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    Pull machine operation slip reason analysis
    Source:Kejian Instrument Time:2016-03-01
    A human factors, resulting in tension skid
    In operating a tensile machine, we often encounter tensile machine slippage phenomenon, resulting in tensile machine slippage of human factors is caused due to the operating personnel in the operation without according to the correct method of the test operation, mainly in the two aspects of factors: clamp jaw choice improper and sample holding length is short.
    1, the improper selection of jaw clamp
    Tensile machine clip with a variety of different specifications and the clamping surface, using different chuck for specimens with different, some operators in the test, use of large size jaw clip holding a small cross-section specimen, or using a flat chuck to large specimen, the specimen holder and not close contact, was found to reduce the friction coefficient, the most intuitive performance squamous spikes of fixture is smooth divisor, friction is greatly reduced. When the stress increases gradually reached the maximum static friction force, will produce a false sample slip phenomenon from the yield surface.
    2, test clamping short length
    In the specimen clamping length and a clamp tooth surface are of the same length. First, with external force pushing the jaw, the initial friction in a gripping surface, and moving through the tensile machine crossbeam of sample loading, force to pull the jaw (wedge) when because of the role of slope and the axial tensile force more, the holding force is greater, tensile machine clip specific has two inclined wedge mouth is basis the clamping way, in accordance with the accept even compressive stress on the design. However, some operators did not operate in accordance with the requirements of the use of pull machine, sample holder to a shorter length, or sample processing is too short, resulting in wedge mouth slope force, wedge mouth local stress much more than material yield strength, so that the wedge mouth produce plastic deformation, severe hallux valgus, the wedge mouth slope collapse or wear. Continue to use the fixture in this case reduces the wedge angle of the mouth, the jig body stress state and the deterioration of slipping phenomenon.
    Two, equipment causes tensile test specimen slips
    The equipment is mainly due to tension in the sample due to pull iron oxide into the wedge block caused by slipping. Metal sample in drawing process produced metal oxide tin, tin oxide will fall into the wedge block combined with the fixture of slope, the slope of roughness is destroyed, surface rough degree of serious decline, wedge mouth (wedge) movement is not flexible, in the increasing tension, a wedge-shaped block along the dovetail slopes sliding crawling (leaps). Often appear during tensile loading and horn, the sound is produced. This is usually said to slip.

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