Abstract:
An integrated system and method to acquire the health state of a structure identifying the presence of damage, and to self-repair the damage in the considered structure. A sensor network installed in the structure is interrogated by a dedicated hardware for damage detection. In case of damage is detected by the sensor network in the structure, the sensor network is triggered and generates harmonic excitation in the structure. Due to the excitation, the natural frequency of vascular microtubes and/or capsules presented in the structure is reached, promoting their disruption. The vascular microtubes and/or capsules disruption along the damage releases the healing compound, repairing the damaged portion of the structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       FIELD 
       [0003]    The technologies herein relate to structural health monitoring (herein called “SHM”) including sensors systems that automatically detect damage to structures including but not limited to aircraft, and to such sensor systems related to smart materials with capabilities of performing self-healing (“SHS”) in the structural damages detected. 
       BACKGROUND 
       [0004]    The human body has an amazing ability to heal itself when hurt in certain ways. For example, when your body incurs a minor cut or scrape, various complex mechanisms activate that heal and repair the damage. Generally speaking, however, our machines are unable to do the same. 
         [0005]    It is highly desirable to reduce maintenance costs by minimizing explicit preemptory maintenance and to prevent catastrophic failures. An ultimate goal is to monitor the integrity of the structure in operating conditions during its entire working life. The development of in-service structural health monitoring (SHM) and damage detection techniques has attracted a large number of academic and industrial researchers. 
         [0006]    Once damage is detected during operation of the structural platform, in general, a management process is performed through damage identification to determine whether to continue operation or to stop operation in order to perform structural repair. 
         [0007]    Different kinds of damage may occur due to severe operational conditions. For example, damage can be caused by fatigue, erosion, corrosion, impact, moisture and/or other effects. The operational life cycle of a structural platform can be significantly reduced. In some cases, the entire structural component must be replaced instead of being repaired. 
         [0008]    Seeking safety improvement, reduction of maintenance cost and human error, efforts are underway to develop automatic SHM systems capable of inspecting and detecting damages in real time without need for human interference or attention. Therefore, new SHM technologies will lead to early detection of damage that often in the past was identified only through scheduled manual inspections. 
         [0009]    In general, “self-healing material” defines those materials that in the presence of damage can self-repair spontaneously or with the aid of a stimulus, and thus maintain its functionality or otherwise continue to function. The literature shows that different strategies and approaches have been investigated to provide this feature in all classes of materials including for example polymers, metals and ceramics. 
         [0010]    The concept of self-healing of damage in materials is of great interest to the industry particularly in the following applications in structural platforms:
       Structural components for which reliability, even in overload conditions, is of critical importance;   Surfaces where damages are not allowed, as in anti-corrosive coatings, decorative paints and thermal barrier coatings;   Structural components inaccessible or access difficult for inspections and repairs;   Structural components that require long life;   Other.       
 
         [0016]    One useful strategy in self-healing polymers has been the incorporation of microcapsules or hollow glass fibers that, when broken, release a healing agent. Other mechanisms, such as the use of micro-vascular networks, have also been used. In the case of polymer matrix materials that have intrinsic self-healing, an external stimulus is required, e.g., heating is applied. 
         [0017]    For self-healing metal, a primary focus in the past has been on the technologies of coatings applied to surfaces of metal alloys. Research conducted in scientific and technological bases on the subject of self-healing metal showed a low number of examples of application of this concept as compared to some other classes of materials. 
