Creep testing device, wood creep testing system and testing method

Abstract

The invention discloses a creep test device and a test system including the improved creep test device of the invention. The wood creep test system provided by the invention can simultaneously test a certain number of test specimens when conducting a creep test on wood. The whole system of the invention can perform long-term, continuous and stable detection, recording and display of the general creep and complex wetting creep deflection, shrinkage and swelling, and environmental temperature and humidity parameters of wood, thereby providing a reliable test basis and test platform for the exploration of the MSC behavior law and creep mechanism of wood, and also providing a reference for the development of moisture absorption / desorption behavior test equipment for moisture adsorbing materials other than wood.

Description

Technical Field

[0001] The invention relates to a device for testing the physical and mechanical properties of wood, in particular to a wood creep testing system. Background Art

[0002] Wood has the ability to absorb gaseous moisture from the surrounding high-humidity air (abbreviated as: moisture absorption) and release gaseous moisture to the surrounding low-humidity air (abbreviated as: desorption). During the moisture absorption / desorption process, the moisture content (Moisture content, abbreviated as: MC) inside the wood is gradient distributed and dynamically changes. When the drier / wetter wood absorbs / desorbs moisture, its moisture content increases / decreases from the surface to the inside layer by layer, accompanied by the gradual increase / decrease of the average moisture content (Average moisture content, abbreviated as: AMC), until it reaches the Equivalent Moisture Content (Equivalent Moisture Content, abbreviated as: EMC) state that is balanced with the moisture content of the surrounding air.

[0003] Researchers have found that the change pattern of the static bending creep deflection of wood after repeated moisture absorption / desorption and repeated increase / decrease of AMC is very different from the positive correlation between EMC and static bending constant humidity creep deflection under current domestic and international standard laboratory conditions, and the total creep deflection of the wet creep is much greater than the total creep deflection of the constant humidity creep under the same long and high EMC. This has become a consensus in this field.

[0004] The applicant found that, contrary to conventional knowledge, the static deflection of wooden beams in the rainy season in natural environments is smaller than that in the dry season. This discovery has attracted great attention from the engineering community at home and abroad, and has also aroused strong interest in the scientific community in exploring the mechanism of wood wetting creep (because the mechanism is unclear, predecessors generally referred to it as "mechanical adsorption creep Mechano-sorptive creep, abbreviated as: MSC"), but the shortcomings of MSC testing technology and the lack of understanding of the gradient distribution and dynamic changes of moisture content in wood during moisture absorption / desorption have hindered people's exploration of the scientific mechanism and engineering application of MSC.

[0005] Therefore, in order to solve the long-standing problems in wood wetting creep testing, such as insufficient control methods and accuracy of environmental parameters (temperature, humidity and wind speed), insufficient sensitivity and accuracy in creep deformation testing, insufficient intelligent data collection and processing, and insufficient system safety protection, a precise test system for wood static bending wetting creep is urgently needed to obtain the accurate behavior laws of static bending MSC that were previously limited by experimental and cognitive conditions, so as to provide a basis for finding the scientific mechanism of MSC and the impact of MSC of load-bearing wood under natural conditions on practical engineering applications. Summary of the invention

[0006] In order to solve the problems of the prior art, the present invention provides a creep testing device and a wood creep testing system using the device. The system can detect, record and display the deflection, shrinkage and swelling, and environmental temperature and humidity parameters of the general creep and complex wetting creep of wood for a long time, continuously and stably, and provide a reliable test basis and test platform for the exploration of the MSC behavior law and creep mechanism of wood, and also provide a reference for the development of moisture absorption / desorption behavior test equipment for moisture adsorbing materials other than wood.

[0007] The present invention is achieved through the following technical contents:

[0008] The creep test device comprises a specimen support, a creep load and a bracket thereof, and a linear displacement sensor, wherein the specimen support is used to place the specimen for testing, the specimen support comprises a pair of identical rollable support rollers, the support rollers are arranged in parallel, and the support rollers are used to horizontally place the specimen for creep test; the creep load provides a force acting on the specimen during creep test; the creep load is hung at the bottom of the bracket and applies a force to the specimen for creep test through the top of the bracket; the linear displacement sensor collects displacement data of the specimen during creep test.

[0009] There are two linear displacement sensors, which are arranged opposite to each other in the vertical direction. The linear displacement sensors are respectively arranged on the upper surface and the lower surface of the specimen to be tested for creep, and are used to collect the vertical displacement of the upper surface and the lower surface of the specimen respectively. The vertical displacement is the creep amount, and at the same time, the shrinkage and swelling change of the thickness of the wood specimen is obtained by calculating the difference between the two.

[0010] As an improvement of the specimen holder, identical placing plates are respectively provided on the supporting rollers, the bottom of the placing plates are fixed on the supporting rollers, and the placing plates rotate coaxially with the supporting rollers; the upper surface of the placing plates is a smooth plane, and the upper surface of the placing plates is used to place the specimens for creep test, and the specimens slide in cooperation with the upper surface of the placing plates, which can minimize the surface indentation of the specimens.

[0011] Generally, the common test standards for static bending performance of wood in dry environment all require the use of a support roller with a certain curvature and can be rolled as the force-bearing support end of the simply supported beam, the purpose of which is to allow the wood to bend and deform freely and reduce indentation. However, in a humid environment, the wood becomes soft due to moisture, and the existing support method will still cause large indentations to the wood. Therefore, the present invention changes the arc support of the support roller into a flat support for the placement board, which can solve the indentation problem while satisfying the test principle.

[0012] The present invention is an improvement on the hanger for mounting creep load. Each hanger for the creep test device of the present invention is provided with two identical hangers, which are arranged parallel and oppositely on both sides of the specimen for the creep test. The same side of the top of each pair of hangers is connected by a connecting piece, and the hangers are placed on the specimen for the creep test through the connecting piece.

