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Streszczenie: Obróbka wstępna oklein na bazie poliestru. Powierzchnia oklein wykonana z politereftalanu etylenu została poddana obróbce wstępnej poprzez wyładowania barierowe plazmy w warunkach ciśnienia atmosferycznego w atmosferze różnych gazów, celem poprawy jej powierzchni i właściwości adhezyjnych. Zmiany w strukturze chemicznej polimeru analizowano metodą osłabionego całkowitego wewnętrznego odbicia. Energia powierzchniowa oraz jej polarna składowa dla politereftalanu etylenu pod wpływem modyfikacji plazmą uległa zwiększeniu. Corresponding author: Ján Sedliačik Department of Furniture and Wood Products Technical University in Zvolen Masaryka 24 960 53 Zvolen, Slovakia sedliacik@tuzvo.sk

317

Annals of Warsaw University of Life Sciences - SGGW Forestry and Wood Technology № 92, 2015: 317-324 (Ann. WULS - SGGW, For. and Wood Technol. 92, 2015) Non-destructive testing of wood – correlation of ultrasonic and stress wave test results in glued laminated timber members TOMASZ NOWAK1), KATARZYNA HAMROL-BIELECKA1), JERZY JASIEŃKO1) 1) Faculty of Civil Engineering, Wroclaw University of Technology Abstract: Non-destructive testing of wood – correlation of ultrasonic and stress wave test results in glued laminated timber members. The paper presents application of selected non-destructive testing techniques –ultrasonic and stress wave methods - for assessment of the physical and mechanical properties of wood. Non-destructive testing is a scientific field related to: identification of mechanical properties and physical parameters of materials and structural members, detecting material defects and discontinuities, measurement of geometrical dimensions without affecting the functional properties of the elements under investigation. The paper provides a short description of selected methods used for non-destructive and quasi non-destructive testing of wood. It also reports on research on the correlation between glued laminated spruce wood properties and parameters of ultrasonic and stress wave propagation The research was carried out with a Sylvatest Trio device, which uses ultrasonic technology and a Fakopp Microsecond Timer device, which uses the stress wave technique. Keywords: timber structures, non-destructive methods, ultrasonic waves, stress waves INTRODUCTION

The key to assessing wood condition of timber structures (in the case of both new-built structures made of glued laminated wood and historical buildings) involves collecting comprehensive information on the degree of wood degradation (qualitative data) and on the physical and mechanical properties of the material (quantitative data). As a natural material, wood is susceptible to destruction by moisture and biological agents. It is also characterised by high heterogeneity, which is why its physical and mechanical properties differ even in individual elements. Extracting samples for destructive testing is usually impossible or extremely difficult. Moreover, interpretation of results of tests performed on only a small set of wood samples can prove difficult [Brol et al., 2012; Nowak et al., 2013]. For the reasons stated above, a reliable and precise assessment of such parameters as: modulus of elasticity, bending strength or wood density, as well as detecting and specifying the extent of defects and discontinuities in wood, requires application of modern non-destructive and quasi non-destructive testing methods. Such testing methods enable the condition of timber structures to be assessed without affecting their functional properties. This is especially important in the case of historical structures. Other advantages of the NDT methods include: mobility, application in various field and atmospheric conditions and much lower costs for testing and analysis when compared to destructive testing methods. SELECTED NON-DESTRUCTIVE AND SEMI-DESTRUCTIVE METHODS FOR TIMBER STRUCTURE ANALYSIS The most commonly used methods for assessment and analysis of timber structures are: organoleptic, acoustic, semi-destructive and radiographic methods. The non-destructive and quasi non-destructive methods can be divided into two categories: global test methods (for example: visual evaluation, ultrasonic or stress wave techniques) and local test methods (for example: resistance drilling, core-drilling, the pilodyn method) [Feio, 2005; Jasieńko et al., 2013].

Resistance drilling (a semi-destructive method). A resistance drilling device uses a micro-drill (1.5-3.0 mm in diameter) to penetrate a wood element and measures the resistance

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encountered as a function of penetration depth. Drill penetration and rotation rates are constant. This means that the torque needed to keep a constant rate of penetration corresponds to the drilling resistance and can be recorded as a function of penetration depth. The drilling resistance profile (Fig. 1) can be generated as a print-out or stored in electronic form. The peaks in the graph correspond to high resistance (density). The troughs and low points correspond to low resistance (density). Completely decayed wood has no drilling resistance. Wood knots are recorded on the graph as peaks, but despite their high drilling resistance and high density, they are not correlated to timber strength. Test results reported for a variety of different specimen types [Rinn et al, 1996; Lourenco et al., 2007] do not provide a clear answer as to whether the drilling resistance method is effective in assessing the density and strength of a wood structure. But it is evident that the device can be used to approximate the mechanical parameters of wood and to detect and locate material defects and internal discontinuities in a way that does not impair the structure or functional properties of the wood. This situation results from the fact that the shape of the resistance drilling profile depends on numerous factors, such as wood moisture, the sharpness of the drilling bit, the angle and direction of drilling. According to [Branco et al., 2010; Witomski, 2008] the primary goal of this method is not evaluation of the mechanical properties of wood, but verification of information obtained from other types of non-destructive testing.

