Analysis of micro-damage evolution in induction-cured thermoset composites
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Andrejs PUPURS (LATVIA), Viesturs LĀCIS , Alens ŠŅEPSTS , Anish Niranjan KULKARNI (LATVIA), Mārtiņš IRBEAbstract :
High performance lightweight composites, such as carbon fiber reinforced polymers are increasingly used in various engineering applications. Nevertheless, conventional manufacturing methods for production of lightweight composites are highly energy consuming. For example, oven curing has been estimated to consume approximately 20 MJ/kg largely due to excess heating of chamber volumes and molds [1]. To reduce the high energy consumption in the composites manufacturing process alternative curing methods that can deliver heat directly to the composite part must be exploited. A highly promising direct curing method which stands out with low power consumption, ability to provide high heating rates, flexibility to deliver contactless energy to a targeted location in complex components and low health and safety requirements is electromagnetic induction heating [1-3].
Induction curing of thermoset composites holds a strong promise for fast, controlled and highly adjustable internal curing of high performance carbon fiber composite parts. Although carbon fibers have favourable electric conductivity and electromagnetic properties, the anisotropic nature of composite layer properties in fiber and transverse directions leads to significant difficulties to obtain uniform heating and a uniform degree of cure [4].
As part of a larger scale research project the non-uniformity of temperature distribution is solved by designing and applying in manufacturing a frame prototype with movable induction coil in 3 dimensions that uses feedback from thermal imaging camera to ensure even volumetric temperature distribution during the curing.
In the present study, the focus is on elastic and micro-damage properties of carbon/epoxy UD, cross-ply and quasi-isotropic lay-up composites manufactured with the above described induction heating rig with movable coil. Material plates of 300 x 300 mm were manufactured from UD carbon/epoxy prepregs. Tensile tests were performed on specimens from the manufactured plates to determine elastic properties of UD composite. Loading-unloading tensile and bending tests with increasing maximum strain levels were performed to study evolution of transverse matrix cracks and delaminations in cross-ply and quasi-isotropic laminates. Additional characterization of the degree of cure were performed using DSC analysis.
Results were compared with corresponding reference materials manufactured from the same raw materials but using hot-press curing. Difference in fiber/matrix bonding in induction-cured and hot-press-cured composites was also analyzed by performing in-situ SEM tensile and bending tests.
Induction curing of thermoset composites holds a strong promise for fast, controlled and highly adjustable internal curing of high performance carbon fiber composite parts. Although carbon fibers have favourable electric conductivity and electromagnetic properties, the anisotropic nature of composite layer properties in fiber and transverse directions leads to significant difficulties to obtain uniform heating and a uniform degree of cure [4].
As part of a larger scale research project the non-uniformity of temperature distribution is solved by designing and applying in manufacturing a frame prototype with movable induction coil in 3 dimensions that uses feedback from thermal imaging camera to ensure even volumetric temperature distribution during the curing.
In the present study, the focus is on elastic and micro-damage properties of carbon/epoxy UD, cross-ply and quasi-isotropic lay-up composites manufactured with the above described induction heating rig with movable coil. Material plates of 300 x 300 mm were manufactured from UD carbon/epoxy prepregs. Tensile tests were performed on specimens from the manufactured plates to determine elastic properties of UD composite. Loading-unloading tensile and bending tests with increasing maximum strain levels were performed to study evolution of transverse matrix cracks and delaminations in cross-ply and quasi-isotropic laminates. Additional characterization of the degree of cure were performed using DSC analysis.
Results were compared with corresponding reference materials manufactured from the same raw materials but using hot-press curing. Difference in fiber/matrix bonding in induction-cured and hot-press-cured composites was also analyzed by performing in-situ SEM tensile and bending tests.