Dynamic Mechanical Studies Research Articles

Rice husk/glass fiber-reinforced poly(lactic acid) hybrid composites: rheological and dynamic mechanical study

Rice husk/glass fiber-reinforced poly(lactic acid) hybrid composites: rheological and dynamic mechanical study

The influence of the molecular structure of binary block‐type styrene‐butadiene rubber on dynamic mechanical properties under normal and high‐pressure conditions

AbstractThrough anionic two‐stage polymerization, block‐type styrene‐butadiene rubber (SSBR) with systematically regulable low‐temperature loss peaks is successfully prepared. The influence of 1,2‐Bd unit in the soft segment of block‐type SSBR on mechanical properties, dynamic mechanical properties, and microscopic morphology is studied, while pressure factors are introduced into dynamic mechanical studies. The block‐type SSBR with a soft segment containing 21.9 wt% of 1,2‐Bd exhibits the highest tensile strength, elongation at break, and tear strength. Under atmospheric pressure, the soft segment 1,2‐Bd unit influences the dynamic mechanical properties by altering the chain segment's motion loss capability. As the mass fraction of 1,2‐Bd increases from 21.9 to 58.6 wt%, tanδmax increases, the glass transition temperature of the soft segment increases from −59.0 to −18.9°C. Additionally, influenced by thermodynamic compatibility, the microscopic morphology transitions from strong separation to weak separation. Pressure affects dynamic mechanical properties by altering the free volume of the chain segments. Pressure reduces tanδmax, increases Tg, and raises the average Tg of the soft segment by 11°C. The K value of the linear equation representing the relationship between the soft segment Tg and the mass fraction of 1,2‐Bd is unaffected by pressure.

Influence of fissure distribution characteristics on the dynamic response of fissured Rock: Quantity and spacing

The impact test of red sandstone with different fissure distribution was carried out by Split Hopkinson Pressure Bar (SHPB). The failure process of the specimen in the time dimension was captured by high-speed camera and digital image correlation (DIC). The crushing characteristics of the specimen were discussed from the fractal dimension. Furthermore, the influence of fissure distribution characteristics (quantity and spacing of fissures) on the mechanical properties and fracture behavior of fissured red sandstone was analyzed. The experimental results show that the fissure spacing is negatively correlated with the dynamic compressive strength and peak strain of specimen, while the fissure quantity is negatively correlated with the dynamic compressive strength and positively correlated with the peak strain. Cracks are categorized into five types based on the manner of their initiation and expansion. The crack initiation and propagation are jointly affected by tensile stress and shear stress, but the tensile stress is dominant. With the increase of the fissure quantity, the failure mode changes from tensile failure to tensile-shear mixed failure. The increase of fissure spacing does not change its failure mode, but the formation mode of the main crack changes. The fractal dimension increases with the increase of the fissure quantity, and decreases with the increase of the fissure spacing, i.e., the larger the fissure quantity is, the higher the degree of fragmentation is, and the larger the fissure spacing is, the lower the degree of fragmentation is. The research results can provide a theoretical reference for the study of dynamic failure mechanism of rock mass with non-persistent discontinuities.

Basalt fabric/(3-aminopropyl) triethoxysilane modified epoxy laminates reinforced with nano-silica, OMMT and GNP: mechanical and dynamic mechanical studies

Basalt fabric/(3-aminopropyl) triethoxysilane modified epoxy laminates reinforced with nano-silica, OMMT and GNP: mechanical and dynamic mechanical studies

Comparative study on dynamic mechanical properties of additive manufacturing high strength steel and wrought high strength steel under high strain rate

Additive manufacturing high-strength steel has a unique manufacturing process and has broad application prospects in military equipment, aerospace, and other fields, but it is often threatened by dynamic loads such as explosion and high-speed impact during use, which has attracted wide attention. In this paper, the dynamic impact of additive manufacturing high-strength steel LMD-BK and wrought high-strength steel BK was carried out at strain rates of 1000 s−1–5000 s−1 by the Split-Hopkinson pressure bar (SHPB) test, respectively, and the differences in the dynamic mechanical properties of the two were investigated under the impact of different strain rates. Using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) micro-observation techniques, the microstructure morphologies of LMD-BK and BK before and after dynamic impact were characterized, and the microstructure evolution mechanism of the two was investigated. The results show that both LMD-BK and BK are strain rate sensitive, and the dynamic compressive strength increases and then decreases with the increase of strain rate, with a maximum at 2000 s−1 and a minimum at 1000 s−1. The maximum and minimum values of dynamic compressive strength for LMD-BK are 1978 MPa and 1757 MPa, respectively; for BK, the maximum and minimum values of dynamic compressive strength are 1389 MPa and 1329 MPa, respectively. The final strain of the material increases as the strain rate increases. At the same strain rate, the final strain of BK is always larger than that of LMD-BK. With the increase in strain rate, the impact work absorbed by the material increases, and at the same strain rate, LMD-BK can absorb more impact work than BK. Microscopic observations show that after dynamic impact, LMD-BK undergoes fragmentation of the columnar structure and compression of the cellular structure to form a deformation localization zone. These results are of great significance for the study of dynamic mechanical properties and microstructure evolution mechanism of high-strength steel made by additive manufacturing under extreme environments such as explosion and high-speed impact.