Figure 1. Example of a graph showing drilling resistance registered on wax paper

Radiographic method. Radiography makes it possible to visualise the internal structure

of a material, to detect its defects and examine its homogeneity. A radiation source (fig. 2) emits a beam of radiation towards the object under investigation. Test specimens have a different radiation absorbing capacity depending on the density of the wood and the thickness of the element. Several studies have confirmed the utility of radiographic methods for assessing the physical properties of wood in a structure [Kruglowa et al., 2013]. Radiography can help determine the density of wood and enable qualitative and quantitative assessments of defects in structural components. Radiographic testing is consistent with and complementary to other NDT methods, such as the resistance drilling (resistographic) method and the ultrasonic method [Lechner et al., 2014].

319

Figure 2. X-Ray source

The Pilodyn method (a semi-destructive method). The Pilodyn method is used to

measure wood hardness. A Pilodyn is a portable device for assessing wood hardness by measuring the penetration depth of a 2.5 mm diameter pin, which is driven into a wooden element with a constant impact energy. The depth of pin penetration is inversely proportional to wood density. A typical measurement covers a depth of 0-40 mm. Numerous studies have shown the Pilodyn tester to be a useful for assessing wood density and locating defects and discontinuities on the material surface, e.g. [Görlacher, 1987; Lourenco et al., 2007].

Ultrasonic and stress wave techniques (acoustic methods). The application of the ultrasonic method and the stress wave techniques enables assessment of the physical and mechanical properties of wood, based on analysis of the velocity of waves propagated through the material. The ultrasonic and stress wave methods can be used to detect internal discontinuities in wood and to evaluate selected strength parameters of the material (modulus of elasticity, bending strength). Sound wood makes for a good conductor for mechanical waves. Waves propagated in a material which contains defects must by-pass damaged spots and local discontinuities in the structure of the material. This means they need more time to pass from the transmitter to the receiver. The techniques enables detection of localised defects only in sections located between the heads of the testing device. Hence a high number of tests performed in various directions is necessary to obtain results, which are significant overall. When the wood density (ρ) and the velocity of the wave propagation (V) are known, it is possible to determine the dynamic modulus of elasticity (MOEdyn), which is strictly correlated with the static modulus of elasticity [Kasal et al., 2010]: 2

dynMOE V (1) The Sylvatest device made by the CBS-CBT company from Switzerland (fig. 3) is a

portable device which can be used to assess physical and mechanical properties of wood in a non-destructive manner [Sandoz, 1989]. The device uses the acoustic-ultrasonic technique and measures the length of time needed for an ultrasonic wave to pass a selected section of the material under testing. It also measures the energy of the wave. Due to the heterogeneous character of wood, it is necessary to run a high number of measurements, both in parallel and perpendicular to the grain, for each tested element in order to obtain complete and reliable results.

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encountered as a function of penetration depth. Drill penetration and rotation rates are constant. This means that the torque needed to keep a constant rate of penetration corresponds to the drilling resistance and can be recorded as a function of penetration depth. The drilling resistance profile (Fig. 1) can be generated as a print-out or stored in electronic form. The peaks in the graph correspond to high resistance (density). The troughs and low points correspond to low resistance (density). Completely decayed wood has no drilling resistance. Wood knots are recorded on the graph as peaks, but despite their high drilling resistance and high density, they are not correlated to timber strength. Test results reported for a variety of different specimen types [Rinn et al, 1996; Lourenco et al., 2007] do not provide a clear answer as to whether the drilling resistance method is effective in assessing the density and strength of a wood structure. But it is evident that the device can be used to approximate the mechanical parameters of wood and to detect and locate material defects and internal discontinuities in a way that does not impair the structure or functional properties of the wood. This situation results from the fact that the shape of the resistance drilling profile depends on numerous factors, such as wood moisture, the sharpness of the drilling bit, the angle and direction of drilling. According to [Branco et al., 2010; Witomski, 2008] the primary goal of this method is not evaluation of the mechanical properties of wood, but verification of information obtained from other types of non-destructive testing.

