Cyclic Environmental Conditions Research Articles

A microclimate model to simulate neutral salt spray testing for corrosion inhibitor evaluation and functional coating development

A microclimate exposure model was developed to simulate the neutral salt spray test (NSS) environment which was used to estimate the pitting corrosion inside an artificial defect of a coating system, when it is exposed to a virtual microclimate. The model uses a dynamic process to simulate salt fog droplet formation, subsequent coalescence, and movement on a coated surface, to determine wet-dry cycles on realistic test samples. While the presented model is formulated to comply with standardised NSS tests, e.g. ASTM B117, the developed method can be tuned to simulate a variety of common cyclic environmental testing conditions, and has wide applicability for the virtual assessment of functional coatings. We will show that when validated against empirical data obtained from inhibitor and pitting studies, the developed model is able to predict the pit growth rate of an AA2024‐T3 aluminium alloy panel placed in a NSS test chamber. We will also explore the adaptation of the model to encompass the virtual assessment of functional coatings such as corrosion inhibiting coatings, and their impact on reducing pitting events and pit growth. This work demonstrates an effective approach for building models and establishing interrelationships with other corrosion models or empirical data to produce a predictive system that could ultimately lead to a rapid methodology for virtually screening new functional coatings and formulations, reducing labour costs and freeing up testing infrastructure for materials validation tasks.

Nuclear geyser model of the origin of life: Driving force to promote the synthesis of building blocks of life

We propose the nuclear geyser model to elucidate an optimal site to bear the first life. Our model overcomes the difficulties that previously proposed models have encountered. Nuclear geyser is a geyser driven by a natural nuclear reactor, which was likely common in the Hadean Earth, because of a much higher abundance of 235U as nuclear fuel. The nuclear geyser supplies the following: (1) high-density ionizing radiation to promote chemical chain reactions that even tar can be used for intermediate material to restart chemical reactions, (2) a system to maintain the circulation of material and energy, which includes cyclic environmental conditions (warm/cool, dry/wet, etc.) to enable to produce complex organic compounds, (3) a lower temperature than 100 °C as not to break down macromolecular organic compounds, (4) a locally reductive environment depending on rock types exposed along the geyser wall, and (5) a container to confine and accumulate volatile chemicals. These five factors are the necessary conditions that the birth place of life must satisfy. Only the nuclear geyser can meet all five, in contrast to the previously proposed birth sites, such as tidal flat, submarine hydrothermal vent, and outer space. The nuclear reactor and associated geyser, which maintain the circulations of material and energy with its surrounding environment, are regarded as the nuclear geyser system that enables numerous kinds of chemical reactions to synthesize complex organic compounds, and where the most primitive metabolism could be generated.

Dynamic moisture sorption and hygroexpansion of Populus euramericana Cv. under two cyclic hygrothermal conditions

Abstract Poplar (Populus euramericana Cv.) specimens, 20 mm in radial (r) and tangential (t) directions with thicknesses of 4 mm and 10 mm along the longitudinal direction, were subjected to cyclic environmental conditions, in the course of which the relative humidity (RH) changed sinusoidally between 75% and 45% at 20°C (condition A), or the temperature (T) was changed sinusoidally within 5–35°C at 60% RH (condition B). Moisture content (MC), as well as the t- and r-dimensional changes were measured as a response to the dynamic environmental conditions. The measured data also changed sinusoidally but they lagged behind the triggering original RH or T data. This effect was much higher under condition A than under condition B. The observed equivalent RH and T changes at different ΔMCs or Δts served for comparison of the responses to RH and T, and the former were less pronounced than the latter. MC and t-dimensional changes per unit change of RH were greater than those per unit change of T but still lower than static values. In summary, the effects of dynamic RH change are larger than those of T, especially concerning MC responses compared to dimensional changes.

Seasonality and the effectiveness of mass vaccination.

Many infectious diseases have seasonal outbreaks, which may be driven by cyclical environmental conditions (e.g., an annual rainy season) or human behavior (e.g., school calendars or seasonal migration). If a pathogen is only transmissible for a limited period of time each year, then seasonal outbreaks could infect fewer individuals than expected given the pathogen's in-season transmissibility. Influenza, with its short serial interval and long season, probably spreads throughout a population until a substantial fraction of susceptible individuals are infected. Dengue, with a long serial interval and shorter season, may be constrained by its short transmission season rather than the depletion of susceptibles. Using mathematical modeling, we show that mass vaccination is most efficient, in terms of infections prevented per vaccine administered, at high levels of coverage for pathogens that have relatively long epidemic seasons, like influenza, and at low levels of coverage for pathogens with short epidemic seasons, like dengue. Therefore, the length of a pathogen's epidemic season may need to be considered when evaluating the costs and benefits of vaccination programs.

