Longitudinal Elastic Modulus Research Articles

Relative strain is a novel predictor of aneurysmal degeneration of the thoracic aorta: An ex vivo mechanical study

ObjectiveCurrent guidelines for prophylactic replacement of the thoracic aorta, primarily based on size alone, may not be adequate in identifying patients at risk for either progression of disease or aortic catastrophe. We undertook the current study to determine whether the mechanical properties of the aorta might be able to predict aneurysmal dilatation of the aorta using a clinical database and benchtop mechanical testing of human aortic tissue. MethodsUsing over 400 samples from 31 patients, mechanical properties were studied in (a) normal aorta and then (b) between normal and diseased aorta using linear mixed-effects models. A machine learning technique was used to predict aortic growth rate over time using mechanical properties and baseline clinical characteristics. ResultsHealthy aortic tissue under in vivo loading conditions, after accounting for aortic segment location, had lower longitudinal elastic modulus compared with circumferential elastic modulus: −166.8 kPa (95% confidence interval [CI]: −210.8 to −122.7, P < .001). Fracture toughness was also lower in the longitudinal vs circumferential direction: −201.2 J/m3 (95% CI: −272.9 to −129.5, P < .001). Finally, relative strain was lower in the longitudinal direction compared with the circumferential direction: −0.01 (95% CI: −0.02 to −0.004, P = .002). Patients with diseased aorta, after accounting for segment location and sample direction, had decreased toughness compared with normal aorta, −431.7 J/m3 (95% CI: −628.6 to −234.8, P < .001), and increased relative strain, 0.09 (95% CI: 0.04 to 0.14, P = .003). ConclusionsIncreasing relative strain was identified as a novel independent predictor of aneurysmal degeneration. Noninvasive measurement of relative strain may aid in the identification and monitoring of patients at risk for aneurysmal degeneration. (JVS–Vascular Science 2021;2:235-46.) Clinical RelevanceAortic aneurysm surveillance and prophylactic surgical recommendations are based on computed tomographic angiogram aortic dimensions and growth rate measurements. However, aortic catastrophes may occur at small sizes, confounding current risk stratification models. Herein, we report that increasing aortic relative strain, that is, greater distensibility, is associated with growth over time, thus potentially identifying patients at risk for dissection/rupture.

Research into the Effect of Grain and the Content of Alundum on Tribological Properties and Selected Mechanical Properties of Polymer Composites.

The subject of the research is a polymer composite with a matrix base of epoxy resin L285 cured with H285 hardener, and a physical modifier of friction in the form of alundum. The article presents an analysis of findings of tribological examinations. The authors evaluated the influence of the modifier properties in the form of alundum, i.e., mass share and grain size, on the abrasive wear of a composite, defined as loss of weight as well as on roughness parameters and selected mechanical properties. The tribological examinations have been extended by measurements of hardness and density of the prepared composites. The obtained results of tribological examinations showed an increase in the average value of weight loss in relation to the loss of sample weight loss between the cycles. The influence of both the grain size and the mass percentage share of alundum upon the increase in the longitudinal modulus of elasticity was also observed. On the basis of the obtained results, it was found that alundum of grain sizes equal to F220 and F240 exerted the best influence on the reduction of abrasive wear of the tested samples. In the case of F220, it was 14.04% of the average value of the weight loss between the cycles for all percentage shares of the used grains.

Investigation of nonlinearity of longitudinal displacement function from mechanical and geometric characteristics of the plate

