This study investigates the mechanical behavior of bio-based sandwich panels (BBSP) composed of flax/epoxy skins and a palm wood core (PWC) under monotonic and repeated bending and indentation loading. PWC, sourced from northern and southern regions of Algeria, was prepared along three principal material directions to capture its anisotropic response. Three-point bending and indentation tests, including Repeated Progressive Loading (RPL), were conducted to assess both static and cyclic behavior. The bending results highlight the anisotropic nature of PWC, with fiber-aligned specimens particularly from the southern region, exhibiting superior mechanical performance. RPL tests reveal the onset of permanent deformation from early cycles; however, below a critical load threshold, the material maintains significant elastic recovery, with residual displacement remaining below 10% of the maximum. The main failure mechanisms identified include core crushing, skin cracking, and interfacial delamination. Acoustic emission analysis confirms that low-amplitude signals (Type A, ∼93%) are dominant and associated with microcrack initiation during the elastic phase. Indentation results show progressive plastic deformation and stiff degradation, accompanied by energy dissipation and permanent deformation. Under cyclic indentation, PWC exhibits a reduction in reduced modulus and hardness followed by stabilization around a normalized cycle ratio of 0.2 due to plastic compression. In contrast, BBSP does not reach stabilization, showing continuous degradation throughout the loading cycles, as reflected by the progressive increase in elastic and plastic energy components up to failure.
Foams are essential materials in engineering designs across the building and transport sectors, as they provide a unique combination of light weight, structural support, thermal and acoustic properties, and energy absorption. This study focuses on a rigid biofoam made from castor-oil polyurethane (PU) and examines its mechanical properties under compressive and three-point bending loads. No chemical additives are used except a castor-oil polyol, diisocyanate, and water. The elastic compressive modulus is evaluated for loads applied both parallel and perpendicular to the foam expansion direction, and results demonstrate that the foam is mildly anisotropic with an anisotropy shape index close to 1. A microtomographic scan analysis is conducted to investigate the internal structure of the foam. The elastic flexural modulus obtained is 9.2 +/- 1.5 MPa. The compressive modulus (9.08 +/- 0.71 MPa) and the elastic collapse stress (405 +/- 29 kPa) are comparable to or higher than those reported for other rigid PU foams within the same density range in the literature. This finding indicates that a rigid biofoam can be successfully produced without the use of additives, such as catalysts and surfactants, while still exhibiting mechanical performance comparable to other rigid PU foams.
Expanded polystyrene (EPS) is a cellular material widely used in energy-absorbing systems due to its ability to dissipate kinetic energy through compression. EPS can be recycled, offering a promising avenue for sustainable material use. This study aims to characterize the mechanical response of recycled EPS under dynamic loading conditions. Both external factors (temperature, impact velocity) and internal factors (density, recycling ratio) were investigated, and the behavior of recycled EPS was compared to that of classical material. The results show that recycled EPS exhibits no significant sensitivity to temperature within the range of -20 degrees C to 18 degrees C. However, its mechanical response is strongly influenced by impact velocity and foam density. No statistical difference was observed between recycled and classical EPS at a density of 60 kg/m3. In contrast, at 80 kg/m3, recycling induced a marked shift in the stress-strain curves, indicating that higher densities amplify the effects of the recycling process on mechanical performance.
This study aims to develop bio-based and biodegradable flexible polyurethane (PU) foams by applying green chemistry principles, a challenging yet essential goal for advancing sustainability. Additionally, these materials must comply with established product standards to ensure their practical viability. In this study, a new type of polyol (OH number: 273 mgKOH/g) was synthesized for the first time through the hydroalkylation reaction of cellulose and propylene carbonate. The synthesis of the cellulose-based polyol was simplified from a two-step to a one-step process, less materials were required and green solvent were employed aligning with green chemistry principles. This cellulose-based polyol was structurally characterized and used to produce flexible viscoelastic PU foams with 10, 20, 30, 40 and 50% of total polyol content. Physical, mechanical, structural, morphological and biodegradability properties of the viscoelastic PU foams were evaluated. While biodegradability of these open-celled foams increased to 35%, up to 40% cellulose-based polyol content, they also fulfill the final product standards (apparent density: 46-50 kg/m3, hardness: 70-75 N, tensile strength: 87-122 kPa, elongation: 300-390%, compression set: 3.3-5.2%, compression strength: 0.6-2.7 kPa, biodegradability: 4-35%). These next-generation materials serve as more sustainable alternatives to conventional flexible viscoelastic PU foams while preserving their quality.
