Mechanical Design
机械设计
About this course：
（1）A total of 48 classes：32 classes teaching and 16 classes project design
（2）Will have test at the end of the course.
（3）Two scores at the end of the semester:
Course for ”Mechanical Design“=
70%test+20%presentation（2 presentations）+10%attendance
Course for “project design” =The quality of the Design Report
Bing Zhang
College of Mechanical Engineering Yangzhou University
Email: bingzhang2021@yzu.edu.cn
Mechanical Design
机械设计
Chapter 1 Introduction to Mechanical Design
第一章 绪论
1. The backgrounds and needs of Mechanical Design
Vehicles
Engineering trucks
Industrial production
Weapons
Aircrafts
Mechanical Design
1. The backgrounds and needs of Mechanical Design
Parts manipulation
Mechanical reducer
Slider motion system
The functions and applications of machines need
a well designed mechanical system
automobiles
Mechanical Design
1. The backgrounds and needs of Mechanical Design
Mechanical Design Frontier
Mechanical Design
1. The backgrounds and needs of Mechanical Design
Mechanical Design Frontier
Mechanical spiders
Smart insect
Mechanical Design
crawling robot
2. Introduction of Design
机械原理
机械设计
机械：machinery
原理：theory; principle
机械
machinery
Theory of machines and
mechanisms
Mechanical Design
机械：machinery
设计：design
机构: mechanism
机器: machine
Design of machines and
mechanisms
2.1 Main contents of:
Mechanical Design
1. Basic knowledge about Mechanical Design: selection of materials; working stresses and
fatigue（工作应力与疲劳/失效）; friction（摩擦）; lubrication（润滑）, etc.
2. Connections: screw joint（螺纹连接）; splined joint（花键连接）; key /no key links(键/无
键连接); pin joint（销连接）
3. Transmission part: screw drive（螺旋传动）; belt drive （带传动）; chain drive（链传
动） ；gear transmission（齿轮传动）；worm gear（蜗杆传动）；friction gearing（摩擦轮
传动）
4. Shafts and associated parts: journal sliding bearing（径向/滑动轴承）; rolling bearing（滚动
轴承）; Shaft coupling（联轴器）; clutch（离合器）
5. Others：spring（弹簧）；transmission（变速器）；housing（箱体）
Mechanical Design
Classification of machine elements
Normal load transmitter: sliding bearings, rolling-element bearings
Torque transmitter: gears, traction drives, chain drives, belt drives, power screws
/to:k/
Energy absorber: brakes and dampers
Supporting elements: shafts, springs, seals(密封件)
Connection and joints: thread fasteners（螺纹紧固件）, keys, couplings联轴器
Classification of machine elements
internal spline
external spline /splaɪn/花键
bearings
pin joint
screw
key link
Mechanical Design
shaft coupling
clutch
Classification of machine elements
chain
springs
belt
gears
shaft
Mechanical Design
Typical machines
2.2 The Design Process
Recognize
the need
Create a
design
Prepare
a model
Test and
evaluate
the model
Communicate
the design
Improve the design
1. Definition of the problem by stating the given quantities（数量）and appropriate
assumptions.
2. Preliminary design decisions and sketches.
3. Mathematical models, detailed design analysis, and evaluation.
4. Documentation of results and comment about the solution.
Mechanical Design
Engineering and the Engineering Design Process
https://www.youtube.com/watch?v=nMwG1wnESDA
2.3 The Design Analysis
1. The engineering modelling: geometric modelling is
(1) Structure is simple enough: theoretical solutions for basic configurations may be
adequate for obtaining the stresses involved.
(2) For more complicated structures: finite-element models not only can estimate the
stresses but also utilize them to evaluate the failure criteria for each element in a
member.
2. Rational理性 design procedure: to meet the strength requirements, tension,
compression, fatigue, all complicated and involved situations…
3. Methods of analysis:-mechanics of materials-the basic principle of analysis can be
summarized as follows:
(1) Statics. The equations of equilibrium（平衡， ˌiːkwɪˈlɪbriəm） must be satisfied.
(2) Deformations（变形）. Stress-strain or force-deformation relations (e,g., Hooke’s
law) must apply to the behavior of materials.
(3) Geometry. The conditions of compatibility of deformations must be satisfied; that is,
each deformed part of the member must fit together with adjacent（临近的） parts.
Mechanical Design
2.4 Computer tools
A wide variety of computational tools can be used to perform design calculations
with success.
