Experimental characterisation of the local mechanical behaviour of cellulose fibres: an in‑situ micro‑profilometry approach

The accurate mechanical characterisation of fibres of micrometric length is a challenging task, especially in the case of organically-formed fibres that naturally exhibit considerable irregularities along the longitudinal fibre direction. The present paper proposes a novel experimental methodology for the evaluation of the local mechanical behaviour of organically-formed (aged and unaged) and regenerated cellulose fibres, which is based on in-situ micro-tensile testing combined with optical profilometry. In order to accurately determine the cross-sectional area profile of a cellulose fibre specimen, optical profilometry is performed both at the top and bottom surfaces of the fibre. The evolution of the local stress at specific fibre locations is next determined from the force value recorded during the tensile test and the local cross-sectional area. An accurate measurement of the corresponding local strain is obtained by using Global Digital Height Correlation (GDHC), thus resulting in multiple, local stress--strain curves per fibre, from which local tensile strengths, elastic moduli, and strains at fracture can be deduced. Since the variations in the geometrical and material properties within an individual fibre are comparable to those observed across fibres, the proposed methodology is able to attain statistically representative measurement data from just one, or a small number of fibre samples. This makes the experimental methodology very suitable for the mechanical analysis of fibres taken from valuable and historical objects, for which typically a limited number of samples is available. It is further demonstrated that the accuracy of the measurement data obtained by the present, local measuring technique may be significantly higher than for a common, global measuring technique since possible errors induced by fibre slip at the grip surfaces are avoided

In depths of paper degradation: A microscale experimental methodology

Speaking of conservation of articles in museums and collections there is no question about the importance of better understanding of how paper degrades. Loss of mechanical properties, due to degradation through the ages, dramatically influences the accessibility of books, artworks and documents. The change in these properties starts from atomic levels and travels across scales to result in tangible changes in the scale of the sheets of paper. One of the most relevant changes is the loss of mechanical properties of paper. Advanced measurement techniques make it possible to dive into the depths of these processes in smaller scales than before with impressively high accuracies. The current study focuses on the development of a thorough experimental methodology to study the mechanical behaviour of cellulose fibres. In-situ micro-tensile testing with optical profilometry in combination with Digital Image Correlation (DIC) technique results in high accuracy mechanical characterization of single cellulose fibres. Such detailed assessment of cellulose fibres’ properties can be applied to naturally aged paper samples, or combined with accelerated aging experiments to shed valuable light on the degradation of paper, and provide better guidance for conservators

In depths of paper: A microscale experimental story

Speaking of conservation of articles in museums and collections there is no question about the importance of better understanding of how paper degrades. Loss of mechanical properties, due to degradation through the ages, dramatically influences the accessibility of books, artworks and documents. The change in these properties starts from atomic levels and travels across scales to result in tangible changes in the scale of the sheets of paper. Advanced measurement techniques make it possible to dive into the depths of these processes in smaller scales than before with impressively high accuracies. In this presentation I will introduce the experimental methodology to study the mechanical behaviour of single cellulose fibres, the building block of paper. An optical profilometer, a micro-tensile stage and Digital Image Correlation (DIC) technique come together to result in a deeper understanding of the mechanics of each fibre. Such detailed assessment of cellulose fibres’ properties can be applied to naturally aged paper samples, or combined with accelerated aging experiments to shed valuable light on the degradation of paper, and provide better guidance for conservators

Experimental Determination of the Mechanical Properties of The Night Watch Canvas using Micro-Tensile Testing

The determination of the structural condition and the mechanical properties of The Night Watch are of high importance when it comes to defining conservation treatments and future preservation policies for the painting. To this end, an advanced minimally-invasive experimental investigation of the mechanical properties of the canvas is performed. Due to its significant contribution to the structural support to the painting, the study principally focuses on the lining canvas, which was applied to the back of the painting in 1975. Considering the limited availability of samples, micro-scale mechanical tests are carried out on single cellulose fibers that have been extracted from the canvas threads. The strength, the stiffness and the fracture strain of the fibers are robustly and accurately measured using a recently developed micro-tensile testing methodology. This information can then be extended to larger scales (thread and thread-network) to provide insight into the long-term stability of the lining canvas and to ensure that the load introduced with the spring-tensioning system will be kept well below the failure threshold of the lining canvas

Correction of scan line shift artifacts in scanning electron microscopy:An extended digital image correlation framework

\u3cp\u3eHigh resolution scanning electron microscopy (HR-SEM) is nowadays very popular for different applications in different fields. However, SEM images may exhibit a considerable amount of imaging artifacts, which induce significant errors if the images are used to measure geometrical or kinematical fields. This error is most pronounced in case of full field deformation measurements, for instance by digital image correlation (DIC). One family of SEM artifacts result from positioning errors of the scanning electron beam, creating artifactual shifts in the images perpendicular to the scan lines (scan line shifts). This leads to localized distortions in the displacement fields obtained from such images, by DIC. This type of artifacts is corrected here using global DIC (GDIC). A novel GDIC framework, considering the nonlinear influence of artifacts in the imaging system, is introduced for this purpose. Using an enriched regularization in the global DIC scheme, based on an error function, the scan line shift artifacts are captured and eliminated. The proposed methodology is demonstrated in virtually generated and deformed images as well as real SEM micrographs. The results confirm the proper detection and elimination of this type of SEM artifacts.\u3c/p\u3