PROPERTIES DEFINITIONS

Strength:

                   Strength is defined as the ability of a material to resists loads without failure. It is expressed in terms of maximum load per unit area called as ultimate strength or maximum stress. Material can withstand without failure and it various according to the type of loading.

Tensile Strength:

                   Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. Tensile strength is not the same as compressive strength and the values can be quite different. Some materials will break sharply, without plastic deformation, in what is called a brittle failure. Others, which are more ductile, including most metals, will experience some plastic deformation and possibly necking before fracture

  N/mm² or KN/m²                                 

                                                        Fig1.1: Strength

Compressive Strength:

                    The compressive strength is the capacity of a material or structure to withstand loads tending to reduce size. It can be measured by plotting applied force against deformation in a testing machine. Some materials fracture at their compressive strength limit; others deform irreversibly, so a given amount of deformation may be considered as the limit for compressive load. Compressive strength is a key value for design of structures. Compressive strength is often measured on a universal testing machine; these range from very small table-top systems to ones with over 53 MN capacity. Measurements of compressive strength are affected by the specific test method and conditions of measurement. Compressive strengths are usually reported in relationship to a specific technical standard.

                     N/mm²

Specific strength:

                   The specific strength is a material's strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength. The SI unit for specific strength is Pa/(kg/m3), or N-m/kg, which is dimensionally equivalent to m2/s2, though the latter form is rarely used.

Shear Strength:

                     Shear strength is the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shear

                         N/mm²

Yield strength:

                    A yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

Stiffness:

                 The property of a material by virtue of which it resists the deformation. Modulus of elasticity is a measure of stiffness of a metal. Stiffness is made use in graduating spring balances and spring controlled measuring instruments.

Elasticity:

                 The ability of material to deform under load and regain its original shape and size after the removal of load. In nature, no material is perfectly elastic, over the entire range of stress up to fracture. Spring deforms under load and returns to its original shape after removing the load. Spring needs to be made from an elastic material.

Plasticity:

                The ability of a material to deform under load and return its new shape when the load is removed is called plasticity. Lead has good plasticity even at room temperature, this property find its use in forming, shaping and extruding operations of materials. Due to this property materials are deformed into required shape without fracture.

Ductility:

            In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure

Malleability:

                               The ability of a material to be deformed plastically without rupture under a compressive load or the plastic flow of material under compressive forces is known as malleability. Due to this property, metals are hammered and rolled into thin sheets. The following common metals have malleability in the decreasing order.

1. Gold,    2.Silver, 3.Aluminium, 4. Copper 5.Tin, 6.Platinum, 7.Lead, 8.Zinc, 9.Iron, 10.Nickel.

Materials which are highly ductile are also highly malleable but the reverse may not be true.

Toughness:

                         Toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for many design applications. The linear-elastic fracture toughness of a material is determined from the stress intensity factor ( ) at which a thin crack in the material begins to grow. It is denoted K and has the units of   or . Plastic-elastic fracture toughness is denoted by J with the unit of J/cm² or l bf-in/in², and is a measurement of the energy required to grow a thin crack.

Impact strength:

           Loads that are suddenly applied to a structure are known as impact loads. The ability of a material to resist the impact loads without failure or fracture is called impact strength.

       Impact strength = E/A   J/mm2

Where,    

       E = Energy required to fracture the specimen, J

     A = Cross sectional area of specimen at notch in mm2

Brittleness:

                 Brittleness is defined as the property of a metal of sudden fracture without any appreciable deformation. This property is opposite to the ductility and toughness of a metal. Glass, cast iron and concrete the brittle materials. In a tensile test, an elongation of the specimen of less than 5 % on a 50 mm gauge length is an indication of brittleness. Brittle material possesses little strength upon tensile loading but may be safely used in compression.

Hardness:

                  Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials, such as metal, are harder than others. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.

Creep:

                   In materials science, creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.

Fatigue:

                     Failure of material under repeated loads and fluctuating loads is called fatigue. Engine crank shafts, air craft components, bridges and machine parts etc., are subjected to fatigue. Fatigue strength is the resistance of a material to withstand cyclic, repeated or fluctuating loads without failure. Fatigue strength can be maintained by keeping the good surface finish of the materials. The maximum stress can be applied for an indefinite time on the material, without failure is known as endurance limit or fatigue limit.

Resilience:

               In material science, resilience is the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading. Proof resilience is defined as the maximum energy that can be absorbed within the elastic limit, without creating a permanent distortion. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion. It can be calculated by integrating the stress-strain curve from zero to the elastic limit. In uniaxial tension,

                                         

    Where         

                              Ur is the modulus of resilience

                              σ_v is the yield strength, and 

                              E is the Young’s modulus.

Surface roughness:

                                Surface roughness, often shortened to roughness, is a component of surface texture. It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. Roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface (see surface metrology). However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose.