Dynamic Mechanical Tests Research Articles

Investigating the effect of cure schedules and cure initiators on sustainable composites for large offshore structures

This study evaluates the effect of post-cure schedules and cure initiator form on the mechanical properties of Glass fibre reinforced polymer (GFRP) laminates manufactured using an infusible reactive thermoplastic resin. Tensile, flexural, shear and dynamic mechanical analysis tests were conducted. Fractography was also performed. Specimens fabricated using liquid cure initiator and subjected to an elevated temperature post-cure were the control specimens. Ambient cured specimens decreased by no more than 12% in the case of tensile properties (modulus of 90° specimens) and by < 14.3% in the case of flexural properties (also modulus in 90° specimens). Furthermore, the difference in mechanical properties of 0° specimens fabricated using a powder cure initiator was observed to be within ≈ 7% of respective properties of control specimens. In the context of fabricating thick laminates for large-size offshore structures, the results suggest that an extended ambient post-cure cycle in conjunction with an initiator in powder form can be employed instead of an elevated temperature post-cure schedule with initiator in liquid form. This is economically beneficial since it eliminates infrastructure required for elevated temperature curing/post-curing. The risk of porosity induced due to liquid-based initiators is also avoided.

Hydrogel Membranes from Chitosan-Fish Gelatin-Glycerol for Biomedical Applications: Chondroitin Sulfate Incorporation Effect in Membrane Properties.

Chondroitin sulfate (ChS), chitosan (Chi), and fish gelatin (FG), which are byproducts of a fish-treatment small enterprise, were incorporated with glycerol (Gly) to obtain dense hydrogel membranes with reduced brittleness, candidates for dressing in wound healing applications. The mechanical properties of all samples were studied via Dynamic Mechanical Analysis (DMA) and tensile tests while their internal structure was characterized using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Diffraction (XRD) instruments. Their surface morphology was analyzed by ThermoGravimetric Analysis (TGA) method, while their water permeability was estimated via Water Vapor Transmission Rate (WVTR) measurements. Wettability and degradation rate measurements were also carried out. Characterization results indicated that secondary interactions between the natural polymers and the plasticizer create the hydrogel membranes. The samples were amorphous due to the high concentration of plasticizer and the amorphous nature of the natural polymers. The integration of ChS led to decreased decomposition temperature in comparison with the glycerol-free sample, and all the materials had dense structures. Finally, the in vitro endothelial cell attachment studies indicate that the hydrogel membranes successfully support the attachment and survival of primary on the hydrogel membranes and could be appropriate for external application in wound healing applications as dressings.

The state of the art in dynamic mechanical testing of yarns and fabrics: A mini review

This mini review provides a succinct overview of dynamic mechanical tests for woven fabrics and ballistic fibers, which are widely used for penetration-resistant applications. Considering the structural hierarchy of woven fabrics, this work highlights recent studies at different scales, encompassing uniaxial tensile tests and transverse impact tests of yarns, yarn pull-out tests from fabrics, and transverse impact tests of fabrics. The dynamic characterization techniques employed in these tests are discussed, along with the associated challenges. This paper serves as a quick guide for those seeking to gain insights into the dynamic behavior of woven fabrics.

