Patent Publication Number: US-11041829-B2

Title: Measurement of fracture characteristics of adhesive polymeric materials using spiral cracking pattern

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application relates and claims priority to U.S. Provisional Patent Application No. 62/625,084, filed Feb. 1, 2018, the entirety of which is hereby incorporated by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to systems and methods for measuring one or more fracture characteristics of adhesive polymeric materials. 
     BACKGROUND 
     Cracking is an important issue in performance of materials such as asphalt, paint layers, and glues, among many other adhesive materials. For example, in the case of asphalt materials, in the U.S. alone every year millions of dollars of taxpayer money is spent fixing and rehabilitating cracks in the roads. 
     Currently available testing methods and systems configured to measure the fracture properties of materials are neither convenient nor cost-effective. In addition, these methods and systems include significant limitations, especially when testing soft adhesive polymers. Moreover, these testing methods and systems suffer from poor repeatability and require significant operator training and care. For example, the equipment cost for currently available testing methods and systems are in the range of USD $150,000 to $200,000 depending upon test device features. 
     Accordingly, there is a continued need for affordable and efficient methods and systems for quickly assessing the cracking characteristics of polymers. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure is directed to a method and/or system for measuring one or more fracture characteristics of adhesive polymeric materials. According to an embodiment, the method comprises the following steps: (i) providing a sample for analysis; (ii) bonding the sample to a rigid substrate; (iii) cooling the sample from a first temperature to a second temperature such that thermally-induced stresses are generated within the sample (due to thermal contraction coefficients mismatch between polymer and the substrate material) leading to development of an inward-growing three-dimensional spiral crack within the sample; (iv) detecting, by three or more Acoustic Emission (AE) piezoelectric sensors mounted on the surface of the specimen and/or the rigid substrate, the emitted mechanical transient waves from generation of new fractured surfaces in the sample due to propagation of the inward-growing three-dimensional spiral crack within the sample; (v) determining the accurate 3D geometry of the spiral crack in the material and measuring the exact varying depth of crack penetration through the specimen thickness along the crack path, using multi-sensor AE source location technique; (vi) implementing the digital image analysis (DIA) to determine the spiral crack width as well as the mathematical model for the 3D geometry of spiral cracks; (vii) calculating the total fractured surface area inside the sample using the exact width, depth, and length of spiral crack measured through integrated AE-DIA approach; (viii) determining the AE-based fracture characteristics of the polymer material using total amount of emitted AE energy and total fracture surfaces within the sample; and (ix) reporting the determined fracture characteristics of the sample. 
     According to an embodiment, the system comprises: (i) a sample bonded to a rigid substrate and cooled down from a first temperature to a second temperature; (ii) three or more AE piezoelectric sensors configured to detect mechanical stress waves originated from generation of the inward-growing three-dimensional spiral cracks within the sample; (iii) a visualization device configured to digitize and perform digital image analysis on the 2D spiral pattern deposit of the material left of the rigid substrate; and (iv) a processor configured to determine AE-based fracture characteristics of the sample using cumulative AE energies of detected mechanical waves as well as the precise 3D geometry of the spiral crack obtained from integrated AE-DIA approach. 
     These and other aspects of the invention will be apparent from the embodiment(s) described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of a system for analyzing a fracture characteristic of an adhesive polymeric material, in accordance with an embodiment. 
         FIG. 2  is a schematic representation of a method for analyzing a fracture characteristic of an adhesive polymeric material, in accordance with an embodiment. 
         FIG. 3  is a schematic representation of a system for analyzing a fracture characteristic of an adhesive polymeric material, in accordance with an embodiment. 
