Abstract:
A fixed value residual stress test block, comprising a main body ( 1 ) and two welded blocks ( 2 ); the main body ( 1 ) and the welded blocks ( 2 ) are all rectangular metal blocks; the welded blocks ( 2 ) are welded onto the two opposite side surfaces of the main body ( 1 ); the main body ( 1 ) is deformed under the upper and lower pressures and generates residual stress. The fixed value residual stress test block has a simple structure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a fixed value residual stress test block and manufacturing and preservation method thereof. The fixed value residual stress test block is adapted to correct an ultrasonic non-destructive testing system for residual stress. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    The non-destructive testing for residual stress is receiving much more attention, and the non-destructive testing method having vast potential of development at present is the residual stress testing with ultrasonic method. The ultrasonic method mainly tests residual stress by means of ultrasonic critical refraction longitudinal wave. The theory of ultrasonic stress testing has been very mature. However, the testing object of this method is relative value of residual stress, according to the theory. In order to test the absolute value of residual stress, it is necessary to develop a quantized standard test block for residual stress to correct a testing result and a testing system. 
         [0003]    The current study relating to a standard test block for fixed residual stress aims mainly at a x-ray diffraction. In this case, the metal powder of material to be tested is cast as a test block of a certain size, and the residual stress is standardized on the basis of the lattice change of the cast test block. Moreover, the researchers of the UK bend steel material to bow shape, so that a residual stress test block is manufactured by bending. The structure of these test blocks is very special, resulting in that the manufacturing method is too complicated to be achieved. For this, it is hoped to get a fixed value residual stress standard test block of simple structure, which is accurate and reliable and obtained by a simple method. 
       SUMMARY OF THE INVENTION 
       [0004]    The purpose of the invention is to provide a fixed value residual stress test block and manufacturing and preservation method for correcting an ultrasonic non-destructive test system for residual stress, so as to detect the absolute value of residual stress accurately and reliably. 
         [0005]    The fixed value residual stress test block comprises a main body and two welded blocks. Both of the main body and the welded blocks are rectangular metal blocks. The welded blocks are welded to two opposite sides of the main body. The main body deforms due to bearing a pressure in up and down direction, and generates residual stress. 
         [0006]    The fixed value residual stress test block according to the invention has a simple, accurate and reliable structure. 
         [0007]    The invention further provides a manufacturing method for fixed value residual stress test block, which has the following manufacturing procedure: manufacturing main body of the test block and two welded blocks; applying a pressure to the main body of the test block in up and down direction so as to deform the main body to generate residual stress; welding the two welded blocks to two opposite sides of the main body; canceling the pressure applied in up and down direction. 
         [0008]    The aforementioned method is very simple. The fixed value residual stress test block manufactured by the method is accurate and reliable. 
         [0009]    The invention further provides a preservation method for fixed value residual stress test block. The test block is stored in an environment with constant-temperature of which the range is 2˜8° C., and is kept away from impact and vibration. 
         [0010]    The preservation method can make the residual stress test block maintain stable residual stress. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  shows the side view of the fixed value residual stress test block; 
           [0012]      FIG. 2  shows the front oblique view of the fixed value residual stress test block; 
           [0013]      FIG. 3  shows the exploded view of position relationship between each parts of the fixed value residual stress test block; 
           [0014]      FIG. 4  shows the front oblique view of locating position of each parts of the fixed value residual stress test block; 
           [0015]      FIG. 5  shows the welding process of the fixed value residual stress test block. 
       
    
    
       [0016]    Symbols:  1 . main body,  2 . welded block,  3 . weld seam,  4 . upper pressure-head of compression-testing machine,  5 . lower pressure-head of compression-testing machine,  6 . measurement area. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    According to the invention, the fixed value residual stress test block is manufactured by weld. According to the invention, two welded blocks are generally welded on symmetric positions of a pressed main body. The tensile stress is generated to the welded blocks by rebound effect of the main body. The different deformation corresponds to the different stress. The test block having desirable stress can be obtained by controlling the deformation of the test block via calculation based on the theory. 
         [0018]    The embodiment of the invention will be described in detail with reference to the drawings. 
         [0019]    Take steel  45  for example, as  FIG. 1  shown, the size of the main body  1  is 30 mm×30 mm×130 mm. The size of the welded blocks  2  is 30 mm×5 mm×70 mm. 
         [0020]    Two welded blocks  2  are welded to both sides of the main body  1  of the fixed value residual stress test body. The welded blocks  2  are arranged at central position of the main body  1 . In a case that the main body  1  is pressed by a compression-testing machine, the welded blocks  2  are welded to the main body  1 . The rebound effect of the main body  1  generates a certain residual stress between the welded blocks  2  and the main body  1 . The residual stress value of the test block can be known on the basis of the deformation of the main body  1  and the welded blocks  2 . The different deformation corresponds to the different stress. 
