Patent Publication Number: US-2022236157-A1

Title: Apparatus and method for evaluating radial compressive strength of a ceramic honeycomb sample

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 62/850,237 filed on May 20, 2019, the content of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     This application generally relates to isostatic strength testing apparatus for testing ceramic honeycomb samples and methods for using the same. 
     SUMMARY 
     All examples and features mentioned below can be combined in any technically possible way. 
     In one aspect, an apparatus for evaluating the radial compressive strength of a ceramic honeycomb sample is provided. The apparatus comprises a housing defining a testing compartment; a pressure subsystem configured to introduce a pressurizing fluid into the testing compartment; a flexible member disposed within the testing compartment and in fluid communication with the pressure subsystem, the flexible member defining a testing area within the testing compartment configured to receive the ceramic honeycomb sample, wherein the flexible member is configured to expand inwardly and subject the honeycomb sample to a compressive force by engaging against the outer surface of the honeycomb sample when pressurized by the pressurizing fluid; an end cap covering an end face of the ceramic honeycomb sample when the ceramic honeycomb sample is positioned in the testing compartment; and an acoustic sensor disposed on the end cap and configured to translate acoustic waveforms propagating through the acoustic sensor to a signal representative of the acoustic waveforms. 
     In some embodiments, the end cap is in direct contact with the end face of the honeycomb sample when the honeycomb sample is loaded in the testing compartment. In some embodiments, the end cap comprises a protective pad that is in direct contact with the end face of the honeycomb sample when the honeycomb sample is loaded in the testing compartment. 
     In some embodiments, the acoustic sensor is engaged with a waveguide defined by the end cap. In some embodiments, the waveguide is comprised of a material having a density greater than a density of the ceramic honeycomb sample. In some embodiments, the waveguide comprises a thickness separating the acoustic sensor from the end face of the honeycomb sample that is equal to a multiple of a quarter-wavelength (nλ/4) of a predetermined frequency, wherein the predetermined frequency is within a range detectable by the acoustic sensor. In some embodiments, the predetermined frequency is selected as a frequency expected to be produced when walls of the honeycomb sample experience cracking. In some embodiments, the end cap comprises a channel and the acoustic sensor is located at an end of the channel that positions the acoustic sensor proximate to the testing compartment. 
     In some embodiments, the apparatus further comprises a pressure sensor configured to monitor a pressure of the pressurizing fluid. In some embodiments, the apparatus further comprises a controller in signal communication with the acoustic sensor and configured to analyze the signal for an indicator of a compromised wall of the ceramic honeycomb sample. In some embodiments, the indicator comprises an amplitude of the acoustic waveform detected by the acoustic sensor exceeding a threshold. 
     In another aspect, a method for testing the compressive strength of a ceramic honeycomb sample is provided. The method comprises the steps of applying a predetermined radial compressive pressure to a ceramic honeycomb sample; generating one or more signals from an acoustic sensor disposed in an end cap covering an end face of the ceramic honeycomb sample; and analyzing the one or more signals for an indicator of a compromised wall of the ceramic honeycomb sample. 
     In some embodiments, the acoustic sensor is disposed engaged with a waveguide defined by the end cap. In some embodiments, the analyzing comprises comparing an amplitude of the acoustic waveform detected by the acoustic sensor to a threshold value. In some embodiments, the analyzing comprises determining whether a count of acoustic waveform amplitudes exceed a threshold. In some embodiments, the analyzing comprises determining whether a risetime of one or more peak of the acoustic waveforms, or an average risetime of the one or more peaks, exceeds a threshold. In some embodiments, the acoustic sensor is engaged with a waveguide defined by the end cap. 
     In some embodiments, the waveguide comprises a thickness separating the acoustic sensor from the end face of the honeycomb sample that is equal to a multiple of a quarter-wavelength (nλ/4) of a predetermined frequency, wherein the predetermined frequency is within a range detectable by the acoustic sensor. In some embodiments, the predetermined frequency is selected as a frequency expected to be produced when walls of the honeycomb sample experience cracking. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section view of an isostatic strength testing apparatus, according to an example. 
