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Aerospace Structures and Materials: Postscript on Crippling

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Presentation on theme: "Aerospace Structures and Materials: Postscript on Crippling"— Presentation transcript:

1 Aerospace Structures and Materials: Postscript on Crippling
Dr. Tom Dragone Orbital Sciences Corporation

2 Buckling / Crippling Interaction
Long Column Length Critical Euler Buckling Applies Short Column Cross Section Critical Crippling Applies What if the column is somewhere in between?

3 Buckling / Crippling Interaction
Radius of Gyration r = I/A Long Column Short Column

4 Buckling / Crippling Interaction
“Johnson-Euler Curves” Increasing Fcc Long Column Short Column

5 Aerospace Structures and Materials: Compression Panel Design
Dr. Tom Dragone Orbital Sciences Corporation

6 Compression Panel Design
Stability Equation is Analogous to Euler Buckling: K depends on End Conditions (Hinged vs Clamped vs Free) Geometry (a/b) Load Type (Compression vs Shear) h depends on material plasticity

7 End Effects COLUMN 2 Sides Restrained FLANGE 3 Sides Restrained PANEL

8 Geometry Effects LOW ASPECT RATIO Single Buckling Wave
HIGH ASPECT RATIO Multiple Buckling Waves

9 Loading Effects COMPRESSION Symmetric Buckling Waves SHEAR Skewed
“BENDING” Offset Buckling Waves

10 Flat Panel Compression Buckling
Pinned Clamped From Fig Free High Aspect Ratio Lower bucking stress Less Restraint Lower buckling stress Clamp->Hinge->Free

11 Elastic Buckling Stress
Plasticity Effects Buckling Resisted by Bending Stress Yielding Limits Bending Stress and Reduces Buckling Resistance Peak Panel Stress is Much Higher than Average Stress Local Yielding Occurs Even if Average Stress < Yield Stress True Buckling Stress < Elastic Buckling Stress Accounted for by h h is Different for Comp vs Shear h is Depends on Material Plastic Buckling Stress Elastic Buckling Stress From Equation

12 Flat Panel Shear Buckling
From Fig From Fig

13 Curved Panel Compression
Curvature Helps Resist Buckling From Fig Flat Plate Highly Curved Panel

14 Local Buckling Instability of the Free Segments of Stringers, Frames, Longerons, Beams, Columns Can Be Predicted by Treating the Segment as a Long Panel (a/b>>1) with a Single Free Edge Clamped Free H L bf

15 Combined Loading Implication: What if: Will structure fail? Define
Stress Ratios: Rs Rc 1.0 Actual: Rc2 + Rs = 1 Linear: Rc + Rs = 1 Absolute: Rc=1 Rs=1 Implication: Cannot use typical margin calculation Must use graphical method (or numerical)

16 Combined Shear / Compression

17 Skin-Stringer Panels

18 Skin-Stringer Panels Flange Web Skin Stringer

19 Skin-Stringer Panels So far, we have treated skin-stringer panels as independent elements Skin Buckling Between Stringers => Panel with Hinged Ends Stringer Column Buckling => Euler Buckling Stringer Flange Buckling => Local Long Panel Buckling Stringer Crippling => Crippling Failure There are other failure modes to consider

20 Combined Panel Failure Modes

21 Skin-Stringer Panel Design
Proper Design of Skin-Stringer Panels Can Increase Buckling Strength Actual Buckling Stress Mode Change Skin Buckling with Clamped Ends Hinged Panel Buckling Stress Lateral / Torsional Instability Stiff Stringer / Thin Skin No Stringers

22 IsoGrid Panels Skin-Stringer Panels Sandwich Panels
Very Weight Efficient Resist Loads in One Direction Only Weak in Transverse Direction Sandwich Panels Bidirectional Strength/Stiffness Interior Cannot Be Inspected Isogrid Construction Isotropic In-Plane Strength and Stiffness Can Be Easily Inspected

23 ISS Node 3 Isogrid Construction
RIB SKIN International Space Station Module

24 Isogrid Panel Examples
Rib Flange Skin Section Through Panel Grid

25 IsoGrid Geometry Nodes are Convenient Hard Points for Attachments Node
Machined Pocket A 60° typ tsk tf h Nodes are Convenient Hard Points for Attachments Section A-A

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