UV-induced gradient aging of bitumen films: A comprehensive study

The aging of bitumen materials under ultraviolet (UV) radiation is a highly intricate process involving volatilization of components and multiple photochemical reactions. To gain a comprehensive understanding of the mechanism and progression of UV aging in bitumen films within bitumen mixtures, this study investigates the formation and evolution of UV aging gradients in bitumen films from various perspectives, including morphology, composition, macro-, and micro-mechanical aspects. Initially, specific bitumen film specimens were subjected to aging, and a protocol for sample handing and testing was developed. Optical microscopy images, functional group indices, and component contents of the bitumen films were then measured and calculated to track the UV aging process from the surface to the interior. Additionally, profiling micro-mechanical tests and layer-by-layer dynamic mechanical tests were conducted to characterize the variations in mechanical properties induced by UV aging gradients within the bitumen films. The results indicate that UV radiation causes significant volatilization of light components on the film surface, resulting in wrinkling. Concurrently, photochromic reactions take place in both bitumen macromolecules (asphaltenes and resins) and small molecules (saturates and aromatic), while molecular photodegradation may also occur. Fluorescence imaging, infrared spectroscopy analysis, and component determination reveal that the degree of UV aging in the bitumen films increases with radiation time and gradually propagates towards the interior. C-S bonds are more sensitive to UV radiation than C = C bonds, leading to oxidation and the formation of sulfoxide groups. Due to the adsorption of light components by aggregates, the modulus values at the surface of aged bitumen films and the aggregate interface are higher, while the intermediate region exhibits lower values. Rheological indicators demonstrate that UV aging, to a certain extent, results in the decomposition of bitumen molecules, leading to a decrease in complex shear modulus and an increase in phase angle. This work significantly enhances our understanding of the mechanism of UV aging in bitumen films and holds important implications for the design and development of UV-blocking materials.

Chemorheology of a Si/Al > 3 Alkali Activated Metakaolin Paste through Parallel Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA).

Although geopolymers, as structural materials, should have superior engineering properties than traditional cementitious materials, they often need to improve their final characteristics' reproducibility due to the need for more control of the complex silico-aluminate decomposition and polymerisation stages. Thermosetting of a reactive geopolymeric paste involves tetrahedral Silicate and Aluminate precursor condensation into polyfunctional oligomers of progressively higher molecular weight, transforming the initial liquid into a gel and a structural solid. Viscosity and gelation control become particularly critical when the geopolymer is processed with 3D printing additive technology. Its physical state modification kinetics should match the flow and setting characteristics required by the deposition process. The reaction kinetics and the elastic and viscous characteristics preceding gelation and hardening have been investigated for an alkali-activated Metakaolin/Sodium Silicate-Sodium Hydroxide paste with a Si/Al ratio > 3. A chemoreological approach has been extended to these inorganic polymerisable systems, as already utilised for organic thermosetting polymers. Differential scanning calorimetry and Oscillatory DMA were carried out to monitor the advancement of the polymerisation reaction and the associated variations of the rheological viscoelastic properties. Dynamic thermal scans were run at 1 °C/min and a frequency of 10 Hz for the dynamic mechanical tests. The observed kinetics of polymerisation and variations of the elastic and viscous components of the complex viscosities and shear moduli are described in terms of polycondensation of linear and branched chains of oligomeric macromolecules of increasing complexity and molecular weight up to gelation (Gel1) and cross-linking of the gelled macrostructure (Gel2) and final glassy state. Geopolymerization can be allocated into two main behavioural zones: a viscoelastic liquid paste below 32.5% of reaction advancement and a viscoelastic solid above. Initial complex viscosities range from 2.3 ± 0.9 × 10-5 MPa*s to 6.8 ± 0.9 × 10-2 in the liquid-like state and from 1.9 ± 0.1 MPa to 9.6 ± 2.1 × 102 MPa in the solid-like state.

Preparation and Characterization of a Biobased Temporary Plugging Material: Self-Healing and Degradable.

Due to the low success rate in high-temperature gas well drilling or workover operations, a new type of biobased temporary sealing material was synthesized using vanillin, succinic anhydride (SA), cellulose, and acetylacetone zinc hydrate (AZH) as catalysts. Infrared analysis proved the synthesis of vanillin-derived epoxy and the formation of a vitrimer with hydroxyl ester. The results of thermodynamic properties tests show that it has excellent thermal stability with a high glass transition temperature (Tg). The dynamic mechanical test results show that the characteristic relaxation time of the material at 120 °C is 3500 s and the self-healing rate can reach 61% within 20 min. The test results of mechanical properties show that under 10 MPa pressure, it has good elastic deformation performance, the rebound rate is more than 36%, and the crushing rate is less than 17%. The degradation performance results show that the decomposition increases to 80% under 120 °C and 1.2% NaOH. The comprehensive performance evaluation results show that the new temporary plugging material has good compatibility, and its plugging performance is better than those of a gel, composite material, and shape memory polymer. The maximum fracture plugging capacity is 5 × 4 mm, with a pressure up to 10 MPa.

