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The oxide dispersion strengthened steel MA956 was friction stir welded using eight different rotational speed/translational speed combinations using a polycrystalline cubic boron nitride tool. Weld parameter conditions with high thermal input produced defect-free, full penetration welds. Electron backscatter diffraction showed a significant increase in grain size in the stir zone, a body centered cubic torsional texture in the stir zone, and a sharp transition in grain size across the thermo-mechanically affected zone. Micro-indentation results showed an asymmetric reduction in hardness across the transverse section of the weld that was sensitive to the heat input. This change in hardness is explained by the increase in grain size and may be described using a Hall-Petch type relationship.

[EN] Premise of the study : Artemisia subgenus Tridentatae plants characterize the North American Intermountain West. These are landscape-dominant constituents of important ecological communities and habitats for endemic wildlife. Together with allied species and genera ( Picrothamnus and Sphaeromeria ), they make up an intricate series of taxa whose limits are uncertain, likely the result of reticulate evolution. The objectives of this study were to resolve relations among Tridentatae species and their near relatives by delimiting the phylogenetic positions of subgenus Tridentatae species with particular reference to its New World geographic placement and to provide explanations for the relations of allied species and genera with the subgenus with an assessment of their current taxonomic placement. • Methods : Bayesian inference and maximum parsimony analysis were based on 168 newly generated sequences (including the nuclear ITS and ETS and the plastid trnS UGA - trnfM CAU and trnS GCU - trnC GCA ) and 338 previously published sequences (ITS and ETS). Genome size by fl ow cytometry of species from Sphaeromeria was also determined. • Key results : The results support an expanded concept and reconfi guration of Tridentatae to accommodate additional endemic North American Artemisia species. The monotypic Picrothamnus and all Sphaeromeria species appear nested within subgenus Tridentatae clade. • Conclusions : A redefi nition of subgenus Tridentatae to include other western North American endemics is supported. We propose a new circumscription of the subgenus and divide it into three sections: Tridentatae, Filifoliae , and Nebulosae . The position of the circumboreal and other North American species suggests that subgenus Artemisia is the ancestral stock for the New World endemics, including those native to South America.

Acoustic fatigue is the result of high frequency lateral vibration of an aircraft panel due to time varying pressure waves caused by engine and/or aerodynamic effects. For example, acoustically induced cracks have been recorded in the lower external surface of the nacelle skin of the F/A-18 aircraft and aft fuselage. In the case of the inlet nacelle overall sound pressure levels of the order of 172 dB have been recorded. Attempts to repair these cracks by applying standard methods of bonded repair developed for in-plane loads were made. However, the cracks continued to grow at a similar rate. While the repair of cracked aircraft structures subjected to in-plane loads using bonded repairs has resulted in considerable aircraft life time extension and hence cost savings, the use of bonded patches to repair panels with acoustically induced cracks (acoustic fatigue) is only recent. In this report a generic design procedure is presented for the repair of panels containing acoustically induced cracks using constrained layer damping (CLD). The application of bonded repairs to acoustically-induced cracks requires analytical tools that take into account high frequency out-of-plane vibration. The analytical tools described in the report will enable the rapid design of effective repairs using closed form solutions. A potential outcome for this study could be application to the repair of the batch 11 F/A-18 aircraft which suffer from acoustic fatigue cracking on the aft fuselage. Over a period of ten years this could result in cost savings of one order of magnitude improvement over those for metallic repairs., The original document contains color images.

When an innovation is inspired by design, it transcends technology and utility. The design delights the user, seamlessly integrating the physical object, a service, and its use into something whole. A design-inspired innovation is so simple that it becomes an extension of the user. It creates meaning and a new language. Design-Inspired Innovation takes a unique look at the intersection between design and innovation, and explores the novel ways in which designers are contributing to the development of products and services. The book’s scope is international, with emphasis on design activities in Boston, England, Sweden, and Milan. Through a rich variety of cases and cultural prisms, the book extends the traditional design viewpoint and stretches the context of industrial design to question - and answer - what design is really all about. It gives readers tools for inspiration, and shows how design can change language and even create human possibilities.

We examine the prototypical Toepler optical arrangement for the visualization of phase objects and consider the effect of different contrast elements placed at the focus of the source. In particular, Wollaston prism beam splitting elements based on the crystallographic birefringence of calcite or quartz find application in differential interferometry systems based on the Toepler arrangement. The focus of the current article is a simple low cost alternative to the Wollaston prism that is realized by inserting a prismatic bar constructed of a photoelastic material into the optical path. It is shown that, under the action of an applied bending moment, the prismatic bar functions as a first-order approximation to a Wollaston prism. Results are derived for the divergence angle of the beam splitter for orthogonally polarized rays. The implementation of a practical device is discussed and representative experimental results are presented, taken from the field of shock wave visualization in supersonic flow.

