Quiz 02/ Machine Design 01

Load

Defined as any external force acting upon a machine part.

Dead Load

does not change in magnitude or direction

Live or variable load

when it changes, continually

Suddenly Applied or Shock Loads

When it is suddenly applied or removed

Stress

When some external system or forces or loads act on a body, the internal forces (equal and opposite) ae set up at various section of body, which resist etxernal Forces.

Strain

A system of forces or loads act on a body, it undergoes some deformation

Tensile Stress

When a body is subjected to two equal opposite axial pulls F.

Tensile Strain

The ratio of the increase in length to the original length

Compressive Stress

When a body is subjected to two equal and opposite axial pushes F.

Compressive Strain

The ratio of the decrease in length to the original length

Hooke’s law

States that when a material is loaded within elastic limit, the stress is directly proportional to strain.

Young’s Modulus or Modulus of Elasticity

Is the proportionally constant in tension.

It is the Slope of the Straight part of the stress-strain curve.

It is the measure of Stiffness

Shear Stress

When a body is subjected to two equal and opposite forces acting tangentially across the resisting section.

Shear Strain

It is measured by the angular deformation accompanying the shear stress.

Single Shear

When the tangential force is resisted by one-cross-section of the rivet

Double Shear

When the tangential force is resisted by two-cross-section of the rivet

Shear Modulus or Modulus of Rigidity

Shear stress is directly proportional to shear strain

Bearing Stress or Crushing Stress

Contact between two members of a machine part that are relatively at rest.

Bearing pressure

Contact between two members of a machine part that are elative in motion.

Gauge length

The original distance between two reference points.

Proportional Limit

It is defined as the stress-strain curve begins to deviate from the straight line.

Elastic Limit

IT is defined as the stress developed in the material without any permanent deformation.

Yield Point stress

Stress corresponding to yield point

Ultimate Stress

Obtained by dividing the largest value of the load reached in a test to the original cross-sectional area of the test piece

Breaking Stress

After the specimen has reached the ultimate stress, a neck is formed which decrease the cross-sectional area of the specimen.

Percentage reduction in Area

Difference between the original cross-sectional area and cross-sectional area at the neck.

Percentage elongation

Percentage increase in the standard gauge length

Working Stress

It is desirable to keep the stress lower than the maximum or ultimate stress at which failure of the material takes place

Factor of Safety

Ratio of the maximum stress to the working stress

Composite Bars

defined as a bar made up of two or more different materials, joined together

Thermal Stresses

Increase or decrease in the temperature of a body, it cases the body to expand or contact

Linear Strain

Direct stress is accompanied by a strain in it’s own direction

lateral strain

Opposite kind of strain in every direction

Poisson’s Ratio

The lateral strain bears a constant ratio to the linear strain

Volumetric Strain

The ratio of change in Volume to the original volume

Bulk modulus

When a body is subjected to three mutually perpendicular stresses.

Impact Stress

The stress produced in the member due to the falling load

Resilience

The strain energy stored in a body due to external loading within elastic limit

Strain Energy

Absorbed in a body when strained within elastic limit

Proof resilience

Maximum energy can be stores in a body up to the elastic limit

Modulus of Resilience

The proof resilience per unit volume of a material

Limit System

In order to control the size of finished part, with duel allowance for error, for interchangeable parts.

Enveloped surface or Shaft

the part which enters into the other.

Enveloping surface or Hole

The other in which one enters

Nominal Size

It is the size of the part specified in the drawing as a matter of convenience.

Basic Size

It is the size of a part which all limits of variation

Actual Size

It is the actual measured dimension of the part.

Upper or High or maximum Limit

The largest permissible size for a dimension of the part

Minimum Limit

The smallest sizes of the part

Allowance

Difference between the basic dimension of the mating parts

Positive

When the shaft size is less than the hole size

Negative

When the shaft size is greater than the hole size

Tolerance

It is the difference between the upper and lower limit of a dimension

Unilateral system of Tolerance

When all tolerance is allowed on one side of the nominal size

Bilateral system of tolerance

When the tolerance is allowed on both sides of the nominal size.

Tolerance zone

It is the zone between the maximum and minimum limit size.

Zero Line

It is a straight line corresponding to basic size

Upper Deviation

It is the algebraic difference between the maximum size and the basic size

ES (Escart Superior)

Represented by upper deviation of a hole

Lower Deviation

It is the algebraic between the minimum and the basic size

EI (Ecart Inferior)

Represented by the lower deviation of a hole

Actual deviation

It is the algebraic difference between an actual size and the basic size

Mean Deviation

It is the arithmical mean between the upper and lower deviation

Fundamental Deviation

It is one of the two deviations which is conventionally chosen to define the position of the tolerance zone .

Fits

The degree of tightness or looseness between two mating parts

Clearance

is the amount by which the actual size of the shaft is less than the actual size of the mating hole.

The difference must be positive

Interference

Is the amount by which the actual size of a shaft is larger than the actual finished sized of the mating hole.

The difference must be negative

Clearance Fit

In this type of fit, the size limit for mating parts are so selected that clearance between them always occur

Interference fit

In this type of fit, the size limit for mating parts are so selected that interference between them always occur.

Transition Fit

In this type of fit, the size limit for mating parts are so selected that either a clearance or interference may occur depending on the actual size

Hole basis System

When the hole is kept a constant member

Shaft basis system

When the shaft is kept as a constant member