scholarly journals Experimental investigations of the human oesophagus: anisotropic properties of the muscular layer in large deformation

2021 ◽  
Author(s):  
Ciara Durcan ◽  
Mokarram Hossain ◽  
Gregory Chagnon ◽  
Djordje Peric ◽  
Lara Bsiesy ◽  
...  
Keyword(s):  
Strain Rate ◽  
Ex Vivo ◽  
Longitudinal Direction ◽  
Tensile Tests ◽  
Endoscopic Biopsy ◽  
Circumferential Direction ◽  
Experimental Investigations ◽  
Uniaxial Tensile ◽  
Rate Dependency ◽  
Muscular Layer

Technological advancements in the field of robotics have led to endoscopic biopsy devices able to extract diseased tissue from between the layers of the gastrointestinal tract. Despite this, the layer-dependent properties of these tissues have yet to be mechanically characterised using human tissue. In this study, the ex vivo mechanical properties of the passive muscularis propia layer of the human oesophagus were extensively investigated. For this, a series of uniaxial tensile tests were conducted. The results displayed hyperelastic behaviour, while the differences between loading the tissue in both the longitudinal and circumferential directions showcased its anisotropy. The anisotropy of the muscular layer was present at different strain rates, with the longitudinal direction being consistently stiffer than the circumferential one. The circumferential direction was found to have little strain-rate dependency, while the longitudinal direction results suggest pronounced strain-rate-dependent behaviour. The repeated trials showed larger variation in terms of stress for a given strain in the longitudinal direction compared to the circumferential direction. The possible causes of variation between trials are discussed, and the experimental findings are linked to the histological analysis which was carried out via various staining methods. Finally, the direction-dependent experimental data was simulated using an anisotropic, hyperelastic model.

scholarly journals Anisotropic mechanical behaviour of calendered nonwoven fabrics: Strain-rate dependency

2020 ◽  
pp. 002199832097679
Author(s):  
V Cucumazzo ◽  
E Demirci ◽  
B Pourdeyhimi ◽  
VV Silberschmidt
Keyword(s):  
Strain Rate ◽  
Mechanical Behaviour ◽  
Mechanical Response ◽  
Tensile Tests ◽  
Elastic Response ◽  
Uniaxial Tensile ◽  
Rate Dependency ◽  
Fibrous Matrix ◽  
Nonwoven Fabrics ◽  
Linear Elastic

Calendered nonwovens, formed by polymeric fibres, are three-phase heterogeneous materials, comprising a fibrous matrix, bond-areas and interface regions. As a result, two main factors of anisotropy can be identified. The first one is ascribable to a random fibrous microstructure, with the second one related to orientation of a bond pattern. This paper focuses on the first type of anisotropy in thin and thick nonwovens under uniaxial tensile loading. Individual and combined effects of anisotropy and strain rate were studied by conducting uniaxial tensile tests in various loading directions (0°, 30°, 45°, 60° and 90° with regard to the main fabric’s direction) and strain rate (0.01, 0.1 and 0.5 s−1). Fabrics exhibited an initial linear elastic response, followed by nonlinear strain hardening up to necking and final softening. The studied allowed assessment of the extent the effects of loading direction (anisotropy), planar density and strain rate on the mechanical response of the calendered fabrics. The evidence supported the conclusion that anisotropy is the most crucial factor, also delineating the balance between the fabric’s load-bearing capacity and extension level along various directions. The strain rate produced a marked effect on the fibre’s response, with increased stress at higher strain rate while this effect in the fabric was small. The results demonstrated the differences of the mechanical behaviour of fabrics from that of their constituent fibres.

