The effect of microstructural morphology on damage in multi-phase materialsCitation for published version (APA):Geus, de, T. W. J., Peerlings, R. H. J., & Geers, M. G. D. (2014). The effect of microstructural morphology ondamage in multi-phase materials. Poster session presented at Mate Poster Award 2014 : 19th Annual PosterContest.

Document status and date:Published: 01/01/2014

Document Version:Accepted manuscript including changes made at the peer-review stage

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Download date: 27. Aug. 2021

MaterialsinnovationinstituteM

The effect of microstructural morphology ondamage in multi-phase materials

Tom de Geus, Ron Peerlings, Marc Geers

/ Department of Mechanical Engineering T.W.J.d.Geus@tue.nl

Industrial background

Important engineering examples of multi-phase materials aremetal matrix composite and dual phase steel (DPS). DPS is of-ten used in complex shaped structural parts of a car-body (figures)due to its unique combination of strength and ductility.

Material properties and failure

stre

ss

strain

weight~

strength

ductility

formability~

har

d

soft

dual phase

hardsoft

(b) microstructure(a)

goal

We consider a general dual phase material with a microstruc-ture that comprises hard particles embedded in a soft matrix(fig. b). The stress–strain response displays a combination ofthese phases (fig. a).

GoalTo improve the failure characteristics a better understanding of thefailure mechanisms is needed. Therefore we characterize

the distribution of phases (morphology) leading to thehighest damage (i.e. the ’worst’ microstructure),

macroscopic fracture initiation as a function of localfracture mechanisms.

Microstructural model

hard

soft

To systematically study the effect of the distribution of phases,a structured microstructural model is used. The damage re-sponse is calculated on an ensemble of many random microstruc-tures, using the finite element method.

Fracture initiationA local damage indicator is defined for ductile fracture inthe soft phase and brittle fracture in the hard phase.

Macroscopic fracture initiates when 1% of the grains in theensemble have fractured.

Morphology around fracture initiation

hardsoft "indifferent"

The average microstructure (phase) around the locations atwhich fracture initiates is calculated for the ensemble. It is re-markably similar for fracture initiation in the soft phase only (left)and hard phase only (right): a band of hard phase intersected bybands of soft phase in the direction of shear are critical.

Macroscopic fracture initiation

ensemble

stress triaxiality (volumetric / shear)

fract

ure

str

ain

plane straintension

plane strainpure shear

-0.5 0.0 0.5 1.0 1.50.00

0.05

0.10

0.15

0.20

The most striking result of the initiation of macroscopic fracture isthe fracture strain (vertical axis) for different stress states (hori-zontal axis). For low triaxialities ductile fracture of the soft phasedominates, whereas brittle fracture of the hard phase dominatesfor high volumetric stresses.

Conclusion and outlookWe have identified a critical morphology for damage.Macroscopic fracture initiation is dominated by the softphase or the hard phase depending on the stress state.

Open questions:

The influence of the sub-surface microstructure.The mechanisms governing the propagation of fracture.