Autohesive strength characterization of semi-crystalline polymer matrix composites

Padaki, S.; Drzal, L. T.

doi:10.1163/156855496x00218

Cited by 3 publications

(16 citation statements)

References 3 publications

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“…Research has shown that crystallization can hinder the molecular diffusion at the layer interface. [15,17] Therefore, it must be considered to occur simultaneously with bond formation, which can lead to poor bonding and reduced mechanical properties. As part properties can also be impacted by the effects of polymer degradation, models describing degradation effects are also considered.…”

Section: Theoretical Investigationmentioning

confidence: 99%

“…For the understanding of semicrystalline polymers, heat transfer, resin flow, and wetting have to be considered in addition to the bonding-rate-controlled chain diffusion. [17,20,31] As the aim of fusion bonding is to achieve a monolithic material with the strength of the bulk polymer, [20,32] the degree of bonding, D b , describes the interlaminar bond strength of identical polymer surfaces that are in contact compared to the strength of the bulk. [17,18] The degree of bonding is calculated from the degree of intimate contact, D ic , and the degree of healing, D h : [32]…”

Section: Fusion Bondingmentioning

confidence: 99%

“…[35] When healed under ideal conditions for a sufficient amount of time, the interface becomes indistinguishable from the bulk polymer. [17,19,20] Under these conditions, crystallization is a competing mechanism with autohesion and is an important phenomenon to consider. [17]…”

Section: Autohesionmentioning

confidence: 99%

“…Furthermore, they offer distinct advantages such as improvements of several mechanical and chemical properties, recyclability and reparability, low costs, and shorter cycle times. [15][16][17] Based on these advantages, they are increasingly being used in the automotive and general transport sector. [18] In additive manufacturing, thermoplastics challenge AM processes by virtue of their high viscosities, as they require high temperatures and pressures to initiate polymer flow during extrusion.…”

Section: Introductionmentioning

confidence: 99%

“…Their morphological structure leads to a high dependency on mechanical properties on the processing conditions and the resulting degree of crystallization. [17,18,21] Processing temperatures above the melting point reduce the viscosity and mobilize molecules for polymer flow. [12] Polyamide 6 (nylon 6) is well suited for high heat and stress resistance applications and thus has become a common engineering polymer used in the automotive industry, for instance, in injection molding processes.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

et al. 2021

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Fusion bonding is understood to be the decisive mechanism for the interlayer strength in extrusion additive manufacturing. This study links the characteristic temperatures of semicrystalline thermoplastics, namely, PA6 with 40% carbon fibers, to the bond formation in respect to real-world processing conditions. Based on theoretical investigations, a process window is proposed for bonding to occur without polymer degradation. This range from the glass transition to the initial degradation temperature was determined through differential scanning calorimetry and thermogravimetric analysis. A second process window for optimal bonding is proposed from the extrapolated onset crystallization temperature, T eic , to the melt temperature, T m . The validation of these process windows was conducted by bending tests according to DIN EN 178. T m was confirmed as the upper limit, with the part's geometric integrity compromised at higher temperatures. T eic had to be refuted as lower limit as no discrete reduction in bond strength was determined in alignment with T eic . Authors suggest the lower limit is defined by the lowest substrate temperature to lead to interface temperatures above the onset of melt temperature. By utilizing thermal analyses, less time and resources are required to detemine a suitable process window for extrusion additive manufacturing.

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Section: Theoretical Investigationmentioning

confidence: 99%

Section: Fusion Bondingmentioning

confidence: 99%

Section: Autohesionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

et al. 2021

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A Consolidation Model for Polymer Powder Impregnated Tapes

Padaki

Drzal

1997

Journal of Composite Materials

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Powder impregnation technology is a relatively new fabrication method for polymer powder composites. A number of processes using this processing route have been developed. However, the transformation of these preimpregnated materials into fully densified composite structures has been performed empirically. A fundamental understanding of the process would therefore prove a good resource to the composite industry. The overall objective of this study was to develop a mathematical model that would describe the consolidation process. Experimental observations were used to categorize the process into three simple unit operations: heating, compression and cooling. Each of these stages was modeled independently. A one dimensional heat flow equation with appropriate boundary conditions was solved from the heating and cooling models. A three dimensional squeeze flow model with corresponding boundary conditions was used to describe the flow of the polymer in the lay-up. An existing fiber deformation model was used in order to predict the additional pressure required for consolidation. Data from experiments designed to test the heating and cooling model fit well with the simulations. Deviations from the model at short times were observed. However, the total heating and cooling times that were predicted were accurate. Experimental verification of the flow model showed that the time and pressure required for flow were extremely small compared to the fabrication cycle.

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Targeted Temperature Manipulation and Analysis of the Influence on Mechanical Properties in Large-Scale Extrusion Additive Manufacturing

2022

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Layer times in large-scale Extrusion Additive Manufacturing (EAM) of carbon fiber-reinforced thermoplastics are often outside the recommended process window. Brief layer times of tall parts with short path lengths lead to high temperatures and thus to melting of the component. In contrast, the substrate temperature decreases too far at longer layer times to achieve sufficient fusion bonding through molecular diffusion across the interface. Heating by infrared emitters and cooling by compressed air were experimentally tested and evaluated as methods for temperature control. Assuming that bond formation is mainly temperature-controlled, mechanical properties were expected to be similar to those of non-manipulated samples at the same temperatures. Samples of short carbon fiber-filled polyamide 6 in pellet form were manufactured in three test series. Infrared heating resulted in comparable tensile properties to samples at the target temperature and in a significant increase compared to the base temperature without heating. Cooling proved to be more effective when closer to the deposition nozzle, with tensile results even exceeding the expected values at temperatures below 170 °C. Overall, the results support the potential for targeted temperature control in EAM and the hypothesis that comparable bond strength can be achieved in dependence of the final substrate temperature.

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Autohesive strength characterization of semi-crystalline polymer matrix composites

Cited by 3 publications

References 3 publications

Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

A Consolidation Model for Polymer Powder Impregnated Tapes

Targeted Temperature Manipulation and Analysis of the Influence on Mechanical Properties in Large-Scale Extrusion Additive Manufacturing

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