Testing of the fatigue strength along wood fibres at different moisture contents

2021 ◽  
Vol 115 ◽  
pp. 45-54
Author(s):  
Ewa Dobrowolska ◽  
Mateusz Niedbała ◽  
Daniel Tabaczyński
Keyword(s):  
Fatigue Strength ◽  
Moisture Content ◽  
Maximum Stress ◽  
Fibre Saturation Point ◽  
Pedunculate Oak ◽  
Saturation Point ◽  
Moisture Contents ◽  
Wood Fibres ◽  
Short Term Strength ◽  
Limited Usefulness

Testing of the fatigue strength along wood fibres at different moisture contents. The paper determines the effect of wood moisture content on the fatigue strength in compression along fibres. The method of determining the maximum stress at the proportional limit was used for the measurements. Fatigue strength was investigated for three wood species: pedunculate oak (Quercus robur L.), bearded birch (Betula pendula Roth.) and Norway spruce (Picea abies L.), with two moisture contents: close to the absolutely dry state and above the fibre saturation point. The ratio of fatigue strength to short term strength depends on moisture content and is similar for birch (70.3% in the dry state and 72.1% in the wet state), for oak (67.4% and 69.5% in both states) and for spruce (66.6% in the dry state and 68.1% in the wet state). The moisture content of the wood clearly influences the fatigue strength of the wood. On average, the fatigue strength of wood with moisture contents above the fibre saturation point constitutes about 0.20 of the fatigue strength of wood with moisture contents close to 0%. This tendency was found regardless of the tested species. The simplified method for testing fatigue strength at the limit of proportionality has shown its limited usefulness, requiring further analysis and comparison with other methods in order to be thoroughly tested and possibly improved.

Effect of Moisture Content on the Morphology of Longitudinal Fracture in Eucalyptus Maculata

IAWA Journal ◽  
1987 ◽  
Vol 8 (2) ◽  
pp. 175-181 ◽  
Author(s):  
John Wilkes
Keyword(s):  
Moisture Content ◽  
Fibre Saturation Point ◽  
Clean Surface ◽  
Fracture Path ◽  
Saturation Point ◽  
Moisture Contents ◽  
Ray Parenchyma ◽  
Ray Cells ◽  
Effect Of Moisture ◽  
Eucalyptus Maculata

The longitudinal surfaces of Eucalyptus maculata wood sampies fractured either artificially (splitting) or naturally (drying stresses) at a range of moisture contents, were examined under a scanning eleetron microscope. In those sam pies above fibre saturation point, a relativeIy clean surface was produced, since the cells either separated in the outer regions of the wall with minimal fibrillation (fibres, some ray parenchyma), or the fracture path travelled abruptly through the wall exposing the lumen (vertical parenchyma, vessels, so me ray cells). Below fibre saturation, particularly as the air dry condition was approached, a fibrous, splintery surface resulted, due mainly to fibrillation and delamination of the secondary walls in fibres and ray parenchyma.

Physical properties of earlywood and latewood of Pinus radiata D. Don: Anisotropic shrinkage, equilibrium moisture content and fibre saturation point

Holzforschung ◽  
2005 ◽  
Vol 59 (6) ◽  
pp. 654-661 ◽  
Author(s):  
Shusheng Pang ◽  
Alfred Herritsch
Keyword(s):  
Moisture Content ◽  
Equilibrium Moisture Content ◽  
Pinus Radiata ◽  
Growth Ring ◽  
Fibre Saturation Point ◽  
Longitudinal Shrinkage ◽  
Saturation Point ◽  
Breast Height ◽  
Second Growth ◽  
Tangential Shrinkage

Abstract Anisotropic shrinkage (tangential and longitudinal), equilibrium moisture content (EMC) and fibre saturation point (FSP) were measured for separated earlywood (EW) and latewood (LW) of a 0.75-m-long log of 20-year old Pinus radiata that was cut at breast height from a selected tree in the forest of Central North Island, New Zealand. The experimental results have shown that at 12% moisture content (MC), tangential shrinkage was 3.23% for EW and 3.90% for LW, with an overall average of 3.56%. Longitudinal shrinkage was 0.23% for EW and 0.21% for LW with an overall average of 0.22%. Shrinkage for the oven dry (OD) state showed similar trends to those at 12% MC in terms of the differences between EW and LW. The tangential and longitudinal shrinkage varied significantly along the radius from pith to bark. The EW tangential shrinkage increased from pith to the seventh growth ring and then remained relatively constant until the last ring adjacent to the bark. The LW tangential shrinkage also increased from the pith outwards until the seventh growth ring, but beyond that was more variable than the EW shrinkage. Both EW and LW showed similar longitudinal shrinkage, with the highest values in the second growth ring, from which the shrinkage decreased exponentially towards the bark. LW had a slightly higher EMC than EW at a relative humidity (RH) below 80%, but the trend was reversed for RH above 80%. The EMC differences between EW and LW were less than 0.6%. The overall average FSP for Pinus radiata was 29.1%, with actual values varying from 25% to 32.8%. The earlywood FSP (28.9%) was slightly lower than that of the latewood (29.4%).