Layered composite materials are characterized by a high transverse anisotropy and low values of relations between the transverse shear modulus and the modulus of longitudinal elasticity. As a result, the behavior of longitudinal displacements and longitudinal normal stresses differs from the linear law, and the behavior of transverse tangential stresses differs from the parabolic law. The paper presents the analysis of the degree of the plate displacement nonlinearity functions depending on its elastic properties and geometric shape. The article considers a 2D square plate deformation problem. In non-dimensional terms, the authors could received a complete and demonstrative solution. A similar 3D problem is more bulky but it has no principle differences. The study of the degree of the longitudinal displacement nonlinearity functions due to elastic properties and the geometric shape of the deformable plate is based on the finite element method. The potential energy of the deformable plate is expressed through a square form of the variables with coefficients that are polynomials of dimensionless parameters such as plate size, ratio of the elasticity and shear moduli, Poisson's modulus. It is shown that the variational principle reduces the problem to the solution of the system of linear equations. As a result, the subareas of linearity and nonlinearity of the plate longitudinal displacements are constructed with an accuracy acceptable for engineering calculations of 5 %. It is necessary to consider the plate nonlinear longitudinal deformations for a length of the composite plate on order more than its thicknesses. As for steel, nonlinearity is characteristic for quite thick plates. The constructed areas of linearity and nonlinearity of the longitudinal displacements make it possible to construct the strain-stress state models with a smaller number of variables.

Concretes with binary mixtures of artificial pozzolans and concrete demolition waste

Abstract The objective of this study is to analyse the use of binary mixtures of pozzolanic materials and concrete demolition waste in concrete mixtures, especially the resulting mechanical properties and durability. A total of ten concrete formulations were produced distinguishing them in different types using different Portland cements, different artificial pozzolans and coarse aggregates from concrete demolition. The particular properties of each formulation were verified by testing the axial compressive strength, longitudinal modulus of elasticity and penetration of chloride under immersion. Substitutions were of 15% w.t. and 30% w.t. natural coarse aggregate substituted with concrete demolition waste and, in the case of binary mixtures, additional 25% w.t. of the binder agglomerate substituted with rice husk ash or fly ash. Results showed that the final strength to axial compression and modulus of elasticity of concrete mixtures were negatively affected by utilising demolition waste, but this effect was balanced by adding supplementary cementitious materials. Regarding the durability test, it was found that the lowest coefficients occurred in the mixtures using CP V-ARI, together with artificial pozzolans, in mixtures with 15% w.t. substitution of natural aggregate with recycled aggregate. It was concluded that using recycled aggregates in concrete is viable but conditioned to the concomitant use of pozzolanic materials.

Influence of geometric elements on the pressure distribution and the state of tension at non-Hertzian wheel-rail contact

In view of the trends of increased traffic speeds, increase axle load, but also the reduction of the losses of material from the wheel and rail due to wear phenomena, the appearance of undulating wear, fractures of the wheel and rail, it is necessary to know the pressure distribution and the state of tension at wheel-rail contact. This can be obtained either by the finite element method (FEM). Using an elastic body modelling, a very rapid FEA model was obtained for solving the pressure distribution at concentrated wheel-rail contact, for real surfaces, modelling absolutely necessary for any study requiring analysis of the state of tension at such a request, for different situations of this interaction, modifying only the input data: geometric model of wheel and rail, longitudinal elasticity modulus, transverse contraction coefficient, load on wheel, etc.

Evaluation of mechanical properties of glass fibers chopped strands mat composite subjected to UV degradation

The paper focuses on the evaluation of physical and mechanical features of ageing glass fibers chopped strands reinforced polymeric composite, denoted MAT300. First, the samples were analyzed with chroma meter in order to determine the coefficients of color change. Then, the control samples were subjected to three points bending since the other samples were exposed to ultraviolet radiation UV-A radiation for 216 hours. After ageing, the color parameters were measured and the bending test was performed in the laboratory of the Department of Mechanical Engineering at the Transylvania University of Braşov, on the LS100 Lloyd's Instruments type test machine. Results showed the characteristic curves of the fibers glass chopped strands MAT samples, the values of the modulus of longitudinal elasticity, the strain and the breaking stress. Also, the color parameters (lightness, greenness and yellowness scale) were measured, both before and after test, in the rupture zone, considering that the sample break is accompanied by the delamination of the fiber and matrix layers.

