View source for Perform Accelerated Life Testing Data Analysis with Stress Profiles

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If you have [http://www.reliasoft.com/alta/index.htm ALTA PRO], you can use the Synthesis API to analyze an ALTA data set with time-dependent stress profiles. In this tutorial, you will learn how to define stress profiles, analyze an ALTA data set, and obtain analysis results from the model.

Note that this tutorial is for demonstration purposes only; it doesn't take efficiency into account and doesn't include any exception handling. 

==Tutorial: Accelerated Life Testing Data Analysis - Stress Profiles ==
This example demonstrates how to use the Synthesis API to analyze an ALTA data set with a single stress profile and obtain an estimate of the B1 life (i.e., time at which reliability is equal to 99%). A discussion of the example follows. The VBA version of the code sample is available [[Perform_Accelerated_Life_Testing_Data_Analysis_with_Stress_Profiles/VBA|here]]. 

The data sets used in this example are:
<div style="width:100%;">
<div style="width:50%; margin: auto;">
<div style="float:left; margin-right:20px;">
{|{{table}}
|+Stress Profile
|Start||End||Stress
|-
|0||200||124
|-
|200||300||175
|-
|300||350||200
|-
|350||375||250
|}
</div>
<div style="float:left;">
{|{{table}}
|+Data Set
|Number in State||State||Time to F or S
|-
|1||F||252
|-
|1||F||280
|-
|1||F||320
|-
|1||S||328
|-
|1||F||335
|-
|1||F||354
|-
|1||F||361
|-
|1||F||362
|-
|1||F||368
|-
|3||S||375
|}
</div>
</div></div>
<div style="clear:both;"></div>
 '''VB.NET'''
 
 {{APIPrefix|Imports}} SynthesisAPI 
 
 {{APIPrefix|Module}} Module1
    {{APIPrefix|Sub}} Main()
  
  {{APIComment|'Declare a new stress profile and define its properties.}} 
    {{APIPrefix|Dim}} myProfile {{APIPrefix|As New}} cProfile ({{APIString|"stressProfile"}})
    myProfile.ProfileType = ProfileTypeEnum.Stress
    myProfile.IsCyclical = False
 
  {{APIComment|'Define four segments for the stress profile.}} 
    {{APIPrefix|Dim}} listofsegments() {{APIPrefix|As}} ProfileSegment = {
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 200, .Value = 124},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 300, .Value = 175},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 350, .Value = 200},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 375, .Value = 250}
       } 
 
  {{APIComment|'Add the segments to the stress profile.}} 
    myProfile.SetSegments(listofsegments)
 
  {{APIComment|'Declare a new ALTADataSet object.}} 
    {{APIPrefix|Dim}} ADS {{APIPrefix|As New}} ALTADataSet
 
  {{APIComment|'Assign the stress profile to the data set.}} 
    ADS.AddStressProfile(myProfile)
 
  {{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)
  
  {{APIComment|'Add the failure times to the data set.}}
    ADS.AddFailure(252, 1, myProfile)
    ADS.AddFailure(280, 1, myProfile)
    ADS.AddFailure(320, 1, myProfile)
    ADS.AddFailure(335, 1, myProfile)
    ADS.AddFailure(354, 1, myProfile)
    ADS.AddFailure(361, 1, myProfile)
    ADS.AddFailure(362, 1, myProfile)
    ADS.AddFailure(368, 1, myProfile)
    
  {{APIComment|'Add the suspensions to the data set.}}
    ADS.AddSuspension(328, 1, myProfile)   
    ADS.AddSuspension(375, 3, myProfile) 
  
  {{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 [[CProfile_Class|cProfile]] class represents a time-dependent stress profile. The <code>IsCyclical</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 properties.}} 
    {{APIPrefix|Dim}} myProfile {{APIPrefix|As New}} cProfile ({{APIString|"stressProfile"}})
    myProfile.ProfileType = ProfileTypeEnum.Stress
    myProfile.IsCyclical = False

The [[ProfileSegment Class|ProfileSegment]] class represents the segments of the associated cProfile object. In this example, the stresses are increased in a stepwise fashion.

  {{APIComment|'Define four segments for the stress profile.}} 
    {{APIPrefix|Dim}} listofsegments() {{APIPrefix|As}} ProfileSegment = {
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 200, .Value = 124},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 300, .Value = 175},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 350, .Value = 200},
       {{APIPrefix|New}} ProfileSegment {{APIPrefix|With}} {.SegmentEnd = 375, .Value = 250}
       } 

After the segments are defined, they are added to the stress profile.

  {{APIComment|'Add the segments to the stress profile.}} 
    myProfile.SetSegments(listofsegments)

Next, 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(myProfile)

Use the [[ALTADataSet.AddStressDefinition|AddStressDefinition]] method to define the name, 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, myProfile)
   ADS.AddFailure(280, 1, myProfile)
   ADS.AddFailure(320, 1, myProfile)
   ADS.AddFailure(335, 1, myProfile)
   ADS.AddFailure(354, 1, myProfile)
   ADS.AddFailure(361, 1, myProfile)
   ADS.AddFailure(362, 1, myProfile)
   ADS.AddFailure(368, 1, myProfile)
     
 {{APIComment|'Add the suspensions to the data set.}}
   ADS.AddSuspension(328, 1, myProfile)   
   ADS.AddSuspension(375, 3, myProfile) 

The <code>AnalysisSetting</code> property stores a reference to the [[ALTAAnalysisOptions Class|ALTAAnalysisOptions]] object, which represents the analysis settings of the data set. In this example, we use the property to change some of the attributes of the object.

 {{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.  

 {{APIComment|'Analyze the data set.}}
   ADS.Calculate()

The <code>FittedModel</code> property gets the [[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 definitions must be equal to the number of stress profiles used in the analysis. For example:

 {{APIComment|'Define two stress profiles.}} 
   {{APIPrefix|Dim}} myProfile1 {{APIPrefix|As New}} cProfile
   {{APIPrefix|Dim}} myProfile2 {{APIPrefix|As New}} cProfile
 {{APIComment|...}}
 
 {{APIComment|'Assign the stress profiles to a data set.}} 
   {{APIPrefix|Dim}} ADS {{APIPrefix|As New}} ALTADataSet
   ADS.AddStressProfile(myProfile1)
   ADS.AddStressProfile(myProfile2)
 
 {{APIComment|'Define the stress transformations and use stress levels.}} 
   ADS.AddStressDefinition({{APIString|"Stress1"}}, ALTASolverLSR.Arrhenius, 100)
   ADS.AddStressDefinition({{APIString|"Stress2"}}, ALTASolverLSR.Power, 4)
 
 {{APIComment|...}}
 {{APIComment|'Add failure times.}}
   ADS.AddFailure(171, 1, SP1, SP2)
   ADS.AddFailure(174, 1, SP1, SP2)
 {{APIComment|...}}

===References===
*[[CProfile Class|cProfile Class]]
*[[ProfileSegment Class]]
*[[ALTADataSet Class]]
**[[ALTADataSet.AddStressProfile|ALTADataSet.AddStressProfile Method]]
**[[ALTADataSet.AddStressDefinition|ALTADataSet.AddStressDefinition Method]]
**[[ALTADataSet.AddFailure|ALTADataSet.AddFailure Method]]
**[[ALTADataSet.AddSuspension| ALTADataSet.AddSuspension Method]]
**[[ALTADataSet.Calculate|ALTADataSet.Calculate Method]]
*[[ALTAAnalysisOptions Class]]
*[[CModel Class|cModel Class]]
**[[CModel.Time|cModel.Time Method]]