Dynamic Mechanical Experiments Research Articles

Synergetic control of multi‐level interface structure of basalt fibers by plasma and chemical functionalization to enhance the mechanical, thermal and interfacial performances of PBZ composites

AbstractThe composites of polybenzoxazine (PBZ) containing functionalized plasma treatment basalt fibers (fP‐BFs) were fabricated through in‐situ polymerization‐mixing technique. fP‐BFs is an effective reinforcement material that can improve the mechanical, thermal, and interfacial properties of composites. Surface activation of fP‐BFs can be enhanced through plasma modification, which improves the interaction between fP‐BFs and 3‐aminopropyltriethoxysilane. A systematic study on fP‐BFs/PBZ composite showed that a processing power of 300 W, a processing time of 5 min, and a fiber content of 9% can achieve good comprehensive mechanical properties. Thermogravimetric analysis results showed that fP‐BFs‐7/PBZ has the highest thermal stability, and its carbon residue rate, decomposition temperature and thermal decomposition activation energy are 36.80%, 452.2 °C and 133.56 kJ/mol, respectively. The dynamic mechanical analysis experiment showed that the addition of fP‐BFs improved the Tg of the composites. Among them, fP‐BFs‐5/PBZ showed the highest Tg, reaching 233.2 °C.Highlights Plasma treatment produced multi‐level structure of basalt fibers (fP‐BFs). Polybenzoxazine (PBZ)/fP‐BFs composites showed excellent performance. Interfacial bonding mechanism between fP‐BFs and PBZ was elucidated. Interfacial interactions between BFs and PBZ contributed to property enhancement. This work provided a green fabrication strategy of PBZ composites.

Polysquaramides.

Thermoplastics, while advantageous for their processability and recyclability, often compromise thermochemical stability and mechanical strength compared to thermosets. Addressing this limitation, we introduce an innovative approach employing reversibly cross-linked polymers, utilizing squaramide moieties to reconcile recyclability and robustness. Herein, we detail the synthesis of supramolecularly cross-linked polysquaramides through the condensation polymerization of diethyl squarate with primary and secondary diamines. This methodology embeds hydrogen-bonding squaramide motifs into the polymer chains, yielding materials with significantly enhanced storage moduli, reaching up to 1.2 GPa. Material characterization via dynamic mechanical analysis, creep-recovery, and stress relaxation experiments delineate a distinctive rubbery plateau across a broad temperature range, excellent creep resistance, and multimodal viscoelastic flow, respectively, attributable to the dynamic nature of the supramolecular cross-links. Additionally, the study showcases the modulation of glass transition temperature (Tg) by altering the monomer composition and stoichiometry, demonstrating the tunability of polymer viscoelastic properties through precise control over hydrogen bonding interactions. Overall, the incorporation of squaramide motifs not only provides the structural integrity and mechanical performance of these thermoplastics but also leads to engineering materials with tailored viscoelastic characteristics.

Dynamic Behavior of Twisted UHMWPE Yarns

Twisting is an effective method to reduce defects during fabric weaving and improve the impact resistance of the armor material. This study examined the dynamic behavior of twisted ultra-high molecular weight polyethylene (UHMWPE) yarns. Material characterization was conducted using three-dimensional X-ray tomography and scanning electron microscopy (SEM). Dynamic mechanical experiments were carried out on the twisted yarns using a Kolsky bar, with the yarn's failure process captured in real time through high-speed imaging. Additionally, the digital imaging correlation (DIC) technique was used to calibrate the strain measured by the Kolsky bar. Post-fracture analysis was performed using SEM. The effects of twisting extent, strain rate, and gauge length on the dynamic behavior of twisted yarns were studied. It was observed that all twisted yarns underwent elongation, shrinkage, fiber breakage, untwisting, and yarn rupture. Furthermore, as the twisting degree and strain rate increased, and the gauge length decreased, the fracture area became more concentrated. The tensile strength peaked at a twisting degree of 250 t/m and decreased thereafter. Moreover, twisting was found to alter the sensitivity of the yarns' stress–strain curves and tensile properties to the strain rate and gauge length.

Investigating the Dynamic Mechanical Properties and Strengthening Mechanisms of Ti-6Al-4V Alloy by Using the Ultrasonic Surface Rolling Process.

