What engineers can learn from a tensile diagram

A tensile diagram is a key tool for determining mechanical properties, actively used in engineering research and production. Such a graph illustrates the relationship between the force applied to a specimen and the deformation that arises in it, helping assess material behavior under load. By building and analyzing the diagram, engineers can draw conclusions about strength, ductility, and brittleness of a blank and make important decisions about choosing steels and alloys for various projects.

Building a tensile diagram

Building the diagram consists of several stages, each important for the accuracy of the data obtained:

1. Specimen preparation. The blank must meet specific size and shape requirements. Cylindrical specimens with diameter from 3 to 25 mm and length from 10 to 200 mm are most often used. For PZPS products, tests may be performed both on strip in its final form and at intermediate production stages for quality control.
2. Equipment setup. The specimen is secured in a special testing machine that applies tensile force to the material. It is important that force application be uniform; only then can specimen deformation be measured accurately.
3. Conducting the test. The machine begins applying force, increasing it until the specimen fails. During the test the machine records data on applied force and deformation arising in the specimen.
4. Building the graph. Based on the data obtained, a diagram is built where deformation is plotted on the horizontal X axis and applied force on the vertical Y axis. The resulting graph shows the dependence of deformation on stress and is called a tensile diagram.

On every tensile diagram three characteristic regions can be seen. The first is called the elastic deformation zone. In it, changes in blank size and shape are directly proportional to applied stress. After such load is removed, the material can return to its original state. The second region reflects uniform plastic deformation of the blank. In this zone, after load removal the material can no longer restore its original shape. The third region is concentrated necking deformation. Under the corresponding load the material thins in one place (a neck forms), leading to specimen failure.

Converting the diagram to conventional coordinates

So that original specimen geometry does not affect test results, the diagram obtained in the study is converted to a conventional one in “stress–strain” coordinates. Force and elongation are related to the initial cross-sectional area and blank length. Such a diagram is called conventional because it reflects stress and strain relative to original parameters, giving a more accurate view of material properties regardless of physical specimen size.

Determining mechanical characteristics

Using tensile diagrams, engineers assess a number of important mechanical material characteristics:

1. Proportionality limit — the maximum allowable stress at which, according to Hooke’s law, a linear relationship between applied force and specimen deformation is preserved.
2. Elastic limit — the stress value at which plastic deformation occurs, i.e., after load removal the material does not restore its shape.
3. Yield strength — the stress value at which deformation continues to increase substantially without load increase. For structural materials this is one of the key indicators.
4. Ultimate strength — the maximum stress that can be applied to a specimen before failure begins.
5. Relative elongation — the ratio of specimen length change to its original geometric dimensions. Characterizes material ductility.

Characteristics determined with a tensile diagram help designers conclude whether a steel or alloy is suitable for specific tasks.

Difference between ductile and brittle materials

From the diagram shape one can easily determine whether the specimen under study is ductile or brittle. Ductile materials such as silver, gold, copper, aluminum, or low-carbon steel have a pronounced yield plateau and significant ultimate strength, indicating their ability to deform strongly before failure. In turn, brittle materials such as cast iron, ceramics, or glass do not show a noticeable yield plateau; their ultimate and yield strengths nearly coincide, and failure occurs quickly without substantial deformation.

The difference between these material types also appears in the nature of their failure. On specimens of ductile steels and alloys a pronounced neck forms before rupture, and rupture occurs at roughly 45° to the tensile axis. This feature is clearly visible on flat blanks. Failure of brittle materials occurs on a plane across the applied load axis. No pronounced neck is observed on the specimen.

PZPS products and tensile tests performed

Analyzing tensile diagrams is extremely important for controlling and improving precision alloy production. Such diagrams are used to check properties and quality of alloys for various purposes, including:

• soft magnetic (for example, 49K2FA-VI and 27KKh);
• for elastic elements (40KKhNM, 36NKhTYu, 17KhNGT);
• corrosion-resistant (12Kh18N10T, 12Kh18N9, and others);
• heat-strength and heat-resistant (20Kh13, KhN78T);
• with high electrical resistivity (Kh15Yu5, Kh23Yu5, and others);
• with specified CTE (29NK, 36N, 42N).

These alloys undergo tensile tests at different processing stages, which makes it possible to strictly control quality and adapt production processes to improve mechanical properties.

PZPS produces high-quality steels and alloys with a guarantee based on detailed tests and checks. We control the quality of products at all production stages using the latest analysis technologies. This allows us to create materials that meet the highest standards in various industries. For purchasing alloys and steels, as well as ordering manufacturing services, call or leave a request on the website.

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