Mathematical Software Packages: MATLAB,…
Computer Aided Design (CAD): AutoCAD, Pro E, UG, Solidworks, Catia,…
Finite Element Analysis (FEA:): Ansys, Abaqus, ...
Dynamic Simulation Software: Adams,…
Professional Simulation Software: Kisssoft, Masta, Romax,…
Mechanical Design
2.4 Computer tools
Mechanical Design
2.4 Computer tools
Top 10 Software for Mechanical Engineers
https://www.youtube.com/watch?v=KQjXs9iXa38
Mechanical Design
2.5 Fundamental design considerations
1 Strength
2 Reliability（可靠性）
4 Corrosion（腐蚀）
5 Wear(磨损)
6 Friction（摩擦）
7 Processing
8 Utility功用
9 Cost
10 Safety
11 Weight
12 Noise
13 Styling
14 Shape
15 Size
16 Flexibility
17 Control
18 Stiffness
19 Surface finish
20 Lubrication
21 Maintenance保养
22 Volume
Mechanical Design
3 Thermal effect（热效应）
3. Basic Requirements for Machine Design
◼ Economics and functionality are always pressing concerns,
and good design inherently means safe, economical, and
functional design.
◼ A primary responsibility of any mechanical designer is to
ensure that the proposed design will function as intended,
safely and reliably, for the prescribed design lifetime and, at
the same time, compete successfully in the marketplace.
Mechanical Design
3.1Functional Requirements
The machine to be designed should fulfill specified functions.
This requires:
Fundamental decisions regarding loading, kinematics, and the
choice of materials must be made properly during the design of a
machine.
Besides, strength, reliability, deformation, tribology (friction,
wear, and lubrication), also need to be considered.
Mechanical Design
3.2 Economic Demands
The objective is to produce a machine that not only is to
function properly for a reasonable time but is also economically
feasible.
The economic requirements need to be addressed over the
entire life circle of design, manufacturing and operation of the
product.
Functional demands and economic demands are generally
contradictory（对立的）.
Mechanical Design
3.3 Other Demands
Safety, labor protection requirements, reliability requirements
and space requirements, convenience in transportation also
need to be considered.
Non-engineering decisions regarding marketability 适 销 性 ,
product liability产品责任, ethics伦理道德, politics政治, etc.,
must be integrated into the design process early.
Mechanical Design
4. Contents and Purpose of the Course
Fundamental design principles of various machine elements.
Even the design of a single bolt螺栓 or spring弹簧 needs the
designer’s thorough understanding of the principles and
methods of machinery design and more.
Master the basic knowledge, methods and procedures and
gain the competence in applying them into practical design.
Mechanical Design
4. Contents and Purpose of the Course
Develop competence of creative design and solving practical
problem
◆
Mechanical system design requires considerable 相 当 大 的
flexibility and creativity to obtain good solutions.
◆
Creativity seems to be aided by familiarity with known
successful designs of related systems, components or
elements.
Mechanical Design
5 Failure Prevention
the Basis for Successful Design of Machine Element
▪ Designer must have a good working knowledge of analytical
and/or empirical techniques for predicting potential failures at
the design stage.
▪ These predictions must then be transformed into selection of a
material, determination of a shape, and establishment of the
dimensions for each part to ensure safe, reliable operation
throughout the design lifetime.
Mechanical Design
5 Failure Prevention
Improper functioning of a machine or machine part constitutes
构成 failure.
When it becomes completely inoperable
When it is still operable but is unable to perform its intended
function satisfactorily
When serious deterioration(恶化) has made it unreliable or
unsafe for continued use.
When a mechanical part fails to work properly for some reason,
which is called failure
Mechanical Design
5.1 Failure Modes
Failure of a machine part might be brought about by any one
or a combination of many different responses to loads and
environments while in service.
1. Force - and/or temperature - induced elastic deformation
2. Yielding - plastic deformation
3. Brittle （脆性）fracture（断裂）; fatigue fracture
4. Surface failure - Wear, Fatigue, Galling （擦伤）,
Seizure（咬粘）, ductile rupture（韧性断裂）, Creep
（蠕变）, Brinnelling（微动磨损）, Corrosion（腐
蚀）, spalling（开裂）, Fretting （ 微振磨损）
5. Violation（违背） of its intended function - overall slip
of belt, Buckling（屈曲） of spring
Mechanical Design
5.1 Failure Modes
Failure Modes of a Shaft 轴
▪ Fatigue fracture/
for common shaft
▪ Excessive elastic deformation/
for precision shaft （精密轴）
▪ Resonant vibration / （共振）
for rotating shaft at high speed
5.2 Factor of safety
Basic definition
The factor of safety, S, is the ratio of the maximum load that produces failure
of the member to the load allowed under service conditions:
S=
failure load
allowable load
The allowable load is also referred to as the service load or working load.
