Uniaxial Tensile Stress Research Articles

Multi-scale numerical simulation of fracture behavior for the gadolinia-doped ceria (GDC) under mechano-electrochemical coupling fields at high temperature

The fracture toughness of gadolinia-doped ceria (GDC) solid oxide fuel cells (SOFCs) electrolyte with a central crack is significantly reduced under the mechano-electrochemical coupling fields at high temperature. In this work, an atom-to-continuum (AtC) multi-scale method combining the finite element method (FEM) and the molecular dynamics (MD) simulation is developed. Firstly, the AtC multi-scale method is validated by investigating the uniaxial tensile stress–strain curves of GDC with a central crack at different temperatures. Then, based on the theory of fracture mechanics, the macrostructure of GDC is transformed into a microscopic intermediate transition model, and a detailed computational procedure for analyzing the fracture toughness of the macrostructure of the GDC is given by the AtC multi-scale method. Finally, the fracture toughness of GDC macrostructure under the mechano-electrochemical coupling fields is studied by the proposed approach. The simulation results show that the fracture toughness of 10GDC and 20GDC under the mechano-electrochemical coupling fields is clearly reduced compared to the uniaxial tensile loading. Among them, the fracture toughness of 10GDC under the mechano-electrochemical coupling fields is decreased by 12.28% and 30.67% at 800℃ and 900℃, and the fracture toughness of 20GDC under the mechano-electrochemical coupling fields is decreased by 17.25% and 29.52% at 800℃ and 900℃. These findings are critical in predicting the fracture behavior of GDC electrolyte under real working conditions.

Numerical investigation of the Poisson's ratio of amorphous graphene sheets

AbstractThe one‐atom‐thick allotrope of graphite, C4 is called monolayer graphene and was discovered in 2004. It is well known for its fantastic electro‐mechanical properties. While transverse contraction and Poisson's ratio were previously studied only for homogeneous or crystalline two‐dimensional (2D) mono‐ and bilayer network structures under uniaxial tensile stress, we now numerically investigate these material properties for amorphous or non‐crystalline monolayer graphene. Here, we pay special attention to the influence of the network heterogeneity. We find the stress‐strain correlation in good agreement with the literature, and we find auxetic behavior, that is, negative Poisson's ratio, over a wide range within the elastic regime.

A Coupled Nonlinear Viscoelastic–Viscoplastic Thermomechanical Model for Polymeric Lithium-Ion Battery Separators

One of the major concerns in ensuring lithium-ion battery (LIB) safety in abuse scenarios is the structural integrity of the battery separator. This paper presents a coupled viscoelastic–viscoplastic model for predicting the thermomechanical response of polymeric battery separators in abuse scenarios under combined mechanical and thermal loadings. The viscoplastic model is developed based on a rheological framework that considers the mechanisms involved in the initial yielding, change in viscosity, strain softening and strain hardening of polymeric separators. The viscoplastic model is then coupled with a previously developed orthotropic nonlinear thermoviscoelastic model to predict the thermomechanical response of polymeric separators before the onset of failure. The model parameters are determined for Celgard®2400, a polypropylene (PP) separator, and the model is implemented in the LS-DYNA® finite element (FE) package as a user-defined subroutine. Punch test simulations are employed to verify the model predictions under biaxial stress states. Simulations of uniaxial tensile stress–strain responses at different strain rates and temperatures are compared with experimental data to validate the model predictions. The model predictions of the material anisotropy, rate and temperature dependence agree well with experimental observations.

Prediction of mechanical properties for typical pressure vessel steels by small punch test combined with machine learning

To understand the fitness of different machine learning methods to small punch test (SPT), three machine learning methods, namely, back propagation (BP) neural network, radial basis function (RBF) neural network and random forest (RF) regression model were used to establish machine learning-based correlation models of SPT load–displacement and uniaxial tensile test true stress–strain curves. Five typical pressure vessel steels were tested to reveal the prediction accuracies of different machine learning methods. Statistical analysis, unveiled the following order of prediction accuracy for pressure vessel steels: BP > RBF > RF. However, the differences in the mean absolute percentage erros between BP and RF decreased from 5.64% to 1.59%, with the training data volume increasing from 50 data sets to 629 data sets. Therefore, if a large training data volume is used, then the three machine learning methods can provide acceptable prediction results. However, if the training data volume is insufficient, then the BP, and RBF neural networks are better choices.