Polyurethane (PU) nanocomposite foam with polydimethyl siloxane (PDMS) was prepared by solution casting method having 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% of Graphene Oxide (GO)/Silica (SiO2) as combined nanofillers. PU-PDMS nanocomposite foam was characterised by different techniques. Field Emission Scanning Electron Microscopy (FESEM) was employed to examine the microstructure in the study field. The crystallinity and phase separation of the PU-PDMS nanocomposite foam were determined using the X-ray diffraction (XRD) technique. Thermal and tensile properties of PU-PDMS nanocomposite foam were analysed. The impact property of the PU-PDMS nanocomposite foam was evaluated using a drop impact testing machine. The thermal stability as well as mechanical properties were improved after addition of GO/SiO 2 hybrid fillers in the composite. The tensile strength of PU-PDMS foam containing 1.0 wt% GO/SiO 2 was 216% higher than that of the base PU-PDMS foam. The impact results show that the PU-PDMS nanocomposite foam with 1.0 wt.% of the combined nanofillers exhibits higher peak load and energy absorption than lower wt% of the fillers in the polyurethane matrix. These nanocomposite foams can be used in impact and thermomechanical applications.
To optimize the cellular structure and enhance the performance of thermoplastic polyurethane (TPU) foams, this work addresses the limitations of conventional microcellular injection molding (MIM) by employing a self-designed mold-opening mold and a mold-opening microcellular injection molding (MOMIM) process, which uses a self-designed expandable-cavity mold to produce finer and more uniform cells with higher cell density and lower foam density. It also simplifies the mold structure without complex linkage mechanisms, improves product surface quality, enhances process versatility, and reduces production costs. The effects of key MOMIM parameters-including mold-opening distance, holding pressure, holding time, mold-opening speed, and mold-opening delay time-on cell size and density, cell wall thickness, foam density (expansion ratio), as well as mechanical and thermal properties are comprehensively investigated. The results demonstrate that the optimal process is: mold-opening distance 3 mm, holding pressure 35 MPa, holding time 6 s, mold-opening speed 20 mm/s, and mold-opening delay time 8 s. Under these conditions, TPU foam exhibits an average cell diameter of 43.40 mu m, which is reduced by 34.63% compared with MIM foams; a cell density of 1.6 & times; 107 cells/cm3, 22.18 times higher than MIM foams; an average cell wall thickness of 4.03 mu m, reduced by 72.36%; and a skin layer thickness of 0.400 mm, reduced by 22.77%. The compressive strength is 4.58 MPa and the compressive modulus is 6.95 MPa, corresponding to reductions of 22.23% and 22.88%, respectively. The thermal conductivity at room temperature is 0.071 W/(m & centerdot;K), representing a 55.91% improvemen. By precisely tuning the MOMIM parameters, this study successfully achieves simultaneous optimization of cell structure and macroscopic performance, balancing mechanical robustness and thermal insulation. It expands the application scope of TPU foams toward lightweight packaging, thermal insulation in new-energy vehicles, and building energy-saving materials, and provide a solid theoretical basis for the fabrication of high-performance, multifunctional foams.
Expanded Polypropylene foams are used in energy-absorbing applications, yet their mechanical response exhibits complex rate-dependency, damage, and permanent set, making accurate constitutive modeling challenging. This work proposes and validates a two-network viscoplastic model to describe the large-deformation compressive behavior of Expanded Polypropylene foams. The framework combines a hyperelastic network to capture the instantaneous nonlinear elastic response with a parallel viscoplastic network governed by an overstress flow rule to account for rate-sensitive effects. Model parameters were calibrated using experimental data from uniaxial compression tests at low (4.5 mm/min) and high (450 mm/min) rates. The model's predictive capability was then assessed against an independent dataset at an intermediate rate (45 mm/min), achieving a coefficient of determination exceeding 0.98. Furthermore, an analysis was performed to quantify uncertainty, showing that the 95% confidence intervals and 95% prediction intervals for the stress response successfully encompassed the experimental validation data. The framework also provided an accurate approximation of key energy absorption parameters, confirming its empirical adequacy.
