The Importance of an Extensometer in Materials Testing
Extensometers and the Value of Materials Testing
The data acquired using ASTM E8 is crucial for material comparisons as well as procedures like alloy creation. In environments where they are employed, testing the tensile strength of steel preparation can help increase safety. For example, it guarantees that steel used in construction can withstand the stresses to which it is normally subjected without breaking.
Extensometers are frequently employed in fields where producers must evaluate the tensile strength of the materials they employ to see if they can resist the usual strain placed on them. Extensometers are also employed in real-world situations, including mines. They are used by geotechnical engineers to determine whether there is a chance that nearby structures could collapse.
To use a contact extensometer, the tensile test specimen must physically be attached to a knife edge or other object using a “clip-on” method. Wherever high-precision measurements are required, these pieces of equipment are used. They are also economical.
Only a very slight amount of the knife’s edge makes contact with the specimen’s surface, creating a minuscule depression. This indentation creates a perfectly positioned contact point that contributes to the measurements’ high accuracy and ensures that the readings are only within a narrow scatter bandwidth.
Typically, the operator applies and removes the tensile test sample manually from the instrument. Results, however, could be impacted by making mistakes. Some variants were equipped with automated application and removal devices to help offset this.
Important Points on Extensometers
The typical range of clip-on extensometers is a few millimeters, and loads are delivered directly to the tensile testing samples. Extensometers with double-sided measuring systems and counter-balance weights may be used to correct for any superimposed bending forces, though.
Traditional contact extensometers, however, might not be appropriate when testing delicate or small materials. As a result, more recent items were created that employed a digital sensor or “feeler” arm. The shortcomings of the older versions were compensated for by the characteristics of these models.
The feeler arms, for instance, were in contact with both sides of the sample to account for bending stresses. The more exact designs made sure that the specimen only received the absolute minimal load.
These tools are also excellent for automated tensile strength testing because, unlike clip-on devices, a motorized system automatically applies the sensor arm to the specimen.
The potential for test equipment damage if the sample reaches its breaking point and shows whiplash is a significant drawback of contact extensometers. For instance, a material with strong elasticity may “snap back” if tested and fractured. The tensile test equipment may sustain damage as a result of this.
By performing tensile testing using video or lasers, non-contact extensometers get around this issue. Even when the sample hits its breaking point, the damage is prevented by doing this.
After the sample has been inserted into tensile test equipment, laser extensometers work by shining a laser on it. A CCTV camera records the specimen’s reflections, which are then evaluated by a sophisticated algorithm.
Also, there is no need to mark the sample with test markings, which saves a lot of time while conducting tests.
These markers, however, might contribute to measuring errors. They could fall off or become blurry and difficult to read when the sample deforms. Putting measuring marks also extends the testing procedure by a stage, raising expenses and raising the possibility of erroneous results.
However, for applications requiring high accuracy, non-contact extensometers are the best choice. As they can measure strain on the sample across a wide range, they may even be superior to other extensometer kinds for specific tests.
Extensometers must be routinely calibrated to ensure reliable measurements. This can be carried out in settings that are equipped with a calibration kit or that specialize in calibration-related activities.
Video 01: The Importance of an Extensometer in Materials Testing