Figure 1. Example of a graph showing drilling resistance registered on wax paper

Radiographic method. Radiography makes it possible to visualise the internal structure

of a material, to detect its defects and examine its homogeneity. A radiation source (fig. 2) emits a beam of radiation towards the object under investigation. Test specimens have a different radiation absorbing capacity depending on the density of the wood and the thickness of the element. Several studies have confirmed the utility of radiographic methods for assessing the physical properties of wood in a structure [Kruglowa et al., 2013]. Radiography can help determine the density of wood and enable qualitative and quantitative assessments of defects in structural components. Radiographic testing is consistent with and complementary to other NDT methods, such as the resistance drilling (resistographic) method and the ultrasonic method [Lechner et al., 2014].

319

Figure 2. X-Ray source

The Pilodyn method (a semi-destructive method). The Pilodyn method is used to

measure wood hardness. A Pilodyn is a portable device for assessing wood hardness by measuring the penetration depth of a 2.5 mm diameter pin, which is driven into a wooden element with a constant impact energy. The depth of pin penetration is inversely proportional to wood density. A typical measurement covers a depth of 0-40 mm. Numerous studies have shown the Pilodyn tester to be a useful for assessing wood density and locating defects and discontinuities on the material surface, e.g. [Görlacher, 1987; Lourenco et al., 2007].

Ultrasonic and stress wave techniques (acoustic methods). The application of the ultrasonic method and the stress wave techniques enables assessment of the physical and mechanical properties of wood, based on analysis of the velocity of waves propagated through the material. The ultrasonic and stress wave methods can be used to detect internal discontinuities in wood and to evaluate selected strength parameters of the material (modulus of elasticity, bending strength). Sound wood makes for a good conductor for mechanical waves. Waves propagated in a material which contains defects must by-pass damaged spots and local discontinuities in the structure of the material. This means they need more time to pass from the transmitter to the receiver. The techniques enables detection of localised defects only in sections located between the heads of the testing device. Hence a high number of tests performed in various directions is necessary to obtain results, which are significant overall. When the wood density (ρ) and the velocity of the wave propagation (V) are known, it is possible to determine the dynamic modulus of elasticity (MOEdyn), which is strictly correlated with the static modulus of elasticity [Kasal et al., 2010]: 2

dynMOE V (1) The Sylvatest device made by the CBS-CBT company from Switzerland (fig. 3) is a

portable device which can be used to assess physical and mechanical properties of wood in a non-destructive manner [Sandoz, 1989]. The device uses the acoustic-ultrasonic technique and measures the length of time needed for an ultrasonic wave to pass a selected section of the material under testing. It also measures the energy of the wave. Due to the heterogeneous character of wood, it is necessary to run a high number of measurements, both in parallel and perpendicular to the grain, for each tested element in order to obtain complete and reliable results.

��0320

Figure 3. The Sylvatest Trio device made by the

CBS-CBT company Figure 4. The Fakopp Microsecond Timer device

The Fakopp Microsecond Timer device (fig. 4) uses the technique of a stress wave

induced by a single tap with a hammer. The device enables measurement of the time of stress wave propagation in wood, between two transducers. Testing wood with this device does not require drilling holes in the material as in the case of the Sylvatest device. The heads of the Fakopp Microsecond Timer device are mounted directly on special metal spikes which have to be embedded in the wood undergoing testing.

Research work on correlating physical and mechanical properties of wood began in the 1980s with investigation of the various ways in which wood conducts ultrasonic waves. The utility of the ultrasonic method lies in its capability to detect wood defects and degradation [Fujii et al., 1990; Karsulovic, 2000], as well as in correlating ultrasonic wave propagation parameters with the mechanical properties of wood. [Garcia et al., 2007; Lourenco et al., 2007] obtained a strong correlation between the MOEdyn and the modulus of elasticity.

Several tests related to the method of measuring the time needed for the stress wave to pass through the wood have been performed using the Fakopp Microsecond Timer device [Ilharco et al., 2015; Lechner et al., 2014]. These tests confirmed the correlation between the values of MOEdyn and the modulus of elasticity [Esteban et al., 2010] and evaluated the efficiency of the Fakopp device application by comparing the results obtained with those obtained using the Sylvatest device [Iniguez et al., 2009; Nowak et al., 2015]. EXPERIMENTAL TESTING – MATERIALS AND METHOD

Tests were performed on 14 short beams (A1a-A7a i A1b-A7b), produced by the same manufacturer making GL24h class prefabricated glued laminated wood elements. The spruce wood (Picea abies) samples used were 1100 mm long, with a cross-section of 140×280 mm. They were both endings (marked as samples a and b) of beams which had originally been 5320 mm long [Jankowski and Nowak, 2015]. The original beams had been previously subjected to strength testing in accordance with the EN 408:2012 standard.