The mechanical properties of polyurethane (PU) grouting materials are susceptible to the influence of water during underground grouting. To elucidate the diffusion mechanism of water within the material and the variation in compressive strength after water immersion. Scanning Electron Microscopy (SEM) was employed to analyze the water diffusion mechanism in polyurethane grouting materials from a microscopic perspective. Furthermore, a series of laboratory experiments were conducted to investigate the effects of factors such as density, surface condition, immersion duration, water pressure, saline environment, and ambient temperature and humidity on the water absorption. Additionally, the compressive strengths before and after immersion were compared and analyzed. The results indicate that the water absorption decreases as a quadratic polynomial function of density (R-2 = 0.98). Specifically, at densities of 0.30 g/cm(3) and 0.42 g/cm(3), the water absorption was merely 4.38% and 1.28%, respectively. Compared with the original surface (water absorption of 15.77%), sealing treatment reduces the rate by 44.32%, whereas surface peeling treatment increases it by 151.11%. Moreover, as the water pressure increases by 2 MPa, the water absorption rises gradually with a diminishing marginal increase. The most drastic variation in water absorption occurs within the initial 24 h; thereafter, for every additional 24 h of immersion, the increment remains below 0.5% and progressively decelerates. In saline environments, the water absorption of specimens with various densities increases by 22%, and the water absorption exhibit an upward trend with elevated environmental temperature and humidity. Notably, compressive strength both before and after absorption increases with density (R-2>0.88). In the density range of 0.070-0.112 g/cm(3), the material exhibits a relatively higher water absorption. Due to the supporting effect of the internal water, the compressive strength experiences a marginal increase of approximately 4.56%. These findings can provide theoretical support for the design and durability evaluation of underwater grouting reinforcement in underground engineering.
Sustainability drives the development of new or optimised methods in plastics technology, one of which is the vacuum assisted rotational foam molding process, as it refrains from the use of chemical blowing agents. Process inherent air inclusions in the polymer melt thereby act as nuclei for cell growth induced by means of an applied vacuum. This manuscript addresses the influence of the moisture content in the employed powders and characterizes its impact on the foaming level. The findings reveal that the formation of air inclusions, beyond those generated during sintering processes in melting is significantly intensified by the evaporation of water molecules during polymer heating. The increased number of initially present gas inclusions allows to obtain higher foaming degrees. Two types of thermoplastic polyurethane (TPU) materials with distinct hardness levels were examined closely, revealing a positive correlation between elevated shore hardness and a shift in the water release to higher temperatures. In materials with lower shore hardness, water release occurs at lower temperatures, before the polymer melt forms, and thus does not contribute significantly to foaming. The effect is believed to be due to a stronger molecular binding of water through hydrogen bonding in the material with a higher hard segment content. Notably, the contribution to foam expansion is more pronounced at higher hardness gradients. This work provides an overview of the possibilities to influence the foaming degree through the initial moisture content in the materials used, as well as the importance of proper material conditioning for better property prediction.
This study presents the design and comprehensive characterization of sustainable rigid polyurethane foam (RPUF) composites reinforced with coconut fiber and mycelium powder to improve their structural, mechanical, thermal, and flame-retardant performance. The incorporation of these bio-based reinforcements aims to enhance the sustainability and multifunctional efficiency of conventional RPUFs through environmentally benign, renewable, and resource-efficient modification strategies. Comprehensive analyses, including particle size distribution, ATR-FTIR spectroscopy, and SEM imaging were performed to evaluate the effects of filler concentration on microstructure, interfacial chemistry, and thermomechanical response. The incorporation of bio-fillers refined the foam morphology, yielding smaller, more uniform, and closed-cell structures at moderate loadings (<= 3 wt.%), which enhanced compressive strength and mechanical integrity through improved interfacial adhesion and hydrogen bonding between filler hydroxyl and matrix carbonyl groups. Thermal conductivity measurements revealed that optimized formulations achieved values as low as 23.39 mW/m & centerdot;K, attributed to reduced cell size, higher closed-cell content, and the intrinsic thermal barrier function of the lignocellulosic-chitinous hybrid structure.The limiting oxygen index (LOI) systematically increased from 18.75% for neat RPUF to 21.75% for the highest filler-loaded composite, accompanied by shorter burning times and reduced burning speeds, confirming significantly improved flame retardancy. Post-combustion surface analysis demonstrated a clear transition from severe cracking and melting in pristine RPUF to the formation of a dense, cohesive char layer in filler-modified systems, evidencing enhanced heat resistance and self-extinguishing behavior. Consequently, the synergistic interplay between coconut fiber and mycelium powder improved interfacial cohesion, stress transfer, and thermal stability, resulting in multifunctional RPUF composites with superior mechanical, thermal, and fire-resistant properties. This work provides a sustainable route toward high-performance, bio-derived polyurethane foams for energy-efficient, fire-safe applications in construction, packaging, and thermal management systems.
