Mechanical Assessment and Hyper-elastic Modeling of Polyurethanes for the Early Design of Vascular Graft

The lack of suitable autologous grafts and poor compliance of existing prostheses have prompted the study of novel materials for vascular graft design. Polyurethanes (PUs) were used in the past because they have high compliance and properties that are similar to those of native tissue. In this work, the mechanical properties of a group of PUs in two states (non-hydrated and hydrated) were studied using uniaxial tensile tests, strain sweep tests, and multi-step creep recovery tests. Additionally, a hyper-elastic model based on the Mooney–Rivlin strain density function was fitted and used to model the performances of the PUs under physiological pressure and geometry conditions. The tensile tests revealed a softening phenomenon after hydration, which could potentially reduce patient discomfort and risk of vascular trauma. The ultimate strength values after hydration were similar to those reported for other vascular conduits. The strain sweep showed a strong strain dependency of the modulus indicating non-linear viscoelasticity. In the creep-recovery tests, increasing the polyethylene glycol(PEG) content enhanced the viscous flow, while the elastic behavior was enhanced with the largest concentration of polycaprolactone diol (PCL). On the other hand, under simulated physiological conditions, the compliance of the PUs showed a cyclic behavior with the time and pressure but was not affected by the radii and thickness variation, which could increase the graft compliance and geometry mismatch. Nevertheless, the compliance could be tuned using the material composition. This paper studied the biomechanics of a group of materials under simulated physiological conditions (Temperature, hydration, and pressure) to select those that could perform better for further vascular graft design.

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Mechanical Assessment and Hyperelastic Modeling of Polyurethanes for the Early Stages of Vascular Graft Design

Materials ◽

10.3390/ma13214973 ◽

2020 ◽

Vol 13 (21) ◽

pp. 4973

Author(s):

Arévalo-Alquichire Said ◽

Dominguez-paz Carlos ◽

Valero Manuel F.

Keyword(s):

Polyethylene Glycol ◽

Ultimate Strength ◽

Vascular Grafts ◽

Material Design ◽

The Body ◽

Cyclic Behavior ◽

Elastic Behavior ◽

Uniaxial Tensile ◽

Creep Recovery ◽

Physiological Conditions

The material design of vascular grafts is required for their application in the health sector. The use of polyurethanes (PUs) in vascular grafts intended for application in the body appears to be adequate due to the fact that native tissues have similar properties as PUs. However, the influence of chemical structure on the biomechanics of PUs remains poorly described. The use of constitutive models, together with numerical studies, is a powerful tool for evaluating the mechanical behavior of materials under specific physiological conditions. Therefore, the aim of this study was to assess the mechanical properties of different PU mixtures formed by polycaprolactone diol, polyethylene glycol, and pentaerythritol using uniaxial tensile, strain sweep, and multistep creep-recovery tests. Evaluations of the properties were also recorded after samples had been soaked in phosphate-buffer saline (PBS) to simulate physiological conditions. A hyperelastic model based on the Mooney–Rivlin strain density function was employed to model the performance of PUs under physiological pressure and geometry conditions. The results show that the inclusion of polyethylene glycol enhanced viscous flow, while polycaprolactone diol increased the elastic behavior. Furthermore, tensile tests revealed that hydration had an important effect on the softening phenomenon. Additionally, after the hydration of PUs, the ultimate strength was similar to those reported for other vascular conduits. Lastly, hyperelastic models revealed that the compliance of the PUs showed a cyclic behavior within the tested time and pressure conditions and is affected by the material composition. However, the compliance was not affected by the geometry of the materials. These tests demonstrate that the materials whose compositions are 5–90–5 and 46.3–46.3–7.5 could be employed in the designs of vascular grafts for medical applications since they present the largest value of compliance, ultimate strength, and elongation at break in the range of reported blood vessels, thus indicating their suitability. Moreover, the polyurethanes were revealed to undergo softening after hydration, which could reduce the risk of vascular trauma.

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Texture Selection Mechanisms during Recrystallization and Grain Growth of a Magnesium-Erbium-Zinc Alloy

Metals ◽

10.3390/met11010171 ◽

2021 ◽

Vol 11 (1) ◽

pp. 171

Author(s):

Fatim-Zahra Mouhib ◽

Fengyang Sheng ◽

Ramandeep Mandia ◽

Risheng Pei ◽

Sandra Korte-Kerzel ◽

...

