Fracture behaviour of wood and its composites. A review COST Action E35 2004-2008: Wood machining - micromechanics and fracture

Fracturing of wood and its composites is a process influenced by many parameters, on the one hand coming from the structure and properties of wood itself, and on the other from influences from outside, such as loading mode, velocity of deformation, moisture, temperature, etc. Both types of parameters may be investigated experimentally at different levels of magnification, which allows a better understanding of the mechanisms of fracturing. Fracture mechanical methods serve to quantify the fracture process of wood and wood composites with different deformation and fracturing features. Since wood machining is mainly dominated by the fracture properties of wood, knowledge of the different relevant mechanisms is essential. Parameters that influence the fracture process, such as wood density, orientation, loading mode, strain rate and moisture are discussed in the light of results obtained during recent years. Based on this, refined modelling of the different processes becomes possibl

Fracture Energy Of Spruce Wood After Different Drying Procedures

The effects of different wood drying procedures, of felling time (winter and summer), and of compass orientation within one tree (north and south side) on the fracture properties of spruce wood have been studied. A most useful parameter to characterize the fracture behavior, the specific fracture energy Gf, has been determined with a new splitting method. High-temperature (100-110 C) drying renders the lowest specific fracture energy (Gf) and fracture toughness (KIC) values in comparison with 20 C fresh air, 50-60 C (kiln)-drying and prefreezing (-20 C), and air-drying. Prefreezing to -20 C before air-drying provides similar values as 20 C and similar or slightly higher values as 50 C drying. Effects of felling time and of compass orientation could not be detected unambiguously

Analyse der Gestaltänderung von Aluminiumpulverpartikeln während eines Naßmahlvorganges / Analysis of Shape Alterations of Aluminium Powder Particles during a Wet-Milling Process

Contrary to brittle material, the equilibrium grainsize for ductile powders is often approached as an oscillatory function of time. The following paper investigates this behaviour by means of a geometrical analysis of the powder particles, using wet-milled aluminium powder as an example. For the description of the milling kinetics we have used Hüttig's milling functions which are obtained from a sieve analysis, the measuring of the specific area of a powder monolayer, and the determination of the space-filling.</jats:p

Time Saving Method for Measuring VHC Fatigue and Fatigue Crack Growth Data with the Ultrasonic Fatigue Technique

AbstractThe principles of the ultrasonic 20 kHz technique are shortly described and its peculiarities explained. Considering the technical requirements, such as an on-line amplitude and frequency feedback control and use of appropriate cooling allow obtaining data of high accuracy and reliability. Life-time data at constant and variable amplitudes, as well as fracture-mechanical values, such as (Δa/ΔN) vs. ΔK curves can be obtained, and especially endurance limit and ΔK thresholds can be obtained in a highly time-saving way. Some examples of performing measurements under superimposed loading conditions are shown. One is on-line observation of specimens during loading and simultaneous mechanical measurements plus fractography after final fracture so that, the correlation of these results allows quantitative information on (Δa/ΔN) and ΔK values in the VHCF regime. Another new technique led to a two-step model of small-crack initiation and propagation from corrosion pits. Investigations on polycrystalline copper likewise rendered interior fatigue-crack formation from persistent slip bands and corroborated that, arrest of small cracks is mainly responsible for several unexpected results in the VHCF regime