         FIG. 2A  is a partial cross-section view of an isostatic strength testing apparatus, according to an example. 
         FIG. 2B  is a partial cross-section view of an isostatic strength testing apparatus, according to an example. 
         FIG. 3A  is a partial cross-section view of an isostatic strength testing apparatus, according to an example. 
         FIG. 3B  is a partial cross-section view of an isostatic strength testing apparatus, according to an example. 
         FIG. 4A  is a top view of an isostatic strength testing apparatus prior to conducting a test on a sample, according to an example. 
         FIG. 4B  is a top view of an isostatic strength testing apparatus after conducting a test on a sample, according to an example. 
         FIG. 5  is a schematic of an isostatic strength testing apparatus, according to an example. 
         FIG. 6  is a cross-section view of an acoustic waveguide, according to an example. 
         FIG. 7A  is a graph depicting a signal from an acoustic sensor in the time domain, according to an example. 
         FIG. 7B  is an example signal from an acoustic sensor in the frequency domain, according to an example. 
         FIG. 8A  is a graph depicting recorded magnitudes from a first acoustic sensor signal, according to an example. 
         FIG. 8B  is a graph depicting recorded magnitudes from a second acoustic sensor signal, according to an example. 
         FIG. 8C  is a graph depicting recorded magnitudes from a third acoustic sensor signal, according to an example. 
         FIG. 9  is a graph depicted recorded counts from three acoustic sensors, according to an example. 
         FIG. 10A  is a cross-section view of an isostatic strength testing apparatus in a first stage of testing, according to an example. 
         FIG. 10B  is a cross-section view of an isostatic strength testing apparatus in a second stage of testing, according to an example. 
         FIG. 10C  is a cross-section view of an isostatic strength testing apparatus in a third stage of testing, according to an example. 
         FIG. 10D  is a cross-section view of an isostatic strength testing apparatus in a first stage of testing, according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Ceramic honeycomb structures, such as those used in catalytic converters, must withstand compressive forces experienced during the “canning” process—the process of being encased in a metal container for use in an automotive exhaust system. To test whether a given batch of ceramic honeycomb structures meets the radial compressive strength requirements (“isostatic strength”), one or more samples  14  from the batch are subjected to isostatic strength testing until sample failure (the sample cracks or otherwise breaks). 
     Some isostatic strength testing apparatus may be slow to operate, test only a subset of samples from a given batch, or necessarily damage the tested samples. Acoustic sensors used on isostatic strength testing apparatus may have poor signal-to-noise ratios due to detecting acoustic waveforms through a compressive boot. 
       FIG. 1  depicts an example apparatus  10  for testing the isostatic strength of a ceramic honeycomb sample  14 . The ceramic honeycomb sample  14  can be formed in any known or discovered manner. For example, in one embodiment, the ceramic honeycomb sample  14  comprises a matrix of intersecting walls defining channels or cells therebetween, which channels or cells extend longitudinally along the length of the honeycomb sample  14 . The channels or cells can be square, triangular, rectangular, hexagonal, polygonal, etc. The honeycomb sample  14  can be formed, for example, by extrusion of a ceramic forming material through an extrusion die as a green body, which is then cut, dried, and fired into a final ceramic honeycomb body. The ceramic forming material can comprise inorganics (e.g., alumina, silica, etc.), binders (e.g., methylcellulose), pore formers (e.g., starch, graphite, resins), a liquid vehicle (e.g., water), sintering aids, or any other additives helpful in the manufacture of the final ceramic honeycomb body. The final ceramic honeycomb body can comprise cordierite, aluminum titanate, alumina, mullite, silicon carbide, and/or other ceramic materials, or combinations thereof. 