Molecular mechanism for the interaction of natural products with ionic liquids: Insights from MD and DFT study

Ionic liquids (ILs) as a class of green sustainable solvents, have been widely studied and used for the extraction, separation, recovery, and catalytic conversion of natural products (NPs). It is well known that elucidating the dynamic interaction behavior and mechanism of NPs in ILs can help rationally design efficient IL solvent systems at the molecular level. However, the interaction mechanism of rutin molecules and ILs is still unclear. In this contribution, an exhaustive theoretical study of dynamic interaction behavior and mechanism of rutin in six imidazolium-based IL systems is presented for the first time by combining molecular dynamics (MD) simulations with density functional theory (DFT) calculations. Meanwhile, the synergistic effect of cation and anion on rutin-IL complexes stability is deeply investigated by the frontier molecular orbital (FMO), electrostatic potential (ESP), radial distribution functions (RDF), averaged non-covalent interaction (aNCI) and non-covalent interaction (NCI). The final result provides a comprehensive molecular mechanism of interaction between rutin and ILs. The combination of various nonbonded forces (such as H-bond, van der Waals, repulsion and cation-π stacking) between molecules determines the stability of rutin-IL complexes. In addition, the structure, size and functional groups of ILs play a decisive role in promoting the formation of nonbonded forces. Our work shows that avoiding substituents with steric hindrance and electron-withdrawing effect in anions, considering the symmetry of the alkyl chain of imidazolium cations, and enhancing the cooperation between anions and cations is a promising pathway to develop a new and efficient ILs solvent systems for the NPs extraction, recovery, separation, detection, and catalytic conversion.

Experimental study of dynamic mechanical properties and damage mechanism of textile reinforced concrete

The flexural characteristics of alkali-resistant (AR) glass textile reinforced concrete slabs (GTRC) at static-to-dynamic loading rates are investigated in the present study. The fabricated GTRC slabs were manufactured with four and six textile layers as reinforcement. Static flexural testing is conducted at 0.5 mm/min, while dynamic flexural tests are conducted at five loading velocities of 1, 2, 3, 4, and 4.5 m/s. The corresponding strain rates at selected impact velocities are 4, 8, 12, 16, and 18 s-1. Two separate mechanical setups, including (i) the MTS load frame and (ii) Instron drop-weight impact system, are used for distinct experimental testing. Furthermore, the mechanical properties of flexural strength, maximum strain, ultimate strain, flexural modulus, and toughness are calculated by using mathematical relations. In addition, failure patterns and the load-bearing intrinsic mechanisms of GTRC samples are analyzed in detail. Flexural experiments at various loading rates revealed that the loading rate and the number of reinforcing layers significantly influence the bending characteristics and mechanical properties of GTRC samples. In addition, the mechanical response is comparatively reduced at six layers of reinforcement than GTRC with four layers, proving better mechanical properties in flexural load at static and dynamic loading conditions.

Effect of electron beam radiation on the mechanical, electrical, heat shrinkable and morphological properties of linear low-density polyethylene/polyolefin elastomer blends

