In Norway and in Northern Countries, historical buildings dated back between the 17th and the 20th century are mostly made of softwood as spruce and/or pine wood. Their architecture is a combination of wood frames and log structures. These structures are currently observable in Trondheim (Norway), both along the river Nidelva and in the city centre districts. Wood may be described as an orthotropic material with independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal (parallel to the fibre), radial (growth ring direction), and tangential (tangent to the growth rings). Beside the density and the directionality, a main factor affecting its mechanical properties is the Moisture Content (MC). Mechanical alteration phenomena on wood driven by gradient of moisture content, as swelling, shrinkage and finally fracture are induced by changes in climate conditions (i.e. temperature and relative humidity). In the field of microclimate studies for cultural heritage conservation there are few studies that apply no destructive technique to directly monitor in situ the effect of MC gradients on wood micro fracturing caused by sudden changes in environmental conditions. Here we propose a synchronous characterization of crack propagation along a Scots pine log (2 cm thick adjacent slices) while it was drying after an abrupt change from 85% RH to 30% RH. Samples for tensile tests were created from each slice and their fracturing process (fracture mode I) was monitored using two independent no destructive techniques: the Acoustic Emission and the Digital Image Correlation. The reported application allows to detect Acoustic Emission signal modification in relation to the moisture content and its gradient. The coupled techniques have potentiality as characterizing methodologies in the field of historical wooden materials to examine both effects of mechanical variation caused by moisture gradients or effects of biological degradation in wood.
Moisture Content influence on Acoustic Emission Parameters in a drying Scots Pine Log / Bartolucci, Beatrice; Frasca, Francesca; Berto, Filippo; Bertolin, Chiara. - (2021). (Intervento presentato al convegno 3° Congresso Nazionale AISAM (Associazione Italiana di Scienze dell'Atmosfera e Meteorologia) tenutosi a L'Aquila (online)).
Moisture Content influence on Acoustic Emission Parameters in a drying Scots Pine Log
Francesca Frasca;Filippo Berto;
2021
Abstract
In Norway and in Northern Countries, historical buildings dated back between the 17th and the 20th century are mostly made of softwood as spruce and/or pine wood. Their architecture is a combination of wood frames and log structures. These structures are currently observable in Trondheim (Norway), both along the river Nidelva and in the city centre districts. Wood may be described as an orthotropic material with independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal (parallel to the fibre), radial (growth ring direction), and tangential (tangent to the growth rings). Beside the density and the directionality, a main factor affecting its mechanical properties is the Moisture Content (MC). Mechanical alteration phenomena on wood driven by gradient of moisture content, as swelling, shrinkage and finally fracture are induced by changes in climate conditions (i.e. temperature and relative humidity). In the field of microclimate studies for cultural heritage conservation there are few studies that apply no destructive technique to directly monitor in situ the effect of MC gradients on wood micro fracturing caused by sudden changes in environmental conditions. Here we propose a synchronous characterization of crack propagation along a Scots pine log (2 cm thick adjacent slices) while it was drying after an abrupt change from 85% RH to 30% RH. Samples for tensile tests were created from each slice and their fracturing process (fracture mode I) was monitored using two independent no destructive techniques: the Acoustic Emission and the Digital Image Correlation. The reported application allows to detect Acoustic Emission signal modification in relation to the moisture content and its gradient. The coupled techniques have potentiality as characterizing methodologies in the field of historical wooden materials to examine both effects of mechanical variation caused by moisture gradients or effects of biological degradation in wood.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