[0013] The upper part of each hanger is a pair of vertical parts parallel to each other, the top ends of the vertical parts are in the same plane and the plane where the top ends are located is perpendicular to the vertical parts; the top ends of the vertical parts on the same side of the two hangers are respectively connected by connecting pieces.

[0014] A rectangular protrusion formed by bending outward is provided below the vertical portion of each hanger. The hanger protrudes outward to facilitate the fixation of the linear displacement sensor below the test piece and also facilitate the operation of the creep test.

[0015] The top of the vertical portion of each hanger is rigidly connected.

[0016] The four-point bending test is a test method for measuring the bending properties of materials. The strip specimen is placed flat in the bending test fixture to form a simply supported beam. The distance between the two lower support points of the specimen can be adjusted depending on the length of the specimen. There are two symmetrical loading points above the specimen. The four-point bending loading method requires two hanging points for hanging weights, but this brings about the problem of evenly distributing the weights at the two hanging points and the problem of the hanging frame shaking with the hanging weights.

[0017] The present invention improves the hanger to solve this problem and provides a double-hanging-point hanger device composed of a double hanger. The hanger is provided with two connecting pieces. When performing a creep test, the hanger can be hung at the three-divided points of the specimen span through the connecting pieces, so that the specimen is subjected to two-point vertical loading, and forms a four-point bending loading mode with the support rollers supported at both ends of the specimen. The top rigid connection of the vertical part of each hanger can prevent the hanger from sliding inward when the specimen is bent and deformed and continue to maintain the fixity of the specimen's force points, further improving the load stability during the creep test.

[0018] The present invention is directed to a further improved technical solution for the connecting piece:

[0019] The connecting member is rotatably matched with the vertical part. Further, the connecting member is a rotating roller, that is, the connecting member is preferably a connecting member of a rolling shaft structure, which can avoid the influence of the hanging frame stuck on the loading direction of the specimen on the one hand, and avoid the displacement of the hanging point after the specimen is bent and deformed under load, causing the change of the loading mode.

[0020] An annular limit groove is provided along the circumference of the middle part of the connector, and the width of the limit groove is equal to the width of the test piece. The connector with the limit groove and the top rigidly connected hanger work together to prevent the hanger from shaking forward and backward and left and right, further improving the load stability during the creep test.

[0021] The position of the creep test specimen in contact with the connector is provided with an anti-pressure gasket, the length of which is greater than the circumference of the connector. The function of the anti-pressure gasket is to prevent the connector from leaving an indentation on the upper surface of the specimen.

[0022] The present invention further improves the technical solution for the load required for creep test: The creep load is hung directly below each pair of hangers through a load distribution member, and the two ends of the load distribution member are respectively connected to the bottom of the hangers on both sides, and the center of gravity of the creep load, the center of gravity of the load distribution member and the top diagonal line of the hanger are on the same vertical line, so that the force of the creep load can effectively act in the same vertical gravity direction.

[0023] The bottom of each hanger is the same U-shaped bend. The load distribution member is cylindrical and horizontally placed in the U-shaped bends of the two hangers. The circumferential side of the load distribution member is provided with a hanging groove at least in the part in contact with the U-shaped bend, and the U-shaped bend is located in the hanging groove.

[0024] A hook is provided at the top of the creep load, and the bottom of the hook is fixedly connected to the creep load. An arc end is provided at the top of the hook, and the load distribution component passes through the arc end of the hook. A hook groove is provided on the circumferential side surface in the center of the load distribution component at least in the part in contact with the hook, and the arc end of the hook is located in the hook groove.

[0025] The setting of the hanging groove and the hook groove is to prevent the uneven load distribution and load shaking of the creep load from affecting the stability of the hanger. Corresponding to the hanger and the hook, the hook groove is located in the center of the load distribution component, and the hanging groove is equidistantly located on both sides of the hook groove. This not only makes the load evenly distributed to the two hangers and prevents large shaking, but also relies on the point contact between the hanging groove and the hook groove to enable the two hangers, the hook and the load distribution component to work together to automatically center the load of the creep load.

[0026] The present invention aims at improving a wood creep test system, comprising a sealable box body, the box body is provided with a constant temperature and humidity device, and at least one group of the improved creep test device of the present invention is arranged in the box body.

[0027] A device frame for fixing the creep test device is arranged in the box body, and the device frame comprises at least a pair of beams horizontally fixed in the box body, and the beams are parallel to each other; at least one set of creep test devices is arranged on the beams.

[0028] Each set of creep test devices has two specimen supports which are arranged on two beams opposite to each other. Each specimen support is provided with a supporting roller which is parallel to the beam.

[0029] A blocking bar is provided on the crossbeam directly below the test piece, and the blocking bar is located between the hangers on both sides of the test piece, and both ends of the blocking bar are fixedly connected to the crossbeam.

[0030] In order to prevent the sudden breakage of specimens of different properties and under different experimental conditions from causing vibration and damage to the entire test system, the technical solution of the present invention provides a blocking bar between the two hangers to prevent the hangers from continuing to fall when the specimen breaks.

[0031] A lifting device for lifting and lowering creep load is provided under the bottom of each creep test device, and a horizontal storage platform is provided on the top of the lifting device, which can carry out simultaneous mounting and unloading of one or more groups of test specimens.

[0032] The lifting device is a hydraulic jack.

[0033] The wood creep test system provided by the present invention requires a certain number of specimen samples when conducting a creep test on wood, and has high requirements for the creep timing starting point of all specimens. In order to obtain the simultaneity of moisture absorption / desorption and creep loading, a device for simultaneously loading the loads of multiple specimens is required. The creep load with a hook is raised to a suitable height by a hydraulic jack so that the load distribution part can pass through the hook and fall on the U-shaped bend at the bottom of the rack. When the creep test is started, the hydraulic jack is opened, and the creep load slowly descends due to its own gravity under the support of the storage table until the hook falls into the hook groove of the load distribution part, and the U-shaped bend of the rack is hung in the hanging groove. At this time, the creep load is separated from the storage table, and the simultaneous loading of the load is achieved. When unloading at the same time, only the opposite operation needs to be performed, and the operation process is very convenient.