The ultrasonic testing with the Sylvatest Trio device was used to measure the time necessary for the ultrasonic wave to pass between the transmitter and the receiver heads of the device. The Fakopp Microsecond Timer device was used for stress wave testing, which involved measuring wave propagation time between two transducers of the device. Two

321

methods for arranging the device heads were used in testing: direct parallel to the grain and direct perpendicular to the grain. Numbers assigned to respective positions of head arrangement are presented in fig. 5.

The moisture content of wood varied between 11.1% and 12.0%.

Figure 5. Numbers of combinations for location of the Sylvatest Trio device transducers and Fakopp

Microsecond Timer device transducers for the direct method parallel and perpendicular to the grain of the beam RESULTS AND CONCLUSION

The MOEdyn was determined (formula 1) based on the wood density ρ and the velocity of ultrasonic wave propagation V for individual beams. The correlation of the dynamic moduli of elasticity of r2=0,77 (Fig. 6) was calculated for measurements perpendicular to the grain. The results presented above lead to the conclusion that both methods correspond with each other and result in similar findings. The correlation of the global static modulus of elasticity for 5320 mm long beams in bending (tab. 1) with the dynamic moduli of elasticity was determined using both ultrasonic and stress wave methods for 1100 mm long beam endings and is presented in Figure 7. The graph also presents the correlation between the static modulus of elasticity and the MOEdyn obtained by aggregating the results obtained using both methods.

Figure 6. The correlation of the dynamic modulus of elasticity determined by applying both stress wave and

ultrasonic methods perpendicular to the grain

y = 1.361x - 0.512R² = 0.771

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.00 1.10 1.20 1.30 1.40 1.50 1.60

MO

Edyn

Syl

vate

st [G

Pa]

MOEdyn Fakopp [GPa]

��1320

Figure 3. The Sylvatest Trio device made by the

CBS-CBT company Figure 4. The Fakopp Microsecond Timer device

The Fakopp Microsecond Timer device (fig. 4) uses the technique of a stress wave

induced by a single tap with a hammer. The device enables measurement of the time of stress wave propagation in wood, between two transducers. Testing wood with this device does not require drilling holes in the material as in the case of the Sylvatest device. The heads of the Fakopp Microsecond Timer device are mounted directly on special metal spikes which have to be embedded in the wood undergoing testing.

Research work on correlating physical and mechanical properties of wood began in the 1980s with investigation of the various ways in which wood conducts ultrasonic waves. The utility of the ultrasonic method lies in its capability to detect wood defects and degradation [Fujii et al., 1990; Karsulovic, 2000], as well as in correlating ultrasonic wave propagation parameters with the mechanical properties of wood. [Garcia et al., 2007; Lourenco et al., 2007] obtained a strong correlation between the MOEdyn and the modulus of elasticity.

Several tests related to the method of measuring the time needed for the stress wave to pass through the wood have been performed using the Fakopp Microsecond Timer device [Ilharco et al., 2015; Lechner et al., 2014]. These tests confirmed the correlation between the values of MOEdyn and the modulus of elasticity [Esteban et al., 2010] and evaluated the efficiency of the Fakopp device application by comparing the results obtained with those obtained using the Sylvatest device [Iniguez et al., 2009; Nowak et al., 2015]. EXPERIMENTAL TESTING – MATERIALS AND METHOD

Tests were performed on 14 short beams (A1a-A7a i A1b-A7b), produced by the same manufacturer making GL24h class prefabricated glued laminated wood elements. The spruce wood (Picea abies) samples used were 1100 mm long, with a cross-section of 140×280 mm. They were both endings (marked as samples a and b) of beams which had originally been 5320 mm long [Jankowski and Nowak, 2015]. The original beams had been previously subjected to strength testing in accordance with the EN 408:2012 standard.

The ultrasonic testing with the Sylvatest Trio device was used to measure the time necessary for the ultrasonic wave to pass between the transmitter and the receiver heads of the device. The Fakopp Microsecond Timer device was used for stress wave testing, which involved measuring wave propagation time between two transducers of the device. Two

321

methods for arranging the device heads were used in testing: direct parallel to the grain and direct perpendicular to the grain. Numbers assigned to respective positions of head arrangement are presented in fig. 5.

The moisture content of wood varied between 11.1% and 12.0%.

