A new approach for decoding displacements from surfaces encoded with random patterns has been developed and validated. The procedure is based on phase analysis of little zones of interest. Resolution in standard conditions (32×32 pixels2) is 2/100th pixel, for a spatial resolution of 9 pixels. Here we adapt new concepts proposed by Badulescu13 on the
grid method to random patterns for the direct measurement of strains. First metrological results are encouraging:
resolution is proportional to strain level, being 1/10th of the nominal value, for a spatial resolution of 9 pixels (ZOI
64×64 pixels2). Random noise have to be carefully controlled. A numerical example shows the relevance of the
approach. Then, first application on a carbon fibre reinforced composite is developed. Fabric intertwining is studied
using a tensile test. Over-strain are clearly visible, and results connect well with previous ones16.
Carbon fiber reinforced polymers have become thicker due to its use in aircraft manufacturers. Their
manufacturing processes implies the generation of important residual stresses. In this work, a L-shaped thick composite
shell is analyzed under moderate temperature changes. A stacking sequence error is voluntarily added in order to
simulate possible manufacturing failure. Displacements are measured on the shell front and on its side using a mixed inplane
and out-of-plane DSPI set-up, limiting the zone of interest to region of maximum curvature. Variations of the Lshape
with temperature are recorded and typical flexure strain effects are outlined. Several parameters of interest can be
deduced from the experiment.
The present study is based on the use of electronical speckle pattern shearing interferometry (ESPSI) on a double lap joint, the joined parts being two steel blocks and two composite plates. ESPSI is used to investigate de strain maps close to the end of the bonding in the center part of the specimen. The ESPSI set-up allows to get the full field strain and slope maps of a given surface. Its architecture is based on optical fibres which gives a portable assembly that can be used in a civil/mechanical engineering laboratory. This presentation emphases the advantages of such a method and its performances. Last some results are given and compared to an analytical approach.
The spreading of optical full-field technique in the world of mechanics needs a strong educational effort at any level: undergraduate, graduate, or continuing education. On that purpose, practicals are very important. In the context of a "Photomechanics summer school" held by CNRS, a practical based on the fringe projection technique has been developed. Even if the basic principle is very simple, a lot of parameters have to be fixed. The set-up enables students to understand the choices of these parameters in order to obtain the best results and shows a way to characterize the errors.
Grating shearography is an extension of moire interferometry where a shearing element is included in the imaging part of the setup. It is possible to obtain all three components of the in-plane strains, the in-plane rotation and the two out-of-plane slopes. The presented application is an experimental investigation of the mechanical behavior of a plain woven graphite fiber reinforced polymer composite lamina under tensile loading.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.