Pseudoplastic Deformation Research Articles

Chitosan-PEG Gels Loaded with Jatropha mollissima (Pohl) Baill. Ethanolic Extract: An Efficient and Effective Biomaterial in Hemorrhage Control.

A lack of control over blood loss can have catastrophic implications, including death. Although several hemostatic medications have been employed to reduce bleeding, a vast majority of them are ineffective, expensive, or pose health risks to the patient. To overcome these constraints, chitosan-polyethylene glycol (CS-PEG) hemostatic gels loaded with ethanolic extract of Jatropha mollissima sap (EES) were prepared and their hemostatic, physicochemical, and cytotoxic properties were evaluated. The gels were produced by mixing CS with PEG (an external plasticizer) and EES. The phytochemical analysis revealed a significant concentration of total polyphenols and tannins content in the extract and catechin was identified as one of the key compounds of EES. Infrared spectroscopy analysis revealed the presence of EES in the gels, as well as the chemical interaction between CS and PEG. The gels were thermally stable between 25 and 37 °C (ambient and human body temperature range), had pseudoplastic deformation behavior (rheological properties preserved after shearing), were simple to inject (compression force 30 N), and were biocompatible. In vivo experiments showed that both CS-PEG-EES gels exhibited greater hemostatic action in preventing tail hemorrhage in Wistar rats, with decreased bleeding time and blood weight compared with unloaded CS-PEG gels (control groups) and Hemostank, a commercial product. However, the gel prepared with acetic acid was more efficient in controlling bleeding. These findings reveal that CS-PEG-EES gels can reduce hemorrhages and are a potent, simple, and safe hemostatic agent.

Nanotwinning-induced pseudoplastic deformation in boron carbide under low temperature

Nanotwinned metals exhibit enhanced strength due to the twin-boundary-dislocation interaction, but nanotwins may play a different role in strong, yet brittle ceramics due to the absence of mobile dislocations under low temperatures. Here, we carry out molecular dynamics (MD) simulations using a machine-learning force field to illustrate how nanoscale twins influence the mechanical properties and deformation mechanisms of superhard boron carbide (B4C). Surprisingly, in contrast to brittle failure in single-crystal B4C, we identify an abnormal pseudoplastic deformation behavior in nanotwinned B4C (nt-B4C) which arises from successive breakage of stretched inter-icosahedral B-C bonds. This pseudoplastic behavior shows a strong dependence on temperature and twin density, and it becomes more prominent as temperature decreases and twin density increases. This abnormal anti-correlation between pseudoplasticity and temperature mainly arises from enhanced atomic shear strain induced by thermodynamic vibrations at high temperatures. Moreover, a nanotwinning-induced softening mechanism is observed in nt-B4C, since amorphization preferentially nucleates near twin boundaries due to stress concentration. This work demonstrates that introducing high-density nanotwins into B4C is effective to enhance its low-temperature ductility.

Self-lubricating epoxy-based composite abradable seal coating eliminating adhesive transfer via hierarchical design

Aluminum-based composite abradable seal coatings are pivotal to improving the efficiency of aero engines or gas turbines. However, the adhesive transfer frequently occurs between metallic blade tips and aluminum-based composite coatings, resulting in engine vibration and even jam. Many past studies had tried to solve this problem by reducing coating hardness, improving lubrication, or strengthening blade tips, but all had failed. In this paper, we proposed a novel epoxy-based composite abradable seal coating, eliminating adhesive transfer by changing metal-to-metal scraping pair to metal-to-polymer scraping pair. The coating was developed via a hierarchical structure design. Large spherical pores were uniformly distributed in the continuous epoxy matrix with fine graphite dispersion. By adding 20 vol.% graphite and 50 vol.% hollow microspheres, a self-lubricating epoxy-based coating of 0.26 friction coefficient with thermal conductivity of 0.28 W/(m·K), coating HR15Y hardness at 54.8, and bonding strength at 18.7 MPa can be reached. When the metallic blades scrape the epoxy-based composite coating, no adhesive transfer occurs. Besides, a smooth scraped surface is formed by pseudoplastic deformation. This epoxy-based composite abradable seal coating opens a new way to improve the efficiency and reliable operations of air engine compressors.

