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www.wood.uni-goettingen.de Wood Biology and Wood Products, Georg-August-University Göttingen, Germany

Contact:

Dr. Hannes Schwager

hannes.schwager@uni-goettingen.de

Physical Testing Laboratory

Mechanical Properties of Natural and Engineered Wood Materials

Our know-how is related to the mechanical char-

acterization of wood materials. For this purpose,

the technical equipment in our laboratory com-

prises systems for all kind of material testing ac-

cording to internationally established DIN EN ISO

or ASTM standards for reliability in industrial ap-

plication as well as procedures for more sophisti-

cated scientific needs.

The testing machinery in the laboratory compris-

es (a) two ZWICK/ROELL universal material testing

machines (10 kN and 100 kN load limits) with op-

tical strain measurement for static tensile, com-

pressive and bending tests, (b) a D-H-M dynamic

test bench for fatigue testing under oscillating

and random cyclic loading, (c) an CEAST instru-

mented impact bending tester and (d) several de-

vices for evaluating surface quality of modified

or varnished wood products.

Expertise and equipment

Universal testing machines per-

form tensile, compressive, bend-

ing, and other mechanical tests

on materials and products.

According to the test set-up, the

material’s elasticity (YOUNG’s

modulus E ) and strength ß under

the applied loading conditions are

determined.

Additional digital image correla-

tion (DIC) systems allow for high

precision contactless deformation

measurements, and thus help to

minimize systematic errors.

Example for the calculation of

compressive properties:

Static material tests

In materials science, fatigue is the

weakening of a material caused

by repeated loading and unload-

ing steps.

The measure for fatigue life is the

number of load cycles N that a

specimen is able to withstand

without being damaged.

During fatigue testing the speci-

men is subjected to either oscil-

lating or randomly distributed cy-

clic loading.

The equipment in the testing la-

boratory allows for cyclic bending

tests with pulsating or tension-

compression tests with pulsating

or alternating stresses.

Dynamic fatigue tests

The instrumented impact bending

is a high strain-rate test for com-

parison between different materi-

als. It is widely applied in indus-

try, since it is easy to prepare and

conduct and results can be ob-

tained quickly and cheaply.

During the test the amount of en-

ergy absorbed by a specimen dur-

ing fracture is recorded. The spe-

cific absorbed energy w is a meas-

ure of the material's toughness.

Although the amount of absorbed

energy might be equal, the force

deformation curve of the same

material might deviate significant-

ly depending on the sample con-

ditioning.

Impact bending tests

The hardness of wood material

might be characterized in the in-

strumented JANKA or BRINELL tests.

During both tests a steel ball is

pressed into the surface of the

sample. The hardness of the ma-

terial is given by only the penetra-

tion force HJ (JANKA)

or calculated from the size of the

indentation and the needed force

HB (BRINELL)

The durability of varnished sur-

faces is determined in either

cross-cut or pull-off adhesion

tests.

Surface quality tests

DIN 52 185 - Compression test

DIN 52 186 - Bending test

DIN 52 188 - Tensile test

DIN 52 189 - Impact bending test

ASTM D1037-12/17 - Hardness test (JANKA)

DIN EN 1534 - Hardness test (BRINELL)

DIN EN ISO 2409 - Cross-cut adhesion test

DIN EN ISO 4624 - Pull-off adhesion test

References

Foto

4,5 x 4,5

Fig. 2: Instrumented impact hammer

Deformation f [mm]

Fo

rce

F [

N]

Fig. 3: Force-Deformation Curves

Fig. 1: Quasi-static compressive test with optical strain measurement Fig. 4: Fatigue tester Fig. 5: Oscillating load cycles Fig. 6: Fatigue hysteresis loop

Fig. 7: BRINELL hardness test Fig. 8: Cross-cut adhesion test Fig. 9: Pull-off adhesion test