PSI - Issue 48

Milan Travica et al. / Procedia Structural Integrity 48 (2023) 280–287 Travica et al / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Previous research [1] utilized structural steel S235JRH to create Pipe Ring Tensile Specimens (PRTS) for the purposes of the current study. The paper also reviewed earlier research to establish a basis for testing the steel PRTS. In recent years, researchers have made several attempts to optimize the shape of test specimens in order to achieve a uniform distribution of stress and strain. These attempts include shear tests, plane strain tests, and tensile tests [2][3]. The objective of these research activities is to obtain reliable experimental data that represents a known stress and strain distribution, which can be used to determine material properties and anisotropy in metal sheets. However, characterizing thin-walled tubular materials poses challenges as they are not flat struc-tures like sheets. Simple procedures such as cutting specimens from flattened pipes and subjecting them to uni-axial tensile tests are still used [4, 5]. However, flattening the pipes introduces pre-strains and residual stresses that affect the material behavior and the accuracy of material parameter identification [6, 7]. To address these issues, researchers developed the Ring Hoop Tensile Test (RHTT), initially designed for evaluating the hoop mechanical properties of thermoplastic tubular materials [8]. The primary advantage of the RHTT method is that it allows examination of the tubular material properties in the hoop direction without the need for flattening, which can cause excessive work hardening. The RHTT technique was first proposed by Price in 1972 to investigate the effect of hydride precipitation on fracture resistance in Zircaloy pipes under high tem-peratures [9]. Subsequently, Mehan et al. utilized the ring hoop test to study the mechanical properties of a low-pressure plasma-deposited nickel-base superalloy in the hoop direction [10]. Arsene and Bai [11] developed an enhanced RHTT method using double-D mandrels and a dog-bone insert to investigate the influence of friction between the ring and D-shaped block, as well as the impact of sample geometry on stress distribution homogeneity. Link et al. [12] employed a large RHTT specimen arrangement to assess the ductility of Zircaloy-4 cladding tubes under near plane-strain deformation. Wang et al. [13] devised a ring hoop tensile test to avoid flattening ring specimens and establish the hoop stress-strain curve of thin-walled tubular materials. Jiang et al. [14] and He et al. [15] conducted RHTT on magnesium-based alloy tubes to study formability at different temperatures. Similarly, Dick and Korkolis [7] performed a ring hoop tensile test on a dog bone-shaped specimen, while Barsoum and Al Ali [17] employed numerical analyses to develop RHTT sam-ples and calculate the friction coefficient. Nagase et al. [18] investigated the mechanical properties of Zircaloy cladding in the hoop direction using analytical and experimental methods for shape optimization of RHTT sam-ples, with a focus on minimizing friction and bending effects. Various researchers have explored the behavior of metallic pipes in the hoop direction using different ring specimen geometries, as summarized in Table 1. However, there is no standard or universally accepted design for metallic RHTT specimens. The recommended dimensions in the literature are often inconsistent, and it re-mains unclear if the employed ring specimens undergo uniaxial tensile strain and stress states. Additionally, the friction between the ring sample and the tooling affects the mechanical properties of the produced ring along the hoop direction. Some studies overlook or underestimate the friction effect, while only a few have considered it [14][18].

Nomenclature DIC Digital Image Correlation PRTS Pipe Ring Tensile Specimen RTHH Ring Hoop Tensile Test