Stress-strain Results Research Articles

Mechanical Properties and Thermal Decomposition Mechanism of Glycidyl Azide Polyol Energetic Thermoplastic Elastomer Binder with RDX Composite.

To improve the reinforcement effect between a binder and high solid filler in a propellant formula, grafting the bonding group into the binder to form a neutral polymeric is a practically novel approach to improving the interface properties of the propellant. In this work, a glycidyl azide polyol energetic thermoplastic elastomer binder with a -CN bonding group (GAP-ETPE) was synthesized, and the mechanical and thermal decomposition mechanism of GAP-ETPE with Hexogeon (RDX) model propellants were studied. The stress-strain results indicated that the tensile strength and strain of GAP-ETPE/RDX model propellants were 6.43 MPa and 32.1%, respectively. DMA data showed that the storage modulus (E') of the GAP-ETPE/RDX model propellants could increase the glass transition temperature (Tg) values, those were shifted to higher temperature with the increase in filler RDX percentages. TG/DTG showed the four decomposition stages of the decomposition process of the GAP-ETPE/RDX model propellants, and the thermal decomposition equation was constructed. These efforts provide a novel method to improve GAP-ETPE/RDX propellants mechanical property, and the thermal decomposition behavior of GAP-ETPE/RDX propellants also provided technical support for the study of propellant combustion characteristics.

Safety evaluation of deformed coke drum with nested stress at cold spot

In this article, the strain limit criterion and classical strength theories are used to evaluate the strength at the cold spot with nested effect of the deformed coke drum. First, the geometric model of the cold spot with nested effect before and after the deformation of the drum wall is established in the selected area, and the nested stress at the cold spot is calculated. Then, according to the calculated stress–strain results, the stress analysis of the drum wall at the cold spot is carried out. The results show that the coke drum yields during the cooling stage according to the strain limit criterion. According to classical strength theories, coke drum yields during the coke production and cooling stages. Finally, the paths are selected to calculate the equivalent stress–strain, and the stress–strain curves along the paths are plotted. By comparing the results of stress and strain evaluation, three evaluation methods are compared and studied.

Tuning the Properties of Xylan/Chitosan-Based Films by Temperature and Citric Acid Crosslinking Agent.

Petroleum-based food packaging causes environmental problems such as waste accumulation and microplastic generation. In this work, biobased films from stable polyelectrolyte complex suspensions (PECs) of xylan and chitosan (70 Xyl/30 Ch wt% mass ratio), at different concentrations of citric acid (CA) (0, 2.5, 5, 7.5 wt%), were prepared and characterized. Films were treated at two temperatures (135 °C, 155 °C) and times (30 min, 60 min) to promote covalent crosslinking. Esterification and amidation reactions were confirmed by Fourier Transform Infrared Spectroscopy and Confocal Raman Microscopy. Water resistance and dry and wet stress-strain results were markedly increased by thermal treatment, mainly at 155 °C. The presence of 5 wt% CA tended to increase dry and wet stress-strain values further, up to 88 MPa-10% (155 °C for 60 min), and 5.6 MPa-40% (155 °C for 30 min), respectively. The UV-blocking performance of the films was improved by all treatments, as was thermal stability (up to Tonset: 230 °C). Contact angle values were between 73 and 84°, indicating partly wettable surfaces. Thus, thermal treatment at low CA concentrations represents a good alternative for improving the performance of Xyl/Ch films.

Exploratory study on experimental and prediction based stress-strain behaviour of corroded prestressing steel strands

Prestressing steel strands have been extensively used in recent years due to the increased popularity of prestressed concrete structures. However, the corrosion of strands has a detrimental effect on these structures. This necessitates a detailed investigation of the mechanical properties of the corroded strands and to understand their influence on the strength of these structures. Therefore, in this paper, a systematic attempt has been made to study the mechanical properties of corroded steel strands corroded using the accelerated corrosion method. Initially, the tensile test was conducted on these corroded steel strands to study the mechanical properties of the strands and X-ray diffraction analysis was done on the corrosion products of these corroded steel strands. Then, resilient backpropagation with backtracking neural network based prediction models were developed to predict the ultimate strength of the corroded strands. The experimental results showed that an increase in the corrosion level reduces the ultimate stress, yield stress, breaking stress and the corresponding strains of the strand. The proposed prediction models give optimum results of cost functions for ultimate stress and ultimate strain predictions. The comparison study of ultimate stress-strain results obtained from the proposed prediction models showed remarkable performance with the experimental results.

