Patent Publication Number: US-2023134300-A1

Title: Cylinder boss cracking detection system

Description:
BACKGROUND 
     1. Field 
     This specification relates to a system for monitoring bosses of composite cylinders. 
     2. Description of the Related Art 
     Vehicles may be used to transport occupants and/or cargo. Some vehicles for transporting cargo are powered using fuel stored in cylinders. Parts of these cylinders may become damaged during installation or during use. When the cylinders become damaged, it is important to repair or replace the cylinders. 
     SUMMARY 
     What is described is a system for detecting a crack in a boss of a cylinder. The system includes a first sensor located on an outer surface of a neck of the boss and configured to detect first deformation data associated with the boss. The system also includes a second sensor located on the outer surface of the neck of the boss at a location opposite the first sensor and configured to detect second deformation data associated with the boss. The system also includes a controller communicatively coupled to the first sensor and the second sensor and configured to determine, based on the first deformation data and the second deformation data, whether a boss cracking event has occurred. 
     The system may optionally include one or more of the following features. The first sensor and the second sensor may be broadband piezoelectric sensors. The controller may determine whether the boss cracking event has occurred using modal acoustic emission (MAE) to analyze the first deformation data and the second deformation data. The controller may be configured to determine whether the boss cracking event has occurred based on detecting a 180 degree phase shift between the first deformation data and the second deformation data. 
     The first deformation data may include a first arrival time of a first waveform. The second deformation data may include a second arrival time of a second waveform. The controller may be further configured to determine whether the boss cracking event has occurred based on a difference between the first arrival and the second arrival time being lower than a threshold time. The controller may be further configured to determine whether the boss cracking event has occurred based on detection of high frequency content occurring at high ΔK levels where the boss cracking event is a crack extension. The controller may be further configured to determine whether the boss cracking event has occurred based on detection of low frequency content occurring at low ΔK levels where the boss cracking event is a crack closure. 
     The first sensor and the second sensor may be a first pair of sensors. The system may further include a second pair of sensors located on the outer surface of the neck of the boss at opposite sides. The controller may be configured to determine whether the boss cracking event has occurred based on deformation data from the sensors of the first pair of sensors and the second pair of sensors. The system may further include an output device communicatively coupled to the controller. The output device may be configured to provide a notification when the controller determines the boss cracking event. 
     Also described is a device for detecting a crack in a boss of a cylinder. The device includes a first sensor located on an outer surface of a neck of the boss and configured to detect first deformation data associated with the boss. The device also includes a second sensor located on the outer surface of the neck of the boss at a location opposite the first sensor and configured to detect second deformation data associated with the boss. The device also includes a controller communicatively coupled to the first sensor and the second sensor and configured to determine, based on the first deformation data and the second deformation data, whether a boss cracking event has occurred. 
     The device may optionally include one or more of the following features. The first sensor and the second sensor may be broadband piezoelectric sensors. The controller may determine whether the boss cracking event has occurred using modal acoustic emission (MAE) to analyze the first deformation data and the second deformation data. The controller may be configured to determine whether the boss cracking event has occurred based on detecting a 180 degree phase shift between the first deformation data and the second deformation data. 
     The first deformation data may include a first arrival time of a first waveform. The second deformation data may include a second arrival time of a second waveform. The controller may be further configured to determine whether the boss cracking event has occurred based on a difference between the first arrival and the second arrival time being lower than a threshold time. The controller may be further configured to determine whether the boss cracking event has occurred based on detection of high frequency content occurring at high ΔK levels where the boss cracking event is a crack extension. The controller may be further configured to determine whether the boss cracking event has occurred based on detection of low frequency content occurring at low ΔK levels where the boss cracking event is a crack closure. 
     The first sensor and the second sensor may be a first pair of sensors. The system may further include a second pair of sensors located on the outer surface of the neck of the boss at opposite sides. The controller may be configured to determine whether the boss cracking event has occurred based on deformation data from the sensors of the first pair of sensors and the second pair of sensors. The system may further include an output device communicatively coupled to the controller. The output device may be configured to provide a notification when the controller determines the boss cracking event. 
