Micro-damage detection method for estimating compressive strength of ancient brick

Abstract

The invention discloses a micro-damage detection method for estimating compressive strength of ancient bricks. The method comprises the following steps: preparing a sample and a standard sample; collecting data; establishing a model and performing strength estimation, namely performing linear fitting analysis on the compressive strength value sigma bc of the standard sample and the corresponding data of the dynamic friction coefficient mu and the water absorption rate M, and establishing a mathematical model. According to the method, under the condition that the cultural relic body is basically not damaged, only the fragments in any shape at the mechanically damaged part are collected, and the compressive strength of the ancient brick is relatively accurately estimated.

Description

Technical Field

[0001] The invention relates to the technical field of cultural relics protection, and in particular to a micro-damage detection method for estimating the compressive strength of ancient bricks. Background Art

[0002] Ancient bricks are important historical and cultural heritages, and their compressive strength is an important indicator for evaluating their preservation status and structural safety. Traditional compressive strength testing methods usually require sampling from the cultural relics themselves and conducting destructive compressive tests, which not only causes irreversible damage to the cultural relics, but also makes it impossible to collect a large number of standard samples from existing ancient buildings to reflect the overall strength distribution of the building.

[0003] Therefore, it is of great significance to develop a method that can perform micro-destructive testing on ancient bricks and accurately estimate their compressive strength. Summary of the invention

[0004] The purpose of the present invention is to provide a micro-destructive detection method for estimating the compressive strength of ancient bricks. This method can collect only fragments of any shape at the mechanical damage site without basically destroying the cultural relics themselves, and relatively accurately estimate the compressive strength of ancient bricks.

[0005] The present invention provides the following technical solutions:

[0006] A micro-destructive testing method for estimating the compressive strength of ancient bricks comprises the following steps:

[0007] 1) Sample preparation: Collect mechanically damaged fragments from the ancient buildings to be tested and grind them into blocks or sheets with parallel upper and lower surfaces;

[0008] 2) Standard sample preparation: Select ancient bricks from non-existing buildings that are similar in composition, craftsmanship, and preservation status to the ancient bricks to be tested and have a large number of existing bricks as standard samples, and grind them into blocks or sheets with parallel upper and lower surfaces;

[0009] 3) Data collection: Use a micrometer scratch tester to perform scratch testing, using the normal loading force F n and tangential friction force F t Perform linear fitting to obtain the slope of the straight line, i.e., the dynamic friction coefficient μ; obtain the dry weight m1 and saturated weight m2 of the sample, and calculate the water absorption rate M value based on the water absorption rate formula M = (m2-m1) / m1×100%; obtain the compressive strength value σ of the standard sample bc average value;

[0010] 4) Build the model: The compressive strength value of the standard sample σ bc Perform linear fitting analysis with the corresponding dynamic friction coefficient μ and water absorption rate M data to establish a mathematical model σ bc =k(1-M) / μn +b, n = -1, 1, 2, 3...N, N is a positive integer, k, b are fitting parameters;

[0011] 5) Strength estimation: Test the samples to be tested, and bring the collected and calculated dynamic friction coefficient μ and water absorption rate M into the mathematical model established in step 4) to calculate the estimated compressive strength of the ancient bricks.

[0012] Preferably, in step 1), the size of the fragments in any direction is greater than 5 mm, and the largest surface is selected and polished using sandpaper or sandpaper with a mesh size of 600-2000 to form blocks or sheets with parallel upper and lower surfaces.

[0013] Preferably, the sample after grinding in step 1) is required to be greater than 5 mm in length or width and 1-5 mm in thickness.

[0014] Preferably, in step 2), there are no less than 5 standard samples, each of which is made into a cube with a size of 5-50 mm or a cylinder with a diameter of 5-50 mm, and the upper and lower surfaces are polished with sandpaper or sand disc with a mesh number of 600-2000 until the upper and lower surfaces are parallel.

