In the world of material analysis, fatigue testing holds a central place when seeking to determine the strength of a piece or component against cyclic loads. It is a procedure that allows for simulating real operating conditions, where a material is subjected to repeated stresses over time, as occurs in sectors such as automotive, aerospace, energy, and machinery construction.
One of the most frequent questions we are asked at Servosis is how long it takes to perform this type of test. And the answer is not unique, because it depends on multiple factors: from the type of material to the frequency of loading, through the configuration of the equipment and the test conditions. In some cases, the process can be completed in a few hours; in others, it can extend over weeks or even months.
What exactly is a fatigue test?
The fatigue test consists of applying a cyclic load (whether axial, bending, torsional, or a combination) to a specimen or component until a crack appears or complete rupture occurs. What is measured is not the maximum load that the material can withstand, but the number of cycles it withstands before failure. This information is key to predicting the service life of a component in service.
The procedure may follow different international regulations (ASTM E466, ISO 1099, Among other things, it can be performed with constant, variable or even under specific environmental conditions (temperature, humidity, corrosive atmospheres) depending on the requirements.
What determines the duration of a fatigue test?
Charging frequency
The frequency of loading is possibly the most determining factor in terms of the total time of the test. Most fatigue tests are performed at frequencies ranging from 1 Hz to 30 Hz, although special equipment is available for higher frequencies in metallic materials. At Servosis, our machines can be configured to operate within this range, optimizing time without compromising the integrity of the test.
As an example:
- At a frequency of 10 Hz, the system performs 36,000 cycles per hour.
- To reach 1 million cycles, the test would take approximately 27.8 hours.
- If the frequency is raised to 20 Hz, it reduces to about 13.9 hours.
However, not all materials tolerate high frequencies. Polymers and compounds can exhibit thermal or viscoelastic effects at frequencies above 5 Hz, which requires reducing the test rate to avoid any changes in the results.
Number of cycles required
Depending on the objective, a fatigue test can end in a few thousand cycles if the material fails quickly, or it can require millions of cycles. It is common to design tests until a threshold of 10⁶ or 10⁷ cycles is reached, which allows determining whether the material reaches a “fatigue limit” below which rupture is not expected.
If the test includes multiple load points to plot an S-N curve (Wöhler), the duration is multiplied, as several tests with different maximum loads must be performed.
Type of load and extent of stress
The applied tension range also has a direct impact. At higher loads, materials tend to fail in fewer cycles, so the tests are shorter. Conversely, when working with low loads, fatigue accumulates slowly and the number of cycles required to detect failure increases, prolonging the test.
In addition, the shape of the load wave (sinusoidal, triangular, trapezoidal) can influence the behavior of certain materials, especially viscoelastic materials, although in most conventional tests a sinusoidal wave is used.
Type of material tested
Each material has a different response to cyclic stresses. Carbon steels, for example, can have a well-defined fatigue limit, whereas aluminum alloys often lack it, which means that they can fail even at very low stresses if subjected to sufficient cycles.
Composite materials, on the other hand, have a much more complex behavior. The orientation of the fibers, the matrix, and the interfaces between layers affect their durability against fatigue, and they usually require lower frequencies to avoid thermal effects or premature degradation.
At Servosis we have designed specific equipment to work with different types of materials, allowing for precise adjustment of the load regime depending on the nature of the test.
Conditions of the test environment
Some applications require testing under specific environmental conditions: climatic chambers, environments with controlled humidity, extreme temperatures, or even immersion in fluids. These conditions not only affect the material's behavior but also the testing rate. For example, if work is performed at high temperatures, it may be necessary to reduce the frequency to avoid overheating.
It is also common to combine fatigue with other variables, such as corrosion or external vibrations. In these cases, the test becomes more complex and usually takes longer.
Equipment capacity and configuration
The type of machine used also plays a relevant role. Electromechanical machines have a limited range of frequencies, while servo-hydraulic systems, such as those manufactured by Servosis, allow higher frequencies, better load control and greater durability in long tests.
The use of digital control systems, automatic detection of cracks, shutdown due to breakage, continuous data acquisition, and advanced management software allows many stages of the process to be automated, minimizing errors and unproductive times.
Technical example: estimated duration
To illustrate, suppose that a fatigue test is to be performed with the following parameters:
- C45 steel probe, heat-treated.
- Maximum load: 50% of the elastic limit.
- Frequency: 15 Hz.
- Number of cycles until failure: 2.5 million.
Under these conditions, the test would take about 46 hours to run continuously, which is perfectly feasible in an automated and well-controlled system.
In contrast, the same test on an epoxy resin with short fiber loading, performed at 3 Hz, may require more than 90 hours to achieve the same number of cycles, and may be interrupted due to the need for thermal rests or intermediate calibrations.
Real test: long-lasting towing balls (Zaragoza)
A concrete example in our customer facilities is given in Zaragoza, where Servosis has supplied a specific system for Fatigue test on vehicle trailers. This type of component is subjected to combined loads and requires simulating millions of charge and discharge cycles with high repeatability.
By regulation, these tests must be performed at low frequencies and simulate real operating conditions, which can prolong their duration. several months. This is one of the most demanding cases we have handled, and it demonstrates how the duration of the trial can greatly exceed standard deadlines when maximum fidelity to the end use is required.
How to reduce time without losing precision
At Servosis we work constantly to shorten testing times without sacrificing the technical validity or reliability of the results. We do this through three channels:
- Precise configuration of the test protocol, Optimizing load, frequency, and fault detection.
- Process automation using control and data acquisition software, avoiding constant monitoring.
- Customized design for the testing team, Adapted to the specific conditions of the customer: desired frequency, environment, type of material and applicable regulations.
In addition, our systems include features such as crack initiation detection, temperature control in the loading environment, and compatibility with climatic chambers or accelerated corrosion systems.
There is no single time for all fatigue tests. The duration can vary from a few hours to several days, depending on factors such as the frequency of loading, the number of target cycles, the type of material, the environmental conditions, and the characteristics of the equipment.
The important thing is to understand the variables involved and to configure the experiment optimally from the start.
At Servosis, we accompany our clients from the design of the protocol to the interpretation of the results, ensuring efficient, precise, and customized fatigue testing. If you are planning an testing campaign or want to improve the efficiency of your current processes, we can help you.
Would you like to know more about how to optimize your fatigue tests?
Contact our technical team. We are here to help you find the most suitable solution.