     Also described is a method for detecting a crack in a boss of a cylinder. The method includes detecting, using a first sensor located on an outer surface of a neck of the boss, first deformation data associated with the boss. The method also includes detecting, using a second sensor located on the outer surface of the neck of the boss at a location opposite the first sensor, second deformation data associated with the boss. The method also includes determining, by a controller communicatively coupled to the first sensor and the second sensor, based on modal acoustic emission analysis of the first deformation data and the second deformation data, whether a boss cracking event has occurred. The method also includes providing, by an output device communicatively coupled to the controller, a notification when the controller determines the boss cracking event. 
     The method may optionally include one or more of the following features. Determining whether the boss cracking event has occurred may include detecting a 180 degree phase shift between the first deformation data and the second deformation data. The first deformation data may include a first arrival time of a first waveform. The second deformation data may include a second arrival time of a second waveform. Determining whether the boss cracking event has occurred may further include determining whether a difference between the first arrival time and the second arrival time is lower than a threshold time. Determining whether the boss cracking event has occurred may further include detecting high frequency content occurring at high ΔK levels or low frequency content occurring at low ΔK levels where the boss cracking event is a crack extension when high frequency content is detected and the boss cracking event is a crack closure when low frequency content is detected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other systems, methods, features, and advantages of the present invention will be apparent to one skilled in the art upon examination of the following figures and detailed description. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention. 
         FIG.  1    illustrates a vehicle having composite cylinders storing fuel to power the vehicle, according to various embodiments. 
         FIGS.  2 A- 2 B  illustrate a composite cylinder, according to various embodiments. 
         FIG.  2 C  illustrates a boss of the composite cylinder, according to various embodiments. 
         FIGS.  3 A- 3 B  illustrate sensors used to detect cracking in the boss, according to various embodiments. 
         FIGS.  4 - 10    illustrate sensor data of the system, according to various embodiments. 
         FIGS.  11 A- 11 B  illustrate block diagrams of boss cracking detection systems, according to various embodiments. 
         FIG.  12    is a flow diagram of a process performed by the system, according to various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are systems, devices, and methods for monitoring bosses of composite cylinders. The systems, devices, and methods disclosed herein automatically detect damage to the boss and take corresponding steps. The systems, devices, and methods described herein improve the safety of vehicles using the composite cylinders, as the integrity of the composite cylinders is able to be accurately evaluated to prevent use of cylinders which have compromised bosses. 
     The systems, devices, and methods disclosed herein detect fatigue crack growth within bosses of composite overwrapped pressure vessels (COPV). In Type 4 COPVs, a metallic boss is integrated into the liner to provide a means of connection for filling operations and can also be used for mounting the cylinders into framing. The bosses may be through ports, or blind (i.e., no open pathway for a compressed gas to atmosphere). Cracking of blind bosses can be particularly challenging to assess due to the inaccessible nature of the fractured surface with traditional non-destructive testing (NDT) probes (e.g., Ultrasound or Eddy Current). Thus, there is a need for improved systems for detecting damage to bosses. The systems, vehicles, and methods described herein use MAE inspection to detect damage to bosses and overcomes these limitations. 
     As used herein, “driver” may refer to a human being driving a vehicle when the vehicle is a non-autonomous vehicle, and/or “driver” may also refer to one or more computer processors used to autonomously or semi-autonomously drive the vehicle. “User” may be used to refer to the driver or occupant of the vehicle when the vehicle is a non-autonomous vehicle, and “user” may also be used to refer to an occupant of the vehicle when the vehicle is an autonomous or semi-autonomous vehicle. As used herein, “cylinder” includes storage tanks, pressure vessels, and other containers that can be used to store a gas and is not necessarily limited to a specific shape such as a right cylinder and/or a cylinder having a constant or unvarying circular shape in cross-section. As used herein, “fuel” or “gas” refers to any fluid used to power a vehicle, such as gaseous fuel or liquid fuel. 
       FIG.  1    illustrates a vehicle  102 . In particular, the vehicle  102  is a tractor configured to couple to and pull a trailer  106 . The vehicle  102  may be powered using fuel stored in a composite pressure cylinder (or “composite cylinder” or “cylinder”). For example, the fuel may be compressed natural gas stored in a composite cylinder. 
     The cylinder may be part of a gas cylinder assembly. The gas cylinder assembly is in fluid communication with and supplies fuel to an engine or any other power generation system (e.g., a fuel cell system using hydrogen) of the vehicle  102 . The vehicle  102  may be a car, a wagon, a van, a bus, a high-occupancy vehicle, a truck, a tractor trailer truck, a heavy-duty vehicle such as a garbage truck, or any other vehicle. In some embodiments, a gas cylinder assembly is configured for use in a ship, an airplane, and a mobile or stationary fuel station. 
