Search Results (28)

Coalbed methane development is constrained by reservoir characteristics including high gas adsorption, high salinity, and high closure pressure, which impose significant limitations on conventional polymer fracturing fluids regarding viscosity enhancement, proppant transport, and fracture maintenance. In this study, a novel polymer fracturing fluid system, Z-H-PAM, was designed and synthesized to achieve strong salt tolerance, low adsorption affinity, and high elasticity to withstand closure pressure. This was accomplished through the molecular integration of a zwitterionic monomer ZM-1 and a hydrophobic associative monomer HM-2, forming a unified structure that combines rigid hydrated segments with a hydrophobic elastic network. The results indicate that ZM-1 provides a stable hydration layer and low adsorption tendency under high-salinity conditions, while HM-2 contributes to a high-storage-modulus, three-dimensional physically cross-linked network via reversible hydrophobic association. Their synergistic interaction enables Z-H-PAM to retain viscoelasticity that is significantly superior to conventional HPAM and to achieve rapid structural recovery in high-mineralization environments. Systematic evaluation shows that this system achieves a static sand-suspension rate exceeding 95% in simulated flowback fluid, produces broken gel residues below 90 mg/L, and results in a core damage rate of only 10.5%. Moreover, it maintains 88.8% of its fracture conductivity under 30 MPa closure pressure. Notably, Z-H-PAM can be prepared directly using high-salinity flowback water, maintaining high elasticity and sand-carrying capacity while enabling fluid recycling and reducing reservoir damage. This work clarifies the multi-scale mechanisms of strongly hydrated and highly elastic polymers in coalbed methane reservoirs, offering a theoretical and technical pathway for developing efficient and low-damage fracturing materials. Full article

This study examines the torsional behavior of an additively manufactured bushing featuring a unique topology, which includes a flexible gyroid core and rigid inner and outer sleeves. The bushing is designed and fabricated using two materials: thermoplastic polyurethane (TPU) and polylactic acid (PLA), which are interpenetrated in successive layers throughout the bushing’s thickness. First, tensile mechanical tests are conducted on both materials with different infill patterns. The 45/135 infill proves to be the most suitable, providing good stiffness, strength, ductility, and data reproducibility. Additionally, the effectiveness of the interlocking created between the two materials through the printing process is evaluated by testing different overlap lengths. With an overlap of 2 mm, the extrusion process remains unaffected, minimizing voids and defects while ensuring strong interlayer bonding. Next, the designed bushing is subjected to torsional loading under both single and repetitive angular rotations, and its response is measured in terms of torque. The aim of this study is to evaluate the suitability of TPU and PLA materials for developing a design intended for dynamic mechanical environments, serving as a proof of concept. The quasi-static results indicate the presence of local damages and a viscoelastic response of the bushing during twisting, while also demonstrating its strong ability to withstand significant angles of rotation. Quasi-static results indicate local damage and the bushing’s viscoelastic response during twisting, as well as its ability to withstand significant angles of rotation. Full article

Aramid fibre has become a critical material for individual soft body armour due to its lightweight nature and exceptional impact resistance. To investigate its energy absorption mechanism, quasi-static and dynamic tensile experiments were conducted on Kevlar^® 29 plain-woven fabric using a universal material testing machine and a Split Hopkinson Tensile Bar (SHTB) apparatus. Tensile mechanical responses were obtained under various strain rates. Fracture morphology was characterised using scanning electron microscopy (SEM) and ultra-depth three-dimensional microscopy, followed by an analysis of microstructural damage patterns. Considering the strain rate effect, a viscoelastic constitutive model was developed. The results indicate that the tensile mechanical properties of Kevlar^® 29 plain-woven fabric are strain-rate dependent. Tensile strength, elastic modulus, and toughness increase with strain rate, whereas fracture strain decreases. Under quasi-static loading, the fracture surface exhibits plastic flow, with slight axial splitting and tapered fibre ends, indicating ductile failure. In contrast, dynamic loading leads to pronounced axial splitting with reduced split depth, simultaneous rupture of fibre skin and core layers, and fibrillation phenomena, suggesting brittle fracture characteristics. The modified three-element viscoelastic constitutive model effectively captures the strain-rate effect and accurately describes the tensile behaviour of the plain-woven fabric across different strain rates. These findings provide valuable data support for research on ballistic mechanisms and the performance optimisation of protective materials. Full article