[0034] It also includes a wind speed regulating device, a hot wire anemometer and a temperature and humidity sensor inside the box, as well as a temperature and humidity alarm device, a computer and a power supply for the test system outside the box. Thus, it has the ability to generate, transport, maintain and discharge wet air with a specific humidity and temperature in a quantitative, constant speed and directional manner to ensure that the wood specimen can stably absorb or discharge gaseous moisture; it also has the ability to regulate the humidity, temperature and flow rate of the wet air and their variation range. The relative humidity control accuracy of the wet air is not greater than ±2%, and the temperature control accuracy is not greater than ±0.1℃.

[0035] The whole system of the present invention can perform long-term, continuous and stable detection, recording and display of the general creep and complex creep deflection, shrinkage and swelling, and environmental temperature and humidity parameters of wood, providing a reliable experimental basis and testing platform for the exploration of the MSC behavior law and creep mechanism of wood, and can also provide a reference for the development of moisture absorption / desorption behavior test equipment for moisture-absorbing materials other than wood.

[0036] The present invention uses the testing method of the wood creep testing system, comprising the following steps:

[0037] Step 1: Pass the specimen horizontally between the two hangers, place both ends of the specimen on the placement plate of the support roller, and gently place the connecting parts of the two hangers on the upper surface of the specimen;

[0038] Step 2, fixing the positions of the linear displacement sensors on the upper and lower sides of the specimen, and placing the contact tips of the linear displacement sensors against the upper and lower surfaces of the mid-span of the specimen respectively;

[0039] Step 3, prepare the creep load, place the creep load on the placement table, place the hook between the bottom of the rack, and pass the load distribution member through the bottom of the rack and the hook in sequence;

[0040] Step 4, lower the placement table by a hydraulic jack until the creep load is suspended on the hanger;

[0041] Step 5, start the constant temperature and humidity device to control the temperature and humidity in the box, start the air inlet device and adjust the wind speed at the location of the test piece through the wind speed regulating device; monitor the data in real time through the temperature and humidity sensor and the wind speed sensor;

[0042] Step 6, inputting the temperature, humidity, wind speed in the box and the displacement signal of the test piece collected in step 5 into the computer for data storage, processing, analysis and display. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic structural diagram of the creep testing device of the present invention.

[0044] Figure 2 It is a front view schematic diagram of the creep testing device of the present invention.

[0045] Figure 3 It is a schematic diagram of the specimen support structure of the present invention.

[0046] Figure 4 This is a diagram showing the use status of the specimen holder of the present invention.

[0047] Figure 5 Another structural schematic diagram of the specimen support of the present invention.

[0048] Figure 6 It is a schematic diagram of the overall structure of the rack of the present invention.

[0049] Figure 7 It is a schematic diagram of the structure of the hanger connecting piece of the present invention.

[0050] Figure 8 Another structural schematic diagram of the hanger of the present invention is shown in FIG.

[0051] Fig. 9 It is a schematic diagram of the position structure of the linear displacement sensor of the present invention.

[0052] Fig.10 It is a schematic diagram of the structure of the load distribution member of the present invention.

[0053] Fig.11 It is a schematic diagram of the creep load structure of the present invention.

[0054] Fig.12 It is a schematic diagram of the structure of the wood creep testing system of the present invention.

[0055] Fig.13 This is a schematic diagram of the box structure of the wood creep testing system of the present invention.

[0056] Fig.14 It is a schematic diagram of the device frame structure of the wood creep testing system of the present invention.

[0057] Fig.15 The device frame of the wood creep test system of the present invention is used in the state Figure 1 .

[0058] Fig.16 The device frame of the wood creep test system of the present invention is used in the state Figure 2 .

[0059] Fig.17 for Fig.16 Enlarged schematic diagram at point A in the middle.

[0060] Fig.18 It is a block diagram of the creep testing system of the present invention.

[0061] Fig.19 These are the temperature, humidity and displacement values ​​in the box measured in real time by six humidity sensors and a linear displacement sensor during the wood creep test of the present invention.

[0062] Fig. 20 This is the wood creep test 112d wood wetting creep diagram of the present invention.

[0063] Fig.21 This is a measured diagram of the dynamic swelling and shrinkage of wood after a 240-hour creep test of the present invention. DETAILED DESCRIPTION

[0064] like Figure 1 As shown, the creep testing device of the present invention includes a specimen holder 100 for placing a specimen 101 for creep testing, a creep load 200 for providing the specimen 101 with the force required for creep testing, a bracket 300 for mounting the creep load 200 on the specimen 101, and a linear displacement sensor 400 for collecting displacement data of the specimen 101 during the creep test.

[0065] like Figure 4 As shown, the specimen holder 100 is used to place a specimen 101 for testing, and includes a pair of identical rollable support rollers 102 . The support rollers 102 are arranged in parallel, and the specimen 101 for creep test is placed horizontally on the support rollers 102 .

[0066] In this embodiment, the specimen holder 100 is as follows Figure 1 and Figure 3As shown, the support roller 102 is arranged in a U-shaped base frame 103. When the structure of the support roller 102 is actually implemented, first, a bolt is directly used to pass through the base frame 103, and then the other end of the bolt is fixed by a nut. The bolt and the two sides of the base frame 103 are rotated to form the support roller 102. Second, the support roller 102 is composed of a bolt and a sleeve sleeved on the bolt. The bolt is fixed on both sides of the base frame 103, and the sleeve can rotate with the bolt as the axis. Regardless of the first or second type, the surface of the object that needs to rotate and cooperate needs to be treated to reduce friction, such as smoothing the surface, filling with lubricating media, etc. Or use bearings to connect, which is very common in the prior art and is selected according to conditions.

