Os autores agradecem Destino Garcia, Serena Ferraro, Erik Quiroz e Steven Kern (Advanced Composites Research, Engenharia e Ciência de laboratório) por sua ajuda em projetar e fabricar a configuração de teste. Shawn Malone, Michael Akahori, David Kehlet (Lab Fabrication Engineering) são reconhecidos por suas sugestões e ajuda no processo de usinagem. O apoio da National Science Foundation (concessão de colaboração CMMI-1265691 e seu suplemento REU) e do Escritório de Pesquisa Naval (N00014-13-1-0604 para A. Muliana, Texas &amp; M University (Investigador Principal), e V. La Saponara , gerido pelo diretor do programa Yapa Rajapakse) são apreciadas.

1. Colocação das Amostras <ol><li> Levante a tampa do tanque e colocá-la em cima dos suportes laterais (Figura 4). </li><li> Coloque a amostra do U-parafuso, e garantir que a barra transversal está fazendo contato com o centro da amostra. </li><li> Descanse as extremidades da amostra sobre os suportes de alumínio pendurados no tampa. As extremidades dos espécimes deve ter 5-10 mm de saliência. </li><li> Repita os passos de 1,2-1,4 para todas as amostras que serão testadas. </li><li> Remover a tampa apoia, inferior da tampa, e certificar-se de que a tampa está encaixada na borda do tanque. </li><li> Aplicar a força desejada pela adição de pesos para a barra de aço ao lado da polia exterior. </li></ol> 2. Deslocamento de medição <ol><li> Certifique-se de que a linha da corda potenciômetro está esticada. </li><li> Usando um multímetro digital, meça a resistência entre os pinos externos do potenciômetro (Figura 3), com o preto no pino 1 e vermelho para o pino 3e registrar a leitura. </li><li> Converter a leitura da resistência de leitura para um deslocamento através do cálculo do factor de calibração (neste caso, 1 kQ corresponde a um deslocamento de 64,895 milímetros). </li><li> Repita os passos de 2,1-2,3 para cada espécime. </li></ol> 3. Pesando os espécimes <ol><li> Antes de iniciar o processo de pesagem, gravar os dados de deslocamento e preparar uma câmara de retenção provisória cheio com o fluido de ensaio à temperatura ambiente, como em ASTM D5229 31, ou a norma de ensaio apropriada. </li><li> Retire os pesos de entalhe das extremidades dos cabos de aço. </li><li> Levante a tampa do tanque e colocá-la em cima dos suportes laterais. </li><li> Remova a amostra e colocá-lo na câmara de retenção provisória preparada. Repita este passo para todos os espécimes. </li><li> Remover os espécimes e secá-las individualmente utilizando um pano de microfibras, a fim de remover o excesso de fluido. </li><li> Coloque a amostra em uma escala de alta precisão e gravar os dados reading. </li><li> Repita os passos de 3,5-3,6 para todas as amostras e siga Protocolo Passo 1. </li></ol>

<ol>
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The authors have nothing to disclose.

A partir dos dados obtidos, pode observar-se que o cenário testes simultâneos afetou a durabilidade das amostras de células fechadas da espuma de poliuretano. Isto pode ser visto comparando os deslocamentos significativamente diferentes (Figura 5) e cargas residuais até a falha (Figura 6) de amostras secas e húmidas. A Figura 7 mostra imagens das amostras após os testes de resistência residual. Deve também ser observado que, enquanto que o deslocamento dos espé...

