A dynamic resistance-based wood stress concentration risk prediction simulation device

Abstract

This invention belongs to the field of wood mechanical property testing and provides a simulation device for predicting the risk of concentrated stress in wood based on dynamic resistance. The device includes: an operating table, a temperature control and sample processing system, a moisture content control device, and a bending test and dynamic resistance measurement device. The temperature control and sample processing system includes a polyurethane insulated box and a liquid nitrogen refrigeration system mounted on the operating table. The moisture content control device includes an electric thermostatic drying oven, an electronic balance, and a heat preservation and humidity control box mounted on the operating table. This invention achieves a wide temperature range adjustment from 20℃ to -196℃ through the liquid nitrogen refrigeration system and the polyurethane insulated box, with temperature fluctuations ≤ ±0.5℃. Combined with the electric thermostatic drying oven, water tank, and other moisture content control devices, it can accurately control four moisture content states: oven-dried, air-dried, etc., solving the problems of narrow temperature and humidity adjustment range and poor linkage of traditional devices. It can simulate the combined working conditions of "low-temperature freeze-thaw + moisture absorption and expansion" in cold regions.

Description

Technical Field

[0001] This invention belongs to the field of wood mechanical property testing, specifically a wood concentrated stress risk prediction and simulation device based on dynamic resistance. Background Technology

[0002] In timber engineering applications, timber is often in a complex environment, subjected to the combined effects of various factors such as temperature changes, humidity fluctuations, and mechanical loads. This can lead to stress concentration inside the timber, which in turn causes structural damage.

[0003] Traditional constant temperature chambers typically have a temperature regulation range of 0℃ to 100℃, which cannot cover the low-temperature environment below -50℃ required for cold-region engineering (such as the service temperature of wooden components in Arctic research stations reaching -60℃). Furthermore, they lack a linkage mechanism with moisture content control, making it impossible to simulate the combined working conditions of "low-temperature freeze-thaw + moisture absorption and expansion". At the same time, although some chambers have the ability to maintain a low temperature of -20℃, they do not integrate a refrigeration system and need to rely on an external cold source, resulting in temperature fluctuation errors exceeding ±5℃, which cannot meet the requirements of high-precision testing. Utility Model Content

[0004] To address the aforementioned technical problems, this invention provides a simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance, thereby solving the problem that existing technologies cannot simulate multiple environments.

[0005] A simulation device for predicting the risk of concentrated stress in wood based on dynamic resistance includes: an operating table, a temperature control and sample processing system, a moisture content control device, and a bending test and dynamic resistance measurement device. The temperature control and sample processing system includes a polyurethane insulated box and a liquid nitrogen refrigeration system installed on the operating table. The moisture content control device includes an electric thermostatic drying oven, an electronic balance, and a heat preservation and humidity control box installed on the operating table. A water tank is installed on the top of the electronic balance. The bending test and dynamic resistance measurement device includes a universal testing machine and an LCR digital bridge installed on the operating table. The sample is placed in the inner cavity of the polyurethane insulated box.

[0006] Preferably, the polyurethane insulation box is used to contain the sample and maintain a stable internal temperature. The liquid nitrogen refrigeration system also includes a freezer and a liquid nitrogen tank installed on the operating table to provide a cold source for the polyurethane insulation box, so that the temperature can be adjusted within the range of 20°C to -196°C. The LCR digital bridge is used to detect the resistance signal of the sample.

[0007] Preferably, the electric thermostatic drying oven is used to dry the sample, and the temperature can be set to 103±2℃. The water tank is used to adjust the moisture content of the sample. The electronic balance has an accuracy of 0.001g and is used to measure the mass of the sample. The heat preservation and humidity control box is used to maintain the temperature and moisture content of the sample.

[0008] Preferably, the universal mechanical testing machine is used to perform a three-point bending test on the specimen, with a range of 300kN, a loading speed of 10mm / min, and a span between the two supports of 240mm. The LCR digital bridge is used to detect the dynamic resistance signal of the specimen during the bending test.

[0009] Preferably, both ends of the sample are coated with conductive paint, and a stainless steel electrode nail with a diameter of 1.5 mm and a length of 10 mm is vertically embedded in the center of both ends of the sample. The stainless steel electrode nail is connected to an LCR digital bridge through a wire, and a clamping assembly is provided on the top of the operating table.

