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What is Tensile Testing?

 

Tensile Testing, also known as tension testing, is a destructive engineering and materials science test whereby controlled tension is applied to a sample either as a load for proof testing or until it fully fails.

This is one of the most common mechanical testing techniques and is used to find out how strong a material is and also how much it can be stretched before it breaks. This test method is used to determine yield strength, ultimate tensile strength, ductility, strain hardening characteristics, Young's modulus and Poisson's ratio.

Test Properties

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.

Hooke's Law

Hooke's Law defines the relationship between the applied force and the elongation shown in the test specimen where the ratio of stress to strain is constant.

Modulus of Elasticity

The modulus of elasticity 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.  

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.

Offset Method

The Offset Method is used on materials where the tensile properties make the yield strength difficult to determine, such as with metals or plastics. 

Alternate Moduli

In materials that do not have a well-defined linear region, alternative methods are used to determine the modulus, including secant modulus and tangent modulus.

Strain

The strain of a specimen is the measurement of the change in length that the item undergoes during testing divided by the original gauge length. Known as Engineering strain or nominal strain.

Tensile Specimen Preparation

Tensile test specimens are prepared in a variety of ways depending on the test specifications. The most commonly used specifications are BS EN ISO 6892-1 and ASTM E8M. Most specimens use either a round or square standard cross section with two shoulders and a reduced section gauge length in between. The shoulders allow the specimen to be gripped while the gauge length shows the deformation and failure in the elastic region as it is stretched under load. The reduced cross section gauge length of specific dimensions assists with accurate calculation of engineering stress via load over area calculation.

Why is Tensile Testing Performed?

Tensile testing provides details of the tensile mechanical properties of a material. These properties can be plotted on a graph as a stress/ strain curve to show details such as the point at which the material failed as well as providing details of properties such as the modulus of elasticity, strain and yield strength.  

Tensile testing has a variety of uses, including:

  • Selecting materials for an application
  • Predicting how a material will perform under different forces
  • Determining whether the requirements of a specification, contract or standard are met
  • Demonstrating proof of concept for a new product
  • Proving characteristics for a proposed patent
  • Providing standard quality assurance data for scientific and engineering functions
  • Comparing technical data for different material options
  • Material testing to provide evidence for use in legal proceedings

The Advantages of using Tensile Testing

Flaws in equipment can prove costly and dangerous to the manufacturer and end user of a product. Tensile testing can greatly reduce this danger by determining the engineering stress and other properties of a material or part.

Tensile testing also gives designers and manufacturers data on new materials and their properties so they can determine qualities for future use.

Tensile Testing Services

Tensile testing is one of the services offered by The Test House at TWI.

Find out more about our mechanical testing services

 

For more information about Tensile Testing please email:


contactus@twi.co.uk