What is the relation between the product reliability that is calculated in lab using ALT (Accelerated Lab Tests) and the reliability in field ?
Is it always in most cases the Lab test reliability is more than field? Can we generalise it like this?
or
In most cases the field reliability is higher compared the ALT reliability?
Dear Dr. Sai Swaroop Maram,
corrosion monitoring is the quali/quantitative method by which the effectiveness of corrosion control and prevention techniques can be evaluated and provides the feedback to enable corrosion control and prevention methods to be optimized. Corrosion tests are usually divided into two main categories: laboratory tests and field tests, each of which has its pros and cons. For example, in laboratory tests, it is possible to accelerate the corrosivity of the environment to obtain results more rapidly, something that is impossible in field testing. On the other hand, the environmental conditions present in real-world applications are different to those in laboratory situations. Therefore, it is difficult to extend the results of laboratory tests to industry settings. Many investigations have been performed in the last years to clarify the role of environmental and climatic factors in the atmospheric corrosion of commonly used structural metals and coatings, as well as to simulate in laboratory their observed corrosion behaviour in field. Sometimes the corrosion performances of materials in accelerated laboratory tests show a degradation that can be correlated with in field expositions whereas, in other cases, it is impossible to compare laboratory tests with outdoor experimentations. In the case of atmospheric degradation, the tests involve exposing metal (coated or not coated) specimens to real marine environment, for specific periods of time, following standardized methods. After this step, detailed analysis of the different samples are carried out. On the contrary, in the case of sea water immersion testing, both anticorrosion and antifouling properties of the coating, that usually cover the substrate, must be considered. Also in these experiments, standardized methods are used.
Best regards, Pierluigi Traverso
The lab test reliability is not necessarily higher than that in the field. I'll give you examples of the opposite:
1) The lab test is conducted in worst case conditions (e.g. at the highest temperature encountered in field).
2) You monitor failure modes by test equipment, which detect "failures" which are not detected by the user. For example the acceleration of a motor is less than required by the spec.
3) When you do a lab test you figure out what the service profile is (e.g. equipment is used 50% if the time); If in reality it is less - then the test results will be pessimistic.
This is a big topic and the answer will depend on the field of application (aerospace, automotive, solar PV, semiconductor, etc...). In general you will find norms (like IEC and MIL for example) that proposes testing methods for reliability of the device. Problem is the correlation of the tests with the reality. Most of the tests relates well with "infant mortality" (bathtube curve) but not all relates or predict well the lifetime of the bdevice (see for example solar PV). Generally speaking, is more difficult to correlate lifetime and reliability to devices that are used outdoor compared with lifetime and reliability of devices that are components for indoor or industrial usage.
The reliability in the field will depend on the methodological design made for the evaluation of the product. It is important that the analysis in the field follows the procedures adopted in the laboratory, at least following the general objectives.
- Badges
- Science topic
- Similar topics
- Methodology
- Laboratory