Investigating mechanical damage mechanisms of tapestries displayed at different angles using 2D DIC

Abstract

Tapestries represent a key but fragile component of many historic collections, as well as a complex challenge for textile conservators who aim to ensure their preservation. Indeed, the heterogeneity of materials, weaving features and conservation history make it difficult to predict the mechanical and physical behaviour of these objects, especially when hung for their display. The reported research postulates and investigates the role of different factors, namely relative humidity related strains and creep, in promoting the mechanical deterioration of tapestries. To track strain, the contactless full-field optical technique digital image correlation (DIC) was used. In particular, 2D DIC was successfully employed to monitor strains across large areas of a tapestry, demonstrating the occurrence of fatigue and creep damage mechanisms. While the former had the most influence on overall expansions and contractions, creep affected damaged areas. In addition, DIC was used for a preliminary evaluation of the efficacy of sloping boards, a non-traditional display method chosen by an increasing number of European museums in an attempt to reduce strain across tapestries. Both theoretical analysis and experimental work showed that, when minimal friction is present, small angles, like 5° from the vertical, do not appear to promote noticeable reductions in strain.