How can you use experimental mechanics to perform a fatigue test?

1 Fatigue testing basics

Fatigue testing involves applying a repeated load or stress to a material or structure until it breaks or shows signs of damage. The load or stress can vary in magnitude, frequency, direction, and duration. The number of cycles required to cause failure is called the fatigue life, and it depends on many factors, such as the material properties, the geometry, the environment, and the loading history. Fatigue testing can help you understand the fatigue behavior and performance of your materials or structures, and design them to withstand the expected loading conditions.

2 Experimental mechanics techniques

Experimental mechanics offers a range of techniques and tools that can help you perform a fatigue test and measure the physical responses of your materials or structures. Strain gauges are sensors that measure the strain or deformation of a material or structure under load, while extensometers measure the change in length or displacement of a material or structure under load. Optical methods, such as digital image correlation (DIC), holographic interferometry, speckle pattern interferometry, and photoelasticity, use light to measure the surface or internal features of a material or structure under load. These techniques can provide accurate and local measurements of strain, stress, displacement, and fatigue damage.

3 Fatigue testing setup

In order to perform a fatigue test using experimental mechanics, one must prepare a suitable setup that includes a fatigue testing machine, a specimen, a data acquisition system, and a control system. The fatigue testing machine can be servo-hydraulic, servo-electric, or electromagnetic and have different configurations like uniaxial, biaxial, or multiaxial. The specimen should have a standard or representative geometry and size and be free of defects or flaws that can affect the fatigue behavior. The data acquisition system collects and records data from the experimental mechanics techniques and tools and includes sensors, amplifiers, signal conditioners, data loggers, and computers. The control system controls the parameters of the fatigue testing machine and monitors the specimen condition to stop the test when failure occurs.

4 Fatigue testing procedure

To perform a fatigue test using experimental mechanics, you need to follow a proper procedure. This includes preparing the specimen by cleaning, polishing, and marking it according to the technique and tool you will use. You also need to calibrate the technique and tool before attaching or applying it to the specimen. The specimen should then be mounted on the fatigue testing machine in accordance with the loading configuration and direction. The data acquisition system and control system should be connected to the fatigue testing machine and specimen. Once this is done, set the parameters of the fatigue testing machine and control system according to the loading scenario that needs to be simulated. Then start the data acquisition system and experimental mechanics technique and tool, running the test until either failure or a predefined number of cycles or damage level is reached. After that, analyze the data collected by both systems and process it using software or algorithms. You can compare and correlate data from different techniques or tools, as well as calculate and interpret the fatigue life, fatigue strength, fatigue crack growth, and fatigue damage of the specimen.

5 Fatigue testing benefits

Experimental mechanics fatigue testing can provide comprehensive and reliable data on the fatigue behavior and performance of materials or structures. This type of testing can also enhance understanding of fatigue mechanisms and factors that influence materials or structures. By utilizing fatigue testing, you can improve the design and optimization of materials or structures for fatigue resistance and durability, as well as reduce costs and risks associated with fatigue failure and maintenance.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?