Abstract

Tensile strength of brittle materials is usually obtained through Brazilian tests. It is accepted that failure is initiated at the centre of the sample and that it propagates through the material, creating a tensile failure plane along the vertical diameter or at the majority of it. Then, the tensile stress developed at the centre of the disc is considered as the tensile strength of the material tested. However, the stress state along the vertical diameter is always biaxial, even in the centre of the sample. This implies that the strength measured using such technique is not the uniaxial tensile strength. In this article, the expressions of the stress state supported by a tubular sample subjected to a novel device to determine the tensile strength of brittle materials are described. Besides, it is noticed that the failure plane contains points with the maximum uniaxial tensile strengths so the testing method is adequate to determine the uniaxial tensile strength of brittle materials.

Introduction

Two of the problems in the calculation of the tensile strength of brittle materials with the universal tensile machine are: the very often breakage of the sample when it is fixed to the jaws of the machine and, the development of micro cracks inside the sample that, although imperceptible to the eyes, produce a deviation in the final value of the tensile strength.

The Brazilian test avoids these problems since it does not need to fix the sample to the jaws because the material is engaged to the jaw at the same time that a stress state is induced in the sample. In addition, in this type of material, obtaining samples with cylindrical geometry is easy. Besides, it is possible to obtain other mechanical properties of the material such as Young’s modulus or Poisson’s ratio [1 - 3].

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