         FIG. 4  is a flowchart of a method for analyzing a fracture characteristic of an adhesive polymeric material, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to a method and/or system for measuring fracture characteristics of adhesive polymeric materials. According to an embodiment, the novel method described herein for measuring AE-based fracture characteristics of an adhesive polymeric material provides simple and rapid determination of the fracture characteristics of adhesive polymeric materials such as paint, liquid glues, and asphalt binders, among many others. This technique addresses the current shortage of a rapid, practical, and cost-effective testing approach for crack resistance characterization of adhesive materials. The outcomes of this innovative technique enable improved engineered design of fracture-resilient adhesive materials, and yield significant payoff to practice for both up-stream and down-stream suppliers and producers. Suppliers of adhesive polymers can, for example, utilize this novel technological development to rapidly assess the cracking characteristics of formulations of polymers and, by modifying the formulation, design crack-resistant materials. 
     According to an embodiment, the method and/or system described or otherwise envisioned herein for measuring one or more fracture characteristics of an adhesive polymeric material utilizes a multi-sensor Acoustic Emission (AE) source location approach in conjunction with Digital Image Analysis (DIA) to meticulously determine the precise geometry and mathematical model of the three-dimensional spiral crack in a bi-axially stressed layer of adhesive polymeric material, and to detect and record all acoustic activities of the crack while the test is conducted. Results from the integrated AE-DIA approach are used to compute the fracture energy of the material. 
     Referring to  FIG. 1 , in one embodiment, is a schematic representation of an AE-DIA system, represented generally by reference numeral  10 , for measuring one or more fracture characteristics of an adhesive polymer. According to this example, a 20 mm thick cylindrical sample of adhesive polymeric material  12  with a diameter of 25 mm is bonded to a rigid substrate  14  such as aluminum. The rigid substrate material will be chosen based on the type of adhesive polymer being tested. The sample is cooled down from about 20° C. to about −70° C., although many other temperatures are possible depending on type of the adhesive polymer. The temperature of the specimen is continuously recorded using a k-type thermocouple  16  positioned at the interface of the specimen  12  and the substrate  14 . As the specimen  12  cools down, differential thermal contraction between the rigid substrate  14  and the polymer induces equi-biaxial thermally-induced stresses within the material, thereby resulting in the formation of an inward-growing three-dimensional spiral crack within the specimen. 
     As the spiral crack propagates inward, it creates new fractured surfaces, which is accompanied by release of stored strain energy in the form of transient mechanical waves inside the specimen. The AE piezoelectric sensors  18  mounted on the surface of the specimen  12  as well as the substrate  14  will continuously monitor and detect these mechanical waves and convert them in to AE signals. According to an embodiment, three of AE piezoelectric sensors  18  are mounted on the surface of the specimen  12  and three of the AE piezoelectric sensors are mounted on the rigid substrate  14 , although many other configurations are possible. Recorded AE signals are carefully analyzed to compute the emitted energy associated with each AE event (i.e. AE event is a rapid physical change such as microcracks in microstructure of the material, appearing as acoustic signal). Moreover, the cumulative AE energy is calculated to measure the total amount of released AE energy due to creation of new fractured surfaces in the sample. The emitted AE energy is proportional to the extent of damage in the material. Accordingly, the larger the size of microdamage, the higher the amount of emitted AE energy. In addition to measuring the cumulative AE energy, a multi-sensor Geiger iterative source location approach can be employed to analyze the recorded AE signals and to precisely visualize the accurate 3D geometry of the spiral crack in the material which will result in measuring the exact varying depth of crack penetration through the specimen thickness along the crack path. 
     Referring to  FIG. 2  is a schematic representation of the spiral crack geometry determination using the multi-sensor AE source location technique. 
     Referring to  FIG. 3  is a schematic representation of the DIA computer vision  100  approach utilized to digitally analyze the HD images of the two-dimensional spiral pattern deposit of the material left of the substrate  14 . The mathematical model will be automatically fit to the crack pattern and the spiral tightness parameter, “b”, and the spiral scaling factor, “A” will be determined. 
     According to an embodiment, the precise calculations of total fractured surface area inside the specimen can be achieved using the exact width, depth, and length of spiral crack measured through the integrated AE-DIA approach. The AE-based fracture energy (G f-AE ) of the material which is the amount of released AE energy per unit of newly created fracture surface area can be computed using the following equation: 
     
       
         
           
             
               
                 