Effects of Test-Specimen Boundary Conditions on the Interpretation of Stress–Strain Results for Hydraulic Asphalt Concrete

Effects of Test-Specimen Boundary Conditions on the Interpretation of Stress–Strain Results for Hydraulic Asphalt Concrete

Research on Mechanical Properties of Steel-Polypropylene Fiber-Reinforced Concrete after High-Temperature Treatments

A mechanical property experiment was carried out on steel-polypropylene fiber-reinforced concrete after elevated temperatures by using a 50 mm diameter SHPB apparatus. The regulations of compressive strength, elastic modulus, Poisson’s ratio, and other mechanical properties under six heating temperature levels (normal temperature, 100 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and three impact pressures (0.3 MPa, 0.4 MPa, 0.5 MPa) were studied. Using ANSYS/LS-DYNA 19.0 numerical simulation software and LS-PrePost post-processing software, numerical simulation analysis was conducted on the dynamic Hopkinson uniaxial impact compression and uniaxial dynamic impact splitting mechanical experiments of C40 plain concrete and steel-polypropylene hybrid fiber concrete. The results show that the dynamic compressive strength of hybrid fiber concrete with the optimal dosage reaches its maximum at a temperature group of 200 °C, and the dynamic compressive strength of hybrid fiber concrete with the optimal dosage increases by 97.1% compared to C40 plain concrete at a temperature group of 800 °C. The impact waveform and stress-strain curve results of the numerical simulation are very similar to the experimental results. The errors in calculating the peak stress and peak strain are within 6%, which can truly and accurately simulate the static mechanical properties and failure process of hybrid fiber-reinforced concrete.

A machine learning constitutive model for plasticity and strain hardening of polycrystalline metals based on data from micromechanical simulations

Machine learning (ML) methods have emerged as promising tools for generating constitutive models directly from mechanical data. Constitutive models are fundamental in describing and predicting the mechanical behavior of materials under arbitrary loading conditions. In recent approaches, the yield function, central to constitutive models, has been formulated in a data-oriented manner using ML. Many ML approaches have primarily focused on initial yielding, and the effect of strain hardening has not been widely considered. However, taking strain hardening into account is crucial for accurately describing the deformation behavior of polycrystalline metals. To address this problem, the present study introduces an ML-based yield function formulated as a support vector classification model, which encompasses strain hardening. This function was trained using a 12-dimensional feature vector that includes stress and plastic strain components resulting from crystal plasticity finite element method (CPFEM) simulations on a 3-dimensional RVE with 343 grains with a random crystallographic texture. These simulations were carried out to mimic multi-axial mechanical testing of the polycrystal under proportional loading in 300 different directions, which were selected to ensure proper coverage of the full stress space. The training data were directly taken from the stress–strain results obtained for the 300 multi-axial load cases. It is shown that the ML yield function trained on these data describes not only the initial yield behavior but also the flow stresses in the plastic regime with a very high accuracy and robustness. The workflow introduced in this work to generate synthetic mechanical data based on realistic CPFEM simulations and to train an ML yield function, including strain hardening, will open new possibilities in microstructure-sensitive materials modeling and thus pave the way for obtaining digital material twins.

Performing laboratory study of the behavior of reactive powder concrete on the shear of RC deep beams by the drilling core test

