Elastic-brittle particles

Most solids are subjected to permanent deformation or breakup once the applied stresses exceed a certain limit. Hence, most solid particles may be classified into two categories elastoplastic particles and elastic-brittle particles. Typical elastoplastic materials include metals and polymers, while typical elastic-brittle materials include coal, activated carbon, and ceramics. Materials that are elastoplastic at room temperature may become brittle at low temperatures and those that are brittle at room temperature may become plastic at high temperatures. 

Expansion of the strip after pressure release is influenced by the physical characteristics of the material to be compacted (plasticity, brittleness, particle size and distribution, particle shape, etc.), the roll diameter, the speed of rotation, and the surface configuration of the rollers. With increasing roll diameter and/or decreasing speed the expansion of compacted material is reduced due to better deaeration during densification and a more complete conversion of elastic into permanent, plastic deformation. 

The mechanism of densification of particulate solids (Fig. 6.6) includes, as a first step, a forced rearrangement of particles requiring little pressure followed by a steep pressure rise causing brittle particles to break and malleable ones to deform plastically. During the entire process, porosity decreases so that fluids which originally occupied the pore space of the bulk feed must be able to escape and the initial elastic deformation must have sufficient time to either cause breakage or convert into plastic deformation (see also Section 8.1). These requirements limit the speed of densification and, therefore, the production capacity. 

Considering a ctrrve integral of the thermal-stress-induced elastic energy density, the critical particle radii related to crack formatiorrs in ideal-brittle particle and matrix. 

Detachment of a particle from a substrate when plastic deformations have occurred is somewhat a more complicated problem than in the case of simple elasticity. Essentially, one has to first determine if the detachment occurs because of a cohesive or interfacial failure and whether the failure is ductile or brittle. For... 

Alternatively, if detachment is associated with a brittle failure, then one must first determine if the fracture followed an elastic loading where an elastic model such as the JKR theory is appropriate or if it follows a plastic or elastic-plastic loading. In this latter case, the force needed to detach the particle from the substrate depends on the specific properties of the materials and the details of the deformations [63]. 

It has been shown that inclusion of fine mbber particles in asphalt reduces the cracking of pavement in adverse weather conditions [60,61]. There are two methods for introducing ground waste mbber into asphalt, namely, wet and dry processes. Wet process is carried out at 170°C-220°C for 45-120 min. Rubber particles absorb components with similar value of solubility parameter (5) from the asphalt, causing them to swell. The interaction between mbber and asphalt is mainly of physical nature. In the dry process, mbber is used as a replacement for part of the aggregate and is added to the mineral material before the latter is mixed with the asphalt binder. Addition of mbber greatly improves the elasticity of the binder and generally lowers its brittle point. Incorporation of GRT... 

Elastic deformation is a reversible process, whereby, if the applied load is released before the elastic yield value is reached, the particles will return to their original state. Plastic deformation and brittle fragmentation are non-reversible processes that occur as the force on the particles is increased beyond the elastic yield value of the materials. Brittle fragmentation describes the process where, as the force is increased, particles fracture into smaller particles, exposing new, clean surfaces at which bonding can occur. For plastically deforming materials, when the force is removed, the material stays deformed and does not return to its original state. Plastic materials are also known as time-dependent materials because they are sensitive to the rate of compaction. We can also speak of viscoelastic-type materials which stay deformed when the force is removed, but will expand slowly over time. 

Brittle erosion is the loss of material from a solid surface due to fatigue cracking and brittle cracking caused by the normal collisional force Fn. Materials with very limited capacity for elastic and plastic deformation, such as ceramics and glass, respond to particle impacts by fracturing. The yield stress for brittle failure Fb for normal impacts is about... 

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