[0010] Preferably, the clamping assembly includes a U-shaped seat fixedly connected to the top of the operating table. Threaded holes are provided on both sides of the U-shaped seat, and a fixing screw is threaded into the inner cavity of each threaded hole. A positioning block is fixedly connected to one side of each of the two fixing screws.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] This invention achieves a wide temperature range of 20℃ to -196℃ through a liquid nitrogen refrigeration system and a polyurethane insulated chamber, with temperature fluctuations ≤ ±0.5℃. Combined with an electric heating constant-temperature forced-air drying oven and water tank for moisture content control, it can precisely regulate four moisture content states: oven-dried, air-dried, etc., solving the problems of narrow temperature and humidity control range and poor linkage of traditional devices. It can simulate the combined working conditions of "low-temperature freeze-thaw + moisture absorption and expansion" in cold regions. The device collects resistance signals in real time through stainless steel electrode nails embedded in the sample and an LCR digital bridge. Combined with a universal testing machine for three-point bending tests, it can simultaneously acquire load-resistance change data. Based on the resistance change rate-stress damage model constructed from 160 Populus tomentosa and Larch samples, it can provide risk warning with a threshold of ΔR / R0 ≥ 150%, providing a quantitative basis for safety assessment of timber engineering. Attached Figure Description

[0013] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0014] Figure 2 For this utility model Figure 1 A three-dimensional structural diagram of the medium-temperature control and sample processing system;

[0015] Figure 3 This utility model Figure 1 A three-dimensional structural diagram of a moisture content control device;

[0016] Figure 4 This utility model Figure 1 A three-dimensional structural diagram of the device for intermediate bending resistance testing and dynamic resistance measurement;

[0017] Figure 5 This utility model Figure 1 A three-dimensional structural diagram of the clamping assembly.

[0018] In the diagram: 1. Operating table; 2. Temperature control and sample processing system; 201. Polyurethane insulation box; 202. Liquid nitrogen refrigeration system; 204. Freezer; 205. Liquid nitrogen tank; 3. Moisture content control device; 301. Electric thermostatic drying oven; 302. Water tank; 303. Electronic balance; 304. Insulation and humidity control box; 4. Bending test and dynamic resistance measurement device; 401. Universal mechanical testing machine; 402. LCR digital bridge; 5. Sample; 6. Clamping assembly; 601. U-shaped seat; 602. Threaded hole; 603. Fixing screw; 604. Positioning block. Detailed Implementation

[0019] The embodiments of this utility model will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of this utility model.

[0020] Example:

[0021] Please refer to Figures 1 to 5As shown, this utility model provides a simulation device for predicting the risk of concentrated stress in wood based on dynamic resistance, including: an operating table 1, a temperature control and sample processing system 2, a moisture content control device 3, and a bending test and dynamic resistance measurement device 4; the temperature control and sample processing system 2 includes a polyurethane insulated box 201 and a liquid nitrogen refrigeration system 202 installed on the operating table 1; the moisture content control device 3 includes an electric heating constant temperature forced air drying oven 301, an electronic balance 303, and a heat preservation and humidity control box 304 installed on the operating table 1; a water tank 302 is installed on the top of the electronic balance 303. The bending test and dynamic resistance measurement device 4 includes a universal mechanical testing machine 401 and an LCR digital bridge 402 mounted on the operating table 1. A polyurethane insulation chamber 201 contains a sample 5 and is used to contain the sample 5 and maintain a stable internal temperature. The liquid nitrogen refrigeration system 202 also includes a freezer 204 and a liquid nitrogen tank 205 mounted on the operating table 1 to provide a cold source for the polyurethane insulation chamber 201, allowing the temperature to be adjusted within the range of 20℃ to -196℃. The LCR digital bridge 402 is used to detect the resistance signal of the sample 5. The electrothermal constant... The forced-air drying oven 301 is used to dry sample 5, and the temperature can be set to 103±2℃. The water tank 302 is used to adjust the moisture content of the sample. The electronic balance 303 has an accuracy of 0.001g and is used to measure the mass of sample 5. The heat preservation and humidity control chamber 304 is used to maintain the temperature and moisture content of sample 5 stably. The universal testing machine 401 is used to perform a three-point bending test on sample 5, with a range of 300kN, a loading speed of 10mm / min, and a span between the two supports of 240mm. The LCR digital bridge 402 is used to detect the dynamics of sample 5 during the bending test. The sample 5 has conductive paint applied to both ends, and stainless steel electrode nails with a diameter of 1.5 mm and a length of 10 mm are vertically embedded in the center of both ends of the sample 5. The stainless steel electrode nails are connected to the LCR digital bridge 402 through wires. The top of the operating table 1 is provided with a clamping assembly 6. The clamping assembly 6 includes a U-shaped seat 601 fixedly connected to the top of the operating table 1. Threaded holes 602 are opened on both sides of the U-shaped seat 601. The inner cavity of the threaded holes 602 is threaded with fixing screws 603. Positioning blocks 604 are fixedly connected to one side of each of the two fixing screws 603.

