Coefficient Of Moisture Expansion Research Articles

Thermal buckling analysis of reinforced composite conical shells in acidic environments: Numerical and experimental investigation on the effects of nanoparticles

This study investigates the effects of acid penetration and temperature on the buckling behavior of conical composite shells, to enhance structural integrity and longevity in corrosive environments. The study explores the impact of acid exposure on thermal properties and examines the efficacy of incorporating nano-silica and nano-clay in preventing buckling. Additionally, it analyzes the influence of nanoparticles on the thermal, moisture, and mechanical properties of the composite material. Experimental assessments are conducted to measure material properties during exposure to a sulfuric acid solution, providing a comprehensive understanding of the material's behavior under extreme conditions. However, due to the complexity of investigating the combined effects of temperature, acid, and nanoparticles on composite shell buckling, a combined numerical and experimental approach is adopted to predict the critical buckling load. To this end, equations of conical shells under hygrothermal loading are derived, and the critical buckling load is determined through pre-buckling analysis. The Generalized Differential Quadrature (GDQ) method is employed to solve the hygrothermal buckling of the composite shell using experimentally obtained material properties. Comparative results are presented for different nanoparticles, shell geometries, and exposure times in acidic environments. The experiments reveal that adding nanoparticles enhances mechanical properties and reduces thermal and moisture expansion coefficients. Conversely, the acidic conditions deteriorate these properties. Numerical analysis demonstrates that incorporating nanoparticles significantly increases the critical buckling temperature, with nano-silica and nano-clay particles resulting in an 11.5 % and 34.2 % increase, respectively. However, acidic environments decrease the critical buckling temperature, with reductions of 32 % for unreinforced, 29 % for nano-silica reinforced, and 46 % for nano-clay reinforced composites after three months of exposure.

Rapid identification of the coefficient of moisture expansion of polymer materials by the employment of plates with asymmetric concentration fields

The paper pursues the development of a novel methodology for the rapid identification of the diffuso-mechanical properties of polymer materials based on the employment of plates subject to asymmetric moisture concentration fields. The study is carried out on epoxy plate samples equipped with a thin aluminium foil on a surface exposed to the environment to promote asymmetric moisture absorption. The asymmetric moisture fields promote deformations of the plate. Mass gain and plate curvatures are measured as a function of time during conditioning. By using a weakly coupled diffuso-mechanical model: 1D Fick’s diffusion model and 2D plane stress hygroelastic model the diffuso-mechanical properties of the material can be then identified. Due to the chosen size of the experimental samples the present study allows the identification of the coefficient of moisture expansion of the epoxy material. For the material under study, the following values can be identified for saturation mass gain, water diffusivity and coefficient of moisture expansion respectively: 1.67%, 0.025 mm2.h−1, 0.1628.

Structural effects on heat capacity, moisture absorption and thermal expansion of epoxy-novolac polymers

Today epoxy novolac resins are of great interest for the aerospace industry. Thermal properties of the polymer matrix, as well as the effect of moisture on the characteristics of polymer composite materials (PCM) under thermomechanical impacts, are critical tasks in creating dimensionally stable structures operating in a wide temperature range. Particularly, thermal and moisture expansion as well as heat capacity are important parameters for evaluating of polymer matrices and modeling their properties. In this work, polymers based on a number of epoxy novolac resins with aromatic amine hardener were studied. The values of the crosslink density were experimentally determined, and a comparative analysis of thermal expansion and heat capacity for epoxy polymers with different crosslink density was carried out. The dependence of thermophysical properties on polymer crosslinking density is shown, both in glass and highly elastic states. Additionally, this study analyzes the process of water sorption by polymers and the coefficient of moisture expansion. The most significant dependence of the diffusion coefficient was observed with coefficient of moisture expansion.

Environmental Durability of Bio-Based and Synthetic Thermoplastic Composites in Large-Format Additive Manufacturing.