Modelling drying processes of fuelbeds of Scots pine needles with initial moisture content above the fibre saturation point by two-phase models

2012 ◽  
Vol 21 (4) ◽  
pp. 418 ◽  
Author(s):  
Sen Jin ◽  
Pengyu Chen
Keyword(s):  
Moisture Content ◽  
Scots Pine ◽  
Initial Moisture Content ◽  
Fibre Saturation Point ◽  
Phase Model ◽  
Fuel Moisture ◽  
Drying Process ◽  
Rating Systems ◽  
Saturation Point ◽  
Two Phase

Modelling the drying process of fuel moisture with initial moisture content above the fibre saturation point can be used to determine when fuel will become sufficiently dry (after precipitation) to burn and provide a more accurate prediction of fire potential. Based on analysis of the mechanism by which the drying process occurs, we propose a model comprising two phases distinguished by a moisture threshold of 0.35 g g–1, the fibre saturation point; one phase is controlled by evaporation and the other by diffusion. Each phase has a distinct equation with a different timelag. We compared our two-phase model with a one-phase model (one-timelag model) and another two-phase model by estimating drying of 15 Scots pine (Pinus sylvestris var. mongolica) needle fuelbeds. The results indicate that the two-timelag model improves moisture modelling, thereby reducing mean absolute error by more than 30%, i.e. from 0.0047 g g–1 (one-phase model) to 0.0030 g g–1. The model yields consistent results, further suggesting its potential for improving fuel moisture prediction of fire danger rating systems. The first timelag of the model is affected by fuelbed properties. Equations based on variables that represent fuelbed properties were established, thus saving time when estimating parameters for stand-specific fuel moisture models.

scholarly journals Experimental study of electrode effects of resistance type electrodes for monitoring wood drying process above fibre saturation point / Elektroodefektide uurimine puidu kuivatamisel niiskussisaldustel üle kiu küllastuspunkti

2012 ◽  
Vol 56 (1) ◽  
pp. 42-55
Author(s):  
Valdek Tamme ◽  
Peeter Muiste ◽  
Regino Kask ◽  
Allar Padari ◽  
Hannes Tamme
Keyword(s):  
Moisture Content ◽  
Electrical Resistance ◽  
Multivariate Calibration ◽  
Fibre Saturation Point ◽  
Saturation Point ◽  
Residual Polarization ◽  
Polarization Voltage ◽  
Measurement Mode ◽  
Repeated Use ◽  
Effect Duration

Abstract Due to practical need to improve the accuracy of measurement of wood electrical resistance via creating multivariate calibration models the study of electrode effects was carried out. The experiments were made in DC mode and five types of electrode effects were measured: electrical resistance of the galvanic contact between the measuring electrode and wood, corrosion of measuring electrodes in wet wood, polarization and depolarization of the double layer forming on the surface of the measuring electrodes, residual polarization voltage between measuring electrodes and effect of repeated use of measuring electrodes. For multi-channel measurement mode effect of neighbouring electrodes was measured. Behind each of these factors is a complex transfer mechanism of free and bounded charge carriers from wood to measuring electrodes. Among the factors, polarization and depolarization have an immediate effect (duration of the processes in seconds) while resistance of electrode/wood contact, corrosion of electrodes and residual polarization have a slow effect (duration of processes in hours). For pine sapwood, coefficients of the Stamm formula were found in moisture contents (MC) above the fibre saturation point. It was determined that wood polarization and depolarization indicators are dependent on wood moisture content as is the case with wood electrical resistance. Compared to wood electrical resistance, wood polarization proved approximately four times and depolarization approximately eight times less sensitive to moisture content variation.

