The extension of Digital Speckle Pattern Interferometry to three-dimensional cases poses new challenges from both the practical and the theoretical points of view. In the present research, a scattering surface was created within a transparent Plexiglas specimen with the aid of atomized aluminum particles, and strain was measured in the interior plane. Test specimen configurations included a beam in bending and a disc in diametral compression. The tests on the beam in bending showed excellent agreement between Embedded DSPI results and resistance strain gages. However, for the disc in compression, large discrepancies were found. The main source of errors was identified in the effect of the refractive index gradient. Based on the assumption that the index of refraction changes proportionally to the local dilatation, the error was calculated and the predicted results were ultimately in good agreement with the DSPI data. In conclusion, the Embedded DSPI technique was found to be a viable tool for direct experimental strain investigation of complex 3-D cases.
Bolted joints involving composite plates used to be almost entirely dedicated to aerospace applications. As the need for energy conservation has increased, the field of composite bolted joints has found new applications in ground armoured vehicles. Thick panels able to withstand large in-plane and impact loads are critical. The present investigation evaluates the interior strain field, through the thickness, of a composite plate connected to an aluminium panel with a single-lap bolted joint. The area of interest is the bearing plane region close to the hole because of the presence of stress concentrations that heavily modify the stress field. Experimental data for the bolted joint were recorded by fibre-optic strain gauges that were embedded in the bearing plane of the composite plate. Numerical analyses were performed using ANSYS as a pre-processor and LS-DYNA as a solver. The overall goal was to evaluate the magnitude of contact strains around the hole and through the thickness of the composite. These values were analysed and compared with the finite-element method results: the finite-element analysis correlated reasonably well with the experiments. An investigation of error causes was also carried out, in particular to evaluate the influence of incorrect gauge positioning and the effect of friction coefficients. General design considerations were finally provided, based on the complete three-dimensional finite-element analysis.
The article deals with the fatigue life of plates with hole made of aluminum\ud
alloy. Specifically, the combined effect of cold working expansion and ring\ud
indentation on improved fatigue life performance was investigated. Multiple\ud
fatigue tests were performed to determine the cycles to failure and the\ud
corresponding W¨ ohler diagram. Experimental results were compared with\ud
those of nontreated specimens. The conclusion was that cold working\ud
expansion and indentation create a delay on crack formation and fatigue\ud
failure
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