CN114441337B - Detection method for opening displacement of metal fracture toughness crack tip - Google Patents
Detection method for opening displacement of metal fracture toughness crack tip Download PDFInfo
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- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
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Abstract
The invention provides a method for detecting the opening displacement of a metal fracture toughness crack tip, which comprises the following steps: carrying out cutting pretreatment on the metal to be evaluated to obtain the metal to be evaluated; performing a three-point bending test on the metal to be tested until the metal to be tested is at the maximum load value to obtain a metal to be tested; performing primary curing liquid perfusion treatment on the crack of the primary metal to be detected to obtain a primary curing mold; and determining the primary surface crack tip opening displacement and the primary internal crack tip opening displacement according to the primary curing mould. The method can accurately test the primary surface crack tip opening displacement and the primary internal crack tip opening displacement of the metal to be evaluated, further can accurately evaluate the fracture toughness of the pipeline prepared by using the metal to be evaluated, and has important guiding significance for engineering application.
Description
Technical Field
The invention relates to the technical field of metal material fracture mechanical property testing, in particular to a method for detecting opening displacement of a metal fracture toughness crack tip.
Background
With the development of pipeline construction, the mileage of the pipeline is increased, and more accidents occur when the pipeline fails. Through statistics of a large number of pipeline failure accidents, the results show that pipeline girth weld failure is one of the main reasons. The fracture toughness is an important index for describing the failure of the circumferential weld of the pipeline, and the fracture toughness of the pipeline is usually expressed by an energy release rate g, a stress intensity factor K, crack Tip Opening Displacement (CTOD) and the like at present. In particular CTOD is an important parameter for evaluating the fracture toughness of pipes.
In the prior art, crack Mouth Opening Displacement (CMOD) is often converted into CTOD through an empirical formula, but a plurality of empirical formulas for calculating CTOD through CMOD exist at present, CTOD values obtained by the same CMOD through different empirical formulas are different, and different results may be caused by selecting different empirical formulas, so that engineering judgment is influenced.
Digital Image Correlation (DIC) methods have been developed in order to more accurately obtain the CTOD value of a metallic material and thus more accurately evaluate the fracture toughness of pipes made using the metallic material. DIC is a non-contact method for measuring relevant physical quantities such as object deformation, and the basic principle is to utilize the change of speckle patterns on the surface of a sample before and after deformation so as to obtain information of physical quantities such as displacement and strain of a region of interest. And (3) spraying matte paint on the surface of the sample, and shooting the loading process of the sample by using a high-speed camera, so that the CTOD value of the surface of the sample at each node can be more accurately determined. However, DIC has been able to obtain only the CTOD of the sample surface, but studies have already revealed that the CTOD of the sample surface is different from the CTOD of the other portions of the crack to some extent, and the change rule of the CTOD value of the sample in the thickness direction is unknown.
Disclosure of Invention
The method for detecting the opening displacement of the metal fracture toughness crack tip can accurately obtain the opening displacement of the crack tip at each position in the thickness direction of the metal to be evaluated, and objectively and truly evaluate the fracture toughness of the pipeline to be evaluated, which is made of the metal.
The invention provides a method for detecting the opening displacement of a metal fracture toughness crack tip, which comprises the following steps:
performing cutting pretreatment on the metal to be evaluated to obtain the metal to be evaluated;
performing a three-point bending test on the metal to be tested until the metal to be tested is at the maximum load value to obtain a metal to be tested;
performing primary curing liquid filling treatment on the crack of the primary metal to be detected to obtain a primary curing mold;
and determining the primary surface crack tip opening displacement and the primary internal crack tip opening displacement according to the primary curing mould.
The inspection method as described above, wherein the determining one surface crack tip opening displacement and one internal crack tip opening displacement from the one curing mold includes:
determining the opening displacement of the primary surface crack tip according to the surface crack tip of the primary curing mold;
performing cutting treatment on the primary curing mold for N times in the length direction to obtain (N + 1) primary internal curing molds;
and respectively determining the opening displacement of the primary internal crack tip according to the surface crack tip of each primary internal curing mold, wherein N is more than or equal to 1.
