68 Cronin StAnnerleyQLD 4103Telephone: 0414416606E-mail: trent.paschkow@gmail.com

29 April 2012

Dr Peter HoQueensland University of TechnologyBrisbane QLD 4000

Dear DoctorI am pleased to present you Timber Practical Report: Flexural Properties of Timber Members. This report presents the results of the flexural properties of four types of timber products that are of interest to Engineers and Architects. I thank you for giving me the opportunity to work on such a report and look forward to receiving your feedback.

Yours Sincerely

Trent PaschkowEngineering Student

Executive Summery

A testing rig was used to analyze the flexural properties of four different timber samples. Flexural stiffness and ultimate fiber strength capacity was calculated to aid in design for both strength and deflection.

A three-point flexure test approach was taken. Included in this report are particulars on testing methods, calculations, and results. In this report will be found discussions on the elastic modulus, modulus of rupture and density as well as relationships between these. An investigation on how moisture correlates to that of strength and stiffness and look into the application of these different timber products will be reviewed.

The overall objectives of the study were met, relationships between density and elasticity were found, as density increases elasticity decreased. Additionally the two composite materials were found to have fallen within the Australian Standard for these materials.

Table of Contents

Executive Summery.......................................................................................................... 3

Introduction........................................................................................................................ 5

1 Testing Methods........................................................................................................ 51.1 Visual Strength Grading..............................................................................................51.2 Three-Point Flexure Test...........................................................................................5

2 Results.......................................................................................................................... 6

2 Load vs. Deflection................................................................................................... 7

3 Calculations:............................................................................................................... 83.1 Density.............................................................................................................................. 83.2 Moment of Inertia (mm^4)........................................................................................83.3 Modulus of Elasticity....................................................................................................8

Softwood.......................................................................................................................................................8Hardwood....................................................................................................................................................9Chipboard.................................................................................................................................................... 9Plywood........................................................................................................................................................9

3.4 Modulus of Rupture...................................................................................................10Softwood....................................................................................................................................................10Hardwood................................................................................................................................................. 10Chipboard..................................................................................................................................................10Plywood..................................................................................................................................................... 11

4 Evaluation................................................................................................................. 11

5 The Effects of Moisture on E and MOR.............................................................12

6 Applications in Building....................................................................................... 136.1 Softwood........................................................................................................................136.2 Hardwood..................................................................................................................... 136.3 Chipboard..................................................................................................................... 136.4 Plywood......................................................................................................................... 13

7 Conclusion................................................................................................................ 14

8 References................................................................................................................ 15

Appendix............................................................................................................................ 16

Introduction

Timber has always been one of the more plentiful natural resources available and consequently is one of the oldest know materials used in construction (Kermani 1999, 1). As walker (2006, 1) points out commercial timber falls into two categories, softwood and hardwood. Softwoods are the timbers of needle like trees i.e. Pines, were hardwoods on the other hand are a product of broader leafed trees such as oaks. Timber is a material that is used for a variety of structural forms, such as beams, columns , trusses and girders (Porteous 2007, 1)

This report will provide information and characteristics of four types of timber samples, namely, softwood, hardwood, chipboard and plywood. All of which are of interest to engineers and architects alike. Included in this report are particulars on testing methods, calculations, and results. In this report will be found discussions on the elastic modulus, modulus of rupture and density as well as relationships between these. An investigation on how moisture correlates to that of strength and stiffness and look into the application of these different timber products will be reviewed.

1 Testing Methods

1.1 Visual Strength GradingDefects in timber, whether natural or caused during conversion or seasoning, will have an effect on structural strength as well as on fixing, stability, durability and finished appearance of timber (Kermani 1999, 7). The visual inspection of timber for grading purposes is quite subjective, as experience and knowledge plays a key role. Timber samples were inspected in this way before applying the three-point flexure test approach. The four timber samples were scrutinized for characteristics such as a bow, spring, cup or twist, knots, slope of grain, wane and shakes or distortion. The results of the inspection can be seen:

Table 1 – Sample Characteristics

Sample Visual CharacteristicsSoftwood Edge Grain, No DefectsHardwood Edge Grain, Slight BowChipboard Particles Visible, No DefectsPlywood 3 Layers, No Defects

1.2 Three-Point Flexure TestFor each test sample provided (softwood, hardwood, chipboard, plywood) the average cross section dimensions, length and mass was recorded. The test span (distance between the supports) was also recorded. The test specimen was placed in the testing rig with the dial gauge beneath the load point ensuring it just slightly touches the specimen. The gauge was then zeroed. The loading arm with a mass of 0.5kg was then placed on the specimen and the deflection was recorded. In increments of 0.5kg, masses were added to the loading arm and the corresponding deflection was recorded. Weights were added until rupture occurred.