Abstract In the past decade, it has been observed that the applications of modern materials have developed a lot, especially effective reactive powder concrete (RPC), due to its superior performance properties. As a result of the superior resistance of RPC, it will give a longer construction life with less maintenance and more resistance to various environmental conditions and exhibits high-performance features such as high porosity, very high strength, and excellent corrosion resistance. The parameters studied in the present research were used to investigate the effect of maximum load, deflection, tensile and strain of concrete, first shear crack, crack pattern, and crack width. Considering the aforesaid cause and objective, one specimen of RPC RC deep beams has a rectangular cross-section of 150 mm in width, 500 mm in depth, and a total length of 1.2 m. One control specimen was tested for comparison. Moreover, 12 control specimens including cylinders and cubes were cast and tested to obtain the mechanical properties of the normal and RPC deep beams. Following the specimens’ processing, they were subjected to two concentrated load pressure tests through a hydraulic jack. Based on the results, the ultimate strength, deflection, and first shear crack capacity for the reactive powder concrete deep beam (RPCDB) have increased by 68, 10.5, and 62.5%, respectively, compared with concrete deep beam (CDB). Moreover, with respect to the width, the delay in the appearance of the first shear crack was reduced by 11 and 78%, respectively, compared with CDB at 65% of the final shear load. In addition, regarding the stress-strain results, RPCDB has increased by 118% at the maximum stress compared with CDB and in contrast, the strain scores for CDB increased by 22.5% at maximum stress compared to RPCDB.

Dynamic constitutive relationship of TiZrHfCu0.5 high entropy alloy based on Johnson-Cook model

High entropy alloy has attracted much attention in the field of national defense due to their excellent low-temperature dynamic mechanical properties. Taking TiZrHfCu0.5 high entropy alloy as the research object, the compressive properties of the specimens under quasi-static and dynamic (strain rate range 600s−1-2600s−1 and temperature range −60 °C–20 °C) conditions are systematically tested. Based on the static/dynamic stress-strain experimental results, the parameters of the original Johnson-Cook constitutive model are determined by fitting. On this basis, a modified Johnson-Cook constitutive model considering the coupling effects of strain, strain rate and temperature is proposed and its parameters are determined. The dynamic compression process of the specimens under different strain rates and temperatures is numerically simulated by ABAQUS finite element software, and the accuracy of the modified Johnson-Cook constitutive model to predict the dynamic compression behavior of TiZrHfCu0.5 high entropy alloy is verified. The experimental and numerical simulation results show that the TiZrHfCu0.5 high entropy alloy exhibits significant strain rate hardening effect and excellent low-temperature mechanical properties during dynamic compression. The ultimate stress can reach 1.79 GPa at −20 °C and strain rate of 2600 s−1. The predicted curves of the modified Johnson-cook constitutive model are in good agreement with the experimental results at low temperature and high strain rate. The modified Johnson-Cook constitutive model is embedded in the finite element software, which effectively improves the reliability of the numerical simulation of the compression performance of TiZrHfCu0.5 high entropy alloy at high strain rate and low temperature. The relative error between the predicted results of the modified Johnson-Cook constitutive model and the experimental results is greatly reduced.

Size effect during dynamic shear tests with hat-shaped specimens

The failure mechanism and size effect during the quasi-static and dynamic shear tests of hat-shaped specimens were investigated in this study. Three types of specimens with different shear ring thicknesses (800, 400, and 50 μm) were designed. Quasi-static tests were carried out using an electronic universal testing machine, while dynamic impact tests were carried out using split Hopkinson pressure bar (SHPB) tests. The adiabatic temperature rises with different strain rates, and the shear ring thickness was calculated. We found that the adiabatic temperature rises of the specimens with shear ring thicknesses of 800 and 400 μm were much larger than those of the specimens with shear ring thicknesses of 50 μm. The failure surfaces after the SHPB test were investigated via scanning electron microscopy, and the failure surfaces after the SHPB test could be divided into three zones: tensile, shear, and impact zones. The effect of the shear ring thickness and impact speed on the failure surface morphology was discussed. The typical shear stress–strain curves could be divided into three sections: elastic, plastic rise, and plastic plateau sections. Subsequently, a modified Johnson–Cook constitutive model was employed to fit the shear stress–strain results, and the fitted curves showed good agreement with the tested curves.

