digital image correlation strain measurements. In addition, finite element simulations have been performed to evaluate whether the experimental observations can be extrapolated to a wider range of conditions. The results indicate that the strain distribution is mostly influenced by the weld strength mismatch, which governs the lateral restraint. For all experiments and simulations, nevertheless, the strain field was highly uniform in an identified zone, resulting in simple guidelines regarding specimen geometry and sensor positioning.

Single-specimen evaluation of tearing resistance in SENT testing

“…Although insulation might be achievable for smaller specimens, this is definitely an asset when considering the evaluation of ductile crack extension in large scale specimens (e.g. curved wide plate specimens [35]). …”

Digital image correlation method in experimental analysis of fracture mechanics parameters

“…This method has found a widespread use in engineering and analytic work, in measuring strain in engineering structures, and analyses of mechanical parameters of engineering materials and biomaterials [15,[23][24][25][26][27]. Using a suitable image processing, the DIC method can quantify even large strains, and is also therefore used to analyse plastic material deformation.…”

Comparison of girth weld tearing resistance obtained from Curved Wide Plate and Single Edge Notch Tensile testing

“…These specimens fit Soete Laboratory's 2500 kN test rig, which provides an excellent visibility of the test specimen. The latter is required for the application of full field deformation measurements [22,23], which were performed during this test program for reasons that are outside the scope of this paper. The initial notch has a near to semi-elliptical shape.…”

“…During this test, the applied load and full field surface deformation is recorded. The latter is evaluated using the Digital Image Correlation (DIC) technique and allows to evaluate the remote strains in both base plates, as described by Hertelé et al [5,23].…”