Void Morphology Research Articles

Investigations on the leak resistance performance and the difference mechanism of composite materials under several typical curing processes

This study aims to investigate the leak resistance of carbon fiber composite products formed by various typical curing processes. Firstly, the leak rates of specimens produced through different curing methods were measured, and the defect were statistically analyzed. After that, the simulation approach was applied to numerically study the impact of these defect characteristics on leak rates was examined from the three factors of porosity, void distribution and void morphology, specimen with prefabricated defects was prepared, and its leak performance were tested to validate the simulation results. Finally, the differences in leak resistance among specimens under different curing processes were analyzed from the perspective of curing defects, and specific defect characteristics contributing to enhanced leak resistance were identified.

Mechanical and absorption properties of carbon-basalt and glass fiber reinforced composites: A comprehensive study with implications for advanced manufacturing technology

In this research, a combination of hybrid and non-hybrid composite materials were tested for their mechanical properties and water absorption rates. The study focused on composites produced through hand-layup techniques, examining their void percentage, morphology, and elemental composition. Specifically, three different stacking sequences of hybrid composites were compared with three non-hybrid composites of equal thickness. Combining carbon and glass allows the composites to balance flexural (367 MPa, 23 GPa) and tensile (440 MPa, 5.7 GPa) strength and modulus, all while remaining cost-effective and easily accessible. The glass fiber-based composites exhibited exceptional impact (27 J/cm2) strength due to their interfacial solid bonding. Additionally, the study found that basalt and carbon-basalt composites had varying degrees of water absorption when exposed to seawater and river water. SEM and EDS Mapping analyses were conducted to understand better fibrous and granular composites' mechanical properties and water absorption behaviors. These analyses provided valuable insights and a comprehensive knowledge of composite properties. Ultimately, the study recommends using hybrid composite materials for specific applications based on desired flexural tensile strength, impact strength, or water absorption characteristics.

A high-throughput statistical homogenization technique to convert realistic microstructures into idealized periodic unit cells

Abstract Metal alloys frequently contain distributions of second-phase particles that deleteriously affect the material
behavior by acting as sites for void nucleation. These distributions are often extremely complex and
processing can induce high levels of anisotropy. The particle length-scale precludes high-fidelity microstructure
modeling in macroscale simulations, so computational homogenization methods are often employed.
These, however, involve simplifying assumptions to make the problem tractable and many rely on periodic
microstructures. Here we propose a methodology to bridge the gap between realistic microstructures
composed of anisotropic, spatially varying second-phase void morphologies and an idealized periodic microstructure
with roughly equivalent mechanical response. We create a high-throughput, parametric study
to investigate 96 unique bridging methods. We apply our proposed solution to rolled AZ31B magnesium
alloy, for which we have a rich dataset of microstructure morphology and mechanical behavior. Our methodology
converts a μ-CT scan of the realistic microstructure to idealized periodic unit cell microstructures that
are specific to the loading orientation. We recreate the unit cells for each parameter set in a commercial finite
element software, subject them to macroscopic uniaxial loading conditions, and compare our results to the
datasets for the various loading orientations. We find that certain combinations of our parameters capture
the overall stress-strain response, including anisotropy effects with some degree of success. The effect of
different parameter options are explored in detail and we find that excluding certain particle populations
from the analysis can give improved results.

Innovative Skin Structures: Synthesis, Void Analysis, and Hysteresis Modeling of Zero Poisson’s Ratio Skin for Span Morphing Wing

This paper explores the use of carbon fiber-reinforced elastomeric skins for advancing flexible morphing wing technologies, highlighting exceptional 1D morphing capabilities. The study focuses on synthesizing a specially engineered elastomer-based skin with a zero Poisson’s ratio, achieved through precise formulation and fabrication onto unidirectional carbon fiber. Poisson’s ratio of the 1D skin is confirmed to be zero via image analysis. Micro-CT tomography evaluates carbon fiber quality and voids under varied prestretch conditions, revealing proportional increases in void sizes. X-ray tomography also provides insights into void distribution and morphology during pre- and post-cyclic stretching. The innovative approach enables seamless 1D morphing, achieving an impressive 200% stretch with a slight increase in actuation force and hysteresis loss percentage. Inspired by continuum mechanics, the proposed “Exp-ln-ln” framework accurately models the loading–unloading stretching of the skin. An extensive parametric investigation assesses key parameters, advancing fiber-reinforced elastomeric materials for aerospace morphing skins.

Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites (3D C/SiC). Represent volume element (RVE) models of microscale, void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites. An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture. The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions. Three RVE models of cuboid, hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale. Besides, the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models. The prediction results at the mesoscale correspond closely to the experimental values. The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration. The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

In situ growth and shrinkage of coated voids in aluminium

Voids can be detrimental to the mechanical and electrical properties of materials but may also find applications in catalysis and plasmonics. Key to the performance of materials containing voids are the sizes and morphologies of the voids, which can be tuned by heat treatment. The present work investigates the morphological evolution of voids, with solute segregation at their surfaces, in an aluminium‑copper‑tin alloy during in situ heating in a transmission electron microscope (TEM). These voids exhibited complex morphological changes that included growth or shrinkage, in contrast to voids in pure Al, which all shrank and disappeared (as reported in an earlier study). Without electron irradiation, the voids never grew. Nearly one fourth of the voids grew under certain heating and electron irradiation conditions, showing distinct growth stages. Growth and shrinkage of the voids both occurred primarily along the surface of the Sn particles to which they were attached. The voids exhibited faceting as they grew and gained morphological isotropy while they shrank. The growth and shrinkage fronts were both found to be primarily the curved surfaces and not the facets at the void surfaces. Growth followed by shrinkage led to a well-defined rounded triangular shape, in projection, with smooth boundaries. This work is, to the best of our knowledge, the first to characterise the growth of nanoscale voids in aluminium using in situ heating TEM. The dual effect of heating and electron irradiation could be utilised to switch the voids between growth and shrinkage to manipulate the void size and shape. This work provides useful insights into tuning void morphologies in the development of advanced materials such as for applications in engineering, catalysis and plasmonics.

Effects of Curing Defects in Adhesive Layers on Carbon Fiber-Quartz Fiber Bonded Joint Performance.

Due to their mechanical load-bearing and functional wave transmission, adhesively bonded joints of carbon fiber-quartz fiber composites have been widely used in the new generation of stealth aviation equipment. However, the curing defects, caused by deviations between the process environment and the setting parameters, directly affect the service performance of the joint during the curing cycle. Therefore, the thermophysical parameter evolution of adhesive films was analyzed via dynamic DSC (differential scanning calorimeter), isothermal DSC and TGA (thermal gravimetric analyzer) tests. The various prefabricating defects within the adhesive layer were used to systematically simulate the impacts of void defects on the tensile properties, and orthogonal tests were designed to clarify the effects of the curing process parameters on the joints' bonding performance. The results demonstrate that the J-116 B adhesive film starts to cure at a temperature of 160 °C and gradually forms a three-dimensional mesh-bearing structure. Furthermore, a bonding interface between the J-116 B adhesive film and the components to be connected is generated. When the curing temperature exceeds 200 °C, both the adhesive film and the resin matrix thermally degrade the molecular structure. The adhesive strength weakens with an increasing defect area ratio and number, remaining more sensitive to triangle, edge and penetration defects. By affecting the molecular structure of the adhesive film, the curing temperature has a significant impact on the bonding properties; when the curing degree is ensured, the curing pressure directly impacts the adhesive's performance by influencing the morphology, number and distribution of voids. Conversely, the heating rate and heat preservation time have minimal effects on the bonding performance.

