Application of plastic tensile testing machine in bending strength
Plastic bending strength refers to the strength when the sample is placed on two fulcrums of plastic tensile testing machine by simply supported beam method, and a concentrated load is applied between the two fulcrums to deform the sample until it is damaged. For non brittle materials, yield occurs when the load reaches a certain value. The load at this time is also called failure load, and its strength is called static bending yield strength. Flexural modulus of elasticity refers to the ratio of bending stress to strain of a material within the proportional limit. --Lixian instrument
Through the test of plastic bending strength by plastic tensile testing machine, we understand the structure and application method of bending test accessories in plastic tensile testing machine, and obtain the bending strength, bending elastic modulus and stress-strain curve of plastics. The plastic tensile testing machine provides two groups of capacity test space, allowing the operator to have a wider range of use, especially when there is a large force gap between raw materials and finished products. The floor type is adopted in the type.
The standard experimental methods of bending strength include three-point bending and four-point bending, and the qualitative distribution of loading mode, bending moment and shear force. The difference between three-point bending and four-point bending is that there is 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, the span of the sample and the radius of the loading indenter can be increased, or the four point bending test method can be used for the experiment. However, the sample required for four-point bending is long, the structure of loading indenter is complex, and the loading balance in the experiment is not easy to ensure. However, the three-point bending experiment is simple and applicable, so three-point bending is a common method for plastic bending experiment by plastic tensile testing machine at present. The three-point bending method was also used in this experiment.
Since the thickness has a great influence on the deflection, if the actual thickness of the plate is different from the required sample thickness, it should be corrected by machining, but at this time, it should be noted that it should be machined from one side, and in the experiment of the plastic tensile testing machine, the machined surface should face the loading indenter to make the surface not machined tensile, which has no impact on the experimental results.
The factors affecting the bending experiment include the size and processing of the sample, the radius of the indenter and the surface radius of the support, the experimental span, the experimental speed, the experimental environment and the properties of the material. Generally, the thickness and width of the bending specimen are related to the bending strength and deflection. Increasing the thickness and width increases the cross section of the specimen, and the ability to resist bending deformation increases.