Figure 5. Numbers of combinations for location of the Sylvatest Trio device transducers and Fakopp

Microsecond Timer device transducers for the direct method parallel and perpendicular to the grain of the beam RESULTS AND CONCLUSION

The MOEdyn was determined (formula 1) based on the wood density ρ and the velocity of ultrasonic wave propagation V for individual beams. The correlation of the dynamic moduli of elasticity of r2=0,77 (Fig. 6) was calculated for measurements perpendicular to the grain. The results presented above lead to the conclusion that both methods correspond with each other and result in similar findings. The correlation of the global static modulus of elasticity for 5320 mm long beams in bending (tab. 1) with the dynamic moduli of elasticity was determined using both ultrasonic and stress wave methods for 1100 mm long beam endings and is presented in Figure 7. The graph also presents the correlation between the static modulus of elasticity and the MOEdyn obtained by aggregating the results obtained using both methods.

Figure 6. The correlation of the dynamic modulus of elasticity determined by applying both stress wave and

ultrasonic methods perpendicular to the grain

y = 1.361x - 0.512R² = 0.771

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.00 1.10 1.20 1.30 1.40 1.50 1.60

MO

Edyn

Syl

vate

st [G

Pa]

MOEdyn Fakopp [GPa]

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Figure 7. Correlation between the MOEdyn determined by applying both the stress wave and ultrasonic methods

(taking into account aggregated results obtained through both) and the static modulus of elasticity Table 1. Mean values of global modulus of elasticity determined using the static bending test in accordance with the EN 408:2012 standard [Jankowski and Nowak, 2015]

Beam A1 A2 A3 A4 A5 A6 A7 MOEstat [GPa] 12.14 11.53 11.21 10.76 12.86 10.96 11.23

The correlation of r2 = 0.66 was obtained for the MOEdyn determined with the Sylvatest

Trio device, and of r2 = 0.49 for the MOEdyn determined with the Fakopp Microsecond Timer device (r2 = 0.58 for the results obtained using both methods). These results were influenced by the fact that non-destructive testing methods provide data on local conditions and mechanical properties of the element under investigation. It is necessary to run a high number of tests covering the whole element to obtain reliable overall results. This may often be impossible in in situ testing due to the character of the building. For this reason, the most reliable and complete results can only be obtained through the application of several non-destructive testing methods simultaneously. ACKNOWLEDGEMENT The project was funded by National Science Centre (Poland), NN 506 048640. REFERENCES

1. BRANCO J., PIAZZA M., CRUZ P., 2010: Structural analysis of two King-post timber trusses: non-destructive evaluation and load-carrying tests, Construction and Building Materials nr. 24(3); 371-383

2. BROL J., DAWCZYŃSKI S., MALCZYK A., ADAMCZYK K., 2012: Testing timber beams after 130 years of utilization, In: Jasieńko J. (ed) Proceedings of the International Conference on Structural Analysis of Historical Constructions - SAHC 2012, Wroclaw, Poland, 15-17; 644-650

3. ESTEBAN M., ARRIAGA F., INIGUEZ G., BOBADILLA I., 2010: Structural assessment and reinforcement of ancient timber trusses, Proc. of the International Conference on Structures & Architecture, 21-23 July, Guimarães, Portugal

4. FEIO A.O., 2005: Inspection and diagnosis of historical timber structures: NDT correlations and structural behavior, PhD thesis, University of Minho

5. FUJII Y., NOGUCHI M., IMAMURA Y., TOKORO M., 1990: Using acoustic emission monitoring to detect termite activity in wood, Forest Products Journal nr. 40(1); 34-36

R² = 0.492 R² = 0.657 R² = 0.584

10.5

11.0

11.5

12.0

12.5

13.0

10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0

MO

E st

at [G

Pa]

MOEdyn Fakopp - MOEstatMOEdyn Sylvatest - MOE statMOEdyn Fakopp+Sylvatest - MOEstatMOEdyn Fakopp - MOEstatMOEdyn Sylvatest - MOEstatMOEdyn Fakopp+Sylvatest - MOEstat

MOE dyn [GPa]

323

6. GARCIA M.C., SECO J.I.F.G., PRIETO E.H., 2007: Improving the prediction of strength and rigidity of structural timber by combining ultrasound techniques with visual grading parameters, Materiales de Construcción nr. 57(288); 49-59

7. GÖRLACHER R., 1987: Zerstörungsfreie Prüfung von Holz: Ein „in situ”-Verfahren zur Bestimmung der Rohdichte, Holz als Roh- und Werkstoff nr. 45(7); 273-278

8. ILHARCO T., LECHNER T., NOWAK T., 2015: Assessment of timber floors by means of non-destructive testing methods, Construction and Building Materials, http://dx.doi.org/10.1016/j.conbuildmat.2015.05.133

9. INIGUEZ G., MARTINEZ R., BOBADILLA I., ARRIAGA F., ESTEBAN M., 2009: Mechanical properties assessment of structural coniferous timber by means of parallel and perpendicular to the grain wave velocity, Proc. of the 16th International Symposium on Nondestructive Testing of Wood, Beijing, China

