Hygrothermal Stress Research Articles

Contact Force and Friction of Generally Layered Laminates with Residual Hygrothermal Stresses under Mode II In-Plane-Shear Delamination

Contact Force and Friction of Generally Layered Laminates with Residual Hygrothermal Stresses under Mode II In-Plane-Shear Delamination

Environmental aging effects on mechanical behavior of an hemp based biocomposite material for structural strengthening

Biocomposites are innovative materials usually made of natural fibers embedded in a natural matrix. The mechanical behavior of such materials when exposed to the environmental agents (i.e. UV radiations, high/low temperature, variable humidity conditions) is a crucial issue. This paper is aimed to investigate an hemp based biocomposite for structural strengthening, addressing a gap in the existing literature concerning the mechanical characterization of the composite constituents (i.e. hemp ropes and natural matrices) under accelerated weathering conditions. In particular, this research involves the mechanical behavior assessment of hemp ropes, four distinct types of matrices (i.e. two organic binder based matrices and two mortar based matrices) and the hemp/matrix interface. Tensile tests, three point bending tests, uniaxial compression tests and pull-out tests are carried out to characterize these components. To simulate accelerated weathering, samples of the biocomposite constituents are subjected to cycles of hygrothermal stress and UV radiation using an accelerated weathering testing apparatus. Subsequently, experimental mechanical tests are performed on the aged biocomposite components, and their mechanical properties are assessed and compared to those of the non-aged materials. The results reveal that aging leads to a significant reduction in the mechanical properties of the hemp ropes, and varying effects on the mechanical properties of matrices depending on their nature (organic binder-based or mortar-based matrices).

Plant species richness, not hygrothermal stress, is the main predictor of gall‐inducing insect richness in Peruvian Amazon forests

AbstractPatterns of gall‐inducing insect diversity tend to be influenced by both habitat‐related and plant‐related characteristics. We investigated the distribution patterns of galling insects in four vegetation types (terra firme forest, white‐sand dry forest, white‐sand wet forest and palm swamp forest) of the Peruvian Amazon to test if the insect gall diversity (1) differs among different types of vegetation and (2) depends on host plant richness. In total, we found 11,579 galls belonging to 249 insect gall morphotypes, distributed across 30 botanical families and 75 plant species. Among host plant families, Fabaceae showed the greatest richness of insect gall morphotypes. We found that galling species richness was lower in palm swamp forest than in white‐sand forests, which can be explained by the lower richness of plants in this type of vegetation. However, we found no evidence of greater richness in xeric habitats (e.g., white‐sand dry forest) than in more mesic vegetation (terra firme forest), contradicting the hypothesis of hygrothermal stress. We also found that plant species richness was positively influenced with the richness and abundance of galling species, regardless of vegetation type. Galling insect species composition differed significantly between vegetation types, similarly to the floristic composition. Our findings show that the diversity of galling insects in the tropical rainforests of Peruvian Amazon are mainly influenced by host plant composition and host plant richness.Abstract in Spanish is available with online material.

Hygrothermal stress increases malignant arrhythmias susceptibility by inhibiting the LKB1-AMPK-Cx43 pathway

High mortality due to hygrothermal stress during heat waves is mostly linked to cardiovascular malfunction, the most serious of which are malignant arrhythmias. However, the mechanism associated with hygrothermal stress leading to malignant arrhythmias remains unclear. The energy metabolism regulated by liver kinase B1 (LKB1) and adenosine monophosphate-activated protein kinase (AMPK) and the electrical signaling based on gap junction protein, connexin43 (Cx43), plays important roles in the development of cardiac arrhythmias. In order to investigate whether hygrothermal stress induces arrhythmias via the LKB1-AMPK-Cx43 pathway, Sprague–Dawley rats were exposed to high temperature and humidity for constructing the hygrothermal stress model. A final choice of 40 °C and 85% humidity was made by pre-exploration based on different gradient environmental conditions with reference to arrhythmia event-inducing stability and risk of sudden death. Then, the incidence of arrhythmic events, as well as the expression, phosphorylation at Ser368, and distribution of Cx43 in the myocardium, were examined. Meanwhile, the adenosine monophosphate-activated protein kinase activator, Acadesine, was also administered to investigate the role played by AMPK in the process. Our results showed that hygrothermal stress induced malignant arrhythmias such as ventricular tachycardia, ventricular fibrillation, and severe atrioventricular block. Besides, hygrothermal stress decreased the phosphorylation of Cx43 at Ser368, induced proarrhythmic redistribution of Cx43 from polar to lateral sides of the cardiomyocytes, and also caused LKB1 and phosphorylated-AMPK expression to be less abundant. While, pretreatment with Acadesine significantly actived the LKB1-AMPK-Cx43 pathway and thus ameliorated malignant arrhythmias, indicating that the hygrothermal stress-induced arrhythmias is associated with the redistribution of gap junctions in cardiomyocytes and the organism's energy metabolism.

