Research on Measurement Method of Geotextile Strain
Abstract: Geotextiles are widely used in various reinforced soil projects. However, due to the difficulty in measuring the wholesale polyester nonwoven geotextile strain and the low precision, it has played a significant role in the project, and it is still unclear how much deformation has occurred. For the flexible materials with low elastic modulus such as high quality polypropylene nonwoven geotextile, it is proposed to use flexible adhesive-bonded strain gauges. By carefully controlling the shape and thickness of the adhesive, the strain gauges can be co-deformed with the geotextile, realizing geotechnical work. Accurate measurement of cloth strain. At the same time, a set of equipment for stress and strain calibration of wholesale polypropylene nonwoven geotextile was developed. The measured values of strain gauges can be converted into the actual force of the polyester nonwoven geotextile for sale tested and applied to the centrifugal model test. The research results provide technical support for the next step to study the reinforcement mechanism of polypropylene nonwoven geotextile factory price and its influence on the stability of the bag sand cofferdam.
Keywords: polypropylene nonwoven geotextile manufacturers; strain measurement; resistance strain gauge; flexible glue; centrifugal model test
1. Research background
In recent years, the geotextile reinforced structure has been widely used in highway, levee, railway and other engineering construction with its good engineering characteristics, bringing good economic and environmental benefits. However, relevant theoretical research is still far behind its practical application, which limits the further development of this technology. In order to understand the working performance of wholesale polyester nonwoven geotextile, study its reinforcement mechanism, and improve its design theory, it is necessary to monitor the deformation of polyester nonwoven geotextile factory price in the structure.
Resistance strain gauge measurement is most commonly used in strain measurement of geosynthetics. In this method, the strain gauge is attached to the surface of the object to be tested, and the strain change process of the measured point is recorded by the principle that the resistance of the strain gauge changes with the mechanical deformation of the object to be measured. Whether the measurement result is reliable depends mainly on two aspects: 1 Whether the glue attached to the strain gauge can ensure that the strain gauge and the measured object are co-deformed, that is, the stiffness of the colloidal material should be less than the stiffness of the measured object; 2 whether the colloidal material can ensure the durability of the strain gauge connected to the object to be tested. At present, the commonly used epoxy resin adhesive and 502 adhesives generally have the disadvantages of high bonding strength and poor ductility and are obviously not suitable for the low elastic modulus and low strength flexible material of polyester nonwoven geotextile manufacturers. This shows that the resistance strain gauge measurement method needs to be improved or improved when used for polypropylene nonwoven geotextile factory price deformation measurement.
Based on the above considerations, this paper has made further research on the measurement method of polypropylene nonwoven geotextile for sale strain. Through a series of tensile tests, the low elastic modulus strain colloid suitable for high quality polypropylene nonwoven geotextile is sought, and the reasonable bonding method is discussed. The calibration of the stress and strain of the polypropylene nonwoven geotextile manufacturers is completed so that the measured value of the strain gauge can be directly converted into the force of the wholesale polypropylene nonwoven geotextile. Size and apply the above results to the centrifugal model test.
2. Selection of strain gauge adhesive
In order to find a suitable strain gauge adhesive, it is necessary to first grasp the basic mechanical properties of the high quality polyester nonwoven geotextile and the alternative adhesive of the tested object, so a series of tensile tests of geosynthetic materials were carried out. The test instrument adopts CSS-3900 series electronic creep tester of Yangtze River Scientific Research Institute. The instrument consists of 3 independent loading and measuring systems with a high degree of automation, direct reading, good precision, and stability. The medical object is selected from medical gauze as the research object. It has low rigidity, small strength, and strong representativeness. It is often used as a model material for polyester nonwoven geotextile for sale in the centrifugal test. The alternative glue has traditional epoxy resin and flexible. 703 glue. According to the requirements of the specification, the gauze is cut into a wide strip sample with a width of 200mm and a length of ≥200mm during the test; the colloid is made into a narrow strip sample with a width of 50mm and a length of ≥200mm; the tensile rate of the set fixture is 20mm/min, Continue running until the sample is pulled.
Figure 1 is a tensile test curve of the gauze of the test object and the candidate glue. As can be seen from Fig. 1, the tensile force of the clamps at both ends increases as the elongation of the three materials increases. The gauze sample is gradually broken when the tensile force is increased to about 250N and the elongation is about 13%; and the deformation of the 703 strips continues throughout the test, just like the rubber band, just purely When the two ends of the clamp reach the maximum opening degree, there is no breakage and breakage, showing excellent ductility; on the contrary, the epoxy resin increases the tensile force to 300N and the elongation is less than 5%. At that time, it is completely broken, and the curve is steeply dropped, which is a typical brittle failure.
