When the distribution of residual stress along the thickness direction is relatively uniform, one-time drilling method can be used to measure the residual stress.

It indicates the stress condition near the tested point : one – and one Z are the residual principal stresses of point 0.P at the interval r from the measured point

At the point, roar and West indicate that the radial stress and tangential stress are released from the borehole respectively, and the included angle is .

1.  drilling equipment and drilling requirements .Type 1 drilling device

1) The steel structure of the drilling equipment should be simple, easy to carry, easy to fix on the components, convenient for centering, easy to control the drilling depth, and able to work on various curved surfaces.Fig. 4 is the structure diagram of the small hole drill, which can better meet the above requirements. With four nuts, the position of X and Y directions and the up and down positions can be adjusted, so as to keep the drilling hole perpendicular to the surface of the small piece. The universal joint is connected with the adjustable speed electric hand drill for drilling.

2) Technical requirements for steel structure drilling .

a. The treatment of the surface to be tested shall meet the technical requirements of strain measurement: the right angle strain gauge shall be accurately pasted at the measuring point with 502 glue

Put it on, and cover the wire grid with adhesive tape to avoid iron chips damaging the wire grid.

b. During drilling, make sure that the drill pipe is perpendicular to the measuring surface, and the deviation of drilling center shall be controlled within ± 0.025mm.

c. When drilling L, it shall be stable and the base shall not shake.If the drilling speed is slow and fast, the temperature of strain gauge will drift and the hole will be cut

The increase of strain makes the measurement unstable.In order to eliminate the influence of cutting strain, a small bit can be used to drill the hole l first and then the milling cutter can be used to enlarge the hole.

2.Measurement of residual stress in butt weld of flat plate.

Select several special points in the test: point a, B and C, close to the fusion line, and see Figure 5 for the location of measuring points.The voltage of the voltage regulator shall be kept at 60-70 V, and the feed amount shall be as small as possible.After the reserved hole depth is 2.0 mm, pull out 3 conclusions

Under the same welding condition, the residual stress of Q235-B is greater than Q345 B.Moreover, the residual principal tensile stress of Q235B is close to or beyond the yield limit of the material.Of course, under the condition of plane stress, the stress of individual points in the welded structure reaches the yield limit of the material, which does not mean that the surrounding materials all reach the yield, and the stress will be adjusted during the use of the structure.However, in order to ensure that the welding residual stress is not large, it is necessary to anneal the workpiece after welding.If the residual stress is too large, the welding process shall be adjusted properly.