A method for ultraviolet light coupling accelerated aging and nondestructive evaluation of larch wood

Abstract

The application discloses a kind of larch wood ultraviolet light coupling accelerated aging and material nondestructive evaluation method, belong to timber protection technical field.The application takes larch as object, adopts ultraviolet, water spraying, condensation coupling cyclic accelerated aging, carries out appearance, microscopic morphology, chemical composition, mechanical property detection according to fixed node, establishes the quadratic correction model of dynamic elastic modulus and aging time, realizes wood material nondestructive accurate evaluation.The application simulates environment real, period controllable, data quantification, engineering application, effectively solves the problem that traditional aging method is large, evaluation precision is low, difficult to use in situ, is applicable to ancient building wood structure safety detection, wood durability evaluation and protection repair.

Description

Technical Field

[0001] This invention belongs to the field of wood science and ancient building protection technology, specifically involving a method for artificially accelerating the aging of wood and a non-destructive assessment technology for wood properties. Background Technology

[0002] Timber is the main load-bearing material for ancient wooden buildings. It is easily affected by environmental factors such as sunlight, moisture, and temperature over a long period of time, which can cause color changes, microstructural damage, and mechanical property degradation, directly affecting the structural safety of ancient buildings.

[0003] Existing accelerated aging methods for wood mostly use single ultraviolet light irradiation, which differs greatly from the actual service environment; there is a lack of ultraviolet-water-heat coupled cyclic aging process; the assessment of material properties mostly uses single indicators, lacking an integrated characterization system of micromorphology, chemical composition and mechanical properties; the dynamic elastic modulus and static elastic modulus have large deviations and there is no unified correction model, resulting in low assessment accuracy and difficulty in meeting the needs of rapid testing and repair of ancient building wood. Summary of the Invention

[0004] To address the problems of distorted aging environment simulation, single detection index, large deviation of dynamic and static elastic modulus, and low evaluation accuracy in existing technologies, this paper provides a method for accelerated aging and non-destructive evaluation of larch wood that is cycle-controllable, environmentally realistic, and quantitatively accurate.

[0005] The technical solution adopted in this invention is a method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling, comprising the following sequentially implemented technical steps:

[0006] Step 1: Pre-treatment of specimens; The larch wood is processed into standard-sized specimens and its initial moisture content is adjusted to no less than 25% by soaking, so that the specimens are in a moisture state similar to the actual service environment before aging, providing the basic conditions for the coupling effect of moisture and ultraviolet radiation during the subsequent aging process.

[0007] Step 2: Grouping and Packing; The pretreated specimens are divided into non-destructive testing group and standard mechanical testing group, and placed into the UV accelerated aging test chamber respectively, so that specimens under the same aging conditions can be used for simultaneous testing of different types of indicators, avoiding interference between the testing method and the specimen condition.

[0008] Step 3: UV-Spray-Condensation Coupled Aging; The aging process is applied in a cycle of UV irradiation, spraying and condensation in the testing machine. UV irradiation simulates the degradation effect of sunlight, spraying simulates the wetting process of rainwater, and condensation simulates the low temperature and high humidity environment at night. The alternating coupling of UV irradiation, spraying and condensation accelerates the simulation of the actual outdoor service environment of wood.

[0009] Step 4: Multi-node and multi-dimensional testing; At the set aging time nodes, the specimens are tested in sequence for appearance color, SEM micromorphology, XPS energy spectrum O / C ratio, non-destructive mechanical properties and standard mechanical properties, so as to obtain the decay law of wood properties from multiple dimensions from macro to micro, from surface to interior, and from chemical to mechanical.

[0010] Step 5: Dynamic and static elastic modulus fitting and correction; Based on the dynamic and static elastic modulus test results obtained at the same aging time node, establish the functional relationship between the two, and convert the dynamic elastic modulus obtained by subsequent non-destructive testing into an equivalent static elastic modulus through a quadratic polynomial correction formula, so as to eliminate the systematic deviation between non-destructive testing and standard mechanical testing and improve the accuracy of material property evaluation.

