What is Tensile test?
Tensile testing is a fundamental type of mechanical testing performed by engineers and materials scientists in manufacturing and research facilities all over the world.
A tensile test (or tension test) applies force to a material specimen in order to measure the material’s response to tensile (or pulling) stress.
This type of testing provides insight into the mechanical properties of a material and enables product designers to make informed decisions about when, where, and how to use a given material.
Why Perform a Tensile Test?
Tensile testing and material characterization are crucial for manufacturers and researchers in all industries. In order for a material to be selected for a new product or use, researchers must ensure that it can withstand the mechanical forces that it will encounter in its end-use application.
For example, tire rubber must be elastic enough to absorb inconsistencies in road surfaces, while surgical sutures must be strong enough to hold living tissue together.
Furthermore, materials and products might be exposed to mechanical forces for short or long periods of time, through cyclical or repeated use, and in a wide variety of different temperature and environmental conditions.
Automotive tires are expected to last for a certain number of miles under a variety of weather conditions, while surgical sutures, though only used once, must maintain a consistent tensile strength for long enough for the body to heal.
In addition to its importance to the R&D process, tensile testing is also used by quality assurance departments to ensure that batches of finished product are meeting the required specifications for tensile properties.
This is important from both a safety and a business perspective, as defective products can be dangerous to the end user and can also cause significant harm to manufacturers in the form of product delays, lost revenue, and damaged reputations.
Why Are Tensile Tests Important?
Tensile tests provide fundamental insights into a material’s strength and stiffness as characterized by its ability to withstand tension or pull forces.
This information is needed in virtually all mechanical products where strength and stiffness are design variables. Tensile test properties make it possible to select and compare materials, design components, ensure quality, and prevent product failures.
- Material Selection – Tensile test data enables comparison of different materials.
- Design Engineering – Tensile properties are used in design to predict how a component made from a specific material will behave.
- Quality Control – Manufacturing processes can be improved using tensile tests to ensure that materials consistently meet strength requirements.
- Research and Development – Tensile testing characterizes new alloys, composites, and advanced materials, assessing their suitability for applications.
- Process Improvement – Researchers use tensile tests to understand how heat treatments, processing techniques, and changes in composition affect a material’s mechanical properties.
- Failure Analysis – researching how and where materials fracture during tensile tests provides valuable insights into failure mechanisms, improving material design.
- Industry Compliance and Safety – Many industries have strict standards and regulations that require materials to undergo tensile testing to ensure they meet design criteria.
How To Perform A Tensile Test?
Before starting the test for tensile strength, use a Tensile Preparation ASTM E8 and mold the sample material. Once the mold is whole, the sample will take on the shape of a slim dogbone or dumbbell.
For more accurate results, make an exact copy of the sample with the same marked intervals, and set it aside for later.
Before choosing materials, the tester must determine how appropriate the specimen is to the grips and faces being used. The quality and choice of test materials need to coincide with the purpose, specification, and method of the test.
For example, serrated faces are only applicable to rigid substances with low ductibility, but can prove to be damaging on plastic materials.
On the other hand, pinned grips can assure the specimen’s safety, as long as the tester is mindful of the threads’ distance.
Position the lower and upper clamps in their proper position to accommodate the length of the test sample.
Next, place the material between the tensile clamps. Vertically align the sample from the upper clamp (the fixed grip) to the lower clamp (the grip in charge of applying tension). This alignment will ensure that the specimen will avoid side loading or bending during the test.
The alignment should be given much of the tester or technician’s attention, as it is the most critical part of the process. The tester’s skill, as well as the type of grips used for the test takes a vital role.
Specimens made of fragile or brittle substances require the utmost care and caution during tensile tests.
Mishandling specimens with the wrong equipment can threaten the process and negatively affect the results. It may even cost the specimen and may require a redo of the entire process.
After securing the sample, attach the extensometer to its length. While it undergoes testing, the extensometer will be monitoring and measuring any changes in the material.
After the extensometer is placed, double check the other equipment to make sure they are in their correct positions.
To begin the tensile stress test, slowly separate the tensile clamps at a constant speed. Depending on the size and shape of the material, the tensile tester machine can pull at a maximum speed of 20 inches per minute. The tensile testing would often take five minutes or less for the material to fracture.
During the test, the specimen will slowly elongate with the standardized speed. The data gathering software will present the material’s test parameters, as well as the changes in the gage length.
It will monitor the force placed upon the specimen and display the stress-strain curve. The stress-strain curve is helpful in analyzing the specimen’s behavior throughout the test.
While the substance undergoes tension, the tester can observe how much elongation is occurring in the process.
The change in length brought about by the pulling forces is a measurement called “strain”. There are two kinds of strain: engineering strain and true strain.
Known as the most basic expression of strain, engineering strain is the comparison between the material’s post-test length to its pre-test length.
While similar to engineering strain, true strain is the measurement of the immediate length of the substance during the test.