Figure 1 – 3 Point Flexure Test

2 ResultsTable 2 – Timber Sample Measurements

Sample Mass (g) Length (mm) Width (mm) Depth (mm)Softwood 46.3 998 12 12Hardwood 35.35 610 9.3 9.1Chipboard 176.16 751 20.1 16.3Plywood 47.88 749 20.4 6.75

Test Span 550mm

Table 3 – Load Deflection

Load Deflection (mm)Load (kg) Newtons Softwood Hardwood Chipboard Plywood

0 0 0 0 0 01.4 13.72 2.96 3.45 1.61 14.821.9 18.62 3.71 4.94 2.28 20.072.4 23.52 4.51 6.73 2.88 25.122.9 28.42 5.31 7.9 3.55 29.433.4 33.32 6.18 9.74 4.24 35.423.9 38.22 6.93 10.91 4.94 42.254.4 43.12 7.83 11.43 5.4 47.164.9 48.02 8.44 13.76 6.26 -5.4 52.92 9.28 14.3 7.05  -

Failure 22.4 kg (219.5 N)

11.4 kg (111.72 N)

10.4 kg (101.92 N)

5.4 kg (52.92 N)

2 Load vs. Deflection

The data was plotted on a graph for all samples (softwood, hardwood, chipboard, plywood) and a line of best fit was drawn. The line of best fit was drawn from the origin and the line equation was calculated.

y=mx+b→ ∆Deflection (mm )∆ load (N )

From this, the gradient (m) was obtained and further analysis could be achieved.

Figure 2 – Load vs. Deflection Graph

0 10 20 30 40 50 600

5

10

15

20

25

30

35

40

45

50f(x) = 1.08008507790546 x

f(x) = 0.128561656517446 x

f(x) = 0.277628339642309 x

f(x) = 0.181190167599298 x

Load vs Deflection

SoftwoodLinear (Softwood)HardwoodLinear (Hardwood)ChipboardLinear (Chipboard)PlywoodLinear (Plywood)

Load (N)

Def

lect

ion

(m

m)

3 Calculations:

3.1 Density

Table 4 – Sample Density

Sample Mass (g)

Length (mm)

Width (mm)

Depth (mm)

Volume (mm^3)

Density (g/mm^3)

Softwood

46.3 998 12 12 143712 3.222E-04

Hardwood

35.35 610 9.3 9.1 51624.3 6.848E-04

Chipboard

176.16 751 20.1 16.3 246050.13 7.160E-04

Plywood

47.88 749 20.4 6.75 103137.3 4.642E-04

3.2 Moment of Inertia (mm^4)

I=bd3

12

Were: I = Moment of Inertia (mm^4)b = Breadth (mm)d = Depth (mm)

Table 5 – Moment of Inertia

Sample Width (mm) Depth (mm) I (mm^4)Softwood 12 12 1.73E+03Hardwood 9.3 9.1 5.84E+02Chipboard 20.1 16.3 7.25E+03Plywood 20.4 6.75 5.23E+02

3.3 Modulus of Elasticity

Softwood

Line of best fit : y=mx+b

y=0.1812 x+0 

m=0.1812=tan∅

tan∅=change∈deflection (mm )change∈load (N )

= L3

48 EI

0.1812= 5503

48E (1728 )

E= 5503

48 (1728 ) (0.1812 )

E=13205.21Mpa

Hardwood

Line of best fit : y=mx+b

y=0.2776 x+0 

m=0.2776=tan∅

tan∅=change∈deflection (mm )change∈load (N )

= L3

48 EI

0.2776= 5503

48E (584.02 )

E= 5503

48 (584.02 ) (0.2776 )

E=21379.69Mpa

Chipboard

Line of best fit : y=mx+b

y=0.1286 x+0 

m=0.1286=tan∅

tan∅=change∈deflection (mm )change∈load (N )

= L3

48 EI

0.1286= 5503

48E (7254 )

E= 5503

48 (7254 ) (0.1286 )

E=3715.59Mpa

Plywood

Line of best fit : y=mx+b

y=1.0801 x+0 

m=1.0801=tan∅

tan∅=change∈deflection (mm )change∈load (N )

= L3

48 EI

0.1286= 5503

48E (522.83 )

E= 5503

48 (522.83 ) (1.0801 )

E=6137.94Mpa

3.4 Modulus of Rupture

Table 6 - Rupture

Load Failure Softwood Hardwood Chipboard Plywood22.4 kg (219.52N)

11.4 kg(111.42N)

10.4 kg (101.92N)

5.4 kg* (52.92N)

Plywood sample did not rupture, deflection became too great and sample was deemed failed.