         [0021]    The unidirectional pressure stress is generated by pressing the main body  1  of the test block within limit of elasticity. The main body  1  will rebound after pressure being canceled. The welded blocks  2  and the main body  1  before rebounding are welded together by welding technique, so as to restrict and interact with each other. Then, the tensile stress or pressure stress is generated between the welded blocks  2  and the main body  1 . According to this theory, the fixed value residual stress test block can be manufactured by pressing and welding and controlling the deformation of the main body  1  and the welded blocks  2 . The weld seam  3  is entirely continuous. 
         [0022]    In the process of manufacturing the test block, the key point is the accurate control for the deformation of the main body  1  and the welded blocks  2 . The accurate control for residual stress of the test block is based on the accurate control for the deformation. However, the preservation technique is also very important during the test block being used. 
         [0023]    The manufacture of the fixed value residual stress test block is as follows: 
         [0024]    Take steel  45  as manufacture material of the test block for example, as  FIG. 1  shown, it is formed to be two parts of the test block. The size of the main body  1  is 30 mm×30 mm×130 mm. The size of the welded blocks  2  is 30 mm×5 mm×70 mm. The surface roughness of the main body  1  and the welded blocks  2  is less than or equal to Ra6.4. 
         [0025]    The main body  1  and the welded blocks are tempered, so as to eliminate process stress of the test block and make the test block be in a stress-free state. 
         [0026]    According to the Hooke&#39;s law, the applied pressure, i.e. load applied by the compression-testing machine to end surface of the main body  1  is calculated, on the basis of the cross-sectional area of the main body  1  and the welded blocks  2  and required stress value of the test block. 
         [0027]    As  FIG. 2  shown, the two welded blocks  2  and the main body  1  are closely attached together by bounding. 
         [0028]    As  FIG. 5  shown, the main body  1  is put between the upper pressure-head  4  and lower pressure-head  5  of the compression-testing machine. The compression-testing machine is set based on predetermined (calculated) load to press the main body  1 . The hollow arrows in the figure show the pressed directions. The 30 mm×30 mm surfaces of the main body  1  are pressed surface. After a calculation load being achieved, the load is maintained stable for a while, and then the welded blocks  2  are welded to the main body  1  in a case that the load is not unloaded. It is ensured as far as possible that the main body  1  and the welded blocks  2  do no have obvious deformation during welding. The contacted edges of the contacted surface between the main body  1  and the welded blocks  2  should be entirely covered by weld seam. 
         [0029]    After the welding for welded blocks  2  being completed, an air cooling is applied to the test block in a case that the load is not unloaded. After the test block being cooled, the compression-testing machine is removed, and the manufacture for the test block is completed. After then, the stress of the fixed value test block is measured and recorded, and is compared to a theoretical value. 
         [0030]    If the welded test block having different residual stress is required, it only needs to apply different pressure to the main body  1 , and then perform an operation according to aforementioned steps. 
         [0031]    During correction of an ultrasonic non-destructive test system for residual stress using the fixed value residual stress test block, a detection sensor is paced on the welded blocks  2  along the pressed direction of the main body  1 , so as to couple the detection sensor to the test block well. After being stable, it starts to detect and correct the test block. As  FIGS. 3 and 5  shown, the fixed value measurement areas  6  of the fixed value residual stress test block are on the outer side surfaces of the two welded blocks  2 , and these two measurement areas  6  are only suitable to a detection method of ultrasonic critical refraction longitudinal wave and a detection method of surface wave. 
         [0032]    Currently, there are methods for eliminating residual stress in domestic and overseas, such as tempering, vibratory stress relief, ultrasonic wave impact, and natural stress relief. These methods achieves that local organization of the welded piece is reorganized under the action of alternative change of temperature and alternative load, such as vibration and impact, so that the residual stress is released. The stable constant temperature may reduce the thermal expansion and reorganization of the test block, so that the residual stress may be maintained for a long time. 
         [0033]    For this, in order to make the fixed value residual stress test block maintain a stable residual stress, the test block should be stored in constant temperature environment, such as calorstat, where the temperature is 2° C.˜8° C., after the fixed value residual stress test block being manufactured and the residual stress being measured, so as to eliminate the thermal expansion of the test block caused by alternative change of temperature, and to avoid the residual stress is continuously loosed. Furthermore, the impact and vibration which may cause the residual stress release should be avoided, during storing the test block. The change of the residual stress of test block is regularly monitored and recorded during storing the test block. The test block should be put back into the calorstat in time after correcting the ultrasonic detection system for residual stress at each time.