     The fuel cylinders may be stored in a compartment or housing  104 A on the sides of the vehicle  102 , in a compartment or housing  104 B on the trailer  106 , or in a compartment or housing  104 C behind the cab of the vehicle  102 , for example. In some embodiments, the fuel cylinders may be stored on a rooftop or mounted to a tailgate of a vehicle. 
       FIG.  2 A  illustrates a cylinder  100  configured to store a fluid, such as compressed natural gas or hydrogen. Cylinder  100  may be formed of a metal such as steel, aluminum, glass fiber, carbon fiber, polymer, or a composite material such as carbon fiber reinforced polymer, another suitable material, or a combination thereof. For example, the cylinder  100  may include an inner liner made of gas-tight, polyethylene plastic that has a high-pressure carbon fiber reinforced plastic structure located over the inner liner. In another example, the cylinder  100  may include a metal liner that is wrapped by a composite or fiber resin. 
     The cylinder  100  includes a central portion  216  and two end portions  208 ,  210 . The central portion  216  may be a cylindrical tubular shape or any other shape. In some embodiments, each of the two end portions  208 ,  210  includes a dome structure. In some embodiments, the two end portions  208 ,  210  are symmetrical to each other. The dome structure may be generally hemispherical at least at the end portions thereof. In some embodiments, the two end portions  208 ,  210  have different shapes such that the cylinder  100  is of an asymmetrical shape. 
     In some embodiments, the cylinder  100  includes at least one boss  212 ,  214 . The boss  212 ,  214  may include a neck projecting from the ends of the cylinder. A first boss  214  may have a bore that extends through the longitudinal length of the boss that provides an inlet and/or an outlet of an internal volume of the cylinder  100 . A second boss  212  may not provide for an inlet and/or an outlet of an internal volume of the cylinder  100 . The second boss  212  may have a bore that extends partially through the longitudinal length of the boss  212 , or the second boss  212  may not have any bore at all. The second boss  212  may be referred to as a blind boss. The blind boss  212  may be used, along with the first boss  214 , to mount the cylinder  100  within a storage area. 
     The boss  212 ,  214  can be made of any number of materials, such as metal. In some embodiments, the boss  212 ,  214  is formed using one or more materials not used for the internal pressure enclosure. In certain embodiments, the boss  212 ,  214  is made of the same material as the internal pressure enclosure. 
       FIG.  2 B  illustrates a side cross-sectional view of the cylinder  100  at the second end  208  having the second blind boss  212 . The cylinder  100  may have a plurality of layers. For example, the cylinder  100  may have an inner layer  222  and an outer layer  220 . The inner layer  222  may be made of metal, plastic, or any other rigid material. The outer layer  220  may be made of a composite or fiber resin that is disposed on top of the inner layer  222  during the manufacturing process. While two layers (e.g., inner layer  222  and outer layer  220 ) are shown in  FIG.  2 B , any number of layers may be used to form the cylinder  100 . 
     The boss  212  projects from the inner structure making up the inner layer  222 , and the composite or fiber resin that is disposed on top of the inner layer  222  may also be disposed on top of the boss  212 . A neck  224  of the boss  212  may be external to the cylinder  100  and exposed. The neck  224  may have a shape that is cylindrical, cuboid, or another prism having a different number of edges. The boss  212  may be coupled to the cylinder  100  by a flange  226  extending from the neck  224 . The flange  226  may attached to the inner layer  222  and/or the outer layer  220  via any means, including adhesives and/or welding. The boss  212  may include a bore  230 . The bore  230  may have an opening  232  at an exposed end  234  of the boss  212 . The bore  230  may extend partially through the longitudinal length of the boss  212  as shown in  FIG.  2 B . In some embodiments, the bore  230  may extend partially or entirely through the longitudinal length of the neck  224 . In some embodiments, the bore  230  may extend partially into the flange  226 . In other embodiments, the boss  212  may not have a bore. The bore  230  may have a shape that conforms to the shape of the boss  212 . For example, the bore  230  may have a shape that is cylindrical, cuboid, or another prism having a different number of edges. The boss  214  located on an opposite side of the cylinder  100  may mirror or have the same specifications as the boss  212 , except the bore of the boss  214  extends entirely through the longitudinal length of the boss  214   
     In some situations, stress on the boss  212  may cause damage to one or more portions of the boss  212 . For example, stress to the neck  224  of the boss  212  (e.g., a bending force exerted onto the neck  224 ) may cause the fracture  228  on the boss  212 . The fracture  228  may extend from a neck  224  of the boss  212  to the flange  226  of the boss  212 . 
