Yuko Fujiwara

Assessment of wood surface roughness: comparison of tactile roughness and three-dimensional parameters derived using a robust Gaussian regression filter

Japanese oak and Japanese beech were sanded by hand with abrasive papers of varying grit number. Two three-dimensional parameters selected to characterize their surface roughness – one parameter for the distribution of roughness-profile peaks and the other for the relative area of the roughness-profile peaks above the threshold height – were compared against tactile roughness. The parameters were obtained from roughness profiles as determined by a robust Gaussian regression filter (RGRF) using seven cutoffs. The RGRF filtering process was adjusted specifically for the evaluation of wood surface roughness. Except for a cutoff wavelength of 0.25 mm, the RGRF lent itself well to the determination of roughness profiles. No distortion of roughness profiles occurred around deep valleys, and there was a good correlation between the parameters and tactile roughness.

Relationship between roughness parameters based on material ratio curve and tactile roughness for sanded surfaces of two hardwoods

The roughness parameters on the material ratio curves were related to tactile roughness for samples of buna and mizunara. The surfaces of the samples were sanded using various grades of coated abrasives and the roughness parameters, reduced peak height (Rpk), core roughness depth (Rk), and reduced valley depth (Rvk), were estimated on the material ratio curves, which were obtained from roughness profiles determined using robust Gaussian regression filter. The values of Rpk and Rk were almost the same for buna and mizunara under the same sanding conditions and increased exponentially with tactile roughness. The coefficients of determination of those parameters and tactile roughness were higher than 0.79 at all cutoff wavelengths. On the other hand, the value of Rvk for mizunara was significantly larger than that for buna because of the deep local valleys. There was no relationship between Rvk and tactile roughness for both species.

Effect of grain direction on transmittance of 100-GHz millimeter wave for hinoki (Chamaecyparis obtusa)

The attenuation coefficients of 100-GHz millimeter waves polarized linearly were measured for cross-cut, quarter-sawn, and flat-sawn boards of hinoki (Chamaecyparis obtusa) that were 0.2–2.0 cm thick. This was done to examine the applicability of free-wave propagation theory for applying electromagnetic waves to wood. It was found that the transmittance of a millimeter wave through the specimen boards was lower when the fiber direction of a board was parallel to the direction of the electric field of the incident wave than when the fiber direction was perpendicular to the electric field, and there was little difference in the transmittance between the tangential and radial directions for the former case. These findings can be quantitatively explained by using propagation theory and the dielectric properties of wood.

Observation of machined surface and subsurface structure of hinoki (Chamaecyparis obtusa) produced in slow-speed orthogonal cutting using X-ray computed tomography

X-ray computed tomography (CT) was applied to non-destructive observation of machined surface and subsurface structure of hinoki (Chamaecyparis obtusa) produced in slow-speed orthogonal cutting. The cutting experiments were conducted under several cutting conditions and the chip formations were observed with a high-speed camera to be classified into four chip types. The difference in the quality of the machined surfaces produced in four types of chip formation was investigated. During type 0 chip formation, the workpiece was cut almost exactly at the path of the cutting edge, so no deformation was found on and beneath the machined surface. During type I chip formation, the direction of the fore-split, which is dependent on the arrangement of cells, determined the machined surface. During type II chip formation, the cutting tool sometimes tore part of the workpiece below the path of the cutting edge and the tore part was then compressed by the tool, remaining on the machined surface. During type III chip formation, part of the workpiece above the path of the cutting edge was compressed by the tool, instead of being removed as a chip, so the compression occurred in wide area. The relationship between the formation of the machining defects such as torn grain or the compressed cells and the way chip is separated, deformed, or removed was clarified in this study.

Development of Radar Apparatus for Scanning of Wooden-Wall to Evaluate Inner Structure and Bio-Degradation Non-Destructively

A nondestructive and small FMCW radar apparatus for scanning of the wooden wall to evaluate inner structure and biodegradation progressed in the wall was developed, and the performance of the apparatus was investigated. The allocations and the properties of the construction members in the wall, such as wooden posts and beams, metal plate connectors and insulating materials was recognized as 2D and 3D images. The moist area of more than 50% in moisture content in the wall was also recognized, and this suggests that the area of potentiality of biodegradation such as fungal and insect attacks in the wall can be detected by this apparatus. The feasibility of the apparatus to evaluate of the loss in the wood substance caused by the bio-degradation was also confirmed.