This research investigates the durability of large-format 3D-printed thermoplastic composite material systems under environmental exposure conditions of moisture and freeze-thaw. Durability was evaluated for two bio-based composite material systems, namely wood-fiber-reinforced semi-crystalline polylactic acid (WF/PLA) and wood-fiber-reinforced amorphous polylactic acid (WF/aPLA), and one conventionally used synthetic material system, namely short-carbon-fiber-reinforced acrylonitrile butadiene styrene (CF/ABS). The moisture absorption, coefficient of moisture expansion, and reduction of relevant mechanical properties-flexural strength and flexural modulus-after accelerated exposure were experimentally characterized. The results showed that the large-format 3D-printed parts made from bio-based thermoplastic polymer composites, compared to conventional polymer composites, were more susceptible to moisture and freeze-thaw exposure, with higher moisture absorption and greater reductions in mechanical properties.

Mechanical properties of wall soils for predicting damage to the substrate of Hiten wall paintings in the Horyu‐ji Temple main hall caused by humidity fluctuation: Measurements with mock‐up materials

AbstractSafe and efficient conservation of cultural artifacts requires preventing artifacts deterioration and energy‐saving environmental control. To achieve this, predicting deterioration caused by environmental conditions is necessary. Predicting the mechanical damage caused by humidity fluctuations necessitates knowledge of the mechanical properties of cultural artifacts materials. Although the mechanical properties of several artifacts have been extensively studied, no investigations have focused on the soils underlying wall paintings. This study aims to clarify some mechanical properties of the upper‐ and middle‐coat soils serving as the substrates for Hiten wall paintings at Horyu‐ji Temple. Mock‐up materials were prepared, and splitting tensile and uniaxial compressive tests were performed. Simultaneously, specimens with various equilibrium humidities were tested to clarify their humidity dependency. The tensile and compressive strengths, Young's modulus, proportional limit, and Poisson's ratio of the upper‐coat soil were 0.103–0.239 MPa, 1.16–2.55 MPa, 0.115–0.209 GPa, and 1.10–2.49 MPa, and 0.152, respectively. Moreover, the humidity‐induced strains for the upper‐ and middle‐coat soils were measured, and the moisture expansion coefficients were approximately 1240 and 2337 μST/−, respectively. The results of this study provide vital data for the conservation of the wall paintings and contribute to a deeper understanding of wall soil properties.

Flax fibre reinforced alginate poloxamer hydrogel: assessment of mechanical and 4D printing potential.

The mechanical and printing performance of a new biomaterial, flax fibre-reinforced alginate-poloxamer based hydrogel, for load-bearing and 4D printing biomedical applications is described in this study. The-self suspendable ability of the material was evaluated by optimising the printing parameters and conducting a collapse test. 1% of the flax fibre weight fraction was sufficient to obtain an optimum hydrogel composite from a mechanical perspective. The collapse test showed that the addition of flax fibres allowed a consistent print without support over longer distances (8 and 10 mm) than the unreinforced hydrogel. The addition of 1% of flax fibres increased the viscosity by 39% and 129% at strain rates of 1 rad s-1 and 5 rad s-1, respectively, compared to the unreinforced hydrogel. The distributions of fibre size and orientation inside the material were also evaluated to identify the internal morphology of the material. The difference of coefficients of moisture expansion between the printing direction (1.29 × 10-1) and the transverse direction (6.03 × 10-1) showed potential for hygromorphic actuation in 4D printing. The actuation authority was demonstrated by printing a [0°; 90°] stacking sequence and rosette-like structures, which were then actuated using humidity gradients. Adding fibres to the hydrogel improved the repeatability of the actuation, while lowering the actuation authority from 0.11 mm-1 to 0.08 mm-1. Overall, this study highlighted the structural and actuation-related benefits of adding flax fibres to hydrogels.