[0067] Generally, the common test standards for static bending performance of wood in dry environment all require the use of a rollable support roller with a certain curvature as the load-bearing end of the simply supported beam, the purpose of which is to allow the wood to bend and deform freely and reduce indentation. However, in a humid environment, the wood becomes soft due to moisture, and the existing support method will still cause a large indentation on the wood. Therefore, in this embodiment, if Figure 3 and 4 As shown, identical placement plates 104 are respectively provided on the support rollers 102 , the bottom of the placement plates 104 is fixed on the support rollers 102 , and the placement plates 104 rotate coaxially with the support rollers 102 .

[0068] In order to reduce the friction between the test piece 101 and the placement plate 104, the upper surface of the placement plate 104 is a smooth plane, and the test piece 101 is placed on the upper surface of the placement plate 104, and the test piece 101 slides with the upper surface of the placement plate 104. Under the premise of satisfying the test principle, this embodiment solves the problem of indentation by setting the placement plate 104.

[0069] The specimen holder 100 in this embodiment is composed of two independent base frames 103 provided with support rollers 102. When in use, the specimen holders 100 are fixed separately by other supporting mechanisms, and a space is formed between the specimen holders 100 as shown in FIG. Figure 1 The space shown in FIG. 1 is convenient for placing the linear displacement sensor 400. However, the structure of the specimen support 100 can also be as follows Figure 5 As shown, the specimen support 100 includes a longer section of a U-shaped bottom frame 103', and support rollers 102 are arranged near both ends of the bottom frame 103'. In order not to hinder the linear displacement sensor 400 from acting on the lower surface of the specimen 101, the middle of the bottom frame 103' must be hollow.

[0070] The creep test requires a force to act on the specimen. In this embodiment, the creep load 200 applies a force to the specimen 101 of the creep test through the hanger 300. The top of the hanger 300 is hung on the specimen 101 of the creep test, and the creep load 200 is hung on the bottom of the hanger 300 and applies a force to the specimen 101 through the top of the hanger 300.

[0071] like Figure 1 As shown, in this embodiment, the creep test device has two identical hangers 300, which are arranged parallel and oppositely on both sides of the creep test specimen 101. The same side of the top of each pair of hangers 300 is connected by a connector 310, which is placed on the specimen 101.

[0072] The bracket 300 is mounted on the three points of the span of the specimen 101 through the connecting member 310, so that the specimen 101 is subjected to two-point vertical loading, such as Figure 1 and Figure 2 As shown, the connecting member 310 and the supporting roller 102 form a four-point bending loading method. The four-point bending loading method is a test method for measuring the bending properties of materials. The strip specimen is placed flat in the bending test fixture to form a simply supported beam. The distance between the two lower supporting points of the specimen is adjustable depending on the length of the specimen, and there are two symmetrical force points on the top of the specimen.

[0073] like Figure 6 As shown, specifically, in this embodiment, the upper portion of each hanger 300 is a pair of vertical portions 320 parallel to each other, the top ends of the vertical portions 320 are in the same plane and the plane where the top ends are located is perpendicular to the vertical portions 320, and the top ends of the vertical portions 320 on the same side of the two hangers 300 are connected by connecting members 310 respectively.

[0074] The length of the vertical portion 320 of the hanger 300 depends on the overall size of the creep test device. The main part of the hanger 300 can be completely vertical, but the hanger 300 is suspended on the specimen 101 through the connector 310. The volume of the specimen 101 does not need to be too large regardless of the actual use environment or test needs. The preferred size of the specimen 101 is 110×10×5mm (length×width×height), so the length of the connector 310 does not need to be much longer than the width of the specimen 101, about 3 times is sufficient, otherwise the hangers 300 on both sides of the specimen 101 are prone to shaking.

[0075] Therefore, the spacing between the hangers 300 on both sides of the test piece 101 and the spacing between the vertical parts 320 on the same hanger 300 are limited. Since a linear displacement sensor 400 is also required to be arranged below the test piece 101, in order not to hinder the linear displacement sensor 400, the required space is reserved for accommodating the linear displacement sensor 400 and its sensor fixing seat 401, such as Figure 2 and Figure 6As shown, a rectangular protrusion 321 bent outward is provided below the vertical portion 320 of each hanger 300 .

[0076] In order to prevent the top of the rack 300 from sliding inward when the specimen 101 is bent and deformed during the creep test so as to keep the stress point of the specimen 101 fixed, the top of each rack 300 is rigidly connected, such as Figure 6 As shown, in this embodiment, the tops of the vertical parts 320 on the same rack 300 are fixedly connected by the stopper 322. In practical applications, the rack 300 can also be formed by bending as a whole, such as Figure 8 As shown, through holes 323 are reserved at the two right-angle corners at the top for the connection member 310 to be fixed.

[0077] The creep testing device of the present invention has double hanging points composed of double hangers, and two hanging points are required for hanging weight. Therefore, there will be problems such as uniform distribution of the weight at the two hanging points and shaking of the hanger with the hanging weight. Therefore, by rigidly connecting the top of the hanger 300, the hanger is prevented from sliding inward when the specimen is bent and deformed, thereby keeping the force point of the specimen unchanged and improving the load loading stability during the creep test.

[0078] like Figure 4 As shown, the distance b between the connection piece 310 at the top of the hanger 300 and the contact point of the test piece 101 is one third of the distance a between the support rollers 102. The length of the test piece 101 is greater than the distance between the support rollers 102, and the distance center between the mid-span of the test piece 101 and the support rollers 102 is on the same vertical line.

[0079] In this embodiment, the connecting member 310 is rotatably matched with the vertical portion 320. The connecting member 310 is a rotating roller, and its rotating connection structure is the same as the supporting roller 102. There are many technical means available in the prior art to realize the function of the rotating roller, such as Figure 7 The connecting member 310 is configured as a roller, which can prevent the loading direction of the specimen from being affected by the stuck hanger, and can also prevent the displacement of the hanging point after the specimen is bent and deformed under load, which causes a change in the loading mode.

