The U.S. Air Force is seeking innovative solutions through the Small Business Innovation Research (SBIR) program to enhance Continuous Fiber Additive Manufacturing (CFAM) processes, specifically targeting improvements in interlaminar adhesion and fiber/matrix bonding. The objective is to develop new thermoplastic resin chemistries or processing techniques that address current material challenges, such as poor adhesion and material property deficits, which hinder the adoption of CFAM technologies for unmanned aircraft manufacturing. Successful proposals will undergo a phased approach, starting with feasibility demonstrations in Phase I, followed by scaling and validation in Phase II, and ultimately leading to commercial applications in Phase III. The solicitation is set to open on May 28, 2025, with applications due by June 25, 2025. Interested parties can find more information and submit proposals through the official DOD SBIR/STTR website.

## Description

The US Air Force must deliver agile, scalable, and tailorable manufacturing approaches to deliver affordable mass via fleets of Autonomous Collaborative Platform (ACP) unmanned aircraft. Continuous Fiber Additive Manufacturing (CFAM) processes are maturing rapidly but continue to face fundamental material challenges that inhibit adoption of the technology. In particular, processes using thermoplastic resins infused with continuous fiber in a tape or filament form experience significant consolidation and adhesion challenges during printing along with severe material property debits owing to poor interlaminar adhesion and poor resin/fiber binding. Adhesion challenges result from a limited dwell time for deposition heating and consolidation pressure and are similar in nature to other fused filament fabrication (FFF) processes using neat resins. These property debits are unacceptable as designers must account for a wide distribution of potential layer to layer and fiber/matrix defects before even considering complex anisotropic effects caused by the directional nature of the deposited carbon fiber. These material and processing deficiencies limit the design envelope and leads to design allowables with insufficient material performance to reliably meet Air Force requirements. To address this shortcoming, this STTR topic proposes to mature, demonstrate, test, and validate new resin chemistries, fiber/matrix combinations, and/or processing techniques that will mitigate interlaminar adhesion issues or resin/fiber binding issues. Any selected solution must be compatible with filamentary or unidirectional tape CFAM methods. Scalable Composite Robotic Additive Manufacturing (SCRAM) is one such method for which a solution is required. SCRAM features a multifunctional production cell capable of 7-axis FFF printing, unidirectional tape laying, and precision machining. Typical manufacturing with SCRAM involves printing and machining a tool surface with ABS material, upon which unidirectional carbon fiber reinforced tapes are deposited. Other CFAM processes are also available and solutions targeted to those processes will be considered. For SCRAM compatible materials, the material or processing solutions should conform to the following characteristics: processible as a unidirectional AFP or ATL type feedstock or tape, resistant to solvents (acetone) used to remove printed tools, glass transition temperature minimum of 250F and target of 350F, consolidated part capable of freestanding following deposition and removal of the tool. Filament form factors are also considered in this topic with similar anticipated performance profiles compatible with those particular processing solutions. Secondary cross-linking chemistry or other proposed solutions shall allow the resin and fiber to be deposited as a thermoplastic at ambient temperature into the desired form factor as current CFAM systems using a heat or laser source for localized heating. The processing conditions or secondary processing steps shall allow for a secondary reaction or process to bond across layers of deposited material and/or improve fiber/matrix adhesion. If the secondary process is required, it must be done under freestanding cure without any need of special tools to preserve the shape of the part. This topic does not specify the cross-linking initiation mechanism, nor the degree of crosslinking, and any approach to achieve the topic goal will be considered. The resin/fiber system shall be processible as a filament and/or unidirectional tape and shall provide at least 80% of the values of resin dominated properties such as shear and compressive strength when compared to aerospace grade polymer matrix composite systems such as 977-3 or 5320-1 based carbon prepreg systems. 

## Objective

This topic seeks new and adapted thermoplastic resin chemistries or processing approaches suitable for continuous fiber additive manufacturing that improve interlaminar adhesion properties and/or fiber/matrix adhesion.

## Phase I

This effort shall demonstrate feasibility of resin chemistry concepts capable of improving interlaminar properties and/or fiber/matrix interaction in CFAM processes. 

## Phase II

Candidate solutions identified in Phase 1 shall be matured and applied to a commercially available CFAM process. Proposer will scale candidate solution with laboratory quantities of material to be processed on a CFAM system and conduct comparative trials to current feedstock materials. Printing trials shall evaluate material processability and identify risk items impeding adoption. Material characterization of coupons or panels will be conducted to establish expected performance of the candidate solution. Validation trials on more complex, representative parts will assess the applicability of the candidate solution to real parts.

## Phase III: Dual Use Applications

Phase III efforts will implement validated material solutions to improve interlaminar properties and/or fiber/matrix adhesion in a commercial continuous fiber additive manufacturing (CFAM) process. Air Force Research Laboratory (AFRL) will reduce risk of implementation through application demonstrations and full-scale testing as well as conduct material and process qualification. AFLCMC program office(s) for unmanned air vehicles will assess technology viability for CFAM as primary, limited life aircraft structure. TRL of the material solution at beginning of Phase III is anticipated to be TRL 5 &ndash; validation in a relevant environment. Additionally, qualified feedstock will be a commercially available product suitable for both commercial and defense part applications. A CFAM feedstock within 80% of interlaminar properties of qualified carbon prepreg composite systems will provide an agile material capable of delivering affordable mass for Air Force Autonomous Collaborative Platform (ACP) unmanned aircraft.

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