Quantitative analysis of the correlation between geometric parameters of pits and stress concentration factors for a plate subject to uniaxial tensile stress

The offshore environment is inherently corrosive. Consequently, pits may nucleate on exposed steel surfaces. Corrosion pits can be a source of crack initiation when the structure is subject to fatigue loading. The criticality of a corrosion pit with respect to the structural integrity depends on its shape and size and can be quantified using a stress concentration factor (Kt). In this work, a parametric 3D finite element model is developed to perform stress analysis of a pitted plate subjected to uniaxial tensile stress. The model is used for an extensive parameter study in which Kt is determined for various pit configurations. It is demonstrated that each one of the geometric parameters holds a substantial influence on the location of the Most Critical Region (MCR). It is shown that Kt increases as the pit gets narrower. Pits with an elliptical mouth yield higher Kt values when the angle between the load direction and the pit mouth major axis increases. Moreover, Kt increases with the increase in the localized thickness loss which is more pronounced for relatively wider pits. Finally, a regression model is presented for estimating Kt based on the geometric parameters of a pit.

Numerical Material Testing Method for Hexagonal Close-Packed Metals Based on a Strain-Rate-Independent Finite Element Polycrystal Model

The purpose of this study was to develop a numerical material testing method applicable to hexagonal close-packed (hcp) materials that can predict complex material behavior such as biaxial test results from relatively easy-to-perform uniaxial tests. The proposed numerical material testing method consists of a physical model that represents the macroscopic behavior of the material and a means of determining the included crystallographic parameters using macroscopic experimental data. First, as the physical model, the finite element polycrystal model (FEPM) previously applied by the authors for face-centered cubic (fcc) materials was applied and modified for hcp materials. A unique feature of the FEPM is that it avoids the use of strain-rate-dependent coefficients, whose physical meaning is ambiguous, because the deformation analysis can be performed while automatically determining the activity of all slip systems. The applicability of FEPM to numerical material testing methods was verified in hcp materials through this study. Then, a material parameter optimization process was developed using a genetic algorithm (GA). The proposed method was validated using literature values of magnesium alloy AZ31. First, the proposed optimization process was performed on cast AZ31 using uniaxial tensile and compressive stress—strain curves as teaching data to confirm that the stress—strain curves for the biaxial state could be predicted. Then, the proposed method was applied to rolled sheet AZ31, where the pseudo-anisotropic crystal orientations generated by numerical rolling were used as initial values. The prediction of unknown material data showed that, even in the case of sheets, the crystallographic parameters could be reasonably determined by the proposed optimization process.

Mechanical Characterization of Collagen Hydrogels by Quasistatic Uniaxial Tensile Experiments

Collagen serves as an essential structural material in the human body. Despite the complex mechanical conditions surrounding the collagen hydrogels, previous studies mostly focus on analyzing the mechanical behavior under dynamically varying compressive or shear loads, but the tensile properties at the quasistatic time scale are relatively less studied. This work aims to investigate the quasistatic tensile behavior of reconstituted collagen hydrogels under uniaxial tensile stresses. The evolution of the collagen fiber network structures with straining is visually observed using the confocal microscope equipped with the tensile strain actuator. While the unfolding of the initially undulated fibers accommodates the early‐stage strains, the deformation mechanism continuously changes to the stretching of fibers through the network alignment to the tensile direction. This transition commences with the buckling of a fiber lying transverse to the loading direction, which otherwise locks the rotation of adjacent fibers.

A Visco-Hyperelastic Constitutive Model to Characterize the Stress-Softening Behavior of Ethylene Propylene Diene Monomer Rubber.

