Dynamic crushing characteristics of spruce wood under large deformations
An extensive series of large deformation crushing tests with spruce wood specimens was conducted. Material orientation, lateral constraint and loading rate were varied. Regarding material orientation, a reduction in the softening effect and the general force level was observed with a higher fiber-load angle. A comparison with characteristics gained by application of Hankinson’s formula showed discrepancies in compression strength and the beginning of the hardening effect. Lateral constraint of the specimens caused a multiaxial stress state in the specimens, which was quantified with the applied measuring method. Further, a higher force level compared to specimens without lateral constraint and significant hardening effect at large deformations resulted. Thus, the influence of a multiaxial stress state on the force level could be determined. An increase in the loading rate led to higher force levels at any displacement value and material orientation.
High strain rate out‐of‐plane compression of birch plywood from ambient to cryogenic temperatures
An extensive series of compression tests with birch plywood specimens is conducted in the out‐of‐plane direction. Various experimental conditions are tested with different temperatures and strain rates. To this end, a specially designed Split Hopkinson pressure bar protocol is defined, and the specimen dimensions are validated from quasi‐static EN789 standards experiments. Temperatures are ranging from ambient down to −170°C, while strain rates are increased from 0.004/s up to 700/s. The analysis of the experimental results focuses on the hardening behaviour and the following densification regime at large strains. Evolution with temperature and strain rate of the four coefficients of the stress versus strain curve interpolation is discussed, and models are proposed.
Compression fracture of wood parallel to the grain
SummaryA theoretical model of wood is presented consisting of a bonded assembly of long hollow tubes. As increasing load is applied to the tubes in the direction of their length, it is assumed that the bonding material breaks until sufficient free lengths exist for portions of the tubes to buckle. The dependence of the buckling stress and the free length on dimensions and properties of the tubes is calculated and the angle of the band of unstable portions is derived. The behaviour of the model is compared with the measured behaviour of wood. Agreement is encouraging and refinements are suggested to reduce the discrepancies observed.