     As shown in  FIG. 1 , apparatus  10  comprises a housing  12  defining a testing compartment dimensioned to receive a ceramic honeycomb sample  14 . For example, a testing compartment can be generally cylindrical so as to be circumferentially disposed about the sample  14 , the sample  14  being shaped, generally, as a cylinder. In an example, the housing  12  can comprise a metallic or composite sleeve. Apparatus  10  further comprises a flexible member  16  disposed within the testing compartment. Flexible member  16  defines a testing area disposed circumferentially about the sample  14  (e.g., a cylindrical testing area) such that the flexible member  16  is between the sample  14  and a surface of the housing  12 . As another example, the ceramic honeycomb sample  14 , the housing  12 , and/or the flexible member  16  may take a different shape, e.g., elliptical. 
     During operation, fluid is supplied into a space  18  (shown, for example, in  FIGS. 2A-2B ) between the exterior wall of flexible member  16  and the interior wall of housing  12  to expand the flexible member  16  inwardly, preferably providing uniform compressive force on the periphery of the sample  14  by engaging the flexible member  16  against the outer surface of the honeycomb sample  14 . As the flexible member  16  expands inwardly, the internal cross-sectional diameter of the testing area will diminish, applying uniform radial pressure to the sample  14 . 
       FIG. 2A , depicts a partial cross-sectional view of the housing  12 , the flexible member  16 , and the space  18  between housing  12  and flexible member  16 , filled with pressurizing fluid  20 . In  FIG. 2B  additional pressurizing fluid  20  has been introduced into space  18 , via fluid inlet  22 , resulting in inward expansion of flexible member  16  (shown as moving leftward in the cross-section view of  FIG. 2B  with respect to  FIG. 2A ) and, consequently, compressive pressure applied to the sample  14 . In an alternate example, shown in  FIGS. 3A-3B , the flexible member  18  comprises an inflatable cuff or sleeve, such that the space into which the pressurizing fluid  20  is introduced is a cavity  24  defined within flexible member  16  between an outer wall  26  and an inner wall  28  of the flexible member  16 . 
     The pressure applied can be a user-defined predetermined pressure. In an example, the predetermined pressure can be a maximum expected pressure the sample  14  will experience during the canning process and/or during use. Alternatively, the predetermined pressure can be some margin greater than the maximum expected pressure (e.g., the maximum expected pressure multiplied by a safety factor) the sample  14  will experience during the canning process and/or during use. A sample  14  that fails as a result of the application of the predetermined pressure will crack or otherwise experience compromised structural integrity. 
       FIG. 4A  depicts a top view of apparatus  10  before compressive pressure is applied to sample  14 . In  FIG. 4A , the exposed end face of sample  14  does not contain any cracks. FIG. 4 B depicts the same end face after the application of a predetermined pressure to intentionally introduce cracks in the sample being evaluated (hence the increased thickness and decreased internal diameter of flexible member  16 ). The end face in FIG. 4 B bears cracks and defects along the end face as a result of the predetermined pressure. That is, the walls of the matrix of intersecting walls crack, break apart, and/or separate from each other due to the applied pressure. A sample  14  that passes the compressive test will not bear any cracks introduced by the testing process. 
     Returning to  FIG. 1 , lower end  30  of testing compartment can be closed, forming, for example, a base on which a sample  14  can be seated. The opposing open end  32  (i.e., terminating in an aperture) can receive the sample  14  to be tested. The lower end  30  of testing compartment can be integrally formed with the housing  12  (e.g., with the interior walls of the testing compartment) or can be configured to be removable. For example, the lower end  30  can be a platform on which the honeycomb sample  14  is first positioned, such that the housing  12  is placed onto the platform over and around the honeycomb sample  14 . Flexible member  16  can, additionally, have one closed end  34 , such that pressure may be applied to both the curved surface of sample  14  and the end face of sample  14  adjacent the closed end  34  of the flexible member  16 . 
