JPH10318897A - Test method for impact fracture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily generate a brittle fracture by a method wherein a tensile shock wave which is introduced as a compressive shock wave from the shock incidence end of a specimen, which is reflected by the free end of the specimen and whose polarity is inverted so as to be turned down and a tensile shock wave which is introduced from a shock incidence end are superposed in the prescribed position of the specimen. SOLUTION: A compressive shock load is applied to the shock incidence end 3 of a specimen 1 in which a defect part 7 is formed. The motion of the specimen 1 to the direction of a compressive shock caused by the compressive shock load is stopped by a rigid block 4 near the shock incidence end. Thereby, a tensile shock wave is introduced into the specimen 1. The time which stops the motion by the rigid block 4 is set in such a way that the tensile shock wave is introduced by the stop of the motion and a tensile shock wave at a time when a compressive shock wave is reflected by the free end of the specimen 1 so as to be turned down by inverting its polarity are superposed in the defect part 7. The length of the specimen 1 is set in such a way that a direction in which a stress wave is propagated is decided to be single, and the cross-sectional shape of the specimen 1 may be an arbitrary shape such as, e.g. a circular shape, an H-shape or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a bridge, an elevated road,
BACKGROUND OF THE INVENTION The present invention relates to an impact fracture test method for testing a material, particularly a steel material, when an impact load caused by an earthquake or the like is applied to a structure such as a building or a tank, particularly a steel structure.

[0002]

2. Description of the Related Art As a test method for impact fracture, split Ho
The pkinson bar method, the stress bar method, the One Bar method, and the like are known (Keizo Kishida "Dynamics of solids" (Baifukan) p.96).

FIG. 5 shows a method most widely used as an impact fracture test method called a split Hopkinson bar method. In this test method, a short columnar test body is sandwiched between two long elastic rods (incident rod and transmission rod).
The stress wave generated by the collision of the impact rod 2 with the incident rod propagates through the incident rod, and a part of the stress wave is introduced into the specimen 1. By measuring the stress wave between them using the strain gauge 6 attached to the incident rod and the transmission rod, it is possible to know the relationship between the stress and the strain caused by the stress wave generated in the specimen sandwiched between the incident rod and the transmission rod. Can be. The stress bar method and the One Bar method are
This is a test method improved from the nson bar method. Initially, all were used as compression tests, but in recent years, they have also been used in tensile tests depending on how to apply an impact load.

[0004] However, all of the above-mentioned test methods are intended for small test specimens. In order to cause impact fracture in materials such as steel and other materials with high ductility and toughness, a large specimen close to the actual material size is required.However, if the above test method is applied to a large specimen as it is, it will be extremely large. An impact load generator is required. For this reason, it was not possible to easily select a steel material capable of withstanding the impact of the earthquake.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for simply testing the impact fracture of materials such as steel used for various buildings without using a large-scale impact load generator. I do.

[0006]

Means for Solving the Problems In the following description, "impact fracture" refers to destruction by a shock wave. The type of fracture is mainly brittle fracture, but low ductility fracture, grain boundary fracture, etc. Including. "Shock waves" will be discussed separately for tensile shock waves and compression shock waves. "Tensile shock wave" means that the tip of the shock wave traveling through the material has a tensile polarity, and "compressive stress wave" means that the tip of the shock wave has the polarity of compression. Point out.

The present inventor was able to confirm the following items by analyzing various types of machinery and buildings in which impact fracture actually occurred.

(A) When the shock wave is not so large,
With a single shock wave, it is difficult to cause impact fracture of a steel material or the like that is rich in toughness and ductility.

(B) When the shock wave introduced from the outside and the shock wave reflected from the end face thereof are superimposed, they are strengthened to form a large shock wave. The position where the large shock wave is generated can be set to an arbitrary position in consideration of the propagation speed of the shock wave in the test object, the reversal of the polarity of the shock wave at the free end of the test object, and the like.

The present invention has been completed by repeating a basic test and an actual size test based on the above matters, and the gist of the present invention lies in the following test method (see FIGS. 1 and 2 described later).

(1) A tensile shock wave 13 introduced from the shock incident end 3 of the specimen 1 as a compression shock wave 11, reflected at the free end 8 of the specimen, inverted in polarity, and turned back, and a tensile shock wave 13 introduced from the shock incident end 3. An impact fracture test method in which a shock wave 12 is superimposed at a predetermined position on a test body and the test body is subjected to impact fracture.

(2) A compressive shock load is applied to the shock incident end 3 of the test piece 1 provided with the defect portion 7 to generate a compression shock wave 11
And the rigid block 4 prevents the movement of the specimen in the direction of the compression impact caused by the compression impact load by the rigid block 4 so that the tensile shock wave 12 is introduced into the specimen and blocked by the rigid block. Is set so that the tensile shock wave 12 introduced by the inhibition is superimposed on the tensile shock wave 13 which is reflected at the free end 8 of the test piece, inverts the polarity and turns back, at the defect portion 7. The impact fracture test method of the above (1).

In the above description, the "specimen" is a specimen having a length such that the direction in which the stress wave propagates is determined in one direction. The cross-sectional shape may be arbitrary, such as circle, square, H-shaped, I
It may be a type or the like. The direction in which the compression impact load is applied is referred to as “compression impact direction”. As a result of the compression impact load, the specimen starts to move in the same direction as the compression impact direction. In (2), specific methods of “blocking by a rigid block” include a method of blocking by making a stationary rigid block collide with the vicinity of a shock incident end of a test piece, and a method of blocking in a direction opposite to a compression shock direction. Includes both methods of moving the block and also colliding and stopping the specimen. The timing of the stop is determined by the tensile shock wave 12 introduced into the specimen by the stop.
Is determined in consideration of the propagation speed of both shock waves of 5000 m / sec so that the returning tensile shock wave 13 and the folded shock wave 13 meet at the defect portion 7. The “defect” corresponds to a notch, poor welding, brittle welding bead, or the like.

