Fatigue paper

  1. Experimental

Sample Prep

Fatigue

SEM

neutron: Bragg edge

neutron: Talbot-Lau

neutron: far-field

  1. Introduction

Growth of AM

SLM: brief description

fatigue is a problem

Imaging defects with X-ray and neutrons, interferometry

What we did: 3 neutron methods applied to fatigued AM and conventional. Best result is dark-field at 1 micron

neutron: tomography (conventional)

interferometry data analysis

autocorrelation length

  1. Results and Discussion

Neutron tomography (conventiona)

Not useful for crack detection. Cannot differentiate between AM and conventional samples. Supports quest for more interferometry systems.

Bragg edge.

Does not find crack formation in this 3mm thick fatigue sample. Bragg nearly found crack in 2 mm tensile stress sample. Why the difference?

Talbot-Lau

xi=1.97 micron and blur was tiny. Great for conventional fatigue
Not a good xi for AM fatigue

far-field

blur is bad and could not find crack in conventional xi scan was great for AM. In an ideal world, would have the low blur of Talbot-Lau and the xi scan of far-field

Post imaging, the fatigued samples were again fatigued, this time to failure. Optical images are compared with neutron dark-field. Does dark-field predict failure?

SEM of fatigued to failure AM. Can SEM explain why neutron dark-field observed crack formation? Answer: there are micron-sized pores near fractures. Next experiment series: dark-field, (fatigue, dark-field, SEM)n

List of Figures

  1. Sketch of dogbone
  1. (Best figure) Dark-field of AM fatigued. With xi scanning, possible crack formation at Xi=0.8 to 1.1 micron. Hum, compare with AM fractured; will there be an evolution of best xi values as fatigue continues?
  1. (Best figure) Scatter size analysis . How will this plot evolve with in situ fatigue and dark-field imaging?
  1. Dark-field at 0.6 and 1 micron. Shows AM pristine has inhomogeneities as printed (sample was not annealed). AM fractured sample shows the fracture at 0.6 micron, but not a 1 micron. Also shows an annealing effect with fatigue.
  1. Dark-field at 1.97 micron of conventional and AM; fractured and fatigued. SHOWS crack formation in conventional fatigued. Does NOT SHOW crack formation in AM fatigued
  1. Post-neutron. The samples studied as fatigued were then fatigued to fracture. Doe the fractures align with the neutron dark-field features?

6 Bragg edge image of AM fatigue. Not possible to identify early crack formation

12 SEM of AM fractured (which one of the two fractured samples in hand post-neutron imaging?)

  1. Bragg edge spectra. Fatigue barely affects crystallography/texture of grains
  1. conventional tomography: optical, volume, and slice.
  1. Example of raw interferogram data and how it is analyzed
  1. Layout of NIST far-field (Talbot-Lau is sort of similar and in previous paper)