Thermo-mechanical response of poly(methyl methacrylate) (PMMA) large volumes exposed to time-dependent environmental conditions

Low thermal conductivity and elevated absorbance of large bulky volumes of poly(methyl methacrylate) (PMMA) exposed to moderately aggressive environmental conditions may cooperate to determine critical mechanical conditions, kindling unexpected high thermal stresses values which lead the material to failure. From the engineering point of view, this can be explained as the result of two concomitant phenomena which activate a cascade of events: very sharp thermal gradients engendered by transient thermal processes induced by cyclic environmental conditions, combined with significant bulk heat generation due to the high thermal inertia of massive PMMA volumes, in turn aggravating the steepness of the thermal gradients, may in fact ingenerate severe stress regimes, potentially undermining the structural stability of the material. Moving from these considerations, the present study is aimed to investigate possible rupture of PMMA blocks experiencing heating processes as a consequence of their exposure to outdoor cyclic environmental conditions. The problem is approached by means of both rigorous analytical arguments and the Finite Element based numerical methods, finally exploiting the theoretical outcomes to formulate a hypothesis which might explain the still unclear phenomenon of the sudden breaking of the PMMA structure, named Huge Wine Glass and designed by the world famous Japanese architect Toyo Ito, which occurred in Pescara (Italy) in 2009.

The evolution of transverse stresses in hybrid composites under hygrothermal loading

This paper presents a hygrothermal analysis of the hybrid composites under the effect of the cyclic environmental conditions in order to determine the transient transverse stresses of the [ θ/− θ] S stacking sequences. Hybrid composite is used to consider an appropriate isolation against the cyclic environmental conditions, as well as the reduction of the hygrothermal transverse stresses at both edges of the plate. To reach this aim, we used initially, the computer code W8gain developed by Springer for the determination of the moisture concentration at the end of each cycle. Thereafter, a computer code is developed to compute the hygrothermal transient stresses with implicit variation of temperature and moisture concentration after each cycle. To reduce the transverse stresses, some cases of hybrid composites are proposed. For each case, the thickness of each material constituting the hybrid plate (T300/5208 or AS/3501-5) is gradually varied, but the total thickness of our plate remains unchanged. This thickness variation enables us to find an appropriate hybrid plate which predicts an optimal reduction of hygrothermal transverse stresses; consequently an increase in durability of our hybrid plate.

Reduction of hygrothermal transverse stresses in unidirectional hybrid composites under cyclic environmental conditions

When fiber-reinforced polymer plates are exposed to cyclic environmental conditions, polymer matrix absorbs or desorbs continuously the moisture due to the variation in service temperature and relative humidity. Both temperature and moisture concentration produce an important hygrothermal transverse stresses, which are maximum on both edges of the composite plates. These transverse stresses which are more important at first times of moisture diffusion, can produce a probable damage of composite plates. To extend the durability of our composite plate, interplay hybrid composites are adopted to reduce the transverse stresses on edges. Therefore, a variation of the relationship between thicknesses of unidirectional hybrid composites constituents AS/3501-5 and T300/5208 is carried out in order to find minimal transverse stresses. This thicknesses variation enables us to find the best configuration which gives favourable service conditions of our hybrid composite, i.e., to predict firstly a considerable reduction of hygrothermal transverse stresses at both edges of our hybrid plate, secondly to reduce or to attenuate the edge effect developed in 6 days and 6 weeks periods.

A time to fast, a time to feast: the crosstalk between metabolism and the circadian clock.

The cyclic environmental conditions brought about by the 24 h rotation of the earth have allowed the evolution of endogenous circadian clocks that control the temporal alignment of behaviour and physiology, including the uptake and processing of nutrients. Both metabolic and circadian regulatory systems are built upon a complex feedback network connecting centres of the central nervous system and different peripheral tissues. Emerging evidence suggests that circadian clock function is closely linked to metabolic homeostasis and that rhythm disruption can contribute to the development of metabolic disease. At the same time, metabolic processes feed back into the circadian clock, affecting clock gene expression and timing of behaviour. In this review, we summarize the experimental evidence for this bimodal interaction, with a focus on the molecular mechanisms mediating this exchange, and outline the implications for clock-based and metabolic diseases.

