Particle radiation effects on shape memory alloy couplers for ultra-high vacuum sealing: a preliminary study

Abstract

A new shape memory alloy (SMA)-based coupling system for ultra-high vacuum (UHV) applications in particle in accelerators is currently under investigation at the European organization for nuclear research (CERN). The use of such technology in some restricted-access radioactive areas within CERN accelerators could result in noticeable advantages, especially during maintenance operations. Bolt-free SMA couplers, can be activated remotely by temperature changes, resulting in significant reduction of the radiation doses collected by the technical personnel. The functional performance of SMA-based prototype systems, in terms of leak tightness, thermal mounting/dismounting and thermal outgassing properties, has been already verified. Radiation-induced microstructural damages usually cause losses in the mechanical properties, such as embrittlement in conventional engineering metals. The particle radiation effects on the functional characteristics of SMAs, in terms of microstructural transition mechanisms, represent a key issue for their application in critical accelerators areas. To this aim, specific research activities are being carried out at CERN for capturing the evolution of SMA mechanical and functional properties during and/or after particle irradiation. In this preliminary study, a few selected SMA-based prototype UHV chambers, have been exposed to a high-energy mixed particle field (up to ∼140 kGy of absorbed dose) at the CERN high-energy accelerator mixed-field (CHARM) facility. The results, in terms of post-irradiation measurements, have revealed that leak tightness and thermal dismounting are unaffected by irradiation.

A simplified analytical model to simulate martensite reorientation and plasticity in shape memory alloy ring couplers

“…SMA couplers developed at CERN have ring radius ratio in the range 1.1-1.4. This range covers also most of SMA couplers studied in literature (Duerig et al, 1990;Liu and Du, 2014;Liu et al, 2013;Mirzaeifar et al, 2011;Niccoli et al, 2017bNiccoli et al, , 2019Piotrowski et al, 2012;Scalet et al, 2019;Tabesh et al, 2018;Videnic et al, 2008) and Radi (2018), and those commercially available. The chart in Figure 2(a) is a log-log plot of e eo (e ei ) for different values of the ring radius ratio (r e =r i ).…”

“…Recent R&D studies have been carried out at the European Organization for Nuclear Research (CERN) to exploit the unique shape and force recovery capabilities of Shape Memory Alloys (SMAs) for developing smart pipe couplers. Their applications are foreseen in Ultra High Vacuum (UHV) systems of particle accelerators (Niccoli et al, 2017a(Niccoli et al, , 2017b(Niccoli et al, , 2019Scalet et al, 2019). The functional features of SMAs are due to a reversible phase transition between a parent phase, the body centered cubic austenite (B2), and a product one, the monoclinic martensite (B19') (Duerig et al, 1990;Otsuka and Ren, 2005).…”

“…It was demonstrated that ring-shaped SMA pipe joints satisfy the requirements for UHV applications (Niccoli et al, 2017b(Niccoli et al, , 2019Scalet et al, 2019). Special thermo-mechanical treatments, the so-called training, must be performed to give the SMA element proper geometrical and functional properties in terms of shape recovery capabilities and transformation temperatures for the development of reliable leak tight junctions.…”

“…Special thermo-mechanical treatments, the so-called training, must be performed to give the SMA element proper geometrical and functional properties in terms of shape recovery capabilities and transformation temperatures for the development of reliable leak tight junctions. To that end, special semi-empirical design approaches need to be adopted (Niccoli et al, 2017b(Niccoli et al, , 2019Scalet et al, 2019).…”

Inverse problems with the digital image correlation: approach and applications

“…The last case study consists in the measurement of the coupling pressure generated by a SMA ring when it is thermally activated on axisymmetric components. SMA rings exploit temperature-induced phase transformation mechanisms to offer new ways to join and seal cylindrical components as demonstrated by some recent research and/or technological studies as well as by a significant number of patents [58][59][60][61][62]. A 38NiCrMo3 steel ring, simulating the pipe system, was clamped with an external commercial Ni46.5Ti45.0Nb8.5 SMA ring.…”