Uniaxial and biaxial cyclic tensile tests and stress relaxation tests were performed on the ethylene propylene diene monomer (EPDM) material to investigate its stress-softening effect. The experimental results reveal that the EPDM material presents a significant Mullins effect during the cyclic stretching processes. Furthermore, it is found that the deformation of the EPDM material does not return to zero simultaneously with the stress, due to the viscoelasticity of the EPDM material. Therefore, this study combines pseudo-elasticity theory and viscoelastic theory to propose a visco-hyperelastic constitutive model. The proposed model is used to fit and analyze the uniaxial and biaxial cyclic test results of EPDM and a comparison is conducted with the corresponding hyper-elastic constitutive model. The results show that the proposed model is in good agreement with the experimental data and superior to the hyper-elastic constitutive model, especially when it comes to the stress-softening unloading process. This work is conducive to accurately characterizing the stress-softening behavior of rubber-like materials at large deformation and can provide some theoretical guidance for their widespread application in industry.

Chloride ion diffusion and distribution characteristics in recycled coarse aggregate concrete under uniaxial and biaxial pressure

Under uniaxial compression, recycled coarse aggregate leads to complex internal stresses (simultaneous uniaxial, biaxial, and multiaxial tensile and compressive stresses at the micro scale) and even micro cracks in concrete, which poses difficulties in accurately predicting the chloride ion diffusion of recycled concrete. By changing the compressive stress level and bi-directional stress ratio of concrete, a self-developed biaxial compression device was used to test the chloride ion diffusion coefficient of recycled concrete under different stress states. In order to analyze the influence of various factors on chloride ion diffusion, DIC digital image technology and microcrack statistics technology were used to analyze the influence of concrete micro deformation on its chloride ion diffusion coefficient under load, and X-ray fluorescence technology was used to accurately analyze the concentration distribution of chloride element in different positions of concrete. The pore structure inside recycled concrete was characterized through experiments, and a real three-dimensional multi-scale model of concrete and the statistical characteristics of porosity at different scales were obtained. Finally, a theoretical model was established to predict the chloride ion diffusion coefficient under biaxial compressive loads, achieving accurate prediction of chloride ion diffusion coefficient close to practical engineering.

Exceptionally small Young modulus in 10M martensite of Ni-Mn-Ga exhibiting magnetic shape memory effect

A Ni50Mn28Ga22 single crystal exhibiting 10M martensitic structure at room temperature was studied by X-ray diffraction measured in situ under uniaxial tensile stress up to 20 MPa and in different initial orientations of the sample. When the c axis lies along the direction of the applied stress, the sample is elongated primarily by the stress-induced reorientation. In comparison, with a or b axis lying along the stress direction, the overall elongation happens primarily due to the change of the lattice parameters and also the modulation amplitude of 10M martensite rapidly decreases with the applied tension. The initial tensile Young modulus calculated from the refined lattice parameters is very low and exhibits gradual stiffening with the increasing tensile stress. Close to zero stress the modulus has an extremely low value of about 0.3 GPa.

Uncertainty quantification and propagation in the microstructure-sensitive prediction of the stress-strain response of woven ceramic matrix composites

Hierarchical multiscale modeling of heterogeneous materials has traditionally relied upon a deterministic estimation of constitutive properties when making microstructure-sensitive predictions of effective response at each subsequent length-scale. Such an approach is wholly unsuitable for a variety of material classes, such as ceramic matrix composites, which exhibit large variability at multiple length-scales. This work demonstrates a framework for approaching two open problems towards improved microstructure-sensitive predictions, namely, (i) probabilistically calibrating complex constitutive models at the mesoscale to sparsely observed macroscale experimental data, and (ii) propagating this stochastic constituent behavior at the mesoscale towards low-cost homogenized predictions for unseen microstructures. The proposed stochastic scale-bridging framework displays a continuity of information flow where no portion of the experimental data is neglected out of convenience, facilitating the greatest information gain from oftentimes costly experiments. In this paper, suitable protocols were developed to address the challenges described above. The protocols were subsequently demonstrated on ceramic matrix composite’s uniaxial tensile stress–strain response, where constituent behavior at the mesoscale was described using continuum damage mechanics, and predictions encapsulating constitutive model parameter uncertainty were made for novel microstructures. The methodology presented in this work is broadly applicable to various material classes and constitutive models with high-dimensional parameter sets.

