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Course Description (catalog):
• MCE 321 Mechanical Design I (3-0-3). Examines properties of ductile and brittle materials. Explores the concepts of stress, strain and deformation analysis of solid elements as applied to mechanical design, and the analysis of long and intermediate compression members. Includes design to prevent static and fatigue failures. Covers the design of mechanical elements, including power screws, bolted and welded joints and mechanical springs.
Course Description
MCE 321 Mechanical Design I (3-0-3).
• Introduction and overview of materials related topics
• Load and stress analysis
• Deflection and Stiffness
• Failure theories: – Steady loading
– Variable loading
• Screws, fasteners and connections
• Welded, brazed, and bonded joints
• Mechanical Springs
Course Description (catalog):
• MCE 322 Mechanical Design II (3-0-3). Covers the design of clutches, brakes and couplings; power transmission equipment (shafts, axles and spindles); flexible mechanical elements (flat and V-belts, wire ropes and chains); rolling and journal bearings; spur, helical, bevel and worm gears; and utilization of commercial computer-aided design software. Requires a design project.
Course Description
MCE 322 Mechanical Design II (3-0-3).
• power transmission equipment (shafts, axles and spindles);
• rolling and journal bearings;
• spur, helical, bevel and worm gears;
• clutches, brakes and couplings;
• flexible mechanical elements (flat and V-belts, wire ropes and chains);
Good to know…
• Instructor: Dr. Lotfi Romdhane
• Email: [email protected]
• Office: EB2-207
• Phone: 06 515 2497
• Class 01: 09:30 am 10:45 am MTWRU
• Room: EB2-109
• Office hours: 11:00 - 12:00 UTR and by appointment
Course Related Information [Cntd.]
• Textbook: Shigley, J.E., Mischke, C.R., Budynas, R.G., Mechanical Engineering Design, 10th edition in SI units, 2014, McGraw-Hill, New York.
• Handouts will be uploaded on iLearn
• The class has a website on iLearn, use it, it will contain all the documents related to the course
• Homework solutions will be posted on iLearn
• Grades will be maintained online on iLearn
• Syllabus might get updated as we go and will contain info about
– Topics covered
– Homework assignments
– Midterm exam date
• Syllabus available at the course website
Grading:
• All submissions are through iLearn, each as a single PDF file, no paper submission is accepted
• No late homework is possible (the submission link disappears automatically after the due date)
Midterm exam 1
Midterm exam 2
Final exam
22.5 %
22.5 %
30 %
(Wednesday June 22, 2016)
(Sunday July 3, 2016)
Project
HW
Quizzes
and attendance
10 %
5 %
10 %
Due July 14, 2016
Final Project
• A topic will be assigned to your group.
• The project requires the use of the “design accelerator” toolbox under Inventor.
• Team size: 3 members.
• Use iLearn to show your progress
Design
• Design is an innovative and highly iterative process. It is also a decision-making process.
• Decisions sometimes have to be made with limited information, occasionally with just the right amount of information, or with an excess of partially contradictory information.
• Engineers have to communicate effectively and work with people of many disciplines.
• Engineering tools (such as mathematics, statics, computer graphics, and languages) are combined to produce a plan 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.
Mechanical Engineering
Mechanical engineering design involves all disciplines of mechanical engineering. • A simple journal bearing involves fluid flow, heat transfer, friction,
energy transport, material selection, thermomechanical treatments, statistical descriptions, and so on.
• A building is environmentally controlled. The heating, ventilation, and air-conditioning considerations are sufficiently specialized that some speak of heating, ventilating, and air-conditioning design as if it is separate and distinct from mechanical engineering design.
• Similarly, internal-combustion engine design, turbomachinery design, and jet-engine design are sometimes considered discrete entities.
The big picture
Mechanics
Statics Dynamics
kinematics Kinetics
Motion
Motion and forces
Change
with time Time not a
factor
rigid bodies
Mechanics of
material
forces Stress and
deformation
Design process
Design process is a collection of procedures and habits that help teams design better products
The Design Process
• Designing is the process of making many decisions that converts an abstract concept into a hardware reality.
Concept Product
http://cct2.edc.org/imagination_place/guide/design.htm
The engineering design process involves a series of steps that lead to the development of a new product or system. The designer should be able to do the following:
• STEP 1: Identify the Problem – the designer should state the challenge problem in their own words. Example: How can I design a __________ that will __________?
• STEP 2: Identify Criteria and Constraints
• STEP 3: Brainstorm Possible Solutions
• STEP 4: Generate Ideas
• STEP 5: Explore Possibilities
• STEP 6: Select an Approach
• STEP 7: Build a Model or Prototype
• STEP 8: Refine the Design
Engineering Design Process
Standard Design Process
• The complete design process from start to finish, is often outlined as in the figure.