The results in Figure 1 were sorted out and the basic mechanical parameters of the three materials were obtained, as shown in Table 1. It can be seen from Table 1 that the strength and rigidity of the commonly used epoxy resin glue are much larger than the gauze of the tested object. If such glue is used to attach the strain gauge, the result can be imagined, even if the polyester nonwoven geotextile factory price is greatly deformed or even pulled off, The strain gauge measurements will also be very weak and obviously not suitable for strain measurement of high quality polypropylene nonwoven geotextile. The flexible 703 glue fully meets the requirements, and its tensile modulus is only 40% of the gauze of the measured object, which is much lower than the rigidity of the measured object, which can ensure the deformation of the resistance strain gauge and the wholesale polyester nonwoven geotextile.
3. How to apply the strain gauge
Through the above tensile test, the basic mechanical parameters of the gauze and the selected glue of the test object were obtained, and the flexible 703 glue was selected as the adhesive of the strain gauge on the wholesale polypropylene nonwoven geotextile. On this basis, the tensile test research on the bonding method of the adhesive is carried out, and the measurement results are true and reliable by finely controlling the bonding shape, size, thickness of the adhesive layer, the spacing of adjacent measuring points, and the like.
At the center of the cut wide gauze sample, apply a round dot and apply two circular dots with a pitch of 150mm on both sides, as shown in Figure 2. Contrast analysis on the premise that the shape of the rubber layer is circular and the spacing between the measuring points is 150mm, the influence of the thickness and size of different rubber layers on the basic mechanical properties of the gauze of the tested object, and the suitable bonding method is discussed.
After a lot of experiments, it is found that when the contact surface between the polyester nonwoven geotextile manufacturers and the adhesive is circular, the diameter D of the adhesive layer is 35mm, the thickness H is 3mm, and the spacing between adjacent measuring points is L≥150mm, which can satisfy the strain gauge on the high quality polyester nonwoven geotextile. Paste the requirements so that the two are cooperatively deformed.
Figure 3 is a tensile test curve of the polyester nonwoven geotextile factory price in the above case. It can be seen from Fig. 3 that the tensile force of the sample increases with the increase of the elongation of the gauze and the deformation tendency thereof is basically the same as that of Fig. 1(a). Whether it is one or two glue points on the polyester nonwoven geotextile for sale, the maximum tensile force is basically between 200 and 250N, and the strain at the time of failure is basically the same.
The results in Fig. 3 were sorted out, and the basic mechanical parameters of the three samples were obtained, as shown in Table 2. It can be seen from Table 2 that, with the above-mentioned pasting method, the tensile strength of the wholesale polypropylene nonwoven geotextile itself is hardly affected regardless of whether there are one or two glue points on the geotextile; the tensile modulus is slightly improved, but the growth rate is also basically controlled. Within 10%, it can be ignored.
In summary, the flexible strain gluing and sticking method recommended by the author does not affect the strength level of the polypropylene nonwoven geotextile for sale itself, but also ensures that the strain gage and the polypropylene nonwoven geotextile manufacturers of the test object are co-deformed, and the colloid itself has good bond strength and durability, can be used for the adhesion of strain gauges on geotextiles, measuring the deformation size.
4. Calibration of stress and strain
4.1 Test equipment and methods
In order to obtain the true force of the wholesale polyester nonwoven geotextile in the structure, firstly, the stress and strain calibration of the geomembrane resistance strain gauge measurement method is completed, that is, the relationship between the strain measured by the resistance strain gauge and the strain of the high quality polypropylene nonwoven geotextile is found. How to accurately measure ε1 and εp (ε1 is the strain measured by the strain gauge, εp is the strain measured by the laser displacement sensor) is the key technical problem to be solved.
Based on the above research results, the deformation of the polypropylene nonwoven geotextile for sale is measured by the flexible adhesive-bonded strain gauge, and ε1 can be obtained. The εp is measured by a self-processing test device using a laser displacement sensor. The measurement principle is shown in Fig. 4, that is, the displacement change amounts ΔL1 and ΔL2 of the measuring point 1 and the measuring point 2 are respectively obtained by the laser displacement sensor, and then the true strain εp=(ΔL2-ΔL1)/L0 of the high quality polyester nonwoven geotextile can be calculated, wherein L0 is the original distance between the measuring point 1 and the measuring point 2. This measurement method is a non-contact measurement and does not affect the stress state of the polypropylene nonwoven geotextile factory price itself. In addition, the sensor has a high acquisition density (1s) and can be accurate to 1nm, which is stable and reliable.
The test adopts the staged loading mode. Each stage applies a pulling force of 6.25N (ie, a weight of one weight), a total of 8 levels of 50N, and the loading interval of each stage in the 60s. The deformation of the polyester nonwoven geotextile manufacturers is performed by a laser displacement sensor and strain gauge during the test. Full process monitoring.
4.2 Equipment feasibility verification
The tensile test of the gauze was carried out by using the self-processing test equipment and the designed test method, and the deformation of the gauze during the test was measured using a laser displacement sensor. The results obtained from the test are compared with the mechanical index parameters measured by the electronic creep test in Section 2 to verify whether the test equipment and test method are feasible.
