Analysis of thin walled structures using the boundary element method

In this article the direct boundary element formulations of stretching and bending plate problems are combined together to solve thin walled structures and other similar frames. The final system is obtained by assuming each individual plane structural element as a subregion. After the necessary transforms of these equations they can be combined together taking into account the displacement compatibility and equilibrium conditions.     

A comparison of leaf-spring with aircushion trailer suspensions in the transport environment

Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies.     

Effect of the addition of Fe2O3 and heat treatment duration on the magnetic susceptibility of V2O5-P2O5-B2O3 glass system

The effect of the addition of Fe₂O₃ and heat treatment duration on the magnetic susceptibility of vanadium borophosphate glass were studied. The magnetic susceptibility of glass samples was found to increase with increasing Fe₂O₃ content, which may be explained by the formation of the FeO₆ group and the change of Fe²⁺ to Fe³⁺ which has higher paramagnetic properties. No detectable changes in the magnetic susceptibility with heat treatment for the samples containing 0.0, 0.5 and 1.0 mol% Fe₂O₃ was observed. The magnetic susceptibility for the heat treated samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃ decreases sharply with increasing duration of heat treatment up to 6 h and then remains almost constant. The sharp decrease in magnetic susceptibility of 2.5 mol% Fe₂O₃ is attributed to the increase in the number of ferrous ions. The sharp decrease for samples containing 5.0 and 7.5 mol% Fe₂O₃ is attributed to the increase in the number of Fe³⁺ in tetrahedral co-ordination. The rate of crystallization owing to the heat treatment was calculated and was found to increase with increasing iron oxide content. The geometry of crystallization was found to be in three-, two-and one-dimension(s) for samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃, respectively.     

Entfestigungsverhalten des Stahls 50 CrV4 bei der thermomechanischen Behandlung

Softening behaviour of 50 CrV4 steel on thermomechanical treatment Determination of static softening of austenite on thermomechanical treatment of steel by rolling. Analysed was the development of the austenite structure and influencing the work softening processes depending on the deformation-temperature-time mode. The static softening processes were modelled mathematically by using Avrami's relationships.     

Performance characteristics of a composite multivariate quality control system.

We present the results of an evaluation of the performance characteristics of a composite multivariate quality control (CMQC) system that incorporates quality control rules for univariate, multivariate, and correlation conditions. The CMQC system evaluated is designed to help analysts detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure of any pair of variables. It is also designed to be tolerant of missing data, to allow analysts to reject as few as one or as many as all variables in a run, and to provide analysts with control statistics and graphics that logically relate to sources of analytical error. We show that the various components of the CMQC system have adequate statistical power to detect systematic errors, random errors, and correlation changes under the conditions likely to be encountered with multivariate analytical measurement systems: (1) a single variable with increased systematic or random error; (2) all variables or a subgroup of variables affected by a common problem that increases systematic or random error; and (3) missing data for one or more variables in a run. We also show that the power of the multivariate component of the CMQC system to detect systematic and random errors is higher than the power of an alternative multivariate test criterion.     

Alumina scale growth at zirconia-MCrAlY interface: a microstructural study

High-temperature oxide scale growth at the ceramic-metal interface is a major contributor to the thermomechanical resistance of thermal barrier coatings for hot stages of gas turbines. In order to better understand this phenomenon, microstructural observations of the alumina scales formed at 1100 and 1200 °C under air, between low-pressure plasma-sprayed NiCrAlY and air plasma-sprayed ZrO₂-8.5 wt % Y₂O₃, have been performed by classical and analytical transmission electron microscopy on transverse thin foil specimens. The evolution of the oxide grain morphology from the metal-oxide to the oxide-oxide interface suggests that the scale growth principally takes place at the metal-oxide interface. Segregation of yttrium at oxide grain boundaries has been detected as well as significant quantities of zirconium inside the alumina grains. The oxide growth seems to be dominated by a classical grain-boundary oxygen diffusion mechanism. The presence of zirconium inside the alumina grains also suggests that Al₂O₃ partially forms by chemical reduction of ZrO₂ by AI. The comparison between the microstructures observed and that of alumina scales grown under similar conditions on bare MCrAlY alloys gives some insight into how the ceramic top-coat modifies NiCrAlY high-temperature oxidation mechanisms.     

Wigner-space synthesis of discrete-time periodic signals

A procedure that facilitates at least-squares synthesis of periodic, discrete-time signals from Wigner quasi-distributions is proposed. The scheme is based on expanding the desired time sequence on a generally nonorthogonal, Gabor-type basis whose associated biorthogonal function presumably exists. The specific basis selection may crucially affect the efficiency and quality of the ensuing synthesis procedure. The cited basis type constitutes a considerable generalization over the standardly used orthogonal variety, thus creating previously unavailable degrees of freedom. Of primary significance is the acquired capability of generating time-frequency basis functions that are well localized. Localization is a highly desirable property that can advantageously serve in various applications. It is shown and numerically demonstrated that benefits of localization as well as the fact that achieving effective time-frequency basis localization renders a certain degree of oversampling unavoidable     

Relative permeability measurements for two phase flow in unconsolidated sands

This paper presents the results of laboratory measurements of relative permeability for two phase flow in partially saturated samples of unconsolidated sands. Relative permeabilities for tap water and air, de-aired water and nitrogen were measured using a steady—state technique. Three different sand samples (fine sand, heterogeneous sand and coarse sand) were tested.     

Designing the world we live in

Engineering designers, who decide the physical shape and technical features of the built world, tend to forget that their predecessors have been making design decisions for hundreds of years. This paper gives several historical examples of design experience which can supply useful insights today, because the essential nature of engineering has not changed.Adapted from: Eugene S. Ferguson,Engineering and the Mind's Eye. Cambridge, Massachusetts: MIT Press, 1992