Effects of vibration welding on the microstructure and tensile behavior of glass fiber reinforced semi-crystalline polymers

Le soudage par vibration est un procédé largement utilisé dans l’industrie automobile pour assembler des pièces en polymère. Lorsque la matière à souder ne contient pas de renforts, le coefficient de soudage, défini comme le rapport entre la contrainte à la rupture du matériau soudé et celle du matériau non soudé est proche de 1. En revanche, il devient difficile d’obtenir des coefficients de soudage dépassant 0,6 lorsque le matériau contient des fibres de verre. Afin de mieux comprendre pourquoi, différents grades de polyamide (PA) 6 et 66 renforcés à 30% de fibres ainsi que du polypropylène (PP) à 0, 20, 35 et 50% de fibres ont été injectés en plaques et soudées par vibration. Pour les échantillons en PA, des corrélations sont obtenues entre la contrainte à la rupture des assemblages soudés et l’orientation des fibres mais aussi avec l’épaisseur de la zone soudée déterminée par tomographie RX. L’étude sur les échantillons en PP indique que des cavités, probablement nocives, sont présentes uniquement dans la zone soudée des polymères renforcés. Leur présence est alors principalement attribuée à la réorientation des fibres pendant l’opération de soudage. Enfin, une simulation par éléments finis du comportement mécanique jusqu’à la rupture a été réalisée sur une éprouvette maillée comprenant une zone soudée. Les résultats obtenus mettent en exergue un phénomène d’amplification et de redistribution des contraintes dans la zone soudée en raison du confinement. Cette triaxialité générée favorise la croissance et la coalescence des cavités dans la zone soudée expliquant ainsi l’affaiblissement de la contrainte macroscopique uniaxiale à la rupture.Vibration welding is a common process used in automotive industry to assembly polymer parts. For pristine polymers, welding ratio, defined as the ratio between weld strength and tensile strength of non-welded material, is close to 1. However, for glass-fiber reinforced polymers, welding ratios are around 0.6 at best. In order to understand this discrepancy, several grades of polyamide (PA) 6 and 66 reinforced with 30% glass fibers as well as polypropylene (PP) with 0, 20, 35 and 50 % glass fibers have been injected in plates and vibration welded. A linear relationship was obtained between tensile strength of welded and non-welded PA specimens and their glass fiber orientation. Correlations were also found when plotting weld strength of samples regarding their welded zone thickness. In addition, voids are present only in the welded zone of glass fiber reinforced specimens, indicating that these voids are due to reorientation of fibers during the welding process. Finally, finite element modeling of mechanical behavior up to failure has been applied on a meshed specimen with a welded zone. Results show an amplification and distribution of stresses in the three directions inside the welded zone due to geometrical confinement. This generated triaxiality promotes growth and coalescence of cavities in the welded zone, explaining the weakening of the macroscopic uniaxial stress at failure

Effets du soudage par vibration sur la microstructure et le comportement en traction de polymères semi-cristallins renforcés par des fibres de verre

Vibration welding is a common process used in automotive industry to assembly polymer parts. For pristine polymers, welding ratio, defined as the ratio between weld strength and tensile strength of non-welded material, is close to 1. However, for glass-fiber reinforced polymers, welding ratios are around 0.6 at best. In order to understand this discrepancy, several grades of polyamide (PA) 6 and 66 reinforced with 30% glass fibers as well as polypropylene (PP) with 0, 20, 35 and 50 % glass fibers have been injected in plates and vibration welded. A linear relationship was obtained between tensile strength of welded and non-welded PA specimens and their glass fiber orientation. Correlations were also found when plotting weld strength of samples regarding their welded zone thickness. In addition, voids are present only in the welded zone of glass fiber reinforced specimens, indicating that these voids are due to reorientation of fibers during the welding process. Finally, finite element modeling of mechanical behavior up to failure has been applied on a meshed specimen with a welded zone. Results show an amplification and distribution of stresses in the three directions inside the welded zone due to geometrical confinement. This generated triaxiality promotes growth and coalescence of cavities in the welded zone, explaining the weakening of the macroscopic uniaxial stress at failure.Le soudage par vibration est un procédé largement utilisé dans l’industrie automobile pour assembler des pièces en polymère. Lorsque la matière à souder ne contient pas de renforts, le coefficient de soudage, défini comme le rapport entre la contrainte à la rupture du matériau soudé et celle du matériau non soudé est proche de 1. En revanche, il devient difficile d’obtenir des coefficients de soudage dépassant 0,6 lorsque le matériau contient des fibres de verre. Afin de mieux comprendre pourquoi, différents grades de polyamide (PA) 6 et 66 renforcés à 30% de fibres ainsi que du polypropylène (PP) à 0, 20, 35 et 50% de fibres ont été injectés en plaques et soudées par vibration. Pour les échantillons en PA, des corrélations sont obtenues entre la contrainte à la rupture des assemblages soudés et l’orientation des fibres mais aussi avec l’épaisseur de la zone soudée déterminée par tomographie RX. L’étude sur les échantillons en PP indique que des cavités, probablement nocives, sont présentes uniquement dans la zone soudée des polymères renforcés. Leur présence est alors principalement attribuée à la réorientation des fibres pendant l’opération de soudage. Enfin, une simulation par éléments finis du comportement mécanique jusqu’à la rupture a été réalisée sur une éprouvette maillée comprenant une zone soudée. Les résultats obtenus mettent en exergue un phénomène d’amplification et de redistribution des contraintes dans la zone soudée en raison du confinement. Cette triaxialité générée favorise la croissance et la coalescence des cavités dans la zone soudée expliquant ainsi l’affaiblissement de la contrainte macroscopique uniaxiale à la rupture