Feasibility of millimeter wave imaging as tool for nondestructive inspection of wood and wooden structures

Dielectric properties of wood were estimated by a reflection imaging using monostatic system of millimeter wave of 100GHz and by a transmission imaging using bistatic system, respectively. The influence of cellular structure, moisture content and inner defect on the imaging performance was clarified. The feasibility of the millimeter imaging as the tool for nondestructive evaluation of quality and deterioration of wood and wooden structure was confirmed.

Relationship between crack propagation and the stress intensity factor in cutting parallel to the grain of hinoki (Chamaecyparis obtusa)

The method of digital image correlation (DIC) was applied to the digital image of orthogonal cutting parallel to the grain of hinoki, and the strain distribution near the cutting edge was evaluated. The wood fracture associated with chip generation was considered as mode I fracture, and the stress intensity factor KI for fracture mode I was calculated from the strain distribution according to the theory of linear elastic fracture mechanics for the anisotropic material. The calculated KI increased prior to crack propagation and decreased just after the crack propagation. The change in KI before and after crack propagation, ΔKI, decreased in accordance with the crack propagation length, although the variance in ΔKI should depend on the relationships between the resolution of DIC method and the dimensions of cellular structure. The calculated KI in this study was almost on the same order as reported in the literatures. It was also revealed, for the case of chip generation Type 0 or I, the stress intensity factor for fracture mode II could be negligible due to the higher longitudinal elastic properties of wood in the tool feed direction than the one radial ones, and the mode I fracture was dominant.

Evaluation of the sensory roughness of some coated wood surfaces by image analysis

Sensory roughness is one of the most important factors that determines the quality and/or value of various wood products. The aim of the present study was to confirm whether the sensory roughness of coated wood surfaces could be estimated by the here proposed image analysis. Twelve white oak (Quercus alba) fancy veneer overlaid plywood samples were prepared with two types of grains and six coating specifications. Forty participants subjectively evaluated the sensory roughness of the samples by rubbing their surfaces without being able to see them. Sample surface images were acquired with a goniophotometric method and were submitted to an image analysis to calculate lightness differences (contrast) between relatively small areas as image characteristics. Three surface profile parameters were also measured based on the conventional stylus method. Three-way analyses of variance for the evaluation of sensory roughness revealed significant main effects of the coating specification and the rubbing direction. Although contrast and surface profile parameters were hard to estimate in terms of sensory roughness for spiny surfaces, both measures were well correlated to sensory roughness for porous surfaces. In particular, the linearity between the sensory roughness of the porous surfaces and contrast was equal to or greater than that of the surface profile parameters.

Nondestructive Visualization Using Electromagnetic Waves for Real and Practical Sensing Technology for Robotics

This section describes novel methods of electromagnetic wave nondestructive visualization (NDV) for assessing qualification and durability of concrete and wooden structures, which involves devices, systems, and image processing. As the first, the basic knowledge and principles on dielectric properties of materials, wave propagation in media involving plane waves in vacuum and in non-conducting and non-magnetic dielectric media were introduced. As the second, the dielectric properties of concrete and NDV techniques for concrete structures were introduced. After the introduction of conventional methods to detect internal cracks in concrete structures, a novel development of a millimeter wave scanner for NDV of concrete was introduced where the performance of the scanner to detect surface cracks covered by other sheet materials was discussed. Miscellaneous image processing techniques to recognize the target using pattern recognition methods were also introduced. Wood is a material made of the plant cells of trees. Wood shows anisotropy in physical and mechanical properties, such as elastic moduli, strength, and dielectric constants. In addition, wood is deteriorated by biological agents such as insects and fungi, and these deterioration often generate in inner or hidden areas of wood and wooden construction. The deterioration is closely associated with moisture content of wood. In this section, the feasibility of technologies using electromagnetic waves for the nondestructive evaluation of properties and deterioration of wood and wooden construction, is introduced. The reaction of wood to electromagnetic wave such as transmission and reflection of millimeter wave through and from wood was discussed. The development of wooden wall scanner for nondestructive diagnoses of wooden houses using FMCW radar was introduced.