Zein as a Basis of Recyclable Injection Moulded Materials: Effect of Formulation and Processing Conditions.

The growing concern about reducing carbon footprint has led to the progressive replacement of traditional polymeric materials by natural-based biodegradable materials. However, materials from natural sources (i.e., plants) typically possess poorer mechanical properties when compared to conventional plastics. To counterbalance this, they need to be adequately formulated and processed to eventually meet the standards for certain applications. Zein is the major storage protein from corn and can be obtained as a by-product from the corn-oil industry. It is an excellent candidate for producing green materials due to its stability, biodegradability, renewability, and suitable mechanical and technical-functional properties. In the present work, zein was blended with a plasticizer (i.e., glycerol) at three different zein/glycerol ratios (75/25, 70/30, and 65/25) and then injection moulded at three different processing temperatures (120, 150, and 190 °C). The properties of both blends and bioplastics were evaluated using dynamic mechanical analysis (DMA), tensile tests, and water absorption capacity (WUC). The properties-structure interrelation was assessed through a scanning electron microscope. Generally, a higher zein content and processing temperature led to a certain reinforcement of the samples. Moreover, all bioplastics displayed a thermoplastic behaviour finally melting at temperatures around 80 °C. The lack of massive crosslinking enabled this melting, which finally could be used to confirm the ability of zein based materials to be recycled, while maintaining their properties. The recyclability of thermoplastic zein materials widens the scope of their application, especially considering its biodegradability.

An acrylic resin system for in‐situ pultrusion: Curing performances and rheology

AbstractIn recent years, the use of low viscosity and in‐situ polymerizable thermoplastic acrylic resins for advanced fiber reinforced composites has grown, specially to address the difficulty of fiber impregnation with high‐melt viscosity thermoplastic polymers. The present work investigated the curing kinetics, chemo‐rheology of an acrylic resin system for in‐situ pultrusion, and proposed the corresponding constitutive models. First, the curing kinetics was studied with the differential scanning calorimetry experiments. The viscosity development was obtained by a rheometer as functions of the degree of cure (DOC) and temperatures. The gelation point was acquired from the intersection point of storage and loss modulus curves through dynamic mechanical analysis test, which occurs at DOC of 0.65 determined by the cure kinetics model. Through the dynamic mechanical analysis, a four step cure hardening modulus model (modified CHILE approach) was proposed. The aforementioned models were applied in a case study to evaluate the influence of process parameters on the DOC, viscosity and physical behavior of the acrylic resin system in the pultrusion die.Highlights Material characterizations of an acrylic resin system are investigated. The cure kinetics and viscosity and elastic modulus models are proposed. A pultrusion case study is given.

Dynamic Mechanical Analysis Test for Evaluating Loose Sands on a Wide Strain Range—Application to the InSight Mission on Mars

Abstract The dynamic properties of loose sands under low stresses are an unexplored topic in soil dynamics because these soil conditions are uncommon in most geotechnical structures on Earth. However, low densities and low-stress conditions prevail on other planets, like, for instance, the surface of Mars, for which particular attention is presently given through the InSight NASA mission. This work presents a new procedure for measuring the dynamic properties of loose sand under low stress by using the dynamical mechanical analysis (DMA) tester, a technique commonly used in asphalt engineering but not in geotechnical engineering. Compared to traditional geotechnical methods (resonant column and cyclic triaxial tests), DMA investigates a broader range of strains using a single apparatus. In this work, we assess the dynamical properties of loose fine sand Dr ≈ 0.2, considered a possible Mars regolith analog, by varying the input strain from γ = 10−6 to γ = 10−2 while applying confining pressures from σ3 = 3 kPa to σ3 = 30 kPa. The results validate the proposed procedure, showing an increment of the shear modulus as the confining pressure increases. Furthermore, they highlight DMA’s advantages for studying the dynamic properties of granular soils under low stress and strain.