                   
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     The G f-AE  is calculated by dividing the cumulative emitted AE energy by the total fractured surface area within the sample  12 . The units of G f-AE  are V 2 .μsec/mm 2 . 
     Referring to  FIG. 4  is a flowchart of a method  400  for measuring AE-based fracture characteristics of an adhesive polymer using a multi-sensor Acoustic Emission (AE) source location approach in conjunction with Digital Image Analysis (DIA). 
     At step  410  of the method, a polymeric material sample is provided. The sample can be any adhesive polymer for testing, including but not limited to paint, glue, asphalt, and many other materials. The sample can be provided by or obtained from any source for testing. 
     At step  420  of the method, the sample is bonded to a rigid substrate. The rigid substrate can be any substrate capable of enabling the method to be performed. According to one embodiment, there are two requirements for the rigid substrate: 1) substrate material should have a strong adhesion with polymer material, 2) there should be a significant difference between thermal contraction coefficient of substrate and polymer material in order to induce enough thermal stress within the sample to develop a spiral crack in the specimen. As one example, the rigid substrate can be aluminum or granite, although many other substrates are possible. 
     At step  430  of the method, the sample is cooled from a first temperature to a lower temperature. The sample is cooled from a first temperature to a second temperature that is sufficient to induce differential thermal contraction between the rigid substrate and the polymer, which results in thermally-induced stresses within the sample. According to just one example, the sample is cooled down from about 20° C. to about −70° C., although many other temperatures are possible. According to an embodiment, this cooling induces equi-biaxial thermally-induced stresses within the sample, which produces one or more inward-growing three-dimensional spiral cracks within the specimen. As the spiral crack propagates inward it creates new fractured surfaces, which is accompanied by release of stored strain energy in the form of transient mechanical waves inside the specimen. 
     At step  440  of the method, three or more AE piezoelectric sensors mounted on the surface of the specimen and the substrate monitor and detect mechanical waves generated in step  430  and convert them in to AE signals. The AE signals may be analyzed in real-time and/or recorded for future analysis. According to an embodiment, the AE signals are carefully analyzed to compute the emitted energy associated with each AE event. Additionally, the cumulative AE energy can be calculated to measure the total amount of released AE energy due to creation of new fractured surfaces in the sample. The emitted AE energy is proportional to the extent of damage in the material. Accordingly, the larger the size of microdamage, the higher the amount of emitted AE energy. In addition to measuring the cumulative AE energy, a multi-sensor Geiger iterative source location approach can be employed to analyze the recorded AE signals and to precisely visualize the accurate 3D geometry of the spiral crack in the material which will result in measuring the exact varying depth of crack penetration through the specimen thickness along the crack path. 
     At step  450  of the method, sample deposited on the substrate as a result of the fracturing is visualized. According to an embodiment, the DIA vision approach described herein is utilized to digitally analyze the HD images of the two-dimensional spiral pattern deposit of the material left of the substrate. 
     At step  460  of the method, the information obtained from steps  440  and  450  is utilized to determine one or more fracture characteristics of the sample. For example, according to an embodiment, calculations of total fractured surface area inside the specimen can be achieved using the width, depth, and/or length of spiral crack measured in steps  440  and  450  of the method. According to an embodiment, the AE-based fracture energy (G f-AE ) of the material which is the amount of released AE energy per unit of newly created fracture surface area can be computed using Equation 1. As depicted in equation (1), the G f-AE  can be calculated by dividing the cumulative emitted AE energy by the total fractured surface area within the sample, where the units of G f-AE  are V 2 .μsec/mm 2 . 
     At step  470  of the method, the determined AE-based fracture characteristics of the sample can be provided to a user, a computer, a server, a user interface, or any other destination or output. For example, the determined G f-AE  fracture characteristics of the sample can be provided as a text report, a graph, and/or any other means of providing the output of the system. 
     Although the present invention has been described in connection with a preferred embodiment, it should be understood that modifications, alterations, and additions can be made to the invention without departing from the scope of the invention as defined by the claims.