Gli autori ringraziano Destiny Garcia, Serena Ferraro, Erik Quiroz e Steven Kern (Advanced Composites Research, Ingegneria e Scienza di laboratorio) per il loro aiuto nel progettare e realizzare la configurazione di prova. Shawn Malone, Michael Akahori, David Kehlet (Ingegneria Fabrication Lab) sono riconosciuti per i loro suggerimenti e assistenza nel processo di lavorazione. Il sostegno della National Science Foundation (contributo collaborativo CMMI-1.265.691 e il suo supplemento REU) e l&#39;Office of Naval Research (N00014-13-1-0604 di A. Muliana, Texas &amp; M University (Principal Investigator), e V. La Saponara , gestito dal direttore del programma Yapa Rajapakse) sono apprezzati.

1. Caricare i campioni <ol><li> Sollevare il coperchio del serbatoio e appoggiarlo sui supporti laterali (Figura 4). </li><li> Posizionare il campione nel cavallotto, e garantire che la barra trasversale è in contatto al centro del campione. </li><li> Appoggiare le estremità del provino sui supporti di alluminio pendono dal coperchio. Le estremità dei campioni dovrebbero avere 5-10 mm di sporgenza. </li><li> Ripetere i passaggi 1,2-1,4 per tutti i campioni che saranno testati. </li><li> Rimuovere il coperchio supporta, palpebra inferiore, e assicurarsi che il coperchio sia posizionato sul bordo della vasca. </li><li> Applicare la forza desiderata aggiungendo pesi al tondino di acciaio accanto alla puleggia esterna. </li></ol> 2. Spostamento di misura <ol><li> Assicurarsi che la linea potenziometro corda viene tesa. </li><li> Utilizzando un multimetro digitale, misurare la resistenza tra i pin esterni del potenziometro (Figura 3), con il nero al pin 1 e rosso al Pin 3,e registrare la lettura. </li><li> Convertire la lettura in uno spostamento lettura calcolando il fattore di calibrazione (in questo caso, 1 k corrisponde ad uno spostamento 64,895 millimetri) resistenza. </li><li> Ripetere i passaggi 2,1-2,3 per ogni campione. </li></ol> 3. Pesatura dei campioni <ol><li> Prima di iniziare la procedura di pesatura, registrare i dati di spostamento e di preparare una camera di contenimento interim riempita di fluido di prova a temperatura ambiente, secondo ASTM D5229 31, o la norma di prova adeguato. </li><li> Rimuovere i pesi asolati dalle estremità dei cavi di acciaio. </li><li> Sollevare il coperchio del serbatoio e appoggiarlo sui supporti laterali. </li><li> Rimuovere il campione e posizionarlo nella camera di detenzione provvisoria elaborata. Ripetere questo passaggio per tutti i campioni. </li><li> Rimuovere i campioni e asciugare utilizzando singolarmente un panno in microfibra per rimuovere il liquido in eccesso. </li><li> Posizionare il campione su una scala di alta precisione e registrare i dati reading. </li><li> Ripetere i passaggi 3,5-3,6 per tutti i campioni e poi seguire il protocollo Fase 1. </li></ol>

<ol>
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The authors have nothing to disclose.

Dai dati acquisiti, si può vedere che lo scenario test simultaneo ha influenzato la durabilità dei campioni schiuma di poliuretano a celle chiuse. Questo può essere visto confrontando notevolmente differenti spostamenti (Figura 5) e carichi residui al fallimento (Figura 6) di campioni asciutto e bagnato. Figura 7 mostra le immagini dei campioni dopo le prove di resistenza residua. Va inoltre osservato che, mentre lo spostamento dei campioni secco fino a stabilizzarsi...