Thermo‐Mechanical Analysis of Epoxy Resins Under the Influence of Moisture‐Heat Coupling by Molecular Dynamics Simulation

AbstractEpoxy resins are used in electronic packaging. However, its low thermal conductivity is a disadvantage and the high moisture absorption leads to defects such as cracking and delamination. In this work, the effect of thermo‐mechanical properties of epoxy resins under moisture‐heat coupling is investigated by molecular dynamics (MD) simulations. The diglycidyl ether of bisphenol A (DGEBA) and polyetheramine D230 are used as epoxy resin matrix and curing agents, respectively. The degree of cross–linking is set from 0% to 98% and the moisture mass fraction is set from 0 wt.% to 10 wt.%. The radius distribution function(RDF) shows that water molecules tend to appear ≈2.75 Å from the epoxy resin. The thermal conductivity of the epoxy resin increases by 54.55% for the maximum cross–linking degrees studied. And it increases by 19.23% when the moisture mass fraction is increased from 0 wt.% to 10 wt.%. The deformation of the epoxy resin is calculated which includes the coefficient of thermal expansion(CTE), coefficient of moisture expansion(CME), and coefficient of linear expansion. It is found that moisture expansion predominated at low temperatures and thermal expansion dominates at high temperatures. The analysis provides a theoretical basis for the study of hygrothermal coupling effects.

Insulated, Passivated & Adhesively-Promoted Bond Wire Using All-in-One Al2O3 Coating

Insulated, Passivated & Adhesively-Promoted Bond Wire Using All-in-One Al2O3 Coating

Metamaterial with Tunable Positive and Negative Hygrothermal Expansion Inspired by a Four-Fold Symmetrical Islamic Motif

A metamaterial with controllable positive and negative thermal and hygroscopic expansions is investigated herein by inspiration from a range of Islamic geometric patterns. Constructing from eight pairs of pin-jointed Y-elements, each unit cell manifests eight rhombi that are arranged circumferentially, thereby manifesting four axes of symmetry. By attachment of bimaterial spiral springs of contrasting expansion coefficients to the far arms of the paired Y-elements, a change in the environment’s thermal or hygroscopic condition alters the offset angle of the paired Y-elements such that the unit cell of the metamaterial ranges from the eight-pointed star to the regular octagon. The effective coefficient of thermal expansion (CTE) and the coefficient of moisture expansion (CME) of this metamaterial were developed for small and large changes in environmental fluctuations using infinitesimal and finite models, respectively. Generated data indicates that the sign and magnitude of the effective thermal and hygroscopic expansion coefficients can be controlled by geometrical descriptors of the bimaterial spiral spring—such as its coil number and the ratio of its mean radius to its thickness—as well as the properties of the bimaterial’s layers such as their expansion coefficients, Young’s moduli and, in the case of effective hygroscopic expansion, their relative absorptivity. The obtained results suggest that the proposed metamaterial can be designed to perform as highly sensitive thermal and/or moisture sensors, as well as other functional materials or devices that take advantage of environmental changes as stimuli.

Design of 3D and 4D printed continuous fibre composites via an evolutionary algorithm and voxel-based Finite Elements: Application to natural fibre hygromorphs

This paper describes a novel voxel-based technique to accurately model 3D printed continuous yarns of fibre composites at printed filament scale. To cater for the constraints of continuous filament printing, the design strategy here makes use of a set of variables that fully define the printing path as input in the model. A voxel-based algorithm is developed to obtain the local orientations of the filaments and local quantities of yarns and matrix from a pixelated flat layout of the printed composite. This voxel-based representation is then translated into a Finite Element model to obtain the required structural properties. This approach simplifies and potentially shortens the design of the part, compared to other analytical techniques. The design space of the part is defined by the variables of the gcode used to print the composite. The voxel model is coupled with an evolutionary algorithm to explore the part of the design space related to the use of continuous yarns. The hygro expansion of the material was measured to determine the coefficients of moisture expansion serving as input in the model. Promising results are obtained from a test case related to a continuous flax fibres-reinforced polylactic acid (PLA) printed structure, mimicking the shape of a leaf. The proposed modelling strategy has the potential to characterise geometric, material, mechanical and actuation properties of general 3D printed structures with negligible out-of-plane (i.e., through thickness) printing. • FEA voxel-based strategy can be used to model continuous fibre 3D printed composite. • Leaf shaped hygromorph printed with continuous flax fibre polylactic acid composite. • 4D printed continuous fibre hygromorphs can be designed via evolutionary algorithm.

