1. selection of materials, stresses
Prepared by:
Modi Parth S

2. machine elements

3. general purpose machine elements
static elements
joints
frames
springs
(mechanical) drive systems
bearings
shafts
couplings & clutches
drives
vessel systems
pipes
valves
tanks
(technical fluids)

4. material
DESIGN
manufacturing
money
optimum - opportunism
time, place

5. aims no failure (surface or volume) no big deformations
enough service time

6. loads mechanical  forces, moments… thermal 
chemical changing in place/ time …
static cyclic dynamic

7. materials metals plastics ceramics composite density conductivity
ferrous/ non~
cast iron
steel
carbon/ alloy
plastics
ceramics
composite
density
conductivity …
elasticity
plasticity
ductility
brittleness
toughness (impact)
creep

8. loads & stresses
Stress distribution uniforn/linear
(Mohr, H-M-H)

9. loss of stability
Buckling
elastic/ plastic

10. Tensile test Load  deformation stress – strain diagrams
ductile – carbon steel
rigid – cast iron

11. simplifyed material models
elasto-plastic
rigid

12. test
YS ReH
UTS Rm
UTS YS
real
eng.

13. strain hardening

14. elastic properties elastic (Young) modulus: E [MPa]
(Hook’s law s = Ee)
shear modulus: G [MPa] (t = Gg)

15. main static properties
elastic limit Rp0.2
yield strength ReH
ultimate tensile strength Rm
maximal strain A
hardness HHB…
Charpy (V-notch) test Kcu

16. Influencing factor – (not only) static load
Stress concentration
shape factor
αk > 1

17. sudden area changes

18. Influencing factor – dynamic load
 Tényl= d 
dynamic load factor
1.1~ 3
Depending on machine type & size (handbooks, measurements, calculations)

19. Periodic stresses fatique propagating crack – final static break
90-95% of all failures!

20. types of varying load σv σr cycle assymetry ratio
Fatique limits
cycle assymetry ratio
cycle mean stress ratio

21. notch sensitivity ηk (0.5-1.0 )