Preferential side chain scission of polytetrafluoroethylene by bending stress

We investigated the chemical composition of polytetrafluoroethylene (PTFE) under bending stress using hard X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy. Our measurements revealed the breaking of C–F bonds in the side chains and conspicuous observation of C–C bonds in the main chain only on the surface under bending stress (carbon-rich). Moreover, we found that the breaking of C–F bonds was dependent on the tensile strain caused by bending. Investigating the effects of tensile and compressive stresses induced by bending, the tensile stress was found to significantly contribute to the breaking of C–F bonds. However, the C–F bonds were hardly broken under uniaxial tensile stress. These findings suggest that tensile stress due to bending, rather than uniaxial tensile stress, causes significant C–F bond scission in the PTFE. This result is attributed to the force acting toward the center of curvature owing to bending, which does not occur under uniaxial tensile stress. Our results provide a better understanding of microscopic PTFE surfaces subjected to flexural tensile stress for nanofluidics and medical engineering applications. Additionally, our findings suggest that carbon-rich structures can be easily fabricated, which may lead to the development of processes for fabrication of two-dimensional materials.

Atomistic study of the properties and behavior under uniaxial tensile stress of some representative UO[formula omitted] grain boundaries

In irradiated polycrystalline uranium dioxide (UO2), the pressure generated at high temperature by the noble gases in the intergranular bubbles as well as the thermomechanical stresses due to temperature gradients cause the fracture of the grain boundaries. In this study, one analyzes through atomistic calculations of static and molecular dynamics type the properties of three UO2 grain boundaries and their behavior under uniaxial tensile loading up to fracture. In these atomistic simulations, the interactions between atoms are described using a many-body variable charge potential. Structural analysis, performed on the three grain boundary structures under uniaxial tensile stresses and over a wide temperature range, reveals no source of plasticity. This suggests a brittle behavior at fracture, in agreement with recent experimental studies carried out on micrometer size specimens containing grain boundaries. A method based on thermodynamic considerations is used to build normal cohesive zone laws for the UO2 grain boundaries using molecular dynamics simulation data. The cohesive zone laws will be employed in a future study in failure simulations at higher scales.

Uniaxial tensile properties of pre-stretched ethylene-tetrafluoroethylene (ETFE) foil

The ETFE foil is a type of good cladding material in the field of architecture and its uniaxial tensile properties are important considerations in the design analysis. In engineering application, the stress of ETFE foil may exceed the first and second yield stress under external load and the large plastic deformation is usually observed. Previous studies mainly focus on its uniaxial tensile properties along the uniaxial pre-stretching direction after the uniaxial pre-stretching stress is over the yield stress. Uniaxial pre-stretch will cause the ETFE film to compress in the other direction due to Poisson’s ratio, while the uniaxial tensile properties perpendicular to the uniaxial pre-stretching direction is still unknown. Besides, the study on its uniaxial tensile properties along the biaxial pre-stretching direction after the biaxial pre-stretching stress is over the yield stress is also quite limited. In order to investigate this issue, the uniaxial pre-stretching tests, the asynchronous biaxial pre-stretching tests and the synchronous biaxial pre-stretching tests were performed to make the uniaxial stress and the biaxial stress reach over the first and second yield stress respectively. Square specimens for subsequent uniaxial tensile tests were prepared from these pre-stretching tests and the uniaxial tensile stress–strain curves of specimens of different pre-stretching tests were obtained. The uniaxial tensile test results demonstrate that in some cases the bearing capacity of ETFE foil was strengthened after pre-stretching tests while in many cases both the uniaxial pre-stretching and the biaxial pre-stretching lowered the bearing capacity of ETFE foil. Additionally, the pre-stretching strain correlates strongly with the bearing capacity of pre-stretched ETFE foil and the relationship between them is discussed.