Experimental and numerical investigation of the intra-ply shear behaviour of unidirectional prepreg forming through picture-frame test

Intra-ply shear behaviour of uncured composite plies strongly influences component quality in advanced manufacturing processes such as prepreg compression moulding (PCM) and double diaphragm forming (DDF). This study investigates a straightforward method to characterise the intra-ply shear behaviour of a carbon fibre/epoxy UD prepreg using a specially designed picture-frame rig, by which specimens can be tested without involving inter-ply shear as would normally be observed in cross-plied UD prepreg stacks. Applying the proposed method, it is seen that specimens tend to suffer transverse buckling/wrinkling and local fibre-splitting at large shear strains. 3D digital image correlation (DIC) and a non-contacting video extensometer were utilised to determine the shear strain distribution throughout the test and particularly to determine the onset of out-of-plane deformations such that the trellis shear deformation portion of the test can be identified. The obtained shear stress-strain results show a temperature- and rate-dependent viscoelastic response, with the greatest influence from the temperature. The obtained in-plane shear properties were applied in the numerical simulation of the picture frame test based on a hypoelastic law. Although the predicted reaction forces are greater than experimental results at high strains due several factors including local fibre-splitting, a good agreement overall between physical test data and simulation results is seen for all test conditions. Finally, it is demonstrated that major advantages of the proposed test with respect to the conventional picture-frame test are that only load-extension data are required from the trellis shear experiment to calculate accurately the intra-ply shear stress-strain relationship and that the deformation rate can be easily controlled.

The synergistic regulation effect on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain

The synergistic regulation effects on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain has been investigated. It is found that the graphene containing Stone-Wales defect (SWG77) has metallicity, when surface adsorbing a CH3+ion, CH3+@SWG77 is a semiconductor with 0.339 eV indirect band gap. The stress-strain curve results indicate that adsorbing different plasma fragments in methane may influence to varying degrees on the ultimate strain of the SWG77 system. The hole mobility has an enhanced tendency as the tensile strain increases for the CH3+@SWG77 system. In addition, the hole mobilities seem to reach saturation when applied equibiaxial strain increase to 2 % or larger. Applying equibiaxial strain on the system substrate, the band gaps of CH3+@ SWG77 and 2CH3+@ SWG77 systems are almost unaffected. In addition, the concentration of CH3+ ion has a certain effect on the light absorption coefficient, reflectivity, and energy loss of the SWG77 system in the visible light region (1.62 eV–3.11 eV) and ultraviolet regions (3.11 eV–5.50 eV). Therefore, defect graphene with appropriate carrier mobility and band gap may be designed by adjusting the equiaxial strain and methyl concentration, which provides useful theoretical support for the development of optical electrical multifunctional electronic devices based on graphene, and is conducive to promoting the application of graphene materials in the field of band gap engineering.

Experimental and Numerical Analysis of Axial Behavior of Triaxial Woven Fabric Confined Concrete Columns

Continuous efforts are being made to improve plain concrete compressive strength and ductility by applying carbon, glass fiber, or hybrid-reinforced epoxy resin composites. The investigation centers on analyzing the axial compressive strength and strain, compressive stress–strain behavior, failure morphology, and crack evolution of the reinforced cylinders. Besides the experiments, non-linear finite element analysis was performed using the finite element (FE) package ABAQUS 2021. The test results indicate that carbon fiber triaxial woven fabric (TWF-C) confinement result in the most significant improvement of 118% in compressive stress than the concrete specimens. On the other hand, glass fiber triaxial woven fabric (TWF-G) confinement shows the highest enhancement of 161% in ductility. The mechanical properties of the sample utilizing glass fiber as the weft yarn and carbon fiber as the warp yarn (TWF-GC2) exhibit superior improvements of 22% in compressive stress and 8% in axial strain compared to the sample using glass fiber as the warp yarn and carbon fiber as the weft yarn (TWF-CG2). Samples with glass fiber as weft yarn show gradual cracks during loading, while carbon fiber as weft yarn show instantaneous damage. The numerical finite element models accurately predict the experimental results of the tested specimens in this study. There were 1.2~3% and 5~10% discrepancies for compressive stress and axial strain, respectively, between experimental and FE results. Overall, the results suggest that Triaxial woven fabric confinement is a valuable technique to improve the strength and strain of concrete and that the type of fibers used could be tailored for appropriate performance characteristics.