         [0018]    For ceramic materials, although the typical self-healing process requires high temperature, the regeneration of properties at lower temperatures can be obtained if the grain boundary contains a vitreous phase. Such ceramic systems are able to surpass inherent problems of traditional ceramics, i.e., low fracture toughness, sensitivity to thermal shock, mechanical stiffness and low reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The following detailed description of exemplary non-limiting illustrative embodiments is to be read in conjunction with the drawings of which: 
           [0020]      FIG. 1  shows an example non-limiting SHM system (in this case analogized to a system resembling the human nervous system) integrated with the SHS (in this case analogized to a system resembling the human vascular system); 
           [0021]      FIG. 2  shows an example non-limiting damage detection and healing by SHM sub-system integrated with SHS sub-system; 
           [0022]      FIGS. 2A and 2B  show more detailed breakouts of  FIG. 2 ; 
           [0023]      FIG. 3  shows an example non-limiting process for structural integrity management evaluation and self-healing; 
           [0024]      FIG. 4A  shows an example non-limiting system for structural integrity management evaluation and self-healing; and 
           [0025]      FIG. 4B  shows an example non-limiting software structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In an example non-limiting embodiment, system and method for damage detection for structural platforms using structural health monitoring is integrated to a system and method capable of repairing the damage in the structure considering a self-healing system. 
         [0027]    Using a sensory network based on a Structural Health Monitoring (SHM) system, the system informs a damage assessment with maturity and robustness. 
         [0028]    An output of the SHM system is the damage characterization, which can be based on: 
         [0029]    Detection; 
         [0030]    Localization; and/or 
         [0031]    Quantification (sizing or/and load intensity). 
         [0032]    After knowing about the characterization of the damage, a Self-Healing System (SHS) that may be independent is integrated to the SHM system. The integrated SHS to SHM arrangement allows self-healing of damage in the structure through the use of smart materials systems containing micro vascular architecture and/or micro capsular architectures. 
         [0033]    Like the human nervous system shown in  FIG. 1 , the example non-limiting SHM system senses the presence of damage. Also like the human vascular system, the non-limiting SHS performs self-healing of the damage. In this approach, these systems are independent but integrated, exchanging information (see  FIG. 1 ). 
         [0034]    In more detail, referring to  FIG. 1 , the SHM senses that there is a problem (“Houston, we have a problem”). Such an optimized SHM can provide a sensory network that can inform of damage based on maturity, robustness and/or online damage assessment. Such an SHM is integrated with an SHS system, which can be independent of the SHM and permit aerospace or other platforms to provide self-healing of structural damage through complex materials systems containing microvascular architectures. Such self-healing can be capsule-based, vascular based, intrinsic, e.g., through use of a polymer healing agent (using microcapsules and catalyst to provide self-healing of cracks or other structural damage for example). This is similar to how the human body characterizes damage by detection, localizes and quantifies damage (e.g., by sizing and/or intensity) such as detecting injury of the hand and then self-heal. 
         [0035]    Therefore, example non-limiting embodiments provide a structural integrity management system providing the integration of a SHM sub-system that continually or continuously evaluates a structural platform. When the system detects damage, the system starts to generate excitation (mechanical, electrical, thermal, etc.) in the region nearby the damage, thereby triggering the self-healing system. In this approach, excitation is applied to the structure creating harmonic response until achieving the natural frequency of vascular microtubes and/or capsules that belong to the SHS sub-system (see FIG.  2 ( 1 )). Such harmonic response in one example implementation causes resonance or other constructive interference (see  FIG. 2   a ). This harmonic response disrupts vascular microtubes and/or capsules (see  FIG. 2(   b )) so that they perform self-healing and repair structural damage in the damaged region (see FIG.  2 ( 3 ),  2 ( 4 )). 
         [0036]    For example, as shown in  FIG. 2(   b ), micro-tubes disposed in an area subjected to a constructively-interfering vibrational wave pattern can self-heal. For example, in one non-limiting example, a micro-encapsulated healing agent is embedded in a structural composite matrix containing a catalyst capable of polymerizing the healing agent. In this example embodiment, the harmonic response selectively induces cracks in the matrix. Different vibrational patterns can induce cracks or other disturbances in different areas. The cracks or other disturbances induced by the harmonic response rupture the microcapsules in the area of the cracks, releasing the healing agent into the crack plane through capillary action. The released healing agent contacts the catalyst, triggering polymerization that bonds the crack faces closed. See e.g., Martinez-Lucci et al., Self Healing in Metal Castings (American Foundry Association, 2011), incorporated herein by reference. 