Durability of self-consolidating concrete to sulfate attack under combined cyclic environments and flexural loading

Classical sulfate immersion tests for concrete have often given different behaviour from that observed in real field exposure. Such tests do not consider other parameters existing in service that can affect the mechanisms and kinetics of sulfate attack. On the other hand, the current shift towards performance-based standards and specifications for concrete requires the development of performance tests that better correlate to field conditions. Such holistic tests can effectively evaluate the service life of normal and emerging types of concrete. With the growing use of self-consolidating concrete (SCC) in various infrastructure applications, it has become necessary to establish reliable data on its durability. In the present study, the durability of a wide range of SCC mixture designs to sulfate attack is assessed when other concomitant damage mechanisms (cyclic environmental conditions and flexural loading) are considered. Based on the tested mixture design variables (type of binders, air-entrainment, sand-to-total aggregates mass ratio, and hybrid fibre reinforcement), potential performance risks (in terms of physico-mechanical parameters) under such a combined exposure were identified. Those risks were not tangible under a full-immersion test method. Thermal, mineralogical and microscopy analyses revealed the coexistence of complex deterioration processes in SCC under the combined exposure, which is fundamentally different from the occurrence of a single damage mechanism (sulfate attack).

Modelling and Experimental Characterisation of Hygrothermoelastic Stress in Polymer Matrix Composites

AbstractSummary: The present paper is concerned with the modelling and the simulation of hygrothermal deformation of composite laminates. The temperature and moisture fields are established by employing the Fick's law for transient and cyclical environmental conditions, then the Classical Plate Theory (CLT) adapted for taking into account such conditions is applied. The hygrothermoelastic law of the composite is supposed to be constant but the diffusion coefficients depend on the temperature. The paper shows the ability of the model to handle complex environmental loading, close to service conditions. Finally, a model of plate with moderate rotations is introduced to predict the nonlinear deformations of unsymmetric plates under temperature and moisture cycling conditions.

Damage of hybrid composites under long term hygrothermal loading and stacking sequence

The exposure of polymeric composite matrix to a cyclic moist environment produces transient residual stresses extremely important at the edges of the laminated plates, particularly at first times. In cases of critical cyclic environmental conditions, the damage of composites becomes very probable, so durability is intensively reduced. To avoid the damage probability, and to reduce the transient hygrothermal stresses, in our paper the hybrid composites with optimal stacking sequences are used. The first aim of this paper is the determination of hygrothermal characteristics for balanced stacking sequences [ θ/− θ] nS . Therefore, in order to locate the favourite directions of each stacking sequence, the polar representation method is adopted. The suitable choice of hygrothermal characteristics, allows thereafter, the reduction of transient hygrothermal stresses. By using the quadratic failure criterion in stress space, the transient strength ratio is evaluated at first ply of the hybrid plate for each sequences [ θ/− θ] nS from initial time until saturation time. Avoid the damage probability is reached by the reduction of transient hygrothermal stresses along the thickness of the hybrid plate. To locate the minimal and maximal stresses, a progressive variation of the relationship between the thicknesses h 1 and h 2 of hybrid composites constituents AS3501 and T300/5208 was carried out. In this way five cases are proposed, on which, the thickness of each material varies gradually, but the total thickness of our plate remains constant. This procedure permits us to find the best configuration which will offer favourable conditions of services, i.e., to predict a considerable reduction of hygrothermal transverse stresses at both edges of the hybrid plate.

Transient and cyclical hygrothermoelastic stress in laminated composite plates: Modelling and experimental assessment

The present paper is devoted to the modelling and the simulation of hygrothermoelastic stresses in composite laminated plates: the hygrothermal fields are established by employing the Fick’s law for transient and cyclical environmental conditions, then the classical laminated plate theory, adapted for taking into account such conditions, is used. The experimental assessment of hygrothermoelastic stresses is performed by measuring the deformation of unsymmetric plates and by adopting the fringe projection method, a full-field optical technique capable to reconstruct the deformed shape of stressed bodies, without any hypothesis on their displacement field. Measurements are performed for plates under pure thermal and transient hygrothermal solicitations. Good agreement is found between numerical simulations and experimental results. The experimental technique turns out to be useful also to identify, through the measurement of curvatures in unsymmetric plates, the thermoelastic properties of the material, coefficients of thermal and hygroscopic expansion.

