State-of-the-art: intermediate and high strain rate testing of solid wood

Abstract

The following state-of-the-art report summarizes important work done in wood science concerning intermediate and high strain rate testing. Intermediate testing may be done with hydraulic machines, which are generally classified as rapid loading. Intermediate testing may also be done using a transverse impact of a beam specimen with a pendulum, drop mass, or toughness tester, whereas high strain rate testing is generally done with the Kolsky bar. The article analyzes the different experimental testing apparatuses, the conclusions past researchers have made about them, and the toughness and strength measurements which were usually done. The transverse impact test is examined in detail because of its adjustability for specimen sizes. The value of this research is it delves into certain impact mechanics principles which are missing from the analysis of impact testing in wood science, which must be included to validate previously held assumptions. The physical response of wood to a dynamic load is not any different from other materials such as metals or rigid foams and is governed by the same principles. Nevertheless, over the years the application of impact mechanics principles to wood testing has been scarce and “black box” experimental, where empirical approaches such as the duration-of-load were often preferred. An example of these principles is the influence of higher modes of vibration plays a greater role on the stress state in testing than its influence on deflections. This principle has been thoroughly investigated for small strain rate vibrations, however, not applied to impact testing. Presently, there is no consensus on a constitutive strain rate model for wood under intermediate and high strain rates. This article provides direction for obtaining dynamic Young’s modulus and yield strength, which can be normally expected in the design of structures subjected to dynamical loadings, for the future creation of applicable constitutive strain rate models.