Experimental Analysis of the Shot Peening Particle Stream Using Particle Tracking and Digital Image Correlation Techniques

The conventional air pressure shot peening process consists of multiple impacts of particles propelled with pressurized air through a nozzle at the surface of mechanical components. An experimental study of the flow of particles exiting the nozzle was conducted. A high speed camera was used for image acquisition of the particle flow. This particle flow was analyzed using a particle tracking (PT) technique and using a digital image correlation (DIC) technique. Those two methods were compared and applied to the characterization of an industrial shot peening flow with several parameters of jet pressure and mass flow rate.IRT M2

An elasto-plastic self-consistent model for damaged polycrystalline materials: Theoretical formulation and numerical implementation

Elasto-plastic multiscale approaches are known to be suitable to model the mechanical behavior of metallic materials during forming processes. These approaches are classically adopted to explicitly link relevant microstructural effects to the macroscopic behavior. This paper presents a finite strain elastoplastic self-consistent model for damaged polycrystalline aggregates and its implementation into ABAQUS/Standard finite element (FE) code. Material degradation is modeled by the introduction of a scalar damage variable at each crystallographic slip system for each individual grain. The single crystal plastic flow is described by both the classical and a regularized version of the Schmid criterion. To integrate the single crystal constitutive equations, two new numerical algorithms are developed (one for each plastic flow rule). Then, the proposed single crystal modeling is embedded into the self-consistent scheme to predict the mechanical behavior of elasto-plastic polycrystalline aggregates in the finite strain range. This strategy is implemented into ABAQUS/Standard FE code through a user-defined material (UMAT) subroutine. Special attention is paid to the satisfaction of the incremental objectivity and the efficiency of the convergence of the global resolution scheme, related to the computation of the consistent tangent modulus. The capability of the new constitutive modeling to capture the interaction between the damage evolution and the microstructural properties is highlighted through several simulations at both single crystal and polycrystalline scales. It appears from the numerical tests that the use of the classical Schmid criterion leads to a poor numerical convergence of the self-consistent scheme (due to the abrupt changes in the activity of the slip systems), which sometimes causes the computations to be prematurely stopped. By contrast, the use of the regularized version of the Schmid law allows a better convergence of the self-consistent approach, but induces an important increase in the computation time devoted to the integration of the single crystal constitutive equations (because of the high value of the power-law exponent used to regularize the Schmid yield function). To avoid these difficulties, a numerical strategy is built to combine the benefits of the two approaches: the classical Schmid criterion is used to integrate the single crystal constitutive equations, while its regularized version is used to compute the microscopic tangent modulus required for solving the self-consistent equations. The robustness and the accuracy of this novel numerical strategy are particularly analyzed through several numerical simulations (prediction of the mechanical behavior of polycrystalline aggregates and simulation of a circular cup-drawing forming process)

A calibration procedure for the assessment of work hardening Part II: Application to shot peened IN718 parts

The objective of this paper is to discuss the application of the calibration methodology exposed in the previous part to shot-peened Inconel 718 specimens. Shot peening is commonly used to increase the fatigue life of critical parts such as Inconel 718 turbine discs. This surface treatment induces residual stresses, work hardening and possibly, gradients of microstructures that, in turn, affect fatigue life. Work hardening is a quantity that represents a set of physical and mechanical phenomena related to the level of disorder reached in the microstructure of the material. Work hardening is seldom taken into account in fatigue life assessment mainly because it is not possible to characterize this quantity directly. We propose to use the calibration methodology (see part I of this paper [1]) on samples shot peened with several conditions. The three complementary experimental techniques (microhardness, XRD and EBSD) are then used to determine through correlation curves the work hardening gradients. The meth-odology for characterizing the work hardening within shot peened specimens is first presented. A dis-cussion of the applicability of the method in this context is then provided. The results obtained for the different characterization methods and microstructural effects are analyzed in two different sections. Finally, the influence of shot peening conditions on residual stresses and on work hardening is dis-cussed, showing the interest of the proposed procedure to obtain a real picture of the mechanical state after shot peening

A calibration procedure for the assessment of work hardening part I: Effects of the microstructure and load type

This paper presents a methodology to define and quantify the level of work hardening locally in a material. The methodology is proposed after a thorough experimental study based on three complementary experimental techniques for microstructural characterizations: microhardness, X-ray diffraction (XRD) and Electron Backscatter Diffraction (EBSD) applied on Inconel 718 samples. In our analysis, several loading histories including single tension, single compression, high strain rates and low cycle fatigue have been investigated. The effects of the microstructure have been further investigated by modifying the size of the grains and the size of the strengthening precipitates. Experimental tests have also been simulated to choose a model variable able to represent work hardening. A reciprocal link between work hardening and experimental characterizations has then been established. Correlation curves have been proposed that enable to quantify the level of work hardening from the knowledge of the experimental data. Accuracy and complementarity of the three experimental approaches are discussed as well as the impact of the microstructure of the material on the measured quantities

Endless forms of sexual selection

In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a "stock-taking\u27\u27 workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the \u27aesthetic sense\u27 proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate \u27null model\u27 of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress

A molecular insight into algal-oomycete warfare : cDNA analysis of Ectocarpus siliculosus infected with the basal oomycete Eurychasma dicksonii

Peer reviewedPublisher PD

Pituitary Adenylate Cyclase Activating Peptide (1-38) and its analog (Acetyl-[Ala15, Ala20] PACAP 38-polyamide) reverse methacholine airway hyperresponsiveness in rats

