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Experimental and Numerical Analysis of an In-Plane Shear

Specimen Designed for Ductile Fracture Studies

Presented byPRIYADARSHAN MAHANA

ROLL NO-10040014MACHINE DESIGN & ANALYSIS

Introduction

Experimental set-up for the first group specimen tests: (a)testing machine and the specimen; (b) extensometer and the specimen

Experimental set-up for the second group specimen tests

Applied force versus elongation for the six uniaxial tensile samples

Comparison of the longitudinal true strain derived from the test date by extensometer and DIC

Experimental and fitted curves of the true stress versus true strain for DP800

DIC is a non-contact optical technique used to measure thedeformation field of an in-plane object. It obtains themeasurement data by matching the grey intensity distributionof two sequential acquired images taken ‘before’ and‘after’ deformation, which are considered as the referenceimage and deformed image respectively. The light intensityat the point (x1, x2) in the reference image can be expressedby the grey matrix, G(x1, x2), over a selected subset. Thepoint (x1, x2) moves to a new location after deformation andis referred as the point ( x1’, x2’ ) in the deformed image, the

Geometry of the in-planeshear specimen: (a) geometricaldimensions; (b) magnification ofthe shear zone

Three in-plane shear specimens Experimental set-up for shear tests on anElelctronic universal testing machine

shear tests

(a) t=90s (b) t=260s (c) t=346s close to fracture

Sequential images captured by DC1 for the in-plane shear sample ‘H32’

(a) t=90s (b) t=260s (c) t=346s close to fracture

Sequential images captured by DC2 for the in-plane shear sample ‘H32’

Relation curves between the applied force and the elongationof the gauge length for three in-plane shear samples

The solid FE model for the in-plane shear specimen Exp Mech

Numerical Simulation

Comparison of the curves of the applied load versus theelongation between experimental and numerical results

Comparisons of theDIC tested logarithmic shearstrain distribution (plotted on theinitial geometry) in the shearzone with FE numerical results

Evolutions of the shear stress S12 distribution in the shear

(c) d=3.86mm, close to fracture

(b) d=2.00mm

(a) d=0.25mm

Equivalent plastic strain distribution of the shear zone on the point to fracture

Variations of the three in-plane stress components at the center point of the shear zone

Comparisons of the experimental nominal shear stress withnumerical shear stress S12 at the center point in the shear zone

Evolutions of the stress triaxiality and the Lode parameterwith the equivalent plastic stain at the potential crack initiation

Concluding Remarks

The stress and strain relationship for DP800 is determined by using uniaxial tensile tests and plastic hardening.

The shear tests are carried out and a non-contact optical field measuring technique, DIC, is adopted to measure the elongation of the gauge length and the shear strain distribution of the shear zone.

The deformation concentrates on the shear zone and no thinning phenomenon has been observed, which implies there exits no plastic instability in this kind of shear test.

It is noted that the numerical results in terms of the relationship of the applied load versus the elongation of the gauge length are in good agreement with the experimental results analyzed by DIC.

It is found that the shear deformation concentrates on the designed shear zone and the shear stress distributes widely and uniformly.

The stress state within the shear zone is dominated by shear stress , and the other two normal stress components are repressed at a relatively low level and fluctuate.

The nominal shear stress and the actual shear stress are generally consistent.

The above obtained results demonstrated the in-plane shear specimen design presented in this work is suitable for fracture studies of high strength materials under the shear stress state.

References

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