The creep of wood destabilized by change in moisture content. Part 3: The influence of changing moisture history on creep behavior

Holzforschung ◽  
2006 ◽  
Vol 60 (3) ◽  
pp. 299-303 ◽  
Author(s):  
Chika Takahashi ◽  
Yutaka Ishimaru ◽  
Ikuho Iida ◽  
Yuzo Furuta
Keyword(s):  
Mechanical Properties ◽  
Moisture Content ◽  
Memory Effect ◽  
Creep Behavior ◽  
Cell Walls ◽  
Load Level ◽  
Moisture Change ◽  
Adsorption Processes ◽  
Rapid Adsorption

Abstract The creep of wood increases remarkably during moisture changes, a phenomenon called mechano-sorptive creep. The microstructure in cell walls of wood is destabilized by changes in temperature and/or moisture content. The mechanical properties of destabilized wood change over long periods of time. In the present study, the influence of moisture conditioning history on bending creep was examined. During changes in moisture, greater creep occurred in wood subjected to the first moisture change after long-term moisture conditioning than immediately after desorption or adsorption. This result indicates a kind of memory effect immediately after moisture change. During desorption processes, greater creep occurred immediately after slow adsorption than immediately after rapid adsorption. In the course of adsorption, the reverse was observed: the creep was greater immediately after rapid desorption than immediately after slow desorption. Accordingly, greater instability immediately after a change in moisture does not always cause greater creep during the next moisture change. The size of the moisture change and the load level affect the recovery of creep during adsorption processes.

scholarly journals Temperature-Dependent Creep Behavior and Quasi-Static Mechanical Properties of Heat-Treated Wood

Forests ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 968
Author(s):  
Dong Xing ◽  
Xinzhou Wang ◽  
Siqun Wang
Keyword(s):  
Mechanical Properties ◽  
Creep Behavior ◽  
Cell Walls ◽  
Treated Wood ◽  
Crosslinking Reaction ◽  
Depth Sensing ◽  
Temperature Dependent ◽  
Heat Treated ◽  
Static Mechanical ◽  
Static Mechanical Properties

In this paper, Berkovich depth-sensing indentation has been used to study the effects of the temperature-dependent quasi-static mechanical properties and creep deformation of heat-treated wood at temperatures from 20 °C to 180 °C. The characteristics of the load–depth curve, creep strain rate, creep compliance, and creep stress exponent of heat-treated wood are evaluated. The results showed that high temperature heat treatment improved the hardness of wood cell walls and reduced the creep rate of wood cell walls. This is mainly due to the improvement of the crystallinity of the cellulose, and the recondensation and crosslinking reaction of the lignocellulose structure. The Burgers model is well fitted to study the creep behavior of heat-treated wood cell walls under different temperatures.

Viscoelasticity of wood cell walls with different moisture content as measured by nanoindentation

RSC Advances ◽  
2015 ◽  
Vol 5 (59) ◽  
pp. 47538-47547 ◽  
Author(s):  
Yujie Meng ◽  
Yuzhi Xia ◽  
Timothy M. Young ◽  
Zhiyong Cai ◽  
Siqun Wang
Keyword(s):  
Mechanical Properties ◽  
Moisture Content ◽  
Cell Walls ◽  
Creep Behaviour ◽  
Instrumental Indentation ◽  
Moisture Conditions

The mechanical properties and creep behaviour of wood cell walls were measured over a range of various steady moisture conditions using instrumental indentation.

scholarly journals Influence of mid-stress on the dynamic fatigue of a light weight EPS bead foam

e-Polymers ◽  
2019 ◽  
Vol 19 (1) ◽  
pp. 349-354
Author(s):  
Jan-Hendrik Keller ◽  
Volker Altstädt
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Complex Loading ◽  
Load Level ◽  
Static Compression ◽  
Long Period ◽  
First Time ◽  
Quasi Static Compression ◽  
Dynamic Fatigue

AbstractExpandable Polystyrene (EPS) is one of the most commonly used material, when it comes to protect thermal sensitive goods, since the thermal conductivity of EPS is very low. The mechanical properties in terms of long-term compression or quasi-static compression are also quite well known. But when the material is loaded with higher amplitudes over a long period of time, not much is known yet about long-term mechanical behavior. For example, as a packaging material, EPS exhibits complex loading situation ranging from small to high amplitudes over a long period of time, when e.g. it is transported in a truck, a ship or in a car. In order to characterize the mechanical behavior under such large amplitude loading, the dynamic fatigue needs to be recorded and evaluated. In this paper, the principles of the hysteresis measurements evaluation are applied on EPS for the first time to unveil long-term mechanical properties in compression. Results show, that after increasing the dynamic load level to a critical level of over 100 kPa, the mechanical behavior, in terms of compression rate, of EPS changes from a linear to a kind of exponential mode.

