Abstract
Among non-destructive testing (NDT) techniques applied to structural health monitoring in existing timber structures, ranging from visual inspection to more sophisticated analysis, acoustic emission (AE) is currently seldomly used to detect mechanical stresses in wooden building assets. This paper presents the results from a systematic literature review on AE NDT applied to monitor micro and macro fracture events in softwood, specifically Scots pine. This survey particularly investigates its application with respect to the tree rings density and grain angle inspection, as influencing factors well correlated with physical and mechanical characteristics of wood. The literature review was performed in a three-step process defined by the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) flow diagram, leading to the selection of 31 documents from different abstract and citation databases (Scopus, Web of Science and Google Scholar). The outcomes have highlighted how laboratory experiments, including several types of tests (tensile, cutting, compressive, etc.), were conducted in most cases, while a very limited number of studies investigated on in situ monitoring. In addition, theoretical approaches were often explored in parallel with the experimental one. It emerges that—for tree ring density studies—a multi-technique approach, which may include microscopic observations, could be more informative. Indeed, although not widely investigated, high/low tree ring density and grain angle were found as influencing factors on the AE parameters detected by the sensors, during condition and structural health monitoring experiments.
Highlights
Deformation and fracture are some of the common problems affecting wood material as it is often used, nowadays as in the past, in the construction of structures and artefacts of cultural value and in need of special care and conservation
The preliminary survey allowed us to define the techniques mostly exploited in structural health monitoring field when dealing with wood, which are summarised in Table A2 reported in the Appendix A, divided into five categories: visual, acoustic, vibration, probing and other non-destructive techniques
This literature review has investigated the role that the grain angle direction and the high/low tree rings density have in detecting acoustic emission burst on Scots pine
Summary
Deformation and fracture are some of the common problems affecting wood material as it is often used, nowadays as in the past, in the construction of structures and artefacts of cultural value and in need of special care and conservation. Research on wood is conducted by using different non-destructive testing (NDT) techniques mainly aimed at timber grading and assessment of existing timber structures [1]. The aim of our review is to analyse the state of the art of the AE NDT technique applied to monitor the occurrence of fracture events in softwoods, Scots pine, focusing on the influence of grain angle and tree ring density on such occurrence. The general framework of NDT used on wood samples was initially defined by means of a preliminary survey, designed to study the influence of high/low tree ring density and grain angle direction on the outcomes obtained through the different methods.
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