SE171finalpresentation

Octagonal Double Step Octagonal Double Step Lap Joint RepairLap Joint Repair

Group 3:Group 3:Zhi ChenZhi Chen

Vincent DuongVincent DuongQunjie (Jay) GuanQunjie (Jay) Guan

Rory MillerRory Miller

Spring Quarter 2008Spring Quarter 2008SE 171 Aerospace Structures Repair – UC San DiegoSE 171 Aerospace Structures Repair – UC San Diego

Dr. KimDr. KimLa Jolla, CA 92092La Jolla, CA 92092

Design RequirementsDesign Requirements

The repaired panel has to have at least 15% The repaired panel has to have at least 15% more strength than the unrepaired panel.more strength than the unrepaired panel. Maximize Performance IndexMaximize Performance Index

Design ConsiderationsDesign Considerations

Priority given to PI maximizationPriority given to PI maximizationManufacturabilityManufacturabilityMaximizing peak load while keeping the Maximizing peak load while keeping the repair light (low mass)repair light (low mass)Minimize the adhesive shear stress and Minimize the adhesive shear stress and NN0k0k

Modeling and AnalysisModeling and Analysis

Preliminary computer modeling and Preliminary computer modeling and analysis were conducted to estimate the analysis were conducted to estimate the stress distribution while the panel is stress distribution while the panel is undergoing tensile loadingundergoing tensile loadingThe preliminary modeling of the The preliminary modeling of the unrepaired panel gave clues as to what unrepaired panel gave clues as to what repairs are suitablerepairs are suitable



From the preliminary model, it was From the preliminary model, it was observed that the stress concentrations observed that the stress concentrations are greatest at the ends of the crackare greatest at the ends of the crackTherefore, proceed to decrease these Therefore, proceed to decrease these stress concentrations by placing two holes stress concentrations by placing two holes at the ends of the crackat the ends of the crackResulting peak stress concentrations Resulting peak stress concentrations decreased by about 50%decreased by about 50%



Step lap joint reduces Step lap joint reduces aa(x) and N(x) and N0k0k(x), (x), therefore, the repair will be in the step lap therefore, the repair will be in the step lap joint configurationjoint configurationThe number of plies is determined by The number of plies is determined by comparing the failure strengths of the comparing the failure strengths of the inner and outer adherendsinner and outer adherendsDimensions of the plies should be as close Dimensions of the plies should be as close to the recommended 1:50 ply drop ratio as to the recommended 1:50 ply drop ratio as possiblepossible

Modeling and AnalysisModeling and Analysis_

_

52000

42000

0.0760 .0.012 .

ult i

ult o

i

ply

o ply

psi

psi

t int in

t n t

_ _

52000 0.0760 42000 0.0127.88

ult o o ult i it t

nnn plies

4 plies on each side


The shape of the patch was narrowed The shape of the patch was narrowed down to either a hexagon or ellipsedown to either a hexagon or ellipseHexagon is easier to manufacture than Hexagon is easier to manufacture than ellipse; however, priority will be placed on ellipse; however, priority will be placed on the robustness of the peak loadthe robustness of the peak loadThe modeling of the repair patch designs The modeling of the repair patch designs were then conductedwere then conducted




From the previous two models, notice that From the previous two models, notice that the hexagonal patch is more robust than the hexagonal patch is more robust than the ellipse/ovular patchthe ellipse/ovular patchHexagonal patch is easier to manufactureHexagonal patch is easier to manufactureHowever, there are isolated locations that However, there are isolated locations that have spikes in the stress concentrations have spikes in the stress concentrations (i.e. corners of the hexagon)(i.e. corners of the hexagon)Remedy stress concentration problem by Remedy stress concentration problem by creating an octagonal repair patchcreating an octagonal repair patch

Final Design Final Design Octagonal patchesOctagonal patches8 plies total, 4 plies on each side8 plies total, 4 plies on each sidePly Drop Ratios from top to bottom are Ply Drop Ratios from top to bottom are 1:40, 1:30, 1:20, and 1:201:40, 1:30, 1:20, and 1:20

Final DesignFinal Design


The failure load is predicted to be The failure load is predicted to be 2518 lb2518 lbff/in (2N/in (2Nxx), or 440.987 N/mm), or 440.987 N/mm

The failure load of the unrepaired panel The failure load of the unrepaired panel was 74 N/mmwas 74 N/mm


After the failure load is predicted, the After the failure load is predicted, the aa(x) (x) and Nand N00(x) is then calculated for the (x) is then calculated for the proposed repairproposed repairPeak Peak aa(x) is 6365 psi when N(x) is 6365 psi when Nxx is 1259 is 1259 lblbff/in /in The predicted failure mode was adhesive The predicted failure mode was adhesive shearshearThe detailed dimensions of the repair patch The detailed dimensions of the repair patch are determined by are determined by aa(x) and N(x) and N00(x) plots(x) plots


0 0.2 0.4 0.6 0.8 1 1.2 1.40

1000

2000

3000

4000

5000

6000

7000

x [in.]

Adh

esiv

e S

hear

Stre

ss [p

si]

Figure 1. Adhesive Shear Stress at Failure (Nx = 1259 lb/in.)