Caractérisation thermomécanique de polymères thermoplastiques pour application photovoltaïque

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Caractérisation thermomécanique de polymères thermoplastiques pour application photovoltaïque

International audienc

Caractérisation thermomécanique de polymères thermoplastiques pour application photovoltaïque

International audienc

Standardized cross-linking determination methods applied to POE encapsulants in lamination recipe emphasizing

International audienceEthylene vinyl acetate is the most common encapsulation material in photovoltaic panels. Due to gradual engineering, it ensures to meet performance requirement of standard cells, low-cost and well understood cross-linking behaviour, both physically and chemically. Nowadays polyolefin elastomers (POE) have been entering the PV industry requirements by advanced cells concepts and/or novel degradation phenomena noticed on bifacial modules. POE exhibit several advantages based on its intrinsic high volume resistivity, low permeation, processability and most importantly, the absence of harmful by-products (such as acetic acid) generated upon humidity exposure[1, 2]. However, this new family of materials may behave differently from EVA during crosslinking, thus it is necessary to verify and adapt standard measurement methods. Therefore, the main objective of this study is to investigate the cross-linking behaviour of POEs with the final goal of exploring the process window of the lamination. The characterization methods like differential scanning calorimetry (DSC) and Soxhlet extraction have been used to determine crosslinking rate and chemical structure of several encapsulants. Similar to EVAs, cross-linking rate of POEs measured by Soxhlet extraction increases with lamination duration until reaching a plateau. The indirect cross-linking rate measurement by DSC analysis is usually favoured through its simple, fast implementation, absence of toxic chemicals when compared to Soxhlet extraction. Remarkable correlations between the two techniques were obtained for a commercially available POE, allowing the extension of the IEC standard to new encapsulants. Nevertheless, in the case of highly engineered materials, clear deviations are recorded, highlighting validity limits of direct correlation between Soxhlet and DSC methods

Standardized cross-linking determination methods applied to POE encapsulants in lamination recipe emphasizing

International audienceEthylene vinyl acetate is the most common encapsulation material in photovoltaic panels. Due to gradual engineering, it ensures to meet performance requirement of standard cells, low-cost and well understood cross-linking behaviour, both physically and chemically. Nowadays polyolefin elastomers (POE) have been entering the PV industry requirements by advanced cells concepts and/or novel degradation phenomena noticed on bifacial modules. POE exhibit several advantages based on its intrinsic high volume resistivity, low permeation, processability and most importantly, the absence of harmful by-products (such as acetic acid) generated upon humidity exposure[1, 2]. However, this new family of materials may behave differently from EVA during crosslinking, thus it is necessary to verify and adapt standard measurement methods. Therefore, the main objective of this study is to investigate the cross-linking behaviour of POEs with the final goal of exploring the process window of the lamination. The characterization methods like differential scanning calorimetry (DSC) and Soxhlet extraction have been used to determine crosslinking rate and chemical structure of several encapsulants. Similar to EVAs, cross-linking rate of POEs measured by Soxhlet extraction increases with lamination duration until reaching a plateau. The indirect cross-linking rate measurement by DSC analysis is usually favoured through its simple, fast implementation, absence of toxic chemicals when compared to Soxhlet extraction. Remarkable correlations between the two techniques were obtained for a commercially available POE, allowing the extension of the IEC standard to new encapsulants. Nevertheless, in the case of highly engineered materials, clear deviations are recorded, highlighting validity limits of direct correlation between Soxhlet and DSC methods

Microstructure-mechanical properties relationships in vibration welded glass-fiber-reinforced polyamide 66: A high-resolution X-ray microtomography study

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