Patent Grant
11854180
This application is a national stage application under 35 U.S.C. § 371 of International Patent Application Serial No. PCT/US2017/013400, filed on Jan. 13, 2017, which claims the benefit of priority of U.S. Provisional Application Serial No. 62/279,397 filed on Jan. 15, 2016, the contents of both are relied upon and incorporated herein by reference in their entireties.
The present disclosure relates to cellular ceramic articles, and in particular relates to a method of characterizing the isostatic strength of ceramic articles such as extruded cellular ceramic articles.
The entire disclosure of any publication or patent document mentioned herein is incorporated by reference, including Pre-Grant Published Patent Application No. US 2013/0212151, and the article by S. T. Gulati et al, “Isostatic strength of extruded cordierite ceramic substrates,” SAE 2004 World Congress and Exhibition, SAE Technical Paper 2004-01-1135, 2004, doi:10.4271/2004-01-1135; published Mar. 8, 2004.
Cellular ceramic articles are used as particulate filters and catalytic converters in internal combustion engines. The cells can be densely arranged to provide a relatively large surface area for catalytic material to react with the exhaust gases that pass through the cells. The walls can have a relatively thin cross-sectional dimension to provide a substantially large open frontal area, thereby reducing back pressure within the entire exhaust system. The cellular ceramic article requires sufficient mechanical and thermal integrity to withstand normal automotive impact and thermal requirements.
In particular, a ceramic article made for use as a vehicular filter or catalytic converter must have sufficient mechanical strength to survive being disposed in a metal housing during a process referred to as “canning.” One measure of mechanical strength of a ceramic article is its isostatic strength. The isostatic strength of a ceramic article can be measured by subjecting the ceramic article to increasing amounts of an isostatic force or pressure to the point of structural failure. However, such a measurement results in damage to or destruction of the ceramic article and so is not a preferred method for characterizing isostatic strength, especially in a manufacturing environment. Such direct measurements of isostatic strength are also very time consuming and can slow down production.
An aspect of the disclosure is a non-contact method for characterizing an isostatic strength SC of a ceramic article having a web defined by walls that in turn define an array of cells. The method comprises: a) capturing a digital image of the web; b) forming a two-dimensional (2D) representation of the ceramic article, comprising the web therein, based on the captured digital image; c) simulating a select amount of isostatic pressure PISO applied to the 2D representation to determine a maximum stress value σC-MAX within the 2D representation of the web; and d) using the maximum stress value σC-MAX to determine the isostatic strength SC of the ceramic article.
Another aspect of the disclosure is the method described above, wherein act b) comprises representing the web using rectangular beam elements.
Another aspect of the disclosure is the method described above, wherein act c) comprises performing a finite-element analysis.
Another aspect of the disclosure is the method described above, wherein act d) comprises: defining a stress concentration factor σF=σC-MAX/PISO; and determining the isostatic strength SC via the relationship 1/σF=α·SC−β, wherein α and β are constants determined by a best-fit to said relationship but using measured values of isostatic strength SM made on test ceramic articles.
Another aspect of the disclosure is the method described above, further comprising after act d): comparing the isostatic strength SC to a threshold value STH.
Another aspect of the disclosure is a non-contact method for characterizing an isostatic strength SC of a ceramic article having a web defined by walls that in turn define an array of cells. The method comprises a) capturing a digital image of the web; b) forming a 2D representation of the ceramic article, comprising the web therein, based on the captured digital image; c) performing a finite-element analysis on the 2D representation of the ceramic article using a select amount of simulated isostatic pressure PISO to determine a maximum stress value σC-MAX within the 2D representation of the web; and d) using the maximum stress value σC-MAX to determine the isostatic strength SC of the ceramic article.
Another aspect of the disclosure is the method described above, wherein forming the 2D representation of the ceramic article of act b) comprises representing the web using 2D rectangular beam elements.