This ratio must always be greater than unit:
S 1
Mechanical Design
A common definition
A common method of design is to use a safety factor with respect to strength
of member. In most situations, a linear relationship exists between the load
and stress produced by the load. Then, the factor of safety may also be
defined as:
S=
material strength
allowable stress
The material strength represents either static or dynamic properties, if
loading is static, the material strength is either the yield strength or the
ultimate strength. For fatigue loading, the material strength is based on the
endurance limit. The allowable stress is also called the applied stress,
working stress, or design stress.-the required strength
Mechanical Design
Stress-strain Diagram
Stress-strain diagram
Mechanical Design
6. Some Terminology Concerning Machine Design
▪ 1) Codes and Standards规范和标准
▪ 2) Reliability可靠性
▪ 3) Safety and Product Liability责任
Mechanical Design
6.1 Codes and standards
Numerous engineering societies
and
organizations
publish
standards and codes for specific
areas of engineering design.
Most
are
merely
recommendations, but some
have the force of law. For the
majority of applications, relevant
factors of safety are found in
various
construction
and
manufacturing codes. Factors of
safety are usually embodied into
computer programs for the
design of specific members.
Mechanical Design
6.2 Reliability
The concept of reliability is closely related to the factor of safety. Reliability is the
probability that a member or structure will perform without failure a specific function
under given conditions for a given period of time. It is very important for the designer
and the manufacturer to know the reliability of the product. The reliability R can be
expresses by a number that has the range:
0  R 1
For instance, reliability of R=0.98 means that there is 98% chance（probability）,
under certain operating conditions, that the part will perform its proper function
without failure; that is, if 100 parts are put into service and an average of 2 parts fail,
then the parts proved to be 98% reliable.
Mechanical Design
6.3 Safety and Product Liability（产品法律责任）
▪ Liability concept states that the manufacturer of a machine is
liable for any damage or harm that results because of a defect.
▪ The best approaches to the prevention of product liability are
good engineering in all analysis and design, quality control,
and comprehensive testing procedures.
Mechanical Design
7 Failure Modes of a gear（齿轮）
1） Stress concentration factors
2） Contact stress distributions
3） Scuffing擦伤，磨损，胶合
Mechanical Design
7.1 Stress concentration factors
轮齿折断：一般发生在齿根部分（齿
根弯曲应力最大，且有应力集中）。
Teeth broken: big bending stress,
Stress concentration
Mechanical Design
Stress Concentration
◆
Stress concentration is caused by discontinuity in a
machine element.
◆
Discontinuities include changes in the cross section of the
parts, holes, grooves凹槽, notches槽口, etc..
◆
Such discontinuities are called stress raisers应力集中处.
Mechanical Design
7.2 Contact stress distributions
齿面点蚀：在载荷多次的重复作用下，
齿面会产生细微的疲劳裂纹，慢慢裂纹
蔓延扩展使齿面微粒脱落形成点蚀。
Pitting and peeling: repeated loading,
fatigue crack, particles shedding
Mechanical Design
7.2 Contact stress distributions
Mechanical Design
7.3 Scuffing（磨损）
齿面胶合：在高速、重载传动
中，因摩擦发热导致齿面金属直
接接触产生粘连，齿面材料发生
移动的现象。
在低速、重载，两啮合齿面间
的润滑油膜不易形成，也容易产
生胶合。提高齿面硬度和减小齿
Scuffing: high speed, heavy loading,
frictional heating, no lubricant film,
metal bonding
Mechanical Design
面表面粗糙度可增强齿面抗胶合
能力。
8 Finite Element Analysis
Finite element analysis (FEA) is a computerized method for
predicting how a product reacts to real-world forces, vibration,
heat, fluid flow, and other physical effects. Finite element
analysis shows whether a product will break, wear out, or work
the way it was designed. It is called analysis, but in the product
development process, it is used to predict what is going to
happen when the product is used.