Influence of microstructure evolution on hot ductility behavior of a Cr and Mo alloyed Fe-C-Mn steel during hot deformation

Cr and Mo alloyed Fe-C-Mn steel was conducted by hot tensile experiments under different strain rates and deformation temperatures. The influence of microstructure evolution on fracture mechanism was studied. The principal failure mechanism was attributed to intergranular crack propagation and microvoid aggregation when deformed at 800–1100 ℃, changing to a mixed ductile-brittle intergranular fracture when deformed at 1200 ℃. After hot deformation, the microstructure transformed from a mixed phase of pearlite and ferrite to a lath martensite structure. Moreover, the lath martensite structure transitioned from disorder to order as the deformation temperature increases. The study revealed that in case of lower temperature when dynamic recovery (DRV) was dominated, the growth of voids was impeded by fine dynamic recrystallization (DRX) grains, resulting in an irregular void morphology. In case of higher temperature, the degree of DRX was high, voids were surrounded and impeded by newly formed DRX grains, which were gradually elongate with deformation. On the other hand, when there were DRX grains present between voids, void coalescence was less likely to occur, thereby inhibiting damage propagation.

The effect of mechanical compaction on the soil water retention curve: Insights from a rapid image analysis of micro-CT scanning

Soil hydrological and agricultural properties are highly affected by the soil water retention characteristics, which are closely related to the void size distribution and structure of the soil. Agricultural lands are often faced with the challenge of soil compaction, which alters the size, shape, connectivity, and morphology of soil voids. To determine the water retention curve and other hydrological and agricultural functions of un-compacted and compacted sandy soils, we used micro-CT techniques and image analysis procedures in both two and three dimensions. We found that these techniques were reliable, as they were validated against physical measurements and empirical physically-based models, and provided a relatively simple and fast way to characterize the key features of soil hydrological and agricultural properties. The findings highlight the impact of compaction on the soil void size distribution, resulting in increased water holding capacity, greater water availability for root uptake, and reduced hydraulic conductivity. We also discussed the differences between the two and three-dimensional analyses, highlighting the better ability to characterize soil hydrological and agricultural functions and soil water retention curve using the three-dimensional image analysis approach.

Interfacial competing interaction eliminates voids in the buried interface for efficient and stable perovskite solar modules on bare NiOX

Perovskite solar cells (PSCs) with impressive efficiency is promising for commercialization. However, when scaling up PSCs to large-area perovskite solar modules (PSMs), the rapid degradation of performance and stability still remains a grand challenge. One of the main causes of the degradation is the presence of local voids in the buried interface for large-area films, which we find could be attributed to the unbalanced interfacial interaction between precursor solvent and substrate. Here we improve a scalable and low-temperature sequential two-step chemical bath deposition process aiming for high quality NiOX. Further with the modulation of A-site cations to enhance the interaction between DMSO and perovskite precursor, the potential for DMSO absorbing on the NiOX could be eliminated. This strategy can inhibit the delay movement of DMSO on NiOX and improve the buried interfacial quality, with compact morphology and absent of voids. The inverted structured PSCs and PSMs based on the bare NiOX and modified perovskite precursor reach a champion efficiency of 22.40% and 19.09%, respectively, which are both among the highest reported values. The highly efficient PSMs also exhibit a long-term operational stability, which retain 84% of the initial performance after 1056 h operating under one-sun illumination.

Resin percolation and intimate contact in fast processing of thermoplastic composites

Fusion bonding of thermoplastic composites (TPCs) requires intimate contact before polymer interdiffusion and solidification can establish an interlaminar bond. The lack of such intimate contact results in voids or disbonds. This study shows through cross-sectional imaging and scaling analysis that percolation flow, rather than squeeze flow, of resin through fibers is the dominant mechanism to achieve intimate contact in rapid TPC processes such as automated fiber placement (AFP) and welding. A 1D intimate contact model based on resin percolation, derived from Darcy’s Law, is presented and compared to experiments. While this model proved effective in comparing processing conditions by adeptly capturing trends, it under-predicted resin content in samples processed using AFP with low pressure. The model was extended to high processing rates, suggesting the importance of heated tools and high processing pressures on achieving intimate contact.. In-situ high-speed imaging and ex-situ microscopy revealed void size and morphology based on AFP processing parameters. The results of this study can guide fast processing of thermoplastic composites.