The detection method as described above, further comprising:
and establishing a crack tip opening displacement curve of the metal to be evaluated according to the primary surface crack tip opening displacement and the primary internal crack tip opening displacement.
The detection method as described above, wherein after the primary curing liquid pouring treatment, the method further includes:
performing a secondary three-point bending test on the primary metal to be tested to obtain a secondary metal to be tested;
performing secondary curing liquid filling treatment on the crack of the secondary metal to be detected to obtain a secondary curing mold;
and determining the secondary surface crack tip opening displacement and the secondary internal crack tip opening displacement according to the secondary curing mould.
The detection method as described above, wherein the load displacement curve is obtained from the primary three-point bending test and the secondary three-point bending test.
The detection method as described above, further comprising:
and evaluating the fracture toughness of the pipeline to be evaluated according to the primary surface crack tip opening displacement, the primary internal crack tip opening displacement and the crack tip opening displacement of the pipeline to be evaluated.
The method for detecting a fracture toughness of a pipe to be evaluated according to the primary surface crack tip opening displacement, the primary internal crack tip opening displacement and the crack tip opening displacement of the pipe to be evaluated comprises the following steps:
if the primary surface crack tip opening displacement and the primary internal crack tip opening displacement are both larger than or equal to the surface crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is of a first level;
and if at least one of the primary surface crack tip opening displacement and the primary internal crack tip opening displacement is smaller than the surface crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is in a second grade.
The detection method as described above, wherein the primary curing liquid and/or the secondary curing liquid includes silicone rubber.
The detection method is characterized in that the loading rate of the three-point bending test is V, and V is more than 0 and less than or equal to 1mm/min.
The detection method as described above, wherein the cutting pretreatment includes cutting in the width direction of the metal to be evaluated, and the cutting length is that the ratio of the width of the metal to be evaluated is greater than or equal to 1:2.
the invention provides a method for detecting the opening displacement of a metal fracture toughness crack tip, which comprises the steps of carrying out primary curing liquid pouring treatment on a crack of a metal to be detected to obtain a primary curing mold. The method can accurately test the primary surface crack tip displacement and the primary internal crack tip opening displacement of the metal to be evaluated, further can accurately evaluate the fracture toughness of the pipeline to be evaluated prepared by using the metal, and has important guiding significance for engineering application.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the related art, the drawings used in the description of the embodiments of the present invention or the related art are briefly described below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a flow chart of a process for detecting the opening displacement of a metal fracture toughness crack tip in accordance with certain embodiments of the present invention;
FIG. 2 is a schematic illustration of a three-point bend test in some embodiments of the invention;
FIG. 3 is a graph showing the primary crack tip opening displacement of the metal to be evaluated in example 1 of the present invention;
fig. 4 is a graph comparing the crack tip opening displacement curve obtained in example 1 of the present invention with the crack tip opening displacement curve obtained in the comparative example.
Description of reference numerals:
1: a first upper clamp;
2: a second upper clamp;
3: a lower clamp;
4: and (5) metal to be detected.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
FIG. 1 is a flow chart of the detection of the opening displacement of a metal fracture toughness crack tip in some embodiments of the present invention. As shown in FIG. 1, the invention provides a method for detecting the opening displacement of a metal fracture toughness crack tip, which comprises the following steps:
s101: performing cutting pretreatment on the metal to be evaluated to obtain the metal to be evaluated;
s102: performing a three-point bending test on the metal to be tested until the metal to be tested is at the maximum load value to obtain a metal to be tested;
s103: carrying out primary curing liquid perfusion treatment on the crack of the primary metal to be detected to obtain a primary curing mold;
s104: and determining the primary surface crack tip opening displacement and the primary internal crack tip opening displacement according to the primary curing mould.
