1 Introduction- 2 Ionizing Radiation Computed Tomography- 3 Thermal Imaging- 4 Microwave Imaging- 5 Ultrasonic Imaging- 6 Nuclear Magnetic Resonance- 7 Neutron Imaging- References- List of Notations- Color Plates

Nondestructive Characterization and Imaging of Wood

The most significant biotic and abiotic stress agents of water extremity, salinity, and infection lead to wood decay and modifications of moisture and ion content, and density. This strongly influences the (di-)electrical and mechanical properties and justifies the application of geophysical imaging techniques. These are less invasive and have high resolution in contrast to classical methods of destructive, single-point measurements for inspecting stresses in trees and soils. This review presents some in situ and in vivo applications of electric, radar, and seismic methods for studying water status and movement in soils, roots, and tree trunks. The electrical properties of a root-zone are a consequence of their moisture content. Electrical imaging discriminates resistive, woody roots from conductive, soft roots. Both types are recognized by low radar velocities and high attenuation. Single roots can generate diffraction hyperbolas in radargrams. Pedophysical relationships of water content to electrical resistivity and radar velocity are established by diverse infiltration experiments in the field, laboratory, and in the full-scale 'GeoModel' at Kiel University. Subsurface moisture distributions are derived from geophysical attribute models. The ring electrode technique around trunks images the growth ring structure of concentric resistivity, which is inversely proportional to the fluid content. Healthy trees show a central high resistivity within the dry heartwood that strongly decreases towards the peripheral wet sapwood. Observed structural deviations are caused by infection, decay, shooting, or predominant light and/or wind directions. Seismic trunk tomography also differentiates between decayed and healthy woods.

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Geophysical imaging of root-zone, trunk, and moisture heterogeneity

Nondestructive evaluation (NDE) research on composite materials has been ongoing for several decades, during which time their use has expanded significantly in the aerospace, marine, petrochemical, energy, construction and transport sectors. Initially, many composites were employed as fairings or reinforcements, but they are being increasingly used in primary and secondary load-bearing structures, where a mechanical failure has significantly greater safety implications. This increased scope has resulted in composite structures of significant thickness and complexity. Despite this, there has not been a corresponding increase in research pertinent to the detection and characterisation of defects in thick structures, apart from a brief period of interest by the NDE community in the early 1990s. This review critically assesses advances reported in the NDE of thick-section composites (structures of thickness above 15 mm are considered for the purposes of this review), and identifies future research opportunities to overcome the limitations of existing technologies.

Nondestructive evaluation of thick-section composites and sandwich structures: A review

This paper reports application of electric, ultrasonic, and georadar tomography for detection of decay in trees and their comparison with the traditional penetrometer Their feasibility in arboriculture is also evaluated, critically considering some "open problems" The experiments were carried out in an urban environment on two plane (Platanus hybrida Brot) trees Both trees, after felling, showed extensive white rot in the central cylinder The electric tomography revealed low resistivity zones roughly centered in the trunk A comparison with the successively cut sections showed a fine correspondence to decayed areas and a strong correspondence between high moisture zones and low resistivity zones Ultrasonic tomography demonstrated to be a very effective tool for the detection of internal decay, accurately locating the position of the anomalies and estimating their size, shape, and characteristic in terms of mechanical properties With the georadar technique, the high contrast of electromagnetic impedance measured between the inner decayed section and the outside sound section allowed the detection of the interface between the sound and decayed section of the tree, using radar acquisition in reflection modality The penetrometer profiles detected the low-resistance areas inside the two trunks

Application and comparison of three tomographic techniques for detection of decay in trees

The viscoelastic thermal compression (VTC) of low-density hybrid poplar (Populus deltoides × Populus trichocarpa) from fast growing trees was performed in order to produce specimens with three different degrees of densification (63, 98, and 132%). The morphology and density profile of the VTC specimens were studied. Three different methods for the preparation of specimens for microscopy were used in order to find a technique that makes it possible to examine the VTC wood microscopically in the completely deformed state. It was found that the abrasive surface preparation of oil-embedded blocks was the most promising technique. Microscopic observation revealed that the deformations in the VTC wood were mostly the result of the viscous buckling of cell walls without fracture. The volume of the void areas in the specimens decreased with the degree of densification. The results showed that the density profile of the VTC wood varied with the degree of densification as a consequence of different temperature and moisture gradients formed before and during wood compression. The density profile is also visible on the cross-section of the VTC specimens.