Dimensional stability and moisture-induced strains in spruce cross-laminated timber (CLT) under sorption/desorption isotherms

The paper presents a comprehensive experimental–numerical study on dimensional stability of spruce CLT panels and provides new insights into understanding the effect of mechanical properties of wood layers on moisture-induced strains. Deformations in Norway spruce CLT as well as their wood layers were studied in two orthogonal planes under sorption and desorption cycles. Coefficients of Moisture Expansion (CME), Coefficient of Moisture Contraction (CMC), as well as Coefficient of Thermal Expansion (CTE) were determined using dimensional measurements at 15° and 50℃. A 3-D nonlinear finite element (FE) model was developed to better understand the effect of glue and wood mechanical properties, as well as their CME and CTE on two CLT cross-sections. Unlike previous studies, the glue layers have been modelled as thin physical layers bonding wood layers. Hence, the effect of glue lines on the performance of CLT panels can be elucidated quantitatively. Results demonstrated good agreement between the FE model predictions of moisture-induced strains and the experimental data under both sorption and desorption isotherms when the wood moisture content is below fibre saturation point (FSB). Discrepancies between experiments and the model were noted at moisture contents above FSB. Such discrepancies may be attributed to measurement inaccuracies at small scale, the annual ring patterns, uncertainties in material properties, glue penetration into wood cell walls, as well as imperfect bonding at the glue lines. Results highlighted the significant effect of the mismatch between CTE and CME (or CMC) of wood in different directions on the development of stresses and consequently delamination, and perpendicular to grain failure in CLT panels subjected to extreme humidity levels.

Viscoelastic and mechanical properties of CNT-reinforced polymer-based hybrid composite materials using hygrothermal creep

In the present work, a combination of experimental and numerical procedure is proposed to study the effects of different hygrothermal conditions on the creep strain, viscoelastic properties of nanocomposites, and mechanical properties of such nanocomposite-based carbon fiber–reinforced polymer (CFRP) hybrid composite materials. Ultrasonic probe sonicator is used to randomly disperse the multiwalled carbon nanotubes into an epoxy to minimize agglomerations. Dynamic mechanical analysis is employed to conduct the creep tests under different hygrothermal conditions of such nanocomposite samples. The Findley power law is used to obtain the long-term creep behavior of nanocomposite materials. Prony series is used to determine the viscoelastic properties of nanocomposite material in the frequency domain. Coefficient of moisture expansion (CME) is independent of moisture concentration; thus, CME of the nanocomposite is also determined. Strength of materials and Saravanos–Chamis micromechanics (SCM) have also been utilized to obtain the mechanical properties of such hybrid composite materials under different hygrothermal conditions. It has been found that the inclusion of multiwalled carbon nanotubes in the nanocomposite and hybrid composites improves storage modulus and loss factor (i.e., tan δ) compared to the conventional CFRP-based composite materials under hygrothermal conditions.

Adjustable positive and negative hygrothermal expansion metamaterial inspired by the Maltese cross.

A metamaterial that can manifest both positive and negative coefficients of moisture and thermal expansion is presented herein, based on inspiration from the Maltese cross. Each unit of the metamaterial consists of a pair of equal-armed crosses pin-joined at their junctions to permit rotation, but elastically restrained by a bimaterial spiral spring, and four pairs of hinge rods to translate the relative rotational motion of the pair of equal-armed crosses into translational motion of the connecting rods. The effective coefficients of moisture and thermal expansion models were developed for small and large changes in the hygrothermal conditions using infinitesimal (approximate) and finite (exact) motion analyses, respectively, with the former giving constant effective coefficients with respect to environmental changes. Results indicate that the approximate method underestimates the magnitude of both the effective expansion coefficients under cooling and drying but overestimates magnitudes of both coefficients during heating and moistening, and that the change in both expansion coefficients is more drastic during cooling and drying than during heating and moistening. In addition to providing another micro-lattice geometry for effecting expansion coefficients of either signs, this metamaterial exhibits auxetic property.

Copolyamide-Imide Membrane with Low CTE and CME for Potential Space Optical Applications.

