wood water relationship and mechanical properties
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Wood Water Relationship
and
Mechanical Properties
Group 04: Kamona Mondal (MS-150505)
Prity Lata Biswas (MS-150506)
Md. Sajjad Hossain Tuhin (MS-150507)
Nafisa Afrin (MS-150522)
Azad Abul Kalam (MS-150523)
Md. Sazib Uddin (MS-140505)
23 November 2016 Group 4 1
Lecture Outline
23 November 2016 Group 4 2
Wood Anisotropisom
Hygroscopicity of wood
Forms/Types of water in wood
Water absorption of wood (Bound water)
Shrinkage and Swelling
Basic of Shrinkage and Swelling
Equilibrium Moisture Content
Fiber Saturation point
Forms or types of water present at EMC and FSP
Effect of moisture on other properties
Mechanical Properties of wood
Parameters used to express Mechanical properties
Factors affecting Mechanical properties of wood
Methods of determining Mechanical Properties
Nondestructive Methods
Semi-destructive methods
Destructive methods
23 November 2016 Group 4 3
Wood Anisotropisom
Wood is an Anisotropic and Orthotropic material
RadialTangential
Longitudinal
Shows different properties in different dimensions
Wood log
23 November 2016 Group 4 4
Hygroscopicity of Wood
Hygroscopicity means the ability to absorb or release water as a function of humidity and temperature
Wood shows hyroscopicity due to presence of –OH group
It soaks water very slowly, not very fast
Hygroscopic behavior affects other properties of wood
It uptakes water vapor from the air and liquid water as well
23 November 2016 Group 4 5
Forms/Types of water in wood
Free Water: Not Chemically Bonded with cell
wall, contained in the cell cavities. It is
comparable to water in a pipe
Bound Water: Attached with cell wall by
chemical bonding (H- Bond). It is held within cell
walls by bonding forces between water and
holocellulose molecules.
Free water increase the weight but bound water
increase the volume of wood.
Free Water Bound Water
Source: SWST Teaching Unit 2 Slide Set 1
23 November 2016 Group 4 6
Wood (Holocellulose) soak water very slowly.
Water is attached with strong hydrogen bonding between microfibrils
Relative humidity and temperature is important.
Crystalline cellulose uptake less water than amorphous
Water absorption of wood (Bound water)
(Wood and moisture relationships, 1995)
23 November 2016 Group 4 7
Shrinkage and Swelling
Longitudinal Shrinkage: Average values for shrinkage from green to
oven-dry are between 0.1% and 0.2%
Radial Shrinkage: Average value 4-8%
Tangential Shrinkage: Average value 6-14%
Tangential
Radial
Longitudinal
Shrinkage means decrease and swelling means the increase in dimensions
Wood handbook, Ch-4
Long : rad : tang = 1 : 10 : 20
23 November 2016 Group 4 8
Swelled wood Green wood Shrinked wood
Addition of water Removal of water
(Wood and moisture relationships, 1995)
Basic of Shrinkage and Swelling
Water forms H- bond with OH- group of cellulose microfibrils
-OH group of cellulose molecules are responsible for hygroscopicity of wood
With increase of temperature and humidity wood shrink by losing water molecules from micro-fibrils
23 November 2016 Group 4 9
Equilibrium moisture content (EMC) is defined as the moisture content at which the wood is neither gaining
nor losing moisture. EMC shows higher value with increasing Relative humidity, and decrease with
temperature ( always below 30%).
Equilibrium Moisture Content
Source: Wood Handbook, Ch-4
23 November 2016 Group 4 10
The moisture content at which all of the free water is removed - the cell
cavities are empty - but the cell walls are still completely saturated.
Usually ranges from 23 to 33% depending on temperature and species
FSP is decreasing with increasing density
Fiber Saturation point
Source: University of LavalFig: FSP, relation to density (A) temperate hardwoods (B) tropical hardwoods.
Why FSP?????
23 November 2016 Group 4 11
Forms or types of water present at EMC and FSP
(Source: University of Florida)
23 November 2016 Group 4 12
Effect of moisture on other properties
Electrical properties
Heat capacityThermal Conductivity
Moisture content of wood affect all physical properties of, such as:-
Specific gravity
Thermal properties
Electrical properties
Mechanical properties
Friction Properties
Nuclear Radiation Properties, etc.
Wood handbook
23 November 2016 Group 4 13
Mechanical Properties of wood
It has unique and independent mechanical properties in the directions of three
mutually perpendicular axies: longitudinal, radial, and tangential (Orthotropic).
In general, depending on the species, wood has MOE and MOR values of
800,000–2,500,000 psi and 5,000–15,000 psi, respectively.
Mechanical properties means the resistance of a particular material to
stress, load of amount of energy it faces
23 November 2016 Group 4 14
Parameters used to express Mechanical properties
Modulus of elasticity (MOE): Modulus elasticity is the
ratio of stress to strain of a material in deflection and is
sometimes called 'Young's modulus.
Modulus of rupture (MOR): Measure of a specimen's
strength before rupture.
23 November 2016 Group 4 15
Compressive strength: compressive strength means by loading a block of
wood parallel to the grain until it breaks
Bending strength: bending strength means by loading a block perpendicular
to the grain
Shear strength: application of stress from two opposite directions causing
portions of an object to move in parallel but opposite directions
Tensile strength: Limit of resistivity to opposite force applied parallel to the
grain
Parameters used to express Mechanical properties Cont..
Compressive strength
Bending strength
Shear strengthTensile strength:
23 November 2016 Group 4 16
Factors affecting Mechanical properties of wood
Specific Gravity: generally mechanical properties increases
with increase of specific gravity
Knots: The influence of knots depends on their size, location,
shape, and soundness; attendant local slope of grain; and type
of stress to which the wood member is subjected.
Slope of Grain (Fiber angle): fiber parallel to grain gives
maximum strength.
23 November 2016 Group 4 17
Annual Ring Orientation: 90° and 0° shows no difference
(Highest) but other shows less mechanical strength
Temperature: Increasing with decrease with temperature
Moisture content
Reaction Wood
Juvenile Wood
Extractives
Factors affecting Mechanical properties of wood
Wood Handbook, 2010
23 November 2016 Group 4 18
Methods of determining Mechanical Properties
Several types of test is used to express mechanical properties of wood
Depending upon the degree of destruction it can be divided into:-
1. Nondestructive Methods: No damage done to the original samples.
2. Semi-destructive methods: Some degree of destruction is allowed to measure
different properties.
3. Destructive methods: Totally destroy the sample, not eligible to use after test.
23 November 2016 Group 4 19
Non-destructive Methods
Ultrasonic sound test
Bending tests (MOE)
Bing software
Transverse Vibration Techniques
Stress Wave Techniques
X-Ray analysis
Ultrasonic sound test
Bending tests (MOE)Bing software
X-Ray
23 November 2016Group 4
20
Semi-destructive methods
Screw withdrawal measurement
Pin pushing
Drawbar with a push-apart wedge
Triangular Bar
Drawbar with a push-apart wedgeTriangular Bar
Pin pushing
Kloiber et al. 2015
23 November 2016 Group 4 21
Destructive methods
Bending test (MOR)
Tensile Strength test
Complete destructive method is used very limited now-a-days
Question?????
Group 423 November 2016 22
Thank You
Group 423 November 2016 23
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