Magneto-mechanical deformation of Ni50Mn28Ga22 shape memory alloy

This study deals with pseudoplastic deformation of Ni50Mn28Ga22 alloy exhibiting mechanically and magnetically induced crystal reorientation. The new approach was introduced, taking into account crystals with single initial variant as well as nucleation of different orientation. Initially, observations from optical microscope and AFM (atomic force microscope) were correlated with the mechanical measurements from stress-strain machine to characterize boundaries between crystal variants. These observations were subsequently used to clarify the results of the mechanical deformation tests. By magnetizing samples in VSM (vibrating-sample magnetometer), analogous magnetic measurements to mechanical tests were conducted. The two types of measurements were then compared with respect to energy. The discrepancy found between the model and measurements is in agreement with previous studies. Some experimental factors and possible errors that may affect measurement have been discussed. Nevertheless, the observed differences remain an unresolved issue suggesting a need for a modification of the model.

ВПЛИВ ІНТЕНСИВНОСТІ РОЗВИТКУ ДЕСТРУКЦІЇ СТРУКТУРИ ОДНОРІДНО СТИСНУТОГО ДРІБНОЗЕРНИСТОГО БЕТОНУ НА ПРОЦЕС ДЕФОРМУВАННЯ ТА РУЙНУВАННЯ

The article presents the results of the performed studies of the process of the intensity of the development of destruction - pseudoplastic deformation and destruction of homogeneously compressed fine-grained oncrete (FGC). However, the issue under study, due to different opinions on the methods for studying the nature of deformation and the process of development of submicro-, micro-, macrodestructions with increasing load, did not bring them closer to specific results. At the same time, the nature of the curvature of the σc-εcх diagrams is explained by the formation of internal microcracks - the formation of pseudoplastic deformations, and in analytical expressions the dependence σc-εcх include the characteristics v_cu and и E_c^0, reflecting the elastic-plastic properties of uniaxially compressed fine-grained concrete and their transfer to non-uniformly compressed concrete. Research has established that the v_cu and и E_c^0 and uniaxially compressed cement concretes recommended by the Building Norms do not quantitatively and qualitatively reflect the nature of the change in the elastic-plastic properties of homogeneously and non-uniformly compressed concretes. Proposed analytical expressions for the dependence of the complete diagrams σc-εcх, as well as the dependences of the change in the elastic coefficients (vc), secant elastic modulus (E_c^sek) and the rate of development of destruction (KD) uniformly compressed FGC with an increase in the load level under «soft» and «hard» loading regimes of the investigated series of samples from FGC using: ε_clx; E_c^sek; v_cu, reflecting the process of changing the elastic-plastic properties of concrete in the ascending and descending sections of the complete diagrams of concrete deformation and their significant difference in homogeneous and inhomogeneous compression. Keywords: coefficient of elasticity; the development of destruction (loosening); secant modulus of elasticity fine-grained concrete; homogeneous (axial) compression; short columns; loading mode; full diagrams.

Feedbacks between subduction dynamics and slab deformation: Combined effects of nonlinear rheology of a weak decoupling layer and phase transitions

Seismic tomography reveals a wide variety of slab deformation in the mantle transition zone and shallow lower mantle. Numerical modeling of subduction has identified several factors that control slab deformation, among them the properties of the mechanical decoupling between subducting and overriding plates was shown to have a major influence on slab velocity, rollback and deformation in the transition zone. Models with weak crust generally yield fast rollback and slab stagnation while stronger crust results in slab penetration into the lower mantle. Here we perform a detailed analysis of the effects of this weak crustal layer. First, in models with constant crustal viscosity, we quantify combined effects of crustal viscosity and thickness. Further we apply nonlinear crustal rheology that combines dislocation creep and pseudoplastic deformation. We test the effects of varying parameterisations of the nonlinear rheological mechanisms and evaluate their effects on slab deformation. We conclude that the variations of subducting slab velocity (controlled by the buoyancy effects of the major phase transitions) induce strong time variations of the crustal viscosity that in turn enforce further acceleration or deceleration of the slab. This feedback between slab velocity and crustal viscosity strenghtens transient behavior of the subducting slabs and enforces slab penetration after a transient period of stagnation.