Slope stability analysis model for the frost-susceptible soil based on thermal-hydro-mechanical coupling

Slope stability analysis has been performed through various analysis methods ranging from general limit equilibrium methods, such as those proposed by Janbu, Bishop, and Fellenius, to finite element methods. Using these methods, analyzing the slope stability considering the change in soil stiffness due to the freezing or thawing conditions resulting from temperature changes is infeasible. Therefore, considering this shortcoming, a thermal-hydro-mechanical slope stability analysis model (THM-SSA model) is proposed for slope stability analysis. The main feature considered in the THM-SSA model was the slope of the critical state line based on the load angle. Additionally, this model could calculate the local factor of safety (LFS) for the slope based on the isotropic tensile strength of the unfrozen soil and the changes in it after being subjected to repeated freeze–thaw cycles. To verify the proposed THM-SSA model, the stress–strain results were compared with those of the experimental triaxial compression tests that were conducted under different temperatures of the frozen soil with a corresponding number of freeze–thaw cycles. Based on this, a simulation of slope stability analysis was performed as demonstration, and using the verified THM-SSA model, the LFS was calculated according to the freeze–thaw cycles of the slope.

Strike‐slip deformation and expansion process of the Qilian fold‐and‐thrust belt: Inferred from gravitational potential energy

In this study, we present a new estimation of the gravitational potential energy (GPE) and explore its relationship with the present‐day stress and strain‐rate field in the Qilian fold‐and‐thrust belt (QFTB), to evaluate how the stress associated with GPE gives rise to tectonic deformation of the QFTB, and to achieve a more comprehensive understanding of stress transfer from the Indian–Eurasian collision belt to the QFTB. Significant features of the stress and deformation in the QFTB derived from our analysis include the following: (1) the stress pattern is verified by the results of the deviatoric stress being inverted by topographic stress modelling, suggesting that topographic stress associated with the lateral variations in crustal thickness and topography should be taken into account when considering the clockwise rotation of the stress field along the strike of the Qilian fold‐and‐thrust belt. (2) Our stress–strain results suggest that the strain derived from the Indian–Eurasian convergence propagated to the north of the Haiyuan Fault. By incorporating with recent seismological results, it is supposed that the Tibetan Plateau has extended to the southern Alxa block, and the Haiyuan Fault may not be the most northeastern crustal boundary of the Tibetan Plateau. (3) The comparison of surface strain, focal stress and topographic stress modelling illustrates that the Qilian fold‐and‐thrust belt is probably deforming in response to the far‐field effect of Indian–Eurasian convergence. The stress transfer from the collisional front to the Qilian fold‐and‐thrust belt appears to be continuous and progressive. Accordingly, we suggest that a diffuse model could better describe the deformation of the Qilian fold‐and‐thrust belt in which lateral expansion is accommodated evenly along the principal axes of stress as a consequence of horizontal lithospheric heterogeneity.

Analysis of amorphous structure with polycaprolactone-hydroxyapatite nanoparticles fabricated by 3D bioprinter technique for bone tissue engineering

New ceramic scaffolds have the ability to be designed to replace the hip bone with different shapes. In this research, the aim is to fabricate a porous scaffold by fused deposition modeling (FDM) with three geometric shapes of circle, multi-circle and square for bone replacement applications. Biological tests included immersing the samples in simulated body fluid (SBF) to monitor the apatite formation and phosphate buffer saline (PBS) to check weight loss and ion concentration changes. Morphological examination was evaluated by examining the surface of the sample before and after immersion in the SBF using scanning electron microscope (SEM) analysis. The obtained mechanical results such as elastic modulus and compressive strength were used in the finite element analysis (FEA). The mechanical results showed that the sample with a multi-circle structure have a higher elastic modulus under the compressive strength about 32 MPa. Also, the porosity percentage showed that the highest porosity belongs to the second sample. The stress-strain results show that the second sample has a compressive strength of about 2.6 MPa. The FEA of the samples show that the sample with square structure has the highest stress compared to the other sample. The apatite growth in all three samples had similar trend. The mechanical and morphological analysis shows the fracture surface of the bone scaffold under compressive loading for the third sample has porosity of about 42% and the lowest compressive strength of about 1.85 ± 0.8 MPa. In order to reduce the amount of remain stress, the first and second samples should be used for the pelvic bone repair.