     In some situations, the damage may result in a visible crack, but in many other situations, the damage may not result in a visible crack. This damage that is not easily visible to a human eye may be as damaging to the cylinder  100  as visible damage. The systems and methods described herein prevent re-use of cylinders that have damage, including cylinders with damage that is not easily visible to the human eye. 
     The cylinder  100  may have a plurality of sensors  202  attached to the boss  212  at various sensor locations. The sensors  202  are configured to detect fracturing events at the boss  212 . The sensors  202  may be broadband piezoelectric sensors which are sensitive to the out-of-plane displacement of the material used to make the boss. The broadband piezoelectric sensors utilize a piezoelectric material in communication with the boss to measure stress waves caused by a fracture (or cracking) event or a rubbing event at a location of an established fracture (or crack). 
     The sensors  202  may be considered passive sensors in that one or more of the sensors do not actively emit a wave to be detected by one or more other sensors. Instead, the sensors  202  may be used to determine when, where on the boss, and to what severity a cracking event occurred. In some embodiments, the sensors  202  may continuously, passively monitor the boss  212  to detect when the boss  212  is stressed from an external source. 
     There may be two or more sensors  202  coupled or attached to the boss  212 . For example, there may be two sensors  202  as shown in  FIG.  2 B . In other embodiments, there may be four sensors  202 , eight sensors  202 , sixteen sensors  202 , or any other even number of sensors  202 . Each sensor  202  may be positioned directly across or diametrically opposite from another sensor  202  around the boss  212 . Particularly, the sensors  202  may be located on an outer surface  236  of the neck  224  of the boss  212 . In some embodiments, the sensors  202  are removably attached to the boss  212 . In other embodiments, the sensors  202  are permanently attached to an outer surface of the boss  212 . In other embodiments, the sensors  202  are integrally formed and embedded within the boss  212 . In some embodiments, the sensors  202  may be coupled or attached directly onto the outer surface  236 . In some embodiments, the sensors  202  may be coupled or attached to a collar  320  (see  FIG.  3 A ), and the collar  320  may be positioned over the neck  224 . 
       FIG.  2 C  illustrates a view of the boss  212  facing the flange  226  of the boss  212 . The fracture line  228  may form in a circular shape corresponding to the neck  224  of the boss  212 . The fracture line  228  may be a semicircle or any portion of a circle, or may be any other shape along the flange  226  of the boss  212 . A fracture of any kind is deleterious to the integrity of the boss  212  and the cylinder  100  at large. If the fracture  228  continues to grow and expand (e.g., along dashed line  238 ) to form a closed shape, the neck  224  of the boss  212  may separate from the flange  226  of the boss  212 , which would be undesirable. 
       FIGS.  3 A- 3 B  illustrate sensors  202  used to detect cracking in the boss  212 / 214 , according to various embodiments. The boss  212 / 214  of the cylinder  100  may be damaged. For example, the cylinder  100  may be damaged during installation of the cylinder  100  or during use of the vehicle  102 . When a fatigue crack in a boss  212 / 214  extends, ultrasonic waves are emitted and the boss  212 / 214  acts as a wave guide. When the crack in the boss  212 / 214  closes (following crack extension), ultrasonic waves may also be emitted, and these events may also be capable of detection, similar to detection of boss cracking events. 
     Based upon the geometry of the boss  212 / 214  and the ultrasonic wavelengths which propagate, both bulk ultrasonic (i.e., longitudinal and shear) and guided ultrasonic rod (i.e., extensional, flexural, and torsional) may propagate. Given the complex nature of the structure being monitored, a number of additional source mechanisms outside of fatigue crack extension are possible (e.g., fiber fracture, matrix cracking, delamination, stiction events between material component interfaces — boss/liner or liner/composite). A number of features of the detected waveforms are leveraged to improve the identification of crack extension and to reduce false indication calls. 
