assessment of fatique life according to fkm-code within hyperworks[1].pdf

ingenieurbüro huß & feickert

AutoFENA 3D

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EHTC 08

Assessment of fatigue life according to FKM-Code

within HyperWorks

Dr.-Ing. Wolfgang Feickert,

Dipl.-Ing. Tim Kirchhoff

Ingenieurbüro Huß & Feickert, Liederbach


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Overview

• German FKM-Code

• The tool AutoFENA 3D

• Demonstration

• Conclusion


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FKM-Code

• The German FKM-code [5. enhanced edition 2003], is a well

accepted code for the analytical strength assessment

for machine components

• The code is widely-used in german speaking

countries.

• Valid for steel (up to 500°C), cast irons (up to 500°C)

und aluminium (up to 200°C)


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FKM-Code

Assessment for:

• Static strength

– limit state

• Fatigue

– fatigue limit

– fatigue life

The calculation bases on:

• Nominal stresses in a section

• Local stresses (effective notch stress)

stress material

strength

construction

values

construction static

strength

construction

alternate strength

construction fatigue

limit


strength

safety factors

assessment

stress material

strength

construction

values

construction static

strength

construction

alternate strength


limit


strength

safety factors

assessment


AutoFENA 3D

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EHTC 08

FKM-Code

• Assessment procedure using local stresses

– Fatigue action: determine effective notch stress

– Fatigue resistance: against effective elastic notch

stress in terms of a universal S-N curve

– Summation of cumulative damage

– Use adequate safety factors depending on

inspection procedure, material, non destructive

testing and consequences of failure (damage)

• Results of FEM-analysis can be used

• Critical points must be chosen by the user


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FKM-Code

Necessary data:

• Amplitude und mean value

of elastic principle stresses

at the surface

• Stress gradient into the

inner part

• Material properties and

treatment

• Thickness


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The Tool

• Parser to the database of HyperWorks

– Export stress values, node- and element-data

• Transform the data into necessary format

– Calculation of load combinations

– Calculation of stress gradients

• Assessment according to FKM-Code

– Static strength

– Fatigue

• Writer to the database of HyperWorks

– Visualizing fatigue damage ratio within HyperView


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Program structure

- read data from HyperWorks

- interpretation of data

- write data into database

- do calculations on the data according to FKM-Code

- reads data from data base

- writes data to HyperWorks

- holds the data

input data from FE-Analysis

result data from static strength and fatigue assessment

data base


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Interpretation and calculation of loadcases

• Static, swelling, alternating loadcases

– Within the tool the load cases can be interpreted to be static,

swelling, alternating or to have an arbitrary stress factor

– All linear combinations of the load cases will be calculated

within AutoFENA3D

• Fixed load cases

– Load case combinations are already calculated within the

FEM-Code

– The stresses vary between the load cases


AutoFENA 3D

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EHTC 08

Calculation of linear combinations

• The load cases will be interpreted as user defined

– static: σ

– swelling: 0 to σ

– alternating: -σ to σ

– arbitrary: R=?

• All possible linear combinations will be calculated

automatically

• The combinations are calculated by adding the stress

tensors within the global coordinate system


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• The combination with the highest and the smallest

principle stress S1 and S3 will be calculated

• In all other load combinations the smallest and the

highest normal stress N3 and N1 in the direction of

the principle stresses are searched

• The mean value and the amplitude are calculated

between the principle stress and the normal stress

S1, N1 and S3, N3 respectively

Critical load combination


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Calculation of stress gradient

• The stress gradient is necessary to

calculate the plasticity factor (additional support)

• The stress gradient is calculated by

the form functions of a 4-Node-

Tetrahedron and a 8-Node-Hexahedron

• The stress gradient is

calculated for every

node on the surface


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Example flange

Load cases

trosional moment

bending moment

normal force

internal pressure


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Example flange

Stress distribution


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Example flange

Different meshing


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Result of FKM-Code

Hexahedron mesh coarse Hexahedron mesh fine

Utilisation ratio(The degree of fatigue strength capacity consumed)


AutoFENA 3D

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Result of FKM-Code

Tetrahedron mesh coarse Tetrahedron mesh fine

Utilisation ratio


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Summary

• Using the tool will lead to a faster assessment

• The selection of critical points by the user is omitted

• The calculation is more reliable

• Easier interpretation of results caused by visualization

over the whole assembly


AutoFENA 3D

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stress material

strength

construction

values

construction static

strength

construction

alternate strength


limit


strength

safety factors

assessment

assessment of fatique life according to fkm-code within hyperworks[1].pdf

Documents

fkmcodenecessary data

datainput data

assessment of fatigue

fkmcode assessment procedure

overview german fkmcode

local stresses fatigue

accepted code

load casesingenieurbro