We describe an investigation of the effects of non-equilibrium thermochemistry on the interaction between a weak oblique shock and the strong bow shock formed by a blunt body in hypersonic flow. This type of shock-on-shock interaction, also known as an Edney type IV interaction, causes locally intense enhancement of the surface heat transfer rate. A supersonic jet is formed by the nonlinear interaction that occurs between the two shock waves and elevated heat transfer rates and surface pressures are produced by the impingement of the supersonic jet on the body. The current paper is motivated by previous studies suggesting that real gas effects would significantly increase the severity of the phenomenon. Experiments are described in which a free-piston shock tunnel is used to produce shock interaction flows with significant gas dissociation. Surprisingly, the data that are obtained show no significant stagnation enthalpy dependence of the ratio of the peak heat transfer rates with and without shock interaction, in contrast to existing belief. The geometry investigated is the nominally two-dimensional flow about a cylinder with coplanar impinging shock wave. Holographic interferometry is used to visualize the flow field and to quantify increases in the stagnation density caused by shock interaction. Time-resolved heat transfer measurements are obtained from surface junction thermocouples about the model forebody. An improved model is developed to elucidate the finite-rate thermochemical processes occurring in the interaction region. It is shown that severe heat transfer intensification is a result of a jet shock structure that minimizes the entropy rise of the supersonic jet fluid whereas strong thermochemical effects are promoted by conditions that maximize the entropy rise (and hence temperature). This dichotomy underlies the smaller than anticipated influence of real gas effects on the heat transfer intensification. The model accurately predicts the measured heat t

We examine the interaction of shock waves by studying solutions of the two-dimensional Euler equations about a point. The problem is reduced to linear form by considering local solutions that are constant along each ray and thereby exhibit no length scale at the intersection point. Closed-form solutions are obtained in a unified manner for standard gasdynamics problems including oblique shock waves, Prandtl–Meyer flow and Mach reflection. These canonical gas dynamical problems are shown to reduce to a series of geometrical transformations involving anisotropic coordinate stretching and rotation operations. An entropy condition and a requirement for geometric regularity of the intersection of the incident waves are used to eliminate spurious solutions. Consideration of the downstream boundary conditions leads to a formal determination of the allowable downstream matching criteria. By retaining the time-dependent terms, an approach is suggested for future investigation of the open problem of the stability of shock wave interactions.

We develop a compact dimensionless framework for the analysis of canonical thermo-chemical nonequilibrium flow fields involving normal, oblique and interacting shock waves. Discontinuous solutions of the conservation equations are coupled with thermodynamic and kinetic models for an ideal dissociating gas. Convenient forms are provided for the variation of the relevant dimensionless parameters across shock waves in dissociating gases. The treatment is carried through in a consistent manner for the pressure–flow deflection angle plane representation of shock wave interaction problems. The contribution of the current paper is a careful nondimensionalization of the problem that yields a tractable formulation and allows results with considerable generality to be obtained.

Currently an increasing number of RAAF F/A-18 aircraft are developing acoustic fatigue cracks on the rear fuselage. Acoustic fatigue is the result of high frequency lateral vibration of an aircraft panel as a result of time varying pressure waves caused by engine and/or aerodynamic effects. While the exact broadband power spectral density (PSD) spectrum is not available for this area of the F/A-18, the PSD is known for the inlet nacelle area in which cracking has occurred. Cracking in the inlet nacelle proceeded cracking in the aft fuselage by a period of several years. As a result the inlet nacelle experiences a more severe spectrum and is the PSD adopted here. Viscoelastic damping materials are used in this repair in conjunction with the constrained layer technique to reduce the lateral vibration. Since viscoelastic materials have a limited temperature range it has been necessary to use two types of damping materials to cover the expected temperature range. A highly damped repair is proposed for the aft fuselage area and is shown to be significantly effective in reducing the crack growth rate.

A new form of surface junction thermocouple sensor has been developed and tested. The novel feature of the design is the use of a tapered fit between two coaxial thermocouple elements to form a thin, robust junction. The gauge has a response time on the order of 1 µs and is suitable for measuring large transient heat fluxes in hypervelocity wind tunnels. Asymptotic analysis is used to demonstrate the operating principles and to assess the errors associated with the finite thickness of the surface junction. Spectral deconvolution methods are used to infer a mean square optimal estimate of the surface heat flux from time resolved surface temperature measurements. This improved signal processing method is applicable to transient heat flux gauges of all types. Potential reducible error sources and other systematic errors are described. Measurements of the heat flux about the forebody of a cylindrical body in a hypervelocity flow demonstrate the functioning of the gauge and are used to obtain statistical estimates of the repeatability of the technique. The measured heat fluxes are compared with established theoretical predictions.

The application of bonded repairs to structures subject to acoustic fatigue is investigated, with a view to developing simple solutions suitable for engineering applications. Acoustic fatigue is caused by a random response of a structure due to time varying pressure waves from engine and/or aerodynamic sources. For vibration problems the use of damping in repairs will reduce the amplitude of vibration and hence the stress intensity factor in the cracked structure. To assess the viability of the composite bonded repairs subject to acoustic fatigue new analytical tools are needed. In this paper the use of a simplified dynamic analysis combined with crack-bridging theory allows the influence of damping to be assessed. This theory is adapted to panels with various edge support conditions with good results. Validation of this work is carried out using a Finite Element (F.E.) analysis in which three-dimensional brick elements are used to model the plate, adhesive and boron patch, and use is made of the power spectral density capability of the NASTRAN program.