     The sensors  202  may be strategically positioned on the boss  212 / 214  at quadratures of the boss as shown in  FIGS.  3 A and  3 B . Because fatigue crack extension is a dipole source and two pairs of sensors (e.g., sensors  202 A- 1  and  202 A- 2 ; sensors  202 B- 1  and  202 B- 2 ; sensors  202 C- 1  and  202 C- 2 ; sensors  202 D- 1  and  202 D- 2 ) are  180 ° opposing one another, such a sensor configuration results in phase inversion of the direct arriving pseudo longitudinal/extensional wave mode component between the two opposing sensors. One portion of the boss  212 / 214  may be put into tensile wave propagation, and another portion of the boss  212 / 214  may be put into a compressed mode. 
     The sensors  202  may be coupled or attached to a collar  320  positioned over the boss  212 / 214 . The collar  320  may be made of metal, plastic, wood, and/or the like. The collar  320  may have a bore or opening configured to receive the boss  212 / 214 . The bore or the opening may conform to the shape of the outer surface  236  of the neck  224  of the boss  212 / 214 . In some embodiments, the collar  320  may be a unitary construction. In some embodiments, the collar  320  may comprise multiple parts as shown in  FIG.  3 A . The multiple parts may be attached together by conventional adhesives or fasteners, such as one or more pins  322  shown in  FIG.  3 A . The one or more pins  322  may include a ring  324  or a handle, grip, or extension to push and pull the pins  322  about a pinhole to latch and unlatch the collar  320 . When the collar  320  is unlatched, the collar  320  may be removed or disconnected from the boss  212 / 214 . The collar  320  may be coupled or attached to the boss  212 / 214  by positioning the collar  320  over and around the boss  212 / 214  and latching the collar  320  onto the boss  212 / 214  via the pins  322  to secure the collar  320  onto the boss  212 / 214 . 
     The collar  320  may have a shape that is cylindrical, cuboid, or another prism in the latched position. Edges of the collar  320  may be chamfered as shown in  FIG.  3 A  or filleted. An outer surface  326  of the collar  320  may include sensor docks  328  configured to receive the sensors  202 . The sensor docks  328  may extend from the outer surface  326  or attached to the outer surface  326  via conventional adhesives or fasteners. The sensor docks  328  may have a shape that is cylindrical, cuboid, or another prism. The sensor docks  328  may have openings or bores that receive the sensors  202 . The openings or bores may conform to the shape of the sensors  202 . 
     While  FIG.  3 B  illustrates four pairs of sensors (e.g., sensors  202 A- 1  and  202 A- 2 ; sensors  202 B- 1  and  202 B- 2 ; sensors  202 C- 1  and  202 C- 2 ; sensors  202 D- 1  and  202 D- 2 ) any even number of sensors  202  located opposite each other may be used. A greater number of sensors may result in greater accuracy of the system. 
     The size of the detecting area of the sensors  202 , referred to as the aperture of the sensors  202 , may be carefully chosen based on the material of the boss  212 / 214  and/or the size of the boss  212 / 214 . When the aperture is too large, some of the signals received by the sensor may be cancelled by other signals having an opposite phase. When the aperture is too small, the sensor may not be sufficiently sensitive to all of the signals. In some embodiments, the aperture of the sensors  202  is between ⅛ of an inch to ¼ of an inch. 
       FIG.  4    illustrates traces of four sensors  202 A- 1 ,  202 B- 1 ,  202 A- 2 , and  202 B- 2 , where sensors  202 A- 1  and  202 A- 2  are located opposite each other along the circumference of the boss  212 / 214 , and sensors  202 B- 1  and  202 B- 2  are located opposite each other along the circumference of the boss  212 / 214 . The phase inversion of the detected direct arriving pseudo longitudinal/extensional wave mode component between the two opposing sensors described above is shown by comparing the traces of sensor  202 B- 1  and  202 B- 2  in  FIG.  4   . The phase of the front end arrival on the traces of sensor  202 B- 1  and  202 B- 2  are 180° out of phase with respect to one another. The aforementioned feature may be used as one factor in identifying crack extension. 
     The next feature to be leveraged is consistency within inter-channel arrival time differences (Δt). As a fatigue crack is discrete in nature and exists in a defined location on the boss  212 / 214 , the arrival time differences will be highly consistent for incremental crack extension. Typically, arrival time differences are input into a mathematical model and the velocity of the ultrasound propagation is utilized to determine the location of the source. If the geometry of the boss  212 / 214  were known, source location would be possible, however, source location is not necessary, as similarity in arrival time differences is adequate to confirm that a source is emitting from a highly similar physical location. 