[0011] Furthermore, in step three, a single aging cycle is 12 hours, performed in the following order: 8 hours of ultraviolet irradiation, blackboard temperature 60±3℃, ultraviolet wavelength 340nm, irradiation intensity 0.68W・m⁻²; followed by 30 minutes of spraying; and finally 3.5 hours of condensation, blackboard temperature 60±3℃.

[0012] Furthermore, the correction formula used in step five is: y = 0.0000001017t 2 -0.0006t+9.77; where y is the corrected equivalent static elastic modulus; t is the cumulative aging time; obtained by regression analysis of the dynamic elastic modulus decay trajectory of larch wood under UV-spray-condensation coupling, used to correct the non-destructive testing results to a range comparable to standard mechanical testing.

[0013] Furthermore, the multi-dimensional detection in step four specifically includes:

[0014] Changes in appearance and color are used to characterize the degree of photodegradation on the wood surface;

[0015] SEM microstructure is used to observe cell wall damage and pitting.

[0016] XPS energy dispersive spectroscopy O / C ratio is used to quantitatively assess the degree of chemical oxidation on the surface of wood.

[0017] Non-destructive mechanical properties, including stress wave propagation velocity and micro-drill impedance;

[0018] Standard mechanical properties include flexural modulus of elasticity, flexural strength, and compressive strength.

[0019] Furthermore, in step one, the specimen size is 2cm×2cm×36cm, and it is derived from 200-300 year old larch wood, processed according to GB1929-2009 standard.

[0020] Furthermore, the method is used for rapid durability assessment of timber in ancient wooden structures, prediction of aging life of outdoor timber, or non-destructive testing of timber property degradation.

[0021] Compared with existing technologies, this invention adopts a UV-spray-condensation coupled cycle, which is closer to the actual aging environment; it achieves integrated characterization of color, microstructure, chemical composition and mechanics in multiple dimensions; it improves the evaluation accuracy through dynamic and static elastic modulus correction formula; the method is non-destructive, fast and reproducible, and is suitable for durability evaluation and engineering testing of timber in ancient building wooden structures. Attached Figure Description

[0022] Figure 1 This is a diagram showing the sawing method for the specimen;

[0023] Figure 2 This is a diagram of the QUV / spray accelerated aging tester and related equipment;

[0024] Figure 3 This is a diagram showing the placement of the specimen in the test chamber;

[0025] Figure 4 The following are the changes in the color of the specimens over aging time: a) No aging; b) Aging for 492h; c) Aging for 1008h; d) Aging for 1572h; e) Aging for 2204h; f) Aging for 2960h; g) Aging for 3368h; h) Aging for 3752h; i) Aging for 4328h; j) Aging for 4796h; k) Aging for 5156h; l) Aging for 5528h.

[0026] Figure 5 This is an image from a FEIQUANTA 200 scanning electron microscope;

[0027] Figure 6 This is a diagram of sample preparation;

[0028] Figure 7 These are scanning electron microscope images at different aging times: a) Unaged - transverse - chordal - radial; b) Aged for 1332h - transverse - chordal - radial; c) Aged for 2960h - transverse - chordal - radial.

[0029] Figure 8 Energy dispersive spectroscopy (EDS) analysis of the O / C ratio as a function of aging time;

[0030] Figure 9 Energy dispersive spectroscopy (EDS) results at different aging times; a) No aging; b) Aging for 4328 h.

[0031] Figure 10 Nondestructive testing parameters versus time; a) Moisture content; b) Density; c) Stress wave propagation velocity; d) E d； e) Rotating needle impedance modulus; f) Infeed needle impedance modulus;

[0032] Figure 11 Comparison of scanning electron microscope images at different aging times; in the figures, a) no aging; b) aging for 3000h;

[0033] Figure 12 The trend and relationship of standard test indicators over time; in the figure, a) MOE; b) flexural strength; c) compressive strength;

[0034] Figure 13 This is a comparison chart of the results from two detection methods.

