Jonathan Newell talks to TÜV SÜD Product Services about how extreme conditions may be closer to home than you think.
When we think about testing for extreme environments, our thoughts naturally fall to military applications and imagine the arduous conditions experienced by a fighter jet pulling high “g” manoeuvres at 75,000 ft over the Arctic Circle before making a heavy landing on a washboard runway in the desert.
Certainly, such applications consume the time of many environmental engineers working in the defence and aerospace industries but an increasingly more demanding consumer base looking for permanently available connectivity, portability and highly reliable, long-lasting products is resulting in the rigours of environmental extremes being applied to more down-to-earth products.
At TÜV SÜD Product Services in Segensworth, the products under test include everything from seemingly mundane consumer goods through to sophisticated space satellites and all are subjected to shock, vibration and climatic tests to make sure they are equipped to face a service life in a variety of environmental conditions.
I spoke to the company’s Sales Team Leader, Craig Foster, about the conditions they test for and what is driving the requirement for such testing outside such obvious extremes as military application.
Induced and natural environments
Most of the extremes encountered as a result of natural environments are associated with extreme applications such as space travel, altitude and exposure to the earth’s temperature and humidity extremes.
For the remainder, the kinds of environments that products are exposed to are more likely to be induced or man-made and are product specific. “To understand the difference between natural and induced, the natural environment was what was here before we arrived on the planet,” Foster explained.
He went on to say that the induced environment is the reason why there are so many product specific standards, such as for aviation. “Except for natural phenomena such as earthquakes, vibration is always induced and hardly ever occurs naturally in any extreme form,” he said. Vibration testing on aircraft is very product specific with the profile for helicopters being different from jet aircraft and those with propellers.
“Propellers create a sinusoidal vibration which we recreate on our tables with an additional random component whereas helicopters have two sine components and one random,” explained Foster.
Product failures due to the induced environment result from low or high temperature, the effects of solar radiation, humidity and vibration.
Extremes of temperature outside the normal operating range of the product can affect the viscosity of fluids or the values of electronic components. At high temperatures, electronics can start burning out and differential thermal properties in materials can cause binding. Material properties also change at high or low temperatures and pigments can be affected leading to unwanted changes in colour.
The rate of change of temperature can also have undesired effects, something which TÜV SÜD tests in its thermal cycling chambers. A fast rate of change of temperature is typically greater than 2C°/min with thermal shock being anything >20C°/min.
According to Foster, one climatic phenomenon that is often overlooked is solar loading, the effect where temperature rises suddenly due to being exposed to direct sunlight. Examples include a mobile phone on a beach towel, a GPS navigator stuck to a car windscreen and telecommunications cabinets installed in exposed locations.
Solar loading has a value of 1120W/m2 and is the same everywhere in the world so the effect of solar loading is the same on a sunny day in Manchester as it is on the Costa Brava.
The TÜV SÜD Product Services facility in Segensworth has a chamber where induced solar testing can be performed at the standard rate of 1120W/m2.
One effect of solar loading is known as actinic degradation, a photochemical process which results in the loss of properties of the material the radiation is falling upon, something very familiar to people who bought red cars in the 70s and 80s which turned into a matte pink colour.
Humidity is a climatic condition that is often overlooked and can have serious consequences on electrical installations. Roadside cabinets for electrical and telecommunications distribution suffer from both solar loading and humidity problems despite appearing to be just a benign box on the side of the road.
Without adequate ventilation, such cabinets “sweat” internally and the moisture can damage electrical circuitry and cause extensive corrosion. Foster gave another example he had witnessed where a railway company had been so thorough in protecting the mechanism for operating points on the track that it was completely sealed. TÜV SÜD Product Services was presented with a product that was suffering from severe corrosion despite being sealed from the weather and quickly diagnosed humidity as being the cause.
Shock and vibration related failure modes include cracking, fractures, impacting and distortion. Resonances within structures and materials can create further problems, all of which can be uncovered through the proactive testing of designs before they are launched onto the market. Corrective redesigns to prevent field failures are an expensive option that can be avoided by providing test houses with vibration test profiles that match the expected induced environment that the final product will be exposed to.
Testing a product to understand the effects of the natural or induced environment can be performed individually or in combination. Examples are ice tests combined with altitude tests or vibration testing combined with thermal cycling.
Test facilities often provide the most common combinations and TÜV SÜD Product Services has vibration tables that can be used in various induced temperature conditions. Products can also be tested as a finished article or at the component or sub-assembly level.
Expect the extreme
To illustrate the increased need for robust products that will be exposed to unexpectedly extreme environments, Foster used the example of a mobile phone.
It wasn’t so long ago that dropping a phone would result in crazed touch sensitive screens and letting it fall into a puddle would write it off. Now, mobile phone suppliers are providing their customers with the kind of extreme protection that is being demanded and protects the phone from extreme situations such as:
* High temperature and humidity during global travel
* A fumbled drop from the hands, typically 1m onto a hard surface
* Exposure to rain and cold temperature whilst texting on the hoof
* Acceleration, shock and vibration in the owner’s pocket while horse-riding or during a trip to an amusement park
* Solar heating on the dashboard of a car
* Exposure to dust and sand at the beach
* Low pressure and low humidity on board an aeroplane
The kind of delicate mechanical structures and electronic circuitry in a mobile phone would once have demanded a controlled environment to assure its precise operation. Oblivious to its intricacies and unable to care less for them, users today expect the device to operate under the most extreme of environments and it’s the manufacturer’s quality responsibilities to ensure that it does.