Multiscale simulation of hygrothermal stress and mechanical properties degradation of carbon fiber reinforced polymers laminates

AbstractA mesoscopic representative volume element (RVE) model of carbon fiber reinforced polymers (CFRP) laminate with 15 plies was established based on the principle of fiber random disturbance. The RVE model was validated by comparing the elastic parameters calculated by the RVE model, Chamis model, and Bridge model. Wet stress and thermal stress were coupled using a sequential method. Macroscopic and microscopic subroutines were developed to calculate the stress–strain field of CFRP laminate and RVE model. A multiscale numerical simulation of three‐point bending of moisture‐saturated CFRP laminate was conducted. Failure process and failure modes of CFRP laminate were discussed based on the multiscale simulation and SEM observations. The results show that the RVE model and the multiscale simulation strategy presented in this work can predict the coupled hygrothermal stress and the strength degradation due to moisture absorption very well. The maximum error between the simulated and experimental averaged force of the moisture‐saturated CFRP laminate subjected to three‐point bending is about 3.4%. Multiscale simulation demonstrated that uneven distribution of fibers can result in the fiber/matrix interfaces bearing a larger transverse stress in the fiber's dense distribution area. It is the main reason that results in fiber/matrix interface failure of CFRP laminates working in hygrothermal environments.Highlights A RVE model of CFRP laminate was presented using fibers random disturbance. Coupled hygrothermal stress of single fiber and surrounded matrix was obtained. A multiscale simulation of the strength change of the CFRP plate due to wet‐thermal stress was conducted. Failure modes of CFRP laminate are discussed based on the multiscale simulation.

Probabilistic analysis of vulnerability to stenospermocarpy due to hygrothermal stress in 'Palmer' mangoes using a copula-based approach

Probabilistic analysis of vulnerability to stenospermocarpy due to hygrothermal stress in 'Palmer' mangoes using a copula-based approach

Specialized herbivores have differential distribution in veredas under different drying levels

AbstractWe investigated the distribution patterns of galling insects in veredas with varying degrees of drying in the Brazilian Cerrado. We tested if the insect gall diversity is higher in degraded veredas (dry veredas) compared to preserved (wet veredas) ones, as predicted by the hygrothermal stress hypothesis. Additionally, we also tested whether the composition of galling insects varied along the veredas and if species richness and abundance of galling insects are higher in the upstream zone of the veredas. In total, we recorded 99 species of galling insects, distributed across 54 plant species and 24 botanical families. We found that galling species richness was high in degraded veredas compared to preserved ones, while the abundance of galling insects was higher in preserved veredas than in degraded ones. When examining the different zones along the veredas, we observed variations in the richness and abundance of galling insects in preserved veredas. Specifically, the galling insect richness was higher in the upstream and middle zones compared to the downstream zone, while the abundance of galling insects was higher in the middle zone compared to the upstream zone. However, in the degraded veredas, there were no significant differences in galling species richness and abundance among the zones studied. The composition of galling insect species differed significantly between degraded and preserved veredas, with a higher faunal similarity observed in preserved veredas for both the downstream and upstream zones compared to degraded veredas (upstream zone). Our results indicate a preference of galling insects for more hygrothermally stressed environments, such as dry veredas and upstream zones of wet veredas.

Tolerance to hygrothermal and high-voltage stresses for Si-related photovoltaic modules with newly-developed polyvinyl butyral encapsulants

Newly-developed polyvinyl butyral (PVB) encapsulants were employed for Si-related photovoltaic modules. Modules of amorphous Si with a glass–glass structure and those of crystalline Si with glass and a back-sheet structure were subjected to hygrothermal stresses by a damp-heat (DH) test and high-voltage stress by a potential-induced degradation (PID) test, respectively. Even after a quite long DH test at 85 °C and 85% relative humidity for 49 000 h, retention of output power of about 85% was obtained without edge sealant. No decrease in output power was also observed after a PID test with −1000 V at 60 °C and 85% relative humidity for 168 h. These facts suggest that newly-developed PVB is well applicable to encapsulant materials for highly reliable photovoltaic modules.