Bearing capacity of steel fiber reinforced concrete with different fiber types

The paper presents study results of the load-bearing capacity of fibroconcrete during dispersed reinforce-ment with steel fiber of three different types - anchor, flattened and corrugated. In all experiments, fiber was added in an amount of 1% by volume, which, as established in the preliminary tests conducted by the authors, is the op-timal percentage of reinforcement. The tests were performed on prisms and cubes measuring 100x100x400 mm and 100x100x100 mm, respectively, aged for 28 days.Four groups of prisms and cubes were manufactured. One - from usual concrete (with the sizes of large aggregate to 10 mm) of the C20/25 class, and three more - with different types of fibers. Each group consisted of six samples. All tests were performed on a press specially prepared for this purpose. Clock-type indicators, one for each, were attached to the side surfaces of the prisms to measure longitu-dinal deformations during loading. The load was applied in equal steps with a holding time of 10 minutes. The test results are presented in the form of graphs of the dependences of the relative deformation on the stress and in tab-ular form. When testing the cubes, only the maximum loads were recorded, due to the impossibility of stable fixing of sensors. It was found that the load-bearing capacity of steel fiber does not depend on the fiber type, but its pres-ence in the concrete changes the nature of the destruction of the sample. Instead of instantaneous brittle destruc-tion, a slow current process is observed, and the prism does not disintegrate into separate parts, but remains a single array with through cracks; fiber fibers keep it from final destruction. Prisms with steel fiber content with-stood loads 11% higher than concrete samples. The use of steel fiber improves not only the load-bearing capacity, but also the deformability. The relative longitudinal deformation of reinforced concrete was on average 36% higher than that of concrete due to the presence of pseudoplastic deformation phase in fibroconcrete.

Effect of PyC interface phase on the cyclic ablation resistance and flexural properties of two-dimensional Cf/HfC composites

Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface.

Study on pressure sensitivity of tight sandstone and its influence on reservoir characteristics

ABSTRACTThe rocks with low permeability have a strong sensitivity to pressure. By changing the size of confining pressure, we can realize the effective stress change of rocks and calculate the permeability change under different effective stress to evaluate the stress sensitivity of the reservoir. We analyzed the factors affecting the stress sensitivity of tight sandstone reservoir, including material composition, fracture development, and pore structure of rock. The results show that the stress sensitivity of microfractured core is very weak, and the permeability change rate is less than 20%. The sensitivity curve is divided into two stages: the permeability decline rate in the first stage is more than 30%, mainly due to the pseudoplastic deformation of the fracture under compression. In the second stage, the decrease of permeability is less than 30%. At this stage, the elastic deformation mainly depends on the compression of the rock skeleton particles, and the net stress of the actual reservoir is mostly at this stage. Therefore, the application of the second stage to evaluate the stress sensitivity of reservoirs is more practical, and the stress sensitivity of microfracture cores is higher than that of matrix cores. Through the analysis of pressure-sensitive mechanism and experimental data, it is concluded that the main controlling factors affecting rock stress sensitivity are fracture development and pore structure of rock, while rock material composition is a relatively minor factor.

Fabrication and formation mechanism of carbon foam with two-level cell structure

A novel method was developed for production of carbon foam with two-level cell structure, which possesses two kinds of cell sizes of about 1μm and 300μm. Results show a carbothermal reduction occurs between the pore wall of first-level foam and the nano-MgO at high temperatures, which results in further bubbling and forming the second-level foam. The carbon foam prepared exhibits a characteristic of pseudoplastic deformation with a relatively compressive strength of 1.72MPa, and possesses a low bulk density of 0.11g/cm3 and a high porosity of 94.2%.