[0022] As can be seen from the above, the preparation and pretreatment of sample 5 are as follows: the sapwood of Populus tomentosa is processed into a sample of 300mm×20mm×20mm, and a transverse crack with a depth of 0.5cm is pre-made at 1 / 2 of the length as the damage group; at the same time, a control group sample without cracks (0cm) is prepared. The two ends of sample 5 are evenly coated with conductive paint, and a stainless steel electrode nail with a diameter of 1.5mm and a length of 10mm is vertically embedded in the center. After the conductive paint dries completely, it is ready for use.

[0023] Moisture content control: Place sample 5 in an electric thermostatic drying oven 301 and dry it at 103±2℃ for about 8 hours. During this period, weigh it every 2 hours using an electronic balance 303 (LQ-C3002, accuracy 0.001g) until the difference between two consecutive weighings is ≤0.0002g, reaching an absolutely dry state (MC=0%). Temperature control: The temperature inside the polyurethane insulation box 201 is reduced to -40℃ at a rate of 20℃ / h using a liquid nitrogen refrigeration system 202 (freezer 204 + liquid nitrogen tank 205). After sample 5 is placed in the box, it is stabilized for 2 hours to ensure uniform temperature.

[0024] Static resistance test: The sample 5 was tested in the polyurethane insulation chamber 201 using an LCR digital bridge 402 for 15 seconds each time, repeated 3 times and the average value was recorded. The initial resistance value R0 was recorded. Three-point bending test and dynamic resistance acquisition: The sample 5 was installed in the universal testing machine 401 with the span between the two supports set to 240 mm. A load was applied vertically downward at a speed of 10 mm / min. At the same time, the DCR detection mode of the LCR digital bridge 402 was started and the test time was set to 4 minutes. The resistance signal was acquired in real time. When the load on the sample 5 dropped rapidly (indicating that the material began to break), the loading and signal acquisition were stopped immediately.

[0025] Test data shows that when the load reaches 70% of the peak value, the resistance of sample 5 suddenly increases to 1.8 times the initial value, corresponding to the expansion of microcracks inside the wood to the macroscopic visible stage. The relationship between moisture content and mass is calculated by formula MC=(M1-M0) / M0. Combined with the temperature-resistance-stress curve, a risk prediction model is established under this working condition: when the resistance change rate (ΔR / R0)≥150%, the wood is judged to have a high stress damage risk.

[0026] Working Principle: Multi-environmental factor collaborative simulation: Through the liquid nitrogen refrigeration system 202 (a combination of freezer 204 and liquid nitrogen tank 205) and polyurethane insulation box 201, the temperature is regulated from 20℃ to -196℃ at a cooling rate of 20℃ / h, with temperature fluctuation ≤±0.5℃, covering extreme low-temperature scenarios in cold-region engineering (Arctic research station operating environment of -60℃). Then, using an electrically heated constant-temperature forced-air drying oven 301 (103±2℃ to constant weight), water tank 302 immersion, and electronic balance 303 (accuracy 0.001g), absolute dryness (0% MC) is achieved. Four states are controlled: air-dried (14% MC), fiber saturation point (30% MC), and saturated (100% MC). The formula MC = (M1 - M0) / M0 quantifies the relationship between moisture content and mass. Through the linkage control of temperature and moisture content, the "low-temperature freeze-thaw + moisture absorption expansion" composite working condition of wood in actual service is simulated: wood fibers shrink under low temperature environment, and changes in moisture content lead to internal stress concentration. Freeze-thaw cycle (such as -20℃ → 20℃) aggravates the propagation of microcracks. Combined with moisture content fluctuation (such as saturated → air-dried), the damage accumulation process in the natural environment is reproduced.