[0015] Preferably, in step 3), the normal loading force F n The values ​​are fixed at 5, 10, 15, 20, 25, and 30 N respectively. At least 3 groups are selected, and the scratch length is 5-10 mm. The tangential scratching force F is obtained. t The average value within the stable range.

[0016] Preferably, in step 3), the sample is dried at 103° C. for 1 hour to obtain a dry weight m1, and the sample is immersed in water for 1 hour to obtain a saturated weight m2.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) Micro-damage detection: Only a small amount of ancient brick fragments of any shape need to be collected to complete the detection, thus minimizing the damage to the cultural relics.

[0019] 2) Accurate estimation: By building a mathematical model to correlate the coefficient of kinetic friction, water absorption and compressive strength values, the compressive strength of ancient bricks can be estimated more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a detection flow chart of the present invention;

[0021] Figure 2 It is a schematic diagram of the fitting model of compressive strength, dynamic friction coefficient and water absorption rate of Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below in conjunction with specific implementation examples, so as to facilitate researchers in this field to implement it with reference to this specification.

[0023] In the following examples, the bricks of the Song Dynasty Cypress Yuan Pagoda in Tongchuan City, Shaanxi Province, and the bricks of the Tang Dynasty Fayuan Temple Pagoda and Luoshan Temple Pagoda in Weinan City, Shaanxi Province are used as the objects to be detected, and the compressive strength is estimated by the method of the present invention. As Figure 1 shown, the steps are as follows:

[0024] Sample preparation: Collect the fragments that have been mechanically damaged on the ancient buildings to be tested, with any dimension greater than 5 mm in any direction. Select the largest surface, and use a sandpaper with a mesh number of 600 to polish it into a block or sheet with parallel upper and lower surfaces, with a length or width greater than 5 mm and a thickness of 1-5 mm. Select 5 pieces of blue bricks from the Ming and Qing Dynasty folk houses in Shanxi region, which are similar in material and technology to the ancient city wall bricks, as the standard samples. For each brick, make 3 cubes with a size of 8 mm, and polish the upper and lower surfaces with a sandpaper with a mesh number of 600 until the upper and lower surfaces are parallel. To verify the estimation results, 3 pieces of each larger fragment of the ancient building bricks to be tested are made into cubes with a size of 8 mm, and the upper and lower surfaces are polished with a sandpaper with a mesh number of 600 until the upper and lower surfaces are parallel for the determination of compressive strength.

[0025] Data collection: Use an Anton Paar NHT+MCT micro-scratch tester to perform scratch tests on the standard samples. The normal loading forces are fixed at 5, 10, and 15 N respectively, and the scratch length is 6 mm to obtain the average value of the tangential scratching force F t within the stable range. Use the obtained 3 groups of normal loading forces F n and tangential scratching forces F t for linear fitting to obtain the slope of the straight line, that is, the dynamic friction coefficient μ. Dry the sample at 103 °C for 1 hour, weigh the dry weight m1, soak the sample in water for 1 hour, weigh the saturated water weight m2, and calculate the water absorption rate M = (m2 - m1) / m1 × 100%. Use an INSTRON 5967 universal testing machine to perform compressive strength tests on the standard samples to obtain the average value of the compressive strength σ bc of the standard samples.

[0026] Model establishment: Perform linear fitting analysis on the compressive strength values σ bc of the standard samples and the corresponding dynamic friction coefficient μ and water absorption rate M data, as Figure 2 shown. Establish a mathematical model between the compressive strength σ bc and the dynamic friction coefficient μ and water absorption rate M parameters as σ bc = 2.16(1 - M) / μ 3 + 4.84, with the unit of MPa.

[0027] Example 1

[0028] In this embodiment, a micrometer scratch tester is used to test the brick sample of the Fayuan Temple Pagoda in the Tang Dynasty. The dynamic friction coefficient of 0.531 and the water absorption rate of 22.35% collected and calculated are brought into the mathematical model σ bc =2.16(1-M) / μ 3 +4.84, the estimated compressive strength of ancient bricks was calculated to be 16.04MPa, the measured value was 16.76MPa, and the relative error was -4.3%.