Polímero e polímero reforçado com fibra (FRP) foram adotados em uma variedade de estruturas de engenharia, que vão desde aviões e naves espaciais, embarcações navais, infra-estruturas civis, (ver, por comentários exemplos de Katnam et al. 1, Hollaway 2, Mouritz et al . 3), carros e trens, pás de turbinas de vento, para próteses e biomateriais para suturas e implantes. Durabilidade Estes materiais &quot;é afetado por cenários complexos de serviços, que podem incluir uma combinação de um carregamento) termo-mecânica, por exemplo, de congelamento e descongelamento ciclos em infra-estrutura civil, 4, vôo subsônico / supersônico perfis 5, o desgaste em polietileno com base metálica de 6) ; b) degradação devido aos agentes ambientais e químicos, por exemplo, água do mar, de degelo, o fluido hidráulico para a indústria aeroespacial e naval estruturas 10/07, de degradação dos compósitos de polimetilmetacrilato dentárias devido à saliva 11; c) inte complexoractions de materiais nas articulações presas ou aduaneiros, por exemplo, corrosão galvânica e descolamento entre materiais diferentes, seja em um reparo de remendo de carbono / fibra em uma pele de alumínio de aeronaves, ou uma placa óssea / PEEK carbono fixado por aço inoxidável 12. Não é, infelizmente, limitada conhecimento do impacto de estímulos simultâneos em serviço, sobre a durabilidade a longo prazo destes materiais. A maioria dos polímeros podem ser classificados como materiais viscoelásticos. Cargas mecânicas e condições ambientais influenciam significativamente a resposta viscoelástico de polímeros. Assim, modelos fiáveis ​​para o comportamento a longo prazo destes materiais deve ser capaz de incorporar as respostas dependentes do tempo para higrotérmica acoplado, estímulos químicos, mecânicos. Este, por sua vez, irá melhorar as previsões de design, segurança e protocolos de manutenção / substituição com base em condições. Há um grande corpo de literatura em testes experimentais sobre os efeitos higrotérmicas, Para os testes de difusão exemplo higrotérmicas: se a escala das amostras permite, as amostras de material pode ser posicionado em uma câmara com níveis de umidade e temperatura desejada. As amostras são removidas periodicamente para medir a sua massa e / ou de volume para um determinado período de tempo, de semanas a anos 10,13-17. O teste higrotérmica pode ser seguido por ensaios mecânicos, ou seja, a força / fadiga estática residual / fractura mecânica ensaios 17-19, o qual só dá informações sobre o efeito de estímulo higrotérmica sobre as respostas mecânicas dos materiais. Os dados de teste podem ser instalados em modelos de difusão de complexidade variada, desde a simples difusão Fickiana a modelos que incluem a dependência de concentração, stress, temperatura, reversível física envelhecimento / plastificação e reações químicas irreversíveis. Esta saída experimental pode ser ainda incorporada em análises estruturais. Poucos autores têm abordado o impacto da hy simultâneagrothermal e estímulos mecânicos. Entre os que pesquisam materiais FRP, Neumann e Garom 20 imerso estressado e átonas espécimes em água destilada. O estresse foi aplicado através do posicionamento dos espécimes dentro molas de aço inoxidável comprimido, ajustando a carga por meio de diferentes rigidezes mola e cargas de compressão. Um processo semelhante está descrito por Wan et al. 21. Helbling e Karbhari 22 empregou um dispositivo elétrico dobra dentro de uma câmara ambiental para diferentes porcentagens de umidade relativa do ar (UR%) e os níveis de temperatura. As amostras de pré-condicionados foram submetidos a um determinado nível de tensão de flexão, o que corresponde a uma percentagem da tensão de tracção máxima estática para que compósito. Kasturiarachchi Pritchard e 23 preparados de um aço inoxidável de 4 pontos gabarito de curvatura (um por amostra) que foi colocada numa prateleira num exsicador grande vidro. O secador foi parcialmente preenchido com água destilada, teve pequenos vazamentos para evitar a buildup de pressão, e foi colocado numa câmara de humidade a 95% HR. Gellert e Turley 7 investigado espécimes FRP compostas marine-grade por sua durabilidade sob o carregamento de fluência combinado e 100% RH. As amostras foram carregadas em flexão de 4 pontos com uma carga constante e igual a 20% da carga de flexão estática falha, ao mesmo tempo totalmente imerso na água do mar. A deflexão fluência foi adquirida periodicamente usando um medidor de espessura entre a superfície exterior do feixe na secção transversal central, e uma placa de vidro (infere-se que tal medição foi realizada no exterior da câmara). Abdel-Magid et al. 24 colocado amostras de vidro / epóxi em um aparelho de iluminação ambiente Invar que foi fornecida pela NASA Langley, como as amostras foram carregadas em tensão ao longo da direcção das fibras, a 20% da carga axial final. Ellyin e Rohrbarcher 25 realizaram testes higrotérmicas para até 140 dias e, em seguida, testou os espécimes em fadiga em uma máquina de ensaio hidráulico. O espécimes foram envolto em um pano molhado queijo conectado a um tubo e uma fonte de água. Earl et al. 26 posicionada sua fixação de carga e os espécimes em uma grande câmara ambiental (5,5 m 3). Como discutido em muitos estudos experimentais, as condições ambientais afetam