Applied Mechanics and Materials Vols. 13-14

Abstract: In this paper, we demonstrate that a dynamic stress concentration around Lüders band can be directly displayed using mechanoluminescence (ML) sensing film of SrAl2O4:Eu (SAO) coated on the surface of metal. Uniaxial tensile test of an aluminum alloy (2.5% Mg) plate coated with the SAO sensing film was performed and the ML images were recorded using a high-speed camera. Captured ML images confirmed the formation and propagation of Lüders band clearly in real time.

Abstract: This paper details progress towards the application of a methodology for Acoustic Emission (AE) detection and interpretation for the monitoring of fatigue fractures in large-scale industrial environments. An artificial acoustic emission source, representative of a fatigue fracture was injected into a test of a substantial landing gear component. An AE monitoring system was then used to successfully locate and identify the source using the new signal processing methodology.

Abstract: There is no simple linear relationship between strain and potential in strain measurement with strain gauges, especially for large strain measurements. In this paper, a modified algorithm was proposed to improve the accuracy of strain obtained from measured voltage. The strain was calculated from a nonlinear relationship between voltage and strain rather than a linear simplification. Moreover, the corrections for different sensitivity factors of strain gauges and lead wire resistance were considered. The proposed method was suitable for both large and small strain measurements using a quarter bridge, and validated by experimental tests. It is also very easy to be implemented as a software form and used in scientific tests and engineering applications.

Abstract: The current trend in automotive design is to optimize components for weight. To achieve this, automotive designers need to have complete understanding of various stresses prevalent in different areas of the component. The chassis frame assembly of a heavy truck used for long distance goods hauling application is chosen for this investigation and dynamic stress-strain response of the component due to braking and cornering maneuvers are experimentally measured and reported. A quasi-static approach that approximates the dynamic maneuvers into number of small processes having static equilibriums is followed to carry out the numerical simulation, approximating the dynamic behavior of frame rail assembly during cornering and braking. With the help of commercial finite element package ANSYS, the quasi-static numerical simulations are carried out and compared with experimental results. This study helps in understanding prevailing stresses in truck frame rails especially during cornering and braking maneuvers and brings out all geometric locations that may be potential failure initiation locations. This study makes a case for further investigation on the effects of residual and assembly stresses on frame rails.

Abstract: The efficacy of thermoelastic stress analysis for use in the study of moderately curved gas turbine blades is considered over a frequency range of 68 Hz to 3.4 kHz. A selection of blades, both industrial examples and simplified planar laboratory specimens, are excited at their natural vibration frequencies using both electromagnetic shakers and piezoelectric stack actuators, in order to develop a cyclic displacement of the blade surface and hence a cyclic variation in surface stress condition. Results are shown using both snapshot array and rolling array infrared detector systems, and the data then used to generate maps of normalized principal surface stress sum, and hence the mode shapes of vibration, including the first four excitation modes.

Abstract: This paper reports on theoretical and experimental investigations into the buckling characteristics of a series of six ring-stiffened circular cylinders that experienced general instability when subjected to external hydrostatic pressure. Each study used between 3-5 designs with the same internal and external diameters, but with different numbers and sizes of ring-stiffeners. Four used designs that were machined to a high degree of precision from steel, while the other two were machined from aluminium alloy. The theoretical investigations focused on obtaining critical buckling pressure values, namely Pcr, for each design from the well-known Kendrick’s Part I and Part III theories, together with an ANSYS finite element prediction. The thinness ratio λ1, which was originally derived by the senior author, was calculated together with a dimensionless quantity called the plastic knockdown factor (PKD), for each model. The plastic knockdown factor was calculated by dividing the theoretical critical buckling pressures Pcr, by the experimental buckling pressures Pexp. The thinness ratio was used because vessels such as these, which have small but significant random out-of-circularity, defy “exact” theoretical analysis and it is because of this that the design charts were produced. Three design charts were constructed by plotting the reciprocal of the thinness ratio (1/ λ1) against the plastic knockdown factor (Pcr / Pexp), using results from Kendrick Part I, Kendrick Part III, and ANSYS. Comparison of the results obtained using Kendrick’s theories and experimentally obtained results was good.