Extension–bending coupling phenomena and residual hygrothermal stresses effects on the Energy Release Rate and mode mixity of generally layered laminates

This article presents a novel analytical solution to the delamination problem of interface deformable generally layered (asymmetric and unbalanced) composite laminates. The governing equation describing the interface forces and moments is obtained for the reduced form of the first-order shear deformation theory of plates (FSDT) under plane strain assumptions and accounts for the extension–bending coupling phenomena and residual hygrothermal stresses, both of which have been neglected in the past. The interface forces and moments are included in a novel generalization of the J-integral which is used for the estimation of the Energy Release Rate (ERR). The analytical results of the ERR and the mode mixity exhibit a great agreement with the results of Finite Element (FE) models developed using the Cohesive Zone Method (CZM) and the Virtual Crack Closure Technique (VCCT) for a Double Cantilever Beam (DCB) test of a generally layered fibre metal laminate.

Influence of natural aging on the chemical composition of hemp mortars

In recent years, bio-based building materials have become increasingly popular in the field of low-carbon construction. Different bio-based solutions are being adopted because of their advantageous hygrothermal properties and low economic and environmental costs. One such bio-based solution is hemp mortar, which is used in France and other countries for various construction purposes, such as thermal or acoustic insulation for interior and exterior walls. However, the use of hemp mortars is hampered by insufficient data on their durability and risk of degradation due to natural environmental conditions. Indeed, hemp mortar is hygroscopic, heterogeneous and anisotropic, which makes it difficult to study its behaviour. Therefore, the main objective of this work is to investigate the effect of natural aging on the chemical composition of hemp mortar exposed outside in specially designed metal cage for two years. Experimentally, XRD and thermogravimetric analyses of hemp mortar samples were performed. All experimental results were compared with the results of reference samples treated under laboratory conditions. The effects of two different compositions and sample depths were also investigated. In general, the results showed a higher degree of degradation of the mineral matrix of hemp mortar during natural aging due to carbonation and hygrothermal stresses.

Effects of membrane swelling on structural deformation and performance of proton exchange membrane fuel cell

ABSTRACT The change of relative humidity (RH) leads to the expansion and shrinkage of the membrane, resulting in hygrothermal stress, performance degradation and mechanical damage of proton exchange membrane (PEM) fuel cell. In this study, a two-dimensional PEM fuel cell deformation model and a three-dimensional computational fluid dynamics (CFD) model are coupled to study the performance of fuel cell. Emphasis is placed on the influence of membrane swelling and clamping force on the performance of fuel cell. It is found that membrane swelling leads to the structural change of membrane electrode assembly (MEA) and stress in the MEA. The simulated fuel cell performance considering membrane swelling is lower than that of the undeformed membrane, due to smaller electrochemical reaction rate under the rib and higher ionic resistance. The membrane deformation and PEM fuel cell performance under different RHs are also investigated, and medium RH values are found to achieve good fuel cell performance if considering the membrane swelling effect.

Wavelet solution for hygrothermomechanical bending of initially defected plate undergoing large deformation on nonlinear elastic foundation

An efficient wavelet approach has been developed for geometrically nonlinear bending analysis of largely deformed plate with arbitrary initial curvature on nonlinear Winkler–Pasternak foundation loaded with sinusoidally hygrothermal stresses. Translational and rotational constraints have been analyzed and equivalently transformed into the Cauchy-type boundary conditions of Airy stress function, which are efficiently approached by interpolating Coiflet-type wavelet. A newly hygrothermomechanical bending model of plate subjected to the adiabatically impermeable edges or with boundaries of sinusoidal temperature and humidity has been firstly formulated. The highly coupled and nonlinear governing equations have been decomposed into linear differential terms by homotopy transformation and successfully solved by the Coiflet-type wavelet Galerkin method. The wavelet strategy has been validated superior in dealing with extremely nonlinear bending and high-precision reconstitution of initial deflection in hygrothermal environment, while the obtained solutions are in excellent agreement with published results. Effect of initial deflection, hygrothermal load and elastic foundation has been investigated, which implies the hygrothermal effect on plate in linear bending is prominent but gradually negligible in large deformation, while the nonlinear effects of elastic foundation become significant by the increase of deflection but not obvious at smally deformed state.

