Machine Component Design I(INME 4011)

by

Pablo G. Caceres‐Valencia (B.Sc., Ph.D. U.K.)

GENERAL INFORMATIONCourse Number  INME 4011 Course Title Machine Component Design ICredit Hours 3Instructor Dr. Pablo G. Caceres‐ValenciaOffice Luccetti L‐212 Phone Ext. 2358Office Hours Tu‐Th from 7:30 to 10:45ame‐mail pcaceres@me.uprm.eduWeb‐site http://academic.uprm.edu/pcaceres

AssessmentThe course will be assessed in the following manner:

1st Partial Exam  22%

2nd Partial Exam 24% 

Project 22%

Quizzes 24% (*)

Class Participation and Attendance  8% (**)

(*) Date due Moodle Quizzes and Pop‐Quizzes (max‐8). Missed quizzes will be graded with zero. Lack of access to Internet (Moodle) is not an excuse for not submitting your answers. 

(**) Class participation and Attendance. After the third missed class, one point will be deducted in the final grade for each missed class (up to 8 points). 

Grades Final Grade Range Final Letter Grade

100 – 90 A

89 – 80 B

79 – 70 C

69 – 60 D

59 ‐ 0 F

AttendanceAttendance and participation in the lecture are compulsory and will be considered in the grading. Students should bring calculators, rulers, pen and pencils to be used during the lectures. Students are expected to keep up with the assigned reading and be prepared tosolve problems in class and for the pop‐quizzes. Please refer to the Bulletin of Information for Undergraduate Studies for the Department and Campus Policies.

TexbooksMy lecture notes are available in the web at

http://academic.uprm.edu/pcaceres“Fundamentals of Machine Elements” B.J. Hamrock, S.R. Schmid, B. Jacobson 

“Machine Design: An Integrated Approach” Robert Norton, 3er Ed. Prentice Hall

“Mechanical Engineering Design” J.E. Shigley, C.R. Mischke, R.G. Budynas.

ExamsAll exams will be conducted outside lecture periods on the specified dates. The final project due date is the date for the end of classes. There will be no final exam. Neatness and order will be taking into consideration in the grading of the exams. Up to ten points can be deducted for the lack of neatness and order. You must bring calculators, class notes and blank pages to the exams.

TENTATIVES DATESWeek Week

09/13 Introduction to Design, Review Load, Stress, Strain.

09/20

10/04

10/18

11/01

11/08 Materials and Manufacturing

Q4

11/15 Materials Selection /Fracture Toughness

12/20 Final Project Presentation

Classes End

12/27 Final Project Presentation

Classes End ‐ GRADES

11/29 

12/13

Review Load, Stress, Strain.

Q1

09/27 Basic Elasticity  Basic Elasticity.

Q2

10/11 3D Stresses and Strains Stress Concentration.

Q3

10/25 Static Failure TheoriesExam 1

Mid‐Term Project Presentation

11/22 Fracture Toughness

Q5

Failure Prediction Cyclic & Impact

12/06 Failure Prediction Cyclic & Impact

Q6

Failure Prediction Cyclic & Impact

Q7 –Exam 2

01/10

OutcomesUpon the completion of the course the student should be able to:

• Calculate the principal stresses and strains in a loaded component

• Identify the location of the critical point on a machine component and calculate the stresses at that point.

• Apply the basic static theories of failure in the designing of machines subjected to static loading.

• Apply the basic fatigue failure theories in the designing of machine subjected to dynamic loading 

Evolution of Engineering Research & Education

1910

1960

2010

Sputnik

Quantum Mechanics

InformationTechnology

“Nano-Bio-Info”

Tables, formulae, etc.

“If it moves, it’s Mechanical,if it doesn’t move, it’s Civil,and If you can’t see it, it’s Electrical”

The era of science-basedengineering

We are entering an era of integrated science &engineering, during whichthe boundaries of the disciplines will grow increasingly indistinct

Engineering disciplines

Engineering disciplines

Sciences

Engineering

Science

?Taken from Tim Sands, Prof. UC. Berkeley

This approach is driven by the understanding that ME is founded in and perpetuated through the innovation and creation of products and therefore ME students should be able to apply learned concepts and make real-world connections.