[0035] Figure 14 This is a graph showing the relationship between the corrected dynamic elastic modulus and time. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] This invention is based on the actual aging mechanism of wood in outdoor service environments, which is simultaneously subjected to solar ultraviolet radiation, rain rinsing, and the coupled effects of diurnal temperature variation. It proposes a method for accelerated aging and non-destructive assessment of material properties through alternating coupling of ultraviolet radiation, rain rinsing, and condensation. The technical principle is as follows:

[0038] The aging of wood is essentially a physicochemical process involving photodegradation, hydrolysis, and thermo-humidity cycling. This invention simulates daytime sunlight, rainfall and humidity, and nighttime low-temperature and high-humidity conditions by sequentially applying three environmental stresses: ultraviolet irradiation, spraying, and condensation. These three stresses are incorporated into a 12-hour cycle to achieve accelerated simulation of multi-factor conditions in actual service environments.

[0039] Ultraviolet irradiation phase: Ultraviolet light with a wavelength of 340 nm and an irradiation intensity of 0.68 W·m -2 The blackboard temperature is 60±3℃. The energy of ultraviolet photons is sufficient to break the C-C and C-O bonds in lignin molecules, triggering a free radical chain reaction, which leads to the degradation of lignin on the wood surface and the formation of chromophores (manifested as a darkening of color). At the same time, the amorphous regions of cellulose also undergo a certain degree of depolymerization.

[0040] Spraying stage: Water penetrates the wood cell walls, causing the degraded lignin and its oxidation products to be washed away, exposing the surface of the underlying fresh wood. At the same time, the presence of water promotes photochemical reactions (photo-water synergistic effect) and may cause swelling and shrinkage micro-damage to the cell walls.

[0041] Condensation stage: In a dark, high-humidity environment, water vapor condenses on the surface of the specimen, further maintaining the wood at a high moisture content, simulating the hygroscopic effect during the day-night cycle. The high-humidity environment during the condensation stage also promotes the slow hydrolysis of residual chemicals.

[0042] The alternating execution of the three stages causes the wood to continuously degrade in terms of material properties during the cycle of "photodegradation, water rinsing, and wet maintenance." Its aging rate is significantly higher than that of a single environmental stress, and it has a good correlation with actual outdoor aging in terms of color evolution, microstructure damage, changes in chemical composition (increased O / C ratio), and mechanical property decay.

[0043] Based on this, the present invention proposes a multi-node, multi-dimensional detection system. By simultaneously acquiring appearance color, SEM microstructure, XPS energy dispersive spectroscopy O / C ratio, non-destructive mechanical properties, and standard mechanical properties at multiple aging time points, a full-chain material property characterization path is established from macro to micro, from surface to interior, and from chemical to mechanical properties.

[0044] Furthermore, addressing the systematic bias between non-destructive testing (dynamic modulus of elasticity) and standard mechanical testing (static modulus of elasticity), this invention establishes a corrected model for the decay of dynamic modulus of elasticity over aging time based on paired dynamic and static modulus data from a large number of aging points, using quadratic polynomial regression analysis. This model can convert the dynamic modulus of elasticity obtained by non-destructive testing at any aging time point into an equivalent static modulus of elasticity, thereby achieving an accurate assessment of the residual mechanical properties of wood without damaging the specimen.

[0045] In summary, this invention achieves accelerated reproduction of aging behavior and quantitative, non-destructive assessment of material property degradation in larch wood through a technical approach of "multi-factor coupled aging + multi-dimensional synchronous detection + dynamic and static modulus fitting correction".

[0046] The technical solution adopted in this invention is a method for accelerated aging of larch wood by ultraviolet light coupling and non-destructive evaluation of its properties, comprising the following steps:

[0047] S1. Specimen preparation and pretreatment: Select 200-300 year old larch trees, process them into 2cm×2cm×36cm specimens according to GB1929-2009, and soak them until the moisture content is ≥25%;

[0048] S2. Grouping and Packing: Using a QUV / spray accelerated aging tester, non-destructive testing specimens are placed in box A, and standard mechanical testing specimens are placed in boxes B and C.

[0049] S3. Coupled accelerated aging: Performed according to ASTM G154-2016, with a UV wavelength of 340nm, an irradiation intensity of 0.68W・m⁻², and a cycle of 12h, including 8h of UV irradiation at a blackboard temperature of 60±3℃, 30min of spraying, and 3.5h of condensation at a blackboard temperature of 60±3℃, with a total aging time of 0~6000h;

[0050] S4. Multi-node detection: Conduct detection of appearance color, SEM microstructure, XPS energy spectrum O / C ratio, non-destructive mechanical properties, and standard mechanical properties at nodes of 12h, 24h, 36h, 48h, 60h...6000h.

