Bong-Kee Lee
School of Mechanical Systems Engineering Chonnam National University
Mechanical Design I
5. Screw (Chap. 5.7)
Design of Screws
인장 응력(축 방향)
– 가정• 축 방향 하중
• 수나사 골지름 단면에서 파괴
a a
a a t
d Q d d d Q
d Q
d Q A F
) 2 8 . 0 : tion (approxima
4
failure : 4
4 1
1 1
2 1
2 1
School of Mechanical Systems Engineering Mechanical Design I
인장 응력(축 방향) 및 전단 응력
– 나사 잭(screw jack), 나사 프레스(screw press) 등
theory DE theory, M SS
4
4 force) 1 (shear
16
16 (torque) 1
4
4 1
2 2 1 1
3 3 1 1 max
2 2 1 1
d F d F A F
d T d T I
r T
d Q d Q A Q
p
Design of Screws
인장 응력(축 방향) 및 전단 응력
2 2 2
2 3
, 2 , 1
2 2
2 2
2
2 0 2
2 2
case stress plane stresses principal three
: 2 , 4 0
0 0
0
0 0
0 0 0
0 0 0 tensor) (stress
0
&
0
z z rz
z r
rz r r
r rz r
z r
School of Mechanical Systems Engineering Mechanical Design I
인장 응력(축 방향) 및 전단 응력
• 구체적인 나사 자료가 없는 경우
a
d Q
3
8
5 . 0 ' tan 2
) 3.0280
&
1 . 1 / assuming (by
9.8264 ' tan ' 1732 . cos 0 '
) 30 using
&
0.15 assuming (by
' tan 2 '
2 tan
16 , 16
4 4
1 2
1 2
1 -
1 2 2
3 1 3
1 2
1 2
1
d d
d d
d Q d
T d
T d d
T Q d
d Q
Design of Screws
인장 응력(축 방향) 및 전단 응력
• 구체적인 나사 자료가 없는 경우
a
d Q
3
8
used.
be can theory M SS or
3 8 2
failure : 32 . 1 5 . 0 3
2 ) ( 2
3 '
stress, plane for
2 2
2 2 2
, 1
2 2 2 1 2 2 2 1
a
a VM
VM
Q d Q
School of Mechanical Systems Engineering Mechanical Design I
충격
– 충격 흡수 능력
• 길이 ↑ & 단면적 ↓
EA l U F
l k EA k U F
k k F
F F U
2 2
2 1
ts screws/bol of
constant spring 2 :
1 2 1
Design of Screws
강도
– 기계적 성질(인장강도, 경도, 신장, 항복점) – 반복 하중에 대한 내피로성
– 충격 하중에 대한 인성
School of Mechanical Systems Engineering Mechanical Design I
Example I (5.18 in textbook)
bolts M 24
3 . 8 22 . 8 0
. 0
mm 8 . 6 17
10 5 . 1 4 4
mm kg 6
kg 10 5 . 1 ton 5 . 1
1 1
3 1
2 f
f 3 f
d d d d d Q Q
t t a
Design of Screws
Example II
– stress analysis of square bolt in 40ton press – d=120mm, d1=100mm, p=22mm
– ductile steel, friction coefficient ~ 0.1
kg mm
363142
kg 4000 711 . 5 662 . 3 2 tan
mm tan 110
2 (torque)
711 . 5 1 . 0 tan
662 . 3 064 . 110 0 tan 22
mm 2 110
100 120 2
f 2
2 1 2
d Q T
d p d d d
School of Mechanical Systems Engineering Mechanical Design I
Example II
f 2
2 2
2 f 2
2 max
2 2 f
f 2
1
2 3 f
f 3
1
mm / kg 023 . 6 3 '
theory) (DE stress M ises von
mm / kg 15 . 2 3
theory) (M SS stress shear maximum
mm / kg 1 . mm 5 100
kg 4000 4 4
) force, axial to due stress ve (compressi
mm / kg 85 . mm 1
100
mm kg 363142 16
16
) torsion, to due stress (shear
VM
d Q
Q d
T
T