Product Realization in Mechanical Engineering

“The key to 21st century competitive advantage will be the development of products with increasing levels of functionality.“Smart Materials” will play a critical role in this development, where we define these as materials that form part of a smart structural system that has the capability to sense its environment and the effects thereof and, if truly smart, to respond to that externalstimulus via an active control mechanism.”

“Smart Materials for the 21st century” a publication of the Institute of Materials, Minerals and Mining (IOM3) http://www.iom3.org/foresight/Smart%20materials%20web.pdf

DesignTransformation of concepts and ideas into useful machinery.

MachineCombination of mechanisms and other components that transforms, transmit or uses energy, load or motion for a specific purpose

Design of Machine ComponentFundamental practice in engineering.

Code of Ethics for Engineers (ASME 1997)“Engineers shall hold paramount the safety, health and welfare ofthe public in the performance of their professional duties”

Product Scope and Characteristics

http://www.prz.tu-berlin.de/~www-kt/lehre/hs/ed/dokumente_ed_vl/2005,WS,ED,VL-01.Termin,Vortrag.pdf

Design• A design must be:

– Functional- fill a need or customer expectation– Safe- not hazardous to users or bystanders– Reliable- conditional probability that product will perform

its intended function without failure to a certain age.– Competitive- contender in the market– Usable- accommodates human size and strength– Manufacturable- minimal number of parts and suitable for

production– Marketable- product can be sold and serviced

Effects of Manufacturing and Assembly

Design of a Reciprocating Power Saw: Effects on Manufacturing and Assembly

(1) Original Design: 41 parts, assembly time: 6:37min.(2) Modified Design: 29 parts, assembly time: 2:58min. (Boothroyd 1992)

Approaches to Product

Development

(a) Over-The-Wall Engineering Approach (from Kalpakjian[1997]).(b) Concurrent Engineering Approach (adapted from Pugh [1996]).

Over-the-Wall (OTW)One designer applies his/her particular skill and send it OTW to the next step in development. If a problem is discovered, for example in manufacturing, the product is send back to be redesigned.

The design is sent to The design is sent to the manufacturerthe manufacturer

In manufacturing: an Engineer must first design something.an Engineer must first design something.

The design phaseThe design phaseFor every design there For every design there is eventually a is eventually a manufacturing phasemanufacturing phase

Design Manufacture

In practice, the design may well be impossible to manufacture.In practice, the design may well be impossible to manufacture.

Concurrent Engineering Approach

Philosophy of involving many disciplines from the beginning of adesign effort and keeping them involved throughout product development.

Design is a multidisciplinary endeavor

Boeing 747 being manufactured in Seattle

Examples of Examples of manufacturingmanufacturing

Boeing 777

One of the first examples of Concurrent Engineering

Design Methodology: what engineers do

Define the functioncomponent to carry a load

Material Selection Component Design

Tentative component design

Approximate stress analysis

Tentative choice of material

Assemble Materials Data

Analysis of Materials Performanceiterate

from Ashby and Jones; Engineering Materials 2

Detailed Specifications and Design

Choice of Production Methods

Prototype Testing

Establish Production

Further Development

iterate

iterateiterate

Example: A Cantilever

• This Cantilever Stand is intended for moderate to heavy-duty use with either the Frontier III or Glas-Hide Boards in certain lengths on residential pools. There are no unusual climatic restrictions for this stand's use.

Look at the Engineering Science of this design scheme:

Define the functioncomponent to carry a load

Material Selection Component Design

Tentative component design

Approximate stress analysis

Tentative choice of material

Assemble Materials Data

End Load

Uniform Distribution

End Moment Intermediate Load

Triangular Distribution

Choose materials for components from metals, ceramics, plastics, composites?