[0029] Example 2

[0030] In this embodiment, a micrometer scratch tester is used to test the brick sample of Luoshan Temple Pagoda in the Tang Dynasty. The dynamic friction coefficient of 0.504 and water absorption rate of 19.61% collected and calculated are brought into the mathematical model σ bc =2.16(1-M) / μ 3 +4.84, the estimated compressive strength of ancient bricks was calculated to be 18.40MPa, the measured value was 20.11MPa, and the relative error was -8.5%.

[0031] Example 3

[0032] In this embodiment, a micrometer scratch tester is used to test the brick samples of the Song Dynasty Cypress Yuanta. The dynamic friction coefficient of 0.527 and water absorption rate of 21.32% collected and calculated are brought into the mathematical model σ bc =2.16(1-M) / μ 3 +4.84, the estimated compressive strength of ancient bricks was calculated to be 16.45MPa, the measured value was 18.25MPa, and the relative error was -9.9%.

[0033] The above embodiments are only examples of the preferred embodiments of the present invention and do not include all the implementation scope of the invention. Various changes and modifications made by ordinary technicians in this field without departing from the spirit and scope of the present invention are considered to be within the scope of protection of the claims of the present invention.

Claims

1. A micro-damage detection method for estimating the compressive strength of ancient bricks, characterized in that, The following steps are involved: 1) Sample preparation: Collect mechanically damaged fragments from the ancient buildings to be tested and grind them into blocks or sheets with parallel upper and lower surfaces; 2) Standard sample preparation: Select ancient bricks from non-existing buildings that are similar in composition, craftsmanship, and preservation status to the ancient bricks to be tested and have a large number of existing bricks as standard samples, and grind them into blocks or sheets with parallel upper and lower surfaces; 3) Data collection: Conduct scratch tests using a micron scratch tester standard sample, and perform linear fitting using the normal loading force F n and the tangential scratching force F t to obtain the slope of the straight line, which is the dynamic friction coefficient μ; obtain the dry weight m1 and the saturated water weight m2 of the sample, and calculate the water absorption rate M value based on the water absorption rate formula M = (m2 - m1) / m1 × 100%; obtain the average value of the compressive strength value σ bc of the standard sample; 4) Establish a model: Use the compressive strength value σ of the standard sample bc and perform linear fitting analysis on the corresponding dynamic friction coefficient μ and water absorption rate M data to establish a mathematical model σ bc = k(1 - M) / μ n + b, where n = -1, 1, 2, 3... N, N is a positive integer, and k and b are fitting parameters; 5) Strength estimation: Test the samples to be tested, and bring the collected and calculated dynamic friction coefficient μ and water absorption rate M into the mathematical model established in step 4) to calculate the estimated compressive strength of the ancient bricks.

2. The method according to claim 1, wherein In step 1), the size of the fragments in any direction is greater than 5 mm. The largest surface is selected and sanded with sandpaper or sand disc with a mesh size of 600-2000 until the fragments are in the shape of blocks or sheets with parallel upper and lower surfaces.

3. The method according to claim 1, characterized in that, The sample after grinding in step 1) is required to be greater than 5 mm in length or width and 1-5 mm in thickness.

4. The method according to claim 1, wherein Step 2) There are no less than 5 standard samples, each of which is made into a cube with a size of 5-50 mm or a cylinder with a diameter of 5-50 mm. The upper and lower surfaces are polished with sandpaper or sand disc with a mesh number of 600-2000 until the upper and lower surfaces are parallel.

5. The method according to claim 1, wherein Step 3) The normal loading force F in the Chinese method n are respectively fixed at 5, 10, 15, 20, 25, 30 N, select no less than 3 groups, the scratch length is 5 - 10 mm, and obtain the average value of the tangential scratching force F t within the stable range.

6. The method according to claim 1, characterized in that, In step 3), the sample is dried at 103° C. for 1 hour, and the dry weight m1 is measured. The sample is immersed in water for 1 hour, and the saturated weight m2 is measured.

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