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Repetitive impact loading causes local plastic deformation in wood
VTT Tech Res Ctr Finland, Espoo, Finland.
VTT Tech Res Ctr Finland, Espoo, Finland.
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.ORCID iD: 0000-0003-3381-5516
Tampere Univ Tech, Dept Automat Sci & Eng, Tampere, Finland.
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 2, p. Art. no. 024901-Article in journal (Refereed) Published
Abstract [en]

The relationship between the impactor velocity and the amount of strain localization in a single impact compression of cellular solids is known. However, few studies report on the effects of repeated high frequency compression. We therefore studied the mechanical behavior of Norway spruce, a cellular viscoelastic material, before, during, and after cyclic high frequency, high strain rate, compression. A custom made device applied 5000-20 000 unipolar (constrained compression and free relaxation) fatigue cycles with a 0.75 mm peak-to-peak amplitude at 500 Hz frequency. The consequences of this treatment were quantified by pitch-catch ultrasonic measurements and by dynamic material testing using an encapsulated Split-Hopkinson device that incorporated a high-speed camera. The ultrasonic measurements quantified a stiffness modulus drop and revealed the presence of a fatigued low modulus layer near the impacting surface. Such a localized plastic deformation is not predicted by classical mechanics. We introduce a simple model that explains several changes in the mechanical properties caused by fatiguing. The high speed images indicated pronounced strain localization in the weakest (thinnest walls) parts of the earlywood layers, and revealed strain propagation as a function of time. We present a hypothesis explaining why there is a fatigued layer formed in a piece of wood that has sustained cyclic compression and free relaxation. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676206]

Place, publisher, year, edition, pages
2012. Vol. 111, no 2, p. Art. no. 024901-
Keywords [en]
ALUMINUM-ALLOY FOAM; RADIAL COMPRESSION; CELL-WALL; UNIAXIAL COMPRESSION; WATER TRANSPORT; STRAIN-RATE; HONEYCOMB; BEHAVIOR; MODULUS; FATIGUE
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-16204DOI: 10.1063/1.3676206ISI: 000299792400099Scopus ID: 2-s2.0-84865271010OAI: oai:DiVA.org:miun-16204DiVA, id: diva2:526269
Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2017-12-07Bibliographically approved

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Engberg, Birgitta A.

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