The test object is also a gauze wide strip sample. During the test, the elongation of the two measuring points ΔL1 and ΔL2 are recorded in the whole process, and the strain corresponding to each loading is calculated by the formula εp=(ΔL2-ΔL1)/L0. The tensile-strain curve of the gauze of the measured object is shown in Fig. 5. It can be seen from Fig. 5 that the strain of the gauze grows steadily as the tensile force increases, and the strain and the tensile force change linearly. The gauze is in the elastic stretching stage. The slope of the curve corresponding to each sample is basically the same, indicating that the test loading process is stable and the equipment is reliable.
The tensile moduli of the six groups of samples were calculated to be 8.41, 7.40, 8.43, 8.39, 7.41, 8.67 kN/m, and the average value was 8.12 kN/m. In Section 2, the tensile modulus was measured by a tensile machine to be 8.65 kN/m. The comparison shows that the tensile modulus of the polyester nonwoven geotextile for sale measured by the two test equipment and methods is basically the same. It can be proved that the self-processing test equipment is reliable, the method is feasible, and the test result is accurate.
4.3 Results calibration
The calibration object is still a wide strip sample. When attaching the strain gauge, ensure that the contact surface between the polypropylene nonwoven geotextile manufacturers and the 703 glue is circular, the diameter D of the glue layer is 35 mm, and the thickness H is 3 mm. During the test, the whole process of deformation of the wholesale polyester nonwoven geotextile was monitored by the resistance strain gauge and the laser displacement sensor. The calibration equipment is shown in Fig. 6.
Figure 7 shows the measurement results of the strain gauge and the laser displacement sensor. It can be seen from Fig. 7 that the gauze strain increases with the increase of the loading strength. The two measurement methods, especially the strain gauge readings, increase in a typical stepwise manner, and the growing range is relatively uniform, and the polyester nonwoven geotextile factory price is always in an elastic deformation state.
The measurement result of the laser displacement sensor in each loading stage in Fig. 7(b) is converted into the strain εp of the high quality polyester nonwoven geotextile, and the relationship curves with the strain ε1 measured by the resistance strain gauge in Fig. 7(a) is plotted, as shown in Fig. 8. Show. By combining the trend line equations of the three sets of samples, the relational expression between ε1 and εp can be obtained, as shown in Equation 1.
At this point, the self-processing test equipment and the designed test method are used to complete the calibration of the stress and strain of the polypropylene nonwoven geotextile for sale, so that the resistance strain gauge reading can be directly converted into the actual strain of the wholesale polypropylene nonwoven geotextile by the formula (1), and then multiplied by The tensile modulus is the force applied to the measured object.
5. Centrifugal model test
In response to the specific conditions of the construction of a reclamation project in Tianjin, the author carried out a centrifugal model test on the filling of sandbags on a soft foundation. During the test, the strain measurement method was used to monitor the whole process of the polyester nonwoven geotextile manufacturers. The results show that this method is feasible, and the stress-strain distribution of different layers of high quality polypropylene nonwoven geotextile is successfully measured, which provides technical support for the next step to study the reinforcement mechanism of geotextiles and its influence on the stability of mold sand cofferdams.
Figure 9 shows the layout of the strain gauges in the model test. The deformation monitoring of the two layers of polyester nonwoven geotextile for sale at different heights was carried out. The specific circumstances of the test can be found in the literature.
Based on the stress-strain calibration formula (1), the curve of the force of the two layers of polypropylene nonwoven geotextile factory price with time can be obtained, as shown in Fig. 10. It can be seen from Fig. 10 that as the centrifugal acceleration increases step by step, the polyester nonwoven geotextile factory price force in the model increases, mainly concentrated on the low-floor geotextile, and the third layer geotextile at the interface between the two platforms is the most stressed.
Aiming at the difficulty of geotextile deformation monitoring and low precision, the strain gauge is selected as the measuring method, and a series of tensile tests are carried out. It is proposed to use the flexible adhesive to attach the strain gauge, and the shape and thickness of the adhesive are finely bonded. The control makes the strain gauges co-deform with the polyester nonwoven geotextile manufacturers, thereby achieving a more accurate measurement of the polypropylene nonwoven geotextile for sale strain. Made the following conclusions:
(1) The traditional epoxy-polyester glue is a typical brittle glue, which has high strength and high rigidity and is not suitable as an adhesive for strain gauges on geotextiles. 703 glue is a kind of flexible glue, which has good ductility, rigidity is much lower than that of high quality polyester nonwoven geotextile, and can be deformed cooperatively with the measured object. When the strain gauge is attached, the contact surface with the object to be tested is guaranteed to be circular, and the diameter of the rubber layer is 35mm. The thickness is 3mm.
(2) A set of equipment for stress and strain calibration of polypropylene nonwoven geotextile manufacturers was developed. The deformation of gauze was successfully measured by the laser displacement sensor, and compared with the microstrain measured by the strain gauge, the actual strain εp of the polypropylene nonwoven geotextile factory price was obtained. The relational expression of the measured value ε1 of the strain gauge.