Polymer e polimero rinforzato con fibre (FRP) compositi sono stati adottati in una serie di strutture di ingegneria, che vanno da aeromobili e veicoli spaziali, navi da guerra, le infrastrutture civili, (vedi ad esempi recensioni di Katnam et al. 1, Hollaway 2, Mouritz et al . 3), automobili e treni, pale eoliche, alle protesi e biomateriali per suture e impianti. Durata Questi materiali &quot;è affetto da scenari complessi di servizi, che possono includere una combinazione di una) termomeccanico carico, ad esempio, i cicli di gelo e disgelo in infrastrutture civili 4, profili subsonico volo / supersonico 5, usura in polietilene metal-backed 6) ; b) la degradazione a causa di agenti atmosferici e chimici, ad esempio, acqua di mare, de-icing, fluidi idraulici per l&#39;industria aerospaziale e navali strutture 7-10, degrado di compositi dentali polimetilmetacrilato a causa di saliva 11; c) inte complessoractions di materiali in articolazioni fissati o legati, ad esempio, la corrosione galvanica e delaminazione tra materiali dissimili, sia in una riparazione di patch di carbonio / fibra su una pelle di alluminio aeronautico, o un / PEEK piastra ossea carbonio fissata in acciaio inox 12. C&#39;è purtroppo limitata conoscenza dell&#39;impatto di concorrenti stimoli in servizio sulla durata a lungo termine di questi materiali. La maggior parte dei polimeri possono essere classificati come materiali viscoelastici. Carichi meccanici e condizioni ambientali influenzano significativamente la risposta viscoelastico dei polimeri. Quindi, modelli affidabili per comportamento a lungo termine di questi materiali dovrebbero essere in grado di integrare le risposte dipendenti dal tempo di igrotermico accoppiati, meccanici, stimoli chimici. Questo a sua volta migliora le previsioni di design, sicurezza e protocolli di manutenzione / sostituzione basate su condizioni. Vi è un grande corpo della letteratura sui test sperimentali sugli effetti igrotermici, Per le prove di diffusione esempio termoigrometrici: se la scala dei campioni consente, i campioni di materiali possono essere posizionati in una camera a livelli di umidità e temperatura desiderate. I campioni vengono rimossi periodicamente per misurare la loro massa e / o cambiamenti del volume per un determinato periodo di tempo, da settimane a anni 10,13-17. Il test termoigrometrico può essere seguita da prove meccaniche, cioè residua resistenza statica / fatica / frattura meccanica test 17-19, che fornisce solo informazioni sull&#39;effetto di termoigrometrico stimolo sulle risposte meccaniche dei materiali. I dati di prova possono essere montati a modelli di diffusione di varia complessità, dalla semplice diffusione Fickiano a modelli che includono dipendenza concentrazione, stress, temperatura, reversibile fisico invecchiamento / plastificazione e reazioni chimiche irreversibili. Questa uscita sperimentale può essere ulteriormente incorporata nelle analisi strutturali. Pochi autori hanno affrontato l&#39;impatto di hy simultaneagrothermal e stimoli meccanici. Tra questi ricercano compositi FRP, Neumann e Garom 20 immerso stressati e campioni atone in acqua distillata. Lo stress è stato applicato posizionando i campioni all&#39;interno molle in acciaio inox compressi, sintonizzare il carico utilizzando differenti rigidezze elastiche e carichi di compressione. Una procedura simile è riportato da Wan et al. 21. Helbling e Karbhari 22 impiegati un dispositivo di piegatura all&#39;interno di una camera ambientale per diverse percentuali di umidità relativa (RH%) e livelli di temperatura. I campioni pre-condizionato sono stati sottoposti ad un dato livello di deformazione di flessione, corrispondente ad una percentuale del ceppo rottura statico per tale composito. Kasturiarachchi e Pritchard 23 preparato un 4 punti dima di piegatura acciaio inox (uno per campione) che è stato posizionato su uno scaffale in un grande essiccatore vetro. L&#39;essiccatore è stato parzialmente riempito con acqua distillata, ha piccole perdite per impedire il buildup della pressione, ed è stato posto in una camera umida, a 95% RH. Gellert e Turley 7 indagati marine-grade campioni FRP composito per la loro durata in condizioni di carico scorrimento combinato e 100% di umidità relativa. I loro campioni sono stati caricati in 4 punti piegatura a carico costante pari al 20% del carico di flessione statica guasto, mentre è completamente immerso in acqua di mare. La deflessione scorrimento stata acquisita periodicamente utilizzando un calibro di spessore tra la superficie esterna del fascio nella sezione centrale, e una lastra di vetro (si deduce che tale misura è stata eseguita all&#39;esterno della camera). Abdel-Magid et al. 24 posizionato campioni di vetro / resina epossidica in un apparecchio ambientale Invar che è stato fornito dalla NASA Langley, i campioni sono stati caricati in trazione lungo la direzione delle fibre, al 20% del carico di rottura assiale. Ellyin e Rohrbarcher 25 corse test igrotermici per un massimo di 140 giorni, e poi testato i campioni di fatica su una macchina di prova idraulica. Il campiones sono stati avvolti in un telo bagnato collegato ad un tubo e un rifornimento idrico. Earl et al. 26 posizionato il loro apparecchio di carico e gli esemplari in una grande camera ambientale (5,5 m 3). Come discusso in molti studi sperimentali, le