Closed-form solution for interfacially cracked layered beams with bending-extension coupling and hygrothermal stresses

This paper investigates the problem of the mechanical behavior of an interfacially cracked layered beam with possible bending-extension coupling (BEC) and residual hygrothermal stresses (RHTS), as well as shear deformations and crack-root rotations. The paper presents a mechanical model of a beam that results by assembling two sublaminates by a semi-rigid interface. The beam is clamped at its one end and interfacially cracked and generally loaded at the other. First, the mathematical problem is formulated and analytically solved in terms of the internal forces, strains, displacements, and interfacial stresses. Novel closed-form expressions are derived regarding these quantities and thoroughly reported in tables. The proposed expressions stand out for their generality; they apply to beams with arbitrary layers of random thicknesses and materials and consider general loading, BEC, and RHTS. Next, we highlight some specific cases by appropriately reducing the general expressions. As an example, we investigate the mechanical responses of composite laminates with possible BEC and RHTS using the double cantilever beam configuration. Lastly, the paper discusses new ways to deepen our knowledge of additional aspects of the fracture response of interfacially cracked beams with BEC and RHTS.

Assessment of the hygrothermal, microstructural and chemical evolution of a hemp-based cementitious mortar under ETICS total weathering aging protocol

Biobased composites are widely used for building insulation because of their hygrothermal performance, and their economic and environmental benefits. Among the different types of organic fibers for these materials, hemp shives are interesting because of their high availability in France and their low price. Nevertheless, the wide application of the hemp-based insulation mortars is hampered by the lack of data on its durability and behavior over the long term. The objective of this study, in a first part, consists in providing an original accelerated aging protocol inspired by the standardized one used for External Thermal Insulation Composite Systems (ETICS). In a second part, the selected aging weathering cycles were applied to investigate the hygrothermal stresses on the morphology, chemical composition and properties of hemp mortar samples. Experimentally, microstructural characteristics (as total porosity, SEM observation) and hygrothermal properties (as thermal conductivity, Moisture Buffer Value (MBV) and water vapor permeability) were measured and evaluated for both the reference state (after 28 days of conditioning) and after aging (after 28 days of conditioning and the aging cycles).Furthermore, X-ray diffraction and PH analysis were performed to investigate the chemical composition, especially the effect of carbonation. The obtained results reveal the presence of two processes in the aged hemp mortars: the carbonatation of the mineral matrix and the cracking of the interface between the hemp shives and the cement matrix. This later was quantified too. Despite the microstructural degradation, small deteriorations were recognized concerning the hygrothermal properties and behavior of hemp mortar, that is essential for an insulation material. These results provide data for better forecast on the degradation of the hemp mortars.

Hygrothermal deformation of spinning FG graphene sandwich cylindrical shells having an auxetic core

A new investigation on hygrothermal stress analysis of rotating functionally graded (FG) graphene/metal sandwich cylindrical shell having an auxetic honeycomb core is presented in this article. It is assumed that the simply-supported sandwich shell is spinning about its axial axis with a constant angular speed. The sandwich faces are composed of concentric multi-shells with uniformly distributed GPLs through the thickness of each shell. The material properties of the face layers are varied based on a layer-wise law. The one-dimensional heat conduction and moisture diffusion equations are used to obtain the applied temperature and moisture, respectively. The first-order shear deformation theory are employed to describe the displacement field. The minimum potential energy principle, which contains the initial hoop tension and the centrifugal effect due to the spinning motion of the cylindrical shell, is used to establish the governing equations. The stresses and displacements of the composite cylindrical shells are obtained from the analytical solution of the governing equations. Parametric examples are presented with focusing attention on the effects of the GPLs weight fraction, spinning speed of the cylindrical shell, core-to-face thickness ratio, length-to-radius ratio, radius-to-thickness ratio, temperature and moisture on the bending response of spinning nanocomposite cylindrical shells with an auxetic core.