[0051] S5. Correction of dynamic and static elastic modulus: The correction formula for dynamic elastic modulus and aging time is obtained by fitting: y=0.0000001017t²−0.0006t+9.77, where y is the corrected dynamic elastic modulus in GPa; t is the aging time in h.

[0052] Example 1

[0053] Experimental materials: new larch trees, 200-300 years old, processed into specimens of 2cm×2cm×36cm;

[0054] Test equipment: QUV / spray accelerated aging tester, FEIQUANTA200 scanning electron microscope, stress wave meter, micro-drill impedance meter, universal press;

[0055] Pretreatment: The specimens were soaked until the moisture content was ≥25%, and then placed in an aging chamber in groups;

[0056] Aging process: 340nm UV, irradiation intensity 0.68W・m⁻², 12h cycle;

[0057] Testing and Analysis: The appearance, microstructure, composition and mechanical properties are tested at each node, and the dynamic elastic modulus correction formula is obtained by fitting.

[0058] Results: The wood color gradually changed from light yellow to dark reddish brown, the cell walls were damaged and the pits were cracked, the O / C ratio increased, the overall elastic modulus decreased, and the stability was significantly improved after correction.

[0059] Example 2

[0060] Accelerated aging and material property assessment of new larch timber

[0061] 1. Specimen preparation (see attached) Figure 1 )

[0062] according to Figure 1 The sawing method shown involves cutting knot-free and crack-free specimens from 200-300 year old larch logs, with final dimensions of 2cm × 2cm × 36cm. Figure 1 ).

[0063] 2. Preprocessing and grouping (see appendix) Figure 2 , 3 )

[0064] Soak the specimens until the moisture content is ≥25%. Figure 2As shown, a QUV / spray accelerated aging test chamber was used. Figure 3 As shown, the specimens were divided into box A (non-destructive testing group) and boxes B and C (standard mechanical testing group) and placed separately to ensure that different types of test data could be obtained simultaneously under the same aging conditions.

[0065] 3. Coupling accelerates aging.

[0066] Performed in a 12-hour cycle: 8 hours of UV irradiation (340nm, 0.68W·m). -2 The process involves 30 minutes of spraying (at a blackboard temperature of 60±3℃) followed by 3.5 hours of condensation (at 60±3℃). The total aging time covers 0–6000 hours.

[0067] 4. Multi-node, multi-dimensional detection

[0068] (1) Changes in appearance color (see appendix) Figure 4 )

[0069] Figure 4 The color evolution of the wood at 12 nodes during the process from unaged to aged for 5528 hours is shown. The wood gradually changes from light yellow (Fig. a) to dark reddish brown (Fig. l), which intuitively reflects the degree of surface photodegradation.

[0070] (2) SEM microstructure (attached) Figure 5 , 6 7, 11)

[0071] A FEIQUANTA 200 scanning electron microscope was used. Figure 5 ),according to Figure 6 Samples were prepared using the following method. Figure 7 Display: Unaged (Fig. a): Cell walls intact, pits clearly visible;

[0072] After 1332 hours of aging (Figure b): slight damage to the cell wall was observed;

[0073] After 2960 hours of aging (Figure c): pits were clearly cracked and cell wall damage was aggravated.

[0074] Figure 11 The microstructure degradation of unaged (Fig. a) and aged for 3000h (Fig. b) was further compared.

[0075] (3) XPS energy dispersive spectroscopy O / C ratio (see appendix) Figure 8 , 9 );

[0076] Figure 8 The results show the increasing trend of the O / C ratio with aging time. Figure 9 The energy dispersive spectroscopy (EDS) spectra of unaged (lower O / C) and aged for 4328 h (significantly increased O / C) were compared to verify the increased degree of surface oxidation.