condizioni ambientali influenzano le proprietà meccaniche e le risposte dei polimeri. Alcuni esperimenti limitati mostrano anche che l&#39;esistenza di meccanica sforzo / deformazione influenza il processo di diffusione nei polimeri. Pertanto, per migliorare la comprensione sulle prestazioni complessive di materiali polimerici sotto effetti sia meccanici e non meccanici, vi è una necessità di test simultaneo. Ci sono stati diversi gli obiettivi alla base della progettazione della piattaforma di prova descritto in questo articolo. In primo luogo, la piattaforma è parte del setup sperimentale in un&#39;indagine pluriennale sul comportamento hygrothermo-meccanico di diversi tipi di compositi sandwich FRP per turbine eoliche dind applicazioni di ingegneria navale. I dati di test sono utilizzati per calibrare i parametri nelle equazioni costitutive viscoelastiche dei compositi polimerici. I modelli costitutivi sono basati sul lavoro svolto negli anni da Muliana e collaboratori 27-30. Il secondo obiettivo era di avere un basso costo e piattaforma di prova user-friendly, per esempio uno che potrebbe essere facilmente trasferito in un laboratorio (ad esempio, ad una scala per misure di massa, o alla sorgente del fluido, ad esempio, quello proveniente da un rubinetto, una fumehood o un armadietto infiammabile). Il terzo obiettivo era quello di creare una piattaforma di test che è resistente a una serie di sostanze chimiche comunemente usate in servizio (fluido particolare idraulica, de-icing, solventi per applicazioni aerospaziali 8-10), quindi i campioni possono essere immersi in tali sostanze chimiche, e la loro durata potrebbe essere valutata. La camera (Figura 1) è stato costruito con polyethyle alta densitàne, che ha alta resistenza chimica. Come accennato in precedenza, si prevede che il lavoro futuro comprenderà hygrothermo-meccanica indagini di compositi immerse nel fluido idraulico, antighiaccio, solventi. Poiché termoregolazione è parte integrante di test, polistirene espanso era adatta intorno ai lati del serbatoio ed è fissato in posizione da nastro e il telaio in acciaio stesso, per impedire lo scambio termico con l&#39;ambiente. Il coperchio della camera (Figura 2) è stato fabbricato da trasparente in policarbonato, 9,525 millimetri di spessore, consentendo agli utenti di osservare i campioni durante la prova senza disturbare il test. Il coperchio è fissato in posizione da alluminio barre a T, che erano lavorati a scivolare sotto sovrastante staffe sui lati del serbatoio. Piegatura nei campioni è emanata da tre blocchi di alluminio, che pendono dal coperchio, e sono fissati attraverso fessure nel coperchio. I tre blocchi consentono fino a quattro specimens da testare in una sola volta, mentre le fessure coperchio consentono la spaziatura blocco da regolare a seconda della lunghezza dei campioni. Ciascun blocco viene arrotondato al bordo di contatto ad un diametro 12,7 millimetri, in aderenza alla norma ASTM D790-10. I campioni sono posizionati sotto due dei tre blocchi, con una forza verso l&#39;alto applicata al suo centro per indurre piegatura (figure 1-2). L&#39;apparecchio è stato progettato con la massima versatilità e facilità d&#39;uso in mente. Ruote di diametro 41,275 millimetri sono fissati sotto la camera da garantire la mobilità. Sopra di loro, il serbatoio è supportato da un telaio in acciaio saldato con fondo rete metallica e traverse di sostegno. Angolo distanziali magazzino per gli angoli esterni del serbatoio sono stati prodotti per mantenere l&#39;isolamento di essere schiacciato dal peso e spostamento indicatori ambientali (apparato pot stringa, discusso più avanti). Intorno al top, angolo stock è stato utilizzato ancora per inquadratura. Pulegge e potenziometro stringa misure mezzeria deflessione sono montati su quattro acciaio, archi quadrati tubi (Figura 3). Il centro due archi su questi quattro portano i potenziometri archi e sono regolabili per tenere conto di campioni versatilità. I potenziometri stringa sono stati costruiti con una molla di torsione (come può essere trovato in cordini chiave a scomparsa) e potenziometri con uscite elettroniche tre punte. Le pulegge sono allineate e montate per l&#39;uso con un cavo d&#39;acciaio che parte da un collegamento rigido dal campione ad un&#39;asta appesa sul lato della camera di applicazione dei pesi regolabile. Il carico viene applicato il campione utilizzando una serie di cavi, pulegge, collegamenti e bulloni. Innanzitutto, il campione viene inserito nel cavallotto modo che la barra trasversale da 10 mm è contatto con il centro della campata. Un tondino di acciaio di diametro 9,525 millimetri con golfari alle estremità viene poi collegata al cavallotto. Questa connessione acciaio passa attraverso il coperchio della camera. Un cavo d&#39;acciaio e kevlar thread sono attaccati al golfare di fronte al cavallotto. Questo permette al filo Kevlar dal potenziometro stringa di leggere i dati da un punto solidale. Il cavo d&#39;acciaio continua verso l&#39;alto e passa sopra due pulegge che permettono il carico da applicare alla periferia del serbatoio. Il cavo viene poi collegato ad un tondino di acciaio di diametro 9,525 millimetri che serve come un gancio di peso scanalata. Questo gancio fornisce un posto dove i pesi asolati possono essere impostati in modo da applicare il carico desiderato.

