ENT 253 MECHANICAL DESIGN SEM 2 - 2007/2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 1 ENT 253...

ENT 253 MECHANICAL DESIGN SEM 2 - 2007/2008

DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP

1

ENT 253MECHANICAL DESIGN

Lecture 1Material

Dr. HAFTIRMANASRUL SAAD

SCHOOL OF MECHATRONICMECHANICAL PROGRAM

UniMAP



2

CHAPTER OUTLINE Mechanical Engineering Design Mechanical Design Material Stress and Strength Uncertainty Units Standards and Codes Design Factor and Factor Safety Reliability Dimensions and Tolerances



3

DESIGN To design is either to formulate a plan for the satisfaction of a specified need or to

solve a problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.

Design is an innovative and highly iterative process. It is also a decision-making process. The engineering designer has to be personally comfortable with a decision-making, problem-solving role.

Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them.

A designer’s personal resources of creativeness, communicative ability, and problem-solving skill are intertwined with knowledge of technology and first principles. Engineering tools such as mathematics, statistics, computers, graphics, and languages are combined to produce a plane that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regardless of who builds it or who uses it.



4

Mechanical Engineering Design Mechanical engineers are associated with the

production and processing of energy and with providing the means of production, the tools of transportation, and the techniques of automation.

The disciplinary base are mechanic of solids and fluids, mass and momentum transport, manufacturing process, and electrical and information theory.

Mechanical engineering design involves all the disciplines of mechanical engineering.



5

MECHANICAL DESIGN

Material Load and Stress Analysis Deflection and stiffness Design of Mechanical Elements



6

MATERIAL Ferrous

Metal

Nonferrous Material

Organic

Non metal Inorganic



7

MATERIAL

Ferrous

Gray Cast Iron

Nodular Cast Iron

White Cast Iron

Malleable Cast Iron

Alloy Cast Iron

Cast Steel



8

MATERIAL

Nonferrous

Aluminum

Magnesium

Bronze

Titanium

Brass

Zinc



9

MATERIAL Organic

RubberPlasticPetroleumLeatherWoodPaper

InorganicCementGraphiteCementGlassCeramics



10

STRESS AND STRENGTH

Stress is a state property at a specific point within a body, which is a function of load, geometry, temperature, and manufacturing processing.

Strength is a property of a material of a mechanical element. The strength of an element depends on the choice, the treatment, and the processing of the material.



11

STRESS AND STRENGTH The capital letter S to denote strength. Ss is a shear strength.

Sy is a yield strength.

Su is an ultimate strength. σ (sigma) to designate normal stress. τ (tau) to designate shear stress.



12

UNCERTAINTY Examples of uncertainties concerning stress and strength include: Composition of material and the effect of variation on properties. Variations in properties from place to place within a bar of stock. Effect of processing locally, or nearby, on properties. Effect of nearby assemblies such as weldments and shrink fits on stress

conditions. Effect of thermomechanical treatment on properties. Intensity and distribution of loading. Validity of mathematical models used to represent reality. Intensity of stress concentrations. Influence of time on strength and geometry. Effect of corrosion. Effect of wear.



13

UNITS

In the symbolic units equation for Newton’s second law, F = ma, F=MLT-2

where, F=force, M=mass, L=length, T= time The International System of Units (SI) F=ML/T2=> (kilogram)(meter)/(second)2

=> kg.m/s2

W=mg=>(1kg)(9.81m/s2)=9.81N



14

STANDARDS AND CODES A standard is a set of specifications for perts, materials,

or processes intended to achieve uniformity, efficiency, and a specified quality.

One of the important purposes of a standard is a place limit on the number of items in the specifications so as to provide a reasonable inventory of tooling, size, shape, and varieties.

A code is a set of specifications for analysis, design, manufacture, and construction of something.

The purpose of a code is to achieve a specified degree of safety, efficiency, and performance or quality.



15

STANDARDS AND CODES All of the organizations and societies listed below have established specifications for

standards and safety or design codes. AA Aluminum Association AGMA American Gear Manufacturers Association AISC American Institute of Steel Construction AISI American Iron and Steel Institute ANSI American National Standards Institute ASM American Society for Metals ASME American Society of Mechanical Engineers ASTM American Society of Testing and Materials AWS American Welding Society ABMA American Bearing Manufactures Association BSI British Standards Institution IFI Industrial Fasteners Institute ISO International Standards Organization SAE Society of Automotive Engineers NIST National Institute for Standards and Technology



16

DESIGN FACTOR AND FACTOR OF SAFETY

nd= loss-of-function strength/allowable stress

nd= S/σ(or τ)

“nd “ is called the design factor The factor of safety has the same definition as

the design factor. The factor safety is called “n”



17

RELIABILITY Reliability of element is the statistical measure of the the

probability that a mechanical element will not fail in use. The reliability R can be expressed by a number having

the range 0≤R≤1 A reliability of R=0.90 means that there is a 90 percent

chance that the part will perform its proper function without failure.

In the reliability method of design, the designe’s task is to make a judicious selection of materials, processes, and geometry (size) so as to achieve a specific reliability goal.



18

DIMENSIONS AND TOLERANCESThe terms are used in dimensioning; Nominal size=>The size we use in speaking of an element. Limits=> The stated maximum and minimum dimensions. Tolerance=> The difference between the two limits. Bilateral tolerance=>The variation in both directions from the basic

dimension. The basic size is between two limits. Unilateral tolerance=>The basic dimension is taken as one of the limits,

and variations is permitted in only one direction. Clearance=> A general term that refers to the mating of cylindrical parts

such as a bolt and a hole. The word clearance is used only when internal member is smaller than the external member. The diametral clearance is the measured difference in the two diameters.

Allowance=>The minimum stated clearance or the maximum stated interference for mating parts.



19

PROBLEMS



20

SOLUTION

ENT 253 MECHANICAL DESIGN SEM 2 - 2007/2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 1 ENT 253...

Documents

Transcript of ENT 253 MECHANICAL DESIGN SEM 2 - 2007/2008 DR. HAFTIRMAN SCHOOL OF MECHATRONIC UniMAP 1 ENT 253...