Large deflection bending analysis of variable-thickness tapered plates under three-dimensionally hygrothermomechanical loads

This paper aims at large deflection bending analysis of variable-thickness tapered plate under three-dimensionally hygrothermal stresses based on Kirchhoff-love assumptions with von Kármán strains. Three dimensionally hygrothermal loads on plate are researched with different heat and moisture boundaries which seems to be overlooked in previous studies. The formulation of varying tapered thickness is further amended by eliminating singular sharp edges in previous literatures. The highly coupled and nonlinear variable-coefficient governing partial differential equations for the variable-thickness plate in hygrothermomechanically bending with arbitrary tapering thickness profiles have been derived and solved by a unified wavelet solving methodology, which overcomes the limitations of additional Neumann boundary of plate thickness in previous homotopy-based work. Numerical convergence is performed to verify the formulation and highly accurate wavelet solutions are given in excellent agreement with published results, while the ultimate deflection to thickness can be up to over 10 rarely obtained by other methods. Parametric studies are carried out to investigate the large deflection behavior of tapered plates with different geometric parameters. It is concluded that the largely deformed characteristics of variable-thickness tapered plate in hygrothermal environment is highly influenced prominently by effects of tapered ratios and profiles’ polynomial orders.

The effect of long‐time moisture exposure and low temperatures on mechanical behavior of open‐hole Cfrp laminate

AbstractCarbon fiber composite laminates (CFRP) used in aerospace are operating under various environmental conditions. Parts are often exposed to moisture which slowly diffuses into the laminate and forms internal stresses. During the flight, the aircraft is also exposed to low or elevated temperatures. The result is negative impact on composite performance due to formation of hygrothermal stresses. Understanding this phenomenon helps with prediction of the damage development which is vital for increasing the components service life. The open‐hole CFRP laminates were conditioned in humid air at 70°C/85% RH for 33,800 h and the effect of low temperatures on quasi‐cyclic tension properties and fracture behavior was investigated. The mechanical tests on two types of CFRP laminate with different number and orientation of plies were performed under − 55°C. The material behavior during the testing was monitored by acoustic emission technique. The light optical microscopy and scanning electron microscopy were used for the identification of failure mechanisms. The study showed that the hygrothermal effect has significant impact on materials toughness reduction. The damage mechanisms and characteristic morphologic features are changing due to the matrix degradation and weakened fiber/matrix interface.

Effect of phase lags of moisture–heat flow on the hygrothermoelastic field of hollow cylinders with convective surfaces

In this article, by considering the Dufour effect and Soret effect, a hygrothermal coupling model based on phase delay of heat and moisture fluxes is established for convective surfaces. The convective surfaces are described by Robin boundary conditions. The Dirichlet boundary conditions (prescribed temperature and moisture on the surfaces) and Neumann boundary conditions (prescribed heat and moisture fluxes) are two extreme cases of the Robin conditions. Using Laplace transform, the effects of different relaxation times and moist-heat coupling on the temperature, moisture, and stress of the hollow cylinder are analyzed from two aspects of time and space. For convective boundary, the dependence of temperature, moisture, and stress on the phase lag of heat and moisture fluxes is examined. The results show that the temperature and moisture distributions along with the hygrothermal stress fields exhibit different behaviors, depending on the coefficient of Robin condition.

A hygrothermal stress finite element analysis of laminated beam structures through hierarchical one-dimensional modeling

A new multi-field beam model based on Carrera’s Unified Formulation (CUF) is offered in this article to efficiently solve the hygro-thermal-mechanical problem of beam structures with high-fidelity. Several beam models have been hierarchically derived in the framework of CUF with consideration of the hygro-thermal stresses. By adopting the principle of virtual displacement, the element stiffness matrix can be derived into a compact form. The temperature and humidity profile is generated from the Fourier’s heat conduction and Fick’s law, respectively. With simply supported and cantilever configurations being adopted, hygro-mechanical and hygro-thermal-mechanical analyses are carried out for different beam slenderness ratios. Results are provided in terms of three-dimensional displacement and stress distributions. The proposed one-dimensional CUF-based beam model has been validated against traditional three-dimensional FEM-based solutions, and an excellent correlation has been achieved. It is found that an accurate result can be obtained through the proposed CUF-based beam model with reduced computational costs.

Hygrothermal stress analysis of laminated composite porous plates

This paper presents the stress analysis of a composite laminated simply supported plate with porosity under hygrothermal rising. In the displacement-strain relation of the plate structure, the first shear plate deformation theory is used. Material properties of laminas are considered as orthotropic. Three different porosity distributions are used. In the solution process, the Navier method is implemented for simply supported laminated composite plate. Non-uniform temperature and moisture rising are considered for laminated plate with three laminas. In the numerical results, the stress distributions of the laminated plate are presented and discussed for different values of moisture, temperature, stacking sequence of laminas and orientation angle of layers. The numerical results show that the hygrothermal condition is very effective in the stress behavior of laminated plates.