The blending of polymers is an efficient means for developing new materials in a less hazardous and more economical way compared to the synthetic route. Polymers with different properties are blended to obtain a new material with combined properties. In this study, a thermoplastic elastomer blend is prepared by melt mixing a metallocene-based polyolefin elastomer (Engage 8003, abbreviated as EN) with linear low-density polyethylene (LLDPE, abbreviated as LL) using a twin-screw extruder in various compositions. To investigate the effect of the electron beam on the properties, LL, EN and their blends are irradiated in the 50–250 kGy dose range. The samples are subjected to gel fraction, mechanical, dynamic mechanical, hardness, heat shrinkability, volume resistivity and morphological studies. The % gel fraction, hardness and heat shrinkability of a sample increase with an increase in the irradiation dose. With increasing LL content, Young’s modulus and ultimate tensile strength of the blends are increased, maintaining the % elongation at break in an attractive region. LE64 (60 wt% LL and 40 wt% EN) and LE46 (40 wt% LL and 60 wt% EN) blends show optimized mechanical and dynamic mechanical properties. Irradiation further increases the tensile strength and Young’s modulus of LE64 up to 150 kGy and LE46 up to 200 kGy. The volume resistivity of the LE64 blend increases tenfold and quadruples for LE46 compared to non-irradiated blends when irradiated at 200 kGy. The morphological structures of the non-irradiated and crosslinked blends support the outcome of the obtained properties nicely.

Irradiation effects and photostability of aerosil-filled polyurethane as a matrix for laser solid-state elements

Photooxidation processes during irradiation of the aerosil-filled polyurethane films, based on oligooxypropylene glycol, toluene diisocyanate and trimethylolpropane, for a use as the active media of solid-state lasers were investigated by means of the IR-spectroscopy and dynamic mechanical analysis (DMA) methods, depending on the inorganic dopant concentration (5 and 7 wt%). The IR-spectroscopic experiments showed that the introduction of aerosil slowed down these processes. Data from dynamic mechanical studies indicated that irradiation of aerosil-filled polyurethane matrices caused an increase in its structural heterogeneity and a drop of the elastic modulus. During irradiation of the polyurethane material with 7 wt% of aerosil, a partial destruction of the nanofiller spatial network was possible due to dispersion of the irradiation energy by the nanoparticles. The obtained results demonstrated a positive effect of the aerosil nanofiller on the polyurethane material stability under irradiation with an ultra-high pressure mercury lamp.

Biobased, Reprocessable Non-isocyanate Polythiourethane Networks with Thionourethane and Disulfide Cross-Links: Comparison with Polyhydroxyurethane Network Analogues

Here, we report the first study of the reprocessability and properties of non-isocyanate polythiourethane (NIPTU) networks in which the cross-links are of two types, thionourethane and disulfide, the latter obtained by auto-oxidation of pendant thiol groups. Our two NIPTU networks are biowaste based because starting materials can be derived from cashew nutshells or rice husks. We use dynamic mechanical analysis, tensile testing, and water sorption studies to compare our NIPTU networks with structurally analogous polyhydroxyurethane (PHU) networks, which are non-isocyanate polyurethanes (PUs). With significant advantages in reactivity, mechanical properties, and cross-link density, NIPTU networks can be favorable alternatives to PHU networks. Our biobased NIPTU networks also exhibit better water resistance, with a factor of ∼3 reductions in water sorption relative to their PHU analogues. Due to their dynamic covalent cross-links, our NIPTUs show excellent reprocessability with complete recovery of cross-link density after multiple reprocessing steps as well as potential as self-healing polymers. Although their creep viscosity activation energies differ by a factor of 2, both NIPTU networks exhibit excellent creep resistance up to 80–100 °C. Thus, with elevated-temperature creep resistance and significant advantages in reactivity, mechanical properties, and water resistance, in many applications, e.g., water-resistant coatings, biobased NIPTU networks are favored as non-isocyanate substitutes for PU networks.

Cenosphere filled epoxy composites: structural, mechanical, and dynamic mechanical studies

Cenosphere filled epoxy composites: structural, mechanical, and dynamic mechanical studies

Thermal and mechanical characterization of polypropylene/basalt fiber/ethylene propylene diene monomer rubber hybrid composite

The current study aims in enhancing the impact properties of polypropylene/basalt fiber composite reinforced with different wt% of ethylene propylene diene monomer (EPDM) elastomer to identify the optimum wt% of EPDM at which a balance in strength and toughness can be obtained. According to a dynamic mechanical study, the composite’s viscoelastic behaviour and damping properties improved as the EPDM weight percentage increased in comparison to virgin polypropylene. Scanning and transmission electron microscopy were utilized to see the composite’s fragmented surface. Finally, it was concluded that the presence of a renewable basalt fiber helped in obtaining stability between the strength and toughness of polypropylene-toughened composites. Finally for up to 20 wt% EPDM there was a balance in the composite stiffness and strength.