Another aspect of the disclosure is the method described above, further comprising, between act a) and act b), processing the captured digital image to form a processed image using at least one of a filtering operation, a dynamic threshold operation, an island-removal operation, a smoothing operation, and a hole-filling operation, and then using the processed image to perform acts b) through d).
Another aspect of the disclosure is the method described above, wherein act d) comprises: defining a stress concentration factor σF=σC-MAX/PISO; and determining the isostatic strength SC via the relationship 1/σF=α·SC−β, wherein α and β are constants determined by a best-fit to said relationship but using measured values of isostatic strength SM made on test ceramic articles.
Another aspect of the disclosure is the method described above, wherein act a) comprises either directly capturing a two-dimensional digital image with a two-dimensional image sensor or capturing a series of one-dimensional images with a linear image sensor.
Another aspect of the disclosure is the method described above, further comprising after act d): comparing the isostatic strength SC to a threshold value STH.
Another aspect of the disclosure is the method described above, comprising basing the threshold value STH on an anticipated use of the ceramic article.
Another aspect of the disclosure is a non-contact method of characterizing an isostatic strength SC of a ceramic article having a web that comprises walls that define an array of cells. The method comprises: a) capturing a digital image of the ceramic article and the web therein; b) processing the digital image to form a processed image; c) generating from the processed image a 2D representation of the ceramic article using rectangular beam elements to represent the web; d) determining a maximum stress value σC-MAX within the web by simulating the application of a select amount of isostatic pressure PISO to the 2D representation of the ceramic article; and e) using the maximum stress value σC-MAX to determine the isostatic strength SC of the ceramic article.
Another aspect of the disclosure is the method described above, wherein processing the digital image comprises performing at least one of a filtering operation, a dynamic threshold operation, an island-removal operation, a smoothing operation, and a hole-filling operation.
Another aspect of the disclosure is the method described above, wherein act d) comprises performing a finite-element analysis.
Another aspect of the disclosure is the method described above, wherein act d) comprises: defining a stress concentration factor σF=σC-MAX/PISO; and determining the isostatic strength SC via the relationship 1/σF=α·SC−β, wherein α and β are constants determined by a best-fit to said relationship but using measured values of isostatic strength SM made on test ceramic articles.
Another aspect of the disclosure is the method described above, wherein act a) comprises either directly capturing a two-dimensional digital image with a two-dimensional image sensor or capturing a series of one-dimensional images with a linear image sensor.
Another aspect of the disclosure is the method described above, further comprising after act e): comparing the isostatic strength SC to a threshold value STH.
Another aspect of the disclosure is the method described above, comprising basing the threshold value STH on an anticipated use of the ceramic article.
Another aspect of the disclosure is the method described above, wherein the anticipated use is canning of the ceramic article.
Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:
Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.
The claims as set forth below are incorporated into and constitute part of this Detailed Description.
Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation.
Given that the walls 30 of web 18 serve in large measure to define the isostatic strength of ceramic article 10, it is expected that wall/cell defects can reduce the isostatic strength. Yet, to date there has not been very good correlation between the type and location of wall/cell defects and isostatic strength. This has made it very difficult to use the characterization and location of wall/cell defects to obtain a reasonable estimate of the isostatic strength.
Characterization Method
An example method for characterizing isostatic strength disclosed herein comprises four main steps or acts: 1) image capture, 2) defining a 2D representation of the ceramic article, 3) calculating the maximum stress in the web, and 4) calculating the isostatic strength.
A fifth step of comparing the calculated isostatic strength to a threshold value can also be included in the method.
Each of the above main steps can comprise one or more sub-steps, operations, acts, etc. as described below.
Step 1—Image Capture
The first step of the method involves capturing an image of the ceramic article 10 and the web 18 therein.
In an example illustrated in
In an example, computer 140 is used to stitch together line-scan images of web 18 to form the larger 2D raw captured image 150R. In an example, the raw captured image 150R comprises the entire front end 12 of ceramic article 10 so that it includes the entire web 18.
