Damage and Stress State Influence on Bauschinger Effect in Aluminum Alloys

In this work, the Bauschinger effect is shown to be intimately tied not only to plasticity but to damage as well. The plasticity-damage effect on the Bauschinger effect is demonstrated by employing different definitions (Bauschinger Stress Parameter, Bauschinger Effect Parameter, the Ratio of Forward-to-Reverse Yield, and the Ratio of Kinematic-to-Isotropic Hardening) for two differently processed aluminum alloys (rolled and cast) in which specimens were tested to different prestrain levels under tension and compression. Damage progression from second phase particles and inclusions that were generally equiaxed for the cast A356-T6 aluminum alloy and elongated for the rolled 7075 aluminum alloy was quantified from interrupted experiments. Observations showed that the Bauschinger effect had larger values for compression prestrains when compared to tension. The Bauschinger effect was also found to be a function of damage to particles/inclusions, dislocation/particle interaction, the work hardening rate, and the Bauschinger effect definition

Experiments And Modeling Of Fatigue And Fracture Of Aluminum Alloys

In this work, understanding the microstructural effects of monotonic and cyclic failure of wrought 7075-T651 and cast A356 aluminum alloys were examined. In particular, the structure-property relations were quantified for the plasticity/damage model and two fatigue crack models. Several types of experiments were employed to adapt an internal state variable plasticity and damage model to the wrought alloy. The damage model was originally developed for cast alloys and thus, the model was modified to account for void nucleation, growth, and coalescence for a wrought alloy. In addition, fatigue experiments were employed to determine structure-property relations for the cast alloy. Based on microstructural analysis of the fracture surfaces, modifications to the microstructurally-based MultiStage fatigue model were implemented. Additionally, experimental fatigue crack results were used to calibrate FASTRAN, a fatigue life prediction code, to small fatigue-crack-growth behavior. Lastly, a set of experiments were employed to explore the damage history effect associated with cast and wrought alloys and to provide motivation for monotonic and fatigue modeling efforts

A Strategy to Optimize Recovery in Orthopedic Sports Injuries

An important goal for treatment of sports injuries is to have as short a recovery time as possible. The critical problem with current orthopedic implants is that they are designed to be permanent and have a high complication rate (15%) that often requires removal and replacement with a second surgery; and subsequently a second rehabilitation cycle. This study was designed to test the feasibility of having a device that could provide the needed mechanical properties, while promoting healing, for a specified amount of time and then degrade away, to shorten the recovery time. The specific strategy was to create a surface layer on a degradable metal alloy with a controllable degradation rate. Previous studies have shown the feasibility of using surface treatments to alter the surface integrity (i.e., topography, microhardness, and residual stress) leading to increased fatigue strength and a decreased degradation rate. This study was an extension of these previous studies to look at the changes in surface integrity and mechanical properties initially as well as the degradation over time for two surface treatments (shot peening and burnishing). Although the treatments improved initial properties and the burnishing treatment slowed degradation rate, the faster degradation of the base material in vitro (compared to previous studies) probably reduced the overall impact. Therefore although the study helped support the feasibility of this approach by showing the ability of the surface treatment to modify surface integrity, initial mechanical properties, and degradation rate; the degradation rate of the base material used needs to be slower and/or the surface treatment needs to create a bigger change in the degradation rate. Further it ultimately needs to be shown that the surface treatment can produce a material that will allow orthopedic devices to meet the required clinical design constraints in vivo

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

A Strategy to Optimize Recovery in Orthopedic Sports Injuries

An important goal for treatment of sports injuries is to have as short a recovery time as possible. The critical problem with current orthopedic implants is that they are designed to be permanent and have a high complication rate (15%) that often requires removal and replacement with a second surgery; and subsequently a second rehabilitation cycle. This study was designed to test the feasibility of having a device that could provide the needed mechanical properties, while promoting healing, for a specified amount of time and then degrade away, to shorten the recovery time. The specific strategy was to create a surface layer on a degradable metal alloy with a controllable degradation rate. Previous studies have shown the feasibility of using surface treatments to alter the surface integrity (i.e., topography, microhardness, and residual stress) leading to increased fatigue strength and a decreased degradation rate. This study was an extension of these previous studies to look at the changes in surface integrity and mechanical properties initially as well as the degradation over time for two surface treatments (shot peening and burnishing). Although the treatments improved initial properties and the burnishing treatment slowed degradation rate, the faster degradation of the base material in vitro (compared to previous studies) probably reduced the overall impact. Therefore although the study helped support the feasibility of this approach by showing the ability of the surface treatment to modify surface integrity, initial mechanical properties, and degradation rate; the degradation rate of the base material used needs to be slower and/or the surface treatment needs to create a bigger change in the degradation rate. Further it ultimately needs to be shown that the surface treatment can produce a material that will allow orthopedic devices to meet the required clinical design constraints in vivo