Engineering Mechanics

Definition of Modulus of Elusticity:

It is often difficult to precisely define yielding due to the wide variety of stress–strain curves exhibited by real materials. In addition, there are several possible ways to define yielding:^[1]
True elastic limit: The lowest stress at which dislocations move. This definition is rarely used, since dislocations move at very low stresses, and detecting such movement is very difficult.
Proportionality limit:Up to this amount of stress, stress is proportional to strain (Hooke's law), so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.

Elastic limit (yield strength):Beyond the elastic limit, permanent deformation will occur. The elastic limit is therefore the lowest stress at which permanent deformation can be measured. This requires a manual load-unload procedure, and the accuracy is critically dependent on the equipment used and operator skill. For elastomers, such as rubber, the elastic limit is much larger than the proportionality limit. Also, precise strain measurements have shown that plastic strain begins at low stresses.^[2][3]

Yield point:The point in the stress-strain curve at which the curve levels off and plastic deformation begins to occur.^[4]

Offset yield point (proof stress):When a yield point is not easily defined based on the shape of the stress-strain curve an offset yield point is arbitrarily defined. The value for this is commonly set at 0.1 or 0.2% strain.^[5] The offset value is given as a subscript, e.g., R_p0.2=310 MPa.^[6] High strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials.^[5]

Upper and lower yield points:Some metals, such as mild steel, reach an upper yield point before dropping rapidly to a lower yield point. The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the upper yield point, and beyond, Lüders bands can develop.^[7]

Narsingdi Railway Foot Over Bridge

Properties of Engineering material

List of materials properties

material's property is an intensive, often quantitative, property of some material. Quantitative properties may be used as a metric by which the benefits of one material versus another can be assessed, thereby aiding in materials selection.

A property may be a constant or may be a function of one or more independent variables, such as temperature. Materials properties often vary to some degree according to the direction in the material in which they are measured, a condition referred to as anisotropy. Materials properties that relate two different physical phenomena often behave linearly (or approximately so) in a given operating range, and may then be modeled as a constant for that range. This linearization can significantly simplify the differential constitutive equations that the property describes.
Some materials properties are used in relevant equations to predict the attributes of a system a priori. For example, if a material of a known specific heat gains or loses a known amount of heat, the temperature change of that material can be determined. Materials properties are most reliably measured by standardized test methods. Many such test methods have been documented by their respective user communities and published through ASTM International.

Contents:

• 1 Acoustical properties
• 2 Atomic properties
• 3 Chemical properties
• 4 Electrical properties
• 5 Environmental properties
• 6 Magnetic properties
• 7 Manufacturing properties
• 8 Mechanical properties
• 9 Optical properties
• 10 Radiological properties
• 11 Thermal properties

Acoustical properties:

• Acoustical absorption
• Speed of sound

Atomic properties:

• Atomic mass
• Atomic number - applies to pure elements only
• Atomic weight - applies to individual isotopes or specific mixtures of isotopes of a given element.

Chemical properties:

• Corrosion resistance
• Hygroscopic
• pH
• Reactivity
• Specific internal surface area
• Surface energy
• Surface tension

Electrical properties:

• Dielectric constant
• Dielectric strength
• Electrical conductivity
• Permittivity
• Piezoelectric constants
• See beck coefficient

Environmental properties:

• Embodied energy
• Embodied water

Magnetic properties:

• Curie temperature
• Diamagnetism
• Hysteresis
• Permeability

Manufacturing properties:

• Cast ability
• Extruding temperature and pressure
• Hardness
• Mach inability rating
• Machining speeds and feeds

Mechanical properties:

• Compressive strength : stress a material can withstand before compressive failure (MPa)
• Creep : the slow and gradual deformation of an object with respect to time
• Ductility : Ability of a material to deform under tensile load (% elongation)
• Fatigue limit : Maximum stress a material can withstand under repeated loading (MPa)
• Flexural modulus
• Flexural strength
• Fracture toughness : Energy absorbed by unit area before the fracture of material (J/m^2)
• Hardness : Ability to withstand surface indentation (e.g. Brinnell hardness number)
• Plasticity (physics) : Ability of a material to undergo irreversible deformations (-)
• Poisson's ratio : Ratio of lateral strain to axial strain (no units)
• Resilience : Ability of a material to absorb energy when it is deformed elastically (M Pa)
• Shear modulus : Ratio of shear stress to shear strain (M Pa)
• Shear strain :in the angle between two perpendicular lines in a plane
• Shear strength : Maximum shear stress a material can withstand
• Specific modulus : Modulus per unit volume (M Pa/ m^3)
• Specific strength  : Strength per unit density (Nm/kg)
• Specific weight  : Weight per unit volume (N/m^3)
• Tensile strength : Maximum tensile stress a material can withstand before failure (MPa)
• Yield strength : The stress at which a material starts to yield (MPa)
• Young's modulus : Ratio of linear stress to linear strain (MPa)
• Coefficient of friction (also depends on surface finish)
• Coefficient of restitution
• Surface roughness

Optical properties:

• Absorptivity
• Birefringence
• Color
• Luminosity
• Photosensitivity
• Reflectivity
• Refractive index
• Scattering
• Transmittance

Radiological properties:

• Neutron cross-section
• Specific activity

Thermal properties:

• Autoignition temperature
• Binary phase diagram
• Boiling point
• Coefficient of thermal expansion
• Critical temperature
• Curie point
• Emissivity
• Eutectic point
• Flammability
• Flash point
• Glass transition temperature
• Heat of fusion
• Heat of vaporization
• Inversion temperature
• Melting point
• Phase diagram
• Pyrophoricity
• Solidus
• Specific heat
• Thermal conductivity
• Thermal diffusivity
• Thermal expansion
• See beck coefficient
• Triple point
• Vapor pressure
• Vic at softening point

 

Yield (engineering):

Mechanical failure modes Buckling Corrosion Corrosion fatigue Creep Fatigue Fouling Fracture Hydrogen embrittlement Impact Mechanical overload Stress corrosion cracking Thermal shock Wear Yielding

Information of some rail Foot steel over bridge on Tongi to Bhairab Bazar Rail Line.

Toma  Construction and Company Limited
TONGI - BHAIRAB BAZAR DOUBLE LINE PROJECT
(Foot Over Bridge Information)
SL No.	Station Name	Station Code	Platform to PL Height in mm	Total Span Length in mm	Clear Height from Rail Top in mm	Name of  Engineer-in-Charge(Toma)	Total Sheets	Work Position
1	Daulatkhandi	DLY	300	31310	7300	Engr M A  Razzak	10	Drawing Approved
2	Srinidhi	SRNI	300	32265	7300	Engr M A  Razzak	10	Drawing Approved
3	Methikanda	MEY	300	30990	7300	Engr M A  Razzak	10	Drawing Approved
4	Hatubhanga	HTGA	300		7300	Engr M A  Razzak		Under Dicision
5	Khanabari	KQC	300	32510	7300	Engr M A  Razzak	10	Drawing Approved
6	Amirgonj	AMRG	300	31410	7300	Engr M A  Razzak	10	Drawing Approved
7	Narshigndi	NRC	300		7300	Engr M A  Razzak		Under Dicision
8	Jinardi	JYD	300	30882	7300	Engr M A  Razzak	10	Drawing Approved
9	Arikhola	AKH	300	33320	7300	Engr M A  Razzak	10	Drawing Approved
10	Pubail	PBY	300	30684	7300	Engr M A  Razzak	10	Drawing Approved
	Prepared By
	Engr M A Razzak
	14.01.2015

Real Estate Page-13

13

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Drawing of a Platform shed for a Railway Station.