Papers by Keyword: Electronic Speckle Pattern Interferometry (ESPI)

Abstract: Tensile residual stress in friction stir welded (FSW) Aluminum alloy joints is well known to be detrimental to fatigue resistance properties of joints imperiled to dynamic loading. Hence, it is important to translate the prevailing tensile residual stress to a more favorable compressive residual stress to enhance the fatigue life cycle of the welded joints. In this study, the longitudinal and transverse residual stress for FSW AA 6061 joints is measured using the hole-drilling method with electronic speckle pattern interferometry (ESPI) for various conditions. This method combines the tried-and-true hole-drilling method with digital imaging and ESPI, eliminating the application of a strain gage through stress depth profile measurements by incremental drilling. The residual stress is measured for the FSW as-welded and high frequency mechanical impact/pneumatic impact treatment (HFMI/PIT)-treated conditions.

Abstract: Quantitative residual stress depth profile measurements are common in metallic parts but not in glass or plastic. This paper describes some experimental stress depth profile measurements using hole-drilling with electronic speckle pattern interferometry (ESPI) in two types of glasses and two thermoplastics. Stress depth profiles in laminated and toughened glass specimens show the expected low stresses in the former and significant compressive stresses near the surface in the latter for the as-is condition. The stress curves shift towards tensile stresses during slight bending deformation, as expected. The bending devices initially used for experiments with Bayblend® and Makrolon® were deforming the specimens too severely to allow proper, static, measurements. Significant stress reductions due to creep were measured for extended bending times. Subsequent measurements for less severe bending show similar stress curve characteristics. Residual stresses in the as-is condition apparently account for some of the differences to the predicted bending stress profile.

Abstract: The incremental hole-drilling method is a well-known mechanical measurement procedure for the analysis of residual stresses. The newly developed PRISM® technology by Stresstech Group measures stress relaxation optically using electronic speckle pattern interferometry (ESPI). In case of autofrettaged components, the large amount of compressive residual stresses and the radius of the pressurized bores can be challenging for the measurement system. This research discusses the applicability of the measurement principle for autofrettaged cylinders made of steel AISI 4140. The residual stresses are measured after AF and after subsequent boring and reaming. The experimental residual stress depth profiles are compared to numerically acquired results from a finite element analysis (FEA) with the software code ABAQUS. Sample preparation will be considered as the parts have to be sectioned in half in order to access the measurement position. Following this, the influence of the boring and reaming operation on the final residual stress distribution as well as the accuracy of the presented measurement setup will be discussed. Finally, the usability of the FEA method in early design stages is discussed in order to predict the final residual stress distribution after AF and a following post-machining operation.

Abstract: Many post-tensioned concrete bridges have been reported to have ruptured tendons due to corrosion [1] and the assessment of their residual structural capacity has to account for the possibility of re-anchorage of failed tendons. This paper presents an experimental programme to validate a numerical model developed by the authors for the re-anchorage of a ruptured tendon in post-tensioned concrete [2]. The experimental programme considered 33 post-tensioned concrete prisms, in which the rupture of tendon was simulated by releasing the tendon at one end. The full field displacement at concrete surface after release was measured using 3D Electronic Speckle Pattern Interferometry (ESPI). A wide range of parameters: tendon diameter, duct material, grout strength, concrete strength and shear reinforcement were investigated to validate the proposed model, which is found to be suitable for use in assessing post-tensioned concrete bridges with damaged tendons.

Abstract: In this paper, two experimental techniques, Electronic Speckle Pattern Interferometry and Stroboscopic Interferometry, and two different finite element analysis packages are used to measure or to analyze the frequencies and mode shapes of a micromachined, cross-shaped torsion structure. Four sets of modal data are compared and shown having a significant discrepancy in their frequency values, although their mode shapes are quite consistent. Inconsistency in the frequency results due to erroneous inputs of geometrical and material parameters to the finite element analysis can be salvaged by applying the finite element model updating procedure. Two updating cases show that the optimization sequences converge quickly and significant improvements in frequency prediction are achieved. With the inclusion of the thickness parameter, the second case yields a maximum of under 0.4% in frequency difference, and all parameters attain more reliable updated values.

Abstract: The Electronic Speckle Pattern Interferometry (ESPI) is a widely used technique for measurement displacement and deformation. But the fringe phase pattern of ESPI always comes with large noise when using phase-shifting technique. In order to ensure the accuracy of the measurement, it is very important to eliminate the noise of the phase fringe pattern. This paper introduced a phase filtering method, comparing with traditional methods, which can be found is a simple and effective method, and the experimental results have shown that the method was feasible used for image processing of ESPI fringes．

Abstract: The residual stress was measured through the proposed method with ESPI measurement system. The proposed measurement method as a basic study combined with theory and experiments applied for residual stresses prediction and developments of safety estimation technique.

Abstract: In this paper, the electronic speckle pattern interferometry (ESPI) and the finite element method (FEM) were used to obtain the thermal deformation induced in a centrally supported thermoelectric cooler (TEC). The results of ESPI and FEM are in good agreement and show that the warpage varies linearly with respect to the temperature difference between the two ceramic plates inside the TEC.

Abstract: This paper describes the principle of measuring small displacement of the object by using electronic speckle pattern interferometry (ESPI). The piezoelectric constant of Lead Lanthanum Zironate Titanate(PLZT) piezoelectric ceramics is determined with ESPI. Compared with other methods , this method is simpler and is operated more easily.The accuracies of ESPI and electrical method are almost at the same level, which shows that it is avalible to measure piezoelectric constant.

Abstract: In this paper, the deformation measurements of impacted and non-impacted composite laminates under compressive loading are taken. [0₃/90₃]_S orientated cross-ply laminated plates with impact delamination and without delamination are tested using an anti-buckling testing device in compression experiment. The delamination is induced by low-velocity impact test at the impact energy level of 3.105J. For both impacted and non-impacted specimens, the compressive deformation is measured by a carrier electronic speckle pattern interferometry (CESPI) optical measurement technique. It is found that the deformation behavior of the two specimens presents a mixed deformation mode. However, the delamination has significant effect on the compressive deformation of composite laminates.