CVG 2141Civil Engineering Materials

Wood Tests

Willian Bogorni Mossmann7997643

Lab Date: November 17th, 2015Report Date: December 1st, 2015TA: Benoît PelletierLab Group: Tuesday, D1

Abstract:

In this lab experiment the mechanical properties of spruce wood specimens were determined. Five specimens were submitted to different tests. Two were tested for compression, one in parallel to the grain and the other perpendicular to it. One specimen was submitted to bending. The other two left were tested for tension, one in parallel to the grain and the other perpendicular to it. The tests gave the loads and the respective deformations for each one of them. Finally, the mode of failure of the specimens will be compared with the ones shown in the laboratory manual.

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Table of Contents:

List of Tables/Figures …………………………………………………………………….4Objective ………………………………………………………………………………….5Theoretical Background ……………………………………………………….………….5Materials and Equipment………………………………………………………………….5Experimental Procedure…………………………………………………………………...6Analysis of Data…………………………………………………………………………...7Discussion of Results…………………………………………………………………….11Conclusion and Recommendations……………………………………………………....11References ……………………………………………………………………………….12

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List of Tables/Figures:

Figure 1: Flexure testTable 1: Wood test resultsFigure 2: Compression Parallel Stress-strain curveFigure 3: Compression Parallel Stress-strain curveFigure 4: Tension Parallel Stress-strain curveFigure 5: Tension Parallel Stress-strain curveFigure 6: Bending Test force-displacement curveFigure 7: Bending Test force-displacement curve

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Objective:

The purpose of this experiment is to determine the tensile strength and compressive strength of woods in parallel and perpendicular to the grain. Additionally, it will also be determined the Modulus of Rupture and Flexural behavior of wood.

Theoretical Background:

In the area of Civil Engineering, one of the most used materials is wood. Used in many kinds of constructions, wood has a great importance in the area; therefore it has to be studied to know if it is safe and economic to be used in a required construction.

Wood has a great thermal characteristic that is it can preserve more heat inside it structure compared to other kinds of materials. But, in civil engineering that is not enough to use it as a material. So, the mechanical properties such compression strength, Modulus of Elasticity and shear strength of wood have to be studied to make sure that a wood can be used to a determined construction.

Equation 1:

σ=McI

Where σ is the modulus of rupture, M is the bending moment, c is the distance from the neutral axis to the edge and I is the moment of Inertia.

Equation 2:

E=(P∆

)L3

48 I

Where τ is the maximum shearing stress, V is the maximum shear force at mid spam and A is the cross-sectional area of the beam.

Materials and Equipment:

- Five spruce wood specimens- Compression and tension test machine- Micrometer calipers- Gauge marker- Extensometers- Strain scale

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Experimental Procedure:

1. The kind of wood used is specified2. All the wood specimens are assigned to a specific kind of test3. Submit two specimens with almost the same dimensions to a compressive test. One

tested in parallel to the force and the other perpendicular to the force.4. Submit two specimens to a tensile test. One specimen in a plate format to be tested

in parallel to the force, and a specimen with the edges in a grip format to be tested perpendicular to the force.

5. Submit a specimen with dimensions higher than the others to a flexure test.6. Observe the mode of failure of the specimens.7. Record the maximum load of each one of the tests.

Figure 1: Flexure test

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Analysis of Data:

Tension// Tension TCompression//

Compression T Bending

W(mm) 6.74 25.92 36.2 35.59 36.54t(mm) 24.77 55.58 36.04 34.75 36.13L(mm) 609 x 204 203 912Area (mm2) 166.9498 1440.6336 1304.648 1236.7525 1320.1902P(failure) N 2659 x 63987 x 1969Type of Failure Wedge split Crushing splitting splitting

Compression and shearing

Stress t (Mpa)

15.92694331 x 49.04541302 x x

E(Gpa) 41.69 x 2.4 x 0.13Table 1: Wood test results

Figure 2: Compression Parallel Stress-strain curve

-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.50

10

20

30

40

50

60

70

Compretion Parallel

Figure 3: Compression Parallel

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Figure 4: Tension Parallel Stress-strain curve

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

-0.5

0

0.5

1

1.5

2

2.5

3

Tension Parallel

Figure 5: Tension Parallel

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Figure 6: Bending Test force-displacement curve

0 2 4 6 8 10 12 14 16 18 20

-0.5

0

0.5

1

1.5

2

2.5

Bending test

Figure 7: Bending Test

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Calculations:

The values of I, c and M were calculated using the following formulas:

I=bh3

12=143612.15mm4

c=12h=18.065mm

M= PL4

=370172N .mm

The value of the Modulus of Rupture σ of the bending test was calculated with the following formula:

σ=McI

=370172 x18,065143612.15

=46.56MPa

The Modulus of Elasticity for the Bending test was calculated with the following formula:

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E=(P/∆)L3

48 I= 1969 x7523

48 x 143612.15=0.13GPa

Discussion of Results:

The modes of failure found in this experiment were Wedge Split for the tension parallel to the grain test, crushing for the tension perpendicular, splitting for both compression, and compression and shearing for the bending test. These results show that the wood has not a great plastic limit and it tends to brake in the same place as the load was applied, especially in the bending test. The compression test show that it resists at first but after the first cracks the wood tends to rupture in the same spot as the force as well.

The graphics of the stress-strain curves show that the wood specimen in the experiment resists better to compression than tension. However, is important to remember a knot in the specimen used in the parallel tension test. The results show that in the tension test the wood suffer four times more strain than in the compression test. In the compression test the strain stops at 0.03 approximately; in the other hand, the strain stops after 0.015 in the tension test. The stress supported in the compression test is almost 49 MPa, while in the tension test it’s just 15.9 MPa.

In the bending test, the wood supported the maximum load of 1969 N, and then it collapsed. The maximum load supported in the bending test it is not as high as the ones in the compression tests. The maximum load in the compression test is 63987 N.

Conclusions and Recommendations:

In can be concluded in this experiment that the spruce specimens are way better dealing with compression than with tension. The specimen resists a several times stronger compression force comparing to the other kinds of force tested. It can be observed that none of the Modulus of Elasticity calculated have a similar values to the other values calculated. The higher one was found in the bending test. It can also be observed that either in compression or in tension the cedar doesn’t have a significant plastic zone, so after the first considerable deformation the wood tents to collapse.

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References:

CVG 3109 – Guide for Writing Laboratory Reports,University of Ottawa, 2013, p.2 – 21

Alaa Abdulridha CVG 2141– Class Notes,University of Ottawa, 2014

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