Right-click Materials and choose Modify Material Parameters.

Figure 1.3: Modify Material Parameters

Scope the part that you would like to analyze with a different material. If elements have more than one Materials Assignment applied to them, the first Material Assignment defined in the tree will be used.

The Materials Assignment properties can be defined from a material used in the analysis, defined within Engineering Data (Manual) or picked from an nCode material *.mxd database (Database).

Manual Material Properties Definition

Pick a Based on Material from engineering data to base the new material on an existing material's data.

For a Strain Fatigue Type analysis, set the Strength Coefficient, Strength Exponent, Ductility Coefficient, Ductility Exponent, Cyclic Strength Coefficient, Cyclic Strain Hardening Exponent, Young's Modulus, Poissons's Ratio, and Tensile Ultimate Strength of the new material.

Figure 1.4: Materials Properties for Strain Analysis

When the material properties are fully defined, the Strain-Life relationship is represented. Shown below is the Coffin-Manson-Basquin formula, defining the relationship between strain amplitude and the number of cycles to failure :

The elastic life is given by:

where is the strength coefficient, E is the Young's Modulus and b is the strength exponent.

The plastic life is given by:

where is the ductility coefficient and c is the ductility exponent.

The total life is given by the sum of the elastic and plastic life:

Graphically, this is displayed as shown below:

Fatigue damage is predicted in the same way as for the S-N method - the damage due to an individual cycle is calculated by looking up the strain amplitude of that cycle on the curve to find the number of reversals to failure 2N_f. The damage assigned to that cycle is then 1/N_f.

For a Stress Fatigue Type analysis, set the S-N Curve, Stress Offset, Scale Factor, Young's Modulus, Poissons's Ratio, and Tensile Ultimate Strength of the new material.

For Stress Analysis, the nCode Multicurve Stress-Life Parameters are set to User Defined and populated from engineering data (if defined) when the Materials Assignment is created.

To import an S-N Curve, select a *.csv file containing the cycles data in the first column and the alternating stress in the second column. Multiple curves must be imported separately.

If nCode Multicurve Stress-Life Parameters are not defined in the engineering data, the definition is set to Program Controlled and default values for Nfc, SEIs, and Ne are used (see below).

Figure 1.5: Materials Properties for Stress Analysis

Each defined S-N curve is displayed as shown below:

Set the nCode Material Type to one of Grey Cast Iron, Nodular Cast Iron, Malleable Cast Iron, Cast Steel, Steel, Aluminum, and Cast Aluminum.

Materials Database Definition

As an alternative to the manual method above, material properties can be selected from an nCode material database.

The default materials applied for the analysis are taken from the iceflow_standard.mxd database, which can be found in the mats folder in the nCode installation. If the Analysis Type is Solid or Shell Seam Weld, the default material is seam_steel. If the Analysis Type is Short Fiber Composite, the default material is Valox 508 GF30.

To modify the default material for Stress, Strain, Gray Iron, Safety Factor, Short Fiber Composite, Solid or Shell Seam Weld analysis:

Insert a Materials Assignment object.

In the case of Stress Life analysis, the S-N Curve Definition property must first be defined as either Mean Stress, R-Ratio, or Temperature.

In the case of Strain Life analysis, the S-N Curve Definition property must first be defined as either Strain or Temperature.

Set the Database by selecting the *.mxd database file where all the nCode materials are defined.

This file is copied to the current directory. The DesignLife add-on filters the materials found in this database.

For Stress Life and Safety Factor, it lists those that are valid for Stress Life analysis (nCodeSNMeanStressCurveContainer or nCodeSNRRatioCurveContainer type).

For Strain Life, it lists those that are valid for EN analysis (nCodeENMatData type).

For Solid and Shell Seam Weld, it lists those that are valid for Seam Weld analysis (nCodeSNSeamWeldMatData type).

For Short Fiber Composite, it lists those that are valid for Short Fiber Composite analysis (nCodeSFCBasquinCurveContainer type).

For Stress Life or Strain Life, if Temperature is selected, it lists those that are valid for temperature-dependent analysis (nCodeSNTemperatureCurveContainer or nCodeENTemperatureCurveContainer types). In this case, the Default Temperature parameter for the material will also be exposed and assigned to the scoped material assignment parts.

Select the new Material.

Surface Finish and Surface Treatment Settings

Surface finish and treatment can have a significant effect on fatigue behavior. Rough surface finishes due to machining marks, for example, will in general reduce the fatigue strength, whereas surface treatments are often applied to increase the fatigue strength.

In nCode, surface finish and treatment effects are modeled in the S-N and E-N engines by means of a single surface factor K_sur. This works in a different way from the scale factor described above, with which it should not be confused. The surface factor is used to adjust the material curve. The application is slightly different for the S-N and E-N methods, but the basic principle is the same—the surface factor is applied to the fatigue strength of the material in the high cycle (long-life) regime, but the effect reduces in the low cycle (short-life) regime. The details of the application of the surface factor are given in the DesignLife Help, with the sections describing the S-N and E-N analysis engines. K_sur is the product of three factors, which can be defined via the material map. Each of these has default value of 1.

K_sur = K_treatment x K_user x K_roughness

Where K_treatment is the Surface Treatment Factor, K_user is the User Surface Factor and K_roughness is the Roughness factor.

Set the Surface Treatment Factor to adjust the fatigue strength to take into account surface treatment. A factor > 1 will result in an improvement in fatigue strength. The Surface Treatment Factor should be a positive float number. The default value is 1.0.

Set the User Surface Factor to adjust the fatigue strength for any unspecified reason. A factor > 1 will result in an improvement in fatigue strength. The User Surface Factor should be a positive float number. The default value is 1.0.

The Roughness factor is defined through the Surface Finish property.

If one of the surface roughness descriptions is selected (Polished, Ground, Machined, Poor Machined, As Rolled, or As Cast), the value for the surface roughness is as shown in the table below.

If the Surface Finish is set to Enter Surface Roughness, the Surface Roughness [microm] setting is exposed. The Surface Roughness Factor will then be calculated based on the specified value.

If the Surface Finish is set to Enter K Roughness, the Roughness Factor setting is exposed to be set directly, based on your experience or on experimental evidence.