Polypropylene (PP) is one of the most commonly used thermoplastics in automotive field owing to its low cost and excellent properties. Microcellular injection molding was an environmental-friendly foaming technique which can fabricate large geometrically complex microcellular structured components. PP foams fabricated by conventional microcellular injection molding (MIM) suffers from poor mechanical properties and surface quality. In this study, we prepared high strength and excellent surface quality PP based foams by adding nano-CaCO3 fillers and using mold-opening microcellular injection molding process. Firstly, PP and nano-CaCO3 were melt blended using twin screw extruder to prepare PP/CaCO3 nanocomposites. The crystallization, as well as viscoelastic properties of nanocomposites were analyzed according to DSC and rheological experiments. Afterwards, MIM and MOMIM were conducted to fabricate PP/CaCO3 nanocomposite foams and then the mechanical performance of MIM and MOMIM foams were compared. Furthermore, optical microscope and white light interferometer were utilized to analyze the surface roughness of foams under various foaming processes. The results showed that nano-CaCO3 fillers greatly refine the cellular morphology by improving PP's viscoelasticity and crystallization. In addition, MOMIM process shows outstanding advantages in optimizing cellular structure, improving mechanical properties and surface quality of PP based foams.
Using structures with triply periodic minimal surfaces (TPMS) is a relatively new field that requires attention. They offer advantages such as high porosity and high area-to-volume ratio, which are essential in applications related to bioengineering, heat exchangers, and energy absorption. This work studied the elastic modulus and structural response in the tension of resin-printed geometries with the gyroid structure. The constants C and n for the Gibson-Ashby model in tension state were estimated using finite element simulations. A numerical-experimental comparison was performed to validate the use of finite element simulation to obtain the constants. The constants were obtained using the relative densities of 20%, 30%, 40%, and 50%. The evaluated constants accurately predict the elastic modulus for test relative densities of 25%, 35%, 45%, and 60% with low errors of 0.64%, 2.48%, 3.42%, and 8.32% respectively. In addition, using Hooke's law and the Gibson-Ashby model, we obtained a practical approach to predicting the reaction force with errors ranging from 0.64% to 5.80%. These findings contribute to the analysis of the application of the Gibson-Ashby model in tension, finding C and n constants to predict the elastic modulus and structural response of the gyroid structure, offering valuable information for structural design and engineering applications. The validated model provides an efficient procedure that predicts material behavior under tensile conditions, saving time and resources compared to full-scale experimental testing. Overall, this study offers potential for further research in analyzing the mechanical properties of TPMS and lattice structures.
Conventional thin-walled metallic tubular structures exhibit material inefficiencies and reduced energy absorption capacity. To overcome these limitations, hierarchical nature-inspired thin-walled multicellular tube structures have shown the promising solution in crashworthiness applications due to their greater mechanical efficacy, lightweight nature, and improved energy absorption capacity. This research article reports the experimental crashworthiness investigation and multi-attribute assessment of additively manufactured hierarchical fruit-inspired multicellular structures. Six hierarchical fruit-inspired tube structures were fabricated using the Fused Deposition Modelling (FDM) technique. The energy absorption properties of these structures were evaluated through axial static crushing experiments. The findings showed that designs of multicellular structures inspired by various fruits improve energy absorption and structural efficiency when compared to conventional metallic tubular structures. The results revealed that the lemon-inspired structure (PE-LE) exhibited the highest total energy absorption of 746 kJ and a maximum specific energy absorption capacity of 9.84 kJ/g, followed closely by the tomato-inspired structure (PE-TO). For multi-criteria decision making, the Complex Proportional Assessment (COPRAS) method was used, incorporating mass efficiency and crashworthiness performance into an integrative ranking system to determine the ideal structure. The PETG-carbon fiber based lemon-inspired structure (PE-LE) offered the best crashworthiness performance according to the obtained results. The overall outcomes offered significant new information for the development of high-performing lightweight energy-absorbing tubular structures used in automobiles and aircraft protective systems.