Characterisation of human posterior rectus sheath reveals mechanical and structural anisotropy

BackgroundOur work aims to investigate the mechanical properties of the human posterior rectus sheath in terms of its ultimate tensile stress, stiffness, thickness and anisotropy. It also aims to assess the collagen fibre organisation of the posterior rectus sheath using Second-Harmonic Generation microscopy. MethodsFor mechanical analysis, twenty-five fresh-frozen samples of posterior rectus sheath were taken from six different cadaveric donors. They underwent uniaxial tensile stress testing until rupture either in the transverse (n = 15) or longitudinal (n = 10) plane. The thickness of each sample was also recorded using digital callipers. On a separate occasion, ten posterior rectus sheath samples and three anterior rectus sheath samples underwent microscopy and photography to assess collagen fibre organisation. Findingssamples had a mean ultimate tensile stress of 7.7 MPa (SD 4.9) in the transverse plane and 1.2 MPa (SD 0.8) in the longitudinal plane (P < 0.01). The same samples had a mean Youngs modulus of 11.1 MPa (SD 5.0) in the transverse plane and 1.7 MPa (SD 1.3) in the longitudinal plane (P < 0.01). The mean thickness of the posterior rectus sheath was 0.51 mm (SD 0.13). Transversely aligned collagen fibres could be identified within the posterior sheath tissue using Second-Harmonic Generation microscopy. InterpretationThe posterior rectus sheath displays mechanical and structural anisotropy with greater tensile stress and stiffness in the transverse plane compared to the longitudinal plane. The mean thickness of this layer is around 0.51 mm – consistent with other studies. The tissue is constructed of transversely aligned collagen fibres that are visible using Second-Harmonic Generation microscopy.

OC-122 CHARACTERISATION OF HUMAN POSTERIOR RECTUS SHEATH REVEALS MECHANICAL AND STRUCTURAL ANISOTROPY

Abstract Background Our work investigated the mechanical properties of the posterior rectus sheath (PRS) in terms of its ultimate tensile stress (UTS), stiffness, thickness and anisotropy as well as assess the collagen fibre organisation of the PRS using Second-Harmonic Generation (SHG) microscopy. Methods For mechanical analysis, twenty-five fresh-frozen PRS samples of were taken from six different cadaveric donors. They underwent uniaxial tensile stress testing until rupture either in the transverse (n=15) or longitudinal (n=10) plane. The thickness of each sample was also recorded using digital callipers. On a separate occasion, ten PRS samples and three anterior rectus sheath samples underwent SHG microscopy and photography to assess collagen fibre organisation. Results PRS samples had a mean UTS of 7.7MPa (SD 4.9) in the transverse plane and 1.2 MPa (SD 0.8) in the longitudinal plane (P&amp;lt;0.01). The same samples had a mean Youngs modulus of 11.1 MPa (SD 5.0) in the transverse plane and 1.7 MPa (SD 1.3) in the longitudinal plane (P&amp;lt;0.01). The mean thickness of the posterior rectus sheath was 0.51mm (SD 0.13). Collagen fibres within the tissue could be identified with SHG microscopy, generally aligned transversely. Conclusion The PRS displayed mechanical and structural anisotropy with greater tensile stress and stiffness in the transverse plane compared to the longitudinal plane. The mean thickness of this layer is around 0.51mm – consistent with other studies. The tissue is constructed of transversely aligned collagen fibres that are visible using SHG microscopy.