[0027] Dynamic resistance signal coupling monitoring: When wood is bent, the expansion of internal microcracks disrupts the conductive pathways (mainly relying on the electrolyte solution in the wood cell walls), leading to an increase in resistance. Stainless steel electrode nails (1.5mm diameter × 10mm) and conductive paint form a stable conductive interface. The resistance change is captured in real time by an LCR digital bridge 402 (accuracy 0.01Ω). In the dynamic resistance test, the error between the moment of sudden resistance increase and the moment of macroscopic crack appearance in sample 5 is ≤5 seconds, establishing a correspondence between "resistance sudden change point - crack initiation". For example, when the resistance of Populus tomentosa sapwood increases to 1.8 times the initial value at -40℃ and in an absolutely dry state, the corresponding load reaches 70% of the peak value, indicating a risk of structural damage. The universal testing machine 401 applies a load at a loading speed of 10mm / min and a span of 240mm. The LCR digital bridge 402 synchronously collects the resistance signal at a sampling frequency of ≥10Hz until the load drops rapidly, completely recording the resistance-load-displacement curve of the entire fracture process.

[0028] Risk prediction model construction: Based on sapwood / heartwood samples (160 each) of Populus tomentosa and Larch, test data were collected at 8 temperature points (20℃ to -196℃) and 4 moisture content states to extract characteristic parameters such as resistivity change rate (ΔR / R0) and stress-strain curve slope. For example, the correlation coefficient between resistivity change rate and bending strength of Populus tomentosa sapwood at -196℃ and in an absolutely dry state reached 0.92. A mathematical model of resistivity change rate and stress damage degree was fitted using machine learning algorithms (such as random forest and neural network), and a risk warning threshold was set: when ΔR / R0 ≥ 150%, it was judged as high risk (corresponding to the expansion of internal cracks in the wood to a critical state). Combining the three-dimensional data of temperature, moisture content, and resistivity, a risk level assessment report was generated, and safe use recommendations were output (such as the maximum allowable load of wood under a certain working condition).

[0029] The embodiments of this utility model are given for the purpose of illustration and description. Although embodiments of this utility model have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the utility model. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this utility model.

Claims

1. A simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance, characterized in that, include: Operating table (1), temperature control and sample processing system (2), moisture content control device (3), bending test and dynamic resistance measurement device (4); The temperature control and sample processing system (2) includes a polyurethane insulation box (201) and a liquid nitrogen refrigeration system (202) set on the operating table (1). The moisture content control device (3) includes an electric heating constant temperature drying oven (301), an electronic balance (303) and a heat preservation and humidity control box (304) set on the operating table (1). A water tank (302) is set on the top of the electronic balance (303). The bending test and dynamic resistance measurement device (4) includes a universal mechanical testing machine (401) and an LCR digital bridge (402) set on the operating table (1). The sample (5) is set in the inner cavity of the polyurethane insulation box (201).

2. The simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance as described in claim 1, characterized in that: The polyurethane insulation box (201) is used to contain the sample and maintain a stable temperature inside the box. The liquid nitrogen refrigeration system (202) also includes a freezer (204) and a liquid nitrogen tank (205) installed on the operating table (1) to provide a cold source for the polyurethane insulation box (201) so that the temperature can be adjusted within the range of 20°C to -196°C. The LCR digital bridge (402) is used to detect the resistance signal of the sample.

3. The simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance as described in claim 1, characterized in that: The electric thermostatic drying oven (301) is used to dry the sample, and the temperature can be set to 103±2℃. The water tank (302) is used to adjust the moisture content of the sample. The electronic balance (303) has an accuracy of 0.001g and is used to measure the mass of the sample. The heat preservation and humidity control box (304) is used to maintain the temperature and moisture content of the sample.

4. The simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance as described in claim 1, characterized in that: The universal mechanical testing machine (401) is used to perform a three-point bending test on the specimen, with a range of 300kN, a loading speed of 10mm / min, and a span of 240mm between the two supports. The LCR digital bridge (402) is used to detect the dynamic resistance signal of the specimen during the bending test.

5. The simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance as described in claim 1, characterized in that: Both ends of the sample (5) are coated with conductive paint, and stainless steel electrode nails with a diameter of 1.5 mm and a length of 10 mm are vertically embedded in the center of both ends of the sample (5). The stainless steel electrode nails are connected to the LCR digital bridge (402) through wires. A clamping assembly (6) is provided on the top of the operating table (1).

6. The simulation device for predicting the risk of concentrated stress in timber based on dynamic resistance as described in claim 5, characterized in that: The clamping assembly (6) includes a U-shaped seat (601) fixedly connected to the top of the operating table (1). Threaded holes (602) are provided on both sides of the U-shaped seat (601). The inner cavity of each threaded hole (602) is threaded with a fixing screw (603). A positioning block (604) is fixedly connected to one side of each of the two fixing screws (603).

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