Advances in Experimental Mechanics V

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Authors: V. Tran, Stephane Avril, Fabrice Pierron
Abstract: The virtual fields method is a tool dedicated to the identification of the mechanical properties of materials from full-field deformation measurements. It is now validated in elasticity and plasticity but one of the remaining problems is the fact that researchers wanting to use the method must invest significant time in order to programme the routines. To help them, a software called CamFit has been developed. The purpose of this paper is to present this software. It is based on MATLAB® and uses a graphical pre-processing interface to produce the geometry, the conditions on the virtual fields, to choose the type of behaviour etc... Then, series of displacement maps are uploaded and the identification is launched. Since no iterative solution of the direct problem is required, computation times are very small compared to updating techniques. An important step in the procedure is the smoothing of the displacement measurements to produce strains. FE based approximations are presently available in the software. The final purpose is to introduce the software onto the market. This will be done in the very near future.
Authors: S.J. Lin, Don R. Matthys, R.E. Rowlands
Abstract: Thermoelastic Stress Analysis (TSA) information is proportional to the change in the sum of the principal stresses. Since one often has to know the magnitude of individual stresses, additional experimental methods or data are frequently required to ‘separate the stresses’. This paper demonstrates the ability to evaluate individual stresses in a uniaxially-loaded finite plate with a central circular hole from TSA-recorded information without supplementary experimental data. Measured temperatures are combined with an Airy stress function and some limited traction-free conditions. The present technique does not presuppose knowing the external geometry or boundary conditions, overcomes traditional difficulties of unreliable edge data, and reduces the number of coefficients needed by satisfying the traction-free conditions analytically on the edge of the hole. Attention is paid to determining an appropriate number of the real (not complex) Airy coefficients.
Authors: G. Silva, R. Le Riche, J. Molimard, A. Vautrin, C. Galerne
Authors: Emma McCummiskey, William M. Dempster, D.H. Nash, T.R. Ashton, D.G. Stevenson
Abstract: Superelastic Ni-Ti (Nitinol) is a member of the shape memory alloy (SMA) family of metals. The physical properties of Nitinol are highly dependant on a number of factors, including manufacturing method, subsequent processing, operating temperature, and strain rate. These factors complicate the prescription of material constitutive models, leading to complexities in the computational analysis of Nitinol components. The current work explores the limitations in the Nitinol material model available in existing commercial finite element (FE) software using a series of specially design experimental tests and representative FE models.
Authors: K. Ashokan, K. Ramesh
Abstract: Digital photoelasticity is an experimental method for determining stresses in 2D and 3D models. In digital photoelasticity one gets a wrapped isoclinic phasemap. The main issue with wrapped isoclinic phasemaps is that the isoclinic values obtained do not uniformly represent the principal stress direction of one of the principal stresses consistently over the entire domain. These zones are labelled as inconsistent zones. Such zones need to be identified and corrected to get unwrapped values of continuous isoclinic phase values. In this paper, a method is developed to plot the simulated wrapped and unwrapped isoclinic phasemap from 2D Finite Element (FE) results so that one can use this as a convenient tool for identification and correction of inconsistent zones in isoclinic phasemaps obtained experimentally for complex problems. The method is explained by using the problem of a circular disc under diametral compression. The application of this method for handling complex problems is demonstrated by solving the cantilever bending of a binocular specimen.
Authors: Muhammed Ali Khan, Andrew G. Starr
Abstract: For machine components like gears and bearings, working life calculation is one of the complex issues to deal with. This is because the mechanics of their operation is dependent on many parameters, like loading, friction and lubrication etc. Also the influence of these parameters on the component failure modes cannot be perfectly idealized. But in this regard, standards like AGMA (American Gear Manufacturers Association); ISO (International Standard Organization) and BS (British Standards) are quite useful on the basis of which theoretical working life for machine components under a specific failure mode can be predicted. In this paper with linear pitting failure mode assumptions, theoretical working life calculation has been made for a helical gear. BS-ISO 6336-2 standard is used for the gear theoretical life calculations. Furthermore, a wear debris analysis based experiment has been performed for the validation of theoretical calculation. A back to back gear testing rig has been used for the experimental validation. The experimental results show that the theoretical life calculation made on the basis of BS-ISO 6336-2 standards is fairly accurate.
