Assessment of Fatique Life According to FKM-Code Within Hyper Works

8/7/2019 Assessment of Fatique Life According to FKM-Code Within Hyper Works

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ingenieurbro hu & feickert

AutoFENA 3D

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EHTC 08

Assessment of fatigue life according to FKM-Codewithin HyperWorks

Dr.-Ing. Wolfgang Feickert,Dipl.-Ing. Tim Kirchhoff

Ingenieurbro Hu & 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 wellaccepted code for the analytical strength assessmentfor machine components

The code is widely-used in german speakingcountries.

Valid for steel (up to 500C), cast irons (up to 500C)und aluminium (up to 200C)


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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 materialstrength

constructionvalues

construction static

strength

construction

alternate strength

construction fatiguelimit

construction fatiguestrength

safety factors

assessment

stress materialstrength

constructionvalues

construction static

strength

construction

alternate strength



safety factors

assessment


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AutoFENA 3D

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FKM-Code

Assessment procedure using local stresses

Fatigue action: determine effective notch stress

Fatigue resistance: against effective elastic notchstress in terms of a universal S-N curve

Summation of cumulative damage

Use adequate safety factors depending oninspection procedure, material, non destructivetesting 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 valueof elastic principle stressesat the surface

Stress gradient into theinner part

Material properties and

treatment

Thickness


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AutoFENA 3D

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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 fromHyperWorks

- interpretation ofdata

- write data intodatabase

- do calculationson the dataaccording toFKM-Code

- reads data fromdata base

- writes data toHyperWorks

- holds the data

input datafrom FE-Analysis

result data from staticstrength and fatigueassessment

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 calculatedwithin AutoFENA3D

Fixed load cases

Load case combinations are already calculated within theFEM-Code

The stresses vary between the load cases


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AutoFENA 3D

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Calculation of linear combinations

The load cases will be interpreted as user defined

static:

swelling: 0 to

alternating: - to arbitrary: R=?

All possible linear combinations will be calculatedautomatically

The combinations are calculated by adding the stresstensors within the global coordinate system


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The combination with the highest and the smallestprinciple 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 ofthe principle stresses are searched

The mean value and the amplitude are calculatedbetween the principle stress and the normal stressS1, N1 and S3, N3 respectively

Critical load combination


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Calculation of stress gradient

The stress gradient is necessary tocalculate 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 iscalculated for everynode on the surface


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Example flange

Load cases

trosional momentbending momentnormal forceinternal 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)


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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 visualizationover the whole assembly


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stress material

strength

construction

values

construction static

strength

construction

alternate strength



safety factors

assessment

Assessment of Fatique Life According to FKM-Code Within Hyper Works

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Transcript of Assessment of Fatique Life According to FKM-Code Within Hyper Works