     As an example,  FIGS.  5 A- 5 D  show representative waveforms that are a part of the deformation data detected by each sensor  202 . The waveforms are a result of a crack extension event detected at each channel, with the arrival time of the waveform indicated by a vertical dashed line. The waveform arrival times exhibit a highly consistent pattern of inter-channel arrival time difference behavior. Thus, when the waveform arrival times detected by the sensors are within a threshold time of each other (i.e., when a difference between arrival times is less than a threshold time), a boss cracking event may be detected. The time range between arrival times that trigger the determination of consistent arrival times may be based on the geometry and/or the size of the boss  212 / 214 . 
     The final pieces of information leveraged would be the design of a loading scheme intended to generate both crack extension (occurring at high stress intensity factor (ΔK) levels with waveforms possessing higher frequency content due to the short duration brittle fracture), as well as frictional rubbing between existing fracture surface events occurring at low ΔK levels following the application of a large tensile stress (with waveforms possessing lower frequency content due to the longer duration of frictional sliding).  FIGS.  6 A- 6 B  provide an example of waveforms and frequency spectra from a crack extension event, whereas  FIGS.  7 A- 7 B  provide waveforms and frequency spectra from a frictional rubbing event.  FIG.  8    provides a double y-axis plot; the left hand y-axis is cumulative events by first detecting channel, the right hand y-axis is internal pressure within a Type 4 COPV, and the x-axis is time. From  FIG.  8   , it can be observed that the crack extension events were all detected at high ΔK levels for the  3600  psi service pressure vessel, while one crack face rubbing frictional event was detected on the final depressurization (low ΔK level). 
     High ΔK levels and low ΔK levels may vary based on the material of the boss  212 / 214 . In general, high ΔK levels may be observed where the loading is above a threshold ΔK level, or ΔK TH , and low ΔK levels may be observed where the loading is below ΔK TH . 
       FIG.  9    illustrates all detected events from the sensors  202 .  FIG.  10    illustrates identification of boss cracking events from among all of the detected events using the methods described herein. As illustrated by  FIGS.  9  and  10   , the systems and methods described herein are capable of efficiently and accurately detecting boss cracking events. 
     In some embodiments, use of MAE and the sensors arranged as described herein allows for the identification of the boss cracking events from among all of the detected events by virtue of the data detected using MAE. 
       FIG.  11 A  illustrates a block diagram of components that may be coupled to the boss  212 / 214 . The system  1100  includes the boss  212 / 214  and sensors  202 , as described herein. The sensors  202  are physically coupled to the boss  212 / 214 , also as described herein. 
     The sensors  202  may be communicatively coupled to a controller  1102  (or “boss controller” or “boss-side controller” or “cracking monitoring controller”). The sensors  202  may be configured to detect deformation data associated with a fracture event received (or experienced) by the boss  212 / 214 . As used herein, “deformation data” may be used to refer to the deformation of the boss  212 / 214 . In this regard, “cracking data,” “fracture data,” or “boss integrity data,” among others, may be used interchangeably with “deformation data.” 
     The deformation data may be provided to the controller  1102 . The controller  1102  may be a computer processor, microprocessor, control unit, or any device configured to execute instructions stored in non-transitory memory. The controller  1102  may be located in a housing that is physically coupled to the cylinder  100  (e.g., located directly on the cylinder  100 , on a housing of the cylinder  100 , or on a device coupled to the cylinder  100 ). While  FIG.  11 A  shows the controller  1102  coupled to only one pair of sensors  202  coupled to boss  212 / 214 , the controller  1102  may be coupled to additional pairs of sensors for monitoring other bosses or additional pairs of sensors for the boss  212 / 214 . 
     The sensors  202  may be communicatively coupled to the controller  1102  via wires, or in a wireless manner, using respective transceivers (e.g., a transceiver for each sensor  202  and a transceiver for the controller  1102 ). While a pair of sensors  202  are shown, any number of sensors  202  may be included in the system  1100  to monitor the boss  212 / 214 , and each sensor  202  may be communicatively coupled to the controller  1102 . 
     The controller  1102  may also be communicatively coupled to a display  1104  and/or a speaker  1106 . The controller  1102  may be configured to render a graphical user interface displayed by the display  1104 . The graphical user interface may include notifications that the boss  212 / 214  is compromised, and the display  1104  may display these notifications. Similarly, a speaker  1106  may emit a noise, alarm, spoken words, or any other indication. 