     In alternate embodiments, the testing compartment can be defined by an open cylinder, that is, a cylinder having substantially cylindrical interior walls but open ends. A cross-section view of this example is shown in FIG. 10 A. In this example, the flexible member  16  can comprise a cuff, likewise having open ends, such that pressure is only applied to the curved circumferential surface of the sample  14  (i.e., radial pressure). The flexible member  16  can be sized to have an axial length shorter than the axial length of the sample  14 , such that one or both end faces of the sample  14  protrude beyond through the open end of the flexible member  16 . For example, the sample  14  can extend by 1-2 inches from the open end of flexible member  16 , although even shorter axial lengths of the flexible member  16  are contemplated. Of course, in another example, the flexible member  16  can have an axial length greater than or equal to the axial length of the sample  14 , such that the periphery of the honeycomb sample  14  is engaged against the flexible member  16  along the entire axial length of sample. 
     As shown in  FIGS. 1 and 10A , an exposed end of the sample  14  can be covered with an end cap  36  prior to initiating the compressive test. In the open cylinder example ( FIG. 10A ), the remaining open end can be similarly covered with an end cap  36  if desired. In an example, end cap  36  can be coupled to housing  12  (e.g., with a screw, bracket, or other mechanical fastener) or be held against housing  12  with, for example, a pneumatically-driven arm, magnetism, etc. Alternatively, end cap  36  can rest on top of housing  12  or the end face of the sample  14 . End cap  36  can function to seal the testing compartment, or can simply cover an end face of the sample  14 . As shown in  FIG. 1 , end cap  36  can further comprise a protective pad  39  (e.g., a gel pad) that contacts the surface of the sample  14  to prevent any chipping or other damage to the end face during the test process. 
     In an example, end cap  36  can be disposed directly against an end face of the honeycomb sample  14 , i.e., without any intervening structure (such as a portion of flexible member  16 ) between end cap  36  and the adjacent end face of sample  14 . As will be described below, this can be used to aid in the detection of failures. 
     As shown in  FIG. 5 , in an example, apparatus  10  further comprises a pressure subsystem  38 . The pressure subsystem  38 , at a high level, can perform tasks such as introducing the pressurizing fluid  20  via fluid inlet  22  to the space  18  (or cavity  24 ), and removing the pressurizing fluid  20  when the test is complete. Pressure subsystem  38  can thus comprise a pump  40  for introducing and removing the pressurizing fluid to and from the space  18  or cavity  24 . The pump  40  can be a pneumatic pump, if the pressurizing fluid is gas, or a hydraulic pump, if the pressurizing fluid is a liquid. The pressure subsystem  38  preferably comprises a pressure sensor  42  to determine when a predetermined pressure has been reached. 
     The pressure subsystem  38  can be in communication with a controller  44  for controlling the application and removal of pressure to the sample  14  (e.g., controlling the actuation of pump  40 ) and for receiving inputs from the pressures sensor  42 , which can be used to determine when a predetermined pressure has been reached or for determining a sudden drop in pressure indicative of a failure of the sample  14 . 
     Apparatus  10  can also comprise one or more acoustic sensors  46  operably positioned about or in housing  12  and/or end cap  36  to detect an acoustic signal (i.e., sound) associated with the failure of the sample  14  as a result of the applied compressive force. Acoustic sensor  46  will detect acoustic waveforms propagating from the sample  14  as a voltage signal having a magnitude and frequency representative of the acoustic waveform. Acoustic sensor  46  can be, for example, a piezo-electric sensor, although any suitable acoustic sensor  46  can be employed. The acoustic sensor  46  can be configured to detect acoustic waveforms in the frequency range of 10-1000 kHz, although other ranges are contemplated. Acoustic sensor  46  can be mechanically coupled to end cap  36  or housing  12 , or elsewhere within or about apparatus  10 , by a couplant, e.g., an adhesive such as hot glue, super glue, gels, etc. 
