PROPERTIES OF ENGINEERING MATERIALS

PRESENTED BY:SANDEEP NAIR(CB.EN.P2MFG15018)PAVAN.G (CB.EN.P2MFG15014)AMRITA SCHOOL OF ENGINEERINGPROPERTIES OF ENGINEERING MATERIALS

INTRODUCTIONThe practical application of engineering materials in manufacturing engineering depends upon through knowledge of their particular properties under wide range of conditions.The term property is a qualitative or quantitative measure of response of materials to externally imposed conditions like forces and temperature.However, the range of properties found in different classes of materials is very large.

CLASSIFICATION OF MATERIAL PROPERTY:

Materials propertiesMechanicalthermalopitcalphysicalmagneticchemicaltechnologicalelectrical

MECHANICAL PROPERTIES:The properties of materials that determines its behaviour under applied forces are called mechanical properties.They are usually related to the elastic and plastic behaviour of the material.These properties are expressed as the function of stress-strain.etcA sound knowledge of mechanical properties of materials provides the basis for predicting behaviour of materials under different load conditions and designing the components out of them.

CLASSIFICATION OF MECHANICAL PROPERTIES:1). ELASTICITY2). PLASTICITY3). TOUGHNESS4). RESILIENCE5). TENSILE STRENGTH 6). YIELD STRENGTH7). IMPACT STRENGTH8). DUCTILITY9). HARDNESS10). FATIGUE11). CREEP12). WEAR RESISTANCE

STRESS -STRAIN

Experience shows that any materials subjected to a load may either deform , yield or break , depending upon- The magnitude of load Nature of the material Cross sectional dimension The engineering stress and strain are based on the original sample dimension which changes during test.True stress and strain on other hand based on actual or instantaneous dimensions and are better representation of deformation behaviour of the material.

Engineering stress and strain curve is based on original area ,it descends after maximum load as the load bearing capacity of sample decrease due to reduction in area.True stress-strain curve, continue to go up till fracture as it is based on actual area

Engineering stress strain curveTrue stress-strain curve

ELASTICITYThe property of material by virtue of which deformation caused by applied loads disappears upon removal of load.Elasticity of the material is the power of coming back to its original position after deformation when the stress or load is removed.

The physical reasons for elastic behavior can be quite different for different materials. In metals, the atomic lattice changes size and shape when forces are applied (energy is added to the system). When forces are removed, the lattice goes back to the original lower energy state.In engineering, the amount of elasticity of a material is determined by two types of material parameter.The first type of material parameter is called amodulus, which measures the amount of force per unit area (stress) needed to achieve a given amount of deformation. The units of modulus are pascals (Pa). A higher modulus typically indicates that the material is harder to deform.

The second type of parameter measures theelastic limit. The limit can be a stress beyond which the material no longer behaves elastic and deformation of the material will take place. If the stress is released, the material will elastically return to a permanent deformed shape instead of the original shape.

PLASTICITY:The plasticity of a material is its ability to undergo some degree of permanent deformation without rupture or failure.Plastic deformation will take only after the elastic limit is exceeded.It increases with increase in temperature.

STRESS-STRAIN CURVE FOR SHOWS ELASTICITY AND PLASTICITY FOR MATERIALS:

DUCTILITY:It is the ability of a material to undergo plastic deformation without fracture.Ex:- Mild steel is ductile material.

There are two common measure of ductility:- 1). Percentage elongation:-% elongation describes the extent to which specimen structure before repture. % elongation=Lf-Lo/Lo*100 where, Lf= final gauge length Lo = initial gauge length

2). Percentage reduction:- % reduction is a measure % change in cross sectional area at point of fracture before and after the test. % reduction=Af-Ao/Ao*100 where, Af= final cross sectional area Ao= initial cross sectional area

The amount of ductility is an important factor when considering forming operations such as rolling and extrusion. Ductility is also used a quality control measure to assess the level of impurities and proper processing of a material.For ductile material, breaking strength is less than UTS ,and necking precedes fracture.For brittle material, fracture usually occur before necking and possibly before the onset of plastic flow.