Authors: Juan Alfonso Beltrán-Fernández, Luis Héctor Hernández-Gómez, R.G. Rodríguez-Cañizo, G. Urriolagoitia-Calderón, G. Urriolagoitia-Sosa, A. González-Rebatú, M. Dufoo-Olvera
Abstract: The main results of a static analysis with a finite element model of the cervical section between C3 – C5 of a human spine are reported. In this case, it is assumed that the element C4 is completely damaged and has to be replaced. Therefore, a bone graft was installed between the anterior side of C3 and C5. Besides, a cervical plate of 55 mm. was fixed at the same side with 4 expansive screws. The resultant stresses caused by compression loads were analyzed and the displacements between the graft and adjacent vertebrae were calculated. Three loading conditions were applied: 80 N, 637.5 N and 6374.5 N. The first one corresponds to the head weight. In the second case, it is assumed that the average patient weight is supported by those vertebrae, while in the last one; the compression load failure is applied on the vertebrae. Results show that displacements were lower than 3 mm between the graft and the adjacent vertebrae. In accordance with the concept of spine stability after Müller [1], the arrangement is a stable one. Another advantage is that no wires are used in this surgical technique. Two more issues should be noticed. There is no risk that the plate may be broken and the geometry of the bone graft allows bone regeneration. These results are on line with those observed in preliminary experimental tests with porcine vertebrae.
Authors: M. Çelik
Abstract: An experimental approach for the solution of the turret stress state and dynamic behavior has been presented using strain gages and accelerometers on Pedestal Mounted Stinger System. The critical stress locations were determined by finite element analysis outputs where rosettes are bonded in order to perform the life profile simulation tests. The fatigue state is determined by cycle counting methods used in data processing of the turret launcher connection zone. The lowest disturbing frequency of the turret determined from the operational tests is further investigated by the experimental modal analysis. Consequently, the servo drive system is operated efficiently after design modifications applied to the turret.
Authors: Yannis Kyriakoglou, Michael Preuss, Paul Bowen
Abstract: Electronic Speckle Pattern Interferometry (ESPI) is used in conjunction with a mechanical test rig to determine the tensile property response when loading cross weld tensile samples of Tungsten Inert Gas (TIG) and Electron Beam (EB) welded Inco718, which include the parent metal, Heat Affected Zone (HAZ) and weld metal. A comparison with cross weld micro hardness testing revealed that such results were misleading when compared with ESPI calculated Proof Stress (PS) variations across the weld region from the same specimens. The effects of ignoring weld related material property variations when modelling welded components are examined.
Authors: M. Kartal, Rafal M. Molak, Mark Turski, S. Gungor, Michael E. Fitzpatrick, Lyndon Edwards
Abstract: The aim of this study was to develop a method of extracting local mechanical properties from weld metal by strain mapping using the digital image correlation (DIC) technique. The feasibility of determining local stress-strain behaviour in the weld zone of a 316H stainless steel pipe with a girth weld was investigated by tensile tests of specimens machined from the pipe so that it contained the weld at its centre. The tensile test was recorded using a high resolution digital camera and the DIC technique was used to obtain the complete set of full field displacement maps during the tensile test. The local strain was calculated at every sub-region of 32×32 pixels, which enabled the local stress-strain behaviour for this region to be determined. Results from these tests show the variability of the elastic modulus, yield stress and UTS across the weld. To check the reliability of the technique, a set of micro tensile samples, with gauge length of 3.7mm and crosssectional area of 0.7×0.7 mm2, were machined from the various locations in and around the weld zone. The comparison of stress-strain curves determined from micro-samples to stress-strain curves from the corresponding locations within a larger more conventional tensile specimen shows reasonably good agreement.

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