Machine Component Design I (INME 4011) by
Pablo G. Caceres‐Valencia (B.Sc., Ph.D. U.K.)
GENERAL INFORMATION Course Number Course Title Credit Hours Instructor Office Office Hours e‐mail Web‐site
INME 4011 Machine Component Design I 3 Dr. Pablo G. Caceres‐Valencia Luccetti L‐212 Phone Ext. 2358 Tu‐Th from 7:30 to 10:45am
[email protected] http://academic.uprm.edu/pcaceres
Assessment The 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 100 – 90 89 – 80 79 – 70 69 – 60 59 ‐ 0
Final Letter Grade A B C D F
Attendance Attendance 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 to solve problems in class and for the pop‐quizzes. Please refer to the Bulletin of Information for Undergraduate Studies for the Department and Campus Policies.
Exams All 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.
Texbooks My 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.
TENTATIVES DATES Week
Week
09/13
Introduction to Design, Review Load, Stress, Strain.
09/20
Review Load, Stress, Strain. Q1
09/27
Basic Elasticity
10/04
Basic Elasticity. Q2
10/11
3D Stresses and Strains
10/18
Stress Concentration. Q3
10/25
Static Failure Theories Exam 1
11/01
Mid‐Term Project Presentation
11/08
Materials and Manufacturing Q4
11/15
Materials Selection /Fracture Toughness
11/22
Fracture Toughness Q5
11/29
Failure Prediction Cyclic & Impact
12/06
Failure Prediction Cyclic & Impact Q6
12/13
Failure Prediction Cyclic & Impact Q7 –Exam 2
12/20
Final Project Presentation Classes End
12/27
Final Project Presentation Classes End ‐ GRADES
01/10
Outcomes Upon 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 Engineering disciplines 1910 Quantum Mechanics
Tables, formulae, etc.
Sputnik
“If it moves, it’s Mechanical, if it doesn’t move, it’s Civil, and If you can’t see it, it’s Electrical”
Engineering disciplines
1960
Sciences
The era of science-based engineering
Information Technology Engineering “Nano-Bio-Info” 2010
Science ?
We are entering an era of integrated science & engineering, during which the boundaries of the disciplines will grow increasingly indistinct
Taken from Tim Sands, Prof. UC. Berkeley
Product Realization in Mechanical Engineering 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. “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 external stimulus 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
Design Transformation of concepts and ideas into useful machinery.
Machine Combination of mechanisms and other components that transforms, transmit or uses energy, load or motion for a specific purpose
Design of Machine Component Fundamental practice in engineering.
Code of Ethics for Engineers (ASME 1997) “Engineers shall hold paramount the safety, health and welfare of the 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.
In manufacturing: an Engineer must first design something. Design Manufacture The design phase
For every design there The design is sent to is eventually a the manufacturer manufacturing phase
In practice, the design may well be impossible to manufacture.
Concurrent Engineering Approach Philosophy of involving many disciplines from the beginning of a design effort and keeping them involved throughout product development.
Design is a multidisciplinary endeavor Examples of manufacturing Boeing 747 being manufactured in Seattle
One of the first examples of Concurrent Engineering
Boeing 777
Design Methodology: what engineers do from Ashby and Jones; Engineering Materials 2
Define the function component to carry a load
Example: A Cantilever
Material Selection
Component Design
Tentative choice of material
Tentative component design
Assemble Materials Data iterate
Approximate stress analysis Analysis of Materials Performance
iterate
Detailed Specifications and Design of Production Methods • This Cantilever StandChoice is intended for moderate to heavy-duty use iterate iterate with either the Frontier III or Glas-Hide Boards in certain lengths on Prototype Testing residential pools. There are no unusual climatic restrictions for this stand's use. Establish Production Further Development
Look at the Engineering Science of this design scheme: Define the function component to carry a load Material Selection
Component Design
Tentative choice of material
Tentative component design
Assemble Materials Data
Approximate stress analysis
Choose materials for components from metals, ceramics, plastics, composites? End Load Assemble Materials Data? Cost, density, elastic properties, yield stress, hardness, tensile stress, strength Uniform Distribution Triangular Distribution to weight ratio, ductility, fracture toughness, fatigue stress, thermal expansion coefficient, thermal conditioning, specific heat, thermal End Moment Intermediate Load shock resistance, creep, oxidation/corrosion rates
Product Liability • “Strict liability” concept prevails in the U.S. – Manufacturers are liable for any damage or harm that results from a defect.
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
Organizations Aluminum 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 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??
Also check deflection!!
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 FOR DUCTILE MATERIALS: •N = 1.25 to 2.0
Static loading, high level of confidence in all design data
•N = 2.0 to 2.5
Dynamic loading, average confidence in all design data
•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
Uncertainty • Stochastic Design Factor Method- uncertainty in stress and strength is quantified for linearly proportional loads
Average Strength nd = = Average Stress σ s
Measures of Strength
• • • • •
S – Strength Ss – Shear Strength Sy – Yield Strength Su – Ultimate Strength S - Mean Strength
Measures of Stress τ – Shear Stress σ – Normal Stress σ1 – Principal Stress σy – Stress in y-direction σr – Radial Stress σt – 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 WORK based 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 average conditions 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 betterknown materials that are to be used in uncertain environments or subject 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