• Begins with an identification of need and a decision to do something about it.
• After many iterations, the process ends with the presentation of the plans for satisfying the need.
• Several design phases may be repeated throughout the life of the product.
Concurrent Engineering*
Introduction
Design Considerations
• Functionality • Strength/stress • Distortion/deflection/stiffness • Wear • Corrosion • Safety • Reliability • Manufacturability • Utility • Cost • Friction • Weight • Life • Noise
• Styling • Shape • Size • Control • Thermal properties • Surface • Lubrication • Marketability • Maintenance • Volume • Liability • Remanufacturing/resource
recovery
The Design Engineer’s Responsibilities
• In general, design engineering is required to satisfy the needs of customers ( management, clients, consumers, etc. ) and is expected to do so in a competent, responsible, ethical, and professional manner.
• Careful attention to the following action steps will help you organize your solution processing technique. Understand the problem.
Identify the known.
Identify the unknown and formulate the solution strategy.
State all assumption and decision.
Analyze the problem.
Evaluate your solution.
• The design engineer’s professional obligations include conducting activities in an ethical manner.
Standards and Codes
• A standard is a set of specifications for parts, materials, or processes intended
to achieve uniformity, efficiency, and a specified quality.
• A code is a set of specifications for the analysis, design, manufacture, and
construction of something.
• Standard means 'the usual way' and code is a very strict, specific way
• All of the organizations and societies listed below have established
specifications for standards and safety or design codes.
• Aluminum Association (AA) • American Gear Manufacturers Association
(AGM) • American Institute of Steel Construction (AISC) • American Iron and Steel Institute (AISI) • American National Standards Institute (ANSI) • ASM International • American Society of Mechanical Engineers
(ASME) • American Society of Testing and Material
(ASTM) • American Welding Society (AWS) • American Bearing Manufactures 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)
Cost and Design
Costs to implement changes increase exponentially as the project lifetime increases
• 80% of the final cost is decided in the early stages of the design process
It is easier to reduce the cost in the early stages of the design process
Economics
• The consideration of cost plays an important role in the design decision process.
• The use of standard or stock sizes is a first principle of cost reduction.
• Among the effects of design specifications on costs, tolerances are perhaps most significant.
• When two or more design approaches are compared for cost, there occurs a point corresponding to equal cost, which is called the breakeven point.
Stress and Strength
• The survival of many products depends on how the designer adjusts the maximum stresses in a component to be less than the component’s strength at specific locations of interest.
• Strength is a property of a material or of a mechanical element. The strength of an element depends on the choice and the processing of the material.
• Stress is a state property at a specific point within a body, which is a function of load, geometry, temperature, and manufacturing processing.
• We shall use the capital letter S to denote strength, the Greek letters σ (sigma) and 𝜏 (tau) to designate normal and shear stresses, respectively.
Uncertainty
• Examples of uncertainties concerning stress and strength include 1. Composition of material and the effect of variation on properties.
2. Variations in properties from place to place within a bar of stock.
3. Effect of processing locally, or nearby, on properties.
4. Effect of nearby assemblies such as welds and shrink fits on stress conditions.
5. Effect of thermomechanical treatment on properties.
6. Intensity and distribution of loading.
7. Validity of stress concentrations.
8. Influence of time on strength and geometry.
9. Effect of corrosion.
10. Effect of wear.
• Engineers must accommodate uncertainty.
Reliability
• The reliability method of design is one in which we obtain the distribution of stresses and the distribution of strengths and then relate these two in order to achieve an acceptable success rate.
• The reliability R can be expressed by a number having the range
0 < 𝑅 < 1
• In the reliability method of design, the designer’s task is to make a judicious selection of materials, processes, and geometry (size) so as to achieve a specific reliability goal.
• It is important to note that good statistical data and estimates are essential to perform an acceptable reliability analysis.
Dimensions and Tolerances
• Nominal size – The size we use in speaking of an element. – Is not required to match the actual dimension
• 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, e.g. 1.005 ± 0.002 𝑖𝑛. Unilateral tolerance – The basic dimension is taken as one of
the limits, and variation is permitted in only one direction, e.g. 25−0.00
+0.05 𝑚𝑚
Dimensions and Tolerances
• Clearance – Refers to the difference in sizes of two mating cylindrical parts such as a bolt and a hole. – Assumes the internal member is smaller than the external member – Diametral clearance – difference in the two diameters – Radial clearance – difference in the two radii
• Interference – The opposite of clearance, when the internal member is larger than the external member
• Allowance – The minimum stated clearance or the maximum stated interference or mating parts
• Fit – The amount of clearance or interference between mating parts • GD&T – Geometric Dimensioning and Tolerancing, a comprehensive
system of symbols, rules, and definitions for defining the theoretically perfect geometry, along with the allowable variation.