X: 1.32Y: 6365


0 0.2 0.4 0.6 0.8 1 1.2 1.40

200

400

600

800

1000

1200

1400

x [in.]

App

lied

Load

[lbf

/in.]

Figure 2. Outer Adherend Load at Failure (Nx = 1259 lb/in.)

X: 1.32Y: 1259

Manufacturing ProcessManufacturing ProcessThe crack needs to be sealed with micro-balloons, turning the crack The crack needs to be sealed with micro-balloons, turning the crack into a butt jointinto a butt joint

Manufacturing ProcessManufacturing Process

The repair patch was produced via the The repair patch was produced via the wet lay up method with fiberglass/epoxywet lay up method with fiberglass/epoxy

The surfaces surrounding the crack are The surfaces surrounding the crack are sanded down to provide better mechanical sanded down to provide better mechanical interlocking faces for adhesiveinterlocking faces for adhesive


Manufacturing ProcessManufacturing ProcessThe repair patch is then laid up onto the The repair patch is then laid up onto the panel one ply at a timepanel one ply at a time

Manufacturing ProcessManufacturing Process Plenty of epoxy to go around…Plenty of epoxy to go around…

Manufacturing ProcessManufacturing ProcessThe semi-finished product, the vacuum awaitsThe semi-finished product, the vacuum awaits

Manufacturing ProcessManufacturing ProcessOne week later…One week later…


The end tabs were originally composed of The end tabs were originally composed of Aluminum bonded by JB weld.Aluminum bonded by JB weld.However, The end tabs became unreliable However, The end tabs became unreliable after holes were drilled in.after holes were drilled in.

Manufacturing ProcessManufacturing ProcessThe end tabs separatedThe end tabs separated

Manufacturing ProcessManufacturing ProcessNew end tabs need to be adhered. Super glue to the rescue.New end tabs need to be adhered. Super glue to the rescue.

Manufacturing ProcessManufacturing ProcessFinally, it’s ready to goFinally, it’s ready to go

Panel’s DemisePanel’s Demise

ResultsResults

The predicted failure load is 2518 lbThe predicted failure load is 2518 lbff/in (2N/in (2Nxx), or ), or 440.987 N/mm.440.987 N/mm.Max. Max. aa is 6365 psi. is 6365 psi.The actual failure load is 3124 lbThe actual failure load is 3124 lbff/in, or 547 /in, or 547 N/mm.N/mm.The unrepaired panel’s failure load is 74 N/mm.The unrepaired panel’s failure load is 74 N/mm.The mass of the repair is 16.6g.The mass of the repair is 16.6g.The PI is approximately 29.The PI is approximately 29.

Comparison of 2Comparison of 2ndnd Ply 0 and 90 Ply 0 and 90 Degree LayupsDegree Layups

0 Degree

90 Degree

ResultsResults

30 30.5 31 31.5 32 32.5 33 33.5 34 34.5 35-100

0

100

200

300

400

500

600Figure 3. Test Panel 3 Displacement vs. Force

Axial Displacement [mm]

Axi

al F

orce

[N/m

m]

X: 34.7Y: 547

ResultsResults

The possible failure modes include The possible failure modes include adhesive failure, inner and outer adherend adhesive failure, inner and outer adherend failure, and lastly, interfacial failurefailure, and lastly, interfacial failureThe predicted failure mode was adhesive The predicted failure mode was adhesive shearshearThe specimen exhibited adhesive failure The specimen exhibited adhesive failure and outer adherend failureand outer adherend failure

ResultsResults

ResultsResults

ResultsResults

Conclusion and RecommendationConclusion and Recommendation

The actual failure load achieved was 3124 The actual failure load achieved was 3124 lbf/in, or 547.10 N/mm.lbf/in, or 547.10 N/mm.Some discrepancies included the Some discrepancies included the manufacturing process and human error.manufacturing process and human error.

Ply orientation was forgotten about, so one or two plies might be 90Ply orientation was forgotten about, so one or two plies might be 90ºº degreesdegrees

The patches could not be cut to exact dimensions due to the given tools The patches could not be cut to exact dimensions due to the given tools and the glass-fiber cloth’s flexibility and ease of warpand the glass-fiber cloth’s flexibility and ease of warp

The analysis was done for the original panel dimensions instead of the The analysis was done for the original panel dimensions instead of the modified tested panel specimen. modified tested panel specimen.

The weight of the adhesive butt-joint in the crack was not accounted.The weight of the adhesive butt-joint in the crack was not accounted.

Conclusion and RecommendationConclusion and Recommendation

Recommended Approaches:Recommended Approaches: Do not use Aluminum and JB Weld end tabsDo not use Aluminum and JB Weld end tabs Map the 0Map the 0º degrees and 90º degrees º degrees and 90º degrees

coordinate system onto the plies before any coordinate system onto the plies before any manufacturingmanufacturing

Design a mold for each step-lap ply on Design a mold for each step-lap ply on AutoCAD with exact dimensions, and then cut AutoCAD with exact dimensions, and then cut it out on acrylic, which would be placed over it out on acrylic, which would be placed over the glass-fiber cloth to make cutting easierthe glass-fiber cloth to make cutting easier

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SE171finalpresentation