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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

Wood water relationship and mechanical properties

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Page 1: Wood water relationship and mechanical properties

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

Page 2: Wood water relationship and mechanical properties

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

Page 3: Wood water relationship and mechanical properties

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

Page 4: Wood water relationship and mechanical properties

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

Page 5: Wood water relationship and mechanical properties

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

Page 6: Wood water relationship and mechanical properties

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)

Page 7: Wood water relationship and mechanical properties

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

Page 8: Wood water relationship and mechanical properties

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

Page 9: Wood water relationship and mechanical properties

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

Page 10: Wood water relationship and mechanical properties

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?????

Page 11: Wood water relationship and mechanical properties

23 November 2016 Group 4 11

Forms or types of water present at EMC and FSP

(Source: University of Florida)

Page 12: Wood water relationship and mechanical properties

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

Page 13: Wood water relationship and mechanical properties

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

Page 14: Wood water relationship and mechanical properties

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.

Page 15: Wood water relationship and mechanical properties

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:

Page 16: Wood water relationship and mechanical properties

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.

Page 17: Wood water relationship and mechanical properties

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

Page 18: Wood water relationship and mechanical properties

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.

Page 19: Wood water relationship and mechanical properties

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

Page 20: Wood water relationship and mechanical properties

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

Page 21: Wood water relationship and mechanical properties

23 November 2016 Group 4 21

Destructive methods

Bending test (MOR)

Tensile Strength test

Complete destructive method is used very limited now-a-days

Page 22: Wood water relationship and mechanical properties

Question?????

Group 423 November 2016 22

Page 23: Wood water relationship and mechanical properties

Thank You

Group 423 November 2016 23