propriedades e respostas mecânicas dos polímeros. Algumas experiências limitados mostram também que a existência de esforço mecânico / estirpe influencia o processo de difusão dos polímeros. Assim, para melhorar o entendimento sobre o desempenho global de materiais à base de polímero em ambos os efeitos mecânicos e não mecânicos, existe uma necessidade para testes simultâneos. Havia vários objectivos por detrás do projeto da plataforma de testes discutidos neste trabalho. Em primeiro lugar, a plataforma é parte da instalação experimental em uma investigação de vários anos sobre o comportamento hygrothermo-mecânico de diferentes tipos de compósitos sanduíche FRP para uma turbina eólicaaplicações de engenharia naval nd. Os dados do teste são utilizadas para calibrar os parâmetros nas equações constitutivas viscoelásticos para os compósitos poliméricos. Os modelos constitutivos baseiam-se no trabalho desenvolvido ao longo dos anos por Muliana e colaboradores 27-30. O segundo objectivo foi o de ter um baixo custo e uma plataforma de teste fácil de usar, por exemplo, um que possa ser facilmente deslocalizada num laboratório (por exemplo, a uma escala de medições de massa, ou para a fonte de fluido, por exemplo, aquele que vem a partir de uma torneira, um fumehood ou um gabinete inflamável). O terceiro objectivo era criar uma plataforma de ensaio que é resistente a um número de produtos químicos usados ​​em serviço (fluido hidráulico particularmente, de degelo, solventes de limpeza para aplicações aeroespaciais 8-10), assim, as amostras podem ser imersos em tais produtos químicos, e sua durabilidade pode ser avaliada. A câmara (Figura 1) foi construído com polyethyle de alta densidadene, que tem uma elevada resistência a produtos químicos. Como mencionado acima, espera-se que o trabalho futuro vai incluir investigação hygrothermo-mecânico de compósitos imersas em um fluido hidráulico, de degelo, solventes de limpeza. Uma vez que a regulação térmica é uma parte integrante da análise, espuma de poliestireno expandido foi ajustar em torno dos lados do tanque e seguros no lugar por meio de fita e a própria armação de aço, para evitar a troca de calor com o ambiente. A tampa da câmara (Figura 2) foi fabricado a partir de transparente, policarbonato 9,525 milímetro de espessura, permitindo aos utilizadores observar as amostras durante os testes, sem perturbar o teste. A tampa é fixada no lugar por barras em T de alumínio, que foram maquinadas para deslizar sob pendendo sobre suportes nos lados do tanque. Dobrando nas amostras é promulgada por três blocos de alumínio, que pendem da tampa, e são presas através de ranhuras na tampa. Os três blocos permitem que até quatro specimens para ser testado de uma só vez, enquanto que as ranhuras da tampa permite que o bloco de espaçamento deve ser ajustada dependendo do comprimento dos espécimes. Cada bloco é arredondado na extremidade de contato para um diâmetro 12,7 milímetros, na adesão a ASTM D790-10 padrão. As amostras são posicionadas por baixo, dois dos três blocos, com uma força ascendente aplicada no seu centro para induzir flexão (Figuras 1-2). O aparelho foi projetado com o máximo de versatilidade e facilidade de uso em mente. Rodízios com 41,275 milímetros de diâmetro são presos por baixo da câmara para fins de mobilidade. Acima deles, o tanque é suportado por uma estrutura de aço soldada com um fundo de rede de arame e vigas transversais de suporte. Ângulo de espaçadores de ações para os cantos do tanque de fora foram fabricados para manter o isolamento de ser esmagado pelo peso e deslocamento calibres aéreos (aparelho pote corda, discutido mais tarde). Around the top, estoque ângulo foi novamente utilizado para o enquadramento. Sistemas de roldanas e corda potenciômetro para measure meio da extensão de deflexão são montados em quatro aço, arcos de tubos quadrados (Figura 3). Os centros de dois arcos desses quatro transportar os potenciômetros de cordas e são ajustáveis ​​para contabilizar espécime versatilidade. Os potenciômetros de cordas foram construídos com uma mola de torção (como pode ser encontrado em colhedores chave retrátil) e potenciômetros com saídas eletrônicos de três pinos. As polias estejam alinhadas e montadas para utilização com um cabo de aço que funciona de uma ligação rígida com o espécime a uma haste pendurado para o lado da câmara de aplicação para o peso ajustável. A carga é aplicada para a amostra usando uma série de cabos, polias, ligações e parafusos. Em primeiro lugar, a amostra é colocada no perno em U de modo que a barra transversal 10 mm em contacto a meio do vão. Uma haste de aço de diâmetro 9,525 milímetros com parafusos de olho em cada extremidade é então ligado ao U-bolt. Esta ligação de aço passa através da tampa da câmara. Um cabo de aço e Kevlar thread estão ligados ao olhal oposto da cavilha em U. Isso permite que o fio de Kevlar do potenciômetro cadeia para ler dados a partir de um ponto rígida. O cabo de aço continua para cima e passa por cima de duas polias que permitem que a carga a ser aplicada na periferia do tanque. O cabo é, então, ligado a uma haste de aço de diâmetro 9,525 milímetros, que serve como um gancho peso ranhurada. Este gancho fornece um lugar onde os pesos de fenda pode ser definida, a fim de aplicar a carga desejada.