A multi-scale analysis of composite structures: Application to the design of accelerated hygrothermal cycles

Hygrothermal cycles are known to cause degradation of fiber-reinforced polymer composite materials due to moisture uptake and thermal expansion. The knowledge of internal stresses due to cyclic environmental conditions is necessary to forecast a possible damage occurrence in the material during its service life. The accelerated cycles are studied so as to define the material geometry and environmental conditions to reproduce the in-service material state in a shorter time. In the present work, a self-consistent (SC) model is used in order to predict the stress state at the microscopic scale (fiber and matrix) induced by the real and accelerated cycles. The main aim is to compare the local states induced by the real and accelerated cycles in particular near to the edges where hold periodic conditions.

Effect of the Cyclic Environmental Conditions on the Hygrothermal Behavior of the Symmetric Hybrid Composites

This paper presents a hygrothermal analysis of the hybrid composites under the effect of the cyclic environmental conditions by the finite element method. During this study, we used the hybrid composites to consider an appropriate isolation against the cyclic environmental conditions, as well as the reduction of the transient hygrothermal stresses. To reach this aim, we used, initially, the computer code W8gain developed by Springer for the determination of the moisture concentration at the end of each cycle. The various cycles suggested by Springer correspond to the succession of plane flights tests, accomplished in the periods of 6 hours, 6 days and 6 weeks respectively. Secondly, we developed a computer code by the finite element which will determine the distribution of the hygrothermal stresses in the hybrid plate at the end of each cycle. To concretize our study, we made some applications on the unidirectional hybrid composites and [ θ / − θ ] sequences. We also studied the influence of the edge effect extension on behavior of the hybrid composites.

Assessment of approximate models to evaluate transient and cyclical hygrothermoelastic stress in composite plates

The present paper aims at assessing an approximate model to evaluate hygrothermoelastic stress in composite laminated plates. The approximate model is based on straight hypotheses (classical lamination theory of plates) and is able to simulate the effects of complex hygrothermal conditionings, such as those encountered in the life of real structures. For the purpose of the assessment, a 3D analytical solution for hygrothermally stressed plates is employed. The approximate model for plates is also compared to an analytical model for cylinders under transient and cyclical hygrothermal loads [Jacquemin, F., Vautrin, A., 2002a. Modelling of the moisture concentration field due to cyclical hygrothermal conditions in thick laminated pipes. European Journal of Mechanics – A/Solids 21, 845–855; Jacquemin, F., Vautrin, A., 2002b. A closed-form solution for the internal stresses in thick composite cylinders induced by cyclical environmental conditions. Composite Structures 58, 1–9]. This is done in order to assess the capabilities and the limits of a simplified model for plates to represent also the behaviour of cylinders.

On the Transient Hygroscopic Stresses in Polymer Matrix Laminated Composites Plates with Cyclic and Unsymmetric Environmental Conditions

The use of aircraft structural parts made of polymer matrix composites subjected to severe environment conditions calls for better knowledge of their long – term behaviour, with an emphasis on their ability to withstand important cyclic variations of moisture and temperature. The influence of temperature and moisture on such structures is receiving special attention, because it induces transient residual stresses within the plies. Such stresses must be taken into account in the design of composite materials, particularly aerospace structures, e.g. aircraft. In the present paper the transient hygroscopic stresses induced by cyclic and unsymmetric environmental loadings which simulate an aeronautical application are investigated. It is shown that the heterogeneity and anisotropy of such plates generally result in transient stress distributions which are very different from the equilibrium stress distribution. Some stacking sequences exhibit important stresses within the plies. These stresses have to be taken into account in the design of composite structures submitted to a moist environment.