Eventually, the specimen will begin to deform in the middle of its length. Changes in the stress-strain curve will begin to appear during this phase. Once the specimen breaks, the tensile testing has officially ended.
After the fracture, unlatch the specimen piece from the tensile clamps. The tensile testers or technicians will calculate the tensile strength, yield strength and ductility of the material.
After taking the final measurements, the broken specimen will be compared to the undamaged copy made before the test.
The tensile strength will determine the material’s maximum tensile stress. Yield strength, otherwise known as breaking strength, is the stress measured from the moment the material begins to permanently deform.
Ductility is the measure of the strain during and after the moment of fracture. By analyzing the results of the tensile test, these three quantitative measurements can gauge the strength and durability of the specimen.
Tensile Test Properties
Yield Strength
The yield strength is the point at which plastic deformation occurs under stress. This is determined during testing over a measured gauge length via the use of devices known as extensometers.
The devices may be either be mechanical clip on or video where non-contact is a limitation, e.g. elevated temperature testing.
Ultimate Tensile Strength (UTS)
The UTS is the maximum stress that a specimen is exposed to during testing. This may differ from the specimen’s strength when breaking depending on if it is brittle, ductile or has properties of both.
These material properties can change depending on environment, for example in extreme hot or cold conditions.
Ductility
Ductility relates to the elongation of a tensile test. The percentage of elongation is calculated by the maximum gage length divided by the original gage length. It is commonly described
Strain Hardening
How much it harderns with plastic defremation.
Modulus of Elasticity
The modulus of elasticity also known as Young’s modulus measures the stiffness of a specimen whereby the material will return to its original condition once the load has been removed.
Once the material has been stretched to the point where it no longer returns to its original length and permanent deformation is shown, Hooke’s Law no longer applies. This is known as the elastic or proportonal limit (also the yield strength).
Tensile Test Applications
A tensile test is used to check the quality of different materials based on their properties such as ductility, hardness, yield strength, and tensile strength. When selecting materials for a final product or prototype, you need to know if they will stand up to real-world use.
Every material has a breaking point, so knowing how strong your materials are can alert you if you are using something that won’t hold up well under stress.
When choosing fabrics, metal alloys, paper pulp and other raw materials, a tensile test can help you select the strongest available options.
Aerospace & Automotive
Tensile testing of aluminum alloys, high-strength steel, and titanium is common in aircraft wings, fuselages, landing gear, and car chassis. Evaluating carbon fiber composites and fiberglass for consideration as lightweight and strong structural components.
Fastener tests of bolts, screws, and rivets are needed to ensure they have the strength for their intended use.
Construction & Infrastructure
Tensile tests ensure that steel rebar used in concrete meets strength and ductility standards. Tensile materials tests of steel l I-beams, girders, and other building elements along with tensile strength tests of cables and wire rope used in bridges and suspension structures.
Wide width tensile strength of geotextile fabrics used in earthworks and soil reinforcement applications.
Manufacturing & Product Development
Determining the tensile strength and flexibility of plastics and polymers is used in thin film packaging, toys, consumer goods, and automotive parts.
Also, evaluating the tensile bond strength of adhesives and bonding agents between different materials and testing a textile or fabric durability and tear resistance of clothing, upholstery, and technical fabrics are important. Characterizing the tensile strength of electrical wires, cables, and ropes.
Medical
Testing the strength and suitability of tissue engineering and biomaterials used in implants, prosthetics, and sutures is critical. Analyzing the tensile properties of bone and soft tissues helps understand injury mechanisms and develop treatments.
Medical devices are tested to prove the safety and reliability of catheters, tubing, and other medical equipment.
Research & Development
Tensile tests evaluate the properties of new advanced experimental alloys, composites, ceramics, and other materials under development. These tests help Investigate the root causes of material failures by analyzing fracture points and deformation patterns.
Understanding how manufacturing processes like heat treatment or forming affect a material’s tensile properties is done daily.
Standards for tensile Testing
There are plenty of tensile testing standards available. Some of the most common include:
ASTM Test Methods
- ASTM E8 Tension Testing of Metals
- ASTM D638 Tensile Properties of Plastics
- ASTM D3039 Tensile Properties of Polymer Matrix Composites
- ASTM D412 Tension Tests of Rubber and Elastomers
- ASTM D882 Tensile Properties of Thin Plastic Sheeting
- ASTM A370 Tensile Testing of Steel Products
- ASTM E21 Elevated Temperature Tension Tests of Metals
- ASTM D828 Tensile Properties of Paper and Paperboard
- ASTM D5035 Breaking Force and Elongation of Textile Fabrics
ISO Test Methods
- ISO 6892-1 Tensile Testing of Metals
- ISO 527 Tensile Testing of Plastics
- ISO 527-5 Tensile Properties of Fiber-Reinforced Plastic Composites
- ISO 13934-1 Tensile properties of Textile Fabrics
- ISO 1924-2 Tensile Properties of Paper and Paperboard