The welded joint is a relatively narrow area, and there is a layered structure distribution of the structure in this narrow area, which leads to a gradient distribution of properties in the area. In the previous welding technology research, the entire welded joint was roughly studied as the same structure, and the mechanical properties of the welded joint were generally qualitatively evaluated by conventional tensile test, bending test and notched impact test. This method can only roughly judge the strength index of the joint performance, but it can't do anything about its plasticity index. In order to quantitatively evaluate the strength index and plasticity index of the welded joint, and provide powerful data for the improvement of the welding process parameters, a micro shear test was carried out. Data acquisition system is included Sintech30/G test machine and its associated computer system. The micro shear test process is: using the processed shear sample 4% nitric acid corrosion to show the weld and heat affected zone; measure the length of each joint area with a tool microscope, select the test starting point, the shear spacing of the base metal should be larger than the weld and heat affected zone, specifically larger How much should be determined by the type of welding; adjust the software parameters in the computer system connected to the test device so that each shear point can directly obtain the shear strength, shear yield strength and cross-sectional indentation rate of the point; In the shearing fixture, tighten the nut and start cutting; after a little shearing, loosen the nut and rotate the spiral micrometer to move the specimen forward by a shearing distance and shear again; after the specimen is cut, The shear strength, shear yield strength and cross-sectional indentation rate obtained at each shear point were input into the Graftool software for data processing to obtain a performance gradient curve of the entire welded joint. The micro-shear test results of 45# steel electron beam welding joints are shown in Table 1. t t a Shear area coordinate t t a Shear area - 419 241 24.86 Base metal -0.50 822 559 26.36 Weld - 430 232 18.18 Base metal -0.25 836 565 15.85 Weld - 408 222 20.01 Base metal 0.00 924 608 10.98 Weld - 428 230 20.98 Base metal 0.25 588 309 19.41 Weld - 420 235 21.70 Base metal 0.50 751 508 16.22 Weld - 457 320 15.01 Heat affected zone 0.75 554 425 16.32 Weld - 416 246 18.84 Heat affected zone 1.00 475 291 21.16 Heat affected zone - 475 260 18.71 Heat affected zone 1.25 420 234 20.70 Heat affected zone - 538 414 12.71 Heat affected zone 1.50 431 241 21.80 Heat affected zone - 858 791 12.85 Weld 1.75 428 249 20.73 Heat affected zone JIANGSU ARTSTYLE DECORATION MATERIALS CO..LTD , https://www.jsadpvcwallpaper.com
The shearing tool in the test system is a r12MoV material with high strength, high hardness, high hardenability and wear resistance for the straight knife edge, and the clamp for the micro-shear test can be firmly clamped during shearing. kind. After a test point has been cut, it must be possible to control the sample to move back and forth in the fixture, and the distance of the movement can be directly measured, that is, the shear gap can be large or small. The micro shear sample is a strip sample of (1.5 ± 0.02) mm × (1.5 ± 0.02) mm square.
This test system is suitable for performance testing of welded joints and for the evaluation of mechanical properties in any narrow area of ​​any heterogeneous material. At present, the shear distance of this test system can reach 0.1 mm by using the multi-sample variable starting point method.
Table 1 Micro-shear test data of 45# steel electron beam welding joint Coordinate /mm