10. JANKOWSKI L.J., NOWAK T., 2015: Experimental assessment of the glued laminated timber beams in 4-point bending tests and photoelastic coating technique, Solid State Phenomena nr. 240; 155-160

11. JASIEŃKO J., NOWAK T., HAMROL K., 2013: Selected methods of diagnosis of historical timber structures – principles and possibilities of assessment, Advanced Materials Research nr. 778; 225-232

12. KARSULOVIC J.T., LEON L.A., GAETE L., 2000: Ultrasonic detection of knots and annual ring orientation in Pinus radiata lumber, Wood and Fiber Science nr. 32(3); 278-286

13. KASAL B., LEAR G., TANNERT T., 2010: Stress waves. In: Kasal B., Tannert T. (eds) In Situ Assessment of Structural Timber, Volume 7 of the series RILEM State of the Art Reports, New York, Springer; 5-24

14. KRUGLOWA T., SANDIN Y., KLIGER R., 2013: Assessment of density in timber using X-ray equipment, International Journal of Architectural Heritage nr 7(4); 416-433

15. LECHNER T., NOWAK T., KLIGER R., 2014: In situ assessment of the timber floor structure of the Skansen Lejonet fortification, Sweden, Construction and Building Materials nr 58; 85-93

16. LOURENCO P.B., FEIO AO., MACHADO J.S., 2007: Chestnut wood in compression perpendicular to the grain: Non-destructive correlations for test results in new and old wood, Construction and Building Materials nr. 21(8);1617-1627

17. NOWAK T., BROL J., JASIEŃKO J., 2013: Estimation of the strength parameters of wood in building structures - preliminary studies, Annals of Warsaw University of Life Sciences - SGGW. Forestry and Wood Technology nr. 83; 303-306

18. NOWAK T., HAMROL-BIELECKA K., JASIEŃKO J., 2015: Experimental testing of glued laminated timber members using ultrasonic and stress wave techniques, In: Jasieńko J. & Nowak T. (eds) Proc. of the International Conference on Structural Health Assessment of Timber Structures – SHATIS’15, Wroclaw, 9-11 September; 523-533

19. RINN F., SCHWEINGRUBER F.H., SCHAR E., 1996: Resistograph and X-ray density charts of wood. Comparative evaluation of drill resistance profiles and X-ray density charts of different wood species, Holzforschung 50(4); 303–311

20. SANDOZ J.L., 1989: Grading of construction timber by ultrasound, Wood Science and Technology nr. 23(1); 95-108

21. WITOMSKI P., 2008: Zmiany wybranych właściwości fizycznych i chemicznych drewna sosny zwyczajnej (Pinus sylvestris L.) pod wpływem rozkładu białego i brunatnego. Warszawa, Wydawnictwo SGGW [in Polish]

22. EN 408+A1:2012. Timber structures. Structural timber and glued laminated timber. Determination of some physical and mechanical properties. CEN, Brussels, Belgium.

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Figure 7. Correlation between the MOEdyn determined by applying both the stress wave and ultrasonic methods

(taking into account aggregated results obtained through both) and the static modulus of elasticity Table 1. Mean values of global modulus of elasticity determined using the static bending test in accordance with the EN 408:2012 standard [Jankowski and Nowak, 2015]

Beam A1 A2 A3 A4 A5 A6 A7 MOEstat [GPa] 12.14 11.53 11.21 10.76 12.86 10.96 11.23

The correlation of r2 = 0.66 was obtained for the MOEdyn determined with the Sylvatest

Trio device, and of r2 = 0.49 for the MOEdyn determined with the Fakopp Microsecond Timer device (r2 = 0.58 for the results obtained using both methods). These results were influenced by the fact that non-destructive testing methods provide data on local conditions and mechanical properties of the element under investigation. It is necessary to run a high number of tests covering the whole element to obtain reliable overall results. This may often be impossible in in situ testing due to the character of the building. For this reason, the most reliable and complete results can only be obtained through the application of several non-destructive testing methods simultaneously. ACKNOWLEDGEMENT The project was funded by National Science Centre (Poland), NN 506 048640. REFERENCES

1. BRANCO J., PIAZZA M., CRUZ P., 2010: Structural analysis of two King-post timber trusses: non-destructive evaluation and load-carrying tests, Construction and Building Materials nr. 24(3); 371-383

2. BROL J., DAWCZYŃSKI S., MALCZYK A., ADAMCZYK K., 2012: Testing timber beams after 130 years of utilization, In: Jasieńko J. (ed) Proceedings of the International Conference on Structural Analysis of Historical Constructions - SAHC 2012, Wroclaw, Poland, 15-17; 644-650

