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If you have [http://www.reliasoft.com/alta/index.htm 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:
{|{{table}}
|+Stress Profile
|Start||End||Stress
|-
|0||200||125
|-
|200||300||175
|-
|300||350||200
|-
|350||375||250
|}
{|{{table}}
|+Data Set
|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'''
{{APIPrefix|Imports}} SynthesisAPI
{{APIPrefix|Module}} Module1
    {{APIPrefix|Sub}} Main()
 
  {{APIComment|'Declare a new stress profile and define its segments.}}
    {{APIPrefix|Dim}} sp {{APIPrefix|As New}} ALTAStressProfile
    sp.AddSegment(200, 125)
    sp.AddSegment(300, 175)
    sp.AddSegment(350, 200)
    sp.AddSegment(375, 250)
    sp.RepeatCycle = False
  {{APIComment|'Declare a new ALTADataSet object.}}
    {{APIPrefix|Dim}} ADS {{APIPrefix|As New}} ALTADataSet
  {{APIComment|'Assign the stress profile to the data set.}}
    ADS.AddStressProfile(sp)
  {{APIComment|'The stress profile uses the logarithmic (power LSR) stress transformation}}
  {{APIComment|'and has a use stress level = 100.}}
    ADS.AddStressDefinition({{APIString|"Stress1"}}, ALTASolverLSR.Power, 100)
 
  {{APIComment|'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)
   
  {{APIComment|'Add the suspensions to the data set.}}
    ADS.AddSuspension(328, 1, sp) 
    ADS.AddSuspension(375, 3, sp)
 
  {{APIComment|'Use the cumulative damage - Weibull model to analyze the data set.}}
  {{APIComment|'Keep all other analysis settings at default.}}
    ADS.AnalysisSettings.ModelType = ALTASolverModel.CumDamage
    ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull
 
  {{APIComment|'Analyze the data set.}}
    ADS.Calculate()
  {{APIComment|'Calculate the B1 life and display the result.}}
    {{APIPrefix|Dim}} r {{APIPrefix|As}} Double
    r = ADS.FittedModel.Time(.99)
    MsgBox({{APIString|"B1 Life: "}} & r)
    {{APIPrefix|End Sub}}
{{APIPrefix|End Module}}
==Discussion==
The [[ALTAStressProfile_Class|ALTAStressProfile]] class represents a time-dependent stress profile. In this example, the stresses are increased in a stepwise fashion. The <code>RepeatCycle</code> property is set to False, indicating that all times after the last segment will use the stress value defined in the last segment.
{{APIComment|'Declare a new stress profile and define its segments.}}
  {{APIPrefix|Dim}} sp {{APIPrefix|As New}} ALTAStressProfile
  sp.AddSegment(200, 125)
  sp.AddSegment(300, 175)
  sp.AddSegment(350, 200)
  sp.AddSegment(375, 250)
  sp.RepeatCycle = False
Next, we create an ALTA data set by declaring a new [[ALTADataSet Class|ALTADataSet]] object, and then using the [[ALTADataSet.AddStressProfile|AddStressProfile]] method to associate the stress profile with the object.
{{APIComment|'Declare a new ALTADataSet object.}}
  {{APIPrefix|Dim}} ADS {{APIPrefix|As New}} ALTADataSet
 
{{APIComment|'Assign the stress profile to the data set.}}
  ADS.AddStressProfile(sp)
Use the [[ALTADataSet.AddStressDefinition|AddStressDefinition]] to define the stress transformation and use stress level of the stress profile.
{{APIComment|'The stress profile uses the logarithmic (power LSR) stress transformation}}
{{APIComment|'and has a use stress level &#61; 100.}}
  ADS.AddStressDefinition({{APIString|"Stress1"}}, ALTASolverLSR.Power, 100)
The data set can contain failures, suspensions or interval data. The following example shows how to use the [[ALTADataSet.AddFailure|AddFailure]] method and [[ALTADataSet.AddSuspension|AddSuspension]] method to add the stress profile to the data points.
{{APIComment|'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)
   
{{APIComment|'Add the suspensions to the data set.}}
  ADS.AddSuspension(328, 1, sp) 
  ADS.AddSuspension(375, 3, sp)
The AnalysisSetting property returns an [[ALTAAnalysisOptions Class|ALTAAnalysisOptions]] object, which represents the analysis settings of the ALTADataSet object. In the following example, we use the <code>ModelType</code> and <code>Distribution</code> properties of the ALTAAnalysisOptions class to specify the life-stress relationship and distribution.
{{APIComment|'Use the cumulative damage - Weibull model to analyze the data set.}}
{{APIComment|'Keep all other analysis settings at default.}}
  ADS.AnalysisSettings.ModelType = ALTASolverModel.CumDamage
  ADS.AnalysisSettings.Distribution = ALTASolverDistribution.Weibull
Use the [[ALTADataSet.Calculate|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 AnalysisSettings property.
{{APIComment|'Analyze the data set.}}
  ADS.Calculate()
The FittedModel property gets a [[CModel Class|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|cModel.Time]] method to calculate for the B1 life.
{{APIComment|'Calculate the B1 life and display the result.}}
  {{APIPrefix|Dim}} r {{APIPrefix|As}} Double
  r = ADS.FittedModel.Time(.99)
  MsgBox({{APIString|"B1 Life: "}} & r)
==Notes==
For analyses that require multiple stress profiles, the number of stress types must be equal to the number of stress profiles used in the analysis. For example:
{{APIComment|'Define two stress profiles.}}
  {{APIPrefix|Dim}} SP1 {{APIPrefix|As New}} ALTAStressProfile
  {{APIPrefix|Dim}} SP2 {{APIPrefix|As New}} ALTAStressProfile
{{APIComment|...}}
{{APIComment|'Assign the stress profiles to a data set.}}
  {{APIPrefix|Dim}} ADS {{APIPrefix|As New}} ALTADataSet
  ADS.AddStressProfile(SP1)
  ADS.AddStressProfile(SP2)
{{APIComment|'Define the stress transformations and use stress levels.}}
  ADS.AddStressDefinition({{APIString|"Stress1"}}, ALTASolverLSR.Arrhenius, 100)
  ADS.AddStressDefinition({{APIString|"Stress2"}}, ALTASolverLSR.Power, 4)
You can then use the overloaded methods to add the stress profiles to the data points:
{{APIComment|...}}
{{APIComment|'Add failure times.}}
  ADS.AddFailure(171, 1, SP1, SP2)
  ADS.AddFailure(174, 1, SP1, SP2)
{{APIComment|...}}
===References===
*[[ALTAStressProfile Class]]
*[[ALTADataSet Class]]
*[[ALTADataSet.AddStressProfile|ALTADataSet.AddStressProfile Method]]
*[[ALTADataSet.AddStressDefinition|AddStressDefinition Method]]
*[[ALTADataSet.AddFailure|ALTADataSet.AddFailure Method]]
*[[ALTADataSet.AddSuspension| ALTADataSet.AddSuspension Method]]
*[[ALTADataSet.Calculate|ALTADataSet.Calculate Method]]
*[[ALTAAnalysisOptions Class]]
*[[CModel Class|cModel Class]]

Latest revision as of 15:37, 7 September 2016

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