1. Lectures 7 and 8 Machine elements D.Sc Harri Eskelinen
BK50A2200 Design Methodologies and Applications of Machine Element Design
Lectures 7 and 8
Machine elements
D.Sc Harri Eskelinen

2. Lecture 7 Machine elements Shaft-hub-joints D.Sc Harri Eskelinen
BK50A2200 Design Methodologies and Applications of Machine Element Design
Lecture 7
Machine elements
Shaft-hub-joints
D.Sc Harri Eskelinen

3. Feedback from exercise 5…
STRENGTH
WEAR
RELIABILITY
LIFETIME
Effecting compression
stress vs.
Materials
compression strength
Deformation of the geometry:
1. Changes of the motion
type
* Rolling vs. sliding
2. Changes of the active
wear phenomenon
* Adhesive vs. abrasive
Size of
The
Overlapping
area of
two
distributions
Contact geometry
between the outer/inner
ring of the bearing and
the ball (roller element)
1.Loading follows normal
Distribution.
2.Load bearing capacity
follows Weibull distribution.

4. MACHINE ELEMENTS Shaft-hub-joints
Main criteria dealing with lifetime evaluation
* Key aspects
Main criteria dealing with reliability
* Key aspects
Reliability level
should be
expressed with the
desired lifetime
Strength calculations form
the basis for lifetime evaluation
Wear rate is needed to
estimate the reliability level
Main criteria dealing with strength
* Key aspects
Main criteria dealing with wear
* Key aspects
Shaft-hub-joints
Wear decreases the
strength of the component

5. SHAFT KEYS Main criteria dealing with reliability
• starndardized dimensioning
• performance range
(= power transmission capacity)
- component failures
- loosening
• assembly errors
• consequences of the failure (fault tree analysis)
• dimensional tolerances
• key types
SHAFT KEYS
Main criteria dealing with strength
• surface pressure in the hub
• surface pressure on the shaft
• shear stress of the key
• combined loading cases
- axial forces
- torque
- dynamic loading
• stress concentrations of the shaft

6. SHAFT KEYS Main criteria dealing with reliability
• starndardized dimensioning
• performance range
(= power transmission capacity)
- component failures
- loosening
• assembly errors
• consequences of the failure (fault tree analysis)
• dimensional tolerances
• key types
SHAFT KEYS
Main criteria dealing with lifetime evaluation
• lifetime of the shaft is critical
- fatigue failure
Main criteria dealing with strength
• surface pressure in the hub
• surface pressure on the shaft
• shear stress of the key
• combined loading cases
- axial forces
- torque
- dynamic loading
• stress concentrations of the shaft
Main criteria dealing with wear
• possible fretting
• corrosion (material pairs)

7. SHAFT-HUB-JOINTS WITH CONICAL GEOMETRY
Main criteria dealing with lifetime evaluation
Main criteria dealing with reliability
CONICAL SHAFT AND HUB
Lifetime
•based on the lifetime
of the shaft
•Failure due to
overloading
Reliability
•utilization of fastening
screws or nuts
•distribution analysis of
torque transmission
ability Mv
•affecting axial loads
•loosering
CONICAL FASTENING RINGS
Main criteria dealing with strength
Main criteria dealing with wear
Strength
•Allowed stresses in each
component and stress
concentrations
Wear
•adhesive/abrasive wear
during opening and
tighting
•possible sliding
•corrosion
•fretting
FASTENING HUB WITH CONICAL STEPS INSIDE

8. Highlight! Importance of the:
Stress analysis of each component of the construction
Clearance and/or fit analysis
3) Reliability of power transmission capacity

9. Conical shaft-hub joint
Fastening hubs with
conical steps inside
Conical fastening rings
Spindle nut joints
Interference fit
shaft-hub joints
Splined shafts and hubs
Parallel shaft key joints
Tapered key joints
Woodruff key joints

10. Lecture 9 Machine elements Belt and chain drives D.Sc Harri Eskelinen
BK50A2200 Design Methodologies and Applications of Machine Element Design
Lecture 9
Machine elements
Belt and chain drives
D.Sc Harri Eskelinen

11. MACHINE ELEMENTS Belt and chain drives
Main criteria dealing with lifetime evaluation
* Key aspects
Main criteria dealing with reliability
* Key aspects
Reliability level
should be
expressed with the
desired lifetime
Strength calculations form
the basis for lifetime evaluation
Wear rate is needed to
estimate the reliability level
Main criteria dealing with strength
* Key aspects
Main criteria dealing with wear
* Key aspects
Belt and chain
drives
Wear decreases the
strength of the component

