The tensile testing of stainless steel is a destructive engineering process with this testing method; we can easily achieve the tensile strength, yield strength, ductility, young’s modulus and poison’s ratio of any stainless steel grade.
In this process, force is applied continuously on the specimen of a specific grade of stainless steel that we have to check till its breaking point. This point shows the strength of this material.
Tensile testing is mostly applied to determine the tensile strength, yield strength and elongation of stainless steel or other materials.
An amount of stress or load that can be sustained by a material before breaking or cracking is called tensile strength. The breaking-resistant ability under tensile strength is one of the essential properties of a material when used in structural applications.
The working load limit (WLL), proof load (PL), and breaking strength are assessed by tensile testing. Wire rope and chain sling assemblies can also be tested to determine their strength when put together.
The Purpose and Importance of Tensile Testing
Tensile testing is a well-known technique for finding the mechanical properties of stainless steel. These characteristics can be represented graphically as a stress/strain curve to display information such as the point at which the material failed and to provide information on properties such as the elastic modulus, strain, and yield strength.
Some points are given below to show why tensile testing is so important.
- Selecting the right materials for a project
- Estimating a material’s performance under various forces
- Evaluating if a specification, contract, or standard’s requirements are fulfilled
- Demonstrating a new product’s proof of concept
- To achieve the manufacturing goals and reduce the material cost
- Supplying standardized quality assurance data for engineering and research purposes
- Comparing technical information for various material choices
- Testing of the material to produce evidence for use in judgment
- To meet the industry and international standards of manufacturing
Tensile testing gives information on the durability of materials, components, and products. This testing method can also assist the producers in making sure their completed goods are suitable for their intended use and produced to the highest standards.
Methodology and Procedures of Tensile Testing
Preparation of specimen
For starting the process of tensile testing, the first step is making a specimen of the stainless steel grade, which can be tested. The variety of specimens depends upon the specifications of the test.
The most widely utilized standards and specs are ASTM E8M, ASTM A370 and BS EN ISO 6892-1.
Mostly conventional cross section is either square or circular, with two shoulders and a shorter gauge length in the middle. While the gauge length demonstrates the deformation and failure in the elastic zone when extended under stress, the shoulders enable the specimen to be gripped. Mostly the dimension ranges for gauges from 50mm to 80mm in length and 12.5mm to 25mm in width or diameter.
The procedure of tensile testing
After making the precise specimen, we use a tensile testing machine to complete this process. Palace this specimen between two grips, also called machine fixtures, for clamping this material. The machine consists of two components: a straining or pulling mechanism and a setup for measuring and registering the load on a dial.
Formula used for tensile testing data calculation
Stress (σ) = Force (F) / cross-sectional Area of the test specimen (A)
The specimen is subjected to a tensile load that gradually increases, and the extension or strain of the specimen that results is seen. A stress-strain curve shows the relationship between applied stress (i.e., load divided by cross-section) and extension or elongation.
Properties and applications of stainless steel tensile testing
Properties of tensile testing
Tensile testing is usually performed to determine stainless steel’s mechanical properties. Some common properties are given below.
Yield strength
The limit of plastic deformation under stress is known as yield strength. This is determined through testing using extensometers over a gauge length that has been measured.
This table shows the mechanical properties of stainless steel grades in the annealed condition.
| Grades | Tensile strength MPa | Yield strength MPa | Elongation % |
| Austenitic | 600 | 250 | 40-70 |
| Ferritic | 500 | 280 | 20-30 |
| Martensitic | 650 | 350 | 10-20 |
| Duplex | 700 | 450 | 25-40 |
Ultimate tensile strength (UTS)
The greatest stress a specimen is subjected to during testing is known as the Ultimate Tensile Strength. Depending on whether the specimen is brittle, ductile, or contains characteristics of both, this might not be the same as its breaking strength. Environmental factors, such as excessive heat or cold, can change these materials’ properties.
Ductility
A tensile test’s elongation is related to ductility. The maximum gauge length divided by the initial gauge length gives the elongation percentage.
Modulus of elasticity
Young’s modulus, also called the modulus of elasticity, is a measurement of a specimen’s stiffness or how quickly it will return to its initial state if a load is removed as soon as the material is stretched past the point where it can no longer be made to return to its original length, permanent deformation is seen.
Applications
There are a large number of industries that apply tensile testing to check the properties of components and materials to maintain the quality of their finished products.
Some common applications of tensile testing are given below
- Automobiles industry
- Beverages and construction,
- Electrical and electronics,
- Medical devices,
- Paper and board, pharmaceuticals
- Plastics and rubber industries
Health, fitness, leisure and textiles are examples of industries that fall under this category.
What are the affecting factors in tensile testing?
There are various factors that can affect the tensile testing results. Some common factors are given below.
Specimen size, shape and accuracy
If the cross-sectional shape differs for the same material in the same state, the measured results will affect the upper and lower yield strength. A specimen with a large cross-sectional area shows lower tensile strength than a smaller size, and the plasticity index is also decreased.
Thus, the specimen’s dimensions and shape must meet the standard’s requirements.
Testing equipment
The precision and reliability of the test results are directly impacted by the test machine and extensometer, two types of test equipment that are frequently used in tensile testing of stainless steel materials. As a result, it’s important to ensure the extensometer and testing machine are frequently calibrated and within the test’s validity period.
Testing environment/temperature
Some metallic materials are extremely sensitive to temperature changes, and even common metallic materials might cause inconsistent test results if the test temperature varies excessively. Generally, when the temperature decreases, the yield strength of body-centered cubic metals rises significantly. The yield strength of a metal often decreases as temperature increases.
Selection of clamping device
The test results may be impacted by improper specimen clamping, fixture selection, and extensometer loading and unloading. The shape of the clamping device’s surface pattern and the test specimen’s shape should not be out of alignment during the testing process.
