Damage mechanics

Fatigue lifetime

2mp )(1mdN/dD

FEA and Fatigue

damage calculation.

Geometry

Material property

Damage evolution law

Mean load change – Prediction models

Linear Cycle Mix (LCM) effect

)L/L(Lmn mnmaxmax)LLCM

•Two constants need to be defined

•Constants change with the type of load spectrum

N [cycles to failure]

Resid

ual lo

ad

‘R

’ [k

N]

Fatigue load decreasing

ab

cd

e

No interaction effect considered

Interaction effect considered

LCMRR bc

Complex loading

Vertical jump approach

•Independent of type of load spectrum

•No constants need to be defined

•Can be applied to any type of interaction effects

N [cycles to failure]

Resid

ual lo

ad

‘R

’ [k

N]

Fatigue load decreasing

a

b

cd

No interaction effect considered

Interaction effect considered

Complex loading

Variable amplitude fatigue

Type of load interaction

Experimental results (No. of cycles)

Miner rule prediction (No. of cycles)

LCM approach (No. of cycles)

Vertical jump approach (No. of cycles)

L1 = 6.5kN; L2 = 8kNn1=10; n2=5

1706 5020 1850 1707

L1 = 6.5kN; L2 = 8kNn1=1000; n2=5 18085 32127 21174 17757

L1 = 8kN; L2 = 9.5kNn1=10; n2=5

976 845 1869 1022

L1 = 8kN; L2 = 6.5kNn1 = 10; n2=5

12966 2704 19925 9518

Results and discussion

AC DC against CAA surface pre-treatment

Static strength

Cycles to failure for max. fatigue load of 60% of static strength

0

2

4

6

8

10

12

14

0 500 1000 1500

Conditioning [ no. of hours]

Stat

ic s

tren

gth

[kN

] v

AC DC

CAA

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

0 500 1000

Cyc

les

to f

ailu

rev

Conditioning [ no. of hours]

CAA

AC DC

ACDC Summary

A two-stage anodisation process has been developed to facilitate interphase formation without compromising corrosion protection.

The process is simple, fast and robust.

Initial results show excellent adhesion and corrosion performance – comparable to CAA.

4. CONCLUDING REMARKS

Given an understanding of film formation mechanisms oxides can be nanoengineered for optimised adhesion.

Hexavalent chromium chemistry is widely used in Al processing within the aerospace, defence, automotive sectors. Drop-in replacements are urgently sought.

ACDC processes offer additional advantages:environmentally benign

simpleincreased processing

speeds.