Carbon Fiber Composite Systems Research Articles

Micromechanical modeling of discontinuous long fiber reinforced composites

The performance of discontinuous fiber composites is intricately linked to the microstructure of the composite material. Therefore, micromechanics prove valuable for the analysis and design of these materials. Two micromechanics theories, the high fidelity generalized method of cells and Carrera Unified Formulation, are used to model a repeating unit cell (RUC) of the Tailorable Universal Feedstock for Forming, a highly aligned discontinuous fiber carbon fiber composite system. The models are evaluated for their ability to predict the effective properties and local stress fields within the RUC. The stress fields between the fiber ends and the fiber-matrix interfacial stresses are of particular interest. The models are used to predict the effective properties of single fiber and multiple fiber RUCs with varying fiber-to-fiber end gap lengths, as well as the local stresses in the fiber and matrix. Both models produced similar results and demonstrated that they could capture the complex local load transfer. A statistical study is also undertaken to understand the effect of gap clustering on the effective properties and local stress fields.

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.

Cobalt-Doped Antimony/Tin Oxide Sol–Gels on Carbon–Silicon Layers for Modeling Sol–Gel-Carbon Fiber Interfaces

This research presents a novel thermo-responsive sol–gel (dopant) combination and evaluation of the actuating responses due to various heat treatment temperatures. In this project, samples of antimony-doped tin oxide (ATO) doped with 0.1% cobalt oxide (0.1% Co2O3) sol–gel on carbon/silicon substrates are used to model the implementation of sol–gel coatings into carbon fiber composite systems. While ATO is a well-known transparent conductive material, the addition of cobalt oxide (Co2O3) alters its morphology and optical parameters at low annealing temperatures. By altering the ATO (0.1% Co2O3) heat treatment temperatures, the grain size starts to increase at 200 °C. However, when approaching 500 °C, Raman spectroscopy shows that the increase in intensity of ATO (0.1% Co2O3) is lower than ATO undoped. Scanning electron microscopy is used for imaging, and energy dispersive spectroscopy will be used for the composition analysis. Optical reflectance is reported via Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy analysis.

Failure plane orientations for transverse loading of a unidirectional fiber composite

Using a recently developed failure theory for transversely isotropic fiber composites, it is shown how the orientation of the failure surface can be determined for transverse tension and compression. It is also shown that failure surface orientations decompose into those of ductile type versus those of brittle type. Experimental data on failure surface orientations have been obtained for carbon fiber composite systems based on both thermoplastic and thermosetting matrix materials. Average compression failure planes for the different composite materials were measured to range from 31° to 38° from the load axis. Reasonable agreement was obtained between these measured angles and those predicted from application of the new failure theory.

Characterization of Damage Modes in Impacted Thermoset and Thermoplastic Composites

Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe losses in strength and stiffness. Impact induced damage is often a complex mixture of transverse cracks, delaminations and fiber failures. An ex perimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. In this paper, impacted com posite specimens have been examined using destructive and nondestructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic and scanning electron microscopy techniques have been used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also stud ied.

Damage Tolerance Estimation of Advanced Composite Materials

Characterization of interlaminar fracture toughness will play an important role in the establishment of a damage-threshold/fail-safe approach to composite materials and structures. Double cantilever beam (DCB) and end notched flexure (ENF) tests are reviewed and revised methods are proposed for accurate and easy estimation of mode I and II interlaminar fracture toughness. Thickness normalized crack length versus cube root of compliance plots are used for data reduction of DCB test. CSD measurement technique is introduced to ENF test and stabilized ENF test is proposed. Mode II interlaminar fracture toughness can be estimated directly from load versus CSD diagram without measuring crack length. Applicability of proposed protocols are well confirmed by experiments of four kinds of carbon fiber composite systems, T300/2500, T800H/3631, APC-2 and Celion6000/PMR-15.