This study examines the impact of varying isocyanate indices on the morphology and properties of bio-based viscoelastic polyurethane (VE PU) foams produced using high-pressure processing and moulding technology. Palm-based polyol, referred to herein as Pioneer E-135, was used as a sustainable alternative to petroleum-based polyol. VE PU foams were formulated with different isocyanate indices (71%, 75%, 79% and 83%) and their physical, mechanical and morphological characteristics were evaluated. Results indicated that the VE PU foam containing 10% Pioneer-E135 polyol and an isocyanate index of 83% exhibited superior mechanical properties compared to the VE PU foam with 100% petroleum-based polyol. The incorporation of 10% Pioneer-E135 polyol significantly enhanced the mechanical properties, including surface texture, morphology and load-bearing capacity, as indicated by indentation force deflection and sag factor measurements. Higher NCO indices contributed to increased tensile strength, tear strength, and ageing resistance, but resulted in lower density and reduced elongation at break. Overall, the optimised processing parameters enabled the successful production of high-quality, bio-based VE PU foams using high-pressure machine technology.
This study investigates the mechanical degradation of expanded polystyrene (EPS) foams under repeated compressive loading, with a focus on energy absorption, hysteresis, and efficiency loss. EPS foams of two densities (8.5 kg/m3 and 24 kg/m3) were tested at a loading rate of 500 mm/min, with five cycles for low-density and ten cycles for high-density specimens. Results show a significant reduction in energy absorption capacity after the first cycle: 70% for high-density foams and 60% for low-density. Hysteresis also declined sharply and stabilized within the first few cycles, indicating progressive structural collapse. Efficiency and ideality curves confirmed the irreversible loss of energy recovery capacity. A phenomenological model was proposed to quantify the exponential decay of maximum energy absorption, with parameters dependent on material density and validated by nonlinear regression. Statistical analysis and microstructural characterization using optical and scanning electron microscopy revealed permanent deformation, fracture, and cell elongation after repeated loading. These findings reinforce the non-recoverable nature of EPS under repeated loading in energy dissipation applications and highlight the relevance of predictive modeling and microstructural evaluation for designing more resilient impact-absorbing materials.
Lattice structures are increasingly employed in aerospace and biomedical applications due to their exceptional strength-to-weight ratios, enabling lightweight designs. These structures include strut and surface-based configurations, which are effectively manufactured through additive manufacturing (AM) techniques. Among these, the integration of multiple lattice designs has been explored to enhance mechanical properties such as stiffness and strength. This study examines the deformation behaviour and compression properties of the octet, gyroid, and blend (merging of octet and gyroid) lattice structures. All the structures were fabricated with poly-lactic acid (PLA) using a material extrusion AM process at a relative density of 64%. Quasi-static compression tests reveal distinct deformation mechanisms across the lattices. The octet lattice exhibited stretching-dominated behaviour, with an increase in the elastic modulus and a 12.3% improvement in stiffness compared to the gyroid. Conversely, the gyroid lattice demonstrated bending-dominated behaviour, resulting in greater energy absorption due to a smooth, longer plateau region and a higher peak stress observed. During quasi-static compression, the blend lattice exhibits post-yield softening, resulting in a decrease in stress after the yield point due to a change in deformation mechanism from stretching to bending-dominated. The energy absorption capacity was measured as 3.53 J/cm3 for the blend lattice, which was intermediate between the octet (0.73 J/cm3) and gyroid (5.19 J/cm3) structures. This balance of properties makes the blend lattice suitable for applications that require moderate energy absorption and improved stiffness. To further explore their application, a combination of octet and gyroid lattice designs was integrated into the topology optimisation of a bracket using a density-based approach.
Additive manufacturing of lattice structures offers superior lightweight and energy-absorbing properties across aviation, automotive, and biomedical sectors. However, achieving dimensional precision remains a primary obstacle to ensuring design compatibility and product functionality. To address this challenge, this study introduces a novel comparative analysis of BCC, Diamond, and Octet Truss geometries, specifically focusing on the interplay between infill density and strut thickness. By evaluating PLA-fabricated plates with thicknesses of 0.8 mm, 1 mm, and 1.2 mm through microscopic CAD-to-print comparison, the research identifies critical accuracy thresholds. Findings demonstrate that higher infill ratios significantly enhance structural stability; notably, Octet Truss structures exhibited substantially lower dimensional deviations (0.694%-1.923%) compared to BCC structures (1.25%-3.546%). Furthermore, increasing strut thickness to 1.2 mm reduced deviation rates by up to 50% compared to 0.8 mm struts. These results provide a significant resource for optimizing additive manufacturing parameters, offering new insights into achieving high-precision fabrication for complex lattice systems.
