Particles-their strengths and weaknesses

摘要

There have been many approaches to the measurement of particle strength. They may be divided roughly into two classes, single particle tests and bulk tests. In turn, two main mechanisms have been utilised to apply the force, either to individual particles or to a whole sample of particles. They are impact and compression. From this literature we have drawn three broad conclusions which are the basis for the developments we describe: 1) Strength is a particle property. Nearly all granular materials have a distribution in size and shape and therefore individual measurement of a sufficiently large sample of granules is required to determine the associated strength distribution. There for assessment of granule strength requires individual testing of a representative sample of granules. 2) Particle Strength is a generic term for a number of mechanical particle properties. Strength is directly related to the failure of a granule, and as this can often happen by different physical mechanisms (such as attrition, yielding or fracture), different parameters are required to quantify the granule's strength. 3) The Particle Strength Characteristics depend on particle history. The history of a particle obviously can have an effect on particle size and shape, but it can also directly effect the particle strength. The drying history, temperature history or the mechanical history of the granules can cause this reduction in strength. The effect of repeated stress cycles, also known as fatigue, is therefore an important aspect of the characterisation of granule strength. This article will discuss two methods for granule strength assessment based on the three principles and will show that accurate strength characterisation does not necessarily becomes more difficult when taking these principles in account.