In the present invention, the metal to be evaluated is not particularly limited, and may be any metal commonly used in the art. The shape of the metal to be evaluated in the present invention is not particularly limited, and any shape that can be used for the subsequent three-point bending test after the cutting pretreatment is included in the scope of the present invention. For example, the shape of the metal to be evaluated may be a shape commonly used in the art for performing a three-point bending test, and the shape of the metal to be evaluated may also be a shape of a CT specimen commonly used in the art. The cutting pretreatment comprises the following steps: and (3) enabling the extending direction of the cutting piece to be parallel to the width direction of the metal to be evaluated, taking the surface of the metal to be evaluated as a cutting starting point, and longitudinally cutting along the thickness direction of the metal to be evaluated until a cutting end point. The purpose of the cutting pretreatment of the metal to be evaluated is to obtain the metal to be tested which can be used for carrying out a three-point bending test.
In order to ensure the accuracy of the three-point bending test, generally, the cutting pretreatment includes cutting in the thickness direction of the metal to be evaluated, and the ratio of the cutting length to the width of the metal to be evaluated is 1 or more: 2.
the present invention is not limited to a specific test mode of the three-point bending test.
FIG. 2 is a schematic illustration of a three point bend test in some embodiments of the invention. Taking fig. 2 as an example, S102 includes: placing the metal 4 to be tested obtained in the step S101 between an upper fixture (including a first upper fixture 1 and a second upper fixture 2) and a lower fixture 3 of a three-point bending tester according to a mode shown in fig. 2, setting the thickness of the metal 4 to be tested to be T, the length of the metal 4 to be tested to be L, the width of the metal 4 to be tested to be W, setting the span (the distance between the first upper fixture 1 and the second upper fixture 2) of the three-point bending tester to be 4W, setting the loading rate to be less than or equal to 1mm/min, performing a three-point bending test on the metal 4 to be tested, and stopping the three-point bending test until the maximum load value of the metal 4 to be tested is obtained, so as to obtain the metal 4 to be tested. It can be understood that, when the metal 4 to be measured is at the maximum load value, the metal 4 to be measured has a primary crack, and the metal 4 to be measured having the primary crack is the primary metal to be measured.
In the present invention, the direction in which the thickness of the metal to be measured is located is referred to as the thickness direction, the direction in which the width of the metal to be measured is located is referred to as the width direction, and the direction in which the length of the metal to be measured is located is referred to as the length direction.
S103 includes: and pouring the primary curing liquid into the primary crack, allowing the primary curing liquid to stay in the primary crack for a certain time for curing, and obtaining a primary curing mold after the primary curing liquid is completely cured, wherein the primary curing mold is a simulation of the primary crack.
In some embodiments, in order to avoid pouring the primary curing liquid to other positions of the primary metal to be detected, the card can be used for covering the edge of the primary crack, the primary curing liquid is poured into the primary crack, then the primary curing liquid stays for 2-10min, and the card is removed to obtain the primary curing mold.
The primary curing liquid is not particularly limited, and any material which can be rapidly cured and can form a primary curing mold for cutting falls within the protection scope of the present invention.
S104 comprises the following steps: and determining the primary surface crack tip opening displacement and the primary internal crack tip opening displacement according to the primary curing mould.
In the invention, because the internal influence of the cutting pretreatment on the metal to be measured is different from the internal influence of the one-time three-point bending test on the metal to be measured, the inner surface of the metal corresponding to the crack formed by the cutting pretreatment and the inner surface of the metal corresponding to the crack formed by the one-time three-point bending test have different roughness. Specifically, the difference in roughness is defined by the cutting end point, and the roughness of the metal inner surface corresponding to the crack formed by the cutting pretreatment is low, the surface is visually smooth, and the roughness of the metal inner surface corresponding to the crack formed by one three-point bending test is high.
The invention refers to the contact surface of the primary curing mold and the primary metal to be measured as the side surface of the primary curing mold. Since the primary curing mold is a simulation of the primary crack, the side surfaces of the primary curing mold have different roughness, correspondingly. That is, the side surface of the primary curing mold has a boundary line at the same level as the cutting end point.
According to the boundary line existing on the side surface of the primary solidification mold, the primary surface crack tip opening displacement and the primary internal crack tip opening displacement of the metal to be evaluated can be determined.