Rapeseed oil as feedstock for the polymeric materials via Michael addition reaction

Rapeseed oil was used to synthesize a Michael donor to obtain polymeric materials after nucleophilic polymerization via Michael reaction. Four different bio-polyols as precursors for the Michael donor monomer synthesis were synthesized from epoxidized rapeseed oil using an oxirane ring-opening reaction. Various alcohols such as methanol, butane-1,4-diol, 2,2′-oxydi(ethan-1-ol), and 2-ethyl-2-(hydroxymethyl)propane-1,3-diol were used to obtain bio-polyols with different OH group functionality. The transesterification reaction between the synthesised bio-polyol hydroxyl groups and tert-butyl acetoacetate ester introduced acetoacetate functional groups into their structure. The acid value, hydroxyl value, viscosity and moisture content of the synthesized polyols and corresponding acetoacetates were analyzed. Size-exclusion chromatography and Fourier transform infrared spectroscopy were used to study the chemical structure of polyols and acetoacetates. From developed acetoacetates and commercially available trimethylolpropane triacrylate, bio-based polymers were obtained via carbon-Michael reaction. The different chemical structures and functionalities of the synthesized bio-based monomers allowed for the development of polymer formulations with diverse cross-linking densities. The structural, physical and thermal properties of the developed polymers were analyzed using solid-state NMR, differential scanning calorimetry, dynamic mechanical analysis and thermal gravimetric analysis testing apparatus.

Soft pneumatic actuators with integrated resistive sensors enabled by multi-material 3D printing

The concept of soft robots has garnered significant attention in recent studies due to their unique capability to interact effectively with the surrounding environment. However, as the number of innovative soft pneumatic actuators (SPAs) continues to rise, integrating traditional sensors becomes challenging due to the complex and unrestricted movements exhibited by SPA during their operation. This article explores the importance of utilising one-shot multi-material 3D printing to integrate soft force and bending sensors into SPAs. It highlights the necessity of a well-tuned and robust low-cost fabrication process to ensure the functionality of these sensors over an extended period. Fused deposition modelling (FDM) offers a cost-effective solution for embedding sensors in soft robots, directly addressing such necessity. Also, a finite element method (FEM) based on the nonlinear hyper-elastic constitutive model equipped with experimental input is developed to precisely predict the deformation and tip force of the actuators measured in experiments. The dynamic mechanical test is conducted to observe and analyse the behaviour and resistance changes of conductive thermoplastic polyurethane (CTPU) and varioShore TPU (VTPU) during a cyclic test. The flexible sensor can detect deformations in SPAs through the application of air pressure. Similarly, the force sensor exhibits the ability to detect grasping objects by detecting changes in resistance. These findings suggest that the resistance change corresponds directly to the magnitude of the mechanical stimuli applied. Thus, the device shows potential for functioning as a resistive sensor for soft actuation. Furthermore, these findings highlight the significant potential of 3D and 4D printing technology in one-shot fabrication of soft sensor-actuator robotic systems, suggesting promising applications in various fields like grippers with sensors and rehabilitation devices.

Design and mechanical testing of an adjustable posterior leaf spring ankle-foot orthosis for patients with drop foot.