       FIG.  11 B  illustrates an example system  1140 , according to various embodiments of the invention. The system  1140  includes boss  212 / 214 , sensors  202 , and controller  1102 , each as described herein. As described herein, the sensors  202  are configured to detect deformation data of the boss  212 / 214  and communicate the deformation data to the controller  1102 . The sensors  202  may be broadband piezoelectric sensors or any other potentially suitable sensors (e.g., fiber Bragg grating, non-contact laser, etc.) configured to detect deformation of the boss  212 / 214 . Also as described herein, the controller  1102  is configured to detect boss cracking events (e.g., crack extension or crack closure) based on the deformation data. Crack closure may also be referred to as crack face rubbing and occurs after the crack is extended and both free surfaces of the extended crack make contact with one another. 
     The system  1140  also includes a memory  1152  coupled to the controller  1102 . The memory  1152  may be a non-transitory memory configured to store instructions for execution by the controller  1102 , which may be a computer processor, such as a microprocessor or microcontroller. The memory  1152  may also store data such as deformation data detected by the sensors  202  or a state of the boss  212 / 214 , for example. The state of the boss  212 / 214  may be represented in multiple tiers (e.g., 2 tiers, 3 tiers, 4 tiers) each associated with a word (e.g., “normal,” “needs inspection,” “damaged”) or number (e.g., 1, 2, 3, 4). 
     If a boss cracking event is detected, the controller  1102  is configured to provide an indication that damage has been experienced by the boss  212 / 214 . The indication may be provided to any number of devices, such as an ECU of the vehicle  102 , a local non-transitory memory, or a remote non-transitory memory. 
     When the indication is provided to a local non-transitory memory  1152 , the controller  1102  may update, on the local non-transitory memory  1152 , a state indication associated with each boss  212 / 214  of the vehicle  102 , and the state indication may be changed from a first state corresponding to a non-damaged condition of the boss to a second state corresponding to a potentially damaged condition of the boss. The local non-transitory memory  1152  may be accessed by another device (e.g., a computing device of a maintenance facility) to determine whether the boss  212 / 214  should be inspected. In some embodiments, refilling of the cylinder  100  may be automatically prevented when there is an indication of potential damage to the boss  212 / 214 . 
     Similarly, when the indication is provided to a remote non-transitory memory, the controller  1102  may update, on the remote non-transitory memory, a state indication associated with each of the bosses  212 / 214  of the vehicle  102 , and the state indication may be changed from a first state corresponding to a non-damaged condition of the boss to a second state corresponding to a potentially damaged condition of the boss. The remote non-transitory memory may be accessed by another device (e.g., a computing device of a maintenance facility) to determine whether the boss  212 / 214  should be inspected. In some embodiments, refilling of the cylinder  100  may be automatically prevented when there is an indication of potential damage to the boss  212 / 214 . 
     The system  1140  also includes a transceiver  1156  coupled to the controller  1102 . The controller  1102  may use the transceiver  1156  to couple to a network such as a local area network (LAN), a wide area network (WAN), a cellular network, a digital short-range communication (DSRC), the Internet, or a combination thereof. 
     The transceiver  1156  may include a communication port or channel, such as one or more of a Wi-Fi unit, a Bluetooth® unit, a Radio Frequency Identification (RFID) tag or reader, a DSRC unit, or a cellular network unit for accessing a cellular network (such as 3G, 4G, or 5G). The transceiver  1156  may transmit data to and receive data from devices and systems not directly connected to the controller  1102 . For example, the controller  1102  may communicate wirelessly with a remote data server  1158  and/or a vehicle  1166  (e.g., vehicle  102 ). Furthermore, the transceiver  1156  may access the network, to which the remote data server  1158  and the vehicle  1166  are also connected. 
     The ECU  1170  of the vehicle  1166  may control one or more output devices  1174  of the vehicle  1166 , including an indicator light, display screen, speaker, or other notification device for alerting a driver or user when the controller  1102  detects damage to the boss  212 / 214 , as described herein. The controller  1102  may communicate with the ECU  1170  of the vehicle via wires or via the transceiver  1156 , with the ECU  1170  being coupled to its own respective transceiver  1168 . In this regard, the ECU  1170  may also be coupled to its own non-transitory memory  1172  similar to memory  1152 . 