TOUGHNESSToughness is the ability of the material to absorb energy during plastic deformation upto fracture..A material with high strength and high ductility will have more toughness than a material with low strength and high ductility.Toughness is a good combination of strength and ductility.one way to measure toughness is by calculating the area under the stress strain curve from a tensile test. This value is simply called material toughness and it has units of energy per volume.Material toughness equates to a slow absorption of energy by the material.

several variables that have a profound influence on the toughness of a material:- 1). Strain rate- metal may possess satisfactory toughness under static loads but may fail under dynamic loads or impact. toughness decrease as the rate of loading increases.

2). Temperature:- Temperature is the second variable to have a major influence on its toughness. As temperature is lowered, the ductility and toughness also decrease.3). Notch effect:- The third variable is termed notch effect, has to due with the distribution of stress. A material might display good toughness when the applied stress is uniaxial.Two of the toughness properties that will be discussed in more detail are:-1).Impact toughness- The impact toughness of a material can be determined with a Charpy test. Impact tests continue to be used as a quality control method to assess notch sensitivity and for comparing the relative toughness of engineering materials.

Toughness is greatly affected by temperature, a Charpy test is often repeated numerous times with each specimen tested at a different temperature.

FIG-CHARPY TESTER

This produces a graph of impact toughness for the material as a function of temperature.It can be seen that at low temperatures the material is more brittle and impact toughness is low. At high temperatures the material is more ductile and impact toughness is higher.The transition temperature is the boundary between brittle and ductile behavior and this temperature is often an extremely important consideration in the selection of a material.

2). Notch-Toughness: Notch toughness is the ability that a material possesses to absorb energy in the presence of a flaw.Notch-toughness is measured with a variety of specimens such as the Charpy V-notch impact specimen or the dynamic tear test specimen.impact testing the tests are often repeated numerous times with specimens tested at a different temperature. With these specimens and by varying the loading speed and the temperature, it is possible to generate curves such as those shown in the graph.The material develops plastic strains as the yield stress is exceeded in the region near the crack tip.

The amount of plastic deformation is restricted by the surrounding material, which remains elastic.When a material is prevented from deforming plastically, it fails in a brittle manner.

HARDNESSIt is the property of a metal, which gives it the ability to resist being permanently deformed when a load is applied.

The greater the hardness of the metal, the greater resistance against the deformation.

Various hardening process

Hall- Petch strengthening (Grain boundary)Work hardeningSolid solution strengtheningPrecipitation hardening Martensitic transformation

MEASUREMENT METHODSRockwell hardness testBrinell hardness testVickers hardness testKnoop hardnessShoreMohs testBarcol hardness test

BRINELL HARDNESS TEST

HARDNESS DEPENDS ON

Ductility ElasticstiffnessPlasticity Strain Toughness Viscosity

FATIGUEMetal fatigueis the progressive and localized structural damage that occurs when a material is subjected to cyclic loadings.

The highest stress that a material can withstand for an infinite number of cycles without breaking called also endurance limit

The greater the applied stress range, the shorter the life.

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Prediction of fatigue1)S-N Curve2)Strain life relationship3)Fracture mechanics approach4) Goodman life equation

Strain-life relationship

Fatigue in steel

CREEP The tendency of asolid material to deform permanently under the influence of mechanicalstresses.

It can occur as a result of long-term exposure to high levels of stress that are still below theyield strengthof the material. Creep is more severe in materials that are subjected toheat for long periods, and generally increases as they near theirmelting point.

Creep development

INFLUENCING FACTORSDiffusionDislocationTemperatureStress

Schematic of the test setup for creep measurements.

WEAR

Wear is related to interactions between surfaces and specifically the removal and deformation of material on a surface as a result of mechanical action of the opposite surface.

CLASSIFICATION1)Adhesive wear2) Abrasive wear3)Surface fatigue4)Fretting wear5)Erosive wear6)Corrosive and oxidation wear

Measurement of wearTribometer Archard equation

Q=KWL/HwhereQis the total volume of wear debris producedKis a dimensionless constantWis the total normal loadLis the sliding distanceHis thehardness of the softest contacting surfacesNote thatis proportional to the work done by the friction forces as described by Reye's hypothesis.