MOR=MyI

Were: M = Bending Moment at Failure = PL/4P = Load at Failure

y = Distance from Neutral Axis to Extreme Fibers = d/2I = Moment of Inertia

Softwood

MOR=( 219.52×5504 )×(122 )

1728

MOR=104.81Mpa

Hardwood

MOR=( 111.72×5504 )×( 9.12 )

584.02

MOR=119.68Mpa

Chipboard

MOR=( 101.92×5504 )×( 16.32 )

7254

MOR=15.74 Mpa

Plywood

MOR=( 52.92×5504 )×( 6.752 )

522.83

MOR=46.97Mpa

4 Evaluation

Density is the best single indicator of the properties of timber and is a major factor determining its strength (Kermani 1999, 7). As Cardarelli (2008, 987) describes, the higher the density, the higher the tensile and compressive strength will be. The following table shows the flexural characteristics of the four samples.

Table 7 – Density, E and MOR

Samples Density ( )ρ(g/mm^3)

Moment of Inertia (mm^4)

Elastic Modulus (E) (Mpa)

E/ ρMpa/(g/mm^3)(10^6)

Modulus of Rupture (MOR) (Mpa)

MOR/ρMpa/(g/mm^3)(10^4)

Softwood 3.222E-4 1728.00 11069.93 34.36 104.81 32.53Hardwood 6.848E-4 584.02 21379.69 31.22 119.68 17.48Chipboard 7.160E-4 7254.00 3715.59 5.19 15.74 2.20Plywood 4.642E-4 522.83 6137.94 13.22 46.74** 10.12

** Plywood Sample did not rupture, deflection became to great and was deemed failed

As can be seen from table 7 hardwood contains the highest density when compared to the softwood sample (chipboard and plywood left out of relationship as these are composite materials). This is distinctive of hardwoods as they grow at a slower rate when compared to softwood. This generally results in a timber of high density and strength, which takes time to mature, over 100 years in some instances (Kermani 1999, 5). Generally speaking density and elasticity go hand in hand. In a study conducted in japan a direct correlation was found between density and elasticity, that being, the more dense a sample the

higher the elastic modulus would be and vice versa (Ayarkwa 1999). These results are backed up by data seen in this report.

The chipboard or particleboard is nearly double in density when compared to that of the plywood. Chipboard is a composite material; principally softwood cut into flakes, dried and then sprayed with an adhesive and then pressed (Dinwoodie 2000, 30) thus allowing it to have such great density. The Modulus of Rupture is very low when compared to the other materials and also falls quite short of the national standard of 15Mpa. The elastic modulus (6137Mpa) is also quite low which seems to suggest that this material is not used for its structural properties.

Different from particleboard, plywood’s are made from either hardwood or softwood. Logs are peeled from rotation against a slowly advancing knife to give a continuous strip. After drying, sheets of veneer for plywood manufacture are cooled with adhesive and are laid up and then pressed with the grain direction at right angles in alternate layers (Dinwoodie 2000, 7). In this experiment the modulus of elasticity and modulus of rupture cannot be accurately compared to that of the other specimens, as the sample did not actually rupture. Instead the sample was deemed to have failed due to the immeasurable deflection after 43.12N. Generally speaking the industry standard of plywood has a modulus of elasticity of 6900Mpa which is very similar to the achieved value of 6137.94Mpa.

5 The Effects of Moisture on E and MOR

Unlike other materials, the strength of timber is dependent on its moisture content (Kermaini 1999, 6).

Figure 3 – Strength/Stiffness and Moisture Content

Kermani. A, 1999, Structural Timber Design, Chapter1, Pg 8

Figure 3 shows the relationship between moisture content and strength or stiffness characteristics. Looking at the graph it can be identified that there is linear loss in strength up to 30% of saturation. Saturation after this point has no effect on strength or stiffness. Most timber is air dried to between 17% and 23% and further reduction results in shrinkage of then fiber (Kermaini 200,6).