This study aimed to design an adjustable posterior leaf spring (PLS) ankle-foot orthosis (AFO) with an affordable material in low-income countries and investigate the mechanical properties between an adjustable PLS AFO and a standard PLS AFO. Static and dynamic mechanical testing. This study preliminarily tested a new adjustable PLS AFO against a standard PLS AFO. Each AFO design was tested with mechanical testing using an Instron 8801 universal testing machine. The stiffness value of the adjustable PLS AFO was greater than that of the standard PLS AFO during the static loading test. The energy dissipated ratios were lower in the adjustable PLS AFO than in the standard PLS AFO. After 110,000 cycles of fatigue testing, the distal rivet of the adjustable PLS AFO became loose, although the standard PLS AFO had no problem. The novel adjustable PLS AFO achieved noninferior mechanical properties except fatigue strength. The connecting area always initiated fatigue failure. It is suggested that this area must be prevented for stress concentration. As a preliminary study, this study is fundamental for future studies.

Enhancement of physical properties of thermoplastic polyurethanes by blending with cyclic olefin copolymer elastomer

AbstractIn this study, two different thermoplastic polyurethanes (TPUs), a poly(ester)‐based TPU including aromatic diisocyanate units (TPU1) and a poly(ester‐ether)‐based TPU including aliphatic diisocyanate units (TPU2) were blended with a cyclic olefin copolymer (COC) elastomer to prepare TPU‐rich blend films via melt compounding in a twin screw extruder equipped with a slit die and film casting rollers. Morphological features and viscoelastic properties of blend films were characterized with scanning electron microscope analysis, different test protocols in melt rheology measurements, and dynamic mechanical analyzer tests, in detail. Viscoelastic properties of blend films were quantified with various mathematical approaches such as Williamson model, discrete retardation spectrum (DRS), Burger, and Findley equation. It was found that COC phase dispersed more homogenously into TPU1 matrix than TPU2. COC elastomer addition significantly increased the melt viscosity and melt elasticity of TPUs and improved the creep strength.Highlights COC addition enhanced the viscosity and elasticity of TPUs in melt state. The creep strains of TPUs decreased by 65% with addition of 40 wt% of COC.

Electrically conductive adhesive-free interconnection of shingle solar cells

This work deals with the usage of electrically conductive adhesives (ECA) for the interconnection of shingle solar cells. In a detailed study on small-format shingle modules characterized by current-voltage, electroluminescence and magnetic field imaging measurements, the impact of an ECA reduction (usage of ECA dashes instead of a continuous ECA line) as well as the complete omission of ECA is investigated with regards to the electrical interconnection quality. Inter alia, it is demonstrated that lamination can improve interconnection quality in ECA-containing shingle joints and establish interconnection in ECA-free shingle joints by pressing adjacent shingles together and thereby forming a busbar-to-busbar contact of decent electrical quality. In a follow-up experiment, the approach of simply omitting the usage of ECA for shingle interconnection is tested with regards to thermal cycling, damp heat and dynamic mechanical load tests finding only minor compromises, if at all, in terms of long-term stability.

Modeling the dynamic magneto-mechanical response of magnetic shape memory alloys based on Hamilton’s principle: The numerical algorithm

This paper is the second part of a variational modeling work on the dynamic magneto-mechanical response of magnetic shape memory alloys (MSMA). In the first part of this series work, the governing equations system for modeling the dynamic response of MSMA samples has been derived based on Hamilton’s principle, which contains the Maxwell’s equations, the magneto-mechanic equations, the evolution equations of internal variables and the twin interface motion criteria. In this paper, we aim to conduct comprehensive numerical simulations on the dynamic magneto-mechanical response of MSMA samples. To solve the governing system, the space–time finite element method is applied and a double-loop iterative numerical algorithm is proposed. By using this algorithm, the independent variables in the governing system and the motion of twin interfaces in the MSMA sample can be determined separately and iteratively. Besides that, a specific discretization of the sample is adopted to simplify the calculation of variant state distribution in the sample. To show the efficiency of the numerical algorithm, the magneto-mechanical response of a MSMA sample in stress-assisted dynamic field loading tests and field-assisted dynamic mechanical loading tests are studied. Based on the numerical results, some global response curves of the MSMA sample are plotted, which show good consistency with the experimental results. Furthermore, the current configuration of the sample and the distributions of some important physical fields in the sample can be simulated. The current work will be helpful for the design of novel actuators or energy harvesters with MSMA.