<table border="0" cellpadding="0" cellspacing="0" width="581">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:127px;">Name of Material/</td>
			<td rowspan="2" style="width:140px;">Company</td>
			<td rowspan="2" style="width:129px;">Catalog Number</td>
			<td rowspan="2" style="width:185px;">Comments/Description</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:127px;">Equipment</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:127px;">Aluminum 6061 rectangular bars</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">8975K268, 1668T72, 7062T17,&#160;</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Aluminum 6061 90 deg. angles</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">8982K91, 8982K14&#160;</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">440C stainless steel</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">6253K52</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">High-density polyethylene sheets</td>
			<td rowspan="2" style="width:140px;">Tap Plastics, USA</td>
			<td rowspan="2" style="width:129px;">N/A (0.236 in. thick x 10.75 in. wide x 16.75 in. long)</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">High-density polyethylene sheets</td>
			<td rowspan="2" style="width:140px;">Tap Plastics, USA</td>
			<td rowspan="2" style="width:129px;">N/A (0.354 in. thick x 6 in. wide x 10 in. long)</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">High-density polyethylene sheets</td>
			<td rowspan="2" style="width:140px;">Tap Plastics, USA</td>
			<td rowspan="2" style="width:129px;">N/A (0.354 in. thick x 6 in. wide x 16.75 in. long)</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">Polycarbonate sheets</td>
			<td rowspan="2" style="width:140px;">Tap Plastics, USA</td>
			<td rowspan="2" style="width:129px;">N/A (0.375 in thick, 11.5 in. wide, 17.5 in long)</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">Expanded polystyrene foam</td>
			<td rowspan="2" style="width:140px;">Home Depot</td>
			<td rowspan="2" style="width:129px;">Model # 310880 Internet # 202532855</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Galvanized steel rope</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">3498T63</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Steel eye bolt</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">3013T341</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">Low-carbon steel 90 deg. angle</td>
			<td rowspan="2" style="width:140px;">McMaster-Carr, USA</td>
			<td rowspan="2" style="width:129px;">9017K444&#160;</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="78">
			<td height="100" rowspan="2" style="height:101px;width:127px;">Low-carbon steel rods</td>
			<td rowspan="2" style="width:140px;">McMaster-Carr, USA</td>
			<td rowspan="2" style="width:129px;">8920K84, 8920K75, 8920K231, 8920K135, 8920K84&#160;&#160;&#160;</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="58">
			<td height="80" rowspan="2" style="height:81px;width:127px;">Low-carbon steel tubes</td>
			<td rowspan="2" style="width:140px;">McMaster-Carr, USA</td>
			<td rowspan="2" style="width:129px;">6527K314, 8910K394, 8910K395, 8920K94&#160;&#160;</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">304 stainless steel U-bolt</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">8896T104</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Steel pulley</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">3099T34</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">1008 carbon steel sheets</td>
			<td style="width:140px;">McMaster-Carr, USA</td>
			<td style="width:129px;">9302T113</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Light duty swivel casters</td>
			<td style="width:140px;">Harbor Freight, USA</td>
			<td style="width:129px;">41519</td>
			<td style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="21">
			<td height="43" rowspan="2" style="height:43px;width:127px;">100-lbf Vinyl Weight Set</td>
			<td rowspan="2" style="width:140px;">Overstock.com</td>
			<td rowspan="2" style="width:129px;">11767059</td>
			<td rowspan="2" style="width:185px;">Part of testing platform</td>
		</tr>
		<tr height="22">
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:127px;">Closed-cell polyurethane foam</td>
			<td style="width:140px;">General Plastics, USA</td>
			<td style="width:129px;">FR-3704</td>
			<td style="width:185px;">Testing samples</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Deionized water</td>
			<td style="width:140px;">Faucet, PurLab filtering system</td>
			<td style="width:129px;">N/A</td>
			<td style="width:185px;">Conditioning fluid of tank</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Torsional spring</td>
			<td style="width:140px;">Retractable Key Clip, Ebay, USA</td>
			<td style="width:129px;">Lot 10</td>
			<td style="width:185px;">Used to build string potentiometer</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">Kevlar thread</td>
			<td style="width:140px;">Cabela&#8217;s</td>
			<td style="width:129px;">IK-321909</td>
			<td style="width:185px;">Used to build string potentiometer</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:127px;">10 kOhm potentiometer</td>
			<td style="width:140px;">Ebay, USA</td>
			<td style="width:129px;">3590S-2-103L</td>
			<td style="width:185px;">Used to build string potentiometer</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:127px;">Digital multimeter</td>
			<td style="width:140px;">Harbor Freight, USA</td>
			<td style="width:129px;">98674</td>
			<td style="width:185px;">Used to take resistance measurements of string potentiometer</td>
		</tr>
	</tbody>
</table>