3. ESTEBAN M., ARRIAGA F., INIGUEZ G., BOBADILLA I., 2010: Structural assessment and reinforcement of ancient timber trusses, Proc. of the International Conference on Structures & Architecture, 21-23 July, Guimarães, Portugal

4. FEIO A.O., 2005: Inspection and diagnosis of historical timber structures: NDT correlations and structural behavior, PhD thesis, University of Minho

5. FUJII Y., NOGUCHI M., IMAMURA Y., TOKORO M., 1990: Using acoustic emission monitoring to detect termite activity in wood, Forest Products Journal nr. 40(1); 34-36

R² = 0.492 R² = 0.657 R² = 0.584

10.5

11.0

11.5

12.0

12.5

13.0

10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0

MO

E st

at [G

Pa]

MOEdyn Fakopp - MOEstatMOEdyn Sylvatest - MOE statMOEdyn Fakopp+Sylvatest - MOEstatMOEdyn Fakopp - MOEstatMOEdyn Sylvatest - MOEstatMOEdyn Fakopp+Sylvatest - MOEstat

MOE dyn [GPa]

323

6. GARCIA M.C., SECO J.I.F.G., PRIETO E.H., 2007: Improving the prediction of strength and rigidity of structural timber by combining ultrasound techniques with visual grading parameters, Materiales de Construcción nr. 57(288); 49-59

7. GÖRLACHER R., 1987: Zerstörungsfreie Prüfung von Holz: Ein „in situ”-Verfahren zur Bestimmung der Rohdichte, Holz als Roh- und Werkstoff nr. 45(7); 273-278

8. ILHARCO T., LECHNER T., NOWAK T., 2015: Assessment of timber floors by means of non-destructive testing methods, Construction and Building Materials, http://dx.doi.org/10.1016/j.conbuildmat.2015.05.133

9. INIGUEZ G., MARTINEZ R., BOBADILLA I., ARRIAGA F., ESTEBAN M., 2009: Mechanical properties assessment of structural coniferous timber by means of parallel and perpendicular to the grain wave velocity, Proc. of the 16th International Symposium on Nondestructive Testing of Wood, Beijing, China

10. JANKOWSKI L.J., NOWAK T., 2015: Experimental assessment of the glued laminated timber beams in 4-point bending tests and photoelastic coating technique, Solid State Phenomena nr. 240; 155-160

11. JASIEŃKO J., NOWAK T., HAMROL K., 2013: Selected methods of diagnosis of historical timber structures – principles and possibilities of assessment, Advanced Materials Research nr. 778; 225-232

12. KARSULOVIC J.T., LEON L.A., GAETE L., 2000: Ultrasonic detection of knots and annual ring orientation in Pinus radiata lumber, Wood and Fiber Science nr. 32(3); 278-286

13. KASAL B., LEAR G., TANNERT T., 2010: Stress waves. In: Kasal B., Tannert T. (eds) In Situ Assessment of Structural Timber, Volume 7 of the series RILEM State of the Art Reports, New York, Springer; 5-24

14. KRUGLOWA T., SANDIN Y., KLIGER R., 2013: Assessment of density in timber using X-ray equipment, International Journal of Architectural Heritage nr 7(4); 416-433

15. LECHNER T., NOWAK T., KLIGER R., 2014: In situ assessment of the timber floor structure of the Skansen Lejonet fortification, Sweden, Construction and Building Materials nr 58; 85-93

16. LOURENCO P.B., FEIO AO., MACHADO J.S., 2007: Chestnut wood in compression perpendicular to the grain: Non-destructive correlations for test results in new and old wood, Construction and Building Materials nr. 21(8);1617-1627

17. NOWAK T., BROL J., JASIEŃKO J., 2013: Estimation of the strength parameters of wood in building structures - preliminary studies, Annals of Warsaw University of Life Sciences - SGGW. Forestry and Wood Technology nr. 83; 303-306

18. NOWAK T., HAMROL-BIELECKA K., JASIEŃKO J., 2015: Experimental testing of glued laminated timber members using ultrasonic and stress wave techniques, In: Jasieńko J. & Nowak T. (eds) Proc. of the International Conference on Structural Health Assessment of Timber Structures – SHATIS’15, Wroclaw, 9-11 September; 523-533

19. RINN F., SCHWEINGRUBER F.H., SCHAR E., 1996: Resistograph and X-ray density charts of wood. Comparative evaluation of drill resistance profiles and X-ray density charts of different wood species, Holzforschung 50(4); 303–311

20. SANDOZ J.L., 1989: Grading of construction timber by ultrasound, Wood Science and Technology nr. 23(1); 95-108

21. WITOMSKI P., 2008: Zmiany wybranych właściwości fizycznych i chemicznych drewna sosny zwyczajnej (Pinus sylvestris L.) pod wpływem rozkładu białego i brunatnego. Warszawa, Wydawnictwo SGGW [in Polish]

22. EN 408+A1:2012. Timber structures. Structural timber and glued laminated timber. Determination of some physical and mechanical properties. CEN, Brussels, Belgium.