Choice of Tolerances
• The designer is responsible for specifying tolerances for every dimension.
• Consideration is given to functionality, fit, assembly, manufacturing process ability, quality control, and cost.
• Excessive precision is a poor design choice, in that it limits manufacturing options and drives up the cost.
• Less expensive manufacturing options should be selected, even though the part may be less than perfect, so long as the needs are satisfactorily met.
Choice of Dimensions
• Dimensioning a part is the designer’s responsibility. • Include just enough dimensions • Avoid extraneous information that can lead to confusion or multiple
interpretations. • Example of over-specified dimensions. With +/– 1 tolerances, two
dimensions are incompatible.
Choice of Dimensions
• Four examples of which dimensions to specify
Tolerance Stack-up
The cumulative effect of individual tolerances must be allowed to accumulate somewhere. This is known as tolerance stack-up. • Chain dimensioning allows
large stack-up of many small tolerances in series.
• Baseline dimensioning minimizes large tolerance stack-up.
Shigley’s Mechanical Engineering Design
Example 1–3
Example 1–7 (Continued)
Solution
Answer
Answer
Units
• In the symbolic units equation for Newton’s
second law, 𝐹 = 𝑚𝑎. Units chosen for any three
of these quantities are called base units.
• The International System of Units (SI) is an
absolute system. The base units are the meter,
the kilogram (for mass), and the second.
Table 1.4
Common Engineering Design Conversion Factors
Given Multiply by To Find
Length [L]
Foot (ft) 0.304800 Meter (m)
Inch (in) 25.4000 Millimeter (mm)
Mile (mi) 1.609344 Kilometer (km)
Area [L]2
ft2 0.092903 m2
in2 645.16 mm2
in2 6.45160 cm2
Volume [L]3 & Capacity
in3 16.3871 cm3
ft3 0.028317 m3
ft3 7.4805 Gallon
ft3 28.3168 Liter (l)
Gallon 3.785412 Liter
Energy, Work or Heat [M] [L]2 [t]-2
Btu 1.05435 kJ
Btu 0.251996 kcal
Calories (cal) 4.184* Joules (J)
ft-lbf 1.355818 J
ft-lbf 0.138255 kgf-m
hp-hr 2.6845 MJ
KWH 3.600 MJ
m-kgf 9.80665* J
N-m 1. J
Common Engineering Design Conversion Factors
Given Multiply by To Find
Force or Weight [M] [L] [t]-2
kgf 9.80665* Newton (N)
lbf 4.44822 N
lbf 0.453592 Kgf
Fracture Toughness
ksi sqr(in) 1.098800 MPa sqr(m)
Mass Density [M] [L]-3
lbm/in3 27.68 g/cm3
lbm/ft3 16.0184 kg/m3
Power [M] [L]2 [t]-3
Btu/hr 0.292875 Watt (W)
ft-lbf/s 1.355818 W
Horsepower (hp) 745.6999 W
Horsepower 550.* ft-lbf/s
Stress [M] [L]-1 [t]-2
kgf/cm2 9.80665 E-2* MPa
ksi 6.89476 MPa
N/mm2 1. MPa
kgf/mm2 1.42231 ksi
http://www.engineershandbook.com/Tables/conversionfactors.htm
Significant Figures • The number of significant figures is usually inferred by the number of
figures given (except for leading zeros). For example, 706, 3.14, and 0.00219 are assumed to be numbers with three significant figures.
• To display 706 to four significant figures, insert a trailing zero and display either 706.0, 7.060 × 102, or 0.7060 × 103.
• Computers and calculators display calculations to many significant figures. However, you should never report a number of significant figures of a calculation any greater than the smallest number of significant figures of the numbers used for the calculation.
• For example, determine the circumference of a solid shaft with a diameter of 𝑑 = 11 𝑚𝑚. The circumference is given by 𝐶 = 𝜋𝑑. Since 𝑑 is given with two significant figures, 𝐶 should be reported with only two significant figures.
• If you have a series of calculations you should keep all the figures until the final calculation and round at the end
• We usually use at least 3 significant figures to represent physical quantities, example: 𝑔 = 9.81 𝑚/𝑠2, 𝐸𝑠𝑡𝑒𝑒𝑙 = 207 𝐺𝑃𝑎, …
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