1. BASIC VOCATIONAL STRENGTH Stress Description
first Newton law is about action and reaction. If a cube on the floor, cube will give action toward the floor, and on the contrary, the floor will give the same reaction, so the object are equilibrium condition. Action force (F) and reaction force (F’) from bottom will work toward each the cube section. If we take section A-A from the cube, Center force (F) that direction goes down, and under section, reaction force work toward to the top.
On the section surface, molecules on the top and bottom of section surface A_A press each other, so each section large unit gets load : F/A
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2. BASIC VOCATIONAL STRENGTH
Load that is received by object molecules of each section area unit is called Stress. Stress is usually stated with Greece letter σ (thau).
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3. BASIC VOCATIONAL STRENGTH KINDS Of STRESS
Stress created because of pressure, pulling, bending and reaction. On pulling loading, there happens pulling stress, on the pressure stress, there happens pressure stress. It happen to other loadings
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4. BASIC VOCATIONAL STRENGTH NORMAL STRESS
Normal stress happens because of reaction given toward object. If inside force is measured in N, mean while section area in, so stress unit Is :
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5. BASIC VOCATIONAL STRENGTH
Normal Stress is If section area = A m2 and Force value Fn = kg. f
tangential Stress:
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6. BASIC VOCATIONAL STRENGTH b. Pull Stress
Pull stress usually happens to chain, rope, rivet, etc. Chain that is given load W will get pull stress that value depends on the weight
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7. BASIC VOCATIONAL STRENGTH Equality Of Pull stress description :
Notes : F = Pull stress
A = Section Area
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8. BASIC VOCATIONAL STRENGTH C) Pressure Stress
Pressure stress happens if a rod ls given force F on the contrary side and laid on one force line, for example its happen to beam of building that haven’t bended yet, bicycle arm, connecting rod.
Pressure stress can be written :
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9. BASIC VOCATIONAL
STRENGTH
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10. BASIC VOCATIONAL STRENGTH d) Move Stress
Move Stress happens if an object work with two force in contrary direction, perpendicular rod axis, force in the same line, but on the section doesn’t happen moment.
This stress usually happens to construction such as rivet, scissor, and bolt joint
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11. BASIC VOCATIONAL STRENGTH
On the picture above, two force with same value in contrary direction. Force F work spread on section A. On the material will appear move stress. The value is
For construction on rivet, so F maximum is
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12. BASIC VOCATIONAL STRENGTH
Move stress happen because of radial force that works on normal section with relative small space, so bending of object is ignored. For this case, the stress that happens is
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13. BASIC VOCATIONAL STRENGTH
If on Construction has amount of rivet, so according to the equality below, the move stress is
D = diameter of rivet
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14. BASIC VOCATIONAL STRENGTH e) Bending Stress
For example on machines shaft and wheel shaft in pillar condition. So It’s tangential stress
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15. BASIC VOCATIONAL STRENGTH Mb = bending moment
Wb = bend resistant moment
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16. BASIC VOCATIONAL STRENGTH f) Twist stress
Twist stress often happen to gear shaft and torque rods of car, drilling process. So it’s tangential stress
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17. BASIC VOCATIONAL STRENGTH
An object that get twist load will create twist stress :
Mt = torque
Wp = polar resistant moment
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