Formation and persistence of glaciovolcanic voids explored with analytical and numerical models

Abstract One fifth of Earth's volcanoes are covered by snow or ice and many have active geothermal systems that interact with the overlying ice. These glaciovolcanic interactions can melt voids into glaciers, and are subject to controls exerted by ice dynamics and geothermal heat output. Glaciovolcanic voids have been observed to form prior to volcanic eruptions, which raised concerns when such features were discovered within Job Glacier on Qw̓elqw̓elústen (Mount Meager Volcanic Complex), British Columbia, Canada. In this study we model the formation, evolution, and steady-state morphology of glaciovolcanic voids using analytical and numerical models. Analytical steady-state void geometries show cave height limited to one quarter of the ice thickness, while numerical model results suggest the void height h scales with ice thickness H and geothermal heat flux $\dot {Q}$ as $h/H = a H^b \dot {Q}^c$ , with exponents b = −n/2 and c = 1/2 where n is the creep exponent. Applying this scaling to the glaciovolcanic voids within Job Glacier suggests the potential for total geothermal heat flux in excess of 10 MW. Our results show that relative changes in ice thickness are more influential in glaciovolcanic void formation and evolution than relative changes in geothermal heat flux.

Micro‐mesoscopic analysis of 3D void formation and evolution in CFRP composite using high‐resolution x‐ray microtomography

AbstractVoid defect is prevalent during the composite manufacturing process and may reduce the mechanical properties of composite structures, while limited information about three‐dimensional void distribution and evolution can be found due to the difficulties in void observation. In this work, void defects at different positions were detected and analyzed using x‐ray microtomography (XRM), and the random forest algorithm was implemented for segmenting components of CFRP samples. Results showed a trend of gradual rising porosity in the axial direction, with an increase of ~250% of porosity at the outlet of resin injection compared to the one at the inlet during the composite manufacturing process. The voids mainly featured with microscale between carbon fibers, with less distribution between fiber bundles and resin‐rich zones. Void defects achieved aggregation at the middle position of manufactured laminate, which is probably related to pressure interception. In the axial direction, the proportion of large‐diameter voids gradually increased, and a large volume of connected voids appeared near the outlet. Due to the shear deformation of resin and fiber and the pressure gradient effect, most of the voids showed stripe shape. The spatial orientation of voids was predominantly along the direction of resin flow and fluctuated due to fiber curl.Highlights 3D void characteristics in CFRP were studied using the XRM technique. Void formation and the effects of fibers on void morphology were analyzed. Dynamic void transport mechanisms during CFRP manufacturing were studied. Location and morphology of voids are helpful for CFRP damage modeling. The effective partitioning of CFRP was achieved using a random forest algorithm.

Phase-field crystal simulation of the evolution of voids in polycrystalline Au–Al bonds with elastic interaction and the Kirkendall effect

In this paper, the modified phase-field crystal (MPFC) model is employed to study the evolution of Kirkendall voids in polycrystalline Au–Al bonds under mechanical loading. The MPFC model can simulate the structural evolution of deformed pure nanocrystalline materials considering instantaneous elastic interactions. Therefore, coupling a concentration field evolved by the Cahn-Hilliard equation with a density field evolved by the existing MPFC model makes it possible to study the phase transformation of a binary system in the presence of mechanical deformation. Using this modified model, we focus on the morphology evolution of the voids in Au–Al bonds under different mechanical loadings. The semi-implicit Fourier spectral algorithm is applied to solve the six-order coupling dynamics equations. The Kirkendall porosity of the diffusion couple is computed and analyzed. The effects of quasi-static and cyclic axial tensile loads on the morphology of voids, and porosity of the system are investigated. It is found that the morphology of Kirkendall voids that result from applying a quasi-static load is different from those that result from applying a cyclic load.