[0080] An annular limiting groove 311 is provided along the circumferential surface in the middle of the connecting member 310, and the width of the limiting groove 311 is equal to the width of the test piece 101. The connecting member 310 with the limiting groove 311 and the top rigidly connected hanger 300 work together to prevent the hanger 300 from shaking forward and backward and left and right, further improving the load loading stability during the creep test.

[0081] In order to prevent the connector 310 from leaving an indentation on the upper surface of the test piece 101, an anti-pressure gasket 312 is provided at the position of the test piece 101 in contact with the connector 310. Figure 4 and Fig.17As shown, the length of the anti-pressure gasket 312 is greater than the circumference of the circumferential surface of the connecting member 310 , thereby preventing the connecting member 310 from slipping out of the anti-pressure gasket 312 .

[0082] During the creep test, in order to prevent the weight of the creep load, i.e., the uneven distribution of the load, and the load shaking from affecting the stability of the rack, the creep load 200 of each set of devices in this embodiment is hung directly below each pair of racks 300 through a load distribution member 330, such as Figure 1 , Figure 2 and Fig.11 As shown, the two ends of the load distribution member 330 are respectively connected to the bottom of the hangers 300 on both sides, and the center of gravity of the creep load 200, the center of gravity of the load distribution member 330 and the top diagonal line of the hanger 300 are on the same vertical line, so that the force of the creep load 200 can not only effectively act in the same vertical gravity direction, but also can act evenly on the force points of the specimen 101 through the hanger 300.

[0083] like Figure 6 The bottom of each rack 300 is the same U-shaped bend 340, such as Fig.11 The load distribution member 330 is cylindrical and is horizontally placed in the U-shaped bend 340 of the two hangers 300. A hanging groove 331 is provided on the circumferential side surface of the load distribution member 330 at least in the portion in contact with the U-shaped bend 340, and the U-shaped bend 340 is located in the hanging groove 331.

[0084] like Figure 1 and Fig.11 A hook 201 is provided at the top of the creep load 200, and the bottom of the hook 201 is fixedly connected to the creep load 200. An arc end is provided at the top of the hook 201, and the load distribution member 330 passes through the arc end of the hook 201. A hook groove 332 is provided on the circumferential side surface in the center of the load distribution member 330, at least in the part that contacts the hook 201, and the arc end of the hook 201 is located in the hook groove 332.

[0085] Combination Fig.10 and Fig.11 In this embodiment, the hanging groove 331 and the hook groove 332 are both arranged around the circumference of the load distribution member 330.

[0086] Corresponding to the hanger 300 and the hook 201, the hook groove 332 is located in the center of the load distribution member 330, and the hanging groove 331 is equidistantly located on both sides of the hook groove 332. This not only allows the load to be evenly distributed to the two hangers 300 and prevents large shaking, but also relies on the point contact between the hanging groove 331 and the hook groove 332 to enable the two hangers 300, the hook 201 and the load distribution member 330 to work together to automatically center the load of the creep load 200.

[0087] Combination Figure 1 , Figure 2 and Fig. 9 The linear displacement sensors 400 are respectively arranged on the upper and lower surfaces of the specimen 101 to be tested for creep, and are used to collect the vertical displacement of the upper and lower surfaces of the specimen 101. The vertical displacement is the creep amount, and the shrinkage and swelling change of the thickness of the wood specimen is obtained by calculating the difference between the two. The specimen deformation test accuracy and resolution are not less than 0.01mm.

[0088] Specifically, the linear displacement sensor 400 is fixed by a sensor fixing seat 401, and the sensor fixing seat 401 is fixed to other fixed structures in the environment where the creep test device is used through a sensor fixing frame 402. For example, the bottom of the sensor fixing frame 402 can be vertically fixed on a table where the creep test device is placed. Depending on the test environment, existing technical means can be selected for fixing.

[0089] like Fig.12 As shown, in the wood creep test system of the present invention, the creep test device is arranged in a sealable box 500, the box 500 is provided with a constant temperature and humidity device 501, and at least one set of creep test devices is arranged in the box.

[0090] Specifically, a device frame 510 for fixing the creep test device is provided in the box 500, and the device frame 510 includes at least a pair of horizontal beams 511 fixed in the box, and the beams 511 are parallel to each other. The two ends of the beams 511 can be directly fixed on the two side walls of the box 500, or can be fixed as shown in FIG. Fig.14 As shown, the device frame 510 in this embodiment is a rectangular frame structure, and the vertical leg structures on both sides can be as shown in FIG. Fig.12 As shown in FIG. 5 , it is vertically fixed on the bottom surface of the interior of the box body 500 .

[0091] In order to solve the test error caused by the heterogeneity and many internal defects of wood, the wood creep test requires a certain number of test pieces to be tested simultaneously under the same environment, so at least one set of creep test devices is provided on the beam 511, such as Fig.15 and Fig.16 As shown, six groups of creep testing devices are provided in this embodiment.

[0092] Combination Figure 1 and Figure 4 The specimen support 100 of each creep test device is composed of two independent base frames 103 with support rollers 102, such as Fig.17 As shown, the specimen holders 100 are relatively arranged on two cross beams 511 , and the supporting rollers 102 on each specimen holder 100 are parallel to the cross beam 511 .

[0093] like Fig.17, a blocking bar 512 is provided on the crossbeam 511 directly below the specimen 101, the blocking bar 512 is located between the hangers 300 on both sides of the specimen 101, and both ends of the blocking bar 512 are fixedly connected to the crossbeam 511. The blocking bar 512 is used to prevent the sudden break of specimens of different properties and different experimental conditions from causing vibration and damage to the entire test system. The blocking bar 512 is provided between the two hangers 300, and when the specimen 101 breaks, the connector 310 of the hanger 300 will be blocked by the blocking bar 512 and stop falling.

