Fatigue properties of wood at different load ratios tested at 50 Hz and 20 kHz

Fatigue properties of sycamore maple (Acer pseudoplatanus) under cyclic tension, compression and tension-compression loading at 50 Hz are investigated. Furthermore, for the first time, fatigue test results wood generated with ultrasonic testing technique 20 kHz presented. Cyclic in line static – tensile strength being more than two times compressive strength. Mean lifetimes 106 cycles found if maximum stress tension is 69 %±8 % stresses 75 %±7 54 %±4 strength, respectively. Tension-compression delivers comparable to servo-hydraulic tests Hz, no pronounced frequency effect on lifetime found. Ultrasonic therefore, principle, appropriate accelerated up very high cycle regime. Tests 109 show evidence a limit maple. Die Ermüdungseigenschaften von Bergahorn wurden unter Zugschwell-, Druckschwell- und Wechselbeanspruchung bei untersucht. Zudem erstmalig Versuche mit dem Ultraschall-Ermüdungsprüfverfahren an Holz durchgeführt. zyklischen Festigkeiten zeigen ein ähnliches Verhalten wie die statischen Zugfestigkeit beträgt mehr als das Doppelte der Druckfestigkeit. Mittlere Lebensdauern Lastzyklen ergaben sich, wenn maximale Zugspannung Zugschwellbeanspruchung Druckspannung bzw. Druckfestigkeit beträgt. ermittelten stimmen gut überein es zeigt sich kein wesentlicher Einfluss Belastungsfrequenz auf Ermüdungslebensdauer Holz. Ultraschall-Ermüdungsversuche sind daher geeignet, auch für innerhalb kurzer Zeit aussagekräftige Ergebnisse im Bereich sehr hoher Lastspielzahlen zu generieren. Bis konnte keine Dauerfestigkeit gefunden werden. Wood most important construction material that used many load bearing structural applications. High specific stiffness, easy machinability, good availability aspects costs sustainability some reasons make attractive material. structures have withstand as well stresses. Wooden beams bridges subjected gravitational acceleration forces motor vehicles, buildings loaded by gusts wind examples dynamically components where superimposed. Considering wood-based materials sustainable alternatives reinforced plastics transportation applications, may be numbers cycles. Therefore, knowledge different ratios regime great scientific practical interest. The advantages terms its low density relatively elastic modulus fibre direction known from historical aircraft 1. also played relevant role vehicle constructions beginning 20th century 2. Morgan Motor Company (http://www.morgan-motor.co.uk) still produces cars wood-aluminium chassis today. Intensive research has been conducted recent years 3 predictability using numerical methods like finite element modelling. Despite these technical fields application, investigations solid special conditions such strain rates behaviour rare. Investigation can already early literature, pine (Pinus) plywood reported approximately 4. Recent available composite panels blades energy bending experiments African mahogany (Khaya ivorensis) veneers laminated epoxy resin, Sitka spruce (Picea sitchensis) beech (Fagus sylvatica) ratios, R = ?min/?max, between ?1 0.5 revealed respect longer higher ratio 5. Further, increase moisture content 5 35 leads decrease strengths, widely species-independent when plotted versus normalised stresses, i. e. failure mechanism formation kinks extend creases finally cause fracture veneer laminates obtained compression, shear indicate strengths 6. morphology strongly influenced type loading, crushed cell ends observed due pulled out bunches cells after With occurring during cycle, (R =?1) damaging 0.1) 10) 7. Of interest 0 several composites furniture, amplitude 40 was allowable avoid 8. (Pinus sylvestris) delivered mean about 9. bonded adhesives showed better ductile brittle adhesive 10. cycling highly performed since reduces times. Norway abies) frequencies 0.01 10 80 exhibits strong influence which interpreted combined creep stressing 11. Under perpendicular grain 1 significantly relative humidity 85 %, but 65 RH 12. For made Russian larch (Larix sibirica) tested were 13. In regime, however, disappeared. studied Japanese cedar (Cryptomeria japonica) Selangan batu (Shorea spp.) 14. Only slight detected not batu, frequency. rather limited. exception laminates, hardly explored. Another shortcoming number typically investigated limited required Few studies 107 cycles, exist 4-7. This leaves interesting question yet answered: whether or not. present investigation, techniques: equipment working 0.1), Stress amplitudes leading one million construct Haigh diagram. =?1). Experiments billion served decide endurance exists time investigate wood. this method, range drastically shortens allows accessible conventional (servo-hydraulic, rotating reversed bending) equipment. well-established method metallic 15. Recently, successfully applied carbon plastic glass 16, 17. study, overlapping find affected drastic comparability properties, determined specimens same shape tests. pseudoplatanus). chosen homogeneous mechanical properties. parallel grain. Typical 610 kg/m3 660 (parallel grain) °C ranging MPa 140 46 62 135 9.1 GPa 12.0 elasticity 18, 19. As shown below, measured actually somewhat literature values. cut trunk equidistantly pith tree. Hereby, similar region year rings obtained, thought reduce variations mass Two samples tests, Figure gauge section cylindrical length mm diameter 6 mm, 1a. Specimens? (diameter 14 59 mm) mounting frame. could specimens. proved rigid enough necessary forces, collet chucks Thus, cross reduced 4.5 1b. Specimen shapes testing: (a) compression-compression 10, (b) tension-tension 0.1). Specimens shorter they must meet resonance condition kHz, 2a. Using analysis software Inventor Nastran Autodesk®, distribution displacement over specimen vibrating shown, 2 b. shape, amplitude. machined lathe. sections ground abrasive paper (up grade P500). Prior testing, stored laboratory environment (23 RH) minimum three days order ensure stable content. It noted adapting temperature standard (i. possible other running laboratory. environmental 630 kg/m3±30 kg/m3. Tensile rate ?3.3 ? 