Investigation on Constitutive and Ductile Damage Mechanism of High-Density Polyethylene under Tensile and Bending Conditions

High-density polyethylene (HDPE) is one of the most commonly used materials for manufacturing pipelines. In this paper, the deformation behavior of HDPE materials under uniaxial tensile stress was investigated by employing uniaxial tensile tests and macroscale/mesoscale morphology analysis. The experimental results indicated that the stress–strain relationship of HDPE is nonlinear, and the ductile fracture characteristics of necking and local failure appear in the sample after the engineering strain reaches 35%. Therefore, for the first time, a hyperelastoplastic constitutive model that describes the elasticity by the Marlow model and combined the isotropic plasticity-ductility damage correction is established, and a corresponding numerical approach is proposed. The simulation scheme was implemented in finite-element software, and the mechanical responses of HDPE under uniaxial tensile and bending loads were predicted. Obtained calculations were relatively consistent with experimental observations. Hence, the proposed model and approach have a good simulation effect on the mechanical properties of HDPE and can be employed for the process prediction of such materials. This study is beneficial to the in-depth understanding of the hyperelastoplasticity and failure mechanism of HDPE and provides ideas for the deformation and failure study of other polymer materials.

Low-profile broadband microwave absorber based on magnetic coating and artificial electromagnetic structures

In order to realize electromagnetic stealth of large equipment, we propose a low-cost, mass-producible composite microwave absorber in this paper. The developed novel EM absorber comprises a pattern-impregnated honeycomb structure with the absorbent of carbon black (CB), a resistive frequency selective surface (FSS) embedded in polypropylene (PP) foam, and a mixture coating covered on a metal plane whose absorbent is flaky carbonyl iron (FCI). CB particles and FCI particles provide electrical and magnetic losses at the microscopic scale. Moreover, the subwavelength-scale artificial electromagnetic structure achieves broadband matching to free space by adjusting macroscopic geometric parameters. The consistency between measurements and simulations proves that the composite absorber achieves over 90% absorption ratio with a thickness of 8.3 mm from 2.06 to 18 GHz (corresponding to a fractional bandwidth of 158.9%). Additionally, this composite absorber possesses good mechanical property with a maximum uniaxial tensile stress of 67.43 MPa.

Modelling of Damage Spatiotemporal Distribution in Saturated Cementitious Materials and its Chloride Transport Evolution

Crack-induced damage significantly affects the chloride transport mechanism in cementitious materials. To quantitatively evaluate the crack effects, a coupled model was proposed in this paper for saturated cement paste with various uniaxial tensile damage. First, the 3D microstructure of hydrating cement paste was simulated based on a voxel-based hydration model, and its damaged spatiotemporal distribution under uniaxial tensile stress was simulated using a finite-element model. Based on the damaged cement paste, an electrical Modelling framework was presented to simulate the chloride transport. The results show that the damage spatiotemporal distribution in saturated cementitious materials with uniaxial tensile and its chloride transport evolution can be successfully modelled using the self-created model and coupled method. the damage of cementitious material is an accumulation process of cracks spread over the main crack. During the process, the crack connectivity and crack width affect chloride transport and its fracture-volume threshold value is 1.40%. Compared to studies published, the coupled model could well simulate chloride transport in saturated cementitious materials with uniaxial tensile damage.

Dependence of microstructural evolution on the geometric structure for serviced DZ125 turbine blades

The turbine blades were directionally solidified by a high-rate solidification process by the Bridgman technique using directional solidified Ni-based master superalloy DZ125 and operated on the engine bench with a high-temperature gas environment of more than 1500 °C from combustor and high-speed rotation of more than 13500 rpm for 400 h. A service-environment-based model was put forward to simulate the distribution of temperature and stress on the DZ125 blade in service. It was found that the distribution of temperature and stress on the serviced DZ125 blade was closely related to its geometric structure. The microstructural evolution of the serviced DZ125 blade was analyzed and the variations of microstructures with temperature and stress were investigated by using a scanning electron microscope. The results revealed that the evolution process of microstructures on the serviced DZ125 blade was different from that of the standard sample tested at constant temperature and uniaxial tensile stress. The reason for this discrepancy was explored using a combination of finite-element calculation and diffusion coefficient calculation.