STREMA Flashcards
Stress
σ = P / A
P = tensile or compressive load
A = cross-sectional area,
Doulble shear
σ = P / nA
n =2 (clevis)
P = tensile or compressive load
A = cross-sectional area
Punching Shear
σ = P / πDt
πDt = punching area
P = tensile or compressive load
A = cross-sectional area,
Thin walled pressured vessel
Tangetial Stress
σₜ = PᵢD / 2t = (Pᵢ - Pₒ)D/2t
σt = 2σL
Thin walled pressured vessel
Longitudinal/Spherical Stress
σₜ = PᵢD/4t = (Pᵢ - Pₒ)D/2t
σt = 2σL
Hooke’s Law
σ = Ε ε
Ε = Young’s Modulus/ Modulus of Elasticity
ε = strain
Factor of Safety
FoS = σᵤ/σₐ
σₐ = σt
Elongation
δL = PL/EA
Elongation due to its weight
δW= ρgL²/2E = mgL/2AE
Total Elongation
δT = δL + δW
Shear Modulus
G = τ / γ
G= shear stress/ shear strain
Poisson’s Ratio
v = - ε lat / ε long
Δd/d / ΔL/L
Modulus of Rigidity
G = E / 2(1+ ⱴ)
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Bulk Modulus
k = E / 3(1-2ⱴ)
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Thermal Stess
σᴛ = αEΔT
σₐ = σᴛ + σ,yield
α = coefficient of linear expansion
Torsion
Torsional Shearing Stress
τ, max = Tr/J
where:
T = torsion
r = radius
J = Polar moment of inertia
Torsion
Polar Moment of Inertia
Solid Shaft
J = πD⁴/32
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Torsion
Polar Moment of Inertia
Hollow Shaft
J = π(Dₒ⁴-dᵢ⁴)/32
Torsion
Angle of Twist
θ = TL/JG x 360°/2π
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Torsion
Power through shaft
P = 2πƒT
ƒ = Hz, cps, rps
Helical Spring
Approximation Method
τ, max = 16PR/πD³ · [ 1 + d/4R]
Helical Spring
AM Wahl’s Formula
Exact Method
τ, max = 16PR/πD³ · [ 4m-1/4m-4 + 0.615/m]
m = 2R/d
R = mean radius
Helical Spring
Spring Deflection/Deformation
δ = 64PR³n/Gd⁴
where:
n = no. of twists of spring
Spring Constant
k = Pᴛ/δᴛ