SLIDE 1
Static Failure Mode Prediction Models
Mechanically Fastened Joints
Joining & Assembly
Static Failure Modes
Net Section Tension Bearing Shear Tear Out Fastener Shear Fastener Pull Out
Static Failure Mode Prediction Models Mechanically Fastened Joints - - PowerPoint PPT Presentation
Static Failure Mode Prediction Models Mechanically Fastened Joints - - PowerPoint PPT Presentation
Static Failure Mode Prediction Models Mechanically Fastened Joints Joining & Assembly Static Failure Modes Net Section Shear Fastener Bearing Fastener Shear Tension Tear Out Pull Out Basic Assumptions for our Predictions Failure of
SLIDE 2
SLIDE 3
Basic Assumptions for our Predictions
- Failure of ductile materials (both the fastener and the sheets)
Ductile Material Brittle Material
Initial stress concentration at hole edge Initial stress concentration at hole edge Plasticity causes load redistribution Failure when stress concentration reaches strength
SLIDE 4
Basic Assumptions for our Predictions
- Failure of ductile materials (both the fastener and the sheets)
- All fasteners carry the same load at static failure
12kN (120MPa)
100mm 25mm 15mm 25mm 1mm 3.5mm
12
total
F kN = 12 1 12
rivet
kN F kN = =
SLIDE 5
Basic Assumptions for our Predictions
- Failure of ductile materials (both the fastener and the sheets)
- All fasteners carry the same load at static failure
- Be mindful of load path
F F F F
Load F is transmitted from one plate to another by two rows of bolts in each case
SLIDE 6
Net Section Tension Failure
Failure will occur when net section area reaches the ultimate strength of the sheet material
NST net tu
F A σ = ⋅
( )
tu
t W n d σ = − ⋅ ⋅
Ultimate tensile strength of sheet material Number of fasteners along net section
NST
F
SLIDE 7
Bearing Failure
Failure will occur when the stress acting on the projected area of the sheet on the bolt exceeds the bearing stress allowable for the sheet material.
br br br
F A σ = ⋅
Bearing strength
- f sheet material
t d
( )1
br
A
( )2
br
A
br
d t σ = ⋅ ⋅
This equation gives you the force acting
- n the sheet by the bolt at failure, not
the force applied to the entire joint!
br
F
SLIDE 8
Shear Tear Out Failure
Failure will occur when the shear stress acting on the area between the bolt and joint edge exceeds the shear strength of the sheet material.
STO STO su
F A σ = ⋅
Ultimate shear strength
- f sheet material
2
su
b t σ = ⋅ ⋅ ⋅
This equation gives you the force acting
- n the sheet by the bolt at failure, not
the force applied to the entire joint!
t b
STO
A
STO
F
SLIDE 9
Bolt Shear Failure
Failure will occur when the shear stress acting on the area of the bolt exceeds the shear strength of the bolt material.
, BS BS s bolt
F A σ = ⋅
Ultimate shear strength
- f bolt material
2 ,
4
s bolt
n d π σ =
This equation gives you the force acting on the bolt at failure, not the force applied to the entire joint!
n = 1 n = 2 n = 3
BS
F
SLIDE 10
Fastener Pull Out Failure
Fastener pull out failure is more complex and highly dependent on bolt head geometry, so it is typically evaluated via
- test. So we will not consider it here.