If a product has to be disassembled for maintenance, repair or end-of-life disposal there are clearly advantages in having fasteners that can disassemble themselves automatically. Several attempts have been made to develop suitable fasteners – and some are now on the market – with shape-memory alloys being a promising technology. For instance, Intrinsic Devices manufactures Unilok rings from Nitinol. These are supplied in the expanded condition and, upon heating to 45-165°C, reduce their diameter by up to 4.5percent. For disassembly, the rings can be cooled to -120°C using liquid nitrogen, whereupon they expand.

For more sophisticated applications, TZ of Australia offers the Intevia range of ‘intelligent’ fastening devices and tools. These products enable a fastener to be locked or unlocked remotely without any physical contact. Inline, radial, ring and beam mechanisms are available to suit different application configurations. Intevia radial fastening mechanisms, for example, feature a series of eight radial locking jaws that engage a specially profiled stud when it is inserted into the body of the fastener (Fig.4). The jaws are released via shape memory alloy actuation that rotates an inner drum, allowing the jaws to disengage and release the stud – even under preload conditions.

By integrating microprocessors into the fastening device, Intevia fastening mechanisms can gather information about their status, log their history, sense the environment and be controlled by a command or digital instruction received from a computer or PDA. When used in conjunction with a network, the Intevia system is said to create a new mode of assembly and disassembly – one that is managed and controlled remotely through software.

While intelligent fasteners and self-disassembly are suitable for a limited number of high-value applications, the relatively high cost-per-fastener means that they are not yet ready to supersede the threaded fastener in the majority of assemblies.