An improved drying model for highly-impermeable hardwoods

Holzforschung ◽  
2009 ◽  
Vol 63 (4) ◽  
Author(s):  
Alfred Herritsch ◽  
Justin James Nijdam
Keyword(s):  
Diffusion Coefficient ◽  
Moisture Content ◽  
Fibre Saturation Point ◽  
Second Law ◽  
Saturation Point ◽  
Drying Models ◽  
Parabolic Form ◽  
Drying Model ◽  
Drying Rates ◽  
Arrhenius Temperature

Abstract Previously reported drying experiments on highly impermeable hardwoods have shown that bell-shaped within-board moisture content profiles develop as drying proceeds, with a change in concavity around the fibre saturation point. However, drying models based on Fick's second law of diffusion with an Arrhenius temperature dependency for the diffusion coefficient predict a parabolic form. The present work showed that the influence of moisture content on the diffusion coefficient must also be considered to improve these drying predictions. A drying model that includes both temperature and moisture content effects on the diffusion coefficient was developed. This model is able to accurately predict the drying rates and within-board moisture content profiles of New Zealand's indigenous red and hard beech timbers for various timber thicknesses over a range of temperatures, relative humidities and air velocities used in practice.

The Smoulder Stream of Cigarettes / Zur Kenntnis des Glimmstromes von Cigaretten

1965 ◽  
Vol 3 (2) ◽  
Author(s):  
F. Seehofer ◽  
W. Schulz
Keyword(s):  
Moisture Content ◽  
Spatial Position ◽  
High Yield ◽  
Physical Conditions ◽  
Moisture Contents ◽  
Cigarette Paper ◽  
First Time

AbstractThe phenomenon of the smoulder stream flowing through the cigarette during smouldering and during the puff intervals is demonstrated for the first time and its dependence upon physical conditions is examined. The volume of the smoulder stream can amount up to 180 ml per cigarette. Increasing draw resistance of the cigarette and augmenting moisture content of the tobacco as well as perforation of the cigarette paper have a decreasing effect on volume and velocity of the smoulder stream. The porosity of the cigarette paper has no perceptible influence. The spatial position of the cigarette affects volume and velocity of the smoulder stream. The influence exercised by the smoulder stream on the yields of total condensate, nicotine, phenols, aldehydes, and acroleine when the cigarette tip is open during the puff intervals is determined. When the moisture contents of the tobacco were extremely high, yield decreases reaching 50 % could be observed.

Developing a Linearization Method to Determine Optimum Blending for Surimi with Varied Moisture Contents Using Linear Programming

2019 ◽  
Vol 0 (0) ◽  
Author(s):  
Hyeon W. Park ◽  
Jae W. Park ◽  
Won B. Yoon
Keyword(s):  
Linear Programming ◽  
Moisture Content ◽  
Standard Procedure ◽  
Unit Cost ◽  
Linearization Method ◽  
Model Parameters ◽  
Additional Information ◽  
Moisture Contents ◽  
Design Variables ◽  
Critical Moisture

AbstractNovel algorithm to determine the least cost formulation of a surimi blend was developed using linear programming (LP). Texture properties and the unit cost of surimi blend at the target moisture content were used as constraint functions and the objective function, respectively. The mathematical models to describe the moisture content dependence of the ring tensile properties were developed using critical moisture content, and the model parameters were used for the least cost LP (LCLP) model. The LCLP model successfully predicted the quality of surimi blend. Sensitivity analysis was used to obtain an additional information when the perturbations of design variables are provided. A standard procedure to determine the least cost formulation for blending surimi with varied moisture contents was systematically developed.

Equilibrium moisture content of dead fine fuels of selected central European tree species

2013 ◽  
Vol 22 (6) ◽  
pp. 797 ◽  
Author(s):  
Christian Schunk ◽  
Clemens Leutner ◽  
Michael Leuchner ◽  
Clemens Wastl ◽  
Annette Menzel
Keyword(s):  
Moisture Content ◽  
Equilibrium Moisture Content ◽  
Input Parameter ◽  
Fire Danger ◽  
Pedunculate Oak ◽  
Salt Solutions ◽  
Test Procedures ◽  
Climate Chamber ◽  
Central European ◽  
Fine Fuels

Fine fuel moisture content is a key parameter in fire danger and behaviour applications. For modelling purposes, equilibrium moisture content (EMC) curves are an important input parameter. This paper provides EMC data for central European fuels and adds methodological considerations that can be used to improve existing test procedures. Litter samples of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were subjected to three different experiments using conditioning in a climate chamber and above saturated salt solutions. Climate chamber conditioning yielded the best results and can generally be recommended, however saturated salt solutions are able to produce lower relative humidities, which are relevant to forest fire applications as they represent the highest fire danger. Results were within the range of published sorption isotherms for forest fine fuels. A fairly clear gradation was present with higher EMC values in leaf litters than in needle litters. These differences are in accord with values from the literature and suggest general differences in the sorption properties of leaves and needles, which may be caused by differing chemical and physical properties. The influence of temperature on EMC described in the literature could be confirmed.

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