Keyword(s):

Grain Growth ◽

Ternary Alloy ◽

Solute Drag ◽

Tensile Tests ◽

Electron Back Scatter Diffraction ◽

Zinc Alloy ◽

Uniaxial Tensile ◽

Microstructural Stability ◽

Solid Solution Strengthening ◽

Zener Drag

Binary and ternary Mg-1%Er/Mg-1%Er-1%Zn alloys were rolled and subsequently subjected to various heat treatments to study texture selection during recrystallization and following grain growth. The results revealed favorable texture alterations in both alloys and the formation of a unique ±40° transvers direction (TD) recrystallization texture in the ternary alloy. While the binary alloy underwent a continuous alteration of its texture and grain size throughout recrystallization and grain growth, the ternary alloy showed a rapid rolling (RD) to transvers direction (TD) texture transition occurring during early stages of recrystallization. Targeted electron back scatter diffraction (EBSD) analysis of the recrystallized fraction unraveled a selective growth behavior of recrystallization nuclei with TD tilted orientations that is likely attributed to solute drag effect on the mobility of specific grain boundaries. Mg-1%Er-1%Zn additionally exhibited a stunning microstructural stability during grain growth annealing. This was attributed to a fine dispersion of dense nanosized particles in the matrix that impeded grain growth by Zener drag. The mechanical properties of both alloys were determined by uniaxial tensile tests combined with EBSD assisted slip trace analysis at 5% tensile strain to investigate non-basal slip behavior. Owing to synergic alloying effects on solid solution strengthening and slip activation, as well as precipitation hardening, the ternary Mg-1%Er-1%Zn alloy demonstrated a remarkable enhancement in the yield strength, strain hardening capability, and failure ductility, compared with the Mg-1%Er alloy.

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Comprehensive study on mechanical properties of coated biaxial warp-knitted fabrics

Journal of Reinforced Plastics and Composites ◽

10.1177/07316844211020499 ◽

2021 ◽

pp. 073168442110204

Author(s):

Bin Yang ◽

Yingying Shang ◽

Zeliang Yu ◽

Minger Wu ◽

Youji Tao ◽

...

Keyword(s):

Mechanical Properties ◽

Failure Modes ◽

Least Squares Method ◽

Tensile Tests ◽

Tensile Creep ◽

Base Layer ◽

Sustained Load ◽

Uniaxial Tensile ◽

Membrane Structures ◽

Knitted Fabrics

In recent years, coated fabrics have become the major material used in membrane structures. Due to the special structure of base layer and mechanical properties, coated biaxial warp-knitted fabrics are increasingly applied in pneumatic structures. In this article, the mechanical properties of coated biaxial warp-knitted fabrics are investigated comprehensively. First, off-axial tensile tests are carried out in seven in-plane directions: 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Based on the stress–strain relationship, tensile strengths are obtained and failure modes are studied. The adaptability of Tsai–Hill criterion is analyzed. Then, the uniaxial tensile creep test is performed under 24-h sustained load and the creep elongation is calculated. Besides, tearing strengths in warp and weft directions are obtained by tearing tests. Finally, the biaxial tensile tests under five different load ratios of 1:1, 2:1, 1:2, 1:0, and 0:1 are carried out, and the elastic constants and Poisson’s ratio are calculated using the least squares method based on linear orthotropic assumption. Moreover, biaxial specimens under four load ratios of 3:1, 1:3, 5:1, and 1:5 are further tensile tested to verify the adaptability of linear orthotropic model. These experimental data offer a deeper and comprehensive understanding of mechanical properties of coated biaxial warp-knitted fabrics and could be conveniently adopted in structural design.

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A Flow Stress Model of 300M Steel for Isothermal Tension

Materials ◽

10.3390/ma14020252 ◽

2021 ◽

Vol 14 (2) ◽

pp. 252

Author(s):

Rongchuang Chen ◽

Shiyang Zhang ◽

Xianlong Liu ◽

Fei Feng

Keyword(s):

Flow Stress ◽

Constitutive Model ◽

Tensile Deformation ◽

Flow Behavior ◽

Tensile Tests ◽

Uniaxial Tensile ◽

Model Parameters ◽

Average Deviation ◽

Cross Sectional ◽

300M Steel

To investigate the effect of hot working parameters on the flow behavior of 300M steel under tension, hot uniaxial tensile tests were implemented under different temperatures (950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C) and strain rates (0.01 s−1, 0.1 s−1, 1 s−1, 10 s−1). Compared with uniaxial compression, the tensile flow stress was 29.1% higher because dynamic recrystallization softening was less sufficient in the tensile stress state. The ultimate elongation of 300M steel increased with the decrease of temperature and the increase of strain rate. To eliminate the influence of sample necking on stress-strain relationship, both the stress and the strain were calibrated using the cross-sectional area of the neck zone. A constitutive model for tensile deformation was established based on the modified Arrhenius model, in which the model parameters (n, α, Q, ln(A)) were described as a function of strain. The average deviation was 6.81 MPa (6.23%), showing good accuracy of the constitutive model.

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Experimental Investigation of Ti-6Al-4V with a Biaxial Tensile Test Setup at Elevated Temperature

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.622-623.273 ◽

2014 ◽

Vol 622-623 ◽

pp. 273-278 ◽

Cited By ~ 1

Author(s):

Marion Merklein ◽

Sebastian Suttner ◽

Adam Schaub

Keyword(s):

Elevated Temperature ◽

Elevated Temperatures ◽

Tensile Tests ◽

Advanced Materials ◽

Uniaxial Tensile ◽

Plastic Yielding ◽

Characterization Methods ◽

Specific Strength ◽

Biaxial Tensile ◽

Stress States

The requirement for products to reduce weight while maintaining strength is a major challenge to the development of new advanced materials. Especially in the field of human medicine or aviation and aeronautics new materials are needed to satisfy increasing demands. Therefore the titanium alloy Ti-6Al-4V with its high specific strength and an outstanding corrosion resistance is used for high and reliable performance in sheet metal forming processes as well as in medical applications. Due to a meaningful and accurate numerical process design and to improve the prediction accuracy of the numerical model, advanced material characterization methods are required. To expand the formability and to skillfully use the advantage of Ti-6Al-4V, forming processes are performed at elevated temperatures. Thus the investigation of plastic yielding at different stress states and at an elevated temperature of 400°C is presented in this paper. For this reason biaxial tensile tests with a cruciform shaped specimen are realized at 400°C in addition to uniaxial tensile tests. Moreover the beginning of plastic yielding is analyzed in the first quadrant of the stress space with regard to complex material modeling.

