In November 2017 the Getty Conservation Institute (GCI) convened a meeting at the Getty Center to discuss recent advances in applying acoustic emission as a direct technique for monitoring physical change in cultural heritage objects. Invited scientists and conservators active in acoustic emission studies considered areas where research is needed and ways data can be shared, as well as ways the conservation community and allied professions (such as curatorship, administration, and facilities) can be apprised and included. They also discussed how acoustic emission technology can inform the exploration of sustainable environmental strategies for the preservation of collections.
Acoustic emission (AE) is defined as the energy released as ultrasound and sound waves during microdisplacements in a structure undergoing deformation. As physical failure of materials is often preceded by a discernible level of AE activity, the monitoring of AE has become an important nondestructive tool in material science and engineering for predicting macrodamage and tracing crack propagation.
When applied to the field of cultural heritage, AE monitoring facilitates tracing physical damage in a historical material or object when a stress field develops because of a deterioration mechanism. Although its use in conservation studies is relatively recent, examples of heritage-focused AE research include studying the decay of porous stone in Spanish architectural heritage due to salt crystallization, monitoring AE from the larval stage of wood-boring insects to detect object infestation, and tracing environmental stress in wooden museum objects.
The Getty Center meeting began with a review of the technical aspects of AE monitoring, including: the importance of calibration in establishing a relationship between AE and the level of damage; the attenuating effect of distance on the AE signal and its effect on the physical range of AE monitoring; the choice of AE sensor placement, which often focuses on a location that is perceived to be vulnerable (e.g., crack tip); and the sensitivity of AE to brittle cracking but not to deformation, which can also be considered damage.
Subsequent discussion focused on field implementations of AE monitoring to target object response when subjected to a new temperature and relative humidity regime, to correlate specific climatic conditions with a survey of well-documented objects that have been damaged, and to explore the evolving vulnerability of an object when exposed to reoccurring environmental stresses.
At the close of the meeting, participants agreed to create a user group platform to facilitate sharing of AE data and provide technical support, and to develop AE guidelines for the cultural heritage field describing monitoring protocols, system calibration, and methods of data interpretation. The use of AE monitoring can assist those responsible for managing collecting to better understand conditions that may contribute to object damage.
This meeting was held as part of the GCI’s Managing Collection Environments Initiative, a multiyear initiative that addresses a number of compelling research questions and practical issues pertaining to the sustainable management of collection environments in museums.
Chiara Bertolin, Norwegian University of Science and Technology
Nigel Blades, National Trust for England, Wales, and Northern Ireland
Lukasz Bratasz, Institute for the Preservation of Cultural Heritage, Yale University
Eric Hagan, Canadian Conservation Institute
Roman Kozlowski, Jerzy Haber Institute
Marcin Strojecki, Jerzy Haber Institute
David Thickett, English Heritage
Managing Collection Environments Initiative Team Members
Vincent Beltran, Assistant Scientist
Foekje Boersma, Senior Project Specialist
Jim Druzik, Senior Scientist (Retired)
Ashley Freeman, Research Lab Associate
Michal Lukomski, Scientist
Joel Taylor, Project Specialist
Emma Ziraldo, Graduate Intern
Beril Bicer-Simsir, Associate Scientist, Getty Conservation Institute
Julie Desarnaud, Assistant Scientist, Getty Conservation Institute
Arlen Heginbotham, Conservator, J. Paul Getty Museum