Research on Improving the Welding Behaviour of Stainless Steels in the Field of Welded Constructions by Using Mechanical Vibrations

Abstract This paper presents a research that has been done on two types of stainless steels, one of Spanish origin and the other of Romanian origin. Both Spanish and Romanian stainless steels have been subjected to several tests, regarding the influence of vibrations on their mechanical properties and their welding behavior. The samples were made of welded stainless steels. They were subjected to a thermal hardening treatment at a temperature of 950 degrees, with a holding time of 4 hours in the presence of mechanical vibrations. Then comparative tests were performed on both stainless steels at: hardness, tensile test, resilience, microstructural analysis and determination of the longitudinal modulus of elasticity. The research has shown a reduction of the thermo-mechanically influenced area, which contributes to the achievement of a high quality welded joints.

NUMERICAL ANALYSIS OF THE INFLUENCE OF TEMPERATURE ON THE FRICTION RESISTANCE OF A METAL-POLYMER SLIDING PAIR

The paper presents numerical calculations of polymer sliding bearings during their operation at low temperatures. Calculations of the frictional moment and the contact area were performed for bearing pans made of PA and PEEK. In the numerical model, the influence of temperature on the mechanical properties (modulus of longitudinal elasticity) and tribological properties (coefficient of friction) were taken into account. The diversified influence of the temperature and thickness of the polymer bearing pans was demonstrated with regards to elements made of different polymer materials. At low temperatures (up to T = -50°C), a different (depending on the used polymer) influence of mechanical and tribological properties on the resistance to motion was found. The ABAQUS calculation package and the finite element method (FEM) were used in the calculations.

Durability of GFRP reinforcing bars in seawater concrete

This paper presents an experimental study that investigated the durability performance of unstressed glass fiber-reinforced polymer (GFRP) bars embedded in concrete mixed with seawater (seawater concrete). GFRP bars were extracted from concrete elements made with two different seawater concrete mix designs and exposed to different environmental conditions for 1, 6, 12, and 24 months. The concrete samples’ exposure environments consisted of typical field conditions of a subtropical region and seawater at 60 °C as an accelerated aging method. The mechanical test results of GFRP bars are reported in residual capacities of tensile strength, longitudinal elastic modulus, transverse shear strength, and apparent horizontal shear strength. Furthermore, the physical evaluations are in terms of glass transition temperature (Tg) and microstructural integrity through scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) analysis. Among all tested properties, tensile strength was the most affected by environmental conditioning. Based on an exponential degradation model, the long-term prediction of the tensile strength capacity was on average 92% under typical field exposure and 72% under the more aggressive conditioning (seawater at 60 °C).

Influence of samarium on some acoustical, physical and radiation shielding characteristics of Bi2O3–ZnO–PbO glasses

Bi2O3–ZnO–PbO glass formulations with various concentrations of samarium oxide Sm2O3 were synthesized using the rapid-quenching route. The deconvoluted FTIR spectra were recorded through the domain of 400–2000 cm−1. System characteristics including density as well as molar volume have been studied. Ultrasonic longitudinal and shear wave velocities and elastic moduli were found to reduce with Sm2O3 concentration. Both bulk compression and Makishima–Mackenzie models were found to diminish with the increase of Sm2O3 and in good harmony with the experimental results. Theoretical radiation shielding properties have been analyzed for the obtained glass system and showed high tendency to be used as radiation protection fabrics for γ rays.

Mechano-chemistry of human femoral diaphysis revealed by correlative Brillouin\u2013Raman microspectroscopy

Brillouin–Raman microspectroscopy is presented as an innovative label-free all-optical investigation approachable to characterize the chemical composition and the mechanical properties of human tissues at micrometric resolution. Brillouin maps unveil mechanical heterogeneities in a human femoral diaphysis, showing a ubiquitous co-existence of hard and soft components, even in the most compact sections. The novel correlative analysis of Brillouin and Raman maps shows that the relative intensity of Brillouin peaks is a good proxy for the fraction of mineralized fibers and that the stiffness (longitudinal elastic modulus) of the hard component is linearly dependent on the hydroxyapatite concentration. For the soft component, a gradient of composition is found, ranging from an abundance of proteins in the more compact, external, bone to abundance of lipids, carotenoids, and heme groups approaching the trabecular, inner, part of the diaphysis. This work unveils the strong potential of correlative mechano-chemical characterization of human tissues at a micrometric resolution for both fundamental and translational research.