The captured raw image 150R has associated therewith a first resolution defined by the relationship between the pixel size and the size of the captured image. In an example, digital camera 120 is configured such that each pixel 124 of image sensor 122 represents a 5 micron×5 micron region of web 18. Different optical resolutions can be used to change this pixel-to-region relationship. The optical resolution can be selected depending on the characteristics of the ceramic articles 10 being measured, e.g., different cell densities. A range of diameters of ceramic articles 10 can be from 4 inches to 14 inches. The cross-sectional shapes can also vary, e.g., round or oval. The captured raw image 150R at 5 microns per pixel level can thus range in size from 20,000×20,000 pixels for a 4 inch part to 70,000×70,000 pixels for a 14 inch part. An example of a portion of a captured raw image is shown in
Once the captured raw image 150R of the front end 12 of ceramic article 10 is obtained, it can be processed using on ore more processing steps to form a processed image 150P, an example of which is shown in
In an example, the image processing step comprises applying a mean filter to the captured image with an appropriate kernel size. The kernel size is chosen so the mean filter result represents the variation in illumination across the part. In an example, the kernel size is large enough so that the filtered image does not show the individual cells but is small enough so the filtered image shows variations in overall lighting in the image. In an example, the kernel size covers between 8 to 16 cells, or even 10 to 12 cells.
Next, a dynamic threshold operation is performed on the original (raw) captured image 150R. This operation finds all pixel values that are brighter than the corresponding pixel value in the mean filtered image by a certain amount. In an example, a threshold value of N grey levels is used. This selects all pixel values that are at least N grey levels brighter than the value of the corresponding pixel in the mean filtered image as possibly belonging to the ceramic article. Pixels having values that are darker than this intensity threshold value are considered to be background pixels that do not represent web 18 or skin 40.
Next, any isolated regions or “islands” of connected bright pixels that are smaller than some fixed size are removed. This “island removal” process is carried out to reduce noise since the small unconnected bright regions in the processed image 150P can be considered as not actually part of ceramic article 10. This can be done for islands having some minimum threshold size, e.g., less than 100 pixels.
Next, a morphological smoothing operation is performed by first closing any small dark regions in the ceramic article that are less than a certain size, and then performing a morphological opening to return the outline of ceramic article image to the original size. In an example, a morphological smoothing radius of approximately 3 pixels is convenient.
Next, any small holes represented by small dark areas in the image that do not meet the dynamic threshold limit are filled. For example, holes smaller than 400 pixels in size are filled. In an example where cells 20 are approximately 160×160 pixels (25,600 pixels in area), holes that are 1.5% the size of a normal cell can be filled. This operation is referred to herein as “hole filling.”
All of the bright pixels that remain in the processed image 150P are considered to be part of the ceramic article 10.
Thus, in an example, the image processing step comprises at least one of a filtering operation, a dynamic threshold operation, an island-removal operation, a smoothing operation, and a hole-filling operation.
The raw captured image 150R and the processed image 150P each defines a two-dimensional representation of the web 18. The filtering, threshold, filling and smoothing operations result in the reduced second resolution for the processed image 150P as compared to the initial captured image 150R. The reduced resolution simplifies the subsequent methods steps or acts and maintaining sufficient information to obtain an accurate characterization of the isostatic strength of the ceramic article 10 being characterized. For example, the captured raw image 150R typically includes noise that can adversely affect the isostatic strength characterization. The processed image 150P is processed in a manner that reduces noise as compared to the captured raw image 150R and therefore can be effectively employed to achieve a more accurate characterization of the isostatic strength.
