Strength grading of hardwoods using transversal ultrasound

Andriy Kovryga, A. Khaloian Sarnaghi, Jan-Willem van de Kuilen

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

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Detection of local wood inhomogeneities is important for accurate strength and stiffness prediction. In hardwood specimens, visual characteristics (e.g. knots or fibre deviation) are difficult to detect, either with a visual surface inspection or by the machine. Transversal ultrasound scan (TUS) is a non-destructive evaluation method with high potential for hardwoods. The method relies on differences in ultrasound wave propagation in perpendicular to the grain direction. The aim of this study is to estimate and analyse the capabilities of TUS for defect detection in hardwoods and prediction of mechanical property values. In the current paper, the TUS was applied to the hardwood species European ash (Fraxinus excelsior) and European maple (Acer sp.). In total, 16 boards of both specimens were completely scanned perpendicular to the grain using a laboratory scanner with drycoupled transducers. The measurements were processed to 2D scan images of the boards, and image processing routines were applied to further feature extraction, defect detection and grading criteria calculation. In addition, as a reference for each board, all relevant visual characteristics and mechanical properties from the tensile test were measured. Using the TUS global fibre orientation, the size and the position of the knots can be detected. Knottiness correlates to the strength properties similarly or even better compared to the manual knottiness measurement. Between the global fibre orientation (measured using TUS and measured on the failure pattern) no correlation could be found. The ultrasound MOE perpendicular to the grain does not show any meaningful correlation to the elastic-properties parallel to the grain. In overall, TUS shows high potential for the strength grading of hardwoods.
Original languageEnglish
Title of host publicationISCHP 2019 - 7th International Scientific Conference on Hardwood Processing
EditorsJan-Willem van de Kuilen, Wolfgang Gard
Place of PublicationDelft
PublisherDelft University of Technology
Number of pages10
Publication statusPublished - 2019
EventISCHP 2019: 7th International Scientific Conference on Hardwood Processing - Delft University of Technology, Delft, Netherlands
Duration: 27 Aug 201930 Aug 2019


ConferenceISCHP 2019: 7th International Scientific Conference on Hardwood Processing
Abbreviated titleISCHP 2019
Internet address


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