Dynamic mechanical properties and ageing studies of coir-sisal yarn reinforced polypropylene commingled composites

This work investigates the dynamic mechanical properties (DMA) and ageing behavior of coir-sisal yarn reinforced polypropylene commingled composites. Moreover, the fibres were subjected to various chemical treatments and their effects on DMA and ageing studies were investigated. DMA reveals that the chemical treatment, especially MAPP treatment, enhances the storage and loss modulus values on the other hand it diminishes the mechanical damping coefficient (tan δ) of the composite. Diffusion studies indicates that treated composites shows a much lower apparent percentage weight gain compared to other treated ones. Solar ageing studies shows that accelerated solar ageing deteriorated tensile strength and modulus of PP/coir-sisal yarn composite.

Impact of Fiber Buildup Stacking Sequence on Thermo-Mechanical Behaviour of Natural Fiber–Reinforced Anamide Composites

This article focuses on the viscoelastic behaviour of the anamide composites using a dynamic mechanical study developed by hot compression moulding technology at higher temperatures. The frequency range for this analysis is 1 Hz. In the nitrogen atmosphere, thermogravimetry analysis differential scanning calorimetry was used to investigate the thermal stability of composite laminates with various fiber orientations. The findings showed that a glass transition temperature close to 100°C can be achieved at 1 Hz to increase the fiber orientation of the basalt fiber-enhanced anamide compounds. Through the thermo-gravimetric analysis experiments, the excellent thermal stability of composite laminates at temperatures above 600°C was conspicuous. Analysis using the Fourier transform infrared (FTIR) spectroscopy envisioned the surface chemical properties of anamide films at various fiber orientations, and the interaction properties between fiber and matrix were determined. Scanning electron microscopy on composite laminate surfaces proclaimed that the interface relationship between the basalt fiber and the anamide material is superior with FTIR findings being assisted. The findings demonstrate that composite laminates may be a good replacement for high-performance and high-temperature applications since they are thermally extremely robust with great rigidity.

Synthesis and Characterization of Polymeric Blends Containing Polysulfone Based on Cyclic Bisphenol.

The elaboration of the composition and methods of preparation of new types of materials is an important issue from the plastics industry’s point of view. The paper presents the polysulfone synthesis based on 4,4′-cyclohexylidenebisphenol (bisphenol Z). This compound was used (in an amount of 5 or 10 wt.% sample) for the synthesis and characterization of new polymeric blends based on the two different acrylic resins (EB-150 and EB-600) and the active solvent N-vinyl-2-pyrrolidone (NVP). The weight ratio of the used resin to solvent was 1:2; 1:1 or 2:1. These new materials were obtained applying the photoinitiated free radical polymerization with 2,2-dimethoxy-2-phenyloacetophenone as a photoinitiator used in an amount of 1 wt.%. Six polymeric blends and six copolymers without polysulfone were cured by this method. By means of ATR/FT-IR (Attenuated Total Reflection–Fourier Transform Infrared) spectroscopy the chemical structure of the synthesized polysulfone was proved. The effect of the presence of the polysulfone presence on the thermal properties of the obtained blends was analyzed by means of thermogravimetry and differential thermogravimetry (TG/DTG), as well as differential scanning calorimetry (DSC). Moreover, the dynamic mechanical studies (DMA) of these materials were also carried out, demonstrating which of the materials showed the influence of the percentage of polysulfone on the selected properties in the blended- and parent-copolymers samples.

Fracture Behavior of Polyrotaxane-Toughened Poly(Methyl Methacrylate).

The fracture behavior of polyrotaxane (PR)-modified poly(methyl methacrylate) (PMMA) was investigated. PR is a supramolecule with rings threaded onto a linear backbone chain, which is capped by bulky end groups to prevent the rings from de-threading. The ring structure is α-cyclodextrin (CD), and it can be functionalized to enhance its affinity with the hosting polymer matrix. Adding only 1 wt % of PR containing methacrylate functional groups (mPR) at the terminal of some of the polycaprolactone-grafted chains on CD promotes massive crazing, resulting in a significant improvement in fracture toughness while maintaining the modulus and transparency of the PMMA matrix. Dynamic mechanical analysis and atomic force microscopy studies reveal that mPR strongly interact with PMMA, leading to higher molecular mobility and enhanced molecular cooperativity during deformation. This molecular cooperativity may be responsible for the formation of massive crazing in a PMMA matrix, which leads to greatly improved fracture toughness.

