Hits:Updated:2020-05-12【Print】
Through the testing test of the plastic bending strength of the tensile testing machine, we understand the structure and use method of the bending test accessories in the tensile testing machine, and obtain the determination of the bending strength, bending elastic modulus and stress-strain curve of the plastic.
The tensile machine provides two sets of test space, which allows the operator to have a wider range of use, especially when the gap between the strength of the raw material and the finished product is large. The floor type is adopted in the type, which is mainly used in steel wire, small screw fabric and other industries.
Bending strength refers to the strength at which the sample is placed on the two fulcrums of the tensile machine by the simple supported beam method, and a concentrated load is applied between the two fulcrums to deform the sample until it breaks. For non-brittle materials, the yield phenomenon will occur when the load reaches a certain value. The load at this time is also called the breaking load, and its strength is called the static bending yield strength. The flexural modulus of elasticity refers to the ratio of bending stress to strain of the material within the proportional limit.
The standard experimental methods of bending strength are two-point bending and four-point bending, and the qualitative distribution of loading method, bending moment and shear force. The difference between three-point bending and four-point bending is that there is a shear force in the middle of the sample, so the measured strength is not the strength under pure bending.
In order to eliminate the effect of shear stress, it can be compensated by increasing the span of the sample and increasing the radius of the loading indenter, or the four-point bending test method can be used for the experiment. However, the sample required for four-point bending is longer, the loading head structure is more complicated, and the loading balance is not easy to guarantee in the experiment. The three-point bending experiment is simple and applicable. Therefore, three-point bending is currently commonly used by tensile machines for plastic bending experiments. Methods. This experiment was also carried out using the three-point bending method.
Because the thickness has a great influence on the deflection, if the actual thickness of the plate and the required sample thickness are different, it must be corrected by mechanical processing, but at this time, it should be machined from one side, and the surface should be processed in the tensile machine experiment. Facing the loading head, the unmachined surface is stretched, which has no effect on the experimental results.
The factors affecting the bending experiment are the size and processing of the specimen, the radius of the indenter and the surface radius of the support, the experimental span, the experimental speed, the experimental environment and the nature of the material. Usually the thickness and width of the bent specimen are related to the bending strength and deflection. Increasing the thickness and width to increase the specimen cross-section increases the resistance to bending deformation.
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