Effects of Cyclic Loading on Velocities of Ultrasonic Waves Propagating Through Wood

The aim of this study was to determine the acoustoelastic phenomenon of wood under cyclic loading-unloading processes. Compression or tension load was repeatedly applied to wood specimens within an elastic range. Ultrasonic waves used in this study were shear and longitudinal waves, and their propagation directions were normal to, and along, the loading directions. The ultrasonic wave velocities were obtained by the sing-around method, which is a method for measuring transit time of ultrasonics. The experimental results revealed that change in the velocity of ultrasonic waves passing through wood under axial stress was a nearly linear function of applied stress level with similar slope for both loading and unloading cycles. The acoustoelastic effect of wood was found to be a repeatable and reversible phenomenon. The acoustoelastic constant seemed to maintain a fixed value regardless of the number of loading cycles. The acoustoelastic technique could be used in the determination of stress conditions of structural components in timber construction

Fatigue Strength of Wood Under Pulsating Tension-Torsion Combined Loading

Fatigue strength of wood under cyclic tension-torsion combined loading was investigated experimentally. The material used for the experiments was a rectangular bar of Japanese cypress. Pulsating tension-torsion combined loadings were respectively applied along and around the longitudinal axis of the specimen, which coincided with the longitudinal direction of the wood. The obtained results of fatigue tests were found to be influenced by the combined-stress ratios and the applied stress levels, and were summarized as follows: 1) All data were located in a slightly wide band on the S-N plot in spite of different combined-stress ratios, but the slope of the S-N curves became low when tensile stress was dominant. 2) Failure modes of the test specimen depended on whether tensile or shear stress was dominant in the biaxial stress ratios. 3) Hill's criterion for the static strength was suitable for evaluating the fatigue strength under combined-stress ratios

Fatigue Behavior in Wood Under Pulsating Compression-Torsion-Combined-Loading

We have experimentally investigated the effects of cyclic compression-torsion-combined loading on the fatigue behavior and stress-strain properties of wood. Pulsating compression and torsion loadings were applied along and around the longitudinal axis of the rectangular bar specimen (Japanese cypress). According to the relationships between stress and strain during fatigue tests, the secant modulus of the stress-strain curve changed with an increase in the number of loading cycles, and the differences between the curves for compression and shear were observed. We found that the experimental results of fatigue tests were influenced by the combined-stress ratios. Compressive stiffness tended to maintain its initial values during almost all loading cycles to failure. Shear stiffness decreased with increasing number of loading cycles, and the final decrease of shear stiffness was larger as compressive stress became dominant. The failure mode was affected by the combined stress states; typical torsion failure was observed in combined stress states with dominant application of shear stress. In contrast, typical compression failure was observed in combined stress states with dominant application of compressive stress. The failure mode under compressive-shear combined stress states was not affected by the stress level, although, as previously demonstrated, it was affected by the stress level under tensile-shear states

Bending Fatigue of Wood: Strain Energy-Based Failure Criterion and Fatigue Life Prediction

In this study, bending fatigue behavior of Japanese cedar and Selangan batu was examined. A nonreversible triangular waveform with loading frequencies of 0.5 and 5 Hz was used as load. Applied loads were about 110-70% of the static strength. The fatigue life of Japanese cedar was found to be longer at 5 Hz, especially at low stress level. For Selangan batu, however, loading frequency did not affect fatigue life. When fatigue life exceeded about 40,000 cycles, a crack formed on the compressive sides of the specimens regardless of the loading frequency and species. Cumulative strain energy at failure was found to be the failure criterion regardless of the loading frequency. This criterion could be estimated using the strain energy through the static test. A fatigue life prediction method based on the strain energy of the second loading cycle was proposed. This prediction method provided a good prediction of fatigue life

Fatigue Damage in Wood Under Pulsating Multiaxial-Combined Loading

A fatigue test was performed under axial-torsion combined loading, with the aim of investigating fatigue damage in wood under multiaxial stresses. This research particularly focused on the energy loss captured during fatigue tests and the fatigue limit for wood. Air-dried samples of Japanese cypress were used for the tests. An electrohydraulic servomachine that could apply axial and torsional loads simultaneously was used for the fatigue tests. An axial load was applied in the fiber direction (along L), and torque was applied around the axis in the same direction as L. A pulsating triangular axial load was applied in the longitudinal direction at 1 Hz while each specimen was also simultaneously subjected to a twisting moment at the same phase. On the basis of the experimental results of the fatigue tests, energy loss was obtained from the stress-strain curve at each loading cycle and examined precisely in relation to the number of loading cycles and combined stress states. The energy loss per cycle in the dominant stress was large and increased gradually toward fatigue failure. The stress level was so high that the energy loss per cycle was extremely large. In the relationship between cumulative energy loss and the number of loading cycles, the cumulative energy loss was so large that the fatigue life was extremely long. The cumulative energy loss for shear in the compression group was larger than that in the tension group. The mean energy loss per cycle for the fatigue limit was also presumed from the relationships between mean energy loss per cycle, stress amplitude, and fatigue life, and was estimated to be about 10 kJ/m3/cycle, as determined on the basis of the equivalent stress principle. That is, the fatigue life will be infinite when the energy loss per cycle is below 10 kJ/m3/cycle

Monitoring Acoustic Emissions to Predict Modulus of Rupture of Finger-Joints from Tropical African Hardwoods