Experimental and Numerical Investigations on Hot Deformation Behavior and Processing Maps for ASS 304 and ASS 316

2018 ◽  
Vol 37 (9-10) ◽  
pp. 873-888 ◽  
Author(s):  
Nitin Kotkunde ◽  
Hansoge Nitin Krishnamurthy ◽  
Swadesh Kumar Singh ◽  
Gangadhar Jella
Keyword(s):  
Experimental Data ◽  
Strain Rate ◽  
Hot Deformation ◽  
Deformation Behavior ◽  
Constitutive Models ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Processing Maps ◽  
Hot Deformation Behavior ◽  
Statistical Measures

AbstractA thorough understanding of hot deformation behavior plays a vital role in determining process parameters of hot working processes. Firstly, uniaxial tensile tests have been performed in the temperature ranges of 150 °C–600 °C and strain rate ranges of 0.0001–0.01s−1 for analyzing the deformation behavior of ASS 304 and ASS 316. The phenomenological-based constitutive models namely modified Fields–Backofen (m-FB) and Khan–Huang–Liang (KHL) have been developed. The prediction capability of these models has been verified with experimental data using various statistical measures. Analysis of statistical measures revealed KHL model has good agreement with experimental flow stress data. Through the flow stresses behavior, the processing maps are established and analyzed according to the dynamic materials model (DMM). In the processing map, the variation of the efficiency of the power dissipation is plotted as a function of temperature and strain rate. The processing maps results have been validated with experimental data.

Superplasticity and Microstructure Evolution of Electrodeposited Nanocrystalline Nickel

2007 ◽  
Vol 551-552 ◽  
pp. 539-544 ◽  
Author(s):  
S. Ding ◽  
Kai Feng Zhang ◽  
Guo Feng Wang
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Room Temperature ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Intergranular Cracking ◽  
Mean Grain Size ◽  
Electrodeposited Nickel ◽  
Superplastic Properties

Nanocrystalline pure nickel (nc-Ni) was produced by pulse electrodeposition and its superplastic properties at and above room temperature were investigated. The electrodeposited nickel has a narrow grain size distribution with a mean grain size of 70nm. Uniaxial tensile tests at room temperature showed that nc-Ni has a limited plasticity but high tensile strength up to 1GPa at strain rates between 10-5 and 10-2s-1. However, when the temperature increased to 420 and higher, test specimens showed uniform deformation and the elongation value was larger than 200%. A maximum elongation value of 380% was observed at 450°C and a strain rate of 1.67x10-3s-1, SEM and TEM were used to examine the microstructures of the as-deposited and deformed specimens. The results indicated that fracture was caused by intergranular cracking and most cracks were originated from the brittle oxide formed during the tensile test. Grain coarsening was observed in the deformed specimen. The role of temperature and strain on grain growth was evaluated by comparing the microstructure of deformed samples with that of samples statically annealed. Deformation mechanism was discussed based upon the deformed microstructure and strain rate jump tests.

Effect of Strain Rate on the Deformation-Induced Martensite Transformation and Mechanical Behavior of Austenitic Stainless Steels for Cold Stretched Pressure Vessels

2010 ◽  
Author(s):  
Cunjian Miao ◽  
Yaxian Li ◽  
Jinyang Zheng
Keyword(s):  
Stainless Steel ◽  
Strain Rate ◽  
Martensite Transformation ◽  
Magnetic Measurement ◽  
Austenitic Stainless Steels ◽  
Tensile Tests ◽  
Pressure Vessels ◽  
Uniaxial Tensile ◽  
Work Hardening Rate ◽  
Proof Strength

Cold stretching (pressure strenghtening) technique has been widely used in austenitic stainless steel pressure vessels in order to increase the proof strength and lighten the weight of the vessels. Cold stretching technique is performed by applying the strengthening pressure under a specified strain rate. Plastic deformation in the process will lead to martensite transformation and may influence material’s strength and ductility. Cold stretching tests of EN 1.4301 stainless steel are carried out at different quasi-static strain rates of 10−3 and 10−5/s, following the uniaxial tensile tests at the same strain rate of 2.5×10−3/s. The α′-martensite transformation is detected by magnetic measurement, meanwhile the work-hardening rate, the flow stress and the mechanical properties of material are studied and the results are presented.

scholarly journals Molecular Dynamics Simulation Study of the Mechanical Properties of Nanocrystalline Body-Centered Cubic Iron

Surfaces ◽  
2020 ◽  
Vol 3 (3) ◽  
pp. 381-391
Author(s):  
Jan Herman ◽  
Marko Govednik ◽  
Sandeep P. Patil ◽  
Bernd Markert
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Strain Rate ◽  
Tensile Tests ◽  
Dynamics Simulation ◽  
Uniaxial Tensile ◽  
Body Centered Cubic ◽  
Bcc Iron ◽  
Average Grain Size ◽  
Study Results