The effect of fiber orientation angle in composite materials on moisture absorption and material degradation after hygrothermal ageing

This paper examines the effect of fiber orientation angle of composite material (T300/5208) on the phenomenon of humidity diffusion. Using an analytical method, humidity concentration through the thickness of plates of E-glass/epoxy and carbon/epoxy (T300/5208) composites are calculated. This method also predicts the saturation in humidity and the time to saturation. Analytical formulations have been proposed [G. Verchery, Moisture diffusion in polymer matrix composites with cyclic environmental conditions, Developments in the Sciences and Technology of Composite Materials, in: A.R. Bunsell, J.F. Jamet, A. Massiah (Eds.), Proceeding of the 5th European Conference on Composites Materials (ECCM5), European Association For Composite Materials (EACM), Bordeaux, France (1992) 505; E. Adda-Bedia, W.S. Han, G. Verchery, Moisture diffusion in polymer matrix composites with cyclic environmental conditions, Textile composites in building construction (TCIBC 1992), in: P. Hamelin, G. Verchery (Eds.), Proceeding of the International Symposium Textile Composites in Building Construction, Pluralis, Paris, Part. 2, Lyon, France (1992a) 127; W.S. Han, E. Adda-Bedia, G. Verchery, Diffusion de l’humidité dans une plaque composite soumise à des conditions d’environnement cycliques”, Anales des Composites, Publication éditée par l’AMAC (1992) 29; E. Adda-Bedia, W.S. Han, G. Verchery, Simplified methods for prediction of moisture diffusion in polymer matrix composites with cyclic environmental conditions, International Journal of Polymers and Polymer Composites 6 (4) (1998) 189] to solve Fick’s equation which describes the kinematics of hygroscopic absorption in materials. The diffusivity in composites being a very important parameter, the present model is described in detail. In addition, a study of the effects of environmental conditions and fiber orientation angle on saturation values and ageing degradation of E-glass/epoxy composites exposed to hygrothermal conditions is proposed.

The role of environmental generalist species in ecosystem function

We constructed a Lotka–Volterra-like competition model to study the role of environmental generalists in maintaining ecosystem function under a range of species richnesses and environmental conditions. Ecosystem function was quantified as community biomass, proportion of initial species that coexist through time, and resilience and resistance to perturbation. Generalist and specialist species were created that differed in their realized growth rates under suboptimal environmental conditions. Generalists were more tolerant of suboptimal conditions but specialists grew faster when conditions were optimal. Model simulations were performed involving generalist-only and specialist-only communities comprised of 4–100 species under constant and cyclical environmental conditions. We used pulses applied to biomass to estimate resilience and pulses applied to the environment to estimate resistance. We also simulated 4-species and 100-species mixed communities of generalists and specialists under the same cyclical environmental conditions. Analysis of model predictions was performed after all simulations reached quasi-equilibrium. Comparisons of total community biomass, proportion of initial species coexisting through time, resilience, and resistance under constant and cyclical environmental conditions showed that, in some situations, a species-poor community of generalists can have equal or greater ecosystem function than a species-rich community of specialists. Results from the mixed community simulations confirmed these results. Our analyses suggest that the environmental tolerances of species can be an important consideration in determining ecosystem function, and should be considered in asking whether all species, or certain key species, drive the positive relationship between diversity and ecosystem function.

A closed-form solution for the internal stresses in thick composite cylinders induced by cyclical environmental conditions

The paper presents a new semi-analytical model to assess the internal stress field in cylindrical pipes due to cyclical temperature and humidity conditions. The solution applies to both thin or thick laminated pipes composed of orthotropic plies following Fick's diffusion laws. The only restriction put on those diffusion laws is that the Arrhénius activation energy should be ply independent. Firstly, the resulting time and space dependent moisture concentration field within the interior of the pipe wall is calculated. It is the sum of the permanent solution, due to the mean relative humidity conditions imposed on the two lateral surfaces of the pipe, and a cyclical vanishing solution. Secondly, the mechanical problem is solved leading to the full stress field solution over the pipe interior and close to the lateral surfaces. The final solution can be implemented in a friendly-user software to assess the combined effects of the pipe thickness, ply stacking sequence and transient service conditions over the internal stress field.

The effect of cyclic hygrothermal conditions on the stresses near the surface of a thick composite pipe

It is necessary to estimate the moisture concentration and the hygrothermal internal stress fields to evaluate the durability of thick composite pipes submitted to cyclic environmental conditions. After some time, the moisture concentration, induced by temperature and relative-humidity cycles, is permanent within the pipe and periodic close to the inner and outer surfaces. The hygrothermal stresses induced are computed by using the classical equations of solid mechanics and assuming a hygrothermoelastic orthotropic behaviour for every ply. The aim of this paper is to model the effects of the periodic boundary conditions on the hygrothermal stresses.