酚醛树脂处理杨木、杉木尺寸稳定性分析

采用酚醛树脂浸渍处理人工林杨木、杉木,然后通过热压定型工艺制得表面密实化木材。对其尺寸稳定性的分析结果表明:处理试材的增重率、抗胀率和阻湿率随树脂浓度的增加而成比例增大,弦向和径向干缩率明显降低,在树脂浓度较低时变化较大,当达到一定量时变化趋于稳定。就压缩变形恢复率而言,当树脂浓度超过10%,压缩变形恢复率很小,说明表面密实化木材的压缩变形几乎被固定。     

Postbuckling of thin wood-based sandwich panels due to hygroexpansion under high humidity

This study was carried out to investigate the postbuckling behavior of thin wood-based sandwich panels under high humidity. Using the Rayleigh-Ritz method based on the von Karman nonlinear theory for the panel, the solutions for both the approximate and the closed form for postbuckling of orthotropic panels were derived to evaluate the deflection for the boundary condition of all clamped edges. The results suggested that the edge movement be considered for evaluation of a critical moisture content and deflection of thin wood-based panels fixed on the core with an adhesive. The numerical solution obtained from the derived model showed some discrepancy with the experimental results. The predicted results overestimated the center deflection of the panels because creep and plastic deformation might be caused by considerable in-plane stress on panels.Appendix: Abbreviations and symbols total potential energy of panel - A _ij ,D _ij extensional and bending stiffness, respectively - _x , _y midplane strains inx andy directions, respectively - _xy midplane shear strain inxy plane - N _x ^M , N _y ^M hygroscopic forces inx andy directions, respectively - h panel thickness - a, b panel length inx andy directions, respectively - x, y, z coordinate system - u, v, w displacement inx, y, andz directions, respectively - MC moisture content change - a _x ,a _y coefficient of linear expansion inx andy directions, respectively - LE linear expansion (MC) - s arc length - R radius of curvature - N _x ,N _y resultant in-plane forces per unit length inx andy directions, respectively - N _n nondimensional loadN _x ^M b ²/E ₂ h ³ - N _cr nondimensional critical load,N _x,cr ^M b ²/E ₂ h ³ - ratio of the core to the total width,a _c /a + a _c - E _c effective core MOE,E +E (i.e., the summation of MOE parallel to the grain and perpendicular to the grain) - h _c core thickness     

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract

The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R² value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.     

Effect of ACQ-D Treatment on the Surface Free Energy of Chinese Fir (Cunninghamia lanceolata)

In this study, the contact angles of three different reference liquids (including distilled water, diiodomethane, and formamide) and PF resin on the surfaces of Chinese fir (Cunninghamia lanceolata) samples untreated or treated with different con- centrations of ACQ-D (ammoniacal copper quat Type D) solutions were measured. Then, the surface free energy was calculated by two approaches: acid-base approach and geometric mean approach. ACQ-D treatment caused higher contact angles and lower surface free energies at a retention level corresponding to the commodity treated wood products. When wood was treated with much higher concentrations of ACQ-D, the total surface free energy of wood would be higher than the untreated control. Acid-base/polar compo- nents related with the hydrogen bonding state in wood were considered to be responsible for the observed changes according to the applied approaches. The hydrophobic properties and also higher contact angles of PF resin drop on wood surfaces after ACQ-D treatment at a reasonable retention level confirms the changes on surface free energy.     

Permeability and meniscus phenomenon in four Korean softwood species

1 Introduction A number of studies have been carried out to examine the process of liquid impregnation into different kinds of wood (Stamm and Raleigh, 1967; Bolton and Petty, 1978; Olsson et al., 2001). Different techniques and methods have been developed so far to obtain quanti- tative and qualitative information about this process (Stamm, 1953; Stone, 1956; Rudman, 1965). Penetra- tion of liquid in wood depends on several factors. The penetration rate and amount varies in different spec…     

Experimental Study for the Movement of Liquid Droplets on the Surface with Gradient Surface Energy

By using the chemical vapor deposition (CVD), a surface with gradient surface energy is fabricated based on the treated silicon chip. The dodecyltrichlorosilane (C_(12)H_(25)Cl_3Si) and Octrytrichlorosilane (C_(8)H_(17)Cl_3Si) are used as the source of silanization. By using the measurement of sessile drop method, the surface with gradient surface energy was characterized by measuring the contact angle of small water which lied on the surface of the treated silicon chip. The experiment shows the liquid droplets are driven to move from hydrophobic to hydrophilic zone on the gradient surface which is placed horizontally, the diameter of the droplets are 1~3 mm, and the single droplet reached the maximum velocity of up to 0.9 m/s. Based on the experimental results, the mechanical of the movement of the liquid droplet on the gradient surface is researched.     

CALCULATION OF THIN PLATES BENDING EEFORMATION AND CRITICAL PRESSURE BY THE TCHEBYCHEV''S POLYNOMIALS

In this paper trial functions of the second Tchebychev's polynomials is used with Cantorovich variational method in energy functional of thin plate. Bending deformaion of rectangle plate under even loads or concentrate force with several bearing and critical pressure in buckling is resolved. Though the first similar is used but calculations indicate that this method is simple and exact in engineering.     

The Technique of Suppressing Noise for Contact Image Sensor Based on Correlated Double Sampling

The simple principle of Contact Image Sensor (CIS) and the noise types existed in CIS are introduced. The theory of suppressing these noise types for CIS by using Correlated Double Sampling(CDS) is described,and the timing relationship between driving signals CP/SP that CIS required and sampling-holding signals SH1/SH2 are also analyzed,these signals are produced by using Complex Programmable Logic Device(CPLD). CDS circuit principle is analyzed,and experiment of suppressing noise for CIS based on CDS is made. The experiment shows that satisfying results are obtained by using the technique of suppressing noise for CIS based on CDS.     

An Experimental Research on the Deformation and Strength Properties of Chongqing Sandstone

An experimental research on the 22 samples of Chongqing sandstone was carried out on the INSTRON press machine. Based on the experimental results, the failure types in the four applied loading paths were analyzed. The deformation and strength properties of Chongqing sandstone were discussed. The quadratic functional relations between the confined pressing and the maximal strain (or the maximal deviated stress) were proposed, which could be applied to the estimating the maximal deformation and strength of Chongqing sandstone under different confined pressing.