This work aims to disclose the strengths and limitations of utilizing hydroxyl-compatible fillers, rice husks and silica (SiO2), in citric acid-crosslinked thermoplastic starch foams. FTIR characterization demonstrated that citric acid could establish ester linkages with starch molecules for both neat and composite foams, with the C = O peak shifting from 1724 cm-1 (neat foam) to 1730-1732 cm-1 (composite foams). The key role of hydroxyl-compatible fillers was the strong starch-filler interactions that enabled more thermally stable composite foams, which elevated thermal decomposition temperatures to 300-302 degrees C with higher residue weights of 22.73-25.33%. These strong starch-filler interactions were also responsible for retarding cell foam expansion. The composite foams showed 16.61-92.03% improved flexural strength, 2.82-10.67% increased densities and lower moisture absorption. However, incorporation of hydroxyl-compatible fillers in composite foams increased water solubility to 16.84-20.73%, compared to 12.14% for a neat foam. These experimental results indicate that the employed fillers might interfere with the crosslinking process, leading to decreased crosslink formation in composite foams. Consequently, possible interruption mechanisms of crosslink formation by the fillers were suggested and confirmed by qualitative analysis. The findings of the strengths and limitations of hydroxyl-compatible fillers illustrate crucial trade-offs in using starch-based composite foams as sustainable food packaging materials.
Reinforcement using bio-waste and recycled materials is increasingly favoured in composite development due to their enhanced sustainability and promising performance when compared to synthetic alternatives. In this study, recycled PET foam was utilized as the core material to control the weight gain in the composite. The composites were fabricated with chopped luffa fiber, recycled PET foam, and walnut shell-derived porous biocarbon, and evaluated for tensile, flexural, impact, hardness, water absorption, and flammability properties, following relevant American Society for Testing and materials (ASTM) standards. Among the specimens, the composite PRC1 (with 3 vol.% filler) exhibited the highest tensile strength (120 MPa), flexural strength (143 MPa), and impact resistance (5.0 J), indicating optimal reinforcement at this filler level. In contrast, PRC2 (5 vol.% filler) achieved the highest hardness and exhibited an excellent flame resistance rate of 6.53 mm/min. The control sample P (100 vol.% vinyl ester) showed the lowest water absorption at 3.2%, reflecting the hydrophobic nature of the matrix. Additionally, scanning electron microscopy (SEM) was performed to examine the fracture surfaces post mechanical testing, providing insights into failure mechanisms and fiber–matrix interactions. Based on the performance characteristics, these composites show strong potential for use in applications such as lower limb prosthetic sockets, upper limb prosthetic frames and covers, cranial and facial prosthetics, and adaptive sports prosthetics.
Polyurethane (PU) grouting materials' dielectric constant is susceptible to moisture and the testing frequency of the instrument. To establish a dielectric model of PU grouting materials based on frequency and moisture effect analysis, a vector network analyzer equipped with an open-ended coaxial probe was used to conduct frequency sweep measurements of the dielectric constant for specimens of different densities within the 0.5 GHz to 6 GHz frequency range. Firstly, the dielectric properties tests of dry specimens were conducted. Based on the influence of frequency on the dielectric constant, the dielectric constant values of the PU matrix and pores were predicted using the fitting relationship between the dielectric constant and density. By introducing the Maxwell-Garnett multiphase mixing model, a dielectric model of dry PU grouting materials considering the frequency effect was constructed and validated, with the mean relative error (MRE) of less than 0.6%. Secondly, to reveal the impact of moisture on the dielectric constant, water absorption tests and dielectric property tests of moist specimens were conducted. According to the influence of water absorption on the dielectric constant and the established dielectric model for dry PU grouting materials, a comprehensive dielectric model considering frequency and moisture effects was constructed and validated with the MRE of less than 8%, demonstrating good applicability for the detection and evaluation of grouting effects.