The demand for titanium alloy has been increasing in various industries, including aerospace, marine, and biomedical fields, as they fulfilled the need for lightweight, high-strength, and corrosion-resistant material for modern manufacturing. However, titanium alloy has relatively low hardness, poor wear performance, and fatigue properties, which limits its popularization and application. These disadvantages could be efficiently overcome by surface strengthening technology, such as the ultrasonic surface rolling process (USRP). In this study, the true thermo-mechanical deformation behavior of Ti-6Al-4V was obtained by dynamic mechanical experiment using a Hopkinson pressure bar. Moreover, USRP was applied on the Ti-6Al-4V workpiece with different parameters of static forces to investigate the evolution in surface morphology, surface roughness, microstructure, hardness, residual stress, and fatigue performance. The strain rate and temperature during the USRP of Ti-6Al-4V under the corresponding conditions were about 3000 s-1 and 200 °C, respectively, which were derived from the numerical simulation. The correlation between the true thermo-mechanical behavior of Ti-6Al-4V alloy and the USRP parameters of the Ti-6Al-4V workpiece was established, which could provide a theoretical contribution to the optimization of the USRP parameters. After USRP, the cross-sectional hardness distribution of the workpiece was shown to initially rise, followed by a subsequent decrease, ultimately to matrix hardness. The cross-sectional residual compressive stress distribution of the workpiece showed a tendency to initially reduce, then increase, and finally decrease to zero. The fatigue performance of the workpiece was greatly enhanced after USRP due to the effect of grain refinement, work hardening, and beneficial residual compressive stress, thereby inhibiting the propagation of the fatigue crack. However, it could be noted that the excessive static force parameter of USRP could induce the decline in surface finish and compressive residual stress of the workpiece, which eliminated the beneficial effect of the USRP treatment. This indicated that the choice of the optimal USRP parameters was highly crucial. This work would be conducive to achieving high-efficiency and low-damage USRP machining, which could be used to effectively guide the development of high-end equipment manufacturing.

Dynamic Shear Mechanical Properties and Microscopic Deformation Characteristics of Laser Cladding IN625 Alloy

To reveal the dynamic shear mechanical properties of laser cladding Inconel 625 (IN625) alloy, dynamic shear mechanical properties experiments are conducted on forged specimens and laser cladding specimens by split Hopkinson press bar experimental device. Optical microscopy, scanning electron microscopy, and electron backscattered diffraction (EBSD) are used to characterize the microscopic morphology, crystal orientation, and grain size of laser cladding specimens before and after dynamic shear deformation. In the results, it is shown that the yield strength and shear strength of both forged and laser clad specimens increase with the increase of shear strain rate, reflecting a remarkable strain‐rate‐strengthening effect, and the shear strength of the laser cladding specimen is higher than that of the forged specimen. After dynamic shear loading, the grains in the shear region of the laser cladding specimen are severely deformed, deformation bands appear, and some dendrites are transformed into equiaxed crystal. After shear deformation, the preferred orientation strength of the crystal increases, the small‐size grain and low‐angle grain boundary increase, and a large number of dislocations are formed in the shear region, which dominates the dynamic shear deformation behavior of the material. Dislocation is an important dominant mechanism of dynamic shear deformation.

Effect of explosive shock on the mechanical property and energy release characteristics of an Al/Ni reactive material

Reactive materials applied to warhead fragments or charge liner will be driven by strong detonation, so their mechanical behavior and energy release characteristics will be affected to a certain extent. In this paper, dynamic and static mechanical tests and impact initiation experiment were carried out on the detonation-loaded Al/Ni reactive material. Compared with materials that have not subjected to explosive shock, it is found that Al/Ni materials have better mechanical strength after explosive shock. Meanwhile, the impact-initiated energy release efficiency of the material is lower, when loaded with 14.76GPa, 21.79GPa and 28.84GPa, the reaction degree decreased by 26.6%, 78.8% and 80.5% respectively. Due to the incompatibility of elastic modulus and melting point between aluminum and nickel particles, the nickel particles move and aggregate in the aluminum matrix during shock loading. The pores appear at the particle boundaries, and gradually expand into cracks. The research results show that the original material parameters cannot be used to judge the working conditions of the reactive materials, and the explosive conditions of the loading are external factors that requires additional consideration.