Step 2—Defining a 2D Representation of the Ceramic Article
Once the image capture step is completed, the resulting image (either the captured image 150R or the processed image 150P) is used to define a two-dimensional (2D) representation (“2D representation”) 10R of the ceramic article 10) suitable for use in carrying out numerical simulations or modeling (see
In an example, the 2D representation 10R is generated by representing the walls 30 of web 18 and the outer wall or skin 40 in the processed image 150P as a series of 2D beam elements BE. In an example, the 2D beam elements BE are rectangular. With reference to
With reference now to
The next step involves generating series of the beam elements BE that approximate the size, shape and location of each wall 30 in web 18. In an example, beam elements BE have a rectangular shape and are generated by following the path of the skeleton 200 along a given wall 30 (see
In an example, direction changes in skeleton 200 or thickness changes in wall 30R that are greater than some number of pixels (e.g., 1 to 3 pixels) are tracked and used to define new beam elements BE. The smaller the change threshold used to define new beam elements BE, the more accurately the actual geometry of ceramic article 10 is captured by the 2D representation 10R. Using a larger change threshold reduces accuracy, but also reduces the number of generated beam elements BE, thus decreasing the computation time needed to calculate the stresses as described below.
The beam elements BE are defined for the various walls 30R to make up web 18R. In an example, standard computer techniques can be used to define the beam elements BE and link them together to form web 18R. This can be done using computer 140 and standard computer techniques, such as by using ANSYS files, which support reading the rectangular beam data from ASCII coded files. The ANSYS files describe individual rectangular beam elements of the ceramic article 10 and how these beam elements are linked together to form web 18R as well as skin 40R (see
In an example, computer 140 comprises instructions embodiment in a non-transient computer-readable medium that walks the list of generated beam elements BE to define web 18R of the 2D representation 10R of ceramic article 10.
Step 3—Calculating the Maximum Stress in the Web
Standard numerical techniques are then used to model (simulate) the 2D mechanical response of the 2D representation 10R of the ceramic article to a select (simulated) isostatic pressure PISO.
This modeling or simulation of the 2D mechanical response can be accomplished using for example finite-element analysis, with the mechanical response being measured in terms of stress at various locations (e.g., beam elements BE) in web 18R. In an example, the output of the finite-element analysis comprises linearized calculated stress values σC for each rectangular beam element RB. The results can be stored in computer 140, e.g., as an ASCII file. The maximum value of the calculated stress is denoted σC-MAX and is easily determined from the list of calculated stress values σC.
In an example, the maximum calculated stress value σC-MAX is used to define a stress concentration factor σF. The stress concentration factor σF is defined by the ratio of the maximum calculated stress value σC-MAX to the applied isostatic pressure PISO, e.g., σF=σC-MAX/PISO. The stress concentration factor σF is unitless since the calculated stress values and the isostatic pressure PISO have the same units, e.g., PSI or bars. In an example, the stress concentration factor σF falls mostly within the range between about 5 and about 80, with lower and higher extremes possible.
Step 4—Calculating the Isostatic Strength
The next step involves calculating the isostatic strength SC. This is accomplished in one example by using an equation (relationship) that relates the stress concentration factor σF to the calculated isostatic strength SC.
An example equation can be expressed as:
1/σF=α·SC−β EQ. 1
Here, α and β are constants determined by a best-fit to EQ. 1 using actual measurements of isostatic strength SM on test ceramic articles in place of SC. The test ceramic articles are also modeled using the method described above to obtain corresponding values of σF so that enough data with different values for the measured isostatic strength SM can be obtained to perform a reasonable curve fit. The test ceramic articles need to be substantially the same (and preferably formed in an identical manner as possible) as the ceramic articles whose isostatic strength is to be characterized using the non-contact methods disclosed herein in order to achieve the best results.
In one example, measurements of isostatic strength SM were performed on test ceramic articles formed from cordierite having square cells with a density of 200 cells per inch and a web wall thickness TH of 0.008 inch. The test ceramic articles had a variety of web and cell defects, comprising sheared cells, distorted cells and missing cell walls and thus had a range of measured isostatic strengths SM. The measurements of isostatic strength SM were carried out using a conventional apparatus. The modeling to obtain the stress concentration factor σF was carried out per the above steps for each of the test ceramic articles. The beam elements BE used were rectangular.
