INTRODUCTION

Carbon fibers are used as a light-weight reinforcement phase to make high-strength light-weight polymeric composite materials. The carbon fibers may be continuous filaments that may be thousands of micrometers (μm) or millimeters (mm) in length. A group of continuous carbon fibers are often categorized as a bundle of continuous carbon fiber filaments. Carbon fiber “tow” is usually designated as a number of filaments in thousands (designated by K after the respective tow number). Alternatively, carbon fiber bundles may be chopped or milled and thus form short segments of carbon fibers (filaments or bundles) typically having a mean fiber length between 50 μm (about 0.002 inches) and 50 mm (about 1.97 inches). While composites incorporating carbon fibers are all light-weight and high-strength, composites incorporating continuous carbon fiber filaments have especially high strength as compared to composites incorporating chopped or milled carbon fibers. By way of non-limiting example, a representative unidirectional continuous carbon fiber filament when incorporated into a composite provides an ultrahigh ultimate tensile strength of about 300 to 1,200 MPa, while composites with chopped carbon fibers have an ultimate tensile strength of about 80 MPa to 350 MPa.

Composite articles or components can be formed by using sheets or strips of a reinforcement material, such as a carbon fiber-based material having continuous carbon fibers. Polymer precursors, such as resins, can be impregnated in carbon fiber-based substrate material systems, known as pre-impregnating (referred to as “pre-preg”) that involves wetting a resin into the carbon fiber-based substrate material in a first step, then optionally winding up the carbon fiber-based substrate material, and storing it for later use.

While the ultrahigh strengths associated with carbon-fiber composites are highly desirable in certain applications, one challenge in using continuous carbon fibers composite pre-pregs is the lack of flowability and formability, because composite pre-pregs incorporating continuous carbon fibers can be too stiff with high resistance to flow. Such inflexibility and rigidity can translate to poor moldability, making it difficult to form three-dimensional shapes from composites having continuous carbon fibers. Further, lack of flowability in the pre-preg material can result in warpage in the final composite product and issues with undesirable surface appearance. It would be desirable to form continuous carbon fiber pre-preg materials having higher flowability, and thus greater moldability, with the capability of readily forming complex and three-dimensionally shaped components with ultrahigh-strengths.

SUMMARY

Methods for fabricating Class-A components (CAC) are provided and include providing a molding precursor which includes a first skin layer including a first polymer matrix and a first fiber reinforcing material embedded within the first polymer matrix, a second skin layer defined by an outer surface and an inner surface oriented towards the first skin layer and including a second polymer matrix and a second fiber reinforcing material embedded within the second polymer matrix, and a third layer disposed between the first and second skin layers and including a third polymer matrix and a filler material interspersed within the third polymer matrix. The first fiber reinforcing material and the second fiber reinforcing material can each include a plurality of substantially aligned carbon fibers defining a major axis and a second axis perpendicular to the major axis, and the plurality of substantially aligned carbon fibers have a plurality of low strength regions staggered with respect to the second axis. The method can further include disposing a molding precursor within a die, compression molding the molding precursor in the die, wherein the die includes a punch and a block, and during compression molding the punch is configured to contact the second skin layer and the block is configured to contact the first skin layer, opening the die to create a gap between the punch and the outer surface of the second skin layer, and injecting a Class-A finish coat precursor into the gap to create a class-A surface layer on the compression-molded molding precursor and form the CAC. The gap between the punch and the outer surface of the second skin layer can define the geometry of the Class-A surface layer. The method can further include removing the CAC from the die and painting the class-A surface layer. The first skin layer of the CAC can have a thickness of about 0.1 mm to about 5 mm, the second skin layer of the CAC can have a thickness of about 0.1 mm to about 5 mm, and the third layer of the CAC can have a thickness of about 0.1 mm to about 10 mm. The formed CAC can have a surface area at least 3% greater than the pre-preg. The first skin layer, the second skin layer, and the third layer can have first, second and third rheological flow properties, respectively, that are substantially similar such that the first skin layer, the second skin layer, and the third layer flow generally in unison at a predetermined compression molding pressure. Compression molding the pre-preg in the die can include applying a pressure of about 0.5 MPa to about 20 MPa via the die. The CAC can be at least semi-structural. The first skin layer can include about 20 v. % to about 75 v. % of the first fiber reinforcing material and the second skin layer can include about 20 v. % to about 75 v. % of the second fiber reinforcing material. The filler material of the third layer can include hollow glass microspheres, silicon particles, wood particles, and calcium carbonate fragments. The first polymer matrix and the second polymer matrix can each include an epoxy, a polyurethane thermoset resin, or a nylon thermoplastic resin. The third polymer matrix can include an epoxy, a polyurethane thermoset resin, or a nylon thermoplastic resin. The molding precursor can further include a layer of woven fibers disposed on the outer surface of the second skin layer. The Class-A finish layer can be clear and at least a portion of the layer of woven fibers can be visible through the Class-A surface layer. The Class-A finish coat precursor can include one or more of a polyurethane, an epoxy, a polyester, and a vinyl ester. The Class-A finish coat precursor can further include conductive carbon. The plurality of substantially aligned carbon fibers of the first fiber reinforcing material and the second fiber reinforcing material can have an average thickness of about 0.1 mm to about 1 mm.

Methods for fabricating Class-A components (CAC) are provided and include providing a molding precursor which includes a first skin layer including a first polymer matrix and a first fiber reinforcing material embedded within the first polymer matrix, a second skin layer defined by an outer surface and an inner surface oriented towards the first skin layer and including a second polymer matrix and a second fiber reinforcing material embedded within the second polymer matrix, and a third layer disposed between the first and second skin layers and including a third polymer matrix and a filler material interspersed within the third polymer matrix. The first fiber reinforcing material and the second fiber reinforcing material can each include a plurality of substantially aligned carbon fibers defining a major axis and a second axis perpendicular to the major axis, and the plurality of substantially aligned carbon fibers have a plurality of low strength regions staggered with respect to the second axis. The method can further include disposing a molding precursor within a die, compression molding the molding precursor in the die, wherein the die includes a punch and a block, and during compression molding the punch is configured to contact the second skin layer and the block is configured to contact the first skin layer, opening the die to create a gap between the punch and the outer surface of the second skin layer, injecting a Class-A finish coat precursor into the gap to create a class-A surface layer on the compression-molded molding precursor and form the CAC, and integrating the CAC with a rigid vehicle frame. The method can further include, prior to integrating the CAC with the rigid vehicle frame, painting the CAC. The Class-A finish coat precursor can include conductive carbon and one or more of a polyurethane, an epoxy, a polyester, and a vinyl ester.

Other objects, advantages and novel features of the exemplary embodiments will become more apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