Experimental Study on the Effect of Limestone Powder Content on the Dynamic and Static Mechanical Properties of Seawater Coral Aggregate Concrete (SCAC).

The development of island construction concrete can serve as a basis for the development and utilization of island resources. Complying with the principle of using local materials to configure seawater coral aggregate concrete (SCAC) that is able to meet the requirements of island and reef engineering construction could effectively shorten the construction period and cost of island and reef engineering construction. In this paper, quasi-static mechanical experiments and dynamic mechanical experiments were carried out on SCAC with different limestone powder contents. High-speed photography technology and Digital Image Correlation (DIC) were used to monitor the dynamic failure process and strain field of SCAC, and the influence of limestone powder content on the dynamic and static mechanical properties of SCAC was investigated. The results showed that, when the limestone powder content was 20% and 16%, the quasi-static compressive strength and quasi-static tensile strength exhibited the best improvement. Additionally, with increasing limestone powder content, the dynamic tensile strength of SCAC first showed and increasing trend and then a decreasing trend, reaching its maximum value when the limestone powder content was 16%. Moreover, the maximum strain value of SCAC with the same limestone powder content increased with increasing strain rate grade, showing an obvious effect on strain rate.

Dynamic Mechanical Analysis on Jute Fiber Reinforced Polymer Composites for Patella Implant

Natural fibres possess convincing properties when reinforced in polymers. In this study, JFRPs viscoelastic behaviour at low and elevated temperatures were explored. The present work focuses on the fabrication of jute reinforced polyester based polymer composites with different fiber compositions. Untreated long Jute fibres and mat structured Jute fibres were used for preparing the specimens. The Dynamic Mechanical Analysis (DMA) test was carried out on selected developed Polymer Matrix Composites (PMC). Density of selected PMCs are nearly equal to the bone density. So, PMC specimens were considered to carry out thermal analysis using DMA. In particular, by dynamic mechanical analysis experiments, properties such as storage modulus, loss modulus, tanδ and glass transition temperature were determined. It was found that the storage modulus (E’) recorded above the glass transition temperature (Tg) varies with increase in temperature. Along with the previous research of material properties for possible bioimplantation, this Tg value is identified for possible implementation as patella bone implant. The loss modulus (E”) and damping peaks (Tan δ) values were found to be reduced with increasing matrix loading and temperature.

Comprehensive modification of emulsified asphalt on improving mechanical properties of crumb rubber concrete

The surface modification of crumb rubber concrete (CRC) by the emulsified asphalt (EA) is presented in this paper. The effect of different EA contents on the mechanical properties of CRC (the fine aggregate was replaced with 5%, 10% and 15% rubber by volume) was studied. Several tests, including the static mechanical experiments of compression, bending, splitting tensile and three-point bending, the dynamic mechanical experiments of the split Hopkinson pressure bar (SHPB) and the micro-analysis of the digital image correlation (DIC) test and SEM image, were carried out to compare with CRC modified by NaOH. The tests depict that CRC modified by EA demonstrates better mechanical properties, such as the higher compressive strength, the higher splitting tensile strength, the more significant strain rate sensitivity at high strain rates, the lower the elastic modulus (Ec) and the bending modulus (Eb). The better modified effects can be attributed to the better interfacial bonding surface between the cement matrix and the rubber particles and the fewer stress concentrations than that of NaOH modification. The modification of CRC by EA can be regarded as a better synergistic method to bring advantages of CRC into full play.

Mechanical property of cylindrical sandwich shell with gradient core of entangled wire mesh

To explore the wide-frequency damping and vibration-attenuation performances in the application of aerospace components, the cylindrical sandwich shell structure with a gradient core of entangled wire mesh was proposed in this paper. Firstly, the gradient cores of entangled wire mesh in the axial and radial directions were prepared by using an in-house Numerical Control weaving machine, and the metallurgical connection between skin sheets and the gradient core was performed using vacuum brazing. Secondly, to investigate the mechanical properties of cylindrical sandwich shells with axial or radial gradient cores, quasi-static and dynamic mechanical experiments were carried out. The primary evaluations of mechanical properties include secant stiffness, natural frequency, Specific Energy Absorption (SEA), vibration acceleration level, and so on. The results suggest that the vibration-attenuation performance of the sandwich shell is remarkable when the high-density core layer is at the end of the shell or abuts the inner skin. The axial gradient material has almost no influence on the vibration frequencies of the shell, whereas the vibration frequencies increase dramatically when the high-density core layer approaches the skin. Moreover, compared to the conventional sandwich shells, the proposed functional grading cylindrical sandwich shell exhibits more potential in mass reduction, stiffness designing, and energy dissipation.

