Python Result fatigue calculation

Pernelle Marone-Hitz
Pernelle Marone-Hitz Member, Moderator, Employee Posts: 859
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Is there an example of fatigue calculation with DPF?

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  • Pernelle Marone-Hitz
    Pernelle Marone-Hitz Member, Moderator, Employee Posts: 859
    500 Comments Photogenic Name Dropper Solution Developer Community of Practice Member
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    edited December 2023

    The following example has no physical meaning and is just an illustration of DPF capabilies.
    It uses the dummy custom stress computed in this example, and reads the S-N curve of the material of the first body in the tree (adapt to your use case!).

    Note - a value of -1 or -2 in the result plot will indicate that the interpolation of the number of cycles to failure could not be performed (usually due to lack of material data to interpolate).

    Complete code:

    def LinearInterpolation(x,x1,y1,x2,y2):
        # Simple linear interpolation
        # Returns -1 if x is outside of [x1,x2]
        if x<x1 or x>x2:
            return -1 # out of range
        if y1==y2:
            return y1
        else:
            a=(y2-y1)/(x2-x1)
            b=y1-a*x1
            return a*x+b
    
    def GetLocalCyclesToFailure(sn_curve, local_stress_si):
        cycles_list = sn_curve["Cycles"][1:]
        alternating_stress_list = sn_curve["Alternating Stress"][1:]
        index = 0
        # Find closest cycle number in stress_data
        for i in range(len(cycles_list)):
            alt_stress = alternating_stress_list[i]
            if alt_stress < local_stress_si:
                index=i
                break
        # Get (cycles, alternating stress) points between which to interpolate
        if index!= len(cycles_list):
            y1=cycles_list[index]
            y2=cycles_list[index-1]
            x1=alternating_stress_list[index]
            x2=alternating_stress_list[index-1]
        else:
            return -2 # value is out of bounds
        return LinearInterpolation(local_stress_si,x1,y1,x2,y2) # return number of cycles
    
    def GetFieldCyclesToFailure(stress_op, sn_curve, analysis):
        import mech_dpf
        import Ans.DataProcessing as dpf
        node_ids = stress_op.outputs.getfields_container()[0].ScopingIds
        limit_field = dpf.FieldsFactory.CreateScalarField(1,'Nodal')
        stress_data = stress_op.outputs.getfields_container()[0]
        for nid in node_ids:
            local_stress =stress_data.GetEntityDataById(nid)[0]
            # Convert local stress to SI units
            local_stress_quantity = Quantity(str(local_stress) + '[' + analysis.CurrentConsistentUnitFromQuantityName("Stress") + ']')
            local_stress_si = local_stress_quantity.ConvertToUnitSystem("SI", "Stress").Value
            limit_field.Add(nid,[float(GetLocalCyclesToFailure(sn_curve, local_stress_si))])
        return limit_field
    
    
    def define_dpf_workflow(analysis):
        import mech_dpf
        import Ans.DataProcessing as dpf
        mech_dpf.setExtAPI(ExtAPI)
        data_source = dpf.DataSources(analysis.ResultFileName)
        model = dpf.Model(data_source)
        mesh =  model.Mesh
    
        # Get SN curves for material defined on first body in the Mechanical tree
        import materials
        first_body = Model.GetChildren(DataModelObjectCategory.Body, True)[0]
        material = ExtAPI.DataModel.GetObjectsByName(first_body.Material)[0]
        mat_enginerring_data = material.GetEngineeringDataMaterial()
        sn_curve = materials.GetMaterialPropertyByName(mat_enginerring_data,"S-N Curve")
    
        # Time sets
        timePointsOp =dpf.operators.metadata.time_freq_provider()
        timePointsOp.inputs.data_sources.Connect(data_source)
        timepoints = dpf.operators.metadata.time_freq_support_get_attribute(time_freq_support=timePointsOp,property_name="time_freqs",)
    
        # S1
        prin1 = dpf.operators.result.stress_principal_1()
        prin1.inputs.data_sources.Connect(data_source)
        prin1.inputs.time_scoping.Connect(timepoints)
        # S3
        prin3 = dpf.operators.result.stress_principal_3()
        prin3.inputs.data_sources.Connect(data_source)
        prin3.inputs.time_scoping.Connect(timepoints)
        # S1-S3
        minus_fc = dpf.operators.math.minus_fc()
        minus_fc.inputs.field_or_fields_container_A.Connect(prin1.outputs.fields_container)
        minus_fc.inputs.field_or_fields_container_B.Connect(prin3.outputs.fields_container)
        # Scale factor
        scale = dpf.operators.math.scale_fc()
        scale.inputs.fields_container.Connect(minus_fc)
        scale.inputs.ponderation.Connect(sqrt(2)/2)
    
        # Get alternate stress
        min_max = dpf.operators.min_max.min_max_over_time_by_entity()
        min_max.inputs.fields_container.Connect(scale)
        min_field_by_time =  min_max.outputs.getmin()
        max_field_by_time =  min_max.outputs.getmax()
        alternate_stress = dpf.operators.math.minus_fc()
        alternate_stress.inputs.field_or_fields_container_A.Connect(min_max.outputs.getmax())
        alternate_stress.inputs.field_or_fields_container_B.Connect(min_max.outputs.getmin())
    
        # Get cycles to failure
        new_field = GetFieldCyclesToFailure(alternate_stress, sn_curve, analysis)
        output = dpf.operators.utility.forward()
        output.inputs.any.Connect(new_field)
    
        # Plot
        dpf_workflow = dpf.Workflow()
        dpf_workflow.Add(output)
        dpf_workflow.SetOutputContour(output)
        dpf_workflow.Record('wf_id', False)
        this.WorkflowId = dpf_workflow.GetRecordedId()