a testing platform for durability studies of polymers and fiber-reinforced polymer composites under concurrent hygrothermo-mechanical stimuli

La durata dei polimeri e compositi polimerici rinforzati con fibre sotto condizione di servizio è un aspetto critico da affrontare per il loro design robusto e basata sulle condizioni di manutenzione. Questi materiali sono adottati in una vasta gamma di applicazioni di ingegneria, di strutture di aeromobili e navi, ai ponti, pale eoliche, biomateriali e impianti biomedici. I polimeri sono materiali viscoelastici, e la loro risposta possono essere altamente non lineare e rendere difficile da prevedere e monitorare le loro prestazioni in servizio così. La piattaforma di test di laboratorio su scala presentato qui assiste l&#39;indagine della influenza di carichi meccanici concorrenti e delle condizioni ambientali su tali materiali. La piattaforma è stata progettata per essere a basso costo e di facile utilizzo. I materiali resistenti agli agenti chimici rendono la piattaforma adattabile a studi di degradazione chimica a causa dell&#39;esposizione in servizio ai fluidi. Un esempio di esperimento è stato condotto a temperatura ambiente su cellule chiuse poliuretanocampioni schiuma caricati con un peso corrispondente a ~ 50% del loro carico statico e secco finale. I risultati mostrano che l&#39;apparecchiatura di prova è appropriato per questi studi. I risultati evidenziano anche maggiore vulnerabilità del polimero sotto carico concomitante, in base ai più elevati spostamenti mid-point e bassi carichi di rottura residue. Raccomandazioni sono fatti per ulteriori miglioramenti alla apparecchiatura di prova.