Moisture content depends on the humidity of the surrounding, the higher the humidity the higher the moisture content will be. As shown by Cardarelli (2008, 986) Wood is categorized into five classes:

Green – Fresh wood, has received no formal drying. Air-Dried – wood having a moisture content of <= 25%. Kiln-Dried – wood dried inside a kiln to a specified water content

depending on the later application of the wood. Partly Air-Dried – wood with an average, moisture content between 25-

45%. Shipping dry – wood partially dried to prevent detrition such as mold or

staining for short periods of transit.

As previously stated, as moisture content increases up to that of 30% saturation strength and stiffness will be effected, hence, so to will the elastic modulus. As moisture content increases the elastic modulus will decrease.

6 Applications in Building

6.1 SoftwoodSoftwoods are generally evergreen with needle like leaves (Kermani 1999, 7).Plantation softwood in general is faster growing, faster drying and also provides greater yields of usable timber.These properties make softwood a very versatile material and used for a range of applications. Softwood in building is generally used for framing i.e. Studs, wall plates, noggins, rafters and other such applications were high strength is not critical.

6.2 HardwoodFrom a structural perspective hardwood is usually stronger then softwood. Hardwood with good strength characteristics offers itself to primarily structural applications such as bearers, lintels and roof beams.

6.3 ChipboardChipboard or particleboard is a panel product made from relatively large particles instead of fibers and is dependent for its strength and durability on the type of quantity of adhesive used to bond the ingredients together.There are three standard types of chipboard under the Australian standard AS/NZS 1859.1-2004.

1. Standard General Purpose Particleboard (STD)a. Internal use in dry conditionsb. Construction of furniture, cupboards and shelvingc. Decorative wall facing

2. Moisture Resistant General Purpose Particle Board (MR)a. Internal use in humid conditionb. Use in bathrooms and kitchens

3. High Performance Particle Boarda. Continuously humid conditions i.e. Tropical climatesb. Load bearing applications in damp or humid conditions

Chipboard may also be used in flooring, but only were permanently dry floors can be assured.

6.4 PlywoodPlywood is produced by assembling veneers and bonding them together to form a panel. As outlined by the Australian Wood Panels Association plywood is only as good as the adhesive used to bond the veneers together, Bonds are classified into four types:

1. Type A – waterproof bond, able to withstand exposure to weather for long periods of time.

2. Type B – waterproof bond, but subject to deterioration after several years. Useful in concrete framework and exterior doors etc.

3. Type C – can withstand occasional dampness, general internal plywood.4. Type D – only suitable for indoors, highly susceptible to moisture.

7 Conclusion

This report has provided details of the flexural properties of four timber samples, namely softwood, hardwood, chipboard and plywood. Through the data provided it was appreciated that chipboard had the highest density and softwood having the lowest. Correlation was discussed between the density of softwood and hardwood and the modulus of elasticity, finding that density is proportional to elasticity.

The modulus of rupture was found for all samples, thus allowing for design in terms of when rupture would occur specific to each specimen. Building applications was examined for each material listing advantages for using a specific timber product depending upon the conditions and characteristics of the project being undertaken.

Both composite materials, plywood and chipboard, were assessed and determined to fall within or close to that of the range outlined by in the Australian Standards.

8 References1. Australian Wood Panels Association Incorporated. Facts about

Particleboard and MDF. Coolangatta: Australian Wood Panels Association Incorporated, 2008.

2. Cardarelli, Francois (2008). Materials Handbook, A Concise Desktop Reference (pp:987)

3. Dinwoodie, J M. Timber Its Nature and Behavior. New York: Spoon Press, 2000.

4. Kermani, Abdy (1999). Structural Timber Design. (pp: 7). Blackwell Publishing.

5. Predicting Static Bending Modulus Of Elasticity Of Tropical African Hardwoods From Density Using A Model Based On Longitudinal Vibration, J. Ayarkwa, Y.Hirashima & Y.Sasaki: Graduate School of Bio-Agricultural Sciences, Nagoya University, Japan, 1999.

6. Structural timber design to Eurocode 5 / Jack Porteous & Abdy Kermani. 2007. Blackwell Pub

Appendix