Tensile testing

Tensile testing is a type of engineering and materials science test in which controlled tension is applied to a test sample. Tension may be applied either as a static load for proof of concept testing purposes or in an incrementally increasing fashion in order to determine the maximum amount of tension the sample can withstand before it breaks. Tensile testing is a common mechanical testing technique that can offer valuable information about the strength of the material being tested. Specifically, tensile testing can be used to determine a material's yield strength, ultimate tensile strength, ductility, strain-hardening characteristics, and more. Tensile testing has a variety of practice purposes. Among other things, it can be used to determine the appropriate material for a given application, prove characteristics for proposed patents, or predict how a certain material will perform when exposed to different forces. Tensile testing is an important and widely used research and development tool.

Background

Tensile testing involves a range of scientific concepts and principles. Foremost is the concept of force. Force is any action that causes a free object with finite mass to accelerate relative to a non-accelerating frame of reference. There are two types of force: contact and non-contact force. Non-contact forces are those that are exerted upon an object without any physical contact with the object in question. Examples of non-contact forces include gravity and magnetism. The exertion of contact forces requires physical contact with an object. There are several types of contact forces. These include normal, applied, muscular, frictional, spring, air-resisting, and tension force.

Tension force is the primary force involved in tensile testing. Tension force is the force that is transmitted through a rope, cable, or wire when it is pulled taut by forces acting from its opposite ends. This force is directed along the entire length of the rope or cable and pulls equally on the objects to which the rope or cable is attached at either end. Because ropes are unable to push effectively, tension acts only as a pulling force. It is also important to note that tension never applies on its own. Rather, it works only by transfer.

Another key element of tensile testing is the concept of tensile strength. The tensile strength of a given material is the maximum level of tension it can endure before failing. This type of failure may be either ductile or brittle. Ductile failure is marked by gradual hardening and breakage, often following the development of a neck formation in the material. In brittle failure, the material abruptly breaks into two or more pieces.

The measure of tensile strength reveals the point at which a material changes from elastic to plastic deformation. There are three types of tensile strength: yield, ultimate, and breaking strength. Yield strength refers to the amount of stress a material can withstand without enduring permanent deformation. Ultimate strength is the maximum amount of stress a material can withstand. Breaking strength is the stress coordinate on the stress-strain curve at the point of rupture.

Overview

Tensile testing is a method of measuring the tensile strength of a given material. In most cases, such testing involves applying a gradually increasing load to a test sample until the sample reaches its point of failure. The data gathered during a tensile test can be used to create a stress-strain curve that precisely shows how the material responds to the application of force at each stage of the test. Tensile testing ultimately sheds light on the mechanical properties of materials and provides quantitative measurements of tensile strength, yield strength, and ductility.

The process of tensile testing involves the use of several key pieces of equipment. These include a universal test machine frame, a load cell, a controller or indicator, and appropriate grips or other similar fixtures. The universal test machine frame is the primary component of any tensile test. It provides the necessary structure and rigidity required to apply tension to a sample at the desired rate. The size and configuration of universal testing machines can vary. As a result, it is important to ensure that the machine being used to carry out a particular test is capable of withstanding the amount of force to be applied. Load cells are used to measure the amount of force that is applied to the sample. Because different load cells have different capacities, it is critical to choose the correct load cell for the sample being tested. If the load cell used in a given test has a capacity that is lower than the breaking strength required for that test, the load cell itself will break before the sample. On the other hand, if the load cell's capacity is too high, the test results may not be as precise as desired. Most tensile testing frames also require a controller or indicator. A controller is a device that controls what the test frame does during the test. Among other things, this includes controlling the frame's test speed and displacement. An indicator is a simpler device that captures and displays the test data. Indicators do not control the test frame in any way. Finally, there are a wide variety of grips and other fixtures available for use in tensile testing. Grips hold the sample in place as force is applied. The type of grip needed for a given test will vary depending on the type of material being tested and how that material behaves as tensile force is applied.

When a tensile test is performed, the test sample is secured to the testing frame at its ends by grips. As the test commences, the grips are pulled apart at a constant rate to apply tension to the sample. This causes the sample to pull and stretch until it reaches its breaking point and snaps. The amount of force applied to the sample and its displacement are constantly monitored during the test and recorded on a stress-strain curve. Afterwards, the test sample is put back together and its final length is measured. The data gathered during the test ultimately reveals key information on the test sample's tensile strength, yield strength, and ductility.

Bibliography

AbouelNour, Youssef, et al. "Tensile Testing Data of Additive Manufactured ASTM D638 Standard Specimens with Embedded Internal Geometrical Features." Scientific Data, vol. 11, no. 506, 24 May 2024, doi.org/10.1038/s41597-024-03369-y. Accessed 7 Nov. 2024.

Ashish. “What Is Ultimate Tensile Strength?” Science ABC, 2017, www.scienceabc.com/pure-sciences/what-is-ultimate-tensile-strength.html. Accessed 17 June 2019.

“Introduction to Tensile Testing.” ASM International, 2004, www.asminternational.org/documents/10192/3465262/05105G‗Chapter‗1.pdf/e13396e8-a327-490a-a414-9bd1d2bc2bb8. Accessed 17 June 2019.

“Tensile Strength.” Corrosionpedia, 2019, www.corrosionpedia.com/definition/1072/tensile-strength. Accessed 17 June 2019.

“Tensile Testing.” Laboratory Testing Inc., 2019, www.labtesting.com/services/materials-testing/mechanical-testing/tensile-testing. Accessed 17 June 2019.

“Tension Testing/Tensile Testing.” ADMET, 2019, www.admet.com/testing-applications/test-types/tension-testing. Accessed 17 June 2019.

“Tensile vs Yield Strength.” Clifton Steel, 3 Apr. 2019, www.cliftonsteel.com/knowledge-center/tensile-and-yield-strength. Accessed 17 June 2019.

“What Is Tension Force?” Vedantu, 2019, www.vedantu.com/physics/tension-force. Accessed 17 June 2019.

“What Is Tensile Testing?” TWI, 2019, www.twi-global.com/technical-knowledge/faqs/what-is-tensile-testing. Accessed 17 June 2019.