The welding process is a critical element in various industries, with welding tests playing a pivotal role in assessing the quality, reliability, and performance of welded components. These tests are instrumental in ensuring that welded joints meet stringent industry norms and specifications, operating reliably in real-world conditions. Among the myriad welding tests available, this article focuses on a specific technique known as tensile testing, a destructive yet indispensable method for evaluating the mechanical characteristics of welded joints.

Tensile Testing Overview

Tensile testing is a destructive test, and it used to assess the mechanical characteristics of a welded joint, in particular its tensile strength, elongation, and reduction in area. These characteristics aid in determining if the weld can sustain applied forces and deformation without failing.

A sample of specified dimensions is loaded in tension until the point of failure. The sample piece is pulled apart to understand the strength, ductility and other characteristics of the weld. The test equipment calculates and displays the ultimate tensile strength (the maximum stress withstood before failure), the yield strength (the stress where plastic deformation occurs) and the percent elongation of the sample.

The process involves creating a welded test plate, machining the plate to produce an appropriately sized test specimen, conducting the test and then analyzing results. Different base metals, joint designs and welding parameters can result in significantly different mechanical properties, even when using the same filler metal. For this reason, filler metal manufacturers and companies test plates in accordance with specifications that control all these factors.

Tensile Testing Procedure

• Sample preparation: Tensile test specimens made from welded joints are manufactured using defined dimensions and shapes. Typically, the specimens are cut or machined to precise dimensions, with a smaller part known as the gauge section being where the failure happens during testing.

Tensile tests are performed with specimens prepared as round bars or flat strips. The simple round bars are often used for testing only the weld metal, sometimes called “all weld metal testing.” 

Round specimens are cut from the center of the weld metal.

Round specimens are cut from the center of the weld metal.

The flat bars are often used to test both the weld and the surrounding metal. They are oriented across the weld so that both parent metals, heat affected zones (HAZs), and the weld metal itself are tested.

Note that it may be necessary to machine several specimens through the thickness of a weld, particularly on very thick joints where the capacity of the tensile machine is insufficient to pull a full thickness specimen.

• Test Setup: Once the specimens are prepared, they are securely fastened into a specialized testing device. This device applies an axial tension or pulling force to the specimen, simulating the conditions under which the weld may experience stress in real-world applications.

• Load Application: The testing machine exerts a steadily increasing tensile load on the specimen, causing it to elongate until it ultimately reaches the point of failure. Throughout this process, the machine records the load and corresponding elongation, generating valuable data on the specimen's behavior under tension.
   
• Data Collection: The recorded load and elongation data are pivotal for calculating key mechanical properties, including ultimate tensile strength (the maximum stress the specimen withstands before failure), yield strength (the stress at which plastic deformation occurs), and percent elongation. These properties provide a nuanced understanding of the weld's performance and structural integrity.

Conclusion

In conclusion, tensile testing is an indispensable technique for evaluating the strength, effectiveness, and overall quality of welds. Despite its destructive nature, this testing method provides unparalleled insights into potential flaws, mechanical attributes, and the anticipated performance of a weld. By applying controlled tension to welds, tensile testing contributes significantly to enhancing the reliability, safety, and overall quality of welded components in diverse industrial applications.