The creep of wood destabilized by change in moisture content. Part 2: The creep behaviors of wood during and immediately after adsorption

Holzforschung ◽  
2005 ◽  
Vol 59 (1) ◽  
pp. 46-53 ◽  
Author(s):  
Chika Takahashi ◽  
Yutaka Ishimaru ◽  
Ikuho Iida ◽  
Yuzo Furuta
Keyword(s):  
Moisture Content ◽  
Adsorption Process ◽  
Unstable State ◽  
Drying Process ◽  
Outward Appearance ◽  
Creep Tests ◽  
Adsorption Processes ◽  
The Difference ◽  
Rapid Adsorption ◽  
Changing Process

Abstract The fluidity of wood remarkably increases during moisture changes. This phenomenon is termed mechano-sorptive creep. The mechanism of mechano-sorptive creep has been studied, including a previous report by our group. Here, creep tests in bending were carried out for wood during and immediately after adsorption of moisture and after a long moisture conditioning. The effects of the rate of moisture adsorption on creep were also examined. The results and conclusions are as follows: (I) Greater creep occurred immediately after the adsorption process as compared with that after a long moisture conditioning, whereas much greater creep occurred during the same adsorption process, similar to the case of drying. Therefore, during the changes in moisture, not only destabilization but also stabilization should occur simultaneously, so that the wood during the changing process is in a remarkably unstable state. (II) Smaller creep occurred immediately after a slower adsorption as compared with that immediately after a more rapid adsorption. This suggests that wood is more stabilized during a slower versus a more rapid adsorption process. However, difference in creep between the final stages of the slower and the more rapid adsorption process was scarcely found. This is considered to result from the difference in degree of stabilization caused by the different duration of both adsorptions. In other words, this result is only an outward appearance. (III) Greater creeps were recognized during larger changes in moisture content (Δu) during the adsorption processes corresponding to the drying process. Therefore, mechano-sorptive creep depends not only on Δu but also on the range of relative humidity (RH). Larger stabilization was found during the changing process of larger Δu.

Examination of moisture content variation within an operational wet deck

TAPPI Journal ◽  
2013 ◽  
Vol 12 (1) ◽  
pp. 45-50 ◽  
Author(s):  
LAURENCE SCHIMLECK ◽  
KIM LOVE-MYERS ◽  
JOE SANDERS ◽  
HEATH RAYBON ◽  
RICHARD DANIELS ◽  
...  
Keyword(s):  
Moisture Content ◽  
Southeastern United States ◽  
Forest Products ◽  
Time Domain Reflectometry ◽  
Water Application ◽  
Wood Moisture ◽  
International Paper ◽  
Content Variation ◽  
Moisture Variation

Many forest products companies in the southeastern United States store large volumes of roundwood under wet storage. Log quality depends on maintaining a high and constant wood moisture content; however, limited knowledge exists regarding moisture variation within individual logs, and within wet decks as a whole, making it impossible to recommend appropriate water application strategies. To better understand moisture variation within a wet deck, time domain reflectometry (TDR) was used to monitor the moisture variation of 30 southern pine logs over an 11-week period for a wet deck at the International Paper McBean woodyard. Three 125 mm long TDR probes were inserted into each log (before the deck was built) at 3, 4.5, and 7.5 m from the butt. The position of each log within the stack was also recorded. Mixed-effects analysis of variance (ANOVA) was used to examine moisture variation over the study period. Moisture content varied within the log, while position within the stack was generally not significant. The performance of the TDR probes was consistent throughout the study, indicating that they would be suitable for long term (e.g., 12 months) monitoring.

scholarly journals Symmetric Nature of Stress Distribution in the Elastic-Plastic Range of Pinus L. Pine Wood Samples Determined Experimentally and Using the Finite Element Method (FEM)

Symmetry ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 39
Author(s):  
Łukasz Warguła ◽  
Dominik Wojtkowiak ◽  
Mateusz Kukla ◽  
Krzysztof Talaśka
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Stress Distribution ◽  
Moisture Content ◽  
Tool Geometry ◽  
Wood Fibers ◽  
Data Set ◽  
Plastic Deformations ◽  
Pine Wood ◽  
Elastic Plastic

This article presents the results of experimental research on the mechanical properties of pine wood (Pinus L. Sp. Pl. 1000. 1753). In the course of the research process, stress-strain curves were determined for cases of tensile, compression and shear of standardized shapes samples. The collected data set was used to determine several material constants such as: modulus of elasticity, shear modulus or yield point. The aim of the research was to determine the material properties necessary to develop the model used in the finite element analysis (FEM), which demonstrates the symmetrical nature of the stress distribution in the sample. This model will be used to analyze the process of grinding wood base materials in terms of the peak cutting force estimation and the tool geometry influence determination. The main purpose of the developed model will be to determine the maximum stress value necessary to estimate the destructive force for the tested wood sample. The tests were carried out for timber of around 8.74% and 19.9% moisture content (MC). Significant differences were found between the mechanical properties of wood depending on moisture content and the direction of the applied force depending on the arrangement of wood fibers. Unlike other studies in the literature, this one relates to all three stress states (tensile, compression and shear) in all significant directions (anatomical). To verify the usability of the determined mechanical parameters of wood, all three strength tests (tensile, compression and shear) were mapped in the FEM analysis. The accuracy of the model in determining the maximum destructive force of the material is equal to the average 8% (for tensile testing 14%, compression 2.5%, shear 6.5%), while the average coverage of the FEM characteristic with the results of the strength test in the field of elastic-plastic deformations with the adopted ±15% error overlap on average by about 77%. The analyses were performed in the ABAQUS/Standard 2020 program in the field of elastic-plastic deformations. Research with the use of numerical models after extension with a damage model will enable the design of energy-saving and durable grinding machines.

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