Methodology for tensile testing historic tapestries

Historic tapestries are very important and complex artworks. Their heterogeneous structure composed with different materials is weaved in warp and weft threads with the objective of render an image to be displayed. Often on open display these objects are exposed to forces caused by their own weight as well as by the strain experience due to moisture adsorption and desorption cycles when temperature and relative humidity of the surrounding environment fluctuate. Since physical damage is usually supported by conservation stitching techniques there is a need to understand how certain decisions would influence future mechanical behaviour of a tapestry. This requires the need of establishing a methodology that helps to understand how different sections of these heterogeneous objects respond when forces are applied to them.

Past research considered tensile testing of primarily new woven aged sections which are not representative of the historic tapestries [1]. Digital image correlation (DIC) was also successfully used in order to characterize the strain states of woven tapestries [2]. However, information on how wool and silk behaves as well as the influence of damage and stitching in some areas is still scarce and there is the lack of a methodology for a full strain analysis.

In this research, tensile mechanical behaviour is being studied in order to inform on how different fragments of historic tapestries behave when a certain tensile force is applied on them. For this, a new methodology of analysis is proposed. Force strain curves collected from tensile tests are analysed together with complementary DIC data to understand the strain states that were present in different stages of the mechanical tests. Results proved that a holistic methodology, using both techniques required for successful interpretation of data. Furthermore, this experimental work demonstrated that tapestry areas behave differently when a tensile force is applied.