     Acoustic sensors  46  can likewise be in communication with controller  44 . As will be described in detail below, controller  44  can be arranged to receive and analyze a signal received from each acoustic sensor. Controller  44  can further determine whether a sample  14  has passed or failed the test, according to the analyzed signal. 
     As described above, and as shown in  FIG. 5 , acoustic sensor  46  can be disposed on or within end cap  36 . Because the end cap  36  can be disposed at the end of the sample  14  (e.g., in direct contact with the end face of the sample  14 ) without an intervening flexible member  16 , and, as a result, without intervening fluid for applying compression to the sample  14 , an acoustic sensor  46  disposed within the end cap  36  is well-positioned to detect the acoustic signature that accompanies the failure of the sample  14 . Indeed, in testing, the signal-to-noise-ratio (“SNR”) of an acoustic sensor  46  in the end cap  36  was found to be higher than the same acoustic sensor  46  positioned on the side of housing  12 . 
     Furthermore, as shown in  FIG. 5 , in addition to the end cap  36 , one or more acoustic sensors  46  can be disposed about the exterior or interior of the housing  12 , operatively positioned to detect the acoustic signal indicative of failure. Although only one acoustic sensor  46  is shown disposed about the exterior of housing  12 , it should be understood that any number of acoustic sensors  46  can be disposed about the housing  12  as is suitable for detecting the acoustic signal. 
     Each acoustic sensor  46 , or a subset of acoustic sensors  46 , can be respectively positioned within a portion of the end cap  36  acting as an acoustic waveguide  48  for guiding acoustic waves to acoustic sensor  46  with diminished loss, permitting better detection of a failure of the sample  14 . In an example, the end cap  36  comprises a channel  50 , as shown in  FIG. 6 . In an example, walls  52  defining channel  50  extend in a direction substantially parallel to the direction in which the acoustic signal emitted from sample  14  propagates through acoustic sensor  46 . The channel  50  enables the acoustic sensor  46  to be protected during use, while also positioning the acoustic sensor  46  proximate to the end face of the honeycomb sample  14 . By positioning the acoustic sensors  46  close to where the acoustic waveforms (audible noises resulting from the honeycomb sample  14  cracking) are originating, the acoustic detection can be improved. In other examples, the interior walls  52  of acoustic waveguide can extend in a direction transverse or oblique to the axial length of sample  14 . 
     End cap  36  comprises a first end  54  and a second end  56 , the first end  54  arranged proximate to or engaged against the end face of the honeycomb sample  14 . In the example shown, the acoustic sensor  46  is disposed at the first end of the waveguide  48 . The second end, by contrast, is free (i.e., the interior walls  52  terminates in an aperture), in the embodiment shown in  FIG. 6 . The example of  FIG. 6  is merely provided as an example, and that, in other examples, the waveguide  48  can be curved or otherwise bent in a way advantageous for propagation or, alternately, filtering of certain frequencies or frequency bands. Furthermore, the acoustic sensor  46  can be placed at points within waveguide  48  found to be advantageous for detecting the acoustic signals emitting from failure of a sample  14 , such as in the channel  50  and as further described below. 
