October 11, 2022
Rebar process performance includes many items, according to the characteristics of different products can be put forward different requirements, such as ordinary rebar requirements for bending and reverse bending (reverse bending) test, some prestressed steel requirements for repeated bending, torsion, winding test.
All these tests are simulated in different degrees in the form of materials in practical use may be involved in the process of ways, such as ordinary steel hook or bend forming, prestressed steel wire sometimes need to coil, etc., and its purpose is to review the material for these specific plastic deformation limit to bear ability, thus, the material requirements of plastic process performance is also, And with the above ductility (elongation) requirements are similar, generally speaking, the elongation of steel, its process performance is good.
Compared with unidirectional stress when stretching, however, the stress of process performance test is much more complex, type and size of specimen deformation anisotropy (axial and radial), steel structure, grain size, especially harmful residual elements content any affect the continuous deformation of the surface and internal defects such as cracks, inclusions and so on can affect and lead to test does not pass. So in a sense, for examining the quality of steel, it can be said that the process performance test is more rigorous.
In addition, the reverse bending test of reinforcement is essentially a strain aging sensitivity test. This is because molten steel generally contains a certain amount of free nitrogen (N), also known as residual nitrogen. If the content is too high, the steel will be embrittlement at room temperature after plastic deformation.
By steel often need to be used after bending forming, has produced plastic deformation, if sexual brittle material, structure and cannot afford to make reinforcement of plastic deformation and load, such as earthquake, so will reverse bend test at home and abroad as an important technical requirements on steel standard, at the same time limit to the nitrogen content of the steel (no more than 0.012%).
Research suggests that for steel microalloyed elements such as vanadium, titanium, niobium, etc., especially vanadium and nitrogen have good affinity, adding vanadium in steel can be effectively combined with free nitrogen, the combination of vanadium and nitrogen can further enhance the strengthening effect of vanadium in steel, so some standards also indicate "if there is enough and nitrogen element nitrogen content can be higher than standard".
Because the anchorage agent is made of high strength material as aggregate, cementing material as binder, supplemented by high flow state micro swelling anti-segregation and other substances, its composition is mainly inorganic materials, organic materials as auxiliary, no rust effect on reinforcement. Therefore, a certain anchorage force can be generated within a few hours. It has the characteristics of fast setting, fast hardening, high strength, no shrinkage, high shear strength and low penetration resistance. This method is applicable to all mine roadway, tunnel, water conservancy, slope support and other projects within 3m surrounding rock bolt support.
Mechanical properties of
The mechanical properties of the steel bar are measured by testing. The mechanical properties of the quality standard of the steel bar are yield point, tensile strength, elongation, cold bending performance and other indicators.
Yield point (fy)
When the stress of the steel bar exceeds the yield point, the tensile force does not increase while the deformation increases significantly, resulting in a large residual deformation, the tensile force value of the steel bar per unit area is obtained by dividing the tensile force value by the cross-sectional area of the steel bar, which is the yield point σs°
Tensile strength (fu)
The tensile strength is the tensile strength obtained by dividing the maximum tensile strength that the steel bar can bear before being pulled apart by the cross-sectional area of the steel bar. The tensile strength is also known as the ultimate strength. It is the largest stress value in the stress-strain curve, although it has no direct significance in the strength calculation, but it is an essential guarantee item in the mechanical properties of reinforcement. Because:
(1) The tensile strength is the ultimate capacity of the steel bar under static load. It can represent the strength reserve of the steel bar after reaching the yield point, and is an important index of resistance to plastic failure.
(2) steel smelting, rolling process defects, and the chemical content of steel is not stable, often reflected in the tensile strength, when the carbon content is too high, the temperature is too low at the end of rolling, tensile strength may be very high; When the carbon content is small, the steel contains too many non-metallic inclusions, the tensile strength is low.
(3) the level of tensile strength has a direct impact on the ability of reinforced concrete structure to resist repeated loads.
elongation
Elongation, also known as elongation, is the maximum strain value when the specimen is pulled in the stress-strain curve. It is an index to measure the plasticity of the steel bar. It is also an essential guarantee item in the mechanical properties of the steel bar, like the tensile strength.
Elongation is calculated as the percentage of the original length of a steel bar that is stretched when it breaks under tension. By combining the two fractured sections of the specimen, the length of the standard segment after fracture, L1, can be measured, and subtracting the original length of the standard segment, L0, is the plastic deformation value. The ratio between this value and the original length is denoted by δ, that is, the larger the elongation δ value, the better the plasticity of the steel. The elongation is related to the standard distance. For the standard distance of the hot rolled steel bar, 10 times the diameter of the specimen is taken as the measurement standard, and the elongation is expressed as δ10. For the steel wire, the mark distance length of 100mm is taken as the maximum test standard, denoted by δ100. For steel strand, δ200.
Cold bending performance
Cold bending performance refers to the steel bar in the cold processing (that is, processing at room temperature) plastic deformation, the resistance to crack. Cold bending test is a test to determine the ability of steel bar to bear bending deformation at room temperature. The test should not consider the size of the stress, and the diameter of the steel specimen d, around the diameter of D bending center (D specified 1d, 3d, 4d, 5d) into 180° or 90°. Then check whether the steel sample has cracks, scales falling, fracture and other phenomena, to identify whether its quality meets the requirements, cold bending test is a strict test, can reveal the internal structure of steel and other defects.
Mechanical properties of
1) The mechanical properties of the steel bar shall conform to the following table: grade nominal diameter mmσs
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2) The total elongation of reinforcement at maximum force δgt is not less than 2.5%. If the supplier can guarantee, no inspection is required.
3) According to the requirements of the buyer, can supply meet the following conditions of reinforcement:
a) The ratio of the measured tensile strength to the measured yield point of reinforcement is not less than 1.25;
b) The ratio of the measured yield point of reinforcement and the minimum yield point specified in the above table shall not be greater than 1.30.
Process performance
1) Bending performance
After bending 180 DEGREES according TO THE bending center diameter specified in the table below, the surface of the bending part of the steel bar shall not produce cracks. Grade nominal diameter a
2) Reverse bending performance
According to the requirements of the customer, the reinforcement can be tested for reverse bending performance.
The diameter of bending center in reverse bending test is correspondingly increased by one steel bar diameter. First forward bend 45 degrees, then reverse bend 23 degrees, then reverse bend 23 degrees. After the reverse bending test, the surface of the bending part of the steel bar should not crack.