Numerical analysis of anisotropic stiffness and strength for geomaterials

In numerical modelling, selection of the constitutive model is a critical factor in predicting the actual response of a geomaterial. The use of oversimplified or inadequate models may not be sufficient to reproduce the actual geomaterial behaviour. That selection is especially relevant in the case of anisotropic rocks, and particularly for shales and slates, whose behaviour may be affected, e.g. well stability in geothermal or oil and gas production operations. In this paper, an alternative anisotropic constitutive model has been implemented in the finite element method software CODE_BRIGHT, which is able to account for the anisotropy of shales and slates in terms of both deformability and strength. For this purpose, a transversely isotropic version of the generalised Hooke's law is adopted to represent the stiffness anisotropy, while a nonuniform scaling of the stress tensor is introduced in the plastic model to represent the strength anisotropy. Furthermore, a detailed approach has been proposed to determine the model parameters based on the stress–strain results of laboratory tests. Moreover, numerical analyses are performed to model uniaxial and triaxial tests on Vaca Muerta shale, Bossier shale and slate from the northwest of Spain (NW Spain slate). The experimental data have been recovered from the literature in the case of the shale and, in the case of the slate, performed by the authors in terms of stress-strain curves and strengths. A good agreement can be generally observed between numerical and experimental results, hence showing the potential applicability of the approach to actual case studies. Therefore, the presented constitutive model may be a promising approach for analysing the anisotropic behaviour of rocks and its impact on well stability or other relevant geomechanical problems in anisotropic rocks.

Stress–strain model for FRP confined heat-damaged concrete columns

This paper is dedicated to the development of a new analysis-oriented model to simulate the axial and dilation behavior of FRP confined heat-damaged concrete columns under axial compressive loading. The model's calibration has considered the experimental results from concrete circular/square cross-section specimens submitted to a certain level of heat-induced damage, which after attained the environmental temperature, were fully confined with FRP jacket and tested. New equations were developed to determine the mechanical characteristics of unconfined heat-damaged concrete by performing regression analysis on a large database of experimental tests. Based on a parametric study on dilation behavior of FRP confined heat-damaged columns, a new dilation model was developed to predict concrete lateral strain at a given axial strain, dependent on the thermal damage level. By using this dilation model, a new methodology was introduced for predicting the axial stress-strain response of FRP confined heat-damaged columns in compliance with the active confinement approach. The adequate predictive performance of the model is demonstrated by estimating experimental axial stress-strain results.

Study of implementation the tensile data of the glass fiber reinforced polyamide into the finite element analyses

The increased demand for newly developed products and the necessity of using plastic materials progressively more, requires a faster way of understanding how the product made of reinforced plastics will behave under certain loads and environmental conditions.By using the finite element method, we can evaluate the performance of one product that is made from reinforced glass fiber. For this purpose, we have evaluated the stress–strain data of two different materials – the same type of polyamide with different reinforcement grades – and included the results in a finite element analysis where the initial stress–strain results were compared to the one obtained in the test.The analysis’ results show, that for the same level of displacement imposed in the finite element method, we are obtaining the same level of stress as the one obtained in the tensile test.

Flexural behaviour of 3D-printed carbon fibre composites: Experimental and virtual tests - application to composite adaptive structure

Flexural properties of 3D-printed carbon fibre (CF) composites are investigated, experimentally and numerically. A series of 3-point bending experimental tests are conducted on CF composite specimens, and a series of 3-point bending virtual tests are simulated in LS-DYNA using a composite modelling approach, which is user defined integration points through the composite thickness. The flexural stress-strain results are compared, and they show good agreement within the elastic region. In the plastic region, the experimental flexural modulus reduces significantly, which remains constant for a certain range of flexural strain, before structural failure. A new hypothesis on the flexural properties of the 3D-printed CF composite is suggested, which is the specimen behaves as two stacks of individual beams, after yielding/delamination. The hypothesis is supported by another series of FE simulations on the composite, modelled as two stacked composite beams, and subjected to 3-point bending load. Then the capability of the composite 3D-printing to manufacture a structure with complex geometries and to manufacture several parts as a single structure, are exploited to fabricate a CF composite corrugated structure with a trailing edge section. The structure which represents an internal structure of a morphing aerofoil is actuated by a NiTi shape memory alloy (SMA) wire with a 1.6% recoverable strain. A trailing edge deflection of 6.0 mm is obtained, which is measured using an IMETRUM optical system. It is reasonably close to the predicted deflection of 7.3 mm shown in the FE simulation, using a newly developed UMAT for SMA-actuation, in an explicit LS-DYNA.