<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

A durabilidade dos polímeros e compósitos poliméricos reforçados com fibras sob condição de serviço é um aspecto crítico de ser abordada por seus designs robustos e manutenção baseada em condição. Estes materiais são adotados em uma ampla gama de aplicações de engenharia, a partir de estruturas de aeronaves e navios, para pontes, pás de turbinas eólicas, biomateriais e implantes biomédicos. Os polímeros são materiais viscoelásticos, e sua resposta pode ser altamente não-linear e, assim, torná-lo difícil de prever e controlar o seu desempenho em serviço. A plataforma de ensaio à escala laboratorial aqui apresentadas auxilia a investigação da influência de cargas mecânicas simultâneas e condições ambientais sobre estes materiais. A plataforma foi projetada para ser de baixo custo e fácil de usar. Seus materiais resistentes quimicamente tornar a plataforma adaptável a estudos de degradação química devido à exposição em serviço para fluidos. Um exemplo de experimento foi conduzido na RT em poliuretano de célula fechadaamostras de espuma carregado com um peso correspondente a ~ 50% da sua carga estática e seco final. Os resultados mostram que o aparelho de teste é adequado para estes estudos. Os resultados também realçam a maior vulnerabilidade do polímero sob carga simultânea, com base nos deslocamentos de ponto médio superior e inferior cargas de ruptura residual. As recomendações são feitas para melhorias adicionais ao aparelho de ensaio.

O aparelho de teste foi realizado com sucesso amostras imersas em um fluido sob três pontos de dobra. Com precisão razoáveis, as amostras podem ser carregadas e testado com leituras precisas dos potenciômetros para meados de ponto muda de deflexão. A alteração da resistência eléctrica pode ser gravado para 4 algarismos significativos, resultando numa resolução de deslocamento da ordem de 0,1 um. Hygrothermo testes mecânicos foram conduzidos à temperatura ambiente em dois grupos ...

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.

A Plataforma de testes de durabilidade Estudos de Polímeros e reforçado com fibra de polímero Composites, sob estímulo Concurrent Hygrothermo-mecânico

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 visualizações.  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.

Vídeo: 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.

Controlando o tamanho, forma e estabilidade de Polímeros Supramoleculares na Água

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.

Condutividade quantitativa concorrente e Medidas mecânicas de materiais fotovoltaicos orgânicos utilizando 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.

Ultrasonic Welding de cupons termoplástica composta de Mecânica Caracterização de Juntas Soldadas através Individual Sobreposição Testing

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.

Avançado Análise da composição dos compósitos de nanopartículas de polímero através da tecnologia Direct Fluorescência de imagem

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.

Composites nanoestruturado Ag-zeólita como sensores de umidade à base de luminescência

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.

Um novo aparelho Biaxial Teste para a Determinação do limite de conformação sob Hot Stamping Condições

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.

Preparação de fibras de aço alinhada reforçado cimento compósito e seu comportamento à flexão

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.

Método de instalação para aprimorar o controle de qualidade para a fibra reforçado polímero Spike âncoras

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

Applicability Analysis of Assessment Methods for Morphological Parameters of Corroded Steel Bars

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly dominate the safety and performance of an existing concrete structure. As a result, it is important to measure the geometry and amount of corrosion of a steel bar in a structure properly to assess the residual bearing capacity and service life of the structure. This paper introduces and compares five different methods for measuring the geometry and amount of corrosion of a steel bar. A single 500 mm long and 14 mm diameter steel bar is the specimen that is subjected to accelerated corrosion in this protocol. Its morphology and the amount of corrosion were carefully measured before and after using mass loss measurements, a Vernier caliper, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT). The applicability and suitability of these different methods were then evaluated. The results show that the Vernier caliper is the best choice for measuring the morphology of a non-corroded bar, while 3D scanning is the most suitable for quantifying the morphology of a corroded bar.

This paper measures the geometry and the amount of corrosion of a steel bar using different methods: mass loss, calipers, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT).

Análise da aplicabilidade dos métodos de avaliação de parâmetros morfológicos das barras de aço corroídas

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly ...

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.

Desenvolvimento de método para estudos espectroscópicos dielétricos de cavidade ressonante sem contato de papel Celulóico

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