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If you have ALTA PRO, you can use the Synthesis API to analyze a data set with time-dependent stress profiles. In this tutorial, you will learn how to define stress profiles, analyze a data set, and obtain analysis results from the model.
Tutorial: Accelerated Life Testing Data Analysis - Stress Profiles
The following example demonstrates how to define a single stress profile for an ALTA data set and use the analysis results to obtain the B1 life (i.e., time at which reliability is equal to 99%). A discussion of the example follows.
The data sets used in this example are:
| Start | End | Stress |
| 0 | 200 | 125 |
| 200 | 300 | 175 |
| 300 | 350 | 200 |
| 350 | 375 | 250 |
| Number in State | State | Time to F or S | Number in State | State | Time to F or S |
| 1 | F | 252 | 1 | F | 354 |
| 1 | F | 280 | 1 | F | 361 |
| 1 | F | 320 | 1 | F | 362 |
| 1 | S | 328 | 1 | F | 368 |
| 1 | F | 335 | 3 | S | 375 |
VB.NET Imports SynthesisAPI Module Module1 Sub Main() 'Declare a new ALTADataSet object. Dim ADS As New ALTADataSet 'Declare a new stress profile and define its segments. Dim sp As New ALTAStressProfile sp.AddSegment(200, 125) sp.AddSegment(300, 175) sp.AddSegment(350, 200) sp.AddSegment(375, 250) sp.RepeatCycle = False 'Use the logarithmic (power LSR) stress transformation. 'Use stress level = 100. ADS.AddStressDefinition("Stress1", ALTASolverLSR.Power, 100) 'Assign the stress profile to the data set. ADS.AddStressProfile(sp) 'Add the failure times to the data set. ADS.AddFailure(252, 1, sp) ADS.AddFailure(280, 1, sp) ADS.AddFailure(320, 1, sp) ADS.AddFailure(335, 1, sp) ADS.AddFailure(354, 1, sp) ADS.AddFailure(361, 1, sp) ADS.AddFailure(362, 1, sp) ADS.AddFailure(368, 1, sp) 'Add the suspensions to the data set. ADS.AddSuspension(328, 1, sp) ADS.AddSuspension(375, 3, sp) 'Use the cumulative damage - Weibull model to analyze the data set. 'Keep all other analysis settings at default. ADS.AnalysisSettings.ModelType = ALTASolverModel.CumDamage ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull 'Analyze the data set. ADS.Calculate() 'Calculate the B1 life and display the result. Dim r As Double r = ADS.FittedModel.Time(.99) MsgBox("B1 Life: " & r) End Sub End Module
Discussion
The ALTADataSet class represents an ALTA standard folio data sheet. The class contains all the methods and properties that allow you to define a data set and fit a life-stress relationship and distribution to the data.
'Declare a new ALTADataSet object. Dim ADS As New ALTADataSet
Use the AddStressDefinition method to define a stress type and the use stress level.
'Define a stress type with use stress level = 300. ADS.AddStressDefinition("Stress1",,300)
The data set can contain failures, suspensions or interval data. The following example shows how to use the AddFailure method to define failures and the AddSuspension method to define suspensions.
'Add failure times to the data set. ADS.AddFailure(245, 1, 353) ADS.AddFailure(110, 1, 373) ADS.AddFailure(180, 1, 373) ADS.AddFailure(200, 1, 373) ADS.AddFailure(50, 1, 393) ADS.AddFailure(70, 1, 393) ADS.AddFailure(88, 1, 393) ADS.AddFailure(112, 1, 393) ADS.AddFailure(140, 1, 393) ADS.AddFailure(160, 1, 393) 'Add suspensions to the data set. ADS.AddSuspension(250, 5, 353) ADS.AddSuspension(250, 3, 373)
The AnalysisSetting property returns an ALTAAnalysisOptions object, which represents the analysis settings of the ALTADataSet object. In the following example, we use the ModelType and Distribution properties of the ALTAAnalysisOptions class to specify the life-stress relationship and distribution.
'Use the Arrhenius-Weibull model to analyze the data set. 'Keep all other analysis settings at default. ADS.AnalysisSettings.ModelType = ALTASolverModel.Arrhenius ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull
To analyze the data set, use the Calculate method. The method returns a message box that shows the estimated parameters of the model, based on the settings specified in the AnalysisSettings property.
'Analyze the data set.
ADS.Calculate()
The FittedModel property gets a cModel object that represents the fitted model of the accelerated life testing data analysis. From the model, you can calculate useful metrics such as reliability, failure rate, mean time, etc. In this example, we calculate for the B10 life.
'Calculate the B10 life and display the result. Dim r As Double r = ADS.FittedModel.Time(.90) MsgBox("B10 Life: " & r)
Notes
For analyses that require a two-stress model, you will need to define two stress types, and then use the overloaded methods to add the data points. For example:
... 'Define two stress types. ADS.AddStressDefinition("Temp",,328) ADS.AddStressDefinition("Voltage",,2) 'Add failure times for Temp = 348 and Voltage = 3. ADS.AddFailure(620, 1, 348, 3) ADS.AddFailure(632, 1, 348, 3) ...