Dynamical relaxation and stress relaxation of Zr-based metallic glass

The relationship among dynamic relaxation, deformation and microstructural heterogeneity of amorphous alloy is one of the important research contents in the field of amorphous physics. In this paper, we utilize Zr<sub>48</sub>(Cu<sub>5/6</sub>Ag<sub>1/6</sub>)<sub>44</sub>Al<sub>8</sub> bulk amorphous alloy with excellent glass forming capability and good thermal stability as a research carrier, and investigate the effects of temperature and structural relaxation on dynamic relaxation and deformation behavior through dynamic mechanical analysis and stress relaxation experiments. The results show that the dynamic relaxation spectrum of the model alloy is sensitive to temperature, showing four stages as the temperature increases, namely, iso configuration, aging, glass transition and crystallization. Based on the isothermal measurement of dynamic mechanical parameters under the glass transition temperature, the structural relaxation causes the amorphous alloy to migrate from the non-equilibrium high energy state to the low energy state, and the evolution of internal friction with aging time can be described by Kohlrausch-Williams-Watts (KWW) stretched exponential function. In addition, based on the KWW equation and activation energy spectrum, the activation of heterogeneous structure in the stress relaxation process of model alloy is analyzed, which involves the transformation from elastic deformation to nonelastic deformation. Owing to the microstructural heterogeneity and energy fluctuations in amorphous alloys, the activation of deformation units is not a single characteristic time, but follows a certain distribution. By considering that the characteristic time distribution of activation of deformation units is symmetric Gauss distribution or asymmetric Gumbel distribution on a logarithmic time scale, the heterogeneous activation process in stress relaxation response can be reconstructed.

Simple and convenient mapping of molecular dynamics mechanical property predictions of bisphenol-F epoxy for strain rate, temperature, and degree of cure.

It is well-known that all-atom molecular dynamics (MD) predictions of mechanical properties of thermoset resins suffer from multiple accuracy issues associated with their viscoelastic nature. The nanosecond simulation times of MD simulations do not allow for the direct simulation of the molecular conformational relaxations that occur under laboratory time scales. This adversely affects the prediction of mechanical properties at realistic strain rates, intermediate degrees of cure, and elevated temperatures. While some recent studies have utilized a time-temperature superposition approach to relate MD predictions to expected laboratory observations, such an approach becomes prohibitively difficult when simulating thermosets with a combination of strain rates, intermediate degrees of cure, and temperatures. In this study, a phenomenological approach is developed to map the predictions of Young's modulus and Poisson's ratio for a DGEBF/DETDA epoxy system to the corresponding laboratory-based properties for intermediate degrees of cure and temperatures above and below the glass transition temperature. The approach uses characterization data from dynamical mechanical analysis temperature sweep experiments. The mathematical formulation and experimental characterization of the mapping is described, and the resulting mapping of computationally-predicted to experimentally-observed elastic properties for various degrees of cure and temperatures are demonstrated and validated. This mapping is particularly important to mitigate the strain-rate effect associated with MD predictions, as well as to accurately predict mechanical properties at elevated temperatures and intermediate degrees of cure to facilitate accurate and efficient composite material process modeling.

Dynamic magnetomechanical behavior of sintered Nd2Fe14B under impact

As an important magnetic functional material, sintered NdFeB has gradually applied from mild places to environments that need to withstand impact. The reliability of materials to work in this environment has received extensive attention, but current research cannot provide corresponding support of experimental data and theoretical model for this problem yet. To tackle this, we carried out research on the magnetomechanical behavior of sintered NdFeB under dynamic impact environment. Specifically, dynamic mechanics and impact demagnetization experiments were conducted separately. Then, according to the characteristics of brittleness and strain rate dependence shown in dynamic mechanical experiments, a dynamic damage constitutive model was established. Additionally, a new magnetic degradation model was proposed in which the stress knee position existed and the relationship between impact load and irreversibility was established. The co-simulation model of impact demagnetization based on dynamic mechanical constitutive model and magnetic degradation model was designed to better display the demagnetization process of materials. Meanwhile, the parameter identification process was carried out to determine the unknown parameters in the model. Finally, the effectiveness of identified parameters were verified by comparing the simulation values with the experimental values.

