And analysis of the slip of the tensile testing machine fixture - Database & Sql Blog Articles

First, human factors cause the electronic tensile testing machine to slip

The human factor causing the slip of the electronic tensile testing machine is caused by the operator not performing the correct method of testing during the test. There are two main factors: the short clamping length of the specimen and the improper selection of the jaws of the clamp. .

1, the test clamping length is shorter

The correct use of the electronic tensile machine test machine fixture should be that when the clamping length of the test piece is the same as the length of the tooth surface of the clamp, the external force is used to push the jaws to generate initial friction on the clamping surface, and then pass the test. The movement of the machine beam is applied to the sample. When the friction force pulls the jaw (wedge shape), the larger the axial pulling force is, the larger the clamping force is due to the action of the inclined surface. The test machine clamp has two inclined wedge-shaped openings. According to the above clamping method, it is designed according to the uniform compressive stress. However, some operators did not operate according to the requirements of the testing machine. The length of the sample clamping was short, or the sample processing was too short, resulting in uneven stress on the wedge-shaped bevel. The local stress of the wedge-shaped opening far exceeded. The yield strength of the material causes the wedge-shaped opening to plastically deform and severely eversion, causing the wedge-shaped bevel to collapse or wear. The jig continues to be used in this case, and the angle of the wedge-shaped opening is reduced, so that the state of the clamp body is deteriorated and the slip phenomenon occurs.

2, the jaws of the fixture are not properly selected

The electronic tensile tester clip has a variety of different specifications and clamping faces. Different chucks are used for different samples. Some operators use large-size jaws to hold small-section specimens or flat collets when testing. The large sample is clamped, so that the contact between the clamp and the sample is not tight, and the friction coefficient is obviously reduced. The most intuitive performance is that the scaly peak of the clamp is smoothed by the divisor and the friction is greatly reduced. When the force of the sample gradually increases to reach the maximum static friction, the sample will slip and produce a false yield phenomenon from the surface.

Second, the equipment causes the electronic tensile testing machine sample to slip

The reason for the equipment is mainly that the tensile machine causes slippage due to the falling of the iron oxide skin into the wedge-shaped slope when the sample is pulled. The metal sample produces a metal oxide scale during the drawing process, and the iron oxide scale falls into the inclined surface of the wedge block and the jig, so that the flatness of the slope is broken, the surface roughness is seriously degraded, and the wedge-shaped opening (wedge block) The movement is inflexible, and as the pulling force continues to increase, the wedge block generates creep (jumping travel) along the sliding of the dovetail slope. This is the result of the sounds of the horns and horns that often occur during the stretching process. This is what is commonly referred to as slipping.

Electronic tensile testing machine fixture slipping solution

In view of the above reasons caused by human factors and equipment factors, Shanghai Enterprise Testing Instrument Co., Ltd. has formulated the following countermeasures, and the implementation of countermeasures can reduce or eliminate the phenomenon of pulling machine slip.

1. Specification of the operating procedures of the testing machine

For the short clamping length of the specimen and the improper selection of the clamp of the clamp, in the operating procedure of the electronic tensile testing machine, it must be specified: "The clamping length of the tensile specimen shall not be less than the length of the tooth surface of the clamp" and "No" Use a jaw for a large section to hold a small section specimen or a flat jaw to hold a large specimen. The operator must test according to the operating procedures.

2. Repair the wedge bevel

Plastic deformation and severe eversion of the wedge block, so that the wedge block slope collapse or wear should be repaired in time, the repair can generally take the following two methods

2.1, repair welding

The trapped or worn parts of the wedge block are first repaired and then restored by the inserting machine (should be scraped if the machining does not meet the roughness requirements). The hardness and strength of the repaired parts are generally improved, and it is ok to use the jig correctly later.