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Tensile testing of Chassis

Tensile testing of Chassis

Tensile testing of Chassis

In the design and calculations for strength, rigidity and resistance elements of mechanisms, machines and structures necessary to know the properties of materials. Therefore materials tested for tensile, compression, shear, torsion, bending and hardness. Detailed descriptions of all types of mechanical tests, and also used with machines and devices are in special courses and manuals for laboratory work on strength of materials. We restrict ourselves to a brief description of some common types of mechanical tests and the obtained results.

If the load is static, then the ground is a tensile test, in which are found the most important properties of the materials. To do this, the test material is manufactured special patterns. Most often they are made ??cylindrical (Fig. 4.1, a), a Sheet metal is usually made ??flat samples (Fig. 4.1, b).

Figure 4.1. Samples for tensile

In the cylinder must be conditioned relationship between length of the specimen and diameter: The long samples, In short - .

These relations can be expressed in another form. Given that

where - Cross section of the sample, we obtain

for a long sample

(4.1)

for a short sample

.

(4.2)

The main use samples with a diameter d 0 = 10 mm with a working length = 100 mm. Allowed to use the samples and other diameters, provided that the length of their working or. Such samples are called proportional.

Stress-strain diagrams

Tensile testing machine used discontinuous, allowing the test to determine the force and corresponding deformation of the sample. From these data, the primary building tension diagram, in which the ordinate efforts lay on the x-axis - the corresponding extension. Diagram of stretching can also be obtained automatically through special diagrammatic apparatus. The nature of stress-strain diagrams depends on the properties of the test material. A typical form of such diagrams for mild steel is shown in Figure 4.2.

The characteristic points of the plots and charts, as well as the corresponding stage of deformation of the sample.

From the beginning of loading up to a certain value of the tensile strength is a direct proportional relationship between the elongation of the sample, and strength. This relationship is expressed in the chart straight OA. At this stage, stretching Hooke's law is valid.

Figure 4.2. Tension diagram of mild steel

Denote the force at which the violation of the law of proportionality in . H a chart to this value forces in the diagram corresponds to a. Tension caused by force , called the limit of proportionality and is given by

(4.3)

Thus, the limit of proportionality is called the voltage, after which Hooke's law is violated.

Recall that the deformation is called elastic if it disappears completely after unloading. Assume that, gradually increasing the load , Will each produce its meaning full discharge of the sample. While the power reaches a certain size, the force strain will disappear when unloading. The process of unloading at the same time ...

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