Crack Growth of Defects in Ti-6Al-4V Under Uniaxial Tension: Measurements and Modeling

Abstract

Background

This study investigates the effects of pores on the mechanical properties of metals produced by additive manufacturing, which can limit strength and ductility.

Objective

This research aims to both measure and model the rate of crack growth emanating from these pores in additively manufactured Ti-6Al-4 V fabricated with laser powder bed fusion.

Methods

Uniaxial tensile samples containing intentionally embedded penny-shaped pores were mechanically tested to failure, and loading was interrupted by a series of unload steps to measure the stiffness degradation with load. The factors contributing to reduction in stiffness, namely (1) elastic and plastic changes to geometry, (2) the effect of plastic deformation on modulus, and (3) crack growth, were deconvoluted through finite element modeling, and the crack size was estimated at each unloading step.

Results

The stiffness-based method was able to detect stable crack growth in samples with large pores (1.6% to 11% of the cross-sectional area). Crack growth as a function of strain was fit to a model where the crack driving force was based on equivalent strain and a model where the crack driving force was based on energy release rate.

Conclusions

Significant crack growth occurred only after the onset of necking in samples containing small pores, while samples containing large pores experienced continuous crack growth with strain.

Graphical Abstract