In the present work, the mechanical properties of nanocrystalline body-centered cubic (BCC) iron with an average grain size of 10 Å were investigated using molecular dynamics (MD) simulations. The structure has one layer of crystal grains, which means such a model could represent a structure with directional crystallization. A series of uniaxial tensile tests with different strain rates and temperatures was performed until the full rupture of the model. Moreover, tensile tests of the models with a void at the center and shear tests were carried out. In the tensile test simulations, peak stress and average values of flow stress increase with strain rate. However, the strain rate does not affect the elasticity modulus. Due to the presence of void, stress concentrations in structure have been observed, which leads to dislocation pile-up and grain boundary slips at lower strains. Furthermore, the model with the void reaches lower values of peak stresses as well as stress overshoot compared to the no void model. The study results provide a better understanding of the mechanical response of nanocrystalline BCC iron under various loadings.

scholarly journals Strain Rate-Dependent Constitutive and Low Stress Triaxiality Fracture Behavior Investigation of 6005 Al Alloy

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Yong Peng ◽  
Xuanzhen Chen ◽  
Shan Peng ◽  
Chao Chen ◽  
Jiahao Li ◽  
...  
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Fracture Behavior ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
Stress States

In order to study the dynamic and fracture behavior of 6005 aluminum alloy at different strain rates and stress states, various tests (tensile tests at different strain rates and tensile shearing tests at five stress states) are conducted by Mechanical Testing and Simulation (MTS) and split-Hopkinson tension bar (SHTB). Numerical simulations based on the finite element method (FEM) are performed with ABAQUS/Standard to obtain the actual stress triaxialities and equivalent plastic strain to fracture. The results of tensile tests for 6005 Al show obvious rate dependence on strain rates. The results obtained from simulations indicate the feature of nonmonotonicity between the strain to fracture and stress triaxiality. The equivalent plastic strain reduces to a minimum value and then increases in the stress triaxiality range from 0.04 to 0.30. A simplified Johnson-Cook (JC) constitutive model is proposed to depict the relationship between the flow stress and strain rate. What is more, the strain-rate factor is modified using a quadratic polynomial regression model, in which it is considered to vary with the strain and strain rates. A fracture criterion is also proposed in a low stress triaxiality range from 0.04 to 0.369. Error analysis for the modified JC model indicates that the model exhibits higher accuracy than the original one in predicting the flow stress at different strain rates. The fractography analysis indicates that the material has a typical ductile fracture mechanism including the shear fracture under pure shear and the dimple fracture under uniaxial tensile.

Experimental Investigations and Finite-Element Modeling of Thermoplastic Effect during Tensile Tests of Metal Material

2013 ◽  
Vol 634-638 ◽  
pp. 2835-2838
Author(s):  
Wei Qing Wang ◽  
Li Yang ◽  
Shi Gui Lv
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Temperature Field ◽  
Surface Temperature ◽  
Strain Rate ◽  
Numerical Procedure ◽  
Infrared Camera ◽  
Tensile Tests ◽  
Experimental Investigations ◽  
Finite Element Software

During plastic deformation of materials, part of the plastic work is converted into heat, and the temperature field will be changed, this phenomenon is well known as thermoplastic effect. Based on the analysis of thermoplastic effect, the surface temperature of Q235 steel during quasi-static tensile tests was measured by using an infrared camera, and the surface temperature field and it versus time for different strain rate were obtained. A numerical procedure was devised to model the thermoplastic effect during the tensile tests by using ANSYS software. The results showed that, the heat loss during deformation process will be smaller as the strain rate increase, and the temperature increase on the specimen surface generated by the plastic deformation will be higher. The simulation results matched well with the experiment results showed that it was a good way to analyse the thermoplastic effect by the commercial finite element software.

scholarly journals Effect of loading rate on tensile and fracture behavior of AA2050-T84 alloy at high temperature

2021 ◽  
Vol 2070 (1) ◽  
pp. 012163
Author(s):  
Nagaraj Ekabote ◽  
Krishnaraja G Kodancha
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Tensile Tests ◽  
Rate Variation ◽  
Strain Rates ◽  
Rate Dependency ◽  
Commercial Aircraft ◽  
Fracture Failure ◽  
Load Rate ◽  
Increased Susceptibility

