lecture 1introduction 1.ppt
- 1. Woliata Sodo University BSc Program in Civil Engineering 1 Construction Materials I By Elsaye B.
- 2. 1.Introduction Materials and types • Material: a substance or thing from which some thing else can be made. Examples: Cement,brick,aluminium,soil,water… •In Engineering, materials are employed to design and build structures or elements. •Material science examines why’s and how's of materials, making it Possible to advance the development of new materials. •Material Engineering refers to the understanding and review of properties and uses of materials commonly used in engineering 2
- 3. Material Types Amorphous Materials: Materials in which atoms are arranged randomly. or those that do not have crystalline structure. Are strong but brittle Examples: soot(impure carbon),glass Crystalline materials can be converted in to an amorphous material by quenching. i.e. heating the material to its melting temperature followed by rapid cooling so that the material has no time to return to its crystalline arrangement Brittle Materials: Brittleness denotes relatively little or no elongation or increase in length at fracture. Examples: cast iron concrete Glass… 3
- 4. Building Materials: Materials that are used in the building industry such as cement, steel ,brick,plastics,wood,glass Cementitious materials: Materials in which the principal binder is Portland cement or another type of hydraulic cements . Ceramic Materials: …The word ceramic comes from Greek, meaning “burned earth”. …ceramic materials are nonmetallic materials based on clay(silicate mineral) …They are usually crystalline and brittle ,do not conduct electricity very well ,and can withstand high temperatures. 4
- 5. Construction Materials: any material used in construction industry. Examples: cement ,soil,aggregates,asphalt,etc Ductile Materials: Ductility is the property that makes the material to be drawn out or stretched to a considerable extent before rupture. It is usually measured as the percentage of elongation (increase in length) or as the percentage of the reduction in the cross-sectional area ,when the material is subjected to tension. Examples :steel ,aluminum etc 5
- 6. Elastic Materials: Elasticity is the ability of a material to deform under load without a permanent set or deformation up on release of the load. It can also be defined as that property of material by virtue of which deformations from the a load or stress disappear after removal of the load. A perfectly elastic material recover completely its original shape and dimensions when loads are removed. None of the materials remain perfectly elastic throughout the range of stress leading up to failure. But all exhibit elastic properties up to some stress level. An elastic material behaves in elastically when the stresses exceeds the elastic limit, beyond which changes in volume ,shape are permanent. 6
- 7. Crystalline materials: Materials in which atoms are arranged in a discernible repeated pattern in three dimensions. Thermoplastic Materials: Materials that turn plastic (soft)when subjected to heat. e.g. petroleum pitch 7
- 8. 2.Classification & Properties of Materials 2.1 Classification of Materials Materials that are used for construction purpose can be broadly classified based on their: Metallic Property Physical nature Mode of production 8
- 9. Classification Based on Metallic Property 1.Metallic : in general metals can be classified in to :Ferrous and Non-ferrous. a. Ferrous: is the metal in which the principal element is iron. Examples:steel,wrought iron & cast iron b. Non-ferrous : is the metal in which the principal element is not iron Examples: copper,aluminium,lead,zinc,etc 2.Non metallic: Examples;concrete,timber,stone,lime etc. 9
- 10. Classification Based on Physical Nature of Materials 10
- 11. Classification Based on Mode of Production a) Naturally Occurring Materials .stone .timber b) Industrially produced materials .Cement .glass C) Materials produced at construction site .Concrete .mortar 11
- 12. 2.2 Properties of Materials Properties Which relate to materials are: 1. Physical properties Density & specific gravity Thermal property Acoustic /sound permeability Fire resistance Porosity 12
- 13. 2, Chemical properties Corrosion Resistance Combustibility Toxicity Decay Resistance 3.Mechanical Properties The resistance of material to: The action of external static forces (compressive, tensile, bending, shear, torsion strength) The action of dynamic external forces(impact and vibratory loads) 13
- 14. Behavior of materials under load Application of external force on solid body in equilibrium results in: ….Internal resisting forces are developed in the body which balances the externally applied force. ….The body is deformed to varying degree ….The intensity of internal force is stress and the deformation per unit is strain. 14
- 15. 15 Depending on the arrangement & direction of the external forces, the stress produced in the body may be : Tensile Compressive Shear Bending Torsion Various combinations of the above.
- 16. 2.3 Testing of Materials for Mechanical Properties ..Mechanical properties are conducted to examine the performance of construction materials under the action of external forces. ..Mechanical tests are classified : A. With reference to the arrangement & direction of the external forces; Tension Test Specimen under tension test is subjected to an axial tensile force Tensile stress is developed on cross-sectional area perpendicular to the line of action of the force. The specimen increase in length. 16
- 17. 17 Compression Test Specimen is subjected to an axial compressive force Compressive stress is produced. The specimen decrease in length. Shear test In this test, shearing stress is determined on the x-sectional area parallel to the line of action of the external forces. Bending Test. Specimen is subjected to forces that give rise to bending moments The resulting stresses are compressive on one side of the neutral axis & tensile on the other side. Shear stress exist throughout the beam. Torsion Test This test is conducted to determine the shearing strength of a material The specimens for torsion test are generally cylindrical in shape.