[0077] (4) Non-destructive mechanical properties (see appendix) Figure 10 )

[0078] Figure 10 The changes of various non-destructive indicators over aging time are shown:

[0079] a) Moisture content: initially decreases and then tends to stabilize;

[0080] b) Density: Decreases slowly;

[0081] c) Stress wave propagation speed: gradually decreases;

[0082] d) Dynamic elastic modulus Ed: Overall decay;

[0083] e) Rotating needle impedance modulus and f) Infeed needle impedance modulus both show a decreasing trend.

[0084] (5) Standard mechanical properties (attached) Figure 12 )

[0085] Figure 12 It shows:

[0086] a) Flexural modulus of elasticity (MOE): decreases with aging time;

[0087] b) Bending strength: continuously decreases;

[0088] c) Compressive strength: The overall trend is downward.

[0089] 5. Correction of dynamic and static elastic modulus fitting (attached) Figure 13 , 14 );

[0090] Figure 13 The deviation distributions of the dynamic elastic modulus and the static elastic modulus before and after the correction were compared. Figure 14 The fitted curve of the corrected dynamic elastic modulus with aging time is shown. The deviation between the corrected dynamic elastic modulus and the static elastic modulus is significantly reduced, and the evaluation accuracy is improved.

[0091] Example 3: Accelerated aging and material property assessment of old building materials;

[0092] 1. Specimen source and pretreatment;

[0093] Samples were taken from old larch timber (original service life unknown, showing initial signs of aging) replaced in ancient wooden buildings and processed into 2cm×2cm×36cm specimens. Due to the low initial moisture content of the old timber, the soaking time was extended to a moisture content ≥25% to ensure consistent moisture levels before aging.

[0094] 2. Group and pack into boxes;

[0095] Similar to Example 1, a QUV / spray testing machine was used ( Figure 2 The old material specimens were placed separately according to the non-destructive testing group and the standard mechanical testing group. Figure 3 An additional set of destructive detection methods for intermediate nodes is added.

[0096] 3. Coupling accelerates aging;

[0097] The process used was exactly the same 12-hour cycle as in Example 1: 8 hours of UV, 30 minutes of spraying, and 3.5 hours of condensation, with a total aging time of 0 to 6000 hours.

[0098] 4. Multi-node, multi-dimensional detection;

[0099] (1) Appearance color;

[0100] The initial color of the older material was darker than that of the newer material (appearing light brown). As it ages, the color further evolves towards a dark reddish-brown, and the rate of color change is slightly faster than that of the newer material, indicating that the older material is more sensitive to ultraviolet radiation (see reference). Figure 4 The color changes, but the initial color is darker.

[0101] (2) SEM microstructure;

[0102] The old material already showed some cell wall damage and pitting in its initial state. After aging:

[0103] After 1008 hours of aging: the original damaged area expands rapidly;

[0104] After 2960 hours of aging: penetrating cracks appeared in the cell walls, and the degree of damage was significantly greater than that of new materials in the same period (comparison). Figure 7 (c) and Figure 11 (b)

[0105] (3) XPS energy dispersive spectroscopy O / C ratio;

[0106] The initial O / C ratio of the old material was significantly higher than that of the new material. During the aging process, the O / C ratio continued to rise, but the rate of increase gradually slowed, indicating that a certain oxide layer had formed on the surface of the old material (see reference). Figure 8 The trend is there, but the starting point is higher.

[0107] (4) Non-destructive mechanical properties;

[0108] The initial values ​​of stress wave propagation velocity, dynamic elastic modulus, and micro-drilling resistance were all lower than those of the new material. With prolonged aging, the degradation trend of these indicators was consistent with that of the new material, but the degradation magnitude was relatively smaller (refer to...). Figure 10 (but the initial value is low).

[0109] (5) Standard mechanical properties;

[0110] The initial values ​​of flexural modulus of elasticity, flexural strength, and compressive strength are approximately 60% to 80% of those of virgin materials. After 6000 hours of aging, these properties decrease to 50% to 60% of their initial values, and the absolute strength falls below the safety threshold (refer to...). Figure 12 However, the starting point is lower.