The method for detecting the opening displacement of the metal fracture toughness crack tip provided by the invention is characterized in that a primary curing liquid is utilized to simulate a crack of a metal to be detected for one time to obtain a primary curing mold, and the primary surface crack tip opening displacement and the primary internal crack tip opening displacement of the metal to be evaluated are obtained by measuring the relative size of the primary curing mold. The method can accurately test the primary surface crack tip displacement and the primary internal crack tip opening displacement of the metal to be evaluated, further can accurately evaluate the fracture toughness of the pipeline to be evaluated, and has important guiding significance for engineering application.
In some embodiments of the present invention, determining one surface crack tip opening displacement and one internal crack tip opening displacement from a primary curing mold comprises:
determining the opening displacement of the primary surface crack tip according to the surface crack tip of the primary curing mold;
carrying out N times of slitting treatment on the primary curing mold in the length direction to obtain (N + 1) primary internal curing molds;
and respectively determining the opening displacement of the primary internal crack tip according to the surface crack tip of each primary internal curing mold, wherein N is more than or equal to 1.
In the present invention, the extended surface formed by the boundary line divides the primary solidification mold into a tip portion away from the cutting start point and a non-tip portion close to the cutting start point. And the surface of the tip part is the surface crack tip of the primary curing mold, wherein the surface of the tip part is the surface of the primary curing mold. In the present invention, the surface of the primary curing mold refers to two opposite surfaces adjacent to the side surface.
The size of the surface coincidence part of the extension plane and the tip part of the primary solidification mold is the primary surface crack tip opening displacement.
In the invention, the extending direction of the cutting piece is parallel to the length direction, and the cutting piece is used for carrying out cutting treatment on the primary curing mold for N times to obtain (N + 1) primary internal curing molds. Wherein (N + 1) primary internal curing molds are distributed at intervals in the width direction.
In the present invention, the boundary line forms an extended surface that divides the primary internal solidification mold into a tip portion that is distant from the cutting start point and a non-tip portion that is close to the cutting start point. The surface of the tip part is the surface crack tip of the primary internal curing mold, wherein the surface of the tip part is the surface of the primary internal curing mold. In the present invention, the surface of the primary internal curing mold refers to two opposite surfaces adjacent to the side surface.
The size of the portion where the extension plane coincides with the surface of the tip portion of the primary internal solidification mold is a primary internal crack tip opening displacement.
In some embodiments, the primary curing mold may be symmetrically cut with the center of the primary curing mold as a central axis.
The present invention is not particularly limited to the method for measuring the primary surface crack tip and the primary internal crack tip, and all methods capable of measuring the size of the primary surface crack tip of the primary curing mold and the size of the primary internal crack tip of each primary internal curing mold are within the scope of the present invention. In some embodiments, the measurement may be performed using a scanning electron microscope.
In some embodiments of the invention, further comprising:
and establishing a crack tip opening displacement curve of the metal to be evaluated according to the primary surface crack tip opening displacement and the primary internal crack tip opening displacement.
In the invention, a crack tip opening displacement curve of the metal to be evaluated can be established according to the distance from the surface of each internal primary curing mold to the surface of the primary curing mold, the primary surface crack tip opening displacement and the primary internal crack tip opening displacement. The crack tip opening displacement curve of the metal to be evaluated is a curve formed by the opening displacement of the crack tips at each position in the width direction of the metal to be evaluated. In one embodiment, a crack tip opening displacement curve of the metal to be evaluated may be established with the distance of the surface of each inner primary curing mold from the surface of the primary curing mold as an abscissa and the crack tip opening displacement as an ordinate.
According to the method, the crack tip opening displacement of the metal to be evaluated at any position in the width direction can be estimated according to the crack tip opening displacement curve, so that the fracture toughness of the pipeline to be evaluated can be better estimated.
