Environmental simulations and vibration tests
Environmental simulation – With realistic test systems to reliable simulation models
Products, components and entire constructions are subject to enormous stresses in daily use. These stresses have their origin either in the use itself or – to an ever greater extent – in the influences of the environment. In other words, the environment. In order to subject the durability and life expectancy of certain constructions to controlled tests and to specifically avoid damage through knowledge of the behaviour under environmental influences, environmental simulation plays a major role today.
What is environmental simulation?
The simplest and certainly most reliable, because most realistic, way to assess the behaviour of constructions is to observe and analyse them in practical use. Because then both the environmental influences and the requirements from use ultimately match reality 100 per cent. Because they are real.
The problems with this approach are obvious. On the one hand, the information is only obtained in the course of the product’s life and can therefore not be incorporated into the development in advance. In addition, the procedure is very lengthy and ultimately lasts as long as the design lasts. On the other hand, it is also not guaranteed that the product under consideration is actually subjected to the maximum stress, so that the knowledge gained only provides reasonably reliable results when the sum of numerous observations is added up.
This is precisely where environmental simulation in a controlled test laboratory comes in. It not only simulates uniform and clearly defined environmental and usage influences. At the same time, it does so in a controlled and considerably accelerated process. The result is reliable results on the behaviour of constructions under or even beyond the maximum expected influences and over a simulated entire service life. In this way, reliable results can already be obtained in the development stage and incorporated into the optimisation of components or constructions before actual use begins.
Mechanical, thermal or chemical simulations – different aspects of reality in environmental simulation
Which aspects of reality are recreated in an environmental simulation depends on the design and objective of the simulation test and the product. Typical simulation contents, i.e. environmental conditions, in the test laboratory can be mechanical loads of various types. However, climate tests with thermal simulations of particularly high or low temperatures or even chemical influences are also possible. For example, there are special climatic chambers in which climatic environmental conditions and temperature ranges can be simulated.
Probably the most widespread environmental simulation is certainly the simulation of vibrations or even movements on a macro and micro level in general. This is because movement is the physical quantity that has a very direct effect on the material and puts its integrity to the test. First and foremost, the movement resulting from movement or alternating load in the form of deformations or also vibrations plays a central role. However, thermal deformation in the course of temperature changes, for example due to exposure to sunlight or shading, can also represent important influences on the material and can be simulated in climate chambers with a wide range of temperatures.
Why an environmental simulation?
If we stay with the topic of mechanical deformation due to load, it quickly becomes clear why an environmental simulation is the tool of choice. If, for example, the joint of bridge components is subject to a load and consequently a “minimal” deformation every time a heavy truck passes over it, then this deformation naturally only occurs when a truck passes over it. If, for example, 500 such vehicles use the bridge every day, we are talking about 500 load cycles, which corresponds to a load every just under 3 minutes. The times in between are lost in terms of assessing the load. An environmental simulation reduces this time to the necessary minimum so that, for example, within a few hours or days, the load cycles can be completed over several years or even decades. In addition, the simulated loads always correspond to the maximum expected weight, i.e. the largest truck on the bridge. If necessary, even overloading can be simulated, so that extreme loads that may only occur a few times or even never in reality can be tested and evaluated for safe assessment of the structure.
Technically implementing an environmental simulation – the vibration test simulation as an example
The requirements of technical environmental simulation can be explained particularly well using the example of vibration test simulation. For this is rightly one of the “parade disciplines” of environmental testing:
Why simulate vibrations?
Vibrations are the most frequently occurring stresses that affect components or structures. They are usually active permanently or over longer periods of time and thus lead to a permanent load that adds up to enormous force effects over the service life. In addition, vibrations can originate from a wide variety of sources and are therefore inevitably the most frequent type of load.
Almost every prevailing load ultimately results in vibrations, which appear either as a direct effect or as a consequence of other types of load. For example, the bridge already introduced as an example resonates as soon as a truck has passed it and the primary loading and unloading is over. In addition, vibrations also occur as a resonance of other loads caused by the passing vehicles. Finally, even wind and sometimes even rain lead to vibrations that affect the components with minimal amplitude, but overall with a force that cannot be neglected.
Precisely because the vibrations occur permanently or at least in the long term with low intensity, environmental simulation offers enormous advantages. This is because the peculiarities of vibrations offer excellent conditions for simulating them at all and, moreover, for allowing them to act on the component or material in a highly accelerated sequence. On the one hand, the results are reliable and, on the other hand, they are obtained in a significantly shorter time.
Environmental simulation as an accelerated “worst case”
It is typical for the environmental simulation that not only an accelerated time sequence is chosen. In addition, there is a clear definition of the intensity, in this case the oscillation. Possible are intensity curves, i.e. load simulations with variable, usually increasing intensity. In doing so, the maximum load to be expected mathematically is targeted and exceeded in a controlled manner. This makes it possible to determine safety margins that can, for example, compensate for special cases resulting from deviating “real” conditions. One can therefore confidently regard the environmental simulation as a kind of controlled and thus also intentionally induced worst case scenario. Only monitored and in fast motion. In this way, it is not only possible to predict mathematically, but also to actually experience in a practical test how the component under consideration will behave under the most adverse conditions imaginable.
Earthquake monitoring – a task for the future
In the course of climate change, mankind must prepare for an increasing number of unexpected environmental events. These include not only extreme weather conditions, which are already noticeable today, but also geological activities. Even in earthquake-poor Germany, an increase in seismic activity can therefore be foreseen in the future – with earthquakes. Long before people even perceive earthquakes as such, they can pose a threat to buildings and infrastructure. That is why it is essential to accurately record and measure even the slightest ground movements and tremors.
From technology to nature – measuring and recording vibration behaviour
The arc from vibration test simulation to earthquake monitoring closes with the observation that an earthquake ultimately also causes “only” ordinary vibrations. But not limited to individual components, but at least on a regional scale. The effect on a building component is the same. Whether a lorry passes a bridge or it is set into vibration by a moving subsoil – basically it is always a vectorised force effect on the material.
Now it is not a big step from actively vibrating matter with determination of the vibration behaviour to an externally generated vibration with an equally exact recording and evaluation of exactly these vibrations – i.e. the step from the vibration test simulation to the seismograph.
Recording and testing vibrations – the interaction of seismography and vibration test simulation
It is not only technically that environmental simulation and the measurement of vibrations generated from the environment are closely connected. There are also meaningful connections in terms of content to make materials and constructions even more reliable, durable and safe.
Earthquake monitoring can be used to record and quantify current influences on our environment. From changes in the earth’s behaviour, conclusions can be drawn about earthquake events to be expected in the future. These findings can now be incorporated into the vibration test simulation for the development of earthquake-resistant constructions, so that people can live safely in the future. Finally, the monitoring of these constructions via seismographs allows us to check whether the future earthquake events actually correspond to the assumptions or whether the assumed maximum loads are exceeded. If this is the case, a targeted check for damage and possible hazards can be carried out.
Conclusion – responding even better to the changing demands of reality through environmental simulation
The detection and simulation of vibrations thus play a central role in the development of a safe environment for people. Climate change, which can no longer be dismissed out of hand, is leading to forecasts of future stresses on materials and components in all areas of daily life that can no longer be covered by empirical values. That is why it is essential today both to record the changing influences and to reliably simulate future expectations. Only in this way can constructions be created that have the “experience” of decades of use right from the start.
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