Fatigue in aerospace engineering is an important aspect that is given high attention, because majority of service failure in an aircraft structure is as a result of it.
Fatigue failure in aircrafts can be caused by stress concentration and high cyclic load or vibration. Although dampers are used to expel vibration, small remnants can overtime, if not monitored properly add to fatigue on aircraft structures which can lead to failure. Unintentional flaws during production or maintenance can also add to fatigue accumulation in the structure.
Fatigue monitoring can begins as early as during the construction phase of an aircraft, because apart from high cycle loads (vibration) fatigue in aerospace structures can arise as a result of other in-service load, for example low cycle loads that are related with maneuvers, gust and landing.
As a result, Structural/stress analysis which involves carrying out a series of test on a structure to obtain stress values for different parts of the structure which can give a good prediction of how the structure will fare when exposed to different form of fatigue, is carried out in most structures.
With the constant advancement in aerospace engineering, issues like fatigue monitoring have been simplified to real time onboard monitoring instead of regular manual inspections (except during routine phase inspections). This can be achieved with the use of SHMs (structural health monitoring systems). They have to do with the application of damage detection processes and assessing the present state of a structure, and this could be by different means, like with the use of sensors and other monitoring devices, they have also proved to be able to reduce maintenance and operational costs.
With the use of these monitoring systems, the structural integrity of an aircraft can be monitored and also used to predict the future state of the aircraft structure. The most commonly used systems are sensors. Since the introduction of sensors, health monitoring has advanced in various ways and they have definitely helped in reducing the expense of monitoring mechanical structures. Several types of sensors are industrially produced today and they work differently in different applications.
For fatigue monitoring in aerospace structures the best form of sensors to apply will be one that has the ability to transform mechanical energy, in form of vibration and more, to electrical output signals that can be seen on a computer system on board an aircraft.
A good sensor with such attributes are piezoelectric sensors, the materials they are made up off have the piezoelectric effect which states that when a particular material experiences mechanical stress, an electric potential is generated conversely, such a material will also change shape when under the influence of an electric field.
When a piezoelectric sensor is deformed by a mass load, the crystals of the piezoelectric materials generate a voltage (positive or negative). This voltages can be represented inform of signals on a monitor, providing signal patterns on the structural state of the aircraft. The size of the sensor also makes it easier to use in different aerospace structures.
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