Investigation on Three-Dimensional Void Mesostructures and Geometries in Porous Asphalt Mixture Based on Computed Tomography (CT) Images and Avizo

To investigate the void mesostructure in porous asphalt mixtures (PA), computed tomography (CT) and Avizo were utilized to scan and reconstruct the three-dimensional (3D) void model of PA-16 specimens. The void mesostructure of the specimen was quantitatively characterized through the anisotropy evaluation index. The equivalent pore network model (PNM) was extracted using the medial axis method. Based on the PNM model, the topological structure of the specimen and the morphological characteristics of the connected pores were analyzed. The results showed that the void anisotropy evaluation method can reflect the microscopic morphology of voids in porous asphalt mixtures. The cross-sectional porosity of representative elementary volume (REV) is mainly distributed between 20% and 25%, and about 90% of the macropores have a diameter between 0.5 mm and 3 mm. The distribution of cross-sectional porosity is uneven along the REV height direction. As the smallest cross-section of the seepage path, the equivalent radius of the throat is mainly between 0.1 mm and 1.5 mm, which is much smaller than the equivalent radius of the pore. The topological structure of pores is quite different, and their coordination numbers are mainly concentrated within 18. The pores with coordination numbers 1 to 10 constitute the main body of the pores inside REV, accounting for over 98% of the total number of pores. In addition, the permeability calculation results show that there is a significant difference in the permeability of each axis of REV compared to the total permeability of the superpave gyratory compactor (SGC) specimen, which illustrates that the permeability distribution presents an obvious spatial anisotropy. This study effectively reveals the heterogeneity of the 3D void morphology of porous asphalt mixtures, and it provides a reference for a better understanding of the void flow rules in drainage pavements.

Automatic micro-scale modelling and evaluation of effective properties of highly porous ceramic matrix materials using the scaled boundary finite element method

This paper presents an approach to the numerical estimation of effective properties of highly porous materials based on the scaled boundary finite element method (SBFEM). The latter can be formulated on quadtree meshes with hanging nodes and thus facilitates the efficient mesh generation and analysis of a large number of randomly created samples. To generate the corresponding Representative Volume Elements (RVEs), an improved Random Sequential Addition (RSA) method with overlap is used. Moreover, an alternative image-based digital matrix method for generating random assemblies of circular particles of the same size is proposed. In addition, a modified smoothing algorithm to treat the staircase boundaries present in a quadtree mesh is developed in order to accurately and efficiently capture the sinter-neck features of overlapping circular particles. The proposed image-based mesh generation and analysis procedure is used to evaluate the relationship between microstructural parameters and effective Young’s modulus considering a large number of samples. In this context, a new dimensionless morphological parameter Nfc is proposed. The latter represents the morphology and connectivity of voids and is shown to be a useful indicator with respect to the effective elastic properties of highly porous ceramic matrix material.

Temperature-dependent voids and their impact on SMA surface course permeability

This study investigates the water permeability characteristics of newly constructed Stone Mastic Asphalt (SMA) surface course, with a specific focus on the influence of connected voids arising from the compaction temperature during pavement construction. On-site evaluation of the permeability coefficient was performed, followed by core sample extraction from the same locations to investigate the correlation between the permeability coefficient and porosity. Industrial CT scanning was used to identify and separate void regions in the core samples. Three-dimensional digital reconstruction techniques were employed to analyze the morphology and spatial distribution of voids within the core. The connectivity of voids was assessed, providing insights into water infiltration pathways within the SMA course. Additionally, finite element simulation of the pavement temperature field was conducted to investigate the spatially differentiated distribution of voids within the SMA course.The findings reveal that approximately 38.3% of the voids are concentrated within a 1 cm depth below the top surface of the 4 cm-thick SMA course. The aggregation of voids enhances the likelihood of interconnection, facilitating water seepage. Water infiltrates through the open voids on the top surface and flows vertically and horizontally along the interconnected pathways. Notably, at a depth of approximately 2.5 cm, the flow transitions to horizontal spreading, aligning with the primary distribution interval of interconnected voids. The non-uniform distribution of voids is primarily influenced by the compaction temperature. The top and bottom portions exhibit higher void percentages, while the middle portion shows relatively fewer voids, consistent with the observed compaction temperature pattern.