In some embodiments of the present invention, after the primary curing liquid pouring treatment, the method further comprises:
performing a secondary three-point bending test on the primary metal to be tested to obtain a secondary metal to be tested;
performing secondary curing liquid filling treatment on the crack of the secondary metal to be detected to obtain a secondary curing mold;
and determining the secondary surface crack tip opening displacement and the secondary internal crack tip opening displacement according to the secondary curing mould.
In the present invention, the three-point bending tests performed after the metal to be measured is under the maximum load are all referred to as secondary three-point bending tests, and the number of times of the secondary three-point bending tests is not particularly limited.
Specifically, after S103, a secondary three-point bending test may be performed on the metal to be measured, the primary crack may continue to expand, so as to form a secondary metal to be measured including a secondary crack, the primary curing mold may be taken out, a secondary curing liquid may be poured into the secondary crack, the secondary curing mold may be left for a certain time, a secondary curing mold may be obtained after the secondary curing liquid is completely cured, and the secondary surface crack tip opening displacement and the secondary internal crack tip opening displacement may be obtained according to the secondary curing mold.
According to the invention, a plurality of times of secondary three-point bending tests can be carried out on a metal to be detected, and secondary surface crack tip opening displacement and secondary internal crack tip opening displacement are respectively obtained. The method comprises the steps of establishing a surface crack tip opening displacement change curve of the metal to be evaluated according to surface crack tip opening displacement (secondary surface crack tip opening displacement and primary surface crack tip opening displacement) and crack mouth opening displacement of the metal to be evaluated, establishing an internal crack tip opening displacement change curve of the metal to be evaluated according to internal crack tip opening displacement (secondary internal crack tip opening displacement and primary internal crack tip opening displacement) and crack mouth opening displacement of the metal to be evaluated at the same width, and can better evaluate the fracture toughness of the pipeline to be evaluated, so that the method has guiding significance for practical application of the pipeline to be evaluated.
In some embodiments, the surface crack tip opening displacement profile of the metal to be evaluated may be established with the crack tip opening displacement of the metal to be evaluated as the abscissa and with the surface crack tip opening displacement (the secondary surface crack tip opening displacement and the primary surface crack tip opening displacement) as the ordinate.
The secondary curing liquid is not particularly limited, and curing liquids commonly used in the field can be selected. The secondary curing liquid and the primary curing liquid may be the same or different. In some embodiments, the primary curing liquid and the secondary curing liquid may be the same curing liquid in order to facilitate comparison between the secondary surface crack tip opening displacement and the primary surface crack tip opening displacement, and between the secondary internal crack tip opening displacement and the primary internal crack tip opening displacement, and to improve objectivity of comparison results.
In some embodiments of the invention, the load displacement curve is obtained from a first three-point bending test and a second three-point bending test.
In the invention, a primary three-point bending test and a secondary three-point bending test are carried out on the metal to be tested, so that a load displacement curve can be obtained, wherein the load displacement curve refers to a curve of Crack Mouth Opening Displacement (CMOD) and load, the inflection point of the load displacement curve is the maximum load value of the metal to be evaluated, and the load after the inflection point of the load displacement curve is the load corresponding to the secondary three-point bending test.
In some embodiments of the invention, further comprising:
and evaluating the fracture toughness of the pipeline to be evaluated according to the primary surface crack tip opening displacement, the primary internal crack tip opening displacement and the crack tip opening displacement of the pipeline to be evaluated.
In the invention, the primary surface crack tip opening displacement and the primary internal crack tip opening displacement of the metal to be evaluated are inherent properties of the metal to be evaluated. The pipe to be evaluated is a pipe made of the metal, and the crack tip opening displacement of the pipe to be evaluated can be obtained by a test method of a pipe crack driving force commonly used in the field. And evaluating the fracture toughness of the pipeline to be evaluated according to the size relationship between the primary surface crack tip opening displacement and the primary internal crack tip opening displacement and the crack tip opening displacement of the pipeline to be evaluated.
Specifically, if the primary surface crack tip opening displacement and the primary internal crack tip opening displacement are both greater than or equal to the crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is of a first grade;
and if at least one of the primary surface crack tip opening displacement and the primary internal crack tip opening displacement is smaller than the crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is in a second stage.