[0094] like Fig.15 As shown, in this embodiment, a sensor fixing beam 403 is provided on the cross beam 511 beside each creep test device, which can be directly made of a section of cut angle steel, and the two ends of the bottom of the sensor fixing beam 403 are respectively fixed on the two cross beams 511. The sensor fixing frame 402 is fixed vertically downward on the sensor fixing beam 403. The fixing method can be bolt connection or welding, but for the convenience of disassembly and assembly, bolt connection is preferred.

[0095] The wood creep test system provided by the present invention requires a certain number of specimens to be tested for wood creep, and has high requirements for the creep timing starting point of all specimens. In order to achieve the simultaneity of moisture absorption / desorption and creep loading, a device for loading multiple specimens simultaneously is required. Figure 1 and Fig.15 A lifting device 513 for lifting the creep load 200 is provided below the bottom of each creep test device, and a horizontal storage platform 514 is provided on the top of the lifting device 513, which can carry out simultaneous loading and unloading of one or more groups of test pieces. In this embodiment, the lifting device 513 is a hydraulic jack.

[0096] Use a hydraulic jack to raise the creep load with the hook to a suitable height so that the load distribution member can pass through the hook and fall on the U-bend at the bottom of the hanger, such as Fig.11 As shown. When the creep test is started, the hydraulic jack is opened, and the creep load 200 slowly descends due to its own gravity under the support of the storage platform 514 until the hook 201 falls into the hook groove 332 of the load distribution member 330, and the U-shaped bend 340 of the hanger 300 is hung in the hanging groove 331. At this time, the creep load 200 is separated from the storage platform 514, and the load is loaded at the same time. When unloading at the same time, only the opposite operation needs to be performed, and the operation process is very convenient.

[0097] Combination Fig.12 and Fig.18The complete creep test system of the present invention also includes an air inlet device 502, a wind speed regulating device and a temperature and humidity sensor 517 arranged in the box 500, and a temperature and humidity alarm device 518, a computer 519 and a power supply 520 of the test system arranged outside the box 500. The wind speed regulating device includes a hot wire anemometer 516 and a speed regulator 515. The wind speed regulating device and the temperature and humidity sensor not only form the ability to stably generate, transport, maintain and discharge wet air with a specific humidity and temperature in a quantitative, constant speed and directional manner, so as to ensure that the wood specimen can stably absorb or discharge gaseous moisture; but also have the ability to regulate the humidity, temperature and flow rate of the wet air and their variation range, and the relative humidity control accuracy of the wet air is not greater than ±2%, and the temperature control accuracy is not greater than ±0.1℃.

[0098] In this embodiment, the present invention uses the Binder MKF720 constant temperature and humidity chamber produced by the German Binder company as the chamber 500 of the test system, and the chamber volume (width×depth×height) is 937×576×1250mm, the humidity adjustable range is RH 10~98% (accuracy ±2%), and the temperature adjustable range is -40~180℃ (accuracy ±0.1℃). The chamber 500 of this model is provided with a constant temperature and humidity device 501 at its lower part and an air inlet device 502 in the chamber 500. Although the basic conditions for supplying low-temperature humid air into the chamber are met, the maximum adjustable wind speed is only 1m / s, and it is impossible to simulate and study the basic law of wood wetting creep under high wind speed airflow (such as the wind speed in plateau or coastal outdoor environment is generally above 2.2 m / s for most of the year).

[0099] To this end, in view of the space limitation in the box and the original layout of the air flow channel, the present invention first improves the air intake device 502 into a set of small adjustable speed dual-turbine fans, which can increase the wind speed in the box to a maximum of 5.6m / s, and at the same time adds a wind speed adjustment device, which includes a hot wire anemometer 516 and a speed regulator 515. The hot wire anemometer 516 is arranged on the device frame 510 near the test piece 101, and the speed regulator 515 is arranged outside the box 500, which is convenient for manual adjustment of the fan speed of the air intake device 502. With the wind speed adjustment device, as well as experimental and theoretical analysis, it is confirmed that the change of wind speed can indeed significantly affect the air flow rate on the surface of the wood test piece, and then affect its moisture absorption or desorption rate.

[0100] In actual implementation, in order to prevent the daily changes in the humidity and temperature of the surrounding environment of the box from affecting the humidity and temperature inside the box, especially the impact of opening the door, and to try to maintain the consistency between the temperature and humidity of the experimental operation space outside the box and the parameters inside the box, the test can be carried out in an environment equipped with a humidifier / dehumidifier and air conditioner. The ambient temperature around the box can be adjusted in the range of 10 to 40°C, with an accuracy of ±1°C; the relative humidity can be adjusted in the range of 40 to 80%, with an accuracy of ±5%.

[0101] The space of the box 500 is limited, so the volume occupied by the creep load 200 is as small as possible and it is convenient to make a standard shape. Considering the economic cost, it is preferred to use a steel plate with a higher density as the creep load 200. Fig.11 As shown, in this embodiment, steel plates with the same length and width but different thicknesses are used to facilitate the use of creep tests at different load levels, as shown in Table 1.

[0102] Table 1 Creep load specifications

[0103]

[0104] At the same time, all steel plates are bluing treated to prevent them from rusting due to excessive humidity in the box during the creep test, which would affect the uniformity and stability of the applied load.

[0105] The most important raw data that need to be collected in real time in the wood static bending creep test are: the ambient temperature and humidity in the box, the wind speed at the location of the specimen, and the displacement of the upper and lower surfaces of the specimen in the middle of the span.

[0106] The test system of the present invention adopts a linear displacement sensor set at the midpoint of the upper and lower surfaces of the test piece. Figure 1 As shown, the vertical displacement measured on the lower surface is used to represent the static deflection of the specimen, and the difference between the displacements of the upper and lower surfaces of the specimen measured simultaneously is used as the swelling or shrinkage in the thickness direction of the specimen, thereby obtaining the real-time swelling and shrinkage rate of the thickness and the moment of inertia of the specimen section to facilitate subsequent analysis and calculation.