- 18. B. With reference to the rate & duration of the load application. Static Tests Made with gradually increasing load. eg. ordinary tests in tension & compression etc. Dynamic Tests Made with suddenly applied loads. Wear Tests Made to determine the resistance to abrasion & impact. Long time Tests These are made with the loads applied to the object for long period of time. Fatigue Tests These tests are made with fluctuating stresses repeated a large number of times. 18
- 19. C.With Reference to the effect on the specimen. Destructive Test The specimens are either crushed or ruptured and made useless at the end of the tests. Tests conducted on the following materials are best examples ..Ultimate strength of steel ..Compressive strength of concrete Non-destructive Tests Are used to test the strength of members of existing structures without affecting their performance. Example: hammer test 19
- 20. 2.4 Stress-Strain Properties in Simple Tension Test In standard conventional tension test, specimen is subjected to a gradually increasing axial tensile force ‘P’ by means of testing machine. At various increments of load ,the change in length ∆L of the specimen is measured. ∆L=L-Lo where L= new length Lo =original length It is assumed that the stress is uniformly distributed for all points on each x-section. This stress is computed as follow; σt =p/Ao where σt =tensile stress Ao=X-sectional area P= applied load 20
- 21. The uniform stress will produce a uniform elongation ∆L.The elongation per unit length is strain & expressed as: ε= ∆L / Lo Where ε =strain ∆L=elongation Lo=original length of the specimen 21 with the values of strain & stress known for various tensile loads ,a diagram showing the relation between stress & strain ,called stress-strain diagram can be plotted
- 22. 22 a b c d Strain(ε ) Stress (σt ) Fig 1. Stress-strain diagram for ductile materials Plastic range a= proportional limit c=Yield strength b=elastic limit d= ultimate strength
- 23. 1.Proportional Limit: is the greatest stress which a material is capable of withstanding without deviation from the law of proportionality of stress to strain. (point a of fig 1) 2.Elastic Limit: is the greatest stress which a material is capable of withstanding without a permanent deformation remaining up on the release of stress. (point b of fig 1) 3.Yield Point :is the stress at which there occurs a considerable increase in strain without an increase in stress. Only ductile materials have both lower & upper yield points. (point c of fig 1) 23 Properties in the elastic range The parameters which are used to describe the mechanical properties of a material in the elastic range are: proportional limit, elastic limit, modulus of elasticity, stiffness etc
- 24. 4.Modulus of Elasticity(young’s modulus) is the slope of the initial linear part of stress-strain diagram. The greater the modulus of elasticity, the smaller the elastic strain resulting from the application of a given values. Methods of determining modulus of elasticity, E. i. For ductile materials, with linear stress – strain portion, E= ∆ σt ∕ ∆ ε 24
- 25. ii. For materials with non-linear stress-strain curves The slope of the stress- strain curve varies and the modulus of elasticity cannot be readily determined. The following three methods are employed to define E: a. Initial-Tangent modulus: The slope of the stress –strain curve at the origin which has a value of E 1 =tanф1 25 ф1 Stress (σt ) Strain(ε )
- 26. b. Secant modulus : the slope of the line joining the origin and the selected point on the stress-strain curve with the value of E2 =tanф2 26 ф2 Stress (σt ) Strain(ε )
- 27. c. Tangent modulus: The slope of the tangent to the stress – strain curve at the selected point with the value of E3 =tanф3 27 ф3 Stress (σt ) Strain(ε )
- 28. 5.Stiffness is the measure of the ability of material to resist deformation. The higher the modulus of elasticity, the stiffer the material. A material has a higher stiffness value when its deformation in the elastic range is relatively small. Comparing steel alloys with E=210Gpa and aluminium alloys with E=70Gpa,the steel alloys are about three times as stiff as the aluminium alloys i.e steel alloys will deform about one-third as much as aluminium alloys for the same stress. 6.Poisson’s Ratio Is the ratio of the unit deformations or strains in transverse direction to the longitudinal direction within proportional limit. µ= ε’∕ ε where ε’ = transverse strain, ε =longitudinal strain Poisson’s ratio is a measure of the stiffness of the material in the direction at right angle to applied load. 28
- 29. Properties for the plastic range The characteristic at the plastic range is that there is a permanent deformation in the stressed body after complete removal of the load. The parameters which are used to describe the mechanical properties for the plastic range are; ultimate strength, ductility and toughness. 1.Ultimate Strength:-is the maximum strength a material can possibly resist before failure. Depending on the stress strain relationship of a particular material, the plastic strength will correspond to the ultimate strength or to the fracture(rupture)strength. 29
- 30. 30 Fracture strength Ultimate strength Ultimate or fracture strength Ductile material Brittle material Stress (σt ) Stress (σt ) Strain(ε ) Strain(ε )
- 31. 2.Ductility:- represents its ability to deform in the plastic range. Ductile materials show relatively higher plastic deformation, i.e they are capable of being drawn-out ,before rupture occurs. Ductility is measured by the percentage elongation or percentage reduction in area. De=Lf –Lo *100 Da =Ao-Af *100 Lo Ao 3.Toughness Is the ability of material to absorb energy in the plastic range. A material with high toughness can absorb high values of strain energy in the plastic range. 31
- 32. Thank you!! 32