[0111] 5. Application of dynamic and static elastic modulus correction;

[0112] Substituting the dynamic elastic modulus of the old material obtained through nondestructive testing into the correction formula, the deviation between the corrected equivalent static elastic modulus and the measured static elastic modulus is within ±5% (refer to...). Figure 13 , 14 The correction effect verified that the correction formula is also well applicable to old materials.

[0113] The above examples collectively demonstrate that this method has good applicability and evaluation accuracy for both new and old materials.

Claims

1. A method for accelerating aging of larch wood using ultraviolet light coupling and non-destructive evaluation of its properties, characterized in that, The following technical steps are implemented sequentially: Step 1: Pre-treatment of specimens; The larch wood is processed into standard-sized specimens and its initial moisture content is adjusted to no less than 25% by soaking, so that the specimens are in a moisture state similar to the actual service environment before aging, providing the basic conditions for the coupling effect of moisture and ultraviolet radiation during the subsequent aging process. Step 2: Group and pack into boxes; The pretreated specimens were divided into non-destructive testing group and standard mechanical testing group, and placed in ultraviolet accelerated aging test chambers respectively. This allowed specimens under the same aging conditions to be used for simultaneous testing of different types of indicators, avoiding interference between the testing methods and the specimen state. Step 3: UV-Spray-Condensation Coupled Aging; The aging process is applied in a cycle of UV irradiation, spraying and condensation in the testing machine. UV irradiation simulates the degradation effect of sunlight, spraying simulates the wetting process of rainwater, and condensation simulates the low temperature and high humidity environment at night. The alternating coupling of UV irradiation, spraying and condensation accelerates the simulation of the actual outdoor service environment of wood. Step 4: Multi-node and multi-dimensional testing; At the set aging time nodes, the specimens are tested in sequence for appearance color, SEM micromorphology, XPS energy spectrum O / C ratio, non-destructive mechanical properties and standard mechanical properties, so as to obtain the decay law of wood properties from multiple dimensions from macro to micro, from surface to interior, and from chemical to mechanical. Step 5: Dynamic and static elastic modulus fitting and correction; Based on the dynamic and static elastic modulus test results obtained at the same aging time node, establish the functional relationship between the two, and convert the dynamic elastic modulus obtained by subsequent non-destructive testing into an equivalent static elastic modulus through a quadratic polynomial correction formula, so as to eliminate the systematic deviation between non-destructive testing and standard mechanical testing and improve the accuracy of material property evaluation.

2. The method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling according to claim 1, characterized in that, In step three, a single aging cycle is 12 hours, executed in the following order: 8 hours of ultraviolet irradiation, black panel temperature 60±3℃, ultraviolet wavelength 340nm, and irradiation intensity 0.68W·m. -2 Spraying for 30 minutes followed by condensation for 3.5 hours, with the blackboard temperature at 60±3℃.

3. The method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling according to claim 1, characterized in that, The correction formula used in step five is: y = 0.0000001017t 2 -0.0006t+9.77; where y is the corrected equivalent static elastic modulus; t is the cumulative aging time; obtained by regression analysis of the dynamic elastic modulus decay trajectory of larch wood under UV-spray-condensation coupling, used to correct the non-destructive testing results to a range comparable to standard mechanical testing.

4. The method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling according to claim 1, characterized in that, The multi-dimensional detection in step four specifically includes: Changes in appearance and color are used to characterize the degree of photodegradation on the wood surface; SEM microstructure is used to observe cell wall damage and pitting. XPS energy dispersive spectroscopy O / C ratio is used to quantitatively assess the degree of chemical oxidation on the surface of wood. Non-destructive mechanical properties, including stress wave propagation velocity and micro-drill impedance; Standard mechanical properties include flexural modulus of elasticity, flexural strength, and compressive strength.

5. The method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling according to claim 1, characterized in that, In step one, the specimen size is 2cm×2cm×36cm, and it is made from larch wood aged 200 to 300 years, processed according to GB1929-2009 standard.

6. The method for accelerated aging and non-destructive evaluation of larch wood using ultraviolet light coupling according to claim 1, characterized in that, The method is used for rapid durability assessment of timber in ancient wooden structures, prediction of aging life of outdoor timber, or non-destructive testing of timber property degradation.

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