ModelSetupThepopsiclesticksaresimulatedbythree-dimensionallinearelasticsolidpartsinalatticepattern.Assembliesarecreatedusingapythonscript.Tangentialfrictionandnormalpressure-overclosurerelationsareusedtosimulatecontactbetweenthebeamsurfaces.Simulationsconsistofthefollowingsteps:

1.Sticksarearrangedinlatticepatternwithoverlap;2.Contactdefinedsticksurfacesandtheself-stressedstateisreached(static);3.Groundcontactwiththesticksisinitiated(CobraWeaveonly)(static);4.Contactisremovedforthetriggerstick(dynamic).

Numerical Analysis of Stick BombsLucas Allegrette,

Purdue University, School of Mechanical EngineeringIMECE Track 16-1NSF Research Poster CompetitionIMECE 2019-12646

ProjectObjectivesandGoals• Investigatethemechanicsofstructuresheldtogether

byself-stress• Createtwosimulationmodels:TheA-frameandthe

CobraWeavestickbombs

BackgroundStickbombsaretoysmadesolelyfrompopsiclesticksandserveasprototypesforself-stressassembledstructures:

Somebirdsbendtwigstoformtheirneststructureinasimilarway[1-3]:

Engineeringstructuresfollowingthisprincipleareofrelevanceduetopotentialnewproperties[4]:

Popsiclestickbombsareprototypesofsuchsystems:

Fromanengineeringperspective,theyconsistofapluralityofbentbeamsheldtogetherbystoredenergy.Thestabilityofthestructureislostwhenoneofthebeamsisremoved.Thestoredenergyisreleasedintheformofachainreactionandisconvertedtokineticenergy.

Simulationsofstabilityarenecessarytounderstandthereliabilityofthestructure.

FutureStudies• Findaquantitativerelationshipbetweenstick

length,width,andthicknesswiththewavepropagationspeed.

• Analyzemodelswhichcombinestickswithdifferentpropertiesorgeometry.TherebyIcananalyzetransientwavepropagationevents

AcknowledgementThismaterialisbaseduponworksupportedbytheNationalScienceFoundationunderGrantNo.1662177.TheauthorswouldalsoliketothankNSFforsupplementaltravelfundstothiscompetitionfromgrantCMMI-1935462.

References1. https://www.nytimes.com/2019/04/16/magazine/how-to-

build-a-birds-nest.html.Lastaccessed11/8/2019.2. https://www.seashoretoforestfloor.com/northern-cardinal-

nest/.Lastaccessed11/8/20193. Weiner,N.,Bhosale,Y.,Gazzola,M.andKing,H.,2019.

Perspective:Mechanicsofrandomlypackedfilaments—thebirdnestasmeta-material.arXiv preprintarXiv:1911.00163.

4. https://inhabitat.com/jayson-fann-builds-giant-spirit-nests-for-humans/spirit-nest-jayson-fann-5/.Lastaccessed11/8/2019

5. Savant,M.,privatecommunication.6. Sautel,J.,Bourges,A.,Caussarieu,A.,Plihon,N.andTaberlet,

N.,2017.Thephysicsofapopsiclestickbomb.AmericanJournalofPhysics,85(10),pp.783-790.

PublicationsThisprojectcurrentlyhasnopublications.

Conclusion• Assemblyintheunstressedstatefollowedby

contactinsertionleadstoself-stressedstructures.• Stabilityofsuchstructuresislimitedifcontactislost

globally(A-frame)orlocally(CobraWeave).• Modelsimulationsareverysensitivetothecontact

conditions.Thesestronglyaffectthenumericalperformanceofthefiniteelementmodel

• Predictedspeedofdisintegrationofthecobraweaveisintherangeofphysicalparameters,however,notmatching.Thisisattributedtotheenergystoredinthecontactsprings.

• Reliablestructureswillneedredundancytoensurestability

[5]

Results:A-Frame

Results:CobraWeave𝑣" =

$.&')($.'+,$-.$.'"&/-)

=

8.13 )-

𝑣4 =$."5+)

($.,"+/-.$.'+,$-)=

7.41 )-

𝑣' =".$8")

($./,8/-.$.,"+/-)=

8.37 )-

(A) Initialstate(strainenergydensity)(B) Removalofsinglestick(C) Sequentialdestruction

𝑣9:; = 7.97 )-

Step4,t=0.3165s

Step4,t=0.3140s

Step4,t=0.3190s

𝑉>?@ = 0.5,3𝑚𝑠 5

𝑉>?@ = 5,20𝑚𝑠 6

(A)

(B)

(C)

Unstressed Stressed

Unstressed Stressed Destruction

𝑉∗ ∝𝑇𝜌

�∝

𝐸. 𝑓 ℎ𝐿

𝜌

�

𝑉∗ ∝ 𝐸𝜌

� ℎ𝐿 [6]