Polyimide diffractive membrane lens can be used in space optical telescope to reduce the size and mass of an imaging system. However, traditional commercial aromatic polyimide membrane is hard to meet the challenging requirements of dimensional stability and optical homogeneity for optical use. Based on molecular structure design and the optimization of fabrication process, the prepared copolyamide-imide membrane achieved the desired performance of membrane as an optical material. It showed a very low coefficient of thermal expansion (CTE), which is 0.95 ppm/°C over a temperature range of −150–100 °C and relatively low coefficient of moisture expansion (CME), which is only 13.30 ppm/% RH (0~90% RH). For the optical use, the prepared copolyamide-imide membrane (φ200 mm) achieved good thickness uniformity with wave-front error smaller than λ/30 (λ = 632 nm) in RMS (root mean square). Besides, it simultaneously meets the optical, thermal, and mechanical requirements for space telescope use. Copolyamide-imide membranes in this research with good comprehensive performance can be used as large aperture membrane optical system architectures.

Measuring the coefficient of moisture expansion of Hysol 9396 loaded with boron nitride powder

The future ATLAS ITk strip tracker [1] will consist of 17,000 silicon strip detector modules mounted on support structures called cores. Cores are assembled from a number of components, among others carbon fibre facings, honeycomb structure and carbon foam surrounding titanium tubes used for cooling, using a two-component epoxy (Hysol 9396) loaded with boron nitride for good thermal conductivity. The adhesive constitutes about 20% of a core's weight. During operation, the detector is cooled down to -40̂C} using bi-phase carbon dioxide and flushed with dry gas to prevent condensation. The effect of this temperature change has been simulated to study the impact of Coefficient of Thermal Expansion (CTE) mismatches between different materials and investigate resulting deformations and misalignment. In addition to the shrinking of an adhesive during cooling, which can be estimated well using its known CTE, flushing the detector volume with dry gas removes the moisture contained in the adhesive, leading to an additional shrinking. In order to estimate the impact of shrinking during drying, the Coefficient of Moisture Expansion (CME) of Hysol samples with different contents of boron nitride as well as their overall moisture absorption were measured and their extent compared to the contraction associated with cooling.

Properties of Porous PDMS and Stretchability of Flexible Electronics in Moist Environment

Abstract Polydimethylsiloxane (PDMS) is a good choice for the substrate and encapsulation of clinical flexible electronics, since it possesses some distinguished characteristics such as high elasticity, excellent optical characteristic, good biocompatibility, and stability. In the present study, the emulsion polymerization technique was used once more to fabricate porous PDMS, which is expected to assure the sweat penetration through the flexible electronics, and therefore to reduce the irritation to the skin due to the flexible electronics. To assess the mechanical performance of flexible electronics with moisture, the saturated moisture concentration, coefficient of moisture expansion, and elastic modulus of porous PDMS for different relative wetness fraction were measured in experiment. Meanwhile, an asymptotic homogenization method (AHM) was adopted to predict these parameters theoretically. Results indicate that the saturated moisture concentration is linear to the porosity, while the coefficient of moisture expansion is independent of the porosity, both of which are well verified by the experimental data. The fitted formula on the elastic modulus for different porosities suggested in our previous study was developed to take account of the relative wetness fraction based on the experimental data. These three parameters were finally applied in calculating the stretchability of a flexible electronic with serpentine interconnects in moist environment. Numerical stimulation reveals that the stretchability increases with the porosity and relative wetness fraction of the substrate and encapsulation. The present work is hoped to pave the way for flexible electronics in clinical applications.

Hygro-thermo-elastic nonlinear analysis of functionally graded porous composite thin and moderately thick shallow panels

This study is dedicated to implement hygro-thermo-mechanical nonlinear analysis of curved thin and moderately thick shallow panels, in which Functionally Graded Materials (FGMs) are employed through the thickness. Based on the rule of mixture, three different patterns of FGMs, including power, exponential and sigmoid patterns are used in formulation. The distribution of porosity within the material is also considered to be uniform. Therefore, the elastic modulus and Poisson’s ratio have a linear function. It is worth mentioning that thermal-dependency of materials is ignored, and it is assumed to be Thermal-Independent (TID). On the other hand, the shell structures are analyzed under the effects of hygro-thermal, mechanical and hygro-thermo-mechanical loads separately. It is aimed to obtain the post-buckling structural behavior, by considering large displacements and rotations. Some well-known benchmark problems are also considered to indicate the high accuracy, capability and performance of the proposed formulation in the nonlinear analysis of FG shells. Moreover, the influences of several parameters, such as, FGM patterns, thermal and moisture expansion coefficients and curvature ration of structure on the obtained results are accurately investigated.