[0107] like Fig.12 and Fig.18 As shown, the present invention uses a transmitter 521 and a data conductor 522 to input the above-collected temperature, humidity, and displacement signals into a computer 519, and then the real-time storage, real-time processing, analysis, and display of the data can be realized through a program software compiled based on the VB language. Among them, the collected real-time raw data is in text format and stored in the form of a database for real-time data processing and analysis by the software. At the same time, the data can also be exported at any time to copy as a backup, which is convenient for offline processing and analysis of the data. The data is obtained by the temperature and humidity sensor 517, and after being recorded and processed by the supporting software, a real-time coordinate diagram with time as the horizontal scale and the temperature and relative humidity in the box as the vertical scale can be obtained. After the above-mentioned raw displacement data is processed in real time by the software, a continuous coordinate diagram with time as the horizontal scale and the static bending deflection and the swelling and shrinkage of the specimen as the vertical scale is formed for real-time monitoring and control.

[0108] In this embodiment, in order to prevent the temperature and humidity sensor 517 from indicating deviation or error due to possible electronic component failure, six temperature and humidity sensors 517 are arranged in the box 500, such as the Ecolog series temperature and humidity recorder (RH±0.5%, T±0.1℃) produced by the Swiss ELPRO Group. This type of temperature and humidity sensor 517 can monitor and record the temperature and humidity data in the box 500 in real time. Fig.12 As shown, among the six temperature and humidity sensors 517, one is placed at each of the four corners inside the box 500, and one is placed at each of the two sides of the upper middle part of the device frame 510, so as to monitor and record the temperature and humidity of different parts in the box and the test piece accessories. Fig.13 In the figure, a temperature and humidity sensor 517 can also be set in the middle of the left door frame near the box 500. In addition to detecting temperature and humidity together with the other 6 temperature and humidity sensors, it can also detect the temperature and humidity data at the door gap of the box 500. When an abnormality is found, the sealing condition of the door of the box 500 can be checked in time.

[0109] like Fig.12 and Fig.18 As shown, in order to prevent unexpected power outages during the test process, this embodiment configures a power generation device with appropriate power as the power supply 520 to supply the power demand of the entire test system and prevent experimental interruptions caused by power outages.

[0110] In order to prevent the test system from failing due to mechanical or electronic failures that cause the environmental parameters in the box to exceed the set parameter range when the experimenter is not on site, the test system is also equipped with a temperature and humidity alarm device 518. For example, the HE2508GSM SMS alarm module produced by Huatu Company is connected to the temperature and humidity recorder placed in the box 500, and the temperature and humidity values ​​are set. Once the values ​​are exceeded, the temperature and humidity alarm device 518 will be activated, such as the device itself beeps, sends a message reminder to the experimenter's mobile phone, and other alarm measures.

[0111] When using the wood creep testing system of the present invention to perform a test, the following steps can be performed:

[0112] Step 1: Pass the specimen horizontally between the two hangers, place both ends of the specimen on the placement plate of the support roller, and gently place the connecting parts of the two hangers on the upper surface of the specimen;

[0113] Step 2, fixing the positions of the linear displacement sensors on the upper and lower sides of the specimen, and placing the contact tips of the linear displacement sensors against the upper and lower surfaces of the mid-span of the specimen respectively;

[0114] Step 3, prepare the creep load, place the creep load on the placement table, place the hook between the bottom of the rack, and pass the load distribution member through the bottom of the rack and the hook in sequence;

[0115] Step 4, lower the placement table by a hydraulic jack until the creep load is suspended on the hanger;

[0116] Step 5, start the constant temperature and humidity device to control the temperature and humidity in the box, start the air inlet device and adjust the wind speed at the location of the test piece through the wind speed regulating device, maintain the environment in the box at a constant temperature of 20°C, a relative humidity of 42%-80% cyclic humidification, and a relative humidity of 65%; monitor the data in real time through the temperature and humidity sensor and the wind speed sensor;

[0117] Step 6: Input the temperature, humidity, wind speed and displacement signal of the specimen collected in step 5 into the computer for data storage, processing, analysis and display. The time interval for data recording can be set according to the material and characteristics of the specimen.

[0118] The real-time detection results of humidity, temperature and displacement in the box, which can be used for humidity, creep deflection, swelling and shrinkage analysis, are measured by the 6 temperature and humidity sensors 517 and the 12 linear displacement sensors 400 in the box. Figures 19 to 21 As shown in the figure, the ambient temperature and humidity data in the box are very uniform and consistent throughout the test. Figures 19 to 21 It can be seen that this system can capture the creep deflection, humidity, temperature and swelling and shrinkage of wood specimens in a long-term, sensitive and stable manner when the humidity changes and the humidity is constant, and the sampling interval can be changed at will during the experiment ( Fig.19 shown in the middle ellipse).

[0119] After trial operation inspection and correction, the scientificity, accuracy, sustainability and reliability of the test system provided by the present invention have been verified, indicating that the system can obtain real-time detection data of static bending, wetting and creep of wood and data that can be used for subsequent detailed research and analysis.

[0120] The precise test results of this system also found important differences from the creep test results of previous researchers who used steam spraying to treat the specimens, such as the static deflection during moisture absorption does not always increase in the opposite direction. Fig. 20 and Fig.21 This provides strong evidence for the innovative revelation of the mechanism of wood static bending and wetting creep.