Degradation of Mechanical Properties of Pine Wood Under Symmetric Axial Cyclic Loading Parallel to Grain.

The mechanical properties of wood, respectively the elastic, plastic, and strength properties, depend on a large number of factors, due both to its structural and physical characteristics, as well as to the size, direction, nature, and speed of application of forces. Wood, generally considered to be a viscous-elastic material, has creep deformations over time under the effect of a constant load. In this study the behavior of pine wood samples was investigated due to its large utilization in different finished products, such as roof construction, furniture, outdoor applications, garden furniture, and toys. The paper aims to analyze the viscoelastic behavior of pine wood subjected to cyclically loading to traction-compression with different loads (1 kN; 1.5 kN; 2 kN), applied at different speeds (1 mm/min; 10 mm/min). It was observed that, at low speeds (1 mm/min) and low intensities of the applied force, it was possible to distinguish the three creep regions specific to wood: the primary area (primary flow), the secondary area, and finally the tertiary creep. As the force increases, the law of variation of the wood flow changes. The degradation of longitudinal elasticity modulus occurs with the increase of the number of cycles, so after 20 alternating symmetrical cycles of traction-compression of the pine wood samples, there is a decrease of its values by 35%.

Global sensitivity analysis of low-velocity impact response of bio-inspired helicoidal laminates

The preform architectures and the variability of the constituents of carbon fiber reinforced polymer (CFRP) composites materials can affect their mechanical behaviors significantly. This paper describes a systematic analysis of the low-velocity impact response and energy absorption capacity of biomimetic architected CFRP laminates. High-fidelity multiscale Finite Element (FE) models considering constituent material property uncertainties are developed to evaluate the effect of pitch angles on the impact performance of Bouligand architected composite laminates. Experimental results extracted from open literature have been used to validate the low velocity impact response of the CFRPs predicted by the numerical model. Constituent material property uncertainties are identified as parametric variables, and the peak impact load and energy absorption responses of the bio-inspired CFRPs are obtained with the verified numerical models. The main effect sensitivity indices of the parameters are then calculated based on a variance-based global sensitivity analysis model. The presented studies clearly shows that smaller pitch angles and larger fiber longitudinal elastic modulus achieve more desirable impact resistance and better energy-absorption characteristics. This study aim to open up new possibilities for improving low velocity impact performance of CFRP composite laminates by adopting bionic design approach and considering constituent materials effect.

Novel Strategy for Fabricating Multilayer Porous Membranes with Varying Porosity.

CO2-assisted polymer compression (CAPC) is a method for fabricating porous polymer materials in which the polymer is plasticized with CO2 and then pressed. In this work, a two-step molding method is adapted, and a porous membrane with multiple layers of varying porosity is fabricated by laminating sheets of a single starting material. A model is constructed in which the expansion owing to CO2 and compression reflected by the longitudinal elastic modulus are considered. The model is constructed based on a two-layer experiment and extended to three layers. From the model simulation, the conditions for fabricating a multilayer porous polymer membrane with three layers of varying porosity (0.6, 0.5, and 0.4) and identical thickness (0.6 mm) are calculated. Finally, a porous membrane with varying porosity is fabricated based on the simulated design.