         [0037]      FIG. 4A  shows an example non-limiting system and  FIG. 3  shows example non-limiting process steps. Referring to  FIG. 4A , an example system  100  may include one or more computer processors  102  coupled to non-transitory storage  104  storing executable program instructions. For example, in one embodiment, processor  102  may comprise a microprocessor, gate array, computer processor, digital signal processor or other device that can perform a sequence of operations. In one example non-limiting embodiment, processor  102  executes a computer program comprising a sequence of program instructions (including a main routine  152  and one more subroutines  154 ,  156 ,  158  shown in  FIG. 4B ) stored in non-transitory storage device  104 . In the example shown, the main routine software  150  executed by processor  102  calls a structural evaluation routine  152  that reads damage sensors  106  to perform structural evaluation  302 . If no damage is detected (“no” exit to decision block  304 ), the main routine  150  can continually monitor the structure of interest until damage is detected (“yes” exit to decision block  304 ). Once such damage is detected, the main routine  150  calls a damage detection subroutine  154  to perform damage detection  306 . Such damage detection can for example determine the precise extent, type and location of the damage, once again using one or more damage sensors  105 . Damage sensors  106  can comprise any type of sensors such as optical, visual, machine vision, vibration testing, flex testing, strain gauges, temperature, deformation testing, audible or sound sensing, ultrasonic, infrared imaging, ultraviolet imaging, or any other type of sensing. 
         [0038]    Once the precise location of the damage has been detected, main routine  150  can call the harmonic response generator excitation routine  156 . Harmonic response generator excitation routine  156  operates in conjunction with harmonic response generator/exciter  106  to generate a harmonic response in the structure of interest. As one example, harmonic response generator  106  can comprise one or more vibrational transducers that generate vibration in a pattern and at a frequency and location that will disrupt capsules and/or nanotubes as described above to provide healing and repair (see block  308 ,  310 ,  312 ). The self-healing system may for example be accomplished as agents microencapsulated or microvascular networks or crosslinked thermo-reversible or adding an additive in thermoplastic thermofix matrix or elastomers with supramolecular structures with hydrogen bonds or molecular interdiffusion or repair photoinduced or living polymer. 
         [0039]    One example non-limiting Structural Health Monitoring System (SHM) can comprise a plurality of transducers, including a plurality of pairs of actuators and sensors, a generator device to excite at least one of said sensors to produce ultrasonic guided waves, and a signal processor device to receive the signals reflected from damage identification. The example Self-Healing System (SHS) can comprise a self-healing material including a matrix of at least one polymer material, wherein a set of capsules are uniformly distributed and embedded in the matrix containing a liquid healing-agent, wherein the SHM system and the SHS system are integrated with a unique or distinct network of sensors/actuators. For example, the integrated system (SHM+SHS) can be exclusively one box control, or the integrated system (SHM+SHS) may be with box control separated for SHM and SHS. In one example non-limiting implementation, the sensors may comprise fiber optics sensors or piezoelectric sensors, and the structural health monitoring may comprise Lamb waves or electromechanical impedance or Fiber Bragg gratings or acoustic emission. In one example non-limiting implementation, the network sensors may be embedded in the structure or not embedded in the structure, and the generator device for the excitation may be mechanical, electrical and/or thermal. 
         [0040]    Main routine  150  may then re-call structural evaluation subroutine  152  to re-evaluate the structure to determine whether it has been sufficiently healed and repaired to continue to be used. The process shown in  FIG. 3  can be performed recursively until the structure is self-healed, or until main routine  150  determines that the structure cannot be self-healed and must instead be manually repaired or replaced (report generating subroutine  158 ). Thus, after healing, the SHM sub-system may also perform a reassessment of the structure certifying if the structure is safe for operation (see  FIG. 3 ). 
         [0041]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.