Design considerations for a novel shape-memory-plate osteosynthesis allowing for non-invasive alteration of bending stiffness.

Biomechanical stimuli play a major role in fracture healing. Changing the fixation stiffness through the course of healing might accelerate bone healing and prevent healing complications. Shape memory alloy (SMA) based implants were developed to allow for non-invasive stiffness alteration during the fracture healing process. To gain a deeper understanding of the implant functionality based on the alloy characteristics and geometric design, the mechanical properties of different shape memory alloys where mechanically characterized. SMA bone plates were manufactured and the structural bending stiffness of the implants was determined at different temperatures and configurations. The temperature required for complete recovery of shape after deformation increased continuously with increasing pseudo-plastic deformation in SMA probes. Full recovery was observed at temperatures ranging from 38°C to 52°C after pseudo-plastic deformations ranging from 0.2% to 1.0% outer fibre strain, respectively. The small fragment inverse-dynamisation implants revealed bending stiffnesses ranging from 0.09Nm2 to 0.34Nm2 in the initial state and from 0.16Nm2 to 0.46Nm2 after shape alteration. Dependent on the design, a relative gain of the implant stiffness ranging from 18.8% to 115.0% could be observed. The large inverse-dynamisation implants revealed bending stiffnesses from 3.7Nm2 to 7.1Nm2 before and 4.1Nm2 to 12.6Nm2 after triggering the shape memory effect. Dependent on the design a gain in stiffness from 11.8% to 117.2% was observed. Warming the SMA implant to 40°C for a short period of time, leads to a moderate increase in implant stiffness of up to 64.5%, while triggering the implant with 50°C leads to a maximum increase in stiffness of up to 127.3%. The Nitinol shape memory bone plates have a huge potential for improving the treatment of long shaft fractures by allowing for the increase, decrease or incremental change of implant stiffness in fracture stabilization. However, the interaction between design, material properties, and manufacturing processes need to be carefully considered for each specific application to achieve optimum function of SMA-based, stiffness altering, fracture-fixation implants.

Stress analysis and probabilistic assessment of multi-layer SiC-based accident tolerant nuclear fuel cladding

Silicon carbide (SiC) fiber, SiC matrix composites (SiC/SiC) are being considered as a cladding material for light water reactors in order to improve safety performance. Engineered, multi-layer cladding designs consisting of both monolithic SiC (mSiC) and SiC/SiC have been examined as promising concepts to meet both strength and impermeability requirements. A new model has been developed to calculate stresses and failure probabilities for multi-layer cladding consisting of SiC-based materials in reactor operating conditions. The results show that stresses in SiC-based cladding are dominated by temperature-dependent irradiation-induced swelling, with the largest stresses occurring during the cold shutdown conditions. Failure probabilities are driven by the resulting tensile stresses at the cladding inner wall, while the outer wall is subject to compressive stresses. This indicates that the inner SiC/SiC, outer mSiC concept has the lowest failure probability, as the pseudo-plastic deformation of the composite reduces tensile loading and the compressed monolith provides a reliable, impermeable barrier to fission product release.

Dynamic pseudoplastic behavior of laminated ceramics with soft and hard interbedded dense layers

Laminated ZrO–Zr2CN/Si3N4 ceramics with soft and hard interbedded dense layers were prepared via tape casting and reactive hot pressing. The dynamic compressive behavior was investigated at various high strain rates ranging from 1000 to 5000s−1 using a split Hopkinson bar, and the dynamic loading pattern was analyzed. With increasing the strain rate, the dynamic strength obtained a peak value, while the failure strain increased continuous. The compressive stress–strain curves exhibited universal four deformation regions, including inelastic deformation region, rapid loading region, pseudoplastic deformation region and failure region. The dynamic pseudoplastic behavior of the laminated ceramics was similar to that of some metal matrix composites.