Study on the ultrastructure and properties of gelatinous layer in poplar

As a fast-growing commercial wood species, poplar often produces tension wood because of the leaning stems of logs, which has a great impact on the production and utilization. The gelatinous layer (G-layer) was the unique component of tension wood, almost entirely composed of cellulose, which was the main reason for the special performance of the poplar tension wood. This study used the transmission electron microscopy, Raman spectroscopy and nanoindentation to examine the ultrastructure and mechanical properties of every wall layer of the poplar cell wall in order to figure out the ultrastructure and properties of G-layer. In particular, the nanoindentation mapping was combined with manual screening to obtain the mechanical performance data of each layer. The fibers in the tension wood were gelatinous wood fibers with obvious G-layers, and the thickness was 2.53 μm, which was much larger than that of other wall layers. Compared with the wood fiber in the opposite wood, the S1 layer was thicker and the S2 layer was thinner, and the entire cell wall thickness was increased in tension wood. G-layer in tension wood had a very high cellulose content, and the Raman strength of lignin was weak. In general, the micromechanical properties of poplar tension wood were better, which was consistent with its macromechanical properties. The characteristics of G-layer, including high cellulose content, small microfibril angle and high crystallinity, made G-layer own better elastic modulus (14.08 GPa) and hardness (0.45 GPa) than other wall layers in the tension wood. Moreover, G-layer had a high proportion in the tension wood cell wall, so the average longitudinal elastic modulus and hardness of wood fiber cells in the tension wood were also higher than those in the opposite wood.

Overstrength requirements to avoid brittle shear failure in RC slender beams with stirrups

In this paper, an analytical expression was derived for the prediction of shear strength of slender reinforced concrete (RC) beams with stirrups. Failure occurring in B and D regions of the beam was considered. An expression derived for the shear strength of the B region was based on a modified constant angle truss model. The analytical expression derived consisted of three terms. The first one was related to the concrete contribution expressed through the square root of cylindrical compressive strength, geometrical ratio of longitudinal bars, and depth to width ratio. The second one was relating to the shear force induced by yielding of stirrups to the inclination of the main crack occurring at failure; its value depends on the geometrical ratio of longitudinal bars, transverse stirrups, and modulus of elasticity of concrete and steel. Finally, the third term was related to the shear force induced by the flexure of steel bars in the space s, which depends on the number and diameter of longitudinal bars and the yielding stress of longitudinal bars. Failure of the D regions was related to the concrete crushing of loaded joint under the effect of shear force and compressive force, including also the confinement effect due to the presence of stirrups. The original contribution of the paper was the determination of the maximum mechanical ratio of longitudinal and transverse steel to ensure over strength in shear respecting the strength hierarchy.Expressions derived and some of those available in the codes were verified against three different data banks of experimental researches available in the literature. The data banks utilized considered a very wide range of the geometrical ratio of longitudinal bars and transverse stirrups, including, for the latter, very high value producing brittle failure due to concrete crushing.

ОПТИМИЗАЦИЯ СТРУКТУРЫ ПОЛА ПРОМЫШЛЕННОГО ЗДАНИЯ

When determining the design of the floor, choosing materials and technology of its device, it is advisable to apply a systematic approach that takes into account its stress-strain state. The physical model of the floor of an industrial building in a simplified form is represented as a two-layer slab on an elastic base. The physical model of the floor of an industrial building in a simplified form is represented as a two-layer slab on an elastic base. The deformation of the ground base is inherent in the stress-strain state of the structure, which is manifested through geometric and mechanical characteristics, boundary conditions., glass fiber concrete is proposed as a coating material. It provides the compressive strength inherent in concrete and a proper crack resistance. The mathematical model is based on the S. Germain equation and the Winkler dependence. When solving the optimization problem in a linear elastic formulation, the criterion of the minimum potential energy of deformation is used, which leads to a minimum of material consumption. Its effectiveness is confirmed by comparing the results on a variational basis with the analysis of the regression equation. The modulus of longitudinal elasticity and the thickness of the layer are accepted as variable parameters. The calculation procedure uses a finite-difference analog of the mathematical model. A two-factor experiment is conducted to complete the study, the results of which are in good agreement with the theoretical calculations performed.

