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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: VB.NET SynthesisAPI Module1 Main sp ALTAStressProfile sp.AddSegment(200, 125) sp.AddSegment(300, 175) sp.AddSegment(350, 200) sp.AddSegment(375, 250) sp.RepeatCycle = False ADS ALTADataSet ADS.AddStressProfile(sp) ADS.AddStressDefinition(, ALTASolverLSR.Power, 100) 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) ADS.AddSuspension(328, 1, sp) ADS.AddSuspension(375, 3, sp) ADS.AnalysisSettings.ModelType = ALTASolverModel.CumDamage ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull ADS.Calculate r Double r = ADS.FittedModel.Time(.99) MsgBox( & r)

Discussion
The ALTAStressProfile class represents a time-dependent stress profile. In this example, the stresses are increased in a stepwise fashion. The  property is set to False, indicating that all times after the last segment will use the stress value defined in the last segment.

sp ALTAStressProfile sp.AddSegment(200, 125) sp.AddSegment(300, 175) sp.AddSegment(350, 200) sp.AddSegment(375, 250) sp.RepeatCycle = False

Next, create an ALTA data set by declaring a new ALTADataSet object, and then using the AddStressProfile method to associate the stress profile with the object.

ADS ALTADataSet ADS.AddStressProfile(sp)

Use the AddStressDefinition method to define the name, stress transformation and use stress level of the stress profile.

ADS.AddStressDefinition(, ALTASolverLSR.Power, 100)

The data set can contain failures, suspensions or interval data. The following example shows how to use the AddFailure method and AddSuspension method to add the stress profile to the data points.

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) ADS.AddSuspension(328, 1, sp) ADS.AddSuspension(375, 3, sp)

The  property returns an ALTAAnalysisOptions object, which represents the analysis settings of the data set. In the following example, we use the  and   properties of the object to specify the life-stress relationship and distribution.

ADS.AnalysisSettings.ModelType = ALTASolverModel.CumDamage ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull

Use the Calculate method to analyze the data set. The method returns a message box that shows the estimated parameters of the model, based on the settings specified in the  property.

ADS.Calculate

The  property gets a cModel object that represents the fitted model of the analysis. From the model, you can calculate useful metrics such as reliability, failure rate, mean time, etc. In this example, we use the cModel.Time method to calculate for the B1 life.

r Double r = ADS.FittedModel.Time(.99) MsgBox( & r)