Sustainability and the circular economy are increasingly recognized as global priorities, particularly in industrial waste management. This study explores the development of a sustainable composite material using wood waste and natural fibers, contributing to circular economy practices. Sandwich panels were manufactured with a green epoxy resin matrix, incorporating wood waste in the core and flax fibers in the outer layers. Mechanical tests on the sandwich panel revealed a facing bending stress of 92.79 MPa and a core shear stress of 2.43 MPa. The panel demonstrated good compressive performance, with an edgewise compressive strength of 61.39 MPa and a flatwise compressive strength of 96.66 MPa. The material’s viscoelastic behavior was also characterized. In stress relaxation tests (from an initial 21 MPa), the panel’s stress decreased by 20.2% after three hours. The experimental relaxation data were successfully fitted by the Kohlrausch–Williams–Watts (KWW) model for both short- and long-term predictions. In creep tests, the panel showed a 21.30% increase in displacement after three hours under a 21 MPa load. For creep behavior, the KWW model was preferable for short-term predictions, while the Findley model provided a better fit for long-term predictions. Full article

Underground structures are subject to deterioration conditions in which water leakage occurs through cracks due to the long-term influence of soil and groundwater. Therefore, composite waterproofing sheets can play an important role in securing the leakage stability of structures by combining them with concrete structures. In this study, a total of eight composite waterproofing sheets were used according to the thickness of the compound and the properties of the material attached to the concrete, and the deformation characteristics at the bonding surface were identified through repeated tensile tests. Types A, B, and C, with a compound thickness of 1.35 to 1.85 mm and a single layer, had strong bonding performance, with a deformation rate of 0.5 to 2 × 10⁻⁴ and a DE/RE ratio of 0.3 to 1.3; tensile deformation progressed while maintaining integrity with the concrete at the bonding surface. Types D and E were viscoelastic and non-hardening compounds with a compound thickness of 1.35 to 3.5 mm, where the strain rate due to tensile deformation was the lowest, at 0.1 × 10⁻⁴ or less, and the DE/RE ratio was −5 to 3; therefore, when internal stress occurs, the high-viscosity compound absorbs it, and the material is judged to have low deformation characteristics. Types F, G, and H, which were 2 to 2.9 mm thick and had two layers using a core material, were found to have characteristics corresponding to tensile deformation, as the strain rate increased continuously from 0.2 to 0.5 × 10⁻⁴, and the DE/RE ratio increased up to 8 mm of tensile deformation. Full article

In this paper, four kinds of flooding systems, high-molecular-weight polymer (HMP), low-molecular-weight polymer (LMP), hydrophobic association polymer (HAP), and LMP/petroleum sulfonate (PS), are preferred. By comparing the static performance, their good basic characteristics as an oil displacement system are clarified. The application concentration range of the polymer solution is optimized and designed in combination with core injectivity experiments and mobility control theory. The oil displacement system and its injection volume have been optimized via three parallel core flooding experiments. The results show that the increase of the polymer molecular weight and the association will enhance the viscosity-increasing performance, viscosity stability, viscoelasticity, and hydrodynamic characteristic size of the solution. According to whether the injection pressure curve reaches equilibrium and the time required for equilibrium, the matching relationship between the polymer and the reservoir can be divided into plugging, flow difficulty and flow smoothly. Based on the mobility control theory, the minimum mobility of the target core occurs when the water saturation is 30–40%. Therefore, the polymer formulation for the application of combined cores with viscosities of 50 mD, 210 mD, and 350 mD is set at 1500 mg/L for LMP and 800 mg/L for MAP. HAP has the best profile improvement effect, but its lowest EOR is 9.68%, which mainly acts on high-permeability layers; LMP can produce more remaining oil in middle-permeability layers, and its EOR can reach 12.01%; LMP/PS can give full play to the oil displacement performance of the polymer and the oil washing ability of the surfactant, and its highest EOR is 21.32%. Meanwhile, the emulsification effect also makes the profile improvement last longer. According to the EOR efficiency and final oil recovery, the optimal injection volume of LMP/PS can be designed to be 0.6–0.7 PV. Full article

In modern engineering applications, the use of sustainable materials and eco-friendly methods has become increasingly important. Wood joints, especially those strengthened with bio-adhesive, have attracted considerable attention due to their inherent environmental benefits and desirable mechanical properties. Compared to traditional joining methods, adhesive joints offer unique advantages such as improved load distribution, reduced stress concentration, and enhanced aesthetic appeal. This study aims to enhance delamination resistance in wooden adhesive joints using a novel method involving reinforced high-toughness resin on surfaces. Additionally, a hybrid substrate approach applies a tough layer to outer plies and a densified wood core with greater fiber direction strength. Normal, toughened, and hybrid single-lap joint specimens were analyzed through both experimental and numerical methods under various loading conditions, including quasi-static and intermediate rates. The proposed method involved bio-adhesive penetration into the wood substrate, forming a reinforced surface zone. The experimentally validated results show a significant improvement in joint strength, exhibiting an approximate 2.8-fold increase for the toughened joints compared to the reference joints under intermediate-rate conditions. Furthermore, the absorbed energy of the toughened joints increased by a substantial factor of up to 4.5 times under the same conditions. The fracture surfaces analysis revealed that the toughening method changed the failure mechanism of the joints from delamination to fiber breakage, indicating that the strength of the substrate was lower than that of the joint under impact conditions. The viscoelastic behavior of the bio-adhesive also influenced the response of the joints to the changing displacement rate. The toughening method enhanced the resilience and load-bearing capacity of the wood joints, making them more suitable for dynamic applications. Full article

