Tensile machine, tensile testing machine is widely used in all kinds of hardware, metal, rubber plastic, footwear, leather, clothing, textile, insulation, wire, cable, terminal…And all kinds of materials, test its stretch, tear, peel, compression, bending and other materials development, inspection test, the function of its complete, widely used.But we in the use of tensile testing machine for testing sample inspection during mechanical testing, tensile testing machine clamp has often found sliding surface, and use the longer, the sliding surface, the more serious, which will affect the accuracy of the testing data, understand the cause of the tensile testing machine fixture skid only analysis and find out the corresponding countermeasures, only can ensure the accuracy and reliability of the experimental data.
Influence of sliding of tension testing machine fixture on test data
One, with a tensile testing machine for metal material tensile experiments, the testing data can be directly on the computer is revealed with yield strength and tensile strength (most commonly used metal materials yield strength and tensile strength test for the target), there is no sliding surface figure – the force deformation and elongation is to carry on the measurement, sample after cracking tensile machine skid has no effect on it, so let’s analyse tension tester jig separation skid to the yield strength and tensile strength of the influence of the two testing data.
Second, the impact on the yield strength of metal materials in general through three deformation while tensile testing time: the time of elastic deformation, yield and plastic deformation time, when a skid force – initial time deformation figure in metal materials, deformation and by external force is generally a linear share link, then if the external force, deformation of the material will also see, restorable, commonly referred to as the time playing time, hooke law of physics, which is the fundamental law of describing this feature.When the stress exceeds the elastic limit, deformation is added quickly, and at this moment, in addition to elastic deformation, there is also some plastic deformation.When plastic strain is added sharply, a small channel of fluctuation appears in the curve, and this appearance is called yield.When the metal material appears the yield representation, the stress point at which the plastic deformation occurs but the force is not added at the experimental time is called the yield strength, and the upper yield strength and the lower yield strength should be distinguished. The maximum stress of the sample before the onset of the yield and the initial decline of the force is called the upper yield strength.The minimum stress at the yield time, regardless of the initial transient effect, is called the lower yield strength.Because of the lower yield point value is relatively stable, so with the aim of it as a material force, known as the yield point or yield strength, but when the external force increases to must degree, deformation and by outside force will no longer be a linear share link, then after the invisible force, deformation of the materials will not be able to completely disappear, exterior scale will not be able to completely restore to the original shape, this time is called plastic deformation.
The tensile strength of metal refers to the steel yield to a certain degree, because the internal grains arranged in a ab initio, its resistance to deformation can be made from scratch progress, deformation at this moment, although the development is very fast, but can only follow the progress of the stress and increase, until the maximum stress.Then, the steel resistance to deformation significantly decreased, and in the thinness of the greater plastic deformation, where the specimen section rapidly decreased, appear necking appearance, until cracking failure.The maximum stress of steel before it is cracked is called strength limit or tensile strength.If the metal tensile time sliding, sliding point in the plastic deformation time 3, because the computer in the tensile strength of point collection is the time for the whole tensile peak are collected, and skid point 3 is certainly under high, detection system will not skid point 3 as the tensile strength point, appeared in the system of the tensile strength of the points is the highest point in the process of tensile experiment, and tensile testing machine fixture skid effect without significant tensile strength.