Understanding of EPS beads on mechanical properties and void morphology of a CO2-solidified foam concrete based on solid wastes

Two major issues of EPS doped concrete are apparent reduction in compressive strength associated with the presence of EPS-formed artificial defects and ultra-light weight related easy segregation in the mixes, even though the thermal conductivity of composites shows a satisfactory reduction. This paper presents a composite lightweight concrete by introducing EPS into a solid waste (carbide slag and quartz sand tailings) prepared industrial grade γ-C2S-based foam concrete (CFC) to partially replace foam-formed voids. Results show that the partially EPS-substituted CFC with reasonable EPS parameters (Especially 1 mm in diameter and 5 wt% in content) exhibits a notable improvement in compressive strength (24.3%) while accompanied by the reduction in sorptivity, drying shrinkage and thermal conductivity. This is attributed to the fact that the EPS can effectively improve the foam stability by delaying foam drainage velocity due to its hydrophobicity and discrete smooth surface during the pre-curing procedure, which results in a refinement of void morphology and distribution as well as the optimized interfacial transition zone (ITZ). Accompanied by the compact inner surface and optimized ITZ, leading to a lower drying shrinkage, thermal conductivity, and also a reduction in sorptivity due to the increasing of tortuous path for the capillary flow. Moreover, magnesium slag (MS) containing dicalcium silicate mineral phase is also used to prepare MS-based CFC to further reduce costs and achieve the resource utilization of solid waste and a large amount of CO2 storage, which contributes to the sustainable development of CFC.

High temperature viscoplastic deformation behavior of sintered nanocopper paste used in power electronics packaging: Insights from constitutive and multi-scale modelling

As a promising technology for high-power and high-temperature power electronics packaging, nanocopper (nanoCu) paste sintering has recently received increasing attention as a die-attachment. The high-temperature deformation of sintered nanoCu paste and its underlying mechanisms challenge the reliability of high-power electronics packaging. In this study, the tensile deformation behaviors of sintered nanoCu paste were firstly characterized by high-temperature tensile tests performed at various temperatures and strain rates ranging from 180 °C to 360 °C, 1 × 10−4 s−1 to 1 × 10−3 s−1 respectively. It was found that the elastic modulus and tensile strength decreased at the higher tensile temperature while the ductility increased accordingly. The highest elastic modulus and tensile strength results were 12.15 GPa and 46.97 MPa, respectively. Second, failure analysis was conducted based on the fracture surface after tensile testing. Recrystallization was revealed as the main factor for ductility improvement. Subsequently, an Anand model was fitted by stress-strain curves to describe the tensile constitutive behavior of the sintered nanoCu paste. Multi-scale modelling techniques also investigated the impact of tensile temperature and strain rate on the tensile response. Molecular dynamics simulation was implemented using a hemispherical Cu nanoparticle model to reveal the properties from an atomistic perspective. In addition, a two-dimensional equivalent model was further established by using a stochastically distributed void morphology. The multi-scale modelling techniques successfully describe the evolution of tensile response to the different tensile temperatures and strain rates. Besides, the equivalent model with random void morphology was demonstrated as the finite element simulation results were highly consistent with the high-temperature tensile experiments.

Effect of crystallinity and morphology on the mechanical properties of CF/PEKK composites manufactured under compression moulding and automated tape placement

The present work aims to establish to what extent crystallisation morphology and kinetics affect the matrix-dominated properties of CF/PEKK composites, two factors which have been minimally investigated together in existing literature. Different compression-moulding cycles and automated tape placement (ATP) were used as the processing routes. Their effects on void content, crystallinity development, morphology and mechanical performance were investigated. Results showed that all compression-moulded laminates undergoing different isothermal crystallisation conditions achieved similar levels of consolidation and crystallinity, although the spherulitic development varied considerably. The effect of different crystalline structures was not evident on the properties investigated, as all compression-moulded laminates performed similarly. However, ATP laminates displayed a higher void content and low crystallinity, resulting in a lower performance across the investigated mechanical properties. While the modification of some ATP parameters resulted in slight improvements in performance in some testing, the results indicated that a thorough understanding of the correlation between processing conditions and development of crystalline structures in PEKK is needed in order to produce good-quality CF/PEKK parts under very rapid processing conditions and ensure the repeatability of this.