Assemble Materials Data?Cost, density, elastic properties, yield

stress, hardness, tensile stress, strength to weight ratio, ductility, fracture toughness, fatigue stress, thermal expansion coefficient, thermal conditioning, specific heat, thermal shock resistance, creep, oxidation/corrosion rates

Codes and Standards• Code- a set of specifications for the analysis, design, manufacture,

and construction of something• Standard- a set of specifications for parts, materials, or processes

intended to achieve uniformity, efficiency, and a specified quality

Product Liability• “Strict liability” concept prevails in the U.S.

– Manufacturers are liable for any damage or harm that results from a defect.

OrganizationsAluminum Association (AA)American Gear Manufacturers

Association (AGMA)American Institute of Steel

Construction (AISC)American Iron and Steel Institute

(AISI)American National Standards

Institute (ANSI)American Society for Metals

(ASM)American Society of Mechanical

Engineers (ASME)American Society of Testing

Materials (ASTM)American Welding Society (AWS)

American Bearing Manufacturers Association (ABMA)

British Standards Institute (BSI)Industrial Fasteners Institute (IFI)Institution of Mechanical

Engineers (I. Mech. E.)International Bureau of Weights

and Measures (BIPM)International Standards

Organization (ISO)National Institute for Standards

and Technology (NIST)Society of Automotive Engineers

(SAE)American Society of Agricultural

and Biological Engineers (ASABE)

Design Philosophy

Also check deflection!!Also check deflection!!

Design•If the load is known and the geometry is specified, determine the material and the safety factor. • If the load is known and the material is specified, determine the safety factor and the geometry (dimensions).

Analysis•If the load is known and the material and geometry are specified, determine the safety factor – Is it safe??

Critical Section

The critical section is the location in the design where the largest internal stress is developed and failure is most likely.

In general, the critical section will often occur at locations of geometric non-uniformity, such as where a shaft changes its diameter along a fillet.

Safety Factors

•N = 1.25 to 2.0 Static loading, high level of confidence in all designdata

•N = 2.0 to 2.5 Dynamic loading, average confidence in all designdata

•N = 2.5 to 4.0 Static or dynamic with uncertainty about loads,material properties, complex stress state, etc…

•N = 4.0 or higher Above + desire to provide extra safety

FOR DUCTILE MATERIALS:

Uncertainty• Stochastic Design Factor Method- uncertainty in stress

and strength is quantified for linearly proportional loads

Stress AverageStrength Average

==σsnd

Measures of Strength

• S – Strength• Ss – Shear Strength• Sy – Yield Strength• Su – Ultimate Strength• - Mean StrengthS

Measures of Stressτ – Shear Stressσ – Normal Stressσ1 – Principal Stressσy – Stress in y-directionσr – Radial Stressσt – Tangential Stress

Stress Allowable (AISC)• Tension: 0.45 Sy ≤ σall ≤ 0.60 Sy

• Shear: τall = 0.40 Sy

• Bending: 0.60 Sy ≤ σall ≤ 0.75 Sy

• Bearing: σall = 0.90 Sy

SUGGESTED SAFETY (DESIGN) FACTORS FOR ELEMENTARY WORKbased on yield strength - according to Juvinall & Marshek op cit.

1.25 - 1.5 for exceptionally reliable materials used under controllable conditions and subjected to loads and stresses that can be determined with certainty - used almost invariably where low weight is a particularly important consideration

1.5 - 2 for well-known materials under reasonably constant environmental conditions, subjected to loads and stresses that can be determined readily.

2 - 2.5 for average materials operated in ordinary environments and subjected to loads and stresses that can be determined.

2.5 - 3 for less tried materials or for brittle materials under averageconditions of environment, load and stress.

3 - 4 for untried materials used under average conditions of environment, load and stress. It should also be used with better-known materials that are to be used in uncertain environments orsubject to uncertain stresses.

Repeated Cyclic loads : the factors established above are acceptable but must be applied to the endurance limit (ie. a fatigue strength ) rather than to the yield strength of the material.

Impact forces : the factors given above are acceptable, but an impact factor (the above dynamic magnification factor ) should be included.

Brittle materials : the ultimate strength is used as the theoretical maximum, the factors presented above should be doubled. Where higher factors might appear desirable, a more thorough analysis of the problem should be undertaken before deciding on their use.

Need to take into account the statistical nature of materials properties