In the invention, the first grade refers to that the fracture toughness of the pipeline to be evaluated is qualified and can be safely applied to industrial production, and the second grade refers to that the fracture toughness of the pipeline to be evaluated is unqualified and has potential safety hazard when applied to industrial production.
According to the method, the fracture toughness of the pipeline to be evaluated is judged according to the size relation between the primary surface crack tip opening displacement and the primary internal crack tip opening displacement and the crack tip opening displacement of the pipeline to be evaluated, and the primary internal crack tip opening displacement is introduced, so that the fracture toughness of the pipeline to be evaluated can be judged more objectively, and the safety of the pipeline to be evaluated is improved.
In some embodiments of the present invention, the primary curing liquid and/or the secondary curing liquid comprises silicone rubber.
In the invention, as the silicon rubber has the advantages of good elasticity and difficult damage, when the primary curing liquid and/or the secondary curing liquid comprises the silicon rubber, the curing time of the primary curing liquid and/or the secondary curing liquid can be saved, and the detection efficiency can be improved; and the primary curing mold and/or the secondary curing mold formed after curing is easy to cut, basically does not deform after cutting, and is beneficial to improving the detection accuracy.
In some embodiments of the invention, in order to ensure that the crack is in a quasi-static expansion state in the three-point bending test, the loading rate of the three-point bending test is V, and V is more than 0 and less than or equal to 1mm/min.
The present invention will be further described with reference to specific examples.
Example 1
The detection method of the embodiment comprises the following steps:
1) Cutting the metal to be evaluated in the width direction of the metal to be evaluated to obtain the metal to be evaluated;
2) Placing the metal to be tested on a three-point bending tester in a mode of referring to FIG. 2, setting the span to be 72mm and the loading rate to be 1mm/min, carrying out a three-point bending test on the metal to be tested, and obtaining a metal to be tested when the metal to be tested is at the maximum load value;
3) Carrying out primary curing liquid perfusion treatment on the crack of the primary metal to be detected to obtain a primary curing mold;
4) Determining the opening displacement of the primary surface crack tip according to the surface crack tip of the primary curing mold;
5) Cutting the primary curing mold for 3 times in the length direction to obtain 4 primary internal curing molds, and respectively determining the primary internal crack tip opening displacement according to the surface crack tip of each primary internal curing mold;
6) Establishing a crack tip opening displacement curve of the metal to be evaluated according to the primary surface crack tip opening displacement and the primary internal crack tip opening displacement;
7) Performing a secondary three-point bending test on the primary metal to be tested to obtain a secondary metal to be tested;
performing secondary curing liquid filling treatment on the crack of the secondary metal to be detected to obtain a secondary curing mold;
referring to step 5), determining the secondary surface crack tip opening displacement and the secondary internal crack tip opening displacement according to the secondary curing mold;
wherein, the material of the metal that awaits the aassessment is X80 material, and the length of the metal that awaits the evaluation is 82.8mm, and the width is 18mm, and thickness is 9mm, and the ratio of cutting length and the thickness of the metal that awaits the aassessment is 1:2; the primary curing liquid and the secondary curing liquid are silicon rubber, and the times of the secondary three-point bending test are 3 times.
Comparative example
DIC was used to test the cracks of the metal to be tested in example 1 at different CMODs to obtain the crack tip opening displacements at different CMODs.
1. FIG. 3 is a graph showing the primary crack tip opening displacement of the metal to be evaluated in example 1 of the present invention. In fig. 3, the abscissa 0 represents the position of the most central portion of the metal to be measured, and ± 1.0 represents the positions of the two surfaces of the metal to be measured. As can be seen from fig. 3, the primary crack tip opening displacement curve of the metal to be evaluated in example 1 of the present invention is a parabola, the opening displacements of the two primary surface crack tips are the same, and the opening displacement of the primary internal crack tip is the largest.