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Streszczenie: Nieniszczące badania drewna – korelacja wyników badań metodą ultradźwiękową i metodą fali napięciowej dla drewna klejonego warstwowo. W artykule przedstawiono zastosowanie wybranych metod nieniszczących: metody ultradźwiękowej i metody fali napięciowej do oceny właściwości fizycznych i mechanicznych drewna. Badania nieniszczące są obszarem nauki obejmującym: identyfikację cech mechanicznych i fizycznych właściwości materiałów i elementów konstrukcji, wykrywanie wad i nieciągłości materiałowych oraz pomiary wymiarów geometrycznych bez naruszania właściwości użytkowych analizowanych elementów. W artykule krótko opisano wybrane metody służące nieniszczącej i quasi nieniszczącej ocenie drewna. W dalszej części przedstawiono wybrane wyniki badań nad korelacją właściwości fizykomechanicznych świerkowego drewna klejonego i parametrów propagacji fal ultradźwiękowej i napięciowej. Do badań wykorzystano urządzenie Sylvatest Trio wykorzystujące technikę ultradźwiękową oraz aparat Fakopp Microsecond Timer dla metody fali napięciowej. Corresponding author: Tomasz Nowak, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland email: tomasz.nowak@pwr.wroc.pl phone: +48 71 3202263

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Annals of Warsaw University of Life Sciences - SGGW Forestry and Wood Technology № 92, 2015: 325-329 (Ann. WULS - SGGW, For. and Wood Technol. 92, 2015) Changes of breaking length of cotton paper with the addition of nanofibers in a PLA/P3HB composite EMIL PATELSKI*, IZABELA MODZELEWSKA*, WERONIKA GIEPARDA** * Institute of Chemical Wood Technology, Poznan University of Life Sciences, Poland ** Institute of Natural Fibers and Medicinal Plants, Poznan, Poland Abstract: In this study it was attempted to enhance strength properties of paper. The aim was to produce paper modified with nanofibers, which would exhibit enhanced strength properties. Tests were conducted on cotton-comber pulp and the composite of PLA (poly(lactic acid)) and P3HB (poly(3-hydroxybutyrate)) nanofibers. Control sheets were formed from cotton-comber pulp, while experimental sheets were produced with a 2% and 5.5% addition of ground nanofibers. Tests of selected strength properties showed their considerable changes. Keywords: cotton pulp, paper, nanofibers, polylactic acid, poly-3-hydroxybutyrate INTRODUCTION

Research initiated at the Institute of Chemical Wood Technology on modification of paper using PLA/P3HB nanofibers brought exceptionally good results. Cotton paper with a 5.5% addition of ground nanofibers showed improved strength properties. Breaking length increased by 17%, folding endurance increased by 14% and air permeability increased by as much as 35% (Modzelewska et al. 2015). Such good results recorded at the preliminary stage provided an incentive to continue these studies.

Cotton-comber pulp is used to produce paper products, of which superior strength properties are required. Such products include e.g. securities. They are produced at the addition of various fillers and chemical additives. Nanofibers exhibit high tensile strength and resilience. Their introduction of paper products may considerably improve strength properties (Przybysz 1997).

Additives introduced to paper pulp have a varied effect on properties of the final product. They may alter its strength, optical properties or eliminate disturbances in the technological process (Wandelt 1996).

The added nanofibers to paper pulp prior to the formation of paper should behave like a secondary fine fraction, which fills free spaces between cellulose fibers. This affects overall strength of paper products by binding fibers together.

The aim of this study is to produce paper modified with nanofibers, which would exhibit enhanced strength properties. Tests were conducted on hardwood pulp and a composite of PLA (polylactide) and P3HB (poly(3-hydroxybutyrate)) nanofibers. Control sheets were formed from cotton-comber pulp, while experimental sheets were produced with an addition of ground nanofibers. Tests for breaking length verified the presented hypothesis. MATERIALS AND METHODS

Materials PLA/P3HB nanofibers

The experimental material comprised nonwoven fabric produced under laboratory conditions from PLA/P3HB nanofibers, paper sheets produced from cotton pulp and sheets produced from a combination of cotton pulp and ground PLA/P3HB nanofibers.