On the identification of diffuso-mechanical properties of polymer matrix materials based on the use of plates with asymmetric moisture concentration field

The aim of the paper is to investigate the possibility to identify the moisture affected mechanical properties and the coefficient of moisture expansion of polymer matrix materials using plates subject to asymmetric concentration field. The study is performed on samples with thin plate configuration using a weakly coupled diffuso-mechanical model: 1D Fick’s diffusion model and 2D plane stress hygroelastic model. Because of the intensity of the deflections caused by the asymmetry of the concentration field, the use of a model taking into account geometrical non-linearities is discussed. The identification is performed according to a constant and linear dependence of Young’s modulus on moisture content. It is shown that diffuso-mechanical properties and the coefficient of moisture expansion can be simultaneously identified by using geometrically linear and non-linear approaches.

Effects of Fiber Surface Grafting with Nano-Clay on the Hydrothermal Ageing Behaviors of Flax Fiber/Epoxy Composite Plates.

Flax fiber has high sensitivity to moisture, and moisture uptake leads to the decrease of mechanical properties and distortion in shape. This paper attempts to graft flax fabric with nano-clay, with assistance from a silane-coupling agent, in order to improve hygrothermal resistance. The nano-clay grafted flax fabric reinforced epoxy (FFRP) composite produced through vacuum assisted resin infusion (VARI) process were subjected to 80% RH chamber for 12 weeks at 20, 40 and 70 °C, respectively. Moisture uptake, dimensional stability, and tensile properties was studied as a function of humidity exposure. Through SEM and FTIR, the effects of hygrothermal exposure was elucidated. In comparison to control FFRP plates, nano-clay grafting decreases saturation moisture uptake and the coefficient of diffusion of FFRP by 38.4% and 13.2%, respectively. After exposure for six weeks, the retention rate of the tensile modulus of the nano-clay grafted flax fiber based FFRP increased by 33.8% compared with that of the control ones. Nano-clay grafting also reduces the linear moisture expansion coefficient of FFRPs by 8.4% in a radial direction and 10.9% in a weft direction.

Moisture and temperature induced swelling/shrinkage of softwood and hardwood glulam and LVL: An experimental study

Abstract To investigate the hygroscopic behaviour of engineered timber, glued-laminated (glulam) timber made of Pacific Teak (Tectona grandis), Tasmanian Oak (Eucalyptus regnans/obliqua/delegatensis), Blackbutt (Eucalyptus pilularis), Radiata Pine (Pinus radiata) and Slash Pine (Pinus elliottii) and laminated veneer lumber (LVL) made of Radiata Pine were exposed to sorption and desorption cycles at two temperatures (i.e. 15 and 50 °C) and the shrinkage and swelling of samples were measured in three orthogonal directions. The samples were conditioned in different relative humidity to produce eight intermediate moisture contents (reading points) between the oven-dried and saturated states. A bilinear model was fitted to the swelling/shrinkage strain-moisture content data to accurately determine the Coefficient of Moisture Expansion (CME) and Moisture Contraction (CMC), and Coefficient of Thermal Expansion (CTE), as well as the Fibre Saturation Point (FSP) for each group of specimens. The experimental results demonstrated a significant difference in swelling/shrinkage behaviour of large glulam and LVL samples compared to small clear wood samples as well as a significant effect of temperature on moisture-induced swelling/shrinkage of glulam and LVL beams in the transverse direction. The CME and/or CMC in the transverse direction were found to decrease with increasing temperature, while swelling/shrinkage coefficients in the longitudinal direction exhibited an opposite pattern. The results of this study can potentially improve the accuracy of the hygro-thermo-mechanical and long-term analysis of glulam and LVL members.