12. BELT DRIVES Main criteria dealing with strength Belt drives
• diameters of pulleys (wheels)
• distance between pulleys (shafts)
• angle of wrap of the pulley
(contact area covered by the belt
on the pulley)
• centrifugal force
• belt tensions due to torque
(driven vs. driving pulley)
• friction between the belt and
pulley
• intial tension
• belt cross-section
Belt drives
Timing belt drives
Flat belt drives
V-belt drives
Main criteria dealing with wear
• abrasive wear
• friction wear (abrasive wear)
• ageing
• surface failures of the belt
• chemical failures of the belt

13. BELT DRIVES Main criteria dealing with reliability
• standardized design
guidelines
• multiple belt drives
• proper belt drive type
- vee belt (v-belt)
- flat belt
- timing belt
• elastic creep of the belt
• friction and sliding
• power transmission
capacity
• adjusting the tension
BELT DRIVES
Main criteria dealing with lifetime evaluation
• belt failure may cause serious
consequences
• visual inspection
• pre-set time for changing the
belt (e.g. running hours/years)
Main criteria dealing with strength
• diameters of pulleys (wheels)
• distance between pulleys (shafts)
• angle of wrap of the pulley
(contact area covered by the belt
on the pulley)
• centrifugal force
• belt tensions due to torque
(driven vs. driving pulley)
• friction between the belt and
pulley
• intial tension
• belt cross-section
Belt drives
Timing belt drives
Flat belt drives
V-belt drives
Main criteria dealing with wear
• abrasive wear
• friction wear (abrasive wear)
• ageing
• surface failures of the belt
• chemical failures of the belt

14. Highlight! Importance of the: Different stress components of the belt
Friction (V- and flat belts)
3) Different cross-section shapes of the belts and different materials
Bending stress
Stress due to intial tension
Stress due to torque
Stress due to centrifugal force

15. ROLLER CHAIN DRIVES Main criteria dealing with strength
• velocity of the chain
• centrifugal force
• radial force
• surface pressure on a link
• vibration phenomena
• speed ratio

16. ROLLER CHAIN DRIVES Main criteria dealing with wear
• abrasive wear
• adhesive wear
• tribochemical wear
• lubrication
• required number of links vs. teeth
(multi-corner effect)
• environmental aspects
• material pairs (chain vs. sprocket)
Main criteria dealing with strength
• velocity of the chain
• centrifugal force
• radial force
• surface pressure on a link
• vibration phenomena
• speed ratio

17. ROLLER CHAIN DRIVES Main criteria dealing with lifetime evaluation
• wear rate
•usually an unexpected failure
• failures of the locking
mechanisms
• chain failure may cause serious
consequences
• pre-set time for changing the
chain
• minimum number of teeth of
sprockets
Main criteria dealing with reliability
• type of driven/driving machine
• required power transmission
capacity
• multiple chains
• adjusting the length /elongation
with a tensioner
• continuous lubrication
Main criteria dealing with wear
• abrasive wear
• adhesive wear
• tribochemical wear
• lubrication
• required number of links vs. teeth
(multi-corner effect)
• environmental aspects
• material pairs (chain vs. sprocket)
Main criteria dealing with strength
• velocity of the chain
• centrifugal force
• radial force
• surface pressure on a link
• vibration phenomena
• speed ratio

18. Highlight! Importance of the:
Allowed ultimate strength of the chain under static and dynamic loading
Allowed surface pressure of the chain and possible wear phenomena
3) Vibration problems (velocity analysis)

19. Exercises
Exercise 7.
Select any industrial applications in which the shaft-hub joint types given in Table 1 are used. Form the approach for the lifetime analysis of the joints and their components by integrating the viewpoints of strength, wear and reliability analysis.
Exercise 8.
Select any industrial applications in which the power transmission systems given in Table 2 are used. Form the approach for the lifetime analysis of these systems and their components by integrating the viewpoints of strength, wear and reliability analysis.
Table Table 2.
Shaft-hub-joint type
Conical shaft-hub joint
Interference fit shaft-hub joints
Parallel shaft key joints
Power transmission system
Timing belt drives
V-belt drives
Single roller chain drives