     Acoustic waveguide  48  can be arranged so that a distance between the acoustic sensor  46  and the end face of the honeycomb sample  14  is approximately equal to a multiple of a quarter wavelength (nλ/4) of an expected or predetermined frequency of the acoustic signal. Advantageously, this can be useful for improving the signal to noise ratio for the expected frequency or frequencies. In other words, the thickness of the waveguide  48  (including the thickness of the protective pad  39 , if included) disposed between the acoustic sensor  46  and the end face of the honeycomb sample  14 , can be set to nλ/4 of the expected frequency. That is, the noise produced by cracking of the walls of the honeycomb sample  14  will have a frequency and/or a range of frequencies. It is expected that similar honeycomb bodies subjected to the same testing will produce cracking noises of a common expected frequency, or common band or range of expected frequencies. The expected frequency, or range or band of frequencies, can be determined, e.g., theoretically or experimentally, such as by mathematical modeling or by breaking honeycomb samples and monitoring the sounds produced. The expected frequency may be different for different types of honeycomb samples (e.g., based on properties such as ceramic material composition, wall thickness, cells per square inch, etc.). In this way, the predetermined frequency, can, for example, be a frequency, or the center frequency of a frequency band, for which the magnitude of the acoustic signal is expected to be greatest, or which is otherwise expected to be readily identifiable by the acoustic sensor  46  during each testing operation. If multiple acoustic sensors  46  are used, the waveguide  48  can have different thicknesses between each acoustic sensor and the end face of the honeycomb sample  14 , such that each acoustic sensor  46  will more readily detect a frequency (or set of frequencies) of the waveform for which the respective the sensor  46  is tuned. 
     In addition, to promote propagation of the acoustic signal through waveguide  48  interior walls of waveguide  48  can preferably be comprised of a material denser than the sample  14 . For example, interior walls of waveguide  48  can be comprised of acrylic or other material having greater density than the sample  14 . In an example, the larger structure in which the waveguide  48  is defined can be comprised of a denser material as well. For example, the end cap  36  can be formed entirely of acrylic. 
     Returning to  FIG. 5 , controller  44  can comprise, in an example, a processor  58  and memory, e.g., a non-transitory data storage medium configured to store program code that, when executed by the processor, carries out the functionalities described in this disclosure, such as analysis of signals from the acoustic sensors  46  and pressure sensor  42  and control of pump  40 . Controller  44  can be implemented by a processor, a microcontroller, or other suitable computing device. Alternately, controller  44  can be implemented in hardware (such as an ASIC or FPGA), firmware, or as a combination of hardware, firmware, and/or software. In addition, controller  44  can be implemented as collection of processors and non-transitory storage mediums (e.g., a collection of microprocessors acting in concert). 
     Controller  44  can be further in communication with user interface  62  for notifying a user of a failure, or absence of a failure, of the sample  14 . User interface  62  can, for example, be an LED or a display, such as a screen. 
     As mentioned above, signal or signals received from each acoustic sensor  46  can be analyzed for features indicative of a failure, i.e., indicators that the honeycomb sample  14  has been compromised, e.g., experienced cracking. That is, the process of the walls of the honeycomb sample  14  breaking, cracking, separating, or otherwise being compromised will be accompanied by one or more sounds, the acoustic waveform of which can be detected by the acoustic sensors  46  as described herein. Thus, the acoustic waveform may have one or more parameters that can be identified as an indicator that the walls of the honeycomb sample  14  have been comprised, i.e., have cracked. In this way, identification of such indicators can be used, for example, to enable apparatus  10 , e.g., via the controller  44 , to determine when cracking has occurred. For example, such indicators can be used by the apparatus  10  to distinguish the sound produced during cracking from ambient noise or other sounds in the testing environment (e.g., the sound produced while pressurizing the honeycomb sample  14  with the pressurizing fluid  20 ). 
     The features analyzed for indicators of cracking can include: frequency, count, risetime, amplitude, fast Fourier transformation (FFT) magnitude, and duration. These are shown, by way of example, in  FIG. 7A . Briefly described, the peak amplitude is the amplitude of the highest observed peak. The risetime is the period of time occurring between the signal crossing of the predetermined threshold and reaching the peak value (this may be performed for each peak following and including the first peak exceeding the threshold). The duration is the period of time between the first peak crossing the threshold and the last peak crossing the threshold. And the count is the number of peaks crossing the threshold over the course of the duration. Each of the above features can be recorded and analyzed. FIG. 7 B depicts the signal in the frequency domain (e.g., having been transformed using an FFT). In this domain, the frequency associated with the greatest magnitude can be recorded and analyzed. The above-described features are merely provided as examples, and it should be understood that any feature useful for determining the occurrence of a failure can be recorded and analyzed. 