2. The primary surface crack tip opening displacement and the secondary surface crack tip opening displacement, the primary internal crack tip opening displacement and the secondary internal crack tip opening displacement measured in example 1, and the crack tip opening displacement at different CMODs measured in the control example were compared. Fig. 4 is a graph comparing the crack tip opening displacement curve obtained in example 1 of the present invention with the crack tip opening displacement curve obtained in the comparative example. As shown in fig. 4, DIC represents the crack tip opening displacement measured in the comparative example, the center of the silicone rubber represents the primary internal crack tip opening displacement and the secondary internal crack tip opening displacement curves obtained in example 1, and the surface of the silicone rubber represents the primary surface crack tip opening displacement and the secondary surface crack tip opening displacement obtained in example 1.
It can be seen that the primary surface crack tip opening displacement and the secondary surface crack tip opening displacement obtained in example 1 are substantially the same as the crack tip opening displacement measured in the comparative example, which proves that the detection method of the present invention has good reliability.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A detection method for the opening displacement of a metal fracture toughness crack tip is characterized by comprising the following steps:
performing cutting pretreatment on the metal to be evaluated to obtain the metal to be evaluated;
performing a three-point bending test on the metal to be tested until the metal to be tested is at the maximum load value to obtain a metal to be tested;
performing primary curing liquid filling treatment on the crack of the primary metal to be detected to obtain a primary curing mold;
determining primary surface crack tip opening displacement and primary internal crack tip opening displacement according to the primary curing mold;
determining primary surface crack tip opening displacement and primary internal crack tip opening displacement according to the primary curing mold, comprising:
determining the opening displacement of the primary surface crack tip according to the surface crack tip of the primary curing mold;
performing N times of cutting treatment on the primary curing mold in the length direction to obtain (N + 1) primary internal curing molds;
and respectively determining the opening displacement of the primary internal crack tip according to the surface crack tip of each primary internal curing mold, wherein N is more than or equal to 1.
2. The detection method according to claim 1, further comprising:
and establishing a crack tip opening displacement curve of the metal to be evaluated according to the primary surface crack tip opening displacement and the primary internal crack tip opening displacement.
3. The detection method according to claim 1, wherein after the primary curing liquid pouring treatment, the method further comprises:
performing a secondary three-point bending test on the primary metal to be tested to obtain a secondary metal to be tested;
performing secondary curing liquid filling treatment on the crack of the secondary metal to be detected to obtain a secondary curing mold;
and determining the secondary surface crack tip opening displacement and the secondary internal crack tip opening displacement according to the secondary curing mould.
4. The method of claim 3, wherein a load displacement curve is obtained from the primary three-point bending test and the secondary three-point bending test.
5. The detection method according to any one of claims 1 to 4, further comprising:
and evaluating the fracture toughness of the pipeline to be evaluated according to the primary surface crack tip opening displacement, the primary internal crack tip opening displacement and the crack tip opening displacement of the pipeline to be evaluated.
6. The inspection method according to claim 5, wherein the evaluating the fracture toughness of the pipe under evaluation based on the primary surface crack tip propagation displacement, the primary internal crack tip propagation displacement, and the crack tip propagation displacement of the pipe under evaluation comprises:
if the primary surface crack tip opening displacement and the primary internal crack tip opening displacement are both larger than or equal to the crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is of a first level;
and if at least one of the primary surface crack tip opening displacement and the primary internal crack tip opening displacement is smaller than the crack tip opening displacement of the pipeline to be evaluated, the fracture toughness of the pipeline to be evaluated is in a second grade.
7. The detection method according to claim 3 or 4, wherein the primary curing liquid and/or the secondary curing liquid comprises silicone rubber.
8. The detection method according to any one of claims 1 to 4 or 6, wherein the loading rate of the three-point bending test is V,0 < V.ltoreq.1 mm/min.
9. The test method according to claim 7, wherein the loading rate of the three-point bending test is V,0 < V.ltoreq.1 mm/min.
10. The detection method according to any one of claims 1 to 4, 6 and 9, wherein the cutting pretreatment comprises cutting in a width direction of the metal to be evaluated, and a ratio of a cutting length to the width of the metal to be evaluated is greater than or equal to 1:2.
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