A nonlinear model dynamics for closed-system, constrained, maximal-entropy-generation relaxation by energy redistribution

We discuss a nonlinear model for the relaxation by energy redistribution within an isolated, closed system composed of non-interacting identical particles with energy levels e_i with i=1,2,...,N. The time-dependent occupation probabilities p_i(t) are assumed to obey the nonlinear rate equations tau dp_i/dt=-p_i ln p_i+ alpha(t)p_i-beta(t)e_ip_i where alpha(t) and beta(t) are functionals of the p_i(t)'s that maintain invariant the mean energy E=sum_i e_ip_i(t) and the normalization condition 1=sum_i p_i(t). The entropy S(t)=-k sum_i p_i(t) ln p_i(t) is a non-decreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions p_i(t) of the rate equations are unique and well-defined for arbitrary initial conditions p_i(0) and for all times. Existence and uniqueness both forward and backward in time allows the reconstruction of the primordial lowest entropy state. The time evolution is at all times along the local direction of steepest entropy ascent or, equivalently, of maximal entropy generation. These rate equations have the same mathematical structure and basic features of the nonlinear dynamical equation proposed in a series of papers ended with G.P.Beretta, Found.Phys., 17, 365 (1987) and recently rediscovered in S. Gheorghiu-Svirschevski, Phys.Rev.A, 63, 022105 and 054102 (2001). Numerical results illustrate the features of the dynamics and the differences with the rate equations recently considered for the same problem in M.Lemanska and Z.Jaeger, Physica D, 170, 72 (2002).Comment: 11 pages, 7 eps figures (psfrag use removed), uses subeqn, minor revisions, accepted for Physical Review

Analysis of Fatigue Strength of L-PBF AlSi10Mg with Different Surface Post-Processes: Effect of Residual Stresses

Space and aerospace industries has been starting in the recent years the replacement process of parts and components obtained by traditional manufacturing processes with those produced by Additive Manufacturing (AM). The complexity of the obtainable parts makes, in general, challenging the superficial post processing of some zones, making a stringent requirement the investigation of the fatigue performances of components with rough superficial state or machined. The aim of this work is then to analyse and compare the fatigue performances of an additively manufactured (AMed) AlSi10Mg material considering both the effects of the manufacturing defects and residual stresses related to three different superficial states, namely machined, net-shape and sandblasted. The residual stress profiles of the three superficial states were found to play a key role in determining the fatigue properties of the analysed material, while the manufacturing defects at the failure origin were found to be comparable among the three series. To take into account the combined effect of residual stresses and manufacturing defects a fracture mechanics approach was considered for the estimation of the fatigue performances in both infinite and finite life regimes. It was found that by considering the nominal measured residual stress profiles in the fracture mechanics model the estimations were satisfactory compared to the experimental data-point. To increase the accuracy of the fatigue life estimations a series of numerical analyses were performed aimed to investigate the residual stresses relaxation during the cyclic loading. The adoption of the relaxed residual stress profiles in the fracture mechanics model resulted in good estimations respect to the experimental data-points, highlighting the necessity in adopting such developed approaches during the design phase of AM parts and components

Creep-Fatigue Crack Growth in Power Plant Components

In components operating at high temperature, the presence of defect, that may derive from manufacturing process or operating under critical conditions, could raise to creep-fatigue crack growth even at low loading conditions. Creep- fatigue experimental tests have been performed on P91 material, at 600 °C according to ASTM E2760-10 standard, with focus on the effects of the initial nominal stress intensity factor range, ranging between 16 and 22 MPa m 0.5, and the hold time, ranging between 0.1 and 10 hours. The results will be presented in the paper, together with their application for residual life prediction of a power plant cracked pipe, as case study

Analisi basata sugli sforzi locali della resistenza a fatica di giunzioni incollate di materiali compositi