Tan Delta reflects the viscoelastic behavior of materials, particularly polymers. In most cases, a high Tan Delta value is associated with transitions (such as glass transition or melting), enabling effective damping properties near these temperature ranges. However, achieving a high Tan Delta over a broad temperature range is challenging, particularly for engineering applications that involve significant temperature fluctuations. This paper presents a straightforward method using layered composites, where a polymer layer is sandwiched between two highly stretchable elastic fabrics, to achieve a wide Tan Delta plateau (TDP) across a broad temperature range. The three-layer configuration consists of a polymer core embedded between two elastic layers. All samples prepared with this architecture consistently exhibit the TDP. Further investigations examine the influence of factors such as the number of layers and the stretchability of the elastic fabrics. The results demonstrate that the TDP can be effectively tailored for engineering applications using this layered design. Full article

The vibration characteristics of a composite bridge with constrained layer damping (CLD) were investigated using the wave and finite element method (WFEM), and the effects of the material and geometrical parameters of the CLD on the vibration reduction in the bridge were analyzed. Firstly, a numerical model for the dynamic response of a composite steel–concrete bridge using WFEM. The calculated acceleration of the bridge under the wheel–rail force obtained using this model was in good agreement with that obtained using the conventional finite element method and field measurements. Second, a segment model of the bridge with a CLD was established. The equation of motion based on the WFEM was solved to determine the dynamic response of the bridge induced by running trains. Finally, the effects of the covering area and CLD parameters on the vibration mitigation of steel–concrete bridges were analyzed. The results show that a reduction of 5–10 dB of the acceleration level of steel members in the full frequency range can be achieved by installing the CLD. A lower shear modulus of the viscoelastic core is beneficial for low-frequency vibration reduction in the bridge. However, a higher shear modulus of the damping layer is required for vibration mitigation in the high-frequency range. The vibration reduction in the composite bridge was more sensitive to the thickness of the constraining layer than to that of the damping layer. Full article

Understanding the long-term performance deterioration trends and mechanisms of asphalt pavement is crucial for effective maintenance strategies. This study characterizes and correlates the multi-scale performance deterioration of a 14-year asphalt pavement. Air void measurements, indirect tensile (IDT) fatigue testing, Fourier transform infrared spectroscopy (FTIR), and dynamic shear rheometer (DSR) testing were conducted on pavement cores and recovered binder. Multiple regression analysis was then performed on various performance indicators. Laboratory results indicate that the chemical composition and viscoelastic properties of SBS-modified binders evolve rapidly in the first few years, followed by a relatively stable aging rate. After 14 years, the mechanical and rheological properties of lower-layer mixtures deteriorate to a similar degree as the surface layer. Correlation analysis revealed that the residual strength of the mixture is more influenced by air voids, while reductions in fatigue life are primarily driven by binder aging. These findings highlight the necessity of applying preventive maintenance within the first 3–5 years to rejuvenate the surface asphalt and rehabilitate both the surface and underlying layers after long-term service. Full article

In engineering practice, the nonlinear vibration effect can easily lead to chaos in the system, which will not only reduce the performance of the system but also lead to premature fatigue of components, control failure, and increased safety risks. In view of the core position of the robotic arm in modern industry, this study relies on the robotic arm brake system to explore the theoretical basis of integrated viscoelastic materials as a vibration isolation layer. By analyzing the dynamic characteristics of the friction braking system with fractional differential terms, it aims to provide a new perspective for understanding and controlling the chaotic phenomena of a class of nonlinear friction systems. Firstly, we construct a model of a friction system and analyze its dynamic characteristics in detail. The self-excited vibration of the system under disturbance is studied. The relationship between amplitude and frequency is calculated by a nonlinear approximate analytical algorithm, and the accuracy of this relationship is verified by a numerical algorithm. Then, we compare the differences between non-fractional systems and fractional systems. It is found that with the increase in the fractional order term, the vibration amplitude of the system decreases significantly, which helps to reduce the nonlinear characteristics generated by the friction system and narrow the range of unstable solutions. Secondly, we also study the influence of parameter coefficients on the amplitude–frequency characteristics and analyze the local static bifurcation characteristics through singularity theory. Finally, we study the dynamic bifurcation behavior under different parameter perturbations and find that the change in system parameters will lead to the alternation of periodic motion and chaotic motion. Full article