Preparation of CoCrFeMnNi-based high-entropy/aluminide laminated composites: Multielement interdiffusion reactions

CoCrFeMnNi-based high-entropy/aluminide laminate (HAL) composites were produced following the hot pressing diffusion sintering method. The microstructure of the samples was analyzed using the SEM, EDS, and EBSD techniques, and the results revealed that the diffusion reaction phases of the HAL composite consisted of a four-layer aluminide structure based on the Al13(Cr, Mn, Fe, Co, Ni)4 phase. The diffusion behavior of iron dominated the resulting phase, leading to the formation of Fe-Al compounds. Under the influence of the hysteresis diffusion effect of high entropy alloys, Al13(Cr, Mn, Fe, Co, Ni)4 phase layers (ASL I–III) with different grain sizes and growth orientations are formed due to the difference of diffusion rates at different interfaces. At the front end of the diffusion reaction, the aggregation layer of the secondary phase Al9(Fe, Co, Ni)2 appears due to the segregation of Co and Ni elements. The growth kinetics model of HAL composites was explored, and it was observed that a mixture diffusion type controlled the growth of the aluminide layer via ‘grain boundary and lattice diffusion’. The mechanical properties and failure modes of the HAL composites were investigated through quasi-static and dynamic mechanical tests. The fracture toughness reached 25 MPa·m1/2, and the main energy dissipation modes were the deformation of the ductile layer and the fracture of the hard, brittle layer. The dynamic impact failure modes were primarily deformation and 45% adiabatic shear bands, and the impact strength and energy consumption reached up to 1800 MPa and 2260 J/mm3. HAL composites with high alumina content exhibited prominent crack propagation and fragmentation properties under high-speed impact. The stress wave was significantly attenuated in the crushed aluminide layer, which significantly improved the energy absorption effect of aluminide.

Dynamic Mechanical Properties and Damage Evolution Characteristics of Beishan Deep Granite under Medium and High Strain Rates.

To study the dynamic mechanical properties and damage evolution mechanism of Beishan deep granite under medium and high strain rates, dynamic mechanical tests for the deep granite specimens with different strain rates were conducted using the split Hopkinson pressure bar (SHPB) device. The improved Zhu-Wang-ang (ZWT) dynamic constitutive model was established, and the relationship between strain rate and strain energy was investigated. The test results show that the strain rate in the dynamic load test is closer to the strain rate in the rock blasting state when the uniaxial SHPB test is applied to the granite specimens in a low ground stress state. Peak stress has a linear correlation with strain rate, and the dynamic deformation modulus of the Beishan granite is 152.58 GPa. The dissipation energy per unit volume and the energy ratio increase along with the strain rate, whereas the dissipation energy per unit volume increases exponentially along with the strain rate. There is a consistent relationship between the damage degree of granite specimens and the dissipation energy per unit volume, which correspond to one another, but there is no one-to-one correspondence between the damage degree of granite specimens and the strain rate. To consider the damage and obtain the damage discount factor for the principal structure model, the principal structure of the element combination model was improved and simplified using the ZWT dynamic constitutive model. The change of damage parameters with strain rate and strain was obtained, and the dynamic damage evolution equation of Beishan granite was established by considering the damage threshold.