Study on the Properties of Waste Oil-Activated Crumb Rubber-Modified Asphalt Based on Molecular Dynamics Simulation and Rheology

To investigate the effect of activated crumb rubber content on the molecular interactions and the properties of crumb rubber-modified asphalt (CRMA) with waste oil, six models of asphalt with various rubber dosages were developed using Materials Studio software, and the molecular dynamics performance of the system was further examined. Then, the fatigue and high- and low-temperature performances of the CRMA binders were characterized by dynamic mechanical experiments in the laboratory. The mean square displacement and diffusion coefficient were used to quantify the migration of molecules. The aggregation state of the components was evaluated using a radial distribution function. The bulk modulus of the CRMA models was calculated to study the mechanical properties. Dynamic shear and bending beam rheometer tests were implemented to evaluate the road performances of the CRMA binders. The results show that increasing the amount of powder could improve the mechanical properties of the asphalt, that is, the modulus of 70% of the asphalt was improved by 57.5%. The rubber and waste oil were evenly dispersed in the system, and the distribution of asphalt components was in accordance with the colloid theory. The temperature-sensitive properties of the rubber led to the improvement of road properties of the CRMA binders with the increase of the admixture. Combined with the distribution of molecules in the asphalt model, the results of rheological indexes show that the waste oil could improve the rheology and stability of binders. This will provide theoretical support for upgrading the content of crumb rubber in CRMA binders.

Development of a High-Fidelity Framework to Describe the Process-Dependent Viscoelasticity of a Fast-Curing Epoxy Matrix Resin including Testing, Modelling, Calibration and Validation.

Fast-curing epoxy resins enable substantial reduction of cycle times during production of thermoset polymer matrix composites. Due to the snap-cure behaviour, both characterisation and processing of these resins are associated with high complexity which motivates the development of a high-fidelity framework for the prediction of the process-dependent behaviour ranging from experiment to model validation. In order to determine influence of time, temperature, and degree of cure, a multitude of rheometer and dynamic mechanical analysis experiments are conducted and evaluated. Building on the experimental results, a material model based on a generalised Maxwell model is developed. It is calibrated on the results obtained in the tests and shown to describe the material’s behaviour with high accuracy under all investigated conditions. The model’s predictive capabilities are further tested by applying it to a dynamic mechanical analysis, exposing the model to previously unknown loading and temperature conditions. It is demonstrated that the model is capable of predicting such changing boundary conditions with high accuracy.

Development of Damage Type Viscoelastic Ontological Model for Soft and Hard Materials under High-Strain-Rate Conditions

By improving the ZWT model, a principal structure model applicable to both soft and hard materials under dynamic loading conditions was obtained. Dynamic mechanical experiments were conducted using SHPB to obtain stress–strain curves for coal rock and foam concrete. The ZWT intrinsic model was simplified according to the dynamic impact characteristics of concrete, and the intrinsic model was established by introducing macroscopic damage quantity D and correction factor δ. The stress–strain curves of coal rock, foamed concrete, steel fiber concrete, granite, lightweight foamed concrete, and EPS concrete at different strain rates were used to validate the present constitutive model and prove the correctness of the model.

Isomorph invariant dynamic mechanical analysis: A molecular dynamics study

We simulate dynamic mechanical analysis experiments for the Kob-Andersen binary Lennard-Jones system. For this, the SLLOD algorithm with time-dependent strain rates is applied to give a sinusoidally varying strain at different densities and temperatures. The starting point is a temperature scan at a fixed reference density. Isomorph theory predicts that for other densities, corresponding temperatures can be identified at which the mechanical properties are unchanged when scaled appropriately. We determine the isomorphically equivalent temperatures by analyzing how particle forces change upon scaling configurations to the new density. Loss moduli expressed in suitable reduced units are compared for isomorphic state points. When plotted against the unscaled temperatures, these reduced loss curves are observed to collapse indicating the validity of isomorph theory for dynamic mechanical analysis experiments. Two different methods to determine isomorphic temperatures are considered. While one of them breaks down for the largest density rescalings considered in this paper, the other one is still applicable in this region. The decorrelation of force vectors upon rescaling is investigated as a possible origin of this effect. Our results demonstrate that the simplification of the phase diagram entailed by isomorph theory for a wide class of systems is relevant also for the mechanical properties of glasses.