Fabrication and dynamic compressive response of laminated ZrO–Zr2CN/Si3N4 ceramics

Laminated ZrO–Zr2CN/Si3N4 ceramics with soft and hard interbedded layers and an in-situ interface were prepared via tape casting and reactive hot pressing, and the dynamic compressive response was investigated using a Split Hopkinson pressure bar tester at a range of high strain rates from 1.1×103s−1 to 3.5×103s−1. With increasing the strain rates, the duration and energy of transmitted wave decreased, but that of reflected wave as well as the failure strain increased continuously. The energy absorptivity kept at a high stable level. The four characteristic stages of the stress–strain curves were inelastic loading region, stable loading region, pseudoplastic deformation region and failure region. The laminated ceramics possessed longer stable loading region but shorter pseudoplastic deformation region at higher high-strain-rates. The failure model consisting of a three-part process of multi-reflection of stress waves, crack initiation and crack deflection at the interfaces was established.

Self-recovering caddisfly silk: energy dissipating, Ca(2+)-dependent, double dynamic network fibers.

Single fibers of the sticky underwater larval silk of the casemaker caddisfly (H. occidentalis) are viscoelastic, display large strain cycle hysteresis, and self-recover 99% of their initial stiffness and strength within 120 min. Mechanical response to cyclical strains suggested viscoelasticity is due to two independent, self-recovering Ca(2+)-crosslinked networks. The networks display distinct pH dependence. The first network is attributed to Ca(2+)-stabilized phosphoserine motifs in H-fibroin, the second to Ca(2+) complexed carboxylate groups in the N-terminus of H-fibroin and a PEVK-like protein. These assignments were corroborated by IR spectroscopy. The results are consolidated into a multi-network model in which reversible rupture of the Ca(2+)-crosslinked domains at a critical stress results in pseudo-plastic deformation. Slow refolding of the domains results in nearly full recovery of fiber length, stiffness, and strength. The fiber toughening, energy dissipation, and recovery mechanisms, are highly adaptive for the high energy aquatic environment of caddisfly larvae.

Croatian

Shape memory alloys (SMAs) belong to a group of functional materials with the unique property of “remembering” the shape they had before pseudoplastic deformation. Such an effect is based on crystallographic reversible thermo-elastic martensitic transformation. There are two crystal phases in SMAs: the austenite phase (stable at high temperature) and the martensite phase (stable at low temperature). Austenite to martensite phase transformation can be obtained by mechanical (loading) and thermal methods (heating and cooling). During martensitic transformation, no diffusive process is involved, only inelastic deformation of the crystal structure. When the shape memory alloy passes through the phase transformation, the alloy transforms from high ordered phase (austenite) to low ordered phase (martensite). There are two types of martensite transformations. First is temperature-induced martensite, which is also called self-accommodating (twinned) martensite. The second is stress-induced martensite, also called detwinned martensite. The entire austenite to martensite transformation cycle can be described with four characteristic temperatures: Ms – martensite start temperature, Mf – martensite finish temperature, As – austenite start temperature, and Af – austenite finish temperature. The main factors influencing transformation temperatures are chemical composition, heat treatment procedure, cooling speed, grain size, and number of transformation cycles. As a result of martensitic transformation in SMAs, several thermomechanical phenomena may occur: pseudoelasticity, shape memory effect (one-way and two-way SME) and rubber-like behavior. Pseudoelasticity occurs when the SMA is subjected to a mechanical loading at a constant temperature above Af. The second thermomechanical behaviour that can be observed in SMA is the shape memory effect (SME), mainly one-way SME, which is the most commonly used SME. When the sample is subjected to a mechanical loading, the stress reaches a critical value and the transformation of twinned martensite into detwinned martensite begins and finishes when the loading process is finished. When the loading-unloading process is finished, the SMA presents a residual strain recoverable by alloy heating, which induces the reverse phase transformation. As a result, the alloy recovers to its original shape. In this paper, a review of thermomechanical properties of shape memory alloys and general characteristics of martensite transformations is shown.