Claims

1. Creep testing device, characterized in that: It includes a specimen support, a creep load and its bracket, and a linear displacement sensor. The specimen support is used to place the specimen for creep test, and the specimen support comprises a pair of identical rolling support rollers, which are arranged in parallel and used to place the specimen for creep test horizontally; The supporting rollers are respectively provided with identical placing plates, the bottom of which is fixed on the supporting rollers, and the placing plates rotate coaxially with the supporting rollers; the upper surface of the placing plates is a smooth plane, and the upper surface of the placing plates is used to place the specimens for creep test, and the specimens are slidably matched with the upper surface of the placing plates; The creep load provides the force acting on the specimen during the creep test. The creep load is hung at the bottom of the hanger and applies force to the specimen of the creep test through the top of the hanger. Two identical hangers are provided, and the hangers are arranged parallel and oppositely on both sides of the specimen for creep test; the same side of the top of each pair of hangers is connected by a connecting piece, and the hangers are placed on the specimen for creep test through the connecting piece; The linear displacement sensor collects displacement data during the creep test of the specimen. Two linear displacement sensors are provided, which are arranged opposite to each other in the vertical direction to collect the vertical displacement of the upper surface and the lower surface of the specimen respectively.

2. The creep testing device according to claim 1, characterized in that: The upper part of each hanger is a pair of vertical parts parallel to each other, the top ends of the vertical parts are in the same plane and the plane where the top ends are located is perpendicular to the vertical parts; the top ends of the vertical parts on the same side of the two hangers are respectively connected by connecting pieces.

3. The creep testing device according to claim 2, characterized in that: A rectangular protrusion is provided below the vertical portion of each hanger and is bent outward.

4. The creep testing device according to claim 2, characterized in that: The top of the vertical portion of each hanger is rigidly connected.

5. The creep testing device according to claim 2, characterized in that: The connecting piece is rotationally matched with the vertical portion.

6. The creep testing device according to claim 5, characterized in that: The connecting piece is a rotating roller, and an annular limiting groove is arranged along the circumferential surface of the middle part of the connecting piece, and the width of the limiting groove is equal to the width of the test piece.

7. The creep testing device according to claim 5 or 6, characterized in that: An anti-pressure gasket is provided at a position where the upper surface of the test piece contacts the connecting piece, and the length of the anti-pressure gasket is greater than the circumference of the circumferential surface of the connecting piece.

8. The creep testing device according to any one of claims 1 to 6, characterized in that: The creep load is hung directly below each pair of hangers through a load distribution member, and both ends of the load distribution member are respectively connected to the bottom of the hangers on both sides. The center of gravity of the creep load, the center of gravity of the load distribution member and the top diagonal line of the hanger are on the same vertical line.

9. The creep testing device according to claim 8, characterized in that: The bottom of each hanger is the same U-shaped bend.

10. The creep testing device according to claim 9, characterized in that: The load distribution member is cylindrical and horizontally placed in the U-shaped bends of the two hangers. A hanging groove is provided on the circumferential side of the load distribution member at least in the portion in contact with the U-shaped bend, and the U-shaped bend is located in the hanging groove.

11. The creep testing device according to claim 10, characterized in that: A hook is provided at the top of the creep load, and the bottom of the hook is fixedly connected to the creep load. An arc end is provided at the top of the hook, and the load distribution component passes through the arc end of the hook. A hook groove is provided on the circumferential side surface in the center of the load distribution component at least in the part in contact with the hook, and the arc end of the hook is located in the hook groove.

12. A wood creep test system, comprising a sealable box, the box being provided with a constant temperature and humidity device, characterized in that: At least one set of creep testing devices according to any one of claims 1 to 11 is arranged in the box.

13. The wood creep testing system according to claim 12, characterized in that: A device frame for fixing the creep test device is arranged in the box body, and the device frame comprises at least a pair of beams horizontally fixed in the box body, and the beams are parallel to each other; at least one set of creep test devices is arranged on the beams.

14. The wood creep testing system according to claim 13, characterized in that: Each set of creep test devices has two specimen supports which are arranged on two beams opposite to each other. Each specimen support is provided with a supporting roller which is parallel to the beam.

15. The wood creep testing system according to claim 14, characterized in that: The hanger is located between the two beams.

16. The wood creep testing system according to claim 15, characterized in that: A blocking bar is provided on the crossbeam directly below the test piece, and the blocking bar is located between the hangers on both sides of the test piece, and both ends of the blocking bar are fixedly connected to the crossbeam.

17. The wood creep testing system according to any one of claims 13 to 16, characterized in that: A lifting device for lifting and lowering creep load is arranged under the bottom of each set of creep test devices, and a horizontal storage platform is arranged on the top of the lifting device.

18. The wood creep testing system according to claim 17, characterized in that: The lifting device is a hydraulic jack.

19. The wood creep testing system according to claim 12, characterized in that: It also includes an air inlet device, a wind speed regulating device and a temperature and humidity sensor arranged inside the box, and a temperature and humidity alarm device, a computer and a power supply of the system arranged outside the box.

20. The wood creep testing system according to claim 19, characterized in that: The wind speed regulating device comprises a hot wire anemometer and a speed regulator.

21. A testing method using the wood creep testing system according to any one of claims 12 to 20, characterized in that: The following steps are included: Step 1: Pass the specimen horizontally between the two hangers, place both ends of the specimen on the placement plate of the support roller, and gently place the connecting parts of the two hangers on the upper surface of the specimen; Step 2, fixing the positions of the linear displacement sensors on the upper and lower sides of the specimen, and placing the contact tips of the linear displacement sensors against the upper and lower surfaces of the mid-span of the specimen respectively; Step 3, prepare the creep load, place the creep load on the placement table, place the hook between the bottom of the rack, and pass the load distribution member through the bottom of the rack and the hook in sequence; Step 4, lower the placement table by a hydraulic jack until the creep load is suspended on the hanger; Step 5, start the constant temperature and humidity device to control the temperature and humidity in the box, start the air inlet device and adjust the wind speed at the location of the test piece through the wind speed regulating device; monitor the data in real time through the temperature and humidity sensor and the wind speed sensor; Step 6, inputting the temperature, humidity, wind speed in the box and the displacement signal of the test piece collected in step 5 into the computer for data storage, processing, analysis and display.

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