Machine Design Lecture Notes

Identification/Recognition of Need

Recognized by a particular adverse circumstance or a set of random circumstance

Definition of Problem

Includes all the specifications for the object that is to be designed.

Synthesis

the step where various schemes must be proposed, investigated, and, quantified in terms of establish metrics.

Analysis and Optimization

Process where competing schemes are compared so that the path leading to the most competitive product can be chosen.

Evaluation

Final proof of a successful design and involves the testing of a prototype to discover if the design satisfies the needs.

Presentation

It is a selling job when the engineer presents a new solution is attempting to sell or prove to the them (Supervisory persons) that their solution is a better one.

Karl Freiherr von Dreis

Invented the bicycle in the 19th century.

Note: the early bicycle was named velocipede, hobby-horse, draisine, and running machine and it does not include a chain, brakes, or pedals.

Standard

A set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality.

Codes

A set of specifications for analysis, design, manufacture, and construction of something. Used to achieve safety, efficiency, and quality.

Ultimate Strength

Maximum tensile, compressive, or shear stress that the material can sustain.

Yield Strength

The stress at which a predetermined amount of permanent deformation occurs.

Elastic Limit

Max stress to which a standardized test specimen may be subjected without permanent damage.

Proportional Limit

The stress at which the stress-strain curve deviates from a straight line.

Modulus of Elasticity/Rigidity

The slope of the straight part of the stress-strain curve. It is a measure of stiffness.

Axial Stress - Tensile and Compressive

This force acts perpendicular to the area. It is developed whenever the external loads tend to push or pull on the two segments of the body.

Bending/Flexure

Produces two kinds of normal stresses, tension on one side and compression on the other.

Transverse Shear

Tens to cause warping of the cross-section. Shear is = 0 where the flexural stresses are max.

Torsion

A shear stress which acts on a transverse cross-section that is caused by the action of a twist. Pure shear can be obtained only from torsion.

Strength of a Material

Depends on its ability to sustain a load without undue deformation or failure.

Tension or Compression Test

Used to determine the relationship between the avg. normal stress and avg. normal strain.

Ductility

It is a solid material’s ability to deform under tensile stress.

Malleability

Solid material’s susceptibility to extreme deformation in rolling or hammering.

Brittleness

The solid material’s tendency to fracture without appreciable deformation.

Natural Rubber

Classified as a polymer and exhibits nonlinear elastic behavior.

Wood

A material that is moderately ductile, and as a result it is usually designed to respond to elastic loadings.

Steel

• Brittle when it has high carbon content

• Ductile when the carbon content is reduced

Temperature Effect

• Low temperature cause materials to be harder and more brittle

  • Higher temperature cause materials to be softer and more ductile.

Strength

The material’s ability to sustain a load without undue deformation or failure.

Toughness

It is the material’s capacity to withstand a shock load without breaking.

Creep

Time-dependent permanent deformation is known as creep.

Fatigue

When a metal is subjected to repeated cycles of stress and strain, it causes its structure to break down

Heat Treatment

An operation or combination of operations involving heating and cooling of metal in the solid state for the purpose of altering its properties.

Ageing

Change in metal by which its structure recovers from an unstable condition that has been produced by cold working

Annealing

The term for heating and slow cooling of a solid metal to soften it.

Graphitizing

It causes combined carbon to transform wholly into free carbon.

Hardening

The heating of certain steels above the transformation range and then quenching.

Malleabilizing

An annealing process whereby combined carbon in white cast iron is transformed to temper carbon

Normalizing

It is the heating of an iron-base alloy to some 100F above the transformation range with cooling.

Spheroidizing

Any heating and cooling of steel that produces a rounded or globular form of carbide.

Stress Relieving

The heating of a metal body to a suitable temperature and holding it at that temperature for a time to reduce internal residual stresses.

Tempering

It is the reheating of hardened steel to a temperature below the transformation range followed by any desired rate of cooling.

Transformation Range

• It is the temperature interval during which austenite is formed during heating.

• The temperature interval during which austenite disappears during cooling.