1. May the force be with you !
기계공학
(機械工學, Mechanical Engineering)
Mechanics : an area of science concerned with the behavior of physical bodies when subjected to forces or displacements,

2. Mechanical Engineering
Statics
고체(재료)역학
Dynamics
동역학
유체역학
열역학

4. Chapt 1. Introduction to Stress & Strain
전남대학교 기계시스템 공학부

5. 1.1 Introduction to the Mechanics of Solids
In statics
rigid body assumption  free body diagram  force & moment equil.
In solid mechanics
 for deformable bodies, force & moment equil. applied
재료 역학

6. Topics of Statics
the use of significant figures and appropriate units in the solution of problems
force and moment vectors
relations at supports in simple structures
free body diagrams
the use of equilibrium equations
the idea of statically determinate and statically indeterminate problems
centroids of composite plane areas; moments of areas
area moments of inertia of composite plane areas
재료 역학

7. Strength of materials in mechanics of solids
by Denison Olmstead, 1838
The importance to the architect and the engineer of ascertaining the form
and position of the materials which he employs, in order to secure the
greatest degree of strength and stability at the least expense, has led
mathematicians and writers on mechanics, to devote much attention to
this subject. How is the strength of a beam affected by giving it to differ-
ent shapes and different positions? How must a given quantity of matter
be disposed in order that it may have the greatest possible strength?
And upon what principles depends the stability of columns, roots and
arches? These, and many similar inquires, have been the objects of
profound investigation…. Strength is the power to resist fracture.
Mechanics of materials  material science
재료 역학

8. 1.2 Uniaxial Normal Stress & Uniaxial Deformation
How a material deforms?
- for a solid bar of
elastic material
: characteristic for a material
재료 역학

9. : Hooke's law
(E=Young's modulus)
- E for materials
재료 역학

10. Stress & Strain - force deformation relation normal stress
normal strain
재료 역학

11. - stress - strain relation for the material - Poisson’s ratio
( for most material )
재료 역학

12. Ex 1.1) →
재료 역학

13. 1.3 Shear Stress & Shear Strain
- acting in the plane of the surface
재료 역학

14. Shear stress char. for a material Difficult to measure twist test
재료 역학

15. for an infinitesimal cube
additional shear stress in the
vertical force for moment equil.
“pure shear”
재료 역학

16. Ex 1.2)
재료 역학

17. Ex 1.2)
재료 역학

18. Ex 1.3)
재료 역학

19. 1.4 Allowable loads Maximum stress allowed in a component
against failures
(yield, fracture, fatigue, creep)
factor of safety
재료 역학

20. Ex 1.4)
재료 역학

21. = 100MPa - allowable stress of BD,CD in tensile or compressive stress
- allowable stress of pin in shear stress = 150MPa
Maximum allowable load P ?
Sol) force equil. at D
재료 역학

22. → Select the smaller P = 34.7KN ㅡ ①
재료 역학

23. For pins of B, D (cf C) max. allowable stress  ㅡ ②
Select ② P= 16.7kN between ① & ② because it’s safer
재료 역학

24. Ex 1.5)
재료 역학

25. Allowable tensile stress: 30ksi Allowable shear stress : 20ksi
Allowable max. load P ?
해) mode- of -failure analysis
1) double shear at the bolt
2) tensile near bolt hole of strap
Stress concentration neglected
재료 역학

26. 3) tensile near the bolt hole of brackets
4) shear-out near bolt hole of strap
5)shear- out near bolt hole of bracket
재료 역학

27. 1.5 Tensile Stress- Strain Test
인장 시편과  ,  측정
( L = 표점 사이 거리 )
재료 역학

28.  -  curve up to 2% of materials
in initial region →
proportional limits, elastic limits
재료 역학

29. Unloading elastically
Permanent strain or
Plastic strain
재료 역학

30. Yield strength (0.2% offset) corresponding to 0.2% plastic strain
upper , lower yield point & material variation
재료 역학

31. Strain hardening, necking, ultimate strength idealization of  - 
재료 역학

32. 1.6 problem solving 1) Review what is required for the solution
2) Draw reasonably neat diagrams to an approximate scale
3) Consider and draw neatly the appropriate free- body diagram for the system
4) Apply the three step approach to the solution of solid mechanics problems
5) Express the final results in a form that allows for checking
6) Finally, again question the statement and formulation of the problem to see if indeed you found what was required
재료 역학