PSI - Issue 64

Ali Jafarabadi et al. / Procedia Structural Integrity 64 (2024) 2059–2066 A. Jafarabadi et al./ Structural Integrity Procedia 00 (2019) 000 – 000

2060

2

Nomenclature SMA

Shape memory alloy

Fe-SMA

Fe-based shape memory alloy Shape memory effect Initial inner diameter Finished inner diameter Recovered inner diameter

SME IID FID RID AR HT P

As-received Heat-treated

Radial stress component

Circumferential stress component Axial principal strain component Interface contact pressure Outer diameter of the steel tube Inner diameter of the steel tube Circumferential principal strain component

Young’s modulus Poisson’s ratio

Absolut inner diameter expansion Absolut inner diameter expansion

1. Introduction Shape memory alloys (SMAs) have emerged as promising materials owing to their remarkable ability to recover their original shape even after significant deformation. Among SMAs, Iron-based SMAs (Fe-SMAs) have garnered significant interest due to their favorable shape memory behavior, pronounced mechanical properties, and cost efficiency (Cladera et al., 2014, Janke et al., 2005). An essential step toward efficient design of Fe-SMA complex components is to gain a fundamental understanding of the recovery strain and stress formation in multiaxial pre straining cases. The majority of products that have been thoroughly developed and commercially employed at scale are limited to 1D bar and sheet elements, and therefore, characterization is mainly limited to the 1D strain and stress recovery (Khodaverdi et al., 2023, Yang et al., 2021, Leinenbach et al., 2012, Ferretto et al., 2021, Mohri et al., 2023, Janke et al., 2005). To harvest the shape memory effect (SME) beyond uniaxial scenarios (Jafarabadi et al., 2023, Cao et al., 2023, Cao et al., 2022), further characterization is crucial. Despite the examination of Fe-SMA tubes for pipe coupling applications, the majority of studies focus on feasibility assessment, emphasizing the overall clamping capability of Fe-SMA materials (Otsuka, 1998, Liu et al., 1995, Cao et al., 2023, Cao et al., 2022, Lee et al., 2015). The comprehensive quantification of the clamping capacity of Fe-SMA couplers remains an essential aspect that is yet to be thoroughly addressed. The rapid assembly process, the suitability for use in confined work areas, and their cost-efficiency, has positioned Fe-SMA couplers as an attractive alternative to traditional welded and bolted joints. In general, the application of shape memory couplers involves two main steps of pre-straining and activation. Initially, the couplers are manufactured with a smaller inner diameter than the outer diameter of the target pipe/work-piece. Then, through a pre straining process, the inner diameter is expanded to a size that is larger than the outer diameter of the pipe, providing enough clearance for the shape memory coupler to be inserted at the pipe joint. Once installed, activation is carried out by heating the joint to trigger the shape memory effect. Early feasibility studies have demonstrated no leakage under hydrostatic tests up to 40 MPa (Liu et al., 1995). Shape memory pipe couplers have been successfully used in the Wakunami tunnel in Japan shortly after preliminary studies (Maruyama et al., 2011, Otsuka, 1998). Li et al. (Li et al., 2002) reported a tensile strength of 20 kN, while maintaining a sealing threshold of 5 MPa for shape memory pipe