Each material has a set of properties that determine its further characteristics. One of these qualities is the resistance to mechanical stress, which is called ultimate stress. This concept is understood not only as the destruction of the material at the fracture point, but also the appearance of permanent deformation. In other words, it is a counteraction to external forces that lead to a weakening of strength. The article talks about what such voltage is, how it is calculated and how it is determined.
What is this indicator?
Ultimate stress of a material is the maximum tensile strength that must be applied to its cross-sectional area, which it can resist until it is completely destroyed or fractured. A simple calculation formula looks like this: stress is equal to force divided by area. It can be seen from it that the larger the area, the less force is needed.attach. The same is true and vice versa. The smaller the cross section of the workpiece, the more force it will take to break it.
However, the stiffness indices of different materials are not the same. Some are brittle, others are flexible. The maximum allowable stress for each is determined by mechanical tests. The result is considered achieved when external signs of integrity violation appear on the surface of the sample. They can be expressed in the form of destruction or fracture. For the latter, the term "yield point" is used. The first speaks of fragility, the second - of plasticity.
Both concepts are associated with the ultimate stress at which the strength of the material is broken. Let us consider in more detail how these two concepts are distinguished.
Tension and fluidity
The stiffness of materials can be divided into two concepts such as brittleness and ductility:
- The first one involves the destruction of the sample structure already at low acting forces. Elastic materials resist external impact, leaving only residual deformation in the form of a fracture. It follows that for plastic elements, the criterion of fragility is bending, since it occurs earlier than complete destruction.
- It takes less effort to bend the sample than to break it. Therefore, for plastic parts, the ultimate stress is the yield strength. Fragile products also have fluidity, but this indicator is too small for them.
Voltage,which occurs in the cross section of the sample is called the calculated one. Next, we will consider it in more detail.
Formulas for calculating stress
The calculation of limit stresses is performed according to the following formula:
s=s(prev.) / n
Where:
- s - normal stress directed perpendicular to the surface of the product;
- s(prev.) - the ultimate stress, which leads to the complete destruction of the sample or to its deformation, and for ductile (soft) materials, the value implies the yield strength, and for brittle elements - the tensile strength;
- n - normalized safety factor, which is necessary to compensate for temporary overloads on working structures made of this material.
To calculate shear loads use the formula:
t=s / 1 + v
In it:
- t - shear stress;
- v - Poisson's ratio, which is applied to a specific construction material.
Conclusion
The stress indicator is an important parameter for calculating the strength of the working structure. It is used in the design of load-bearing elements. Helps determine the extent to which a part has fulfilled its function and its service life.
