Cornerstone Research Group Inc. (CRG) has developed and demonstrated a composite structural solution called
reflexive composites for aerospace applications featuring CRG's healable shape memory polymer (SMP) matrix. In
reflexive composites, an integrated structural health monitoring (SHM) system autonomously monitors the structural
health of composite aerospace structures, while integrated intelligent controls monitor data from the SHM system to
characterize damage and initiate healing when damage is detected. Development of next generation intelligent
controls for reflexive composites were initiated for the purpose of integrating prognostic health monitoring
capabilities into the reflexive composite structural solution.
Initial efforts involved data generation through physical inspections and mechanical testing. Compression after
impact (CAI) testing was conducted on composite-reinforced shape memory polymer samples to induce damage and
investigate the effectiveness of matrix healing on mechanical performance. Non-destructive evaluation (NDE)
techniques were employed to observe and characterize material damage. Restoration of mechanical performance
was demonstrated through healing, while NDE data showed location and size of damage and verified mitigation of
damage post-healing. Data generated was used in the development of next generation reflexive controls software.
Data output from the intelligent controls could serve as input to Integrated Vehicle Health Management (IVHM)
systems and Integrated Resilient Aircraft Controls (IRAC). Reflexive composite technology has the ability to
reduce maintenance required on composite structures through healing, offering potential to significantly extend
service life of aerospace vehicles and reduce operating and lifecycle costs.
Seamless skins for morphing vehicles have been demonstrated as feasible but establishing robust fastening methods for
morphing skins is one of the next key challenges. Skin materials previously developed by Cornerstone Research Group
and others include high-performance, reinforced elastomeric and shape memory polymer (SMP)-based composites.
Recent focus has shifted to improving performance and increasing the technology readiness level of these materials.
Cycling of recently demonstrated morphing skins has determined that an abrupt interface between rigid and soft
materials leads to localized failure at the interface over time. In this paper, a fundamental understanding between skin
material properties and transition zone design are combined with advanced modeling techniques. A thermal gradient
methodology is simulated to predict performance benefits. Experimental testing and simulations demonstrated
improvement in morphing component performance for a uniaxial case. This work continues to advance development to
eliminate fastening as the weak link in morphing skin technology and provides tools for use in morphing structure
Cornerstone Research Group Inc. has developed reflexive composites achieving increased vehicle
survivability through integrated structural awareness and responsiveness to damage. Reflexive
composites can sense damage through integrated piezoelectric sensing networks and respond to damage
by heating discrete locations to activate the healable polymer matrix in areas of damage. The polymer
matrix is a modified thermoset shape memory polymer that heals based on phenomena known as
In theory, the reptation healing phenomena should occur in microseconds; however, during
experimentation, it has been observed that to maximize healing and restore up to 85 % of mechanical
properties a healing cycle of at least three minutes is required. This paper will focus on work conducted
to determine the healing mechanisms at work in CRG's reflexive composites, the optimal healing cycles,
and an explanation of the difference between the reptation model and actual healing times.
Aerospace systems stand to benefit significantly from the advancement of reflexive aerostructure
technologies for increased vehicle survivability. Cornerstone Research Group Inc. (CRG) is developing
lightweight, healable composite systems for use as primary load-bearing aircraft components. The
reflexive system is comprised of piezoelectric structural health monitoring systems, localized thermal
activation systems, and lightweight, healable composite structures. The reflexive system is designed to
mimic the involuntary human response to damage. Upon impact, the structural health monitoring system
will identify the location and magnitude of the damage, sending a signal to a discrete thermal activation
control system to resistively heat the shape memory polymer (SMP) matrix composite above activation
temperature, resulting in localized shape recovery and healing of the damaged areas. CRG has demonstrated SMP composites that can recover 90 percent of flexural yield stress and modulus after postfailure
healing. During the development, CRG has overcome issues of discrete activation, structural health monitoring integration, and healable resin systems. This paper will address the challenges associated with development of a reflexive aerostructure, including integration of structural health monitoring, discrete healing, and healable shape memory resin systems.
Cornerstone Research Group, Inc. (CRG) is developing a unique adaptive wing structure intended to enhance the capability of loitering Unmanned Air Vehicles (UAVs). In order to tailor the wing design to a specific application, CRG has developed a wing structure capable of morphing in chord and increasing planform area by 80 percent. With these features, aircraft will be capable of optimizing their flight efficiency throughout the entire mission profile. The key benefit from this morphing design is increased maneuverability, resulting in improved effectiveness over the current design. During the development process CRG has overcome several challenges in the design of such a structure while incorporating advanced materials capable of maintaining aerodynamic shape and transferring aerodynamic loads while enabling crucial changes in planform shape. To overcome some of these challenges, CRG is working on integration of their shape memory polymer materials into the wing skin to enable seamless morphing. This paper will address the challenges associated with the development of a morphing aerospace structure capable of such large shape change, the materials necessary for enabling morphing capabilities, and the current status of the morphing program within CRG.