Failure characteristics and meso-deterioration mechanism of pre-stressed coal subjected to different dynamic loads

The study of dynamic fracture mechanism of pre-stressed coal is of great importance to the coal bursts prevention and the coal pillar reinforcement subjected to the dynamic disturbance. In this paper, the effect of pre-static load and dynamic load on the initiation fracture evolution and destruction states of coal were studied using experimental and theoretical approaches. The results show that the coal usually splits into several blocks along the dominant fractures when subjected to the static load. The increase of pre-static load can make the post-peak dynamic stress–strain curve of the specimen gradually transform from type II to type I. The dynamic load plays the same role as that of pre-static load in terms of the effect on the dynamic stress–strain curve, but different in dynamic failure state of the coal. The enhancement of the former will make the dominant fracture expansion and leading the dynamic failure of coal gradually transform from the surface peeling to failure into several large pieces along the dominant fractures, while the increase of the latter will provid increasing kinetic energy to activate the internal fracture expansion of the specimen, and causing the failure state of the specimen transform from the surface peeling to the complete destruction into pieces. For the specimen with the surface peeling failure form, the peeling degree of the specimen depend on both the length of the fracture and the distance of the fracture to the free surface. Based on these results, the dynamic instability mechanism and protection focus of coal pillars under coupled static and dynamic loads were further discussed.

Mechanical and thermal properties of cellulose nanocrystals from jute fibers reinforced epoxy composites

This study investigated the effects of loadings of cellulose nanocrystals (CNC) extracted from jute fibers on the chemical, mechanical and thermal properties of the Epoxy matrix. The CNC/Epoxy composites were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometry, tensile tests, dynamic mechanical analysis, and thermogravimetric analysis. Experimental results showed that the tensile strength, modulus, and work of fracture showed a statistically significant increase from 1 to 5 wt.% CNC loading. In addition, TG measurements revealed that the onset temperature (Tonset) and temperature at maximum decomposition rate (Tmax) for composites decreased compared to neat epoxy with increasing CNC concentration. Dynamic mechanical analysis studies showed that the storage modulus values at 35 °C and 120 °C decreased for lower 1 wt% CNC content sample compared to neat epoxy, then increased for samples loaded with 3 and 5 wt% of CNC.

Nano‐metal oxide fillers in thermo‐responsive polycaprolactone‐based polymer nanocomposites smart materials: Impact on thermo‐mechanical, and shape memory properties

AbstractThe present study introduces the properties of three thermo‐responsive shape memory polymer nanocomposites (SMPCs), viz. SMPC–NiO (SMP with nickel oxide), SMPC‐Fe2O3 (SMP with iron oxide), and SMPC‐Fe2NiO4 (SMP with iron nickel oxide) along with the neat SMP blend. Styrene‐Butadiene rubber and poly ε‐caprolactone (PCL) polymer are the vital part, which forms the backbone of polymer‐elastomer blend matrix. This study helps to understand the effect and influence of these metal oxide nanofillers' integrated blend on their different inbuilt properties. The tensile test and dynamic mechanical analysis studies confirmed that SMPC‐Fe2NiO4 holds a large elastic modulus value and very rigid compared to other SMPCs. Thermal decomposition studies using differential scanning calorimetry, thermogravimetric (TG) analysis, and TG‐gas chromatography and mass spectrometry results show that the nanocomposites undergoes a two‐stage decomposition process. The shape memory test reveals that the time taken for temporary shape recovery is high for SMPC‐Fe2NiO4 because of its rigid nature and low for SMPC‐Fe2O3. The results revealed that, from this exploratory study, the integration of metal oxide nanopowder fillers, especially Fe2O3 with neat SMP, showed better properties.

Dynamic analysis of disease progression in Alzheimer’s disease under the influence of hybrid synapse and spatially correlated noise

Alzheimer’s disease (AD), characterized by cognitive impairment, mainly affects middle-aged and elderly people. As the aging process of the world continues to intensify, AD harms people’s life, economy and society more and more seriously. Therefore, it has become an urgent problem to study the pathogenesis of AD and seek treatment on this basis. Hybrid synapse, autapse and spatial correlated noise in diverse neural activities have been investigated separately, however, theoretically understanding combination of them still has not been fully studied. Here in this paper, a neural network with multiple associative memory abilities is established from the perspective of the degeneration of associative memory ability in AD patients under the conditions of hybrid synapse, autapse and spatial correlated noise. In order to explore the pathogenesis, a synaptic loss and synaptic compensation model are established to analyze the associative memory ability of AD in different degrees of disease. The simulation results demonstrate the effectiveness of the proposed models and pave a way in the study of dynamic mechanism with higher bio-interpretability in neural networks.