Texture Determination from Ultrasonic Wave Speeds for Hexagonal Close Pack and Cubic Materials

Crystallographic texture in polycrystalline hexagonal close pack (HCP) and cubic materials, often developed during thermomechanical deformations, has profound effects on properties at the macroscopic or component level. In this talk, a novel theoretical convolution model is presented, which couples the single crystal wave speed (the kernel function) with the polycrystal crystallographic orientation distribution function to give the resultant polycrystal wave speed function. Firstly developed on HCP [1] and then successfully extended to general anisotropic materials [2], the theoretical model expresses the three functions as harmonic expansions, thus enabling the calculation of any one of them when the other two are known. Hence, the forward problem of determination of polycrystal wave speed is solved for all crystal systems. Verifications are provided on various textures, showing near-perfect representation of the sensitivity of wave speed to texture as well as quantitative predictions of polycrystal wave speed. More importantly, the model also presents a solution to the long-standing inverse problem of detecting texture using ultrasound, with proof of principle established where the wave velocities propagating in groups of HCP and cubic polycrystals with different known textures are computationally calculated, and then the texture information is recovered solely from simulated velocities through the model, and the results show good agreements with the original textures. With possibilities of developing a powerful tool for bulk texture measurement and wave propagation studies in general for HCP, cubic materials now shown, further experimental validations of the proposed model are then conducted. A series of samples cut from typical HCP and cubic materials, including commercially pure (CP) Ti, copper, Ti-6Al-4V, are examined by carefully designed experimental setup for the measurement of the angular variations of ultrasonic wave velocities. Texture information of the samples are extracted out from these measured velocities using the model, for the comparison and calibration against the set of information of the same samples measured independently by the well-established neutron diffraction technique. This part of the research is still ongoing and we hope to be able to show results soon

Slip intermittency and dwell fatigue in titanium alloys: a discrete dislocation plasticity analysis

Slip intermittency and stress oscillations in titanium alloy Ti-7Al-O that were observed using in-situ far-field high energy X-ray diffraction microscopy (ff-HEDM) are investigated using a discrete dislocation plasticity (DDP) model. The mechanistic foundation of slip intermittency and stress oscillations are shown to be dislocation escape from obstacles during stress holds, governed by a thermal activation constitutive law. The stress drop events due to -basal slip are larger in magnitude than those along -prism, which is a consequence of their differing rate sensitivities, previously found from micropillar testing. It is suggested that interstitial oxygen suppresses stress oscillations by inhibiting the thermal activation process. Understanding of these mechanisms is of benefit to the design and safety assessment of jet engine titanium alloys subjected to dwell fatigue

Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis

Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at root s = 8 TeV. The data correspond to an integrated luminosity of 19.7 fb(-1). The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t (t) over bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95 confidence level for the product of the production cross section and branching fraction sigma(gg -> X) B(X -> HH -> b (b) over barb (b) over bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with amass scale Lambda(R) = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV

Search for supersymmetry in events with one lepton and multiple jets in proton-proton collisions at root s=13 TeV

Peer reviewe

Measurement of the top quark mass using charged particles in pp collisions at root s=8 TeV

Peer reviewe

Search for anomalous couplings in boosted WW/WZ -> l nu q(q)over-bar production in proton-proton collisions at root s=8TeV

Peer reviewe

Comparative assessment of dissipated energy and other fatigue criteria

Amongst a large number of fatigue criteria proposed for the prediction of crack initiation in thermo-mechanical fatigue, various approaches have been found to be particularly useful for certain categories of material over specific domains of temperature and cyclic strain. However, no particular approach appears to give invariably better predictions than others, so that the choice of the lifting model must be based on validation for the relevant circumstances. In this paper, the focus is placed on the energy dissipation criterion (EDC). We present physical arguments in favour of this approach's versatility, and illustrate its performance by the application of this approach both on the macroscopic and micromechanical context. Firstly, by way of illustration we consider cyclic deformation of a Ramberg-Osgood material, with a view to establish the equivalence between the EDC and some selected classical criteria. For this simple but analytically tractable case several interesting results can be established, including the equivalence between EDC and both stress range and strain range lifting criteria. Secondly, we consider fatigue loading of polycrystalline FCC material deforming by the combination of anisotropic linear elasticity and crystal slip. Energy dissipation density in this case is location-dependent even for a polycrystal subjected to a macroscopically uniform stress and strain. Crack initiation then is predicted to occur at the 'weakest link' location corresponding to the most intense dissipation. The above two versions of energy dissipation criteria are each compared against experimental data. The comparative performance of Walker Strain, Smith-Watson-Topper (SWT) and EDC lifting methods is assessed. It is concluded that EDC provides improved reliability, particularly for cases of complex loading paths and mechanisms interactions

Microstructural Effects on Thermal-Mechanical Alleviation of Cold Dwell Fatigue in Titanium Alloys

Cold dwell fatigue is a well-known problem in the titanium components of aircraft engines. The high temperature and low dwell stress of in-service conditions have been reported to give rise to dwell fatigue resistance through a thermal-mechanical alleviation process. Here, dwell fatigue tests at room temperature and the component operating temperature were performed on IMI834 titanium alloy to assess the microstructural effects on thermal-mechanical alleviation of cold dwell fatigue while eliminating the effect of chemical composition. The ratcheting strain rates under different loading conditions were quantitatively investigated to aid the understanding of thermal-mechanical alleviation