Il lavoro prende spunto dai risultati di un’analisi sperimentale del comportamento a fatica di giunzioni incollate di materiali compositi laminati di elevato spessore formati da strati di unidirezionale e di tessuto di fibra di carbonio. I giunti sono stati realizzati in modo tale da saggiare l’influenza della lunghezza di sovrapposizione (da 25,4 mm a 110,8 mm), della forma del giunto (con e senza rastremazione), e della composizione degli aderendi (sostituzione di uno degli aderendi in composito con uno in acciaio). Mediante analisi 2D elastiche con il metodo degli elementi finiti sono state ricavate le distribuzioni degli sforzi all’interno dello strato di adesivo, al fine di individuare un parametro utile alla descrizione del comportamento a fatica in termini di sforzi locali - numero di cicli a rottura. Il ruolo della fase di propagazione viene discusso alla luce di osservazioni dell’avanzamento della frattura, condotta su alcuni dei giunti testati

Strong solutions of the thin film equation in spherical geometry

We study existence and long-time behaviour of strong solutions for the thin film equation using a priori estimates in a weighted Sobolev space. This equation can be classified as a doubly degenerate fourth-order parabolic and it models coating flow on the outer surface of a sphere. It is shown that the strong solution asymptotically decays to the flat profile

Efficient Hardware Design Of Iterative Stencil Loops

A large number of algorithms for multidimensional signals processing and scientific computation come in the form of iterative stencil loops (ISLs), whose data dependencies span across multiple iterations. Because of their complex inner structure, automatic hardware acceleration of such algorithms is traditionally considered as a difficult task. In this paper, we introduce an automatic design flow that identifies, in a wide family of bidimensional data processing algorithms, sub-portions that exhibit a kind of parallelism close to that of ISLs; these are mapped onto a space of highly optimized ad-hoc architectures, which is efficiently explored to identify the best implementations with respect to both area and throughput. Experimental results show that the proposed methodology generates circuits whose performance is comparable to that of manually-optimized solutions, and orders of magnitude higher than those generated by commercial HLS tools

Effetto dell’intermittenza della corrente di protezione nei sistemi di protezione catodica dell’acciaio

The paper reports the results of a preliminary research study on the effects of protection current intermittence on the cathodic protection conditions of buried or immersed pipelines. It is well known that cathodic protection has chemical and electrochemical beneficial effects on carbon steel, which do not disappear instantly in correspondence to the current interruption. According to this premise, laboratory tests of intermittent cathodic protection in which the current has been interrupted cyclically were carried out on carbon steel specimens in soil-simulating solution. The effects of the duration of the current-off time, the number of on-off cycles, and of the applied current density have been studied. Potential has been monitored weekly and the residual corrosion rate was calculated by means of a simple electrochemical model

Productivity and Keynes’s 15-Hour Work Week Prediction for 2030: An Alternative, Macroeconomic Analysis for the United States

This paper analyses Keynes’s 1930 prediction that technical advances would cut people’s working week to 15 h by 2030 and investigates why actual working hours are significantly higher in the United States. Elaborating on Keynes’s forecast to provide a general productivity formula while keeping its simplicity, we ran tests on macro-data from 1929 to 2019 and on estimates for 2030, demonstrating that productivity is surprisingly still insufficient to allow for a reduction in working hours across the US economy. This finding represents a substantial contribution to the literature, which has mostly explained long working hours by means of new consumer needs. Even by using microdata, we show that consumption does not explain the stickiness of working hours to the bottom. Hence, this paper combines a macroeconomic, logical-analytical approach based on historical time series with rigorously constructed time series at the microeconomic level. Finally, we also provide policies to narrow the productivity differential to Keynes’s prediction for 2030 while fostering work-life balance and sustainable growth. To understand long working hours in the US despite technical advances—this being one of our main findings—productivity remains crucial

Experiments on crack propagation and threshold at defects in press-fits of railway axles

Fatigue strength under fretting fatigue is one of the open problems in the area of fatigue. In the case of railway wheel-axle press-fits, there are no records of recent failures because design rules are today based on making the shape of geometrical transitions the most stressed point. However, it is important to analyze correctly the acceptability of defects and micro-cracks at press-fits. In this paper, after a preliminary presentation of the results obtained by a new criterion for predicting the non-propagation of cracks under rolling contact fatigue conditions, a new series of experiments on full-scale axle press-fits containing artificial defects is presented and discussed. Results show the modified Dang Van criterion is adequate for describing the development of natural cracks and cracks from artificial defects. The latter, characterized by a depth of 250 350 m, are competitors of fretting cracks naturally developed from surface scars and surface damage