Density profile and morphology of viscoelastic thermal compressed wood

Environmental Acoustics.- Acoustics of Forests and Acoustic Quality Control of Some Forest Products.- Wood and Wood-Based Materials in Architectural Acoustics.- Material Characterization.- Theory of and Experimental Methods for the Acoustic Characterization of Wood.- Elastic Constants of Wood Material.- Wood Structural Anisotropy and Ultrasonic Parameters.- Quality Assessment.- Wood Species for Musical Instruments.- Acoustic Methods as a Nondestructive Tool for Wood Quality Assessment.- Environmental Modifiers of Wood Structural Parameters Detected with Ultrasonic Waves.- Acoustic Emission.- Acousto-Ultrasonics.- High-Power Ultrasonic Treatment for Wood Processing.

Acoustics of Wood

X-ray microdensitometric analysis was employed for the detection of fungi attack in wood of pine and beech in comparison with the studies of specimen weight loss tests. Two species of fungi were used:Gloeophyllum trabeum (Pers.:Fr. Murrill) andTrametes versicolor (L.:Fr. Pilat). We select these species to induce typical decay attack mainly on cellulose in pine (brown rot) and mainly on lignin in beech (white rot). The attack was conducted for 1, 2, 3, 4 and 5 months in sterile laboratory conditions. After 5 months all the values of density components decreased. In beech the loss was of about 25% for all components. In pine the decreasing of the earlywood density component was of about 10% and in latewood of about 22%. The corresponding mass density losses, determined by gravimetric method, were approximately 18% for beech and 16% for pine.

Kinetics of wood degradation by fungi with x-ray microdensitometric technique

The effect of hydrostatic pressure on the density, the ultrasonic velocities and the microstructure of spruce and cherry wood has been studied. Generally speaking, under hydrostatic pressure wood becomes less heterogeneous and less anisotropic than natural wood. In spruce, crushing and buckling of the thinwalled cells in the earlywood takes place. This also has the effect of disrupting the medullary rays, which assume a zig-zag path through the structure. Cherry has a much more homogeneous structure, and the main effect of the hydrostatic pressure is compaction of the vessels by buckling of the walls. The fibres are scarcely affected by the treatment. The width of the earlywood zone decreased after the application of pressure by 26% in spruce, and by 11% in cherry. The average density was increased by the hydrostatic pressure by 26% for spruce and by 46% for cherry. The densitometric profile of spruce demonstrates significant changes following the pressure treatment, with the minimum density D Min increasing and the maximum density D Max decreasing. For cherry, the densitometric profile is shifted rather uniformly towards higher densities, and the annual ring profile is spatially slightly compacted but otherwise similar to that of untreated wood. The anisotropy of wood (expressed by the ratio of acoustic invariants) decreased by 56% for spruce and by 33% for cherry. The structural damage in spruce is predominantly found in the radial (R) direction, and this corresponds to a reduction of 73% in the velocity of the longitudinal ultrasonic waves in the radial direction, V RR . In cherry, the structural damage is mainly in the transverse, T direction. The velocity of the longitudinal ultrasonic waves in the transverse direction, V TI , is reduced by 44%. The medullary rays in cherry seem to be the most important anatomical feature influencing the propagation of ultrasonic waves.

The Effect of Hydrostatic Pressure on Physical Properties and Microstructure of Spruce and Cherry

Physical methods have been used to compare the mechanical properties of wood based panel products in relation to their microstructure. Three types of composites were considered: medium density fiberboard (MDF), oriented strandboard (OSB) and chipboard (CB). The overall elastic properties of panels were assumed to be orthotropic. The diagonal terms of stiffness matrix were determined with ultrasonic velocity method. The properties of the skin and the core of the panel were characterized using X-ray microdensitometry, ultrasonic velocity measurements, dynamic thermo-mechanical analysis (DMTA) and low voltage scanning electron microscopy (LVESEM). Clear differences have been established in the physical properties of the three panel products. Average mechanical properties have shown that the highest anisotropy is in OSB and the lowest in CB. Always the mechanical characteristics of the skin are higher than average characteristics of the panels while that of the core are inferior to average characteristics. E elastic modulus is much more higher (2 to 5 times) in the skin than in the core. X-ray microdensitometric technique has shown that the heterogeneity in the skin and core is the highest in OSB.

Voichita Bucur

Papers

Acoustics of Wood

Kinetics of wood degradation by fungi with x-ray microdensitometric technique

The Effect of Hydrostatic Pressure on Physical Properties and Microstructure of Spruce and Cherry

Physical methods for characterizing wood composite panel products

Acoustics of Wood (2nd edition)