Abstract AA2050-T84 alloy is commonly used in the fabrication of modern commercial aircraft wing parts. Load and temperature variation during aircraft take-off, flight, and landing at different environmental conditions is substantial. Mechanical properties variation of AA2050-T84 alloy at sub-zero and room temperatures are significant and well documented in the literature. In the present work, at a high temperature of 200°C, the effect of load rate variation on tensile and fracture properties of AA2050-T84 alloy are experimentally and numerically studied. The load rates represented in strain rates were applied at 0.01, 0.1, and 1s−1. Experimental tensile tests exhibited the positive strain rate dependency on the yield and ultimate strength of the alloy. 2D numerical elastic-plastic fracture analysis was carried out using Abaqus 6.14. Similar to tensile results, the fracture parameters dependency on strain rates was witnessed. Overall, higher strain rate causes the increased susceptibility of fracture failure with the increase in yield stress of the material.

Constitutive Modeling of the Rate-Dependent Behavior of Ti-6Al-4V Using an Arrhenius-Type Law

2012 ◽  
Vol 591-593 ◽  
pp. 949-954
Author(s):  
Jun Jie Xiao ◽  
Dong Sheng Li ◽  
Xiao Qiang Li ◽  
Chao Hai Jin ◽  
Chao Zhang
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Tensile Tests ◽  
Alloy Sheet ◽  
Uniaxial Tensile ◽  
Thin Wall ◽  
Rate Dependent ◽  
Hot Environment ◽  
Dependent Behavior ◽  
Element Simulation

Uniaxial tensile tests were performed on a Ti-6Al-4V alloy sheet over the temperature range of 923K-1023K with the strain rates of 5×10-4s-1-5×10-2s-1 up to a 25% length elongation of the specimen. The true stress-strain curves reveal that the flow stress decreases with the increase of the temperature and the decrease of the strain rate. In the same process, the accompanying softening role increases. It is found that the Ti-6Al-4V shows the features of non-linearity, temperature sensitivity and strain rate dependence in hot environment. Finally, an Arrhenius-type law has been established to predict the experimental data and the prediction precision was verified by the plotting of parameter and flow stress, which revealed that the error of stress exponent was only 4.99%. This indicates the flow stress model has high precision and can be used for the process design and the finite element simulation of hot forming thin-wall Ti-6Al-4V alloy components.

scholarly journals Biomechanical Properties of Human Dilated Ascending Aorta

2019 ◽  
Vol 73 (2) ◽  
pp. 107-111
Author(s):  
Ivars Brečs ◽  
Pēteris Stradiņš ◽  
Mārtiņš Kalējs ◽  
Uldis Strazdiņš ◽  
Iveta Ozolanta ◽  
...  
Keyword(s):  
Modulus Of Elasticity ◽  
Linear Part ◽  
Longitudinal Direction ◽  
Biomechanical Properties ◽  
Ascending Aorta ◽  
Circumferential Direction ◽  
Human Aorta ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Tangential Modulus

Abstract Aneurysms of ascending aorta are dilatation of the first part of the human aorta. They commonly show no clinical symptoms. This condition increases the risk of aorta dissection, which is a life-threatening condition. In this study we attempted to elucidate the changes in the biomechanical properties that occur in the dilated human ascending aorta. Fourteen specimens of ascending aorta wall were mechanically tested under a uniaxial tensile test. Two specimens from each ascending aorta anterior region were cut in longitudinal and circumferential directions. The samples were stretched until rupture of the sample occurred. The obtained experimental data were processed to determine maximal stress, maximal strain and the tangential modulus of elasticity in the linear part of the stress-strain curve. The obtained results showed a remarkable anisotropy of the ascending aorta tissue. We found higher strength of the tissue in the circumferential direction than in the longitudinal direction. There were no statistically significant differences between the strains of the samples. Tangential modulus of elasticity of the aortic samples in the longitudinal direction was significantly lower than the elastic modulus of the samples in the circumferential direction. The tissue in the circumferential direction is stronger and stiffer than in the longitudinal direction.

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