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Effect of Polyvinyl Alcohol Concentration on the Mechanical Properties of Collagen/Polyvinyl Alcohol Blends

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.732.161 ◽

2015 ◽

Vol 732 ◽

pp. 161-164 ◽

Cited By ~ 5

Author(s):

Jan Vesely ◽

Lukas Horny ◽

Hynek Chlup ◽

Milos Beran ◽

Milan Krajicek ◽

...

Keyword(s):

Mechanical Properties ◽

Tensile Stress ◽

Polyvinyl Alcohol ◽

Modulus Of Elasticity ◽

Tensile Tests ◽

Ultimate Tensile Stress ◽

Alcohol Concentration ◽

Uniaxial Tensile ◽

Initial Modulus ◽

Water Saturated

The effects of the polyvinyl alcohol (PVA) concentration on mechanical properties of hydrogels based on blends of native or denatured collagen / PVA were examined. Blends of PVA with collagen were obtained by mixing the solutions in different ratios, using glycerol as a plasticizer. The solutions were cast on polystyrene plates and the solvent was allowed to evaporate at room temperature. Uniaxial tensile tests were performed in order to obtain the initial modulus of elasticity (up to deformation 0.1), the ultimate tensile stress and the deformation at failure of the material in the water-saturated hydrogel form. It was found that the material was elastic and the addition of PVA helped to enhance both the ultimate tensile stress and modulus of elasticity of the films. Samples prepared from denaturated collagen showed the higher ultimate tensile stress and the deformation at failure in comparison with those prepared from native collagen. The results suggest that we could expect successful application of the collagen/PVA biomaterial for tissue engineering.

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Mechanical properties of PVDF-coated fabric under tensile tests

Journal of Polymer Engineering ◽

10.1515/polyeng-2014-0087 ◽

2015 ◽

Vol 35 (4) ◽

pp. 377-390 ◽

Cited By ~ 11

Author(s):

Andrzej Ambroziak

Keyword(s):

Mechanical Properties ◽

Polyvinylidene Fluoride ◽

Cyclic Load ◽

Tensile Tests ◽

Woven Fabrics ◽

Uniaxial Tensile ◽

Cyclic Tests ◽

Comprehensive Investigation ◽

Coated Fabric ◽

Coated Fabrics

Abstract This article describes the laboratory tests necessary to identify the mechanical properties of the polyvinylidene fluoride (PVDF)-coated fabrics named Precontraint 1202S and Precontraint 1302S. First, a short survey of the literature concerning the description of coated woven fabrics is presented. Second, the material parameters for PVDF-coated fabrics are specified on the basis of biaxial tensile tests. A comparison of the 1:1 biaxial and the uniaxial tensile tests results is also given. Additionally, biaxial cyclic tests were performed to observe the change of immediate mechanical properties under cyclic load. The article is aimed as an introduction to a comprehensive investigation of the mechanical properties of coated fabrics.

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Correlation among Microstructure, Texture, and Properties along the Thickness Direction in As-Hot-Rolled and As-Solution-Quenched Al7055 Thick Plates

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1026.65 ◽

2021 ◽

Vol 1026 ◽

pp. 65-73

Author(s):

Kai Zhu ◽

Hong Wei Yan

Keyword(s):

Mechanical Properties ◽

Yield Strength ◽

Tensile Tests ◽

Rolled Plate ◽

Uniaxial Tensile ◽

Thickness Direction ◽

Electron Backscattered Diffraction ◽

Thick Plates ◽

Aluminum Plates ◽

Hot Rolled

Both microstructure inhomogeneity and mechanical property diversity along the thickness direction in rolled thick aluminum plates have been considered to have a remarkable impact on the performance and properties of the products made from the plates. In this study, scanning electron microscopy (SEM) and electron backscattered diﬀraction (EBSD) characterizations of microstructure and texture types along the thickness directions of Al7055 thick plate specimens prepared using two conditions, hot-rolling and solution-quenching, were performed. To examine the mechanical properties, uniaxial tensile tests were also carried out on specimens machined from both types of thick plates, using a layered strategy along the thickness direction. The results indicate that both the microstructure and mechanical properties are inhomogeneous under the two conditions. Furthermore, it is evident that there is a hereditary relationship between the mechanical properties of the two plates—areas with higher yield strength in the as-hot-rolled plate correspond to areas with the higher yield strength in the as-solution-quenched plate

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