In situ synchrotron X-ray diffraction study of deformation behavior and load transfer in a Ti2Ni-NiTi composite

The deformation behavior and load transfer of a dual-phase composite composed of martensite NiTi embedded in brittle Ti2Ni matrices were investigated by using in situ synchrotron x-ray diffraction during compression. The composite exhibits a stage-wise deformation feature and a double-yielding phenomenon, which were caused by the interaction between Ti2Ni and NiTi with alternative microscopic deformation mechanism. No load transfer occurs from the soft NiTi dendrites to the hard Ti2Ni matrices during the pseudoplastic deformation (detwinning) of NiTi, which is significantly different from that previously reported in bulk metallic glasses matrices composites.

In Situ Synchrotron Studies of Reversible and Irreversible Non-elastic Strain in a Two-Phase TiAl Alloy

This paper contrasts the cyclic tensile loading of two-phase titanium aluminide Ti-44Al-8Nb-1B microstructures, namely fully lamellar (FL) and duplex (DP). The former, in contrast to the latter, shows premature yielding and hysteresis loops on cycling. These phenomena were studied by in situ cyclic loading of these specimens using high energy synchrotron X-ray diffraction. The results show significant differences in the micromechanics of deformation. Load transfer between the γ and α 2 phases has been identified at stresses below the macroscopic yield point in the FL microstructure, while the DP microstructure showed no signs of such load transfer before its well-defined macroscopic yield point. A partially reversible pseudo-plastic deformation mechanism seems to be operating at relatively low stresses in the FL specimen. This mechanism is believed to be twinning/partial reversible twinning of the γ phase. The presence of twins at relatively low applied stresses has been confirmed for the FL microstructure by electron channeling contrast imaging. Further support of twinning/partial reversible twinning in FL but not DP microstructures below the macroscopic yield point was obtained by following the evolution of the integrated intensity of particular diffraction peaks measured during the in situ synchrotron X-ray experiments.

A phenomenological two-phase constitutive model for porous shape memory alloys

We present a two-phase constitutive model for pseudoelastoplastic behavior of porous shape memory alloys (SMAs). The model consists of a dense SMA phase and a porous plasticity phase. The overall response of the porous SMA is obtained by a weighted average of responses of individual phases. Based on the chosen constitutive model parameters, the model incorporates the pseudoelastic and pseudoplastic behavior simultaneously (commonly reported for porous SMAs) as well as sequentially (i.e. dense SMAs; pseudoelastic deformation followed by the pseudoplastic deformation until failure). The presented model also incorporates failure due to the deviatoric (shear band formation) and volumetric (void growth and coalescence) plastic deformation. The model is calibrated by representative volume elements (RVEs) with different sizes of spherical voids that are solved by unit cell finite element calculations. The overall response of the model is tested against experimental results from literature. Finally, application of the presented constitutive model has been presented by performing finite element simulations of the deformation and failure in unaixial dog-bone shaped specimen and compact tension (CT) test specimen. Results show a good agreement with the experimental data reported in the literature.

Pseudoplastic deformation pits on polished ceramics due to cavitation erosion

In a previous study, pseudoplastic deformation pits created by cavitation exposure were reported in silicon nitride and zirconia. In this research, further comparison of the size and number of pits between several silicon nitride and zirconia materials is carried out. The pits are larger and much more numerous in silicon nitride than in zirconia although silicon nitride is harder than zirconia. An explanation of this phenomenon is given. Also, in the previous study it was reported that apparently a partially stabilized zirconia with yttria oxide developed a delay in the phase transformation from tetragonal to monoclinic after being exposed to cavitation. In this research, further experiments related with this phase transformation delay are carried out. Also, the phase transformation is verified with X-ray diffraction analysis. It is concluded that the “activation” of the partial stabilized zirconia happens regardless of the oxide used to stabilize it.