Mechanical Design
8 Finite Element Analysis
Mechanical Design
Examples
Mechanical Design
The Multibody Dynamics Simulation
As the world's most famous and widely used Multibody
Dynamics (MBD) software, Adams improves engineering
efficiency and reduces product development costs by enabling
early system-level design validation. Engineers can evaluate and
manage the complex interactions between disciplines including
motion, structures, actuation, and controls to better optimize
product designs for performance, safety, and comfort.
Mechanical Design
The Multibody Dynamics Simulation Solution
Mechanical Design
The Multibody Dynamics Simulation Solution
Mechanical Design
The Multibody Dynamics Simulation Solution
Mechanical Design
The Multibody Dynamics Simulation Solution
Mechanical Design
The Multibody Dynamics Simulation Solution
steering
Satellites extend solar panels
Excavator /ˈekskəveɪtə(r)/ 挖掘机 through obstacle
The moving system of a car
The internal movement of combustion engine
Example：Nonlinear Finite Element Analysis - Ansys analysis (bolted joint)
https://www.youtube.com/watch?v=IYGdyTttcOg
Mechanical Design
9. Basic requirements of designing
mechanical parts
Avoid failure within the predetermined life span避免在预定寿命期内失效
Processability of product structure结构工艺性
Economic requirement经济性要求
Lightweight轻量化要求
Reliability requirements可靠性要求
9.1 Avoid failure within the predetermined life span
避免在预定寿命期内失效
Parts should have sufficient strength, stiffness and life.强度、刚
度、寿命
Strength requirements:
✓ Use high strength materials
✓ Make the parts have enough cross section size界面尺寸
✓ Rationally design the section shape of the part and increase the moment
carbonizing phosphorization
of inertia
✓ Heat treatment and chemical treatment are used to improve the strength
shot blasting
properties of the materials
✓ Improve the manufacturing precision of parts to reduce the dynamic load
during work
✓ Reasonable configuration of the relative position of the parts to reduce
the load of the parts
9.1 Avoid failure within the predetermined life span
避免在预定寿命期内失效
Stiffness requirements:
The elastic deformation of a part at work cannot exceed the allowable range ,
which is known as the stiffness requirement of the part.
✓ Increase the section size of the part or the moment of inertia;增大零件的
截面尺寸或增大惯性矩；
✓ Shorten the span of the support or adopt multi-point support.缩短支承的
跨距或采用多点支承。
9.1 Avoid failure within the predetermined life span
避免在预定寿命期内失效
Life requirements:
The main factors affecting the life of parts are fatigue failure, corrosion
and wear.
Fatigue failure疲劳失效: Most parts work under variable stress, so fatigue
failure is the main cause of part failure. Factors affecting fatigue strength
include stress concentration, part size, part surface quality, and
environmental conditions
Corrosion腐蚀: The parts may be corroded when working in corrosive
medium. Corrosion resistance measures include surface flange, surface
coating, surface anodization, etc.
9.2 Processability of product structure结构工艺性
Mark of good manufacturability of parts - in specific production
conditions, parts to facilitate processing and processing costs
are very low.零件工艺性良好的标志——在具体的生产条件下，零件要
便于加工而加工费用又很低。
(1)The blank selection is reasonable. Preparation methods:
Profile, casting, forging, stamping and welding, etc.制备方
法：选用型材、铸造、锻造、冲压和焊接等。
(2)Simple and reasonable structure结构简单合理
(3)Reasonable manufacturing accuracy and surface
roughness合理的制造精度和表面粗糙度
(4)Minimize the amount of parts processed尽量减小零件的加工
量
9.2 Processability of product structure结构工艺性
Economic requirement 经济性要求
Lightweight 轻量化要求
Reliability requirements 可靠性要求
10 Courses learnt before this course
工程制图：设计的图形表达。Engineering drawing: The graphical representation of a design.
工程材料：非金属材料、金属材料及热处理。Engineering materials: non-metallic materials, metallic
materials and heat treatment.
机械制造基础：冷加工工艺，热加工工艺。Fundamental of Mechanical Manufacture: cold and hot
processing technology.
公差配合与技术测量：解决精度设计问题。Tolerance fit and technical measurement: solve the problem
of precision design.
理论力学：解决力分析与动力计算。Theoretical mechanics: Force analysis and dynamic calculation.
材料力学：解决强度分析问题。Mechanics of materials: Solving strength analysis problems.
机械原理：解决机械的方案设计。Mechanical principle: design of mechanical solutions.
Mechanical Design
Thanks for your attention!
Bing Zhang
College of Mechanical Engineering Yangzhou University
Email: bingzhang2021@yzu.edu.cn
Mechanical Design