     Example outputs of a compressive test, using an apparatus  10  similar to the apparatus  10  shown in  FIG. 1 , are depicted in  FIGS. 8A-8C .  FIGS. 8A and 8B  depict the outputs of two acoustic sensors  46  disposed in waveguides  48  defined in the end cap  36 , and  FIG. 8C  depicts the output of an acoustic sensor  46  disposed on the exterior of the housing  12 . In each of  FIGS. 8A-8C , the x-axis is time over which pressure is applied to the sample  14 . The pressure is slowly ramped over time, such that the applied pressure, in psi, follows the line  64 ; each of  FIGS. 8A-8C  thus shows the application of pressure over time.  FIGS. 8A-8C  also depict the amplitude of the signal in decibels, at a respective point in time. Until approximately  550  seconds into the test of these figures, corresponding to approximately  300  psi applied to the sample  14 , nearly all recorded amplitudes fell below a threshold  66  indicative of failure (this threshold can be different than the predetermined threshold for conducting the analysis, described above). The amplitudes falling below the threshold are collectively marked as “No Failure.” For example, there may be some level of ambient or background noise during the testing process, which is below the level set by the threshold  66  (in the region marked “No Failure”), with detected noises above the threshold  66  (in the region marked “Failure”) interpreted as the result of cracking, and thus, failure of the honeycomb sample  14  at the currently applied pressure. Analysis of the received acoustic waveforms and comparison to the threshold  66  can be performed by the controller  44 . 
     Once, however, sufficient pressure (approximately  300  psi in the plotted data of  FIGS. 8A-8C ) is applied by apparatus  10  to cause cracking, honeycomb sample  14  fails and a plurality of audio signals are recorded at above the threshold magnitude. The amplitudes rising above the threshold are collectively marked as “Failure.” The “Failure” amplitudes correspond, for example, to the relatively sudden audible popping and cracking noises that result from the intersecting walls of the honeycomb sample  14  breaking apart and/or separating from other walls in the matrix, as cracks form and propagate in the honeycomb sample  14 . Again, by setting the threshold  66  as a noise level that above that of the level of the background or ambient noise, recorded audio signals above the threshold  66  can be determined as failure (cracking) of the sample  14  being tested. 
     If the predetermined pressure (e.g., a maximum pressure to which the honeycomb bodies are expected to be subjected during use, as discussed above) is fully applied without the acoustic sensor  46  detecting a magnitude above the threshold  66 , then the honeycomb samples can be non-destructively tested. 
     It can be observed that acoustic sensors  46  disposed in the acoustic waveguides  48  of the end cap  36  were capable of recording more audio samples than the acoustic sensor  46  disposed on the side of the housing  12 , due to the improved signal to noise ratio at the end cap waveguides  48 . 
       FIG. 9  depicts the results of the same test, measuring, instead, the count of the signal received from the respective acoustic sensors, over time. The various channels, channel  1 , channel  2 , and channel  3 , correspond, respectively, to the first acoustic sensor  46  disposed in the end cap  36  wave guide, the second acoustic sensor  46  disposed in the end cap  36  waveguide  48 , and the acoustic sensor  46  disposed on the housing  12  exterior. At approximately  550  seconds, the recorded counts (representing an increase in frequency of peaks exceeding the predetermined threshold, as described above) sharply increase, indicating a failure. Again, it can be observed that the channel  1  and channel  2  were more sensitive than channel  3  due to the improved signal-to-noise ratio of the acoustic sensors  46  disposed in the end cap  36  waveguide  48 . 
