TWI provides a wide range of mechanical testing services through our in-house testing laboratory. Mechanical test procedures are used to produce data that can inform engineering designs, material joining procedures, or operator acceptance schemes.
Of these, the provision of design data is the most important function, as it determines the mechanical properties of materials under different conditions, and thereby the values that a structure can withstand before failure. Adequate control of raw material properties by suppliers and the use of the correct joining procedures are also crucial to ensuring the safety of a product, asset or structure.
Tensile testing is a mechanical test method that can be used to both determine the yield strength of metallic materials for design calculations and to ensure compliance with the strength requirements of a material’s specification. These tests can inform the design of everything from component parts to entire structures, as with mechanical fastener testing.
Tensile Testing at TWI
We provide tensile testing of metals and other materials among the mechanical test methods on offer at TWI. These services are offered via our subsidiary, The Test House, a UKAS-accredited testing laboratory based at our headquarters near Cambridge.
As a destructive engineering and materials science test, tensile testing involves the use of applied force to assess the tensile properties of a range of specimens, parts, and components. The force is applied until the part is permanently deformed and, finally, fully fails.
Measuring these results allows us to determine features such as the ultimate tensile strength, the yield point (where elastic behaviour becomes plastic behaviour and deformation occurs), the percentage elongation at failure, and the percentage reduction of area at the point of failure.
Tensile testing is used to determine ultimate tensile strength, yield strength, ductility, strain hardening characteristics, Young's modulus of elasticity, and Poisson's ratio in different materials.
As one of the most common mechanical testing methods, it can provide both quantitative numerical data for design and analysis as well as qualitative information about material behaviours in comparison to others.
We can also take account of other factors such as metals that have been strengthened through alloying, heat treatment or cold working where the yield point is found by measuring the proof stress.
Tensile testing can be performed as a standalone service or as part of a larger project for our Industrial Members.
Tensile Specimen Preparation
The exact method for preparing a test specimen differs according to the test specifications, although commonly-used specifications include BS EN ISO 6892-1 and ASTM E8M Specimens are typically designed with a round or square cross-sectional area in the middle with two wider shoulders at either end. The shoulders allow the specimen to be gripped for the testing while the middle bar shows the deformation in the elastic region as it is stretched under an increasing uni-axial load until failure. It is important to standardise test pieces so that they produce comparable and repeatable results. This can include the tensile testing of materials at elevated, reduced or ambient temperatures.
Why Perform Tensile Testing
Tensile testing allows you to determine the tensile mechanical properties of a material, which can then be plotted as stress/strain curves on a graph, showing information such as the point of failure, modulus of elasticity strain, and yield strength.
This allows users to:
- Select materials for an application
- Predict how a material will perform under different forces
- Determine whether the requirements of a specification, contract or standard are met
- Demonstrate proof of concept for a new product
- Prove characteristics for a proposed patent
- Provide standard quality assurance data for scientific and engineering functions
- Compare technical data for different material options
- Provide evidence for use in legal proceedings
To find out more about tensile testing services at TWI, please email contactus@twi.co.uk.