L&#39;apparecchiatura di prova è svolta con successo campioni immersi in un fluido in tre punti piegatura. Con precisioni ragionevoli, i campioni possono essere caricati e testati con letture accurate dei potenziometri per mid-point deflessione modifiche. La variazione di resistenza elettrica può essere registrato 4 cifre significative, con conseguente spostamento risoluzione dell&#39;ordine di 0,1 micron. Test Hygrothermo-meccaniche sono state condotte a temperatura ambiente su due gruppi...

Watch this Scientific Journal Video about A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli at JoVE.com

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

Una piattaforma di prova per una durata Studi di polimeri e fibra-Reinforced Polymer Composites sotto Stimoli Concurrent Hygrothermo-meccanico

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

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13.7K Views.  University of California, Davis. The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

Video: A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

Controllo della dimensione, forma e stabilità dei polimeri supramolecolari in acqua

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

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Concurrent Quantitative Conductivity and Mechanical Properties Measurements of Organic Photovoltaic Materials using AFM

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. Thus, understanding of spatial variations in composition as well as electrical properties of OPV materials is of paramount importance for moving PV technology forward.1,2 In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution. Currently, materials properties measurements performed using commercially available AFM-based techniques (PeakForce, conductive AFM) generally provide only qualitative information. The values for resistance as well as Young's modulus measured using our method on the prototypical ITO/PEDOT:PSS/P3HT:PC61BM system correspond well with literature data. The P3HT:PC61BM blend separates onto PC61BM-rich and P3HT-rich domains. Mechanical properties of PC61BM-rich and P3HT-rich domains are different, which allows for domain attribution on the surface of the film. Importantly, combining mechanical and electrical data allows for correlation of the domain structure on the surface of the film with electrical properties variation measured through the thickness of the film.

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution.

Concurrent conducibilità quantitativa e meccaniche Misure Proprietà dei materiali organici fotovoltaici utilizzando AFM

Organic photovoltaic  (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale  inhomogeneity of OPV materials affects performance ...

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

Saldatura ad ultrasuoni di tagliandi termoplastico composito per la caratterizzazione meccanica dei giunti saldati attraverso singolo giro Shear Test

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.

Here we present a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of cadmium selenide quantum dots can be accurately visualized through cross-sectional fluorescence imaging.

Avanzate analisi composizionale di Compositi nanoparticelle-polimero Uso diretto imaging di fluorescenza

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise ...

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.

A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.

Compositi nanostrutturati Ag-zeolite come Sensori di umidità a base di luminescenza

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high ...

A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional experimental approaches, such as out-of-plane and in-plane tests, are not applicable to the determination of forming limits when heating and rapid cooling processes are introduced prior to forming for tests conducted under hot stamping conditions. A novel in-plane biaxial testing system was designed and used for the determination of forming limits of sheet metals at various strain paths, temperatures, and strain rates after heating and cooling processes in a resistance heating uniaxial testing machine. The core part of the biaxial testing system is a biaxial apparatus, which transfers a uniaxial force provided by the uniaxial testing machine to a biaxial force. One type of cruciform specimen was designed and verified for the formability test of aluminum alloy 6082 using the proposed biaxial testing system. The digital image correlation (DIC) system with a high-speed camera was used for taking strain measurements of a specimen during a deformation. The aim of proposing this biaxial testing system is to enable the forming limits of an alloy to be determined at various temperatures and strain rates under hot stamping conditions.

This protocol proposes a novel biaxial testing system used on a resistance heating uniaxial tensile test machine in order to determine the forming limit diagram (FLD) of sheet metals under hot stamping conditions.

Una nuova apparecchiatura biassiale test per la determinazione del limite di formatura in stampa a caldo Condizioni

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional ...

Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

Preparazione di allineati fibra d'acciaio rinforzato cementizia composito e il relativo comportamento flessionale

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the ...

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Metodo di installazione per migliorare il controllo di qualità per fibra rinforzata polimero Spike ancore

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

Sviluppo del metodo per studi spettroscopici distesina di cavità senza contatto della carta cellulosica

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Fabbricazione e progettazione di compositi ad alte prestazioni basati sul legno

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...