     Controller  44  can determine whether any of the observed features exceeds a respective threshold (e.g., whether the count exceeds a count threshold, whether the risetime of any given peak, or the average risetime of each peak, exceeds the risetime threshold, etc.) or whether any of the observed features falls within a predetermined window. The various thresholds and windows corresponding to failure of a sample  14  can be determined empirically, e.g., by observing the values recorded upon the occurrence of a failure. In this way, controller  44  can determine whether a given sample  14  has failed or passed the compressive test. A failure or pass can be indicated to the user via a user interface  62 , such as an LED or screen. However, in another example, instead of determining whether a sample  14  has passed or failed, the controller  44  can output, via e.g., a screen or print out, the recorded values for additional analysis by the user. 
       FIGS. 10A-10D  depict a cross-sectional view of apparatus  10  at various stages of testing a ceramic honeycomb sample  14 , according to an example. During a first stage, shown in  FIG. 10A , the sample  14  can be placed (either by user or robotically) in the testing compartment. At this stage, the flexible member  16  is not yet expanded to apply compressive force to the exterior of the sample  14 . 
     As shown in FIG. 10 B, at a second stage an end cap  36  comprising one or more acoustic sensors  46  can be placed at one end face of the sample  14 . The end cap  36  can be placed at either end. Alternately, two end caps  36 , one at each end, can be used. In yet another example, one end cap  36  can remain on housing  12 , while the sample  14  loaded from the other end. 
     During the next stage, shown in FIG. 10 C, a predetermined compressive force is applied, radially, to the sample  14 . The pressure can be applied by the pressure subsystem to a predetermined pressure value. During the test, the controller  44  can record signals received from the acoustic sensors, each of which can be analyzed for features indicative of a failure, as described above. The pressure value can be monitored by the pressures sensor  42  in communication with the controller  44 . Once the predetermined pressure is reached, the controller  44  can deactivate or reverse the pump  40  to cease applying pressure to the sample  14 . 
     After the test is completed, as shown in FIG. 10 D, the sample  14  can be ejected (by a user or robotically) from an open end of apparatus  10  (in an alternate example, the sample  14  can be ejected from the top of the apparatus  10 ). The above apparatus  10  and method depicted in  FIGS. 10A-10D  permits rapid in-line testing of each produced honeycomb ceramic body within a batch. For example, samples  14  to be tested can be continuously loaded into the test apparatus (e.g., via a first end), tested by applying pressure circumferentially and monitoring for audio signals indicative of failure (cracking), and then ejected from the testing apparatus (e.g., via a second end opposite to the first end) once the predetermined pressure has been reached. For example, a sequence of samples  14  (e.g., on a conveyor) can be continuously conveyed to the testing apparatus, and then loaded, tested, and ejected in this manner. Those of the samples that “fail” can be discarded or designated for discarding, e.g., placed in a scrap receptacle, while those of the samples that “pass” can be designated for installation in an exhaust treatment system. 
     Thus, various embodiments disclosed herein comprise isostatic strength testing apparatuses configured for rapid in-line testing, and which include acoustic sensors with high signal-to-noise ratios with respect to waveforms received from tested samples, as well as methods for testing such samples. 
     The functionality described herein, or portions thereof, and its various modifications (hereinafter “the functions”) can be implemented, at least in part, via a computer program product, e.g., a computer program tangibly embodied in an information carrier, such as one or more non-transitory machine-readable media or storage device, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components. 
     A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a network. 
     Actions associated with implementing all or part of the functions can be performed by one or more programmable processors executing one or more computer programs to perform the functions of the calibration process. All or part of the functions can be implemented as, special purpose logic circuitry, e.g., an FPGA and/or an ASIC (application-specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Components of a computer include a processor for executing instructions and one or more memory devices for storing instructions and data. 
     While several inventive examples have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive examples described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive examples described herein. It is, therefore, to be understood that the foregoing examples are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive examples may be practiced otherwise than as specifically described and claimed. Inventive examples of the present disclosure are directed to each individual feature, system, article, material, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and/or methods, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.