Abstract
This work concerns basic research on the concept of wood hardness in a sense similar to Brinell or in the modified sense of Monnin. The experimental part of this article is based on research carried out on beech wood with six indenters: three ball indenters of 10, 15 and 30 mm and three cylindrical indenters of 10, 15 and 30 mm. On the basis of measurements for a wide range of loads, relations analogous to Meyer power law of were obtained, with the exponent determined both for balls equal to 5/2 and for cylinders equal to 3/2. These exponents turned out to be exactly the arithmetic mean of exponents for ideally elastic and ideally plastic bodies. On this basis, new hardness formulae were proposed, taking into account Meyer law and the diameters of indenters. Therefore, the proposed two hardness formulae (for the ball and cylinder) are a generalization and development of Meyer hardness law.
Highlights
Review of measures and hardness tests The concept of hardness is included in the science of material strength, but it is associated with a branch of mechanics called contact mechanics
Results of research and discussion The experimental and theoretical results are presented in three stages. First it is tested on the basis of measurements of Meyer law in opposition to Brinell measure
New hardness measures for ball and cylindrical indenters are developed on the basis of the collected measurement results and assumptions of i–ix
Summary
Review of measures and hardness tests The concept of hardness is included in the science of material strength, but it is associated with a branch of mechanics called contact mechanics. Heinrich Hertz made pioneering progress in this area [1]. There are basically three types of hardness as resistance: scratch resistance, static indentation and dynamic indentation [4, 5]. Permanent (plastic) indentation differs significantly from elastic indentation. Indenters with a sharp end such as a cone (Rockwell test), a regular pyramid (Vickers test) or an extended pyramid (Knoop test) work well. Rounded indenters, such as a ball (Brinell, Janka, Krippel and Meyer tests) and a cylinder (Monnin test), are much better suited for wood. Due to the specific structure of wood, we basically distinguish the hardness at the longitudinal sections and the significantly higher hardness at the cross section
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