10?3. A 159 MPa±15 70 MPa±5 eight each. controlled. sinusoidally changing resulting oscillating stress, ?min ?max, Loading continued until fractures limiting reached. case, MTS 810.10 frame used. R, correspondent 10), including schematically 3. Superimposed ?mean, amplitudes, ?a, applied. Schematic corresponding ?min/?max. following procedure: first, load, 0.1 =?1, remained zero. Then, nominal force initial Hz. Subsequently, slowly increased (by per second) slow inaccuracies instabilities control. Finally, accumulated. mounted into means chucks, circumferentially clamped their ends, pressurised air heating concomitant pull-out clamping sections. developed built in-house Institute Physics Materials Science University Natural Resources Life Sciences, Vienna. Functioning principle summary experimental setups extensively described elsewhere stimulated vibrations stressed external forces. Both oscillate opposite directions amplitude, forming vibration node centre. There, reaches maximum, enabling specimen. linear performed, each antinode centre linearly proportional. either specimen‘s end another antinode, induction coil control loading. closed-loop circuit, accurate deviation pre-selected realised ±1 %. Since and, controlled, proportional, considered second keeps stimulating accuracy 18. now, set-up had developed. design allow kHz. designed finite-element values stiffness Real feature varying slightly frequencies. However, system perform wide frequencies, 17.8 21.8 glued onto aluminium thread ARALDITE® 2014-1 adhesive, serves attach them train, To enable sound transmission, layer thin possible. cycled continuously pulsed mode, pulse lengths 100 ms pauses 500 4000 ms, prevent excessive self-heating. effective 3.3 Additionally, cooling specimens’ applied, combination additional keep surface below 30 °C. train =?1. Displacement proportionality factor experimentally gauges attached sides calibrate test, Strain controlled compared known. calculated ?a, Young's modulus, E, Hooke's law: ?a E ?a. subsequently steps MPa). At step, (that amplitude). seven specimens, 15.3 GPa±1.5 GPa. GPa±15 GPa±5 typical published explained alignment specimens? direction, stiffest strongest data presented ways, 6: Hz: absolute max |?| (a); 0.1, =?1 (b); (c); Data did fail marked arrows. diagram shows |?|, 6a. ?max) value ?min), stress. presents MPa) 6b. normalise limits third 6c. clear separation conditions, S?N highest MPa±12 MPa. Compared that, curve runs lower 53 lowest 38 MPa±3 damage caused plus half part causes damage, shifted towards presentation. diagram, curves lot geometry ±4 slope steeper compression. steepest way lies consists less cycle. descriptively led all ratios. indicated. materials, it striking those Approximations fit Goodman straight line, Gerber parabola) would suggest decreases increasing whereas difference mechanism: process metals initiation microcrack local concentrations weak areas microstructure followed crack propagation fracture. Due closure, cracks solely propagate fraction becomes larger consequently Moreover, while lead metals, stop propagating certain vanishing tip. metals. Similar 6, Presenting both among conditions. presenting the, Khaya These findings coincide Mahogany Lifetimes study. Bending side pure No 71 respective again 106. potential applications industry, compare materials. cellulose fibres embedded lignin matrix. suggests plastics, technically frequently polymers 350 MPa, 1000 17, 20, 21. 120 180 200 respectively, does similarly presently maple, kg/m3, (or general) promising industry offers weight reduction fuel savings. S-N Servo-hydraulic comparison. lines power-law dependence assumed approximate data. Dashed represent deviations assuming Gauss-distribution logarithms 22. data, fall within scatter Solid lifetimes, dashed deviations. Some influences An loads Residual failures lower, interaction creep. superimposes damage. zero, therefore significant excluded. absence imply applicable superimposed likely. Three 18 failed 108 safe (e. g. industry), needs determined. result time-saving suitable kind time. run intermitted heating. obtained. lie between. Predictions sensitivity according parabola often diagrams applicable. lifetimes. rapid generation Sycamore Comparing latter. densities reveals highlighting transport authors grateful funding Federal Ministries BMK BMDW Province Styria COMET - Competence Centers Excellent Technologies programme, companies ACstyria Mobilitätscluster GmbH, Collano AG, IB STEINER, DYNAmore Gesellschaft FEM Ingenieurdienstleistungen mbH, EJOT Austria GmbH & Co KG, Forst-Holz-Papier, Fill m.b.H, Glanzstoff Management Consulting Holzcluster Steiermark Klumpp Coatings LEAN Volkswagen AG Weitzer Solutions GmbH. programme administered Austrian Research Promotion Agency (FFG 882.509) Styrian Business (SFG 1.000.065.896).