High‐performance epoxy hybrid non‐isocyanate polyurethanes prepared from diol‐cyclocarbonation bisphenol A dicyclocarbonate

AbstractA new synthesis route different from convenient epoxy/CO2 method was established to synthesize a five‐membered dicyclocarbonate of bisphenol A (BisA‐5dCC), and its hybrid non‐isocyanate polyurethanes with epoxy resins (HNIPUs) were reported. Bisphenol A was first reacted with 3‐chloro‐1,2‐propanediol to prepare a bisphenol A tetraol (BisA‐4OH), and then was reacted with excess diethyl carbonate to obtain BisA‐5dCC. Three polyhydroxyurethanes with H2N‐terminal groups (PHUs) were synthesized from the aminolysis polyaddition of BisA‐5dCC and excess hexanediamine. The PHUs were crosslinked with 1,4‐butanediol diglycidyl ether and bisphenol A diglycidyl ether, respectively, and different HNIPUs were prepared. The structures of BisA‐4OH, BisA‐5dCC, and PHUs were confirmed, and the HNIPUs were characterized by Fourier transform infrared, differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, and tensile tests. HNIPUs prepared from aromatic epoxy showed higher Tg (up to 81°C) and better tensile strength (as high as 60 MPa) than those from aliphatic epoxy. High‐performance HNIPUs with excellent thermal and mechanical properties were successfully synthesized.Highlights Dicyclocarbonate of bisphenol A (BisA‐5dCC) was prepared from a BisA tetraol. H2N‐terminated PHUs were synthesized further from the aminolysis of BisA‐5dCC. Hybrid non‐isocyanate polyurethanes (HNIPUs) were obtained from PHUs and epoxys. HNIPUs prepared from aromatic epoxy showed high Tg up to 81°C. They showed excellent tensile strength as high as 60 MPa.

Incorporation of Lignin in Bio-Based Resins for Potential Application in Fiber–Polymer Composites

Bio-based resins, obtained from renewable raw materials, are a more sustainable alternative to oil-based resins for fiber-reinforced polymer (FRP) composites. The incorporation of lignin in those resins has the potential to enhance their performance. This paper presents results of an experimental study about the effects of Lignoboost lignin incorporation on a partially bio-based vinyl ester (VE) resin. Two resins were prepared—without (reference) and with lignin addition (4% by weight) to its main chain—and their chemical, thermophysical, and mechanical properties were compared using Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and tensile and shear tests. Results suggest that the addition of lignin to the base resin resulted in a copolymer of increased heterogeneity and higher molecular weight, incorporating stiff and complex aromatic structures in the polymer chain. While requiring high-temperature curing, the VE–lignin copolymer presented improvements of 27% in tensile strength, 4% in shear strength, and increased glass transition temperature by about 8 °C, thus confirming the potential of this natural biopolymer for FRP composite applications.

Influence of Dynamic Strain Sweep on the Degradation Behavior of FeMnSi-Ag Shape Memory Alloys.

Iron-based SMAs can be used in the medical field for both their shape memory effect (SME) and biodegradability after a specific period, solving complicated chirurgical problems that are partially now addressed with shape-memory polymers or biodegradable polymers. Iron-based materials with (28-32 wt %) Mn and (4-6 wt %) Si with the addition of 1 and 2 wt % Ag were obtained using levitation induction melting equipment. Addition of silver to the FeMnSi alloy was proposed in order to enhance its antiseptic property. Structural and chemical composition analyses of the newly obtained alloys were performed by X-ray diffraction (confirming the presence of ε phase), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The corrosion resistance was evaluated through immersion tests and electrolyte pH solution variation. Dynamic mechanical solicitations were performed with amplitude sweep performed on the FeMnSi-1Ag and FeMnSi-2Ag samples, including five deformation cycles at 40 °C, with a frequency of 1 Hz, 5 Hz and 20 Hz. These experiments were meant to simulate the usual behavior of some metallic implants subjected to repetitive mechanical loading. Atomic force microscopy was used to analyze the surface roughness before and after the dynamic mechanical analysis test followed by the characterization of the surface profile change by varying dynamic mechanical stress. Differential scanning calorimetry was performed in order to analyze the thermal behavior of the material in the range of -50-+200 °C. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) along with Neaspec nano-FTIR experiments were performed to identify and confirm the corrosion compounds (oxides, hydroxides or carbonates) formed on the surface.