O objetivo deste estudo foi investigar funcionalmente e estruturalmente efeito broncodilatador do peptídeo ativador da adenilato ciclase pituitária (PACAP1-38) e da acetil-[Ala15, Ala20]PACAP 38-poliamida, potente análogo do PACAP-38, nos ratos desafiados pelo metacolina (MeCh). Ratos Wistar machos foram aleatoriamente divididos em cinco grupos. Grupos 1 e 2, inalando aerossóis de solução salina ou doses crescentes de MeCh (0,5, 1, 2,12, 4,25, 8,5, 17, 34 e 68 mg/L). Os outros grupos recebendo terbutalina (Terb) (250 µg/rato) (10-6M), PACAP-38 (50 µg/rato) (0.1 mM) ou análogo do PACAP-38 (50 µg/rato) associados a MeCh na dose de 4,25 mg/L. A resistência pulmonar total (RL) foi registrada antes e 2 min após a administração de Mech pelo equipamento pneumomultiteste. A administração MeCh induziu aumento significativo e dose dependente (pThe aim of this study was to investigate both functionally and structurally bronchodilator effects of Pituitary adenylate cyclase activating peptide (PACAP38) and acetyl-[Ala15, Ala20] PACAP38-polyamide, a potent PACAP38 analog, in rats challenged by methacholine (MeCh). Male Wistar rats were divided randomly into five groups. Groups 1 and 2 inhaled respectively aerosols of saline or increasing doses of MeCh (0.5, 1, 2.12, 4.25, 8.5, 17, 34 and 68mg/L). The other groups received terbutaline (Terb) (250 µg/rat) (10-6 M), PACAP38 (50 µg/rat) (0.1 mM) or PACAP38 analog (50 µg/rat) associated to MeCh from the dose of 4.25 mg/L. Total lung resistances (RL) were recorded before and 2 min after MeCh administration by pneumomultitest equipment. MeCh administration induced a significant and a dose-dependent increase (

Effect of alirocumab on mortality after acute coronary syndromes. An analysis of the ODYSSEY OUTCOMES randomized clinical trial

Background: Previous trials of PCSK9 (proprotein convertase subtilisin-kexin type 9) inhibitors demonstrated reductions in major adverse cardiovascular events, but not death. We assessed the effects of alirocumab on death after index acute coronary syndrome. Methods: ODYSSEY OUTCOMES (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab) was a double-blind, randomized comparison of alirocumab or placebo in 18 924 patients who had an ACS 1 to 12 months previously and elevated atherogenic lipoproteins despite intensive statin therapy. Alirocumab dose was blindly titrated to target achieved low-density lipoprotein cholesterol (LDL-C) between 25 and 50 mg/dL. We examined the effects of treatment on all-cause death and its components, cardiovascular and noncardiovascular death, with log-rank testing. Joint semiparametric models tested associations between nonfatal cardiovascular events and cardiovascular or noncardiovascular death. Results: Median follow-up was 2.8 years. Death occurred in 334 (3.5%) and 392 (4.1%) patients, respectively, in the alirocumab and placebo groups (hazard ratio [HR], 0.85; 95% CI, 0.73 to 0.98; P=0.03, nominal P value). This resulted from nonsignificantly fewer cardiovascular (240 [2.5%] vs 271 [2.9%]; HR, 0.88; 95% CI, 0.74 to 1.05; P=0.15) and noncardiovascular (94 [1.0%] vs 121 [1.3%]; HR, 0.77; 95% CI, 0.59 to 1.01; P=0.06) deaths with alirocumab. In a prespecified analysis of 8242 patients eligible for ≥3 years follow-up, alirocumab reduced death (HR, 0.78; 95% CI, 0.65 to 0.94; P=0.01). Patients with nonfatal cardiovascular events were at increased risk for cardiovascular and noncardiovascular deaths (P<0.0001 for the associations). Alirocumab reduced total nonfatal cardiovascular events (P<0.001) and thereby may have attenuated the number of cardiovascular and noncardiovascular deaths. A post hoc analysis found that, compared to patients with lower LDL-C, patients with baseline LDL-C ≥100 mg/dL (2.59 mmol/L) had a greater absolute risk of death and a larger mortality benefit from alirocumab (HR, 0.71; 95% CI, 0.56 to 0.90; Pinteraction=0.007). In the alirocumab group, all-cause death declined wit h achieved LDL-C at 4 months of treatment, to a level of approximately 30 mg/dL (adjusted P=0.017 for linear trend). Conclusions: Alirocumab added to intensive statin therapy has the potential to reduce death after acute coronary syndrome, particularly if treatment is maintained for ≥3 years, if baseline LDL-C is ≥100 mg/dL, or if achieved LDL-C is low. Clinical Trial Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01663402

Global hydrogen development - A technological and geopolitical overview

International audienceHydrogen is an energy carrier that will certainly make an important and decisive contribution to the global energy transition and lead to a significant reduction in greenhouse gas (GHG) emissions over the coming decades. It is estimated that 60% of GHG emission reductions in the last phase of the energy transition could come from renewables, green hydrogen and electrification based on green energy development. Coordinated efforts by governments, industry and investors, as well as substantial investment in the energy sector, will be required to develop the hydrogen value chain on a global scale. This paper summarizes the technical and technological advances involved in the production, purification, compression, transportation and use of hydrogen. We also describe the roadmaps and strategies that have been developed in recent years in different countries for large-scale hydrogen production