[0014]

FIG. 1 is a diagram schematically illustrating a test method of the present invention. As the impact incident end 3 of the test body 1,
For example, a striker is attached, and the compression impact load 2 is a bullet flying at a high speed, for example.

FIG. 2 is a diagram showing a position of a shock wave on a test body.

When the bullet collides, a compression shock wave 11 is introduced into the specimen. Thereafter, when the striker integrated with the test piece is prevented from moving by the rigid block 4, a tensile shock wave 12 is introduced into the test piece 1 by inertial force. The initially introduced compression shock wave 11 travels about 5000 m in the specimen.
Per second and reaches one end, which is a free end, and turns back as a tensile shock wave 13. The propagation speed of the tensile shock wave is about 5000 m / sec, which is the same as the propagation speed of the compression shock wave.

FIG. 2 shows the position of each shock wave on the test piece. When the tensile shock wave 13 is superimposed on the tensile shock wave 12 that is incident later, a large tensile shock wave 14 is generated. Therefore, when the two tensile shock waves 12, 13 are superimposed on the defect 7, the superimposed tensile shock 14 is instantaneously generated at the defect 7, and the defect is exposed to a tensile stress having a very high strain rate. As a result, if there is a defect such as an appropriate notch or poor welding near the position where the amplitude of the superimposed tensile shock wave 14 is maximum, impact fracture occurs at this portion. At this defect, a triaxial stress state with a high strain rate appears and often takes the form of brittle fracture, but when the amplitude of the tensile shock wave is large, low ductile fracture may occur.

The propagation timing of the shock wave is about 5,000 m by the timing of the incidence of the tensile shock wave which is incident later on the first compression shock wave.
It is always possible to form the superimposed tensile shock wave 14 at a predetermined position such as a defective portion by appropriately shifting in consideration of / sec.

[0019]

Next, the effects of the test method of the present invention will be described with reference to examples.

FIG. 3 shows the test method of the present invention. The test material is a reinforcing bar (nominal diameter of 9.53 mm) having a length of 5 m. A steel slab was attached to one end of this reinforcing bar as a shock incidence end face, and used as a striker. Clearance between striker and rigid block △ L
Was 10 mm. In addition, a strain gauge was attached at a position 2 m from the free end, and a brittle weld bead 7 was placed at the surface position facing the strain gauge at a position 2 m.

The test was performed in the following procedure. A bullet weighing 5 kg was fired at 10 m / sec by high-pressure gas and hit a striker. The time interval between the first compressive stress wave and the tensile stress wave incident by the subsequent collision with the rigid block is about 0.001 second.

As a result of the above test, impact fracture occurred at the toe of the weld.

FIG. 4 shows a time change of the strain measured by the strain gauge 6. First introduced compression shock wave 1
A superimposed tensile shock wave 14 as large as 1 was measured. The impact fracture is generated by the superimposed tensile shock wave 14.
The fracture surface generated by the impact fracture exhibited a brittle fracture surface having a cleavage surface.

[0024]

The superimposed tensile shock wave in the test method of the present invention can easily generate a brittle fracture even in a steel structure where brittle fracture cannot be caused by the shock wave according to conventional common sense. As a result, useful data can be obtained on materials having a seismic resistance and construction methods, which greatly contributes to the advancement of technologies for seismic materials and construction.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the test method of the present invention.

FIG. 2 is a view showing a position in a test body of a stress at a tip end of a shock wave in the test method of the present invention.

FIG. 3 is a diagram showing a test method according to an example of the present invention.

FIG. 4 is a diagram showing a change with time of strain measured in an example.

FIG. 5 is a view showing a Split Hopkinson bar method which is a conventional test method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Test body 2 ... Impact load object 3 ... Shock incidence end 4 ... Rigid block 5 ... Specimen support 6 ... Strain gauge 7 ... Defect part 8 ... Free end 11 ... Stress at the tip of compression shock wave 12 ... At the tip of tensile shock wave Stress 13: Stress at the tip of folded tensile shock wave 14: Stress distribution at the time of occurrence of superimposed tensile shock wave

Claims (2)

[Claims] A tensile shock wave which is introduced from a shock incident end (3) of a test body (1) as a compression shock wave, reflected at a free end (8) of the test body, inverts the polarity and turns back, and a shock incident end (3).
And a tensile shock wave introduced from the above is superimposed at a predetermined position on the test body to cause the test body to break. 2. A compressive shock load is applied to a shock incident end (3) of a test piece (1) provided with a defect portion (7) to introduce a compressive shock wave into the test piece (1), and the compressive shock load is caused by the compressive shock load. The rigid block (4) blocks the movement of the test specimen in the direction of the compression shock in the direction of the compression shock, thereby introducing a tensile shock wave to the test specimen, and the timing of the blockage by the rigid block is
The tensile shock wave introduced by the inhibition is characterized in that the compressive shock wave is reflected at the free end (8) of the test specimen, reverses the polarity and overlaps with the returning tensile shock wave at the defect (7). 2. The method of claim 1, wherein