Direct Load Flashcards
Stress
internal resistance of the material to the applied load per unit area
Direct stress=
applied load/cross-sectional area
MPa=
N/mm^2
psi=
lbs/in^2 (imperial)
Direct normal tensile stress
σ (axial load/cross sectional area) pulling out
Direct normal compressive stress
σ (axial load/cross sectional area) pushing in ->
Direct shear stress
τ (shear force/shear area)
Bearing stress
σb=load/contact area
contact area is the area of the interface between two flat surfaces, one supports the other
Normal strain
ε or εa, aka axial strain, the deformation per unit length
ε=
δ/l= (Δl)/l= (lf-li)/li
Axial deformation
δ the change in length
δ=lf-li
Lateral strain
εl=(Δh)/h =(hf-hi)/hi
Poisson Ratio
v, the ratio of the lateral strain to the axial strain
v=-εl/εa
shear strain
γ, the change in the right angle of the stress element, due to shearing load
measured in radians
Hooke’s law: Uni-axial loading
E=σ/ε
E a material property representing stiffness
σ stress
ε strain
Hooke’s law: shear loading
G=τ/γ
G is the shear modulus of elasticity/rigidity, represents material rigidity
τ shear stress
γ shear strain
Axial Loading: design stres
σd, the maximum allowable level of stress the member can develop while performing safely under load
Sy
yield strengths
Sn
fatigue strength
Axial Loading: Design factor N
accounts for uncertainty in factors such as load, material, environment, conditions, misuse
Design Criteria based on normal stress: Static stress
σd=Sy/N
σ≤σd
σ=Faxial/Across-section
Design Criteria based on normal stress: Dynamic stress
σd=Su/N
- Su is the ultimate strength of the material
- Sy is the yield strength of the material
- Su of the material is correlated to Sn
Shear Loading: Design shear stress
τd is the maximum allowable level of shear stress the member can develop while performing safely under load
- τd=Sys/N for ductile material
- Sys is the shear yield strength of the material
- τ≤τd
- τ=Fshear/Ashear
design bearing stress
σbd
Max stress
σmax=Kt*σnom
- Kt stress concentration factor
- σnom=F/A
Deformation due to axial load
δ =ε*L =(σ/E)L ={(F/A)/E}L
- F axial force
- L initial Length
- E modulus of elasticity
- A cross sectional area
- σ direct normal stress
- ε axial strain
Deformation due to thermal loading
δ=αL(ΔT)
- δ thermal deformation
- α coefficient of thermal expansion
- L initial length of member
- ΔT temperature change
Thermal stress
σ=Eα(ΔT)
- α coefficient of thermal expansion
- ΔT temperature change
