Physical and structural characteristics of natural stone

Specific mass of stone

The specific gravity of a rock is the ratio of the specific gravity of the rock to the specific gravity of water or the ratio of the specific gravity of rock to the specific gravity of water .The specific gravity is a function of the pores, joints and cracks and other open spaces in the rock, so that the specific gravity of a specific sample of rock increases with increasing depth and thus increasing the pressure of the upper rocks and closing the joints and cracks in the rock .Since the specific gravity is directly related to the strength of the rock .It can be said that it has an inverse relationship with the performance of cutting tools in the cutting process. In general, the denser and denser the stone, the less it can be cut.

Stone texture

One of the most important and fundamental factors in the engineering behavior of rocks, especially in the cutting process, is the texture of the rock .Therefore, this parameter should be considered in selecting the correct equipment and cutting machines, determining the mechanical behavior and predicting the performance of cutting equipment .The main characteristics of the texture include size, shape, orientation, grain ratio and stone matrix. Among the texture characteristics, grain size is also very important .Because lateral cracks grow and spread mainly at the grain boundaries. And the larger the grain size, the larger the size of the secondary chips formed .Elongated angular grains and fine rock particles reduce the cutting speed and increase the abrasiveness of the stones .In terms of stone cutting ability, what is clear from the results of researchers' studies, with increasing the amount of tissue coefficient, the cutting rate will decrease and the wear rate will increase .The greater the strength and adhesion between the grains, the lower the formation and growth of lateral cracks, followed by the thickness of the chip under the influence of the segment, and consequently the cutting speed decreases.

The porosity of the stone

Another important physical parameter of rock in terms of cutting ability is the porosity of the rock .Rocks are not completely solid objects and generally contain pores in the form of more or less connected cavities or separate cavities. The presence of these cavities is of great importance in the mechanical and engineering properties of the stone as well as the formation and expansion of lateral and radial cracks .In fact, porosity and joints in the structure of the rock material play the role of defects and primary cracks .The greater the amount of these joints and porosity, the easier it is for secondary chips to form.

Mechanical properties of natural stones

  • Rock compressive strength

Resistance is the degree of stability of a rock against external stresses .These stresses may be at rest (static) or at motion (dynamic).As the strength or strength of the rock increases, the formation of the secondary chip becomes more difficult, and consequently more shear forces are required to form a certain amount of the chip .One of the parameters of rock resistance is compressive strength .Compressive strength can be considered as the most important and widely used feature of rocks.

  • Tensile strength of stone

Another important parameter of rock strength is the tensile strength of rock .Tensile strength is the maximum tensile stress that a rock can withstand .What is certain is that with increasing the strength parameters of the stone, the cutting ability of the stone decreases.

  • Hardness of stone

Hardness is the resistance that a mineral or stone shows to the abrasive tool (abrasive), so as not to cause scratches (abrasion) in it .The abrasive tool is in contact with the mineral or rock and causes a force (due to the movement of the mineral or rock).Not all minerals or rocks are flexible against all scratching objects .If the rock's resistance to scratches from another object is desired, it is called static stiffness, and if the rock's stiffness against impact is considered, it is called dynamic stiffness. These two difficulties are not equal.

  • Stone abrasion

In the cutting process, abrasion refers to a property of the stone .Which is capable of destroying segments of steel, carbonate, or diamond .The abrasion of a rock depends on the hardness of the minerals, the shape and size of the grains, the locking of the grains and the matrix of the rock. Sharp, angular beads produce more abrasion than round beads .Also, sharp and angled chips create deep scratches on the cutting tools and prevent the stone from being crushed under the energy transmitted by the segment .On the other hand, fine and round particles of stone cause segment polishing and sluggishness of the disk .Abrasion in natural

Abrasion in natural rocks generally depends on three factors:

  • Quartz content
  • Seed size
  • Shear strength of rocks
  • Elastic and plastic properties of natural stones

Deformability, fracture mode, and fracture type of rocks depend on their elastic and plastic properties.

 Based on how the rock deforms as a function of stresses produced by static loads, three groups of rocks can be distinguished:

A) Crisp elastic, or those that follow Hooke's law.

B) Crisp plastic, which deforms the plastic before breaking.

C) Ultra-plastic, or very porous, in which there is no obvious elastic deformation.

Most minerals in rock have a brittle elastic behavior .The elastic properties of the rock are determined by the elastic modulus .Some researchers have used elastic modulus in their studies and others have used rock brittleness indices to study and analyze the cutting process.

Structural and environmental characteristics of stone:

The structural characteristics of the rock are a function of geological factors such as stratification, cleavage and orientation of minerals, joints and cracks, fault surfaces or any type of cracks due to faults or folds that create suitable conditions for the influence of weathering and frost factors .Among the structural characteristics of the rock, we can mention the joint, crack, clearance and orientation of minerals in the rock .In general, environmental factors, including weathering, joints and hair cracks in the rock, reduce the strength parameters of the rock, which in turn increases the cutting ability of the rock.It can be inferred that with the increase of joints and hair cracks in the rock, the chip removal capability of the segment has increased at a constant amount of shear force, which will be followed by an increase in shear rat.

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