Study on degradation of macro performances and micro structure of concrete attacked by sulfate under artificial simulated environment

Based on the similarity principle, the similarity criterion of concrete attacked by sulfate corrosion was deduced, and the change laws of concrete sulfate attack under natural condition and artificial simulated environment were revealed. The variations of micro structure, morphology and compositions of concrete before and after sulfate attack were investigated by Environmental Scanning Electron Microscope (ESEM), Mercury Intrusion Porosimetry (MIP), Fourier Infrared Spectrometer (FTIR), Differential Scanning Calorimetry and Thermogravimetric (DTA-TG). The results showed that the artificial simulated environment test method could be used to simulate the real deterioration of concrete under sulfate environment. Moreover, the concrete root rot phenomenon could also be reappeared by artificial simulated environment. The ultimate bearing capacity of concrete specimens attacked by sulfate decreased with erosion age. The transverse and longitudinal dynamic modulus of elasticity of concrete first increased and then decreased with erosion age. The changes of the micro structure, compositions and morphology of concrete were caused by the generation of expansive substances and decomposition of hydration products. The numerical simulation indicated that the optimal accelerated ratio of concrete sulfate attack between natural condition and artificial simulated environment was about 50.

Detecting Mechanical Anisotropy of the Cornea Using Brillouin Microscopy.

PurposeThe purpose of this study was to detect the mechanical anisotropy of the cornea using Brillouin microscopy along different perturbation directions.MethodsBrillouin frequency shift of both whole globes (n = 10) and cornea punches (n = 10) were measured at different angles to the incident laser, thereby probing corneal longitudinal modulus of elasticity along different directions. Frequency shift of virgin (n = 26) versus cross-linked corneas (n = 15) over a large range of hydration conditions were compared in order to differentiate the contributions to Brillouin shift due to hydration from those due to stromal tissue.ResultsWe detected mechanical anisotropy of corneas, with an average frequency shift increase of 53 MHz and 96 MHz when the instrument probed from 0° to 15° and 30° along the direction of the stromal fibers. Brillouin microscopy did not lose sensitivity to mechanical anisotropy up to 96% water content. We experimentally measured and theoretically modeled how mechanical changes independent of hydration affect frequency shift as a result of corneal cross-linking by isolating an approximately 100 MHz increase in frequency shift following a cross-linking procedure purely due to changes of stromal tissue mechanics.ConclusionsBrillouin microscopy is sensitive to mechanical anisotropy of the stroma even in highly hydrated corneas. The agreement between model and experimental data suggested a quantitative relationship between Brillouin frequency shift, hydration state of the cornea, and stromal tissue stiffness.Translational RelevanceThe protocol and model validated throughout this study offer a path for comprehensive measurements of corneal mechanics within the clinic; allowing for improved evaluation of the long-term mechanical efficacy of cross-linking procedures.

Mechanical and Rheological Behaviour of Composites Reinforced with Natural Fibres.

The paper deals with the mechanical behaviour of natural fibre composites subjected to tensile test and dynamic mechanical analysis (DMA). Three types of natural fibre composites were prepared and tested: wood particle reinforced composites with six different sizes of grains (WPC); hemp mat reinforced composites (HMP) and flax reinforced composite with mixed wood particles (FWPC). The tensile test performed on universal testing machine LS100 Lloyd’s Instrument highlights the elastic properties of the samples, as longitudinal elasticity modulus; tensile rupture; strain at break; and stiffness. The large dispersion of stress–strain curves was noticed in the case of HMP and FWPC by comparison to WPC samples which present high homogeneity of elastic–plastic behaviour. The DMA test emphasized the rheological behaviour of natural fibre composites in terms of energy dissipation of a material under cyclic load. Cole–Cole plots revealed the connection between stored and loss heat energy for studied samples. The mixture of wood particles with a polyester matrix leads to relative homogeneity of composite in comparison with FWPC and HMP samples which is visible from the shape of Cole–Cole curves. The random fibres from the hemp mat structure lead to a heterogeneous nature of composite structure. The elastic and viscous responses of samples depend on the interface between fibres and matrix.