Experimental Study on Damage Characteristics of Copper-Reinforced Polytetrafluoroethylene Shaped-Charge Warhead Liner.

Polymer materials have important applications in the4 terminal effect and damage by shaped-charge warheads. However, the low strength of pure PTFE materials reduces the penetrability of the expansive jet from these warheads, hindering its application. This study improves the strength of pure PTFE material by adding Cu powder to the shaped-charge liner. Three types of PTFE/Cu composites with different densities are prepared. The effect of increasing the density on the performance of an expansive jet is studied by a dynamic mechanical property experiment, microscopic analysis, numerical simulation, and a penetration experiment. The results show that the toughness and impact strength of the PTFE/Cu composites improve when 18–50.5% Cu is added. The strength of the composite increases linearly with the increase in Cu content. Numerical simulations and X-ray pulse experiments reveal that the addition of Cu powder enhances the cohesiveness of the head of the expansive jet. The jet head becomes more cohesive as the Cu content is increased. However, the length and diameter of the jet become smaller. The jet can create a deeper hole in the steel target and increase damage as more Cu is added to the liner.

DYNAMIC AND BALLISTIC PERFORMANCE OF GLASS/CARBON FIBER/ALUMINUM 1100 WIRE MESH REINFORCED COMPOSITE

Increase in the demand for high-performance and lightweight structural materials in the automobile and aircraft industries may inspire a strong tendency to develop fiber metal laminates (FMLs). In this work, the FML composites are fabricated using different stacking sequences of glass/carbon fibers, aluminum wire mesh, BaSO4 filler and epoxy resin. Six different combinations of composites with different stacking sequences and wire mesh angles are fabricated using the hand-lay technique. Dynamic mechanical analysis (DMA), ballistic and wear experiments were used to investigate the fabricated composites’ performance. The FML6 Al wire mesh with BaSO4 filler increases the storage modulus by 16.12% and enhances the energy absorption capacity by 3.19%. From the ballistic, the carbon fiber composite (FML3) shows 4.47% improvement compared to the glass fiber composite (FML1) for the same 90∘ wire mesh orientation.

Explosion Test and Numerical Simulation of Coated Reinforced Concrete Slab Based on BLAST Mitigation Polyurea Coating Performance

The mechanical strength, thermal stability, thermal performance, and microstructure of Qtech T26 blast mitigation polyurea (T26 polyurea) were studied using quasi-static and dynamic mechanical experiments, thermogravimetric experiments, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) experiments, and contact explosion and non-contact explosion experiments with polyurea-coated reinforced concrete slabs. Additionally, the energy dissipation mechanism of the coating was analyzed. The blast mitigation ability and blast mitigation mechanism of T26 polyurea-coated reinforced concrete slabs were investigated by analyzing the macroscopic morphology of reinforced concrete slabs with or without coatings and the contact explosion simulation of polyurea-coated reinforced concrete slabs. The results showed that T26 polyurea exhibited a certain strain rate effect. Its initial thermal decomposition temperature reached 286 °C, and its thermal stability was good. After carbonization, carbon slag can form and adhere to the structural surface. The glass transition temperature Tgs of the soft segment was −44.9 °C, and the glass transition temperature Tgh of the hard segment was 36.5 °C, showing a certain amount of microphase separation morphology. After the explosion test, there was a small pit on the front surface of the coated reinforced concrete plate, and there was no damage on the back surface. The integrity of the plate was good. The uncoated reinforced concrete slab had a large crater on the front of the explosion surface, and the back of the explosion surface experienced explosion collapse, concrete crushing, and an overall loss of stability. The numerical simulation results showed that the failure mode of the coated plate was consistent with the test. The kinetic energy conversion rate of the uncoated reinforced concrete plate was 87.27%, and the kinetic energy conversion rate of the coated reinforced concrete plate was 95.36%. The T26 coating improved the kinetic energy conversion rate of the structure and improved the blast mitigation ability of the reinforced concrete plate structure.