Exploring the differences between HALT and ALT, or Highly Accelerated Life Test and Accelerated Life Test. Plus when to use which when.
[Read more…]HALT or ALT
Articles tagged Life testing and accelerated life testing (ALT)
An experiment conducted to ascertain the time-to-failure characteristics of an item attributable to a specific failure mechanism. ALT shortens the time to failure by using more stressful conditions or higher use rates.
What is Wrong With Success Testing?
Three prototypes survive the gauntlet of stresses and none fail. That is great news, or is it? No failure testing is what I call success testing.
We often want to create a design that is successful, therefore enjoying successful testing results, I.e. No failures means we are successful, right?
Another aspect of success testing is in pass/fail type testing we can minimize the sample size by planning for all prototypes passing the test. If we plan on running the test till we have a failure or two, we need more samples. While it improves the statistics of the results, we have to spend more to achieve the results. We nearly always have limited resources for testing.
Let’s take a closer look at success testing and some of the issues you should consider before planning your next success test. [Read more…]
ALT or Durability Test?
A brief discussion on the difference and similarities of accelerated life testing (ALT) and durability testing. For one difference, ALT used high stress conditions to shorten the time to failure. Whereas, durability testing typically uses whole products and normal use condition.
[Read more…]Accelerated Life Testing Part-3 (Case Study in Minitab Software)
Dear viewers, I am happy to release this third video on Accelerated Life Testing. In this video of part-3, we have explained how to use Minitab software to analyse data of accelerated life test. The illustration uses Arrhenius Model, but the technique can be applied to other models as well.
The video will be useful to all those who want to learn and apply technique of Accelerated Life Testing. It would be of help to those who wish to take ASQ CRE certification exam. It would also be useful to DFSS practitioners.
[Read more…]Accelerated Life Testing (ALT) Part-2
Dear viewers, I am happy to release this second video on Accelerated Life Testing. In this video, we have discussed (i) Various models used to estimate the acceleration factor, such Arrhenius, Power law etc. (ii) Application examples showing calculation of acceleration factor (iii) Some mathematical relationships to estimate reliability at normal operating conditions and illustrated examples (iv) Types of stress loading used in ALT.
The video will be useful to all those who want to learn ALT and its mathematical relationships. It would be of great help to those who wish to take ASQ CRE certification exam. It would also be useful to DFSS practitioners.
[Read more…]Accelerated Life Testing (Part 1)
This is our first video on ALT in a series of videos on this important topic in reliability engineering. In this video, Hemant Urdhwareshe has introduced basic concepts of ALT. In our subsequent videos on ALT, we will do a more detailed discussion on mathematical treatment, selection of appropriate model and statistical distribution. We will explain these with application example on Minitab software. Hemant is a Fellow of ASQ and is ASQ CRE, CMBB, CSSBB, CQE and CMQ/OE. We are sure that viewers will find it useful.
[Read more…]What is Acceptable Test Duration?
And again there is no one answer for such simple question. Strongly depends on what type of test you need to conduct.
It is also very important to understand at which stage, design of the product. Usually at very early stages of the design there is many unexpected failures, when design is mature enough – failures become predictable, and there is one last period, called – wear out/aging stage.
[Read more…]What is ALT?
A short introduction to accelerated life testing or ALT. It is a method used to enhance product reliability by subjecting prototypes to stress levels significantly higher than those encountered in actual use. The idea is to rapidly induce failures which is equivalent to speeding up time.
[Read more…]Arrhenius or Erroneous
The following is a recent discussion on the sister Linkedin NoMTBF Group. It was and may continue to be a great discussion. Please take a look and comment on where you stand. Do you have some form of the Arrhenius reaction rate equation in your reliability engineering work? Join the discussion here with a comment or on the Linkedin group conversion.
Fred
[Read more…]Acceleration Factors
Temperature acceleration factor for ALT planning (question posted to Linkedin Society of Reliability engineers group, 5/7/12
Hello, can anyone advise me how to calculate temperature acceleration factor for a complex system including cards, RF elements, cables, motors and moving parts? Is the Arrhenius model valid for such systems, or there are more precise models? Thank you!
System or Component Testing
[Read more…]Fred i was asked this question and wanted to know what your thoughts were on this. R and D asked me what was the criteria to decide if to test at a component level or at a system level , my answer was that it should depend on what is the reliability and confidence level of the component
your thoughts?
thanks
sd
The Eyring Model
The Eyring Model for Accelerated Testing
Sometimes the reaction rate of a process relies on two stresses. For chemical reactions temperature seems to influence the rate of the reaction. Yet, other stresses such as humidity or voltage may also play a significant role.
H. Eyring suggested a model that assumes the contribution of each stress on the reaction rate is independent thus one could multiple the respective stress contributions to the rate of reaction.
The Erying model provides a means to account for the contributions of temperature and another stress when modeling the time to failure of select failure mechanisms. [Read more…]
ALT Allocation of Test Units
One question that you should consider when planning multiple stress accelerated life test (ALT) is the allocation of test units to the various stresses.
We want to create a model detailing the relationship between stress and time to failure. We also want to project the time to failure estimates to use conditions. Ideally, we test at nominal conditions only and gather time to failure information. We do not have the luxury of time thus explore using ALT.
One method of allocation is to place an equal number of samples with each stress level. Is that the best approach? [Read more…]
Electromigration Accelerated Life Testing
Black’s Equation
Black’s equation for estimating the time to failure due to electromigration is a classic. James Black explored and wrote about electromigration in aluminum metallization within semiconductors since 1969.
He and others have explored other materials used as conductors prone to electromigration. Thus, there are a number of models and constants available to match your particular system.
Let’s take a look at the general equation for a microcircuit conductor after a brief description of the failure mechanisms called electromigration. [Read more…]
Metal Fatigue Failure Mechanism Accelerated Life Testing
Metal is a wonderful, strong, material. Yet under certain types of stresses metal can fail One in particular is fatigue due to cyclic motion.
Metals in a solid state have an atomic level lattice structure. This provides the strength and flexibility. It is the flexibility part that causes trouble. We don’t get the benefit of flexibility for free. As the metal bends it ‘adjusts’ the lattice to accommodate the motion. In doing so, it changes the metal properties becoming a bit more brittle, for example.
In most cases a very small motion causes imperceptible changes and loss of functionality. In some cases, like bending a wire coat hanger with the intent to break it, just a few cycles of dramatic bending is enough to break the wire.
In metal applications that experience cyclic motion and the risk of metal fatigue failure may occur during the expected duration of product use, we may need to characterize the time to failure behavior. An accelerated life test for a metal fatigue failure mechanism is not difficult, yet does take some planning to get meaningful results. [Read more…]