MATERIALS OF CONSTRUCTION_T.ERDOĞAN

1.MATERIALS AND ENGINEERING
Engineering structures have to be :
1.safe
2.servicable
3.economical

Among the properties of materials, "mechanical properties that show behaviour under loads" and "durability" are the most important.

Commonly used organizations and related standards :
• TSE : TS
• ASTM : American Society for Testing and Materials : ASTM specs
• ACI : American Concrete Institute : ACI specs
• ISO : ISO
• CEN : European Committee for Standardization : EN

2.BEHAVIOR OF MATERIALS UNDER LOADS
1.INTRODUCTION
Forces :
1.Compressive
2.Tensile
3.Shear

a.Static
b.Dynamic

i.isotropic
ii.anisotropic

2.STRESS AND STRAIN
Stress : The intensity of a reaction force at any point in the body
stress (sigma) = F / A (kgf/cm2 or MPa)

Principal stresses :
1.uniaxial
2.bi- or tri-axial
3.shear

Strain : Deformation per unit length of the body. (dimensionless)
strain (epsilon) = DL / L0

3.ELASTICITY
A material is called elastic if the deformation produced by the effect of a force totally disappears after removal of the force. Acc. to Hooke's law, stress in an elastic body is proportional to strain (E). Hooke's Law usually applies to very small deformations.

Elastic Constants :
1.Modulus of elasticity, Young's modulus (E)
when an elastic material is subjected to an axial force, the magnitude of the deformation is directly proportional to force and length in the same direction.
DL ~ F x L / A
DL = F x L / A x E,
E = stress / strain

2.Modulus of compressibility, Bulk Modulus (K)
K = hydrostatic pressure / volumetric strain

3.Modulus of rigidity, shear modulus (G)
G = shear stress / shear strain

4.Poisson's ratio, (mü)
mü = lateral strain / long. strain (both caused by longitudinal stress)

4.PLASTICITY AND FLOW
Many materials exhibit elasticity up to a certain minimum stress and show permanent (nonrecoverable) deformation if min. stress is exceed, this is callled elastoplastic material. The minimum stress is called yield stress. Permanent deformation is described as plastic deformation.

5.DUCTILITY AND BRITTLENESS
Ductility is the capacity of the load resisting material while resisting, Brittleness is the tendency to break when stress exceeding the elastic limit. (i.e.materials that have plastic deformation capacity is called ductile whereas if they break shortly after elastic deformation, they are called brittle.

Ductile materials : steel, plastic, fibers etc.
Brittle materials : concrete, clay bricks, cast iron

6.STRESS-STRAIN CURVES
Ductile materials are investigated under tensile stress, whereas birttle under compressive.
Some properties :
Proportional limit
Elastic limit
Yield point
Strain hardening
Ultimate strength
Breaking strength

12.TOUGHNESS AND RESILIENCE
Toughness is the ability to absorb energy during plastic deformation. Modulus of toughness is max. energy without fracture. (area under stress-strain curve)

Toughness is desirable when materials are to be subjected to dynamic loads.

Resilience is the capacity to absorb energy in the elastic range.

13.VISCOSITY
Property of resistance to flow; internal friction that the materials exhibits during flow. It affected from heat.

14.CREEP
The slow and progressive deformation of a material with time under a constant stress is called Creep. This is observed in all materials.

15.FATIGUE
The phenomenon of fracture caused by the progressive damage due to the repetition of applied stresses is called fatigue. To show relation, Stress and number of cycles are plotted for different stresses. Fatigue limit or endurance limit is defined as the maximum stress that can be applied repeatedly an infinite number of times without fracture. For example, fatigue limit of concrete is around %55 of its maximum static strength.

16.HARDNESS
It is defined as the resistance of a material to scratching or indentation. It is determined by Moh's hardness test. It is used usually for rock and stone. For metals, Brinell and other methods are used.

3.FERROUS METALS
1.INTRODUCTION

2.PIG IRON
It is obtained by heating iron ore to high temperature, and removing oxide from Fe2O3, Fe3O4 in blast furnace. Pig iron include high carbon, it makes it brittle.

3.CAST IRON
It is produced by remelting pig iron in another furnace to eliminate impurities.

The rate of cooling affects the properties, if cool slowly, some carbon combines with iron and remainder is large crystals of graphite or carbon. It makes iron weak and brittle. But rapid cooling set up high initial stresses, in order to prevent this, annelaling (process involving heating and cooling to induce softening) is used and malleable cast iron produces and it has capability to shape by hammer.

Cast irons are hard and brittle, ultimate strength is 110-250 MPa, easy to form.

It is used for members in which tensile stress is low, like parts of machinery and pipe fittings.

4.STEEL
It is produced from pig iron by removing impurities. As taking out molten steel, it may be cast into containers or cas into directly into the desired shape. It can be produced by forging (placing a plate), rolling (cont. passed b/w two sides) The rolling may be carried in elevated temp. (hot rolled), or in room temp. (cold rolling). In hot temp. it allows to move atoms. so not change properties too much, if low temp, properties is changed, tensile str. is increased nd cutility is reduced. The another techniques are extrusion and drawing.

The carbon content is usually %1.5. By increasing carbon, str. inc. ductility dec. Low carbon steels are called mild steels, soft very ductile.

d= 12mm 0.888 kg/m
d= 18mm 2.000 kg/m