A best-fit calculation to the data in
1/σF=α·SM−β EQ. 2
The best-fit calculation was carried out using standard spreadsheet software and yielded values for the curve-fitting constants α and β of α=0.0041 and β=0.0054, with an R2 value of 0.9, indicating good correlation between the stress concentration factor σF and the measured isostatic strength SM. These values of α and β can be used in EQ. 1 for non-contact characterizing the isostatic strength for like ceramic articles as described above.
The curve-fitting approach to establish a relationship between the stress concentration factor σF and the isostatic strength can be carried out for any type of ceramic articles 10, particularly extruded ceramic articles, irrespective of the composition, cell design (hexagonal, triangular, square, octasquare, asymmetric, etc.) and web/cell geometry (e.g., cell sizes and densities, wall thicknesses, etc.).
In characterizing the isostatic strength, only the maximum value of the stress σC-MAX is required. Thus, an embodiment of the method comprises using only the maximum stress value σC-MAX to characterize the isostatic strength SC of the ceramic article.
Step 6—Comparing the calculated isostatic strength to a threshold value.
Once the calculated isostatic strength SC is obtained, it can be compared to a threshold value STH. The threshold value STH can be defined by a use for the ceramic article 10, and the demands such use will place on the particular ceramic article. For example, the threshold value STH can be defined by or required by a canning process and whether the ceramic article can survive the process. Not all canning processes have the same isostatic strength requirements, so that the threshold value STH can vary between different canning processes. For example, some canning processes might have an isostatic strength threshold value STH=10 bars, while others can have an isostatic strength threshold value STH=30 bars or 50 bars or greater. A benefit of having a non-contact characterization of the isostatic strength is that ceramic articles can be grouped by their characterized isostatic strength and then used for applications where the threshold value requirement can be met without damaging or destroying the ceramic articles.
The non-contact method of characterizing the isostatic strength of ceramic articles as disclosed herein has the advantage that it is based on a single parameter namely, the maximum value of the calculated stress σC-MAX (or the stress concentration factor, which is based only on the maximum stress value σC-MAX). The method does not require an examination or characterization of the many different types of possible cell or web defects, such as sheared cells, distorted cells, missing webs, thinned webs, etc., and does not require determining the location(s) of such defects.
Without wishing being bound by theory, it is conjectured that a single location of sufficiently high stress within the web 18 of a ceramic article 10 can compromise the structural integrity of the entire ceramic article and lead to a substantial reduction in the isostatic strength, e.g., to be below a desired threshold value STH. For example, when an isostatic force or pressure is applied to the outer surface 16 of ceramic article 10 that comprises a cell or web defect, the force is communicated through web 18 and to a highest-stress location, which may not identically correspond to a web or cell defect. The force can cause failure of one or more walls 30 within the web 18 at or near the high stress location. This wall failure causes the applied force to be immediately redistributed to the surrounding walls 30 of the nearest web 18. The added force can then lead to failure of one or more of the surrounding walls, thereby causing the applied force to be redistributed once again to the adjacent surrounding walls 30. This failure process can end up cascading through substantial portions of web 18, leading to the structural failure of the ceramic article.
In an example, the non-contact method disclosed herein is used in the production of ceramic articles and can be performed at any step along the manufacturing process where an image of the web can be obtained. In one example, the non-contact method is performed on newly extruded wet logs, while in another example the non-contact method is performed on dried logs, while in yet another example the non-contact method is performed on dried and fired logs. In an example, the non-contact method is performed in less than 1 minute, thereby providing a relatively quick characterization of the isostatic strength as compared to direct contact-based methods. Thus, in this regard, the term “ceramic article” as used herein is intended to also include “ceramic-forming article” such as greenware or unfinished ware, such as newly extruded wet logs, or dried logs or green logs, or fired logs, or newly extruded wet cellular structured bodies, or dried cellular structured bodies, and the like.
It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.
| Filing Document | Filing Date | Country | Kind |
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| Publishing Document | Publishing Date | Country | Kind |
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| WO2017/123919 | 7/20/2017 | WO | A |
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