The acoustic emission patterns generated from bending tests of finger-joints from three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii), and Moabi (Baillonella toxisperma) were evaluated to determine the possibility of using them to predict finger-joint modulus of rupture.The patterns of acoustic emissions generated from the bending tests were observed to differ, depending on the type of finger profile and wood species. The regression coefficient of the regression of cumulative acoustic emission count on applied stress squared also varied with the profile and species type. When modulus of rupture was correlated with this regression coefficient, for stresses applied up to 50% of mean ultimate strength, the logarithmic regression model developed could predict modulus of rupture of the finger-joints accurately to ±10%. ±12%, and ±21% for Obeche, Makore, and Moabi, respectively. The models developed also seemed sensitive to the quality of the finger-joints from the three tropical African hardwoods.The results of the study gave an indication that this acoustic emission monitoring procedure could be useful for nondestructively predicting modulus of rupture of finger-joints from the three tropical African hardwoods

Compressive Deformation Process of Japanese Cedar (Cryptomeria Japonica)

We examined the compressive deformation behavior, and methods of compression fixation were considered. Furthermore, we examined the mechanical characteristics of compressed wood for each method of fixation and each compression ratio. As a result of the examination, the deformation behavior was found to differ depending on the direction of compression. The deformation progressed without causing destruction in compression into the tangential surface, but compression into the radial surface caused partial buckling of the cell walls in the process of deformation. The compression stress showed the tendency to decrease as the temperature and moisture content increased. Steam treatment by the closed heating method was compared with heat treatment by the open heating method as methods of fixation. The closed heating method was found to be effective for deformation fixation in a short time. As the result of the mechanical properties of compressed wood, the moduli of rupture (MOR) and elasticity (MOE) increased as the compression ratio increased, and they showed the tendency to be roughly proportional to the increase in density. However, hardness increased only nominally up to 40 % compression and then increased rapidly from 40 %. Moreover, in 480-min heat treatment by open heating, the influence of heat deterioration on impact-absorbed energy was found

THEORETICAL ESTIMATION OF MECHANICAL PROPERTIES OF PLYWOOD-SHEATHED SHEAR WALL WITH COMBINED USE OF ADHESIVE TAPE AND WOOD DOWELS

Shear walls often function as elements that provide resistance to horizontal external forces exerted on wooden frames. Many shear walls with superior strength performance have been developed for this purpose. Amidst this backdrop, we have attempted to develop a shear wall that, in addition to strength performance, decreases the time and labor required for disposal. More specifically, the authors proposed a novel “metalless” shear wall: a shear wall in which industrial double-sided adhesive tape is used to attach plywood to the framework. Also, wood dowels are used as supplementary connectors with the aim of enhancing strength performance. Unlike conventional shear walls that use nails and metal fixtures, separation at the time of disposal is unnecessary, and therefore, disposal time and labor of the wall are anticipated to be significantly decreased. Thus, this study involved demonstrating and verifying a methodof theoretical analysis for the mechanical performance of these kinds of shear walls toward in-plane shear force. Specifically, this study derived a method to estimate the mechanical behavior (load-deformation angle relationship) of plywood-sheathed shear walls based on shear performance obtained from double shear tests of joint specimens with the combined use of adhesive tape and wood dowels. Also, the validity of the method was experimentally verified. The results showed that the method proposed in this study was able to estimate the mechanical behavior and mechanical properties of the newly proposed shear wall, and the validity of the method was confirmed

Direct Supply Chain from Forest to House Builder: A Japanese Business Model

AbstractWe developed a direct supply chain from a forest to a house builder for environment-friendly wooden long-life housing based on the “progressive market-in” method. This business model successfully incorporates the external environmental value of the house into its market price.In this paper, we discuss the direct supply chain business model and its environmental effect in Japan, using a micro approach (for individual economic bodies) and a macro approach for the country

A novel indole compound MA-35 attenuates renal fibrosis by inhibiting both TNF-α and TGF-β1 pathways

Renal fibrosis is closely related to chronic inflammation and is under the control of epigenetic regulations. Because the signaling of transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α) play key roles in progression of renal fibrosis, dual blockade of TGF-β1 and TNF-α is desired as its therapeutic approach. Here we screened small molecules showing anti-TNF-α activity in the compound library of indole derivatives. 11 out of 41 indole derivatives inhibited the TNF-α effect. Among them, Mitochonic Acid 35 (MA-35), 5-(3, 5-dimethoxybenzyloxy)-3-indoleacetic acid, showed the potent effect. The anti-TNF-α activity was mediated by inhibiting IκB kinase phosphorylation, which attenuated the LPS/GaIN-induced hepatic inflammation in the mice. Additionally, MA-35 concurrently showed an anti-TGF-β1 effect by inhibiting Smad3 phosphorylation, resulting in the downregulation of TGF-β1-induced fibrotic gene expression. In unilateral ureter obstructed mouse kidney, which is a renal fibrosis model, MA-35 attenuated renal inflammation and fibrosis with the downregulation of inflammatory cytokines and fibrotic gene expressions. Furthermore, MA-35 inhibited TGF-β1-induced H3K4me1 histone modification of the fibrotic gene promoter, leading to a decrease in the fibrotic gene expression. MA-35 affects multiple signaling pathways involved in the fibrosis and may recover epigenetic modification; therefore, it could possibly be a novel therapeutic drug for fibrosis