     The boss  212 / 214 , sensors  202 , controller  1102 , memory  1152 , and transceiver  1156  may be collectively referred to as a boss monitoring device  1150 . The boss monitoring device  1150  may be physically located on a vehicle (e.g., vehicle  102 ). In some embodiments, “boss monitoring device” may refer to the sensors  202 , controller  1102 , memory  1152 , and/or transceiver  1156 , with the boss  212 / 214  being separate from the boss monitoring device. Although  FIG.  11 B  illustrates various elements connected to the controller  1102 , the elements of the boss monitoring device  1150  may be connected to each other using a communications bus. 
     The controller  1102  may communicate the deformation data from the sensors  202  and/or an update to the state of the boss  212 / 214  to a remote data server  1158 . The remote data server  1158  may include a processor  1160 , a memory  1162 , and a transceiver  1164 . The processor  1160  may be any computing device configured to execute instructions stored in a non-transitory memory. The memory  1162  may be similar to memory  1152  and configured to store instructions for execution by the processor  1160  as well as deformation data detected by the sensors  202  or a state of the boss  212 / 214 , for example. 
     The transceiver  1164  is similar to transceiver  1156  and is configured to transmit and receive data from one or more other devices, such as the boss monitoring device  1150  and the vehicle  1166 . 
     In some embodiments, instead of the controller  1102  performing determinations based on the deformation data from the sensors  202 , the processor  1160  may receive the deformation data and perform one or more of the responsibilities of the controller  1102  described herein. In these embodiments, it may be computationally more efficient to communicate the deformation data detected by the sensors  202  to the remote data server  1158  (via respective transceivers  1156 ,  1164 ) for processing by the processor  1160  than having the controller  1102  perform the processing. 
     While one remote data server  1158  is shown, there may be a plurality of remote data servers  1158  configured to distribute the computational load to improve computational efficiency. In some embodiments, the remote data server  1158  may be any device capable of communicating with the boss monitoring device  1150  and capable of performing computer processing, such as an ECU of the vehicle or a mobile device (e.g., a smartphone, laptop, tablet). 
     As used herein, a “unit” may refer to hardware components, such as one or more computer processors, controllers, or computing devices configured to execute instructions stored in a non-transitory memory. 
       FIG.  12    illustrates a flowchart of a process  1200  performed by the systems described herein. A first sensor (e.g., sensor  202 ) located on an outer surface of a neck (e.g., neck  224 ) of the boss (e.g., boss  212 / 214 ) detects first deformation data associated with the boss (step  1202 ). A second sensor (e.g., sensor  202 ) located on the outer surface of the neck of the boss at a location opposite the first sensor (e.g., sensors  202 A- 1  and  202 A- 2 ) detects second deformation data associated with the boss. The first sensor and the second sensor may be broadband piezoelectric sensors and the deformation data may be represented by waves corresponding to voltage generated by the respective piezoelectric elements of the sensors over time. 
     A controller (e.g., controller  1102 ) communicatively coupled to the first sensor and the second sensor determines, based on modal acoustic emission analysis of the first deformation data and the second deformation data, whether a boss cracking event has occurred (step  1206 ). The boss cracking event may be a crack extension or a crack closure. 
     As described herein, the controller may determine that the boss cracking event has occurred by detecting a 180 degree phase shift between the first deformation data and the second deformation data, as illustrated in  FIG.  4   . 
     Also as described herein, the first deformation data includes a first arrival time of a first waveform (as detected by a first sensor) and the second deformation data includes a second arrival time of a second waveform (as detected by a second sensor). The second waveform is a first waveform detected by the second sensor and associated with the second deformation data, and the second arrival time is the arrival time associated with this detected waveform. The controller may determine that the boss cracking event has occurred by determining whether a difference between the first arrival time and the second arrival time is lower than a threshold time, as illustrated in  FIGS.  5 A- 5 D . 
     Also as described herein, the controller may determine that the boss cracking event has occurred by detecting high frequency content occurring at high ΔK levels or low frequency content occurring at low ΔK levels. When high frequency content is detected, the boss cracking event is a crack extension, and when low frequency content is detected, the boss cracking event is a crack closure. 
     An output device (e.g., output device  474 ) communicatively coupled to the controller provides a notification when the controller determines the boss cracking event (step  1208 ). For example, the output device may be a light in a passenger cabin or instrument panel of the vehicle that illuminates when the boss cracking event is detected. In another example, the output device may be a display screen that displays text and/or images warning of a boss cracking event being detected. 
     Exemplary embodiments of the methods/systems have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents. Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.