The incorporation of viscoelastic layers in laminates can markedly enhance the damped dynamic characteristics. This study focuses on integrating viscoelastic layers into the composite facesheet of the bowtie-shaped honeycomb core composite sandwich panel (BHC-CSP). The homogenization of the damped BHC-CSP is performed by employing the variational asymptotic method. Based on the generalized total energy equation, the energy functional of the representative unit cell of the damped BHC-CSP is asymptotically analyzed. The warping function, derived following the principle of minimum potential energy, provides a basis for obtaining the corresponding Euler–Lagrange equation to ascertain the equivalent elastic properties of the damped BHC-CSP. Utilizing the developed two-dimensional equivalent model, the free-vibration characteristics of the damped BHC-CSP are examined across diverse boundary conditions while delving into the impact of an external viscous damping layer on the natural frequency of the damped BHC-CSP. The results reveal that intensified boundary constraints effectively diminish the effective vibration region of the damped BHC-CSP, thereby enhancing its overall stability. The introduction of a PMI foam layer proves effective in adjusting the stiffness and mass distribution of the damped BHC-CSP. Resonance characteristics are explored through frequency and time-domain analyses, highlighting the pivotal roles of the excitation position and receiver point in influencing the displacement and velocity responses. Although the stiffness is improved by incorporating a PMI foam layer, its effect on the damping performance of the damped BHC-CSP is minimal when compared to the T-SW308 foam layer. Full article

This paper presents the results of an experimental modal analysis of a beam covered by polymer materials used as a passive vibration isolation. The main aim of this study was to determine the damping properties of selected viscoelastic materials. In order to check the damping properties of tested materials, an experimental modal analysis, with the use of an electrodynamic vibration system, was performed. In this study, four kinds of specimens were considered. In the first step of the work, the beam made out of aluminum alloy was investigated. Afterwards, a cantilever beam was covered with a layer of bitumen-based material acting as a damper. This method is commonly known as a free layer damping treatment (FLD). In order to increase the damping capabilities, the previous configuration was improved by fixing a thin aluminum layer directly to the viscoelastic core. Such a treatment is called constrained layer damping (CLD). Subsequently, another polymer (butyl rubber) in the CLD configuration was tested for its damping properties. As a result of the performed experimental modal analysis, the frequencies of resonant vibrations and their corresponding amplitudes were obtained. The experimental results were used to quantitatively evaluate the damping properties of tested materials. Full article

This paper focuses on the geometrically nonlinear dynamic analyses of a three-layered curved sandwich beam with isotropic face layers and a time-dependent viscoelastic core. The boundary conditions and equations of motion governing the forced vibration are derived by using Hamilton’s principle. The first-order shear deformation theory is used to obtain kinematic relations. The spatial discretization of the equations is achieved using the generalized differential quadrature method (GDQM), and the Newmark-Beta algorithm is used to solve the time variation of the equations. The Newton–Raphson method is used to transform nonlinear equations into linear equations. The validation of the proposed model and the GDQM solution’s reliability are provided via comparison with the results that already exist in the literature and finite element method (FEM) analyses using ANSYS. Then, a series of parametric studies are carried out for a curved sandwich beam with aluminum face layers and a time-dependent viscoelastic core. The resonance and cancellation phenomena for the nonlinear moving-load problem of curved sandwich beams with a time-dependent viscoelastic core are performed using the GDQM for the first time, to the best of the authors’ knowledge. Full article

This analysis investigated the impact wave response and propagation on a composite sandwich shell when subjected to a low-velocity external shock, considering hygrothermal effects. The sandwich shell was crafted using face layers composed of functional gradient metal–ceramic matrix material and a core layer reinforced with negative Poisson’s honeycomb. The honeycomb layer consisted of a combination of viscoelastic polymer material and elastic material. The equivalent parameters for the functional gradient material in the face layers were determined using the Mori–Tanaka and Voigt models, and the parameters for the negative Poisson’s ratio honeycomb reinforcement core layer were obtained through Gibson’s unit cell model. Parameters relevant to a low-velocity impact were derived using a modified Hertz contact law. The internal deformations, strains, and stress of the composite sandwich shell were described based on the higher-order shear deformation theory. The dynamic equilibrium equations were established using Hamilton’s principle, and the Galerkin method along with the Newmark direct integration scheme was employed to calculate the shell’s response to impact. The validity of the analysis was confirmed through a comparison with published literature. This investigation showed that a multilayer negative Poisson’s ratio viscoelastic polymer material honeycomb-cored structure can dissipate impact wave energy swiftly and suppress shock effectively. Full article