Stress-strain tests on the reinforced composite materials Study on the electrical properties of force

[Abstract] steel stress in reinforced concrete structures, in the use phase is difficult to detect. General application of a limited range of strain gauges, easily damaged during construction, and explore a new type of sensor is to reform the basis of steel stress test.

[Keywords:] composite piezoresistive effect sensor

First, the material properties and manufacturing processes do
Epoxy resin and curing agent from Eastern Chemical Industry Co., Ltd., Guangzhou City, the production of E-44 EP-type epoxy resin and hardener. Nanometer carbon black as Huaguang Chemical Plant, Shandong Zibo HG-IP (black powder), particle size of 33nm, nitrogen adsorption specific surface area of 1056m �� 2 / g, specific resistance to 0.22o.cm composite resin production process: first, the length of 200mm, the light circle ��14 smooth polished steel surface with ethanol surface cleaning, drying, its surface coated with a thin layer of epoxy resin (50% of adding Stir resin curing agent) about 0.2-0.5mm, to ensure the reinforcement and composite insulation. and put on the surface of reinforced foil strain gauge, model: BX120-3AA, Zhejiang Huangyan Testing Instrument Factory, and other curing day. The second step, check the certain ratio of epoxy resin and hardener, mix well, add diluent and tackifier, stirring a few minutes, then add a little something in the nano-carbon black, nano-carbon black as light and easy to join, easy mixing, add several additional points when, each sure to mix, together with the material. The third step in the reinforcement 2.5cm long middle painted within the composite resin mixing sufficient thickness appropriate, take about 1mm appropriate. let the winding copper wire, four, inside the two apart 1cm, the two lateral distance 2cm, finally outer layer of plastic film wound composite resin, let it cure.

Second, the test method and process
Composite resin curing polarization resistance measured after 3 days, 7 days curing Pressure resistance effect. Test the resistance testing methods used for the four-electrode method, the resistance measuring instruments for the Agilent Co.Ltd production HP34401A digital multimeter. Loading equipment produced by CMT5105 SANS Microcomputer controlled electronic universal testing machine. Gallas force in the test before the first specimen of the four-phase electrode and meter and multimeter with a data cable to the computer Unicom, and then measure the electrical zero load group. When the measurement of resistance to stable piezoresistive further test. Gallas force to 0.5mm/min speed of axial tensile specimens, and real-time collection of computer resistance, tension and strain.

Third, test results and analysis
As a smart coating thickness is a factor can not be ignored, the same conductive material Stir composite resin content, the different resistance of different thickness will be great to take this group B1 was studied in three thickness: 0.5mm, 1mm , 1.5mm, three specimens of each thickness, the conductivity of composite resin coating mix at the same time, with different thickness are also great differences, the coating is thin, the resistance greater, with the coating thickness increases, resistance decreases, due to the internal coating thickness of the conductive path changes with the change caused by epoxy resin is a thermosetting material itself is not conductive, the role of the curing agent to form a polymer structure of space, the addition of nano-carbon black, due to the conductivity of nano-materials, ability to increase the conductance of the polymer, the same mix of composite resin, inside the conducting channel increases with the thickness increased, the reduction reduced, which is the resistance decreases with increasing thickness of the reasons. consider the use of process issues, if resin coating is too thick, not easy to apply evenly, use the structure of the defects induced larger stress concentration serious. to take suitable thickness of about 1mm.

The nature of epoxy resin and curing agent largely related to the number of curing agent content on the resistance of composite resin has a great influence, but also affect the flow curve of composite resins, epoxy curing agents accounted for resin percentages were: 25%, 50%, 75%. With the reduction of the content of curing agent, the overall resistance decreased significantly, especially in nano-content is relatively low, the resistance was lower by orders of magnitude, with the nano-carbon black content increased, the difference is increasingly small, because with the increase of nano-materials, the density of the internal electrical conductivity through conductivity increases, the increase or decrease the curing agent only change the relative number of internal circuit, the conductive pathway reduced.

Links to Research Papers Download http://www.hi138.com piezoresistive effect of composite resin coating curing agent content tests taken were 25% and 50% for both groups. Nanoparticles concentration of 15% compound piezoresistive effect of the resin is poor, with 20%, 22.5%, 25%, 27.5% to study their alertness. with cyclic loading, the maximum load values were taken 30KN, 40KN. Each class load of five cycles. reinforced steel bar for the HPB235 diameter of 14mm, can be calculated obtaining the yield strength f �� y = 32.31KN. loaded cross-elasticity, plasticity in two stages. R0 is the initial resistance value is relatively stable, two sets of tests for seven days when the composite resin piezoresistive curve.

The first group, and the epoxy curing agent ratio of 0.25:1, the percentage from four different nano-composite resin coating of the smart characteristic curve, we can see that in the amplitude load cycles, the complex piezoresistive resin between the curve and the stress-strain curves there is a good mapping, with the increase of steel stress, the resistance rate of change of approximately linear change in the percentage of four different nano-composite resin content, the content of nano-particles 20% and 22.5% of the two curves than the 25% and 27.5% of the two curves more linear change is more obvious. With the increase of nano-carbon black content, the linear rate of change of resistance change slightly worse.

The second group, the ratio of epoxy resin curing agent is 0.5:1, the percentage of members from four different piezoresistive nano test results graph, we can see, this group nanoparticle content of 20% compound resin alertness becomes unstable, the cyclic loading process, the resistance change rate curve began to have more non-linear, 22.5% group still showed a good linear mapping, 25%, 27.5% group with the resistivity curve of cyclic loading performance is not stable, linear mapping worse.

IV, Conclusion
1. With the ratio of epoxy and curing agent to adjust the resistance showed regular changes, the greater the content of curing agent, the same nano-carbon black composite resin content the greater the resistance, the resistance of composite resin with reduced curing agent decreases when the ratio of epoxy resin and curing agent is fixed, resistance changes with the increase of nano-carbon black content decreases, the production process of the limit and even to know the characteristics of material properties with a combined ratio of resin, the resistance but there are some discrete.

2. Alertness performance also with the percentage of curing agent and epoxy resin and nano-carbon black content was the regularity of changes in the levels of two stress amplitude cyclic loading, the composite resin showed strength and resistance Good rate of change of the mapping, when reinforced by the elastic phase to plastic phase transition, the rate of change of the stress curve and resistance curve and strain curves showed good correspondence. With the role of cyclic loading time increases when the steel residual strain occurs, the resistance rate of change also will be irreversible changes.

3. Nanometer carbon black reinforced epoxy coating as a strain of the sensing material is possible.


References:
[1] LI. Shantou University, a master's degree thesis, 2006.

[2] Yang Baowu. Epoxy curing agents [J]. Bonding, 1993,14 (4), 1013 (9).

[3] Kwok-keung. Semiconductor strain gauge sensor application. Shandong Mining Institute, 1994,13 (3) :264-268.

[4] Zhang Lide, Mou. Nano materials and structures [M]. Beijing: Science Press, 2002.

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