Construction of a high-resolution moiré interferometer for investigating microstructural displacement fields in materials.
A high-magnification moiré interferometer has been constructed with a spatial resolution of the order of 1 microm to measure the local in-plane displacement field associated with a material's microstructure. Laser illumination passes through phase-stepping optics and is delivered to the microscope head by polarization-preserving single-mode optical fibres. The head itself is a compact unit consisting of collimating optics, an objective lens and a charge coupled device (CCD) camera. Thin-phase gratings are cast onto the sample surface with a compliant epoxy resin and coated with ca. 5 nm of gold to enhance the fringe contrast and reduce speckle noise. By switching between the laser illumination and white-light illumination, the underlying microstructure is viewed in exact registration with the measured displacement fields. The application of the instrument is illustrated here by visualization of displacement fields in polymer-bonded explosives (PBXs) during deformation to failure. PBXs are highly filled polymers consisting of up to 95% by weight crystalline explosive bound in a variety of polymeric binders. The mechanical properties of PBXs are highly dependent on the microstructure, and moiré interferometry is an ideal tool for investigating the relationship between the 1-100 microm sized crystals and the displacement fields. Methods such as this are required if computer models of inhomogeneous materials are to be accurately validated.
Goldrein
H T
HT
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
Rae
P J
PJ
Palmer
S J P
SJ
Field
J E
JE
D001392:Azocines / Q000737:chemistry*; D003461:Crystallography / Q000379:methods*; D004548:Elasticity; D004867:Equipment Design; D005240:Feasibility Studies; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D007368:Interferometry / Q000295:instrumentation / Q000379:methods; D008422:Materials Testing / Q000295:instrumentation* / Q000379:methods; D015903:Moire Topography / Q000295:instrumentation* / Q000379:methods; D009038:Motion; D011786:Quality Control; D013314:Stress, Mechanical; D013718:Tensile Strength
D001392:Azocines; D006573:Heterocyclic Compounds, 1-Ring; C007950:octogen