Some published and unpublished ultrasonic research on wood

1. Some published and unpublished ultrasonic research on wood Frank Beall University of California, Berkeley

2. Background • Ultrasonic technology: acoustic emission (AE) • Advantages and disadvantages with wood • Examples of several studies in 1986, 1987 while at Weyerhaeuser

3. AE SYSTEM BLOCK DIAGRAM 0 – 40 dB 40 – 60 dB

4. AE TRANSDUCER PZT 25 MM EPOXY SHOE

5. AE EVENT WAVEFORM

6. R, T L

7. AE Characteristics/Challenges • Need active fractures to generate waves • Placement/coupling are issues • Attenuation/anisotropy of wood

8. AE SYSTEM

9. Radial Compressive Strength (RCS) • 1% mass loss from decay can result in up to 90% loss in dynamic mechanical properties • Is AE sensitive to strength loss?

10. RCS • White fir • 10 x 10 x 20 mm • Brown rot decay (Poria placenta) • 0, 1.3, 13, 28% mass loss

11. RADIAL COMPRESSION WOOD SPECIMEN TRANSDUCER LOAD CELL

13. RCS Results • AE very sensitive to decay • Separation at <1% elastic compression (NDE) • Curve shape as indication of failure mode

14. SPRINGBACK • “Springback” occurs from stress relieval of pressed boards (6 - 10% increase in thickness) • Industrial particleboard • 20 (thick) x 50 x 50 mm • Exposure: 50/90/50/90/50 %RH; 22 C • One month at each exposure

15. Causes of Springback • Shape recovery of compressed particles • Failure of adhesive bonds between particles • Swelling from moisture adsorption • Which comes when??

16. PARTICLEBOARD SPRINGBACK

17. 2: 2-3-4 1: 0-1-2 INITIAL SPRINGBACK

18. x x

19. SPRINGBACK • Initial springback (6% recovery) has AE, indicating combined shape recovery, swelling, and bond failure • After this point (6 - 9% recovery), there are no AE, indicating largely shape recovery and particle swelling in equal amounts • Most bond failures occurs very early

20. MACRO-FISSURING OF WOOD DURING COMBUSTION Shrinkage O2 Glowing CO Flaming

21. FISSURING OF WOOD • Hard maple • 3 (thick) x 25 x 165 mm • Exposed to pyrolysis and flaming combustion • Monitoring of AE for micro- and macro-fissuring

22. FISSURING • Can mcro- and macro-fissuring be separately detected? • If so, does microfissuring precede macrofissuring (like earthquakes)??

23. WOOD PYROLYSIS 30 175

25. 96 kJ/mol

26. 350ºC

27. FISSURING • Microfissuring precedes macrofissuring • Process is activated • AE could be used to track char front during combustion • Airborne AE similar in numbers to visible macrofissures

28. TREE WATER STRESS • A number of studies using AE conducted in mid-1980s • Most done with excised material • None done with intact controls • Embolism or “capillary snap” most likely source of AE

29. TREE WATER STRESS • Two Pinus contorta; 2-m potted • Good and poor form • In uncontrolled greenhouse • AE transducers attached to stems

30. TREE STRESS

31. TREE WATER STRESS • Could AE output be used to manage drought-sensitive loblolly pine plantations in the US south? • Such an approach would monitor a sampling of trees and selectively harvest when stress is detected

32. TREE WATER STRESS • “Good” tree watered on day 1 • “Poor” tree not watered • Greenhouse floor flooded on day 5 • Data printed daily (but not saved)

33. POOR TREE DAY 1

34. GOOD TREE DAY 1

35. POOR TREE DAY 1

36. POOR TREE DAY 2

37. POOR TREE DAY 5

38. GOOD TREE DAY 1

39. GOOD TREE DAY 2 TREE 1 DAY 1

40. GOOD TREE DAY 5

41. TREE WATER STRESS • AE followed diurnal cycle, in phase with presumed stem dia changes • AE characteristics were remarkably similar between trees • Min AE at sunset • Tree AE reacted to ΔRH within minutes • Poor tree had much greater indication of stress from AE level and range

42. Water Stress Lesson • Document everything, even if presumed to be preliminary; it